[0001]The present invention relates to a plant power control system and a control method thereof. [Background Art] [0002]As a system that improves a power factor of a plant power source, PTL 1 is known. PTL 1 discloses a technique of providing a plant power factor control method using a plant power control system, the plant power control system optically controlling an overall power factor of a plant by maximizing a remaining current capacity of an inverter drive having a high power ratio in the plant. That is, in PTL 1, reactive power is supplied from the control system to the plant in a direction in which reactive power which the plant receives from the system is reduced. [Citation List] [Patent Literature] [0003]
PTL 1: Japanese Patent No. 3682544 [Disclosure of the Invention] [Problem that the Invention is to solve] [0004]

PTL 1 describes that the power factor of the plant power source is improved. However, PTL 1 does not describe that values of reactive power to be assigned to a plurality of inverter drives and output timings thereof, and there is room for improvement.
[0005]
For example, in a plant such as a steel mill, when a mill motor clamps a steel sheet, the torque rapidly increases, and the rotation speed decreases. Therefore, a power converter increases a torque current command to maintain the rotation speed. As the torque current increases, the remaining current capacity of the power converter decreases. Therefore, sufficient reactive power cannot be supplied from the power converter, and the overall power factor of the plant power source may decrease.
[0006]
The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a plant power control system that can efficiently improve an overall power factor of a plant, and a control method thereof.
[Means for solving the Problem]
[0007]
In order to achieve the problems, according to one aspect of the present invention, there is provided a plant power

control system including: a power converter positioned between a power system of a plant and each of electric motors to be provided for each of the electric motors; a reactive power load facility connected to the power system; a control device that generates a predetermined command for instructing each of the power converters to supply reactive power to the power system; and a reactive power detection device that detects reactive power at a power receiving point between the reactive power load facility and the power system, wherein the control device calculates an amount of reactive power required to allow the reactive power supplied from each of the power converters to the power system to cancel out the reactive power detected by the reactive power detection device, and calculates a command value for distributing the calculated amount of reactive power required to each of the power converters for each of the power converters according to a remaining capacity of the power converter based on the amount of reactive power required and predetermined information relating to each of the electric motors.
[Advantage of the Invention]
[0008]
According to the present invention, a command value for distributing the amount of reactive power required to each of the power converters can be calculated according to the remaining capacity of each of the power converters, and the

overall power factor of the plant can be efficiently improved.
[Brief Description of the Drawings]
[0009]
[Fig. 1] Fig. 1 is an overall configuration diagram illustrating a plant power control system according to a first example.
[Fig. 2] Fig. 2 is a configuration diagram illustrating a power control device.
[Fig. 3] Fig. 3 is a diagram illustrating a positional relationship between a group of electric motors and a steel sheet.
[Fig. 4] Fig. 4 is a graph illustrating changes in the torque and speed of an electric motor.
[Fig. 5] Fig. 5 is a flowchart illustrating a process of estimating a time at which a steel sheet arrives at an electric motor (corresponding power converter).
[Fig. 6] Fig. 6 is a flowchart illustrating a process of determining a reactive power command.
[Fig. 7] Fig. 7 is a flowchart illustrating another process of determining a reactive power command.
[Fig. 8] Fig. 8 is a diagram illustrating a reactive power distributed state in the related art prepared for a comparison to the example.
[Fig. 9] Fig. 9 is a diagram illustrating a reactive power distributed state in the example.

[Fig. 10] Fig. 10 is a diagram illustrating another positional relationship between a group of power converters and a steel sheet.
[Fig. 11] Fig. 11 is an overall configuration diagram illustrating a plant power control system according to a second example.
[Fig. 12] Fig. 12 is a configuration diagram illustrating a power control device.
[Fig. 13] Fig. 13 is a flowchart illustrating an arrival time estimation process.
[Fig. 14] Fig. 14 is a flowchart illustrating another arrival time estimation process.
[Fig. 15] Fig. 15 is a diagram illustrating a positional relationship between a group of electric motors and a steel sheet.
[Fig. 16] Fig. 16 is a flowchart illustrating a process of determining a reactive power command.
[Fig. 17] Fig. 17 is a configuration diagram illustrating a power control device according to a third example.
[Fig. 18] Fig. 18 is a configuration diagram illustrating a function of estimating a steel sheet speed based on a sensor signal.
[Fig. 19] Fig. 19 is a graph illustrating changes in the torque and speed of an electric motor.
[Fig. 20] Fig. 20 is a configuration diagram illustrating
6

a power control device according to a fourth example.
[Fig. 21] Fig. 21 is an overall configuration diagram illustrating a plant power control system according to a fifth example.
[Fig. 22] Fig. 22 is a configuration diagram illustrating a power factor adjustment device.
[Fig. 23] Fig. 23 is a configuration diagram illustrating a power control device.
[Fig. 24] Fig. 24 is a graph illustrating a reactive power distributed state.
[Fig. 25] Fig. 25 is an overall configuration diagram illustrating a plant power control system according to a sixth example.
[Fig. 26] Fig. 26 is a configuration diagram illustrating a power control device.
[Fig. 27] Fig. 27 is a flowchart illustrating a process of determining a reactive power command.
[Fig. 28] Fig. 28 is a configuration diagram illustrating a power control device according to a seventh example.
[Fig. 29] Fig. 29 is a flowchart illustrating a process of determining a reactive power command.
[Fig. 30] Fig. 30 is a configuration diagram illustrating a power control device according to an eighth example.
[Fig. 31] Fig. 31 is a flowchart illustrating a process of comparing reactive powers to each other.
7

[Fig. 32] Fig. 32 is a configuration diagram illustrating a power control device according to a ninth example.
[Fig. 33] Fig. 33 is a configuration diagram illustrating a function of estimating active power.
[Fig. 34] Fig. 34 is a diagram illustrating a positional relationship between a group of electric motors and a steel sheet.
[Fig. 35] Fig. 35 is a flowchart illustrating a process of estimating a shortfall of reactive power. [Best Mode for Carrying Out the Invention] [0010]
An embodiment of the present invention will be described with reference to the drawings. The embodiment described below do not limit the present inventions according to the claims, and, all the elements described in the embodiment and combinations thereof are not necessarily indispensable for solving means of the invention. [0011]
In the embodiment, a steel plant where a steel sheet is rolled will be described as an example. However, the embodiment is also applicable to plants other than the steel plant. For example, the embodiment is applicable to any plant including a plurality of electric motors that are driven in cooperation. [0012]
8

In the embodiment, as described below, a torque current is estimated from each of power converters included in a plant power control system, and reactive power is preferentially supplied from a power converter having a higher remaining current capacity. As a result, an overall power factor of a plant power source is improved. [0013]
A plant power control system according to the embodiment includes: electric motors 10A to 10C that receive electric energy and rotate; power converters 5A to 5C that are arranged between the electric motors 10A to 10C and a power system 1; a reactive power load facility 3 connected to the power system 1; a control device 4 that generates a reactive power command or a reactive current command to be supplied to the power system 1 from the power converters 5A to 5C to the power system 1; a communication network CN1 that connects the power converters 5A to 5C and the control device 4 to each other; and a reactive power detection device 2 that measures or estimates reactive power at a power receiving point RP at which the power system 1 and the reactive power load facility 3 are connected to each other. [0014]
The control device 4 calculates a total reactive power output target value or a total reactive current output target value of the power converters 5A to 5C based on a reactive power
9

estimated value detected by the reactive power detection device 2. The control device 4 determines the reactive power command or the reactive current command for instructing each of the power converters 5A to 5C using the reactive power output target value or the reactive current output target value, arrangement information of each of the electric motors 10A to 10C, at least one of an active power detection value, an active current command value, an active current detection value, a torque command value, and a torque detection value of each of the power converters 5A to 5C, a command value or a detection value of an angular velocity of each of the electric motors 10A to 10C, and rated apparent power of each of the power converters 5A to 5C. [0015]
Further, the control device 4 can include an arrival time estimation unit 17 that estimates an arrival time at which a steel sheet 13 as a target to be processed in the plant arrives at each of the electric motors 10A to 10C using the arrangement information of each of the electric motors 10A to 10C, at least one of the active power detection value, the active current command value, the active current detection value, the torque command value, and the torque detection value of each of the power converters 5A to 5C, and the command value or the detection value of an angular velocity of each of the electric motors 10A to 10C. Further, the control device 4 can include
10

a reactive power command determination unit 16 that calculates the reactive power command or the reactive current command for instructing each of the power converters 5A to 5C using the rated apparent power, the total reactive power output target value or the total reactive current output target value of the power converters 5A to 5C, and the arrival time of the steel sheet 13 estimated by the arrival time estimation unit 17. [0016]
The control device 4 includes a reception unit 20C that receives an output of each of sensors 21A to 21C, and the arrival time estimation unit 17 can estimate the arrival time of the steel sheet 13 using the arrangement information of each of the electric motors 10A to 10C, at least one of the active power detection value, the active current command value, the active current detection value, the torque command value, and the torque detection value of each of the power converters 5A to 5C, and the command value or the detection value of an angular velocity of each of the electric motors 10A to 10C, and the output of each of the sensors 21A to 21C. [Example 1] [0017]
First, a plant power control system according to a first example will be described with reference to Figs. 1 to 10. [0018]
Fig. 1 is an overall configuration diagram illustrating
11

a plant power control system according to the first example. For example, the plant power control system includes a power source 1, a plurality of power converters 5A to 5C, a control device 4, a power source voltage detector 9, a current detector 8, a reactive power detection device 2, a lagging power factor load facility 3 connected through a transformer 7 for the lagging power factor facility, each of transformers 6A to 6C for the power converter, each of electric motors 10A to 10C, each of rolling roller upper portions 11A to 11C, and each of rolling roller lower portions 12A to 12C. One or more steel sheets 13 pass through gaps between the rolling rollers 11A to 11C and the rolling rollers 12A to 12C. [0019]
The power source 1 of the plant corresponds to a "power system". The lagging power factor load facility 3 corresponds to a "reactive power load facility". The control device 4 is a controller (CTL) that controls each of the power converters 5A to 5C and can also be referred to as a "power control device". The steel sheet 13 is a target to be processed by each of the electric motors 10A to 10C. [0020]
The reactive power detection device 2 detects or estimates reactive power (reactive power detection value QM) supplied from the system to the lagging power factor load facility 3 based on a detection value of the current detector
12

8 and a detection value of the power source voltage detector 9. The reactive power detection value QM may be estimated from at least two of active power, apparent power, and a power factor. The reactive power detection value QM may be estimated from a difference between the reactive power of the power source 1 and the reactive power of each of the power converters 5A to 5C. The control device 4 calculates a reactive power command based on the reactive power detection value QM and signals (speed information, torque information, and active power information) obtained from the power converters 5A to 5C, and distributes the calculated reactive power command to each of the power converters 5A to 5C to transmit the reactive power command at a predetermined timing. [0021]
The power converters 5A to 5C control the rotation speeds of the corresponding electric motors 10A to 10C, respectively. That is, the power converter 5A controls the electric motor 10A, the power converter 5B controls the electric motor 10B, and the power converter 5C controls the electric motor 10C. [0022]
The electric motors 10A to 10C are mechanically connected to the rolling roller upper portions 11A to 11C and the rolling roller lower portions 12A to 12C, respectively. The rolling roller upper portions 11A to 11C and the rolling roller lower portions 12A to 12C roll the steel sheet 13.
13

[0023]
The details of the control device 4 will be described with reference to Fig. 2. In the drawing, the word "unit" is omitted. For example, the "reception unit" is represented by "reception". [0024]
The control device 4 includes, for example, hardware such as a processor, a memory, a storage, an input/output interface, a communication interface, and the like, and software such as an operating system, a predetermined computer program, and the like (all of which are not illustrated in the drawing). The control device 4 can also be configured as a calculator or can also be configured as a programmable controller or a control panel. The processor as an arithmetic device reads the predetermined computer program to the memory and executes the read computer program such that functions as the control device 4 are implemented. The functions realizable as a computer program may be implemented as a hardware circuit. [0025]
The control device 4 includes a reactive power command determination unit 16, an arrival time estimation unit 17, an electric motor arrangement storage unit 18, a rated apparent power storage unit 19, a transmission unit 15, and reception units 20A and 20B. When it is not necessary to distinguish the reception unit 20A and the reception unit 20B from each
14

other, the reception unit 20A and the reception unit 20B may be referred to as a "reception unit 20". Likewise, regarding the other configurations, configurations represented by reference symbols with alphabets may be represented by only the reference symbols without the alphabets. [0026]
The reception unit 20A receives a reactive power detection value output from the reactive power detection device 2. The reception unit 20B receives torque information (a torque command, a torque feedback, an active current command, or an active current detection value), speed information (a speed command or a speed feedback), and active power information (an active power command or an active power detection value) that are output from the respective power converters 5A, 5B, and 5C to the respective electric motors 10A, 10B, and 10C. The torque information may be an active power command or an active power detection value. [0027]
The arrival time estimation unit 17 calculates an arrival time estimated value at which the steel sheet 13 arrives at the rolling roller upper portion 11 or the rolling roller lower portion 12 based on the torque information and the speed information received by the reception unit 20B and an electric motor arrangement read from the electric motor arrangement storage unit 18, and outputs the arrival time estimated value
15

to the reactive power command determination unit 16. [0028]
The reactive power command determination unit 16 calculates the reactive power command based on the arrival time estimated value read from the arrival time estimation unit 17, the rated apparent power read from the rated apparent power storage unit 19, the reactive power detection value received by the reception unit 20A, and the active power detection value of each of the power converters received by the reception unit 20B, and outputs the reactive power command to the transmission unit 15. [0029]
The transmission unit 15 outputs the reactive power command of each of the power converters read from the reactive power command determination unit 16 to each of the power converters 5A, 5B, and 5C. The reactive power command determination unit 16 may determine the reactive current command instead of the reactive power command value. [0030]
The reactive power command determination unit 16 and the arrival time estimation unit 17 will be described with reference to Fig. 3. Fig. 3 illustrates a change in the positional relationship between the group of electric motors 10A to 10C and the steel sheet 13. Fig. 3 illustrates three sets of rolling rollers. The first rolling rollers 11A and
16

12A come to contact with the steel sheet 13 first and roll the steel sheet 13. The second rolling rollers 11B and 12B further roll the steel sheet 13 that has been rolled by the first rolling rollers 11A and 12A. The third rolling rollers 11C and 12C roll the steel sheet 13 in the end. In the drawing, for the convenience of explanation, three sets of rolling rollers are illustrated, but the embodiment is not limited thereto. For example, plural sets of rolling rollers may be present. [0031]
In Fig. 3, the rolling rollers 11A and 12A are arranged at a position XA, the rolling rollers 11B and 12B are arranged at a position XB, and the rolling rollers 11C and 12C are arranged at a position XC. In Fig. 3, the left side represents an upstream side, the right side represents a downstream side, and the steel sheet 13 moves from the upstream side to the downstream side. [0032]
Time t11 represents a state where the rolling of the steel sheet 13 is started from a position upstream of the rolling rollers 11A and 12A. Time t12 represents a state where the steel sheet 13 is being rolled by the rolling rollers 11A and 12A. Time t13 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is completed and the steel sheet 13 is positioned at a position downstream of the rolling rollers 11A and 12A. Time t14 represents a state where the
17

rolling of the steel sheet 13 by the rolling rollers 11B and 12B is started. Time t15 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11C and 12C is started. In the description of Fig. 3, the steel sheet 13 is not rolled by the plurality of rolling rollers 11 and 12 at the same time. In addition, hereinafter, the rolling roller may be abbreviated as a "roller". [0033]
Fig. 4 illustrates changes over time in the torque of the electric motor 10A and the speed (angular velocity; hereinafter the same shall be applied) of the electric motor 10A. In Fig. 4, at time t11, the steel sheet 13 arrives at the electric motor 10A, and the speed of the electric motor 10A decreases due to a torque generated for rolling the steel sheet 13. In a speed controller (not illustrated) of the power converter 5A that controls the electric motor 10A, an acceleration torque for following the speed command value is generated. At time t12, the steel sheet 13 is being rolled. Therefore, a torque for rolling the steel sheet 13 is generated. At time t13, the rolling is completed. Therefore, the torque of the electric motor 10A decreases. [0034]
A process of the arrival time estimation unit 17 will be described with reference to Fig. 5. Fig. 5 illustrates an example of calculating time tB at which the steel sheet 13
18

arrives at the rollers 11B and 12B corresponding to the power converter 5B. Hereinafter, the expression "the steel sheet 13 arrives at the rollers 11 and 12" may be expressed as "the steel sheet 13 arrives at the power converter 5" . To be exact, when the steel sheet 13 comes into contact with the rolling rollers 11 and 12, the torque or speed of the electric motor 10 connected to the rollers 11 and 12 changes, and the output of the power converter 5 that controls the electric motor 10 changes. [0035]
In Fig. 5, the arrival time tB represents a time at which the steel sheet 13 arrives at the rolling rollers 11B and 12B. [0036]
The control device 4 reads an electric motor arrangement, a torque TA(t), and a speed command VA (t) of the power converter 5A and an electric motor arrangement XB and a torque xB(t) of the power converter 5B (S101) . [0037]
The control device 4 compares the torque TA(t) and a predetermined threshold TH1 to each other to determine whether the steel sheet 13 is being rolled by the rolling rollers 11A and 12A (S102). When the torque TA(t) is higher than the threshold TH1 (S102: Yes), the control device 4 determines that the steel sheet 13 is being rolled by the rolling rollers 11A and 12A and proceeds to Step S103. When the torque TA(t) is
19

lower than the threshold TH1 (S102: No), the control device 4 determines that the steel sheet 13 is not being rolled by the rolling rollers 11A and 12A and proceeds to Step S107. [0038]
In Step S103, the control device 4 detects a timing at which the steel sheet 13 arrives at the rolling rollers 11A
and 12A. When a torque TA (t-tCAL) at time t-tCAL, which is earlier than time t by one cycle of the corresponding flowchart calculation, is higher than the threshold TH1 (S103: Yes), the control device 4 determines that the steel sheet 13 is also being rolled by the rolling rollers 11A and 12A at time t-tCAL and proceeds to Step S105. [0039]
On the other hand, when the torque TA (t-tCAL) is lower than the threshold TH1 (S103: No), the control device 4 determines that the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is started at time t and proceeds to Step S104. [0040]
After the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is started, the control device 4 resets a distance LSTA-EST of the steel sheet 13 having passed through the rolling rollers 11A and 12A to 0 (S104) . [0041]
The control device 4 updates the distance of the steel
20

sheet 13 having passed through the rolling rollers 11A and 12A (S105). The distance of the steel sheet 13 having passed through the rolling rollers 11A and 12A can be calculated by Formula 1. [0042]
[Formula 1]

wherein VA(t) represents a moving speed of the steel sheet 13 being rolled by the rollers 11A and 12A. The moving speed VA(t) of the steel sheet 13 being rolled by the rollers 11A and 12A can be calculated by Formula 2. [0043]
[Formula 2]

wherein rA represents a radius (m) of the roller 11A. TOA(t) represents an angular velocity (rad/sec) of the roller 11A. [0044]
Next, the control device 4 updates a time at which the steel sheet 13 arrives at the rolling rollers 11B and 12B (S106). Time tB at which the steel sheet 13 arrives at the rolling rollers 11B and 12B can be calculated by Formula 3. [0045]
[Formula 3]
21


The control device 4 compares the torque TB (t) of the power converter 5B and a predetermined threshold TH1B to each other to determine whether the steel sheet 13 is being rolled by the
rolling rollers 11B and 12B (S107) . When the torque TB(t) is higher than the threshold TH1B (S107: Yes) , the control device 4 determines that the steel sheet 13 is being rolled by the rolling rollers 11B and 12B and proceeds to Step S108. [0046]
On the other hand, when the torque TB(t) is lower than the threshold TH1B (S107: No), the control device 4 determines that the steel sheet 13 is not being rolled by the rolling rollers 11B and 12B and proceeds to Step S109. [0047]
In Step S108, the control device 4 updates the time at which the steel sheet 13 arrives at the rolling rollers 11B and 12B (S106). At time t, the steel sheet 13 is moving to the rolling rollers 11B and 12B, and an arrival time estimated value tBEST is updated by Formula 4. [0048]
In Step S109, the control device 4 detects a timing at
22
[Formula 4]


which the rolling of the steel sheet 13 by the rolling rollers
11B and 12B is completed. When a torque TB (t-tCAL) at time t-tCAL, which is earlier than time t by one cycle, is higher than the threshold TH1B (S109: Yes), the control device 4 determines that the rolling of the steel sheet 13 by the rolling rollers 11B and 12B is completed at time t-tCAL and proceeds to Step S110. [0049]
On the other hand, when the torque TB (t-tCAL) is lower than the threshold TH1B (S109: No), the control device 4 determines that the steel sheet 13 is being rolled by the rolling rollers 11A and 12A at time t and ends the process. [0050]
In Step S110, the control device 4 updates the time at which the steel sheet 13 arrives at the rolling rollers 11B and 12B. Since the arrival of the steel sheet 13 is completed at time t, the arrival time estimated value is reset to a greater value according to Formula 5. [0051]
[Formula 5]

For example, time tSETB is a value that is sufficiently greater than a maximum value of the time required for the steel sheet 13 in operation to arrive at the roller 12B from the roller 12A.
23

[0052]
The above-described process of Fig. 5 illustrates the example of estimating the arrival time at the rolling rollers 11B and 12B. However, the arrival time at the rolling rollers 11C and 12C can also be calculated from the same process above. Accordingly, the description of a method of estimating a time at which the steel sheet 13 arrives at the rollers 11C and 12C will not be repeated. [0053]
An example of a process of the reactive power command determination unit 16 will be described with reference to Fig. 6. The control device 4 reads the reactive power detection value QM, arrival time estimated values tB and tC of the steel sheet 13 at the power converters 5A to 5C calculated by the arrival time estimation unit 17, rated apparent powers SA, SB, and SC, and active powers PA, PB, and PC and proceeds to Step S202. [0054]
In Step S202, the control device 4 calculates an amount of reactive power required QTMP used for an internal calculation to calculate reactive powers QREFA, QREFB, and QREFC that are distributed to the power system 1 in the plant by the power converters 5A to 5C, and proceeds to Step S203. [0055]
In order to adjust the power factor received from the
24

power system 1 by the plant to "1", it is necessary to calculate the amount of reactive power required to cancel out the reactive power detection value. Therefore, the control device 4 calculates the amount of reactive power required QTMP by Formula 6. [0056]
[Formula 6]

In Step S203, the control device 4 compares the arrival time estimated values tB and tC of the load (steel sheet 13) at the power converter 5B and the power converter 5C to each other. When tB > tC is satisfied (S203: Yes), the control device 4 proceeds to Step S204. On the other hand, when tB > tC is not satisfied (S203: No), the control device 4 proceeds to Step S210. [0057]
In Step S204, the control device 4 calculates the reactive power command QREFB of the power converter 5B. The reactive power command can be calculated by Formula 7. [0058]
wherein SIGN is a function that outputs 1 when the input
25
[Formula 7]


in the parentheses is positive, outputs 0 when the input in the parentheses is 0, and outputs -1 when the input in the parentheses is negative. MIN is a function that outputs the smallest value among the inputs in the parentheses. ABS is a function that outputs the absolute value of the inputs in the parentheses. [0059]
When the steel sheet arrival time estimated value tB and the current time t are different from each other (when the rollers 11B and 12B are not rolling), it can be assumed that the active power in the rollers 11B and 12B is sufficiently low. Accordingly, in Formula 7, the active power PB may be fixed to 0 without using the detection value of PB. [0060]
When the reactive current command is given instead of the reactive power command, a reactive current output command may be calculated by using a rated apparent current instead of the rated apparent power and using active current instead of the active power in Formula 7. [0061]
In Step S205, the control device 4 updates the amount of reactive power required QTMP. The control device 4 updates the amount of reactive power required QTMP according to Formula 8 such that the amount of reactive power required changes by the reactive power command calculated in Formula 7.
26

[0062]
[Formula 8]

In Step S206, the control device 4 determines whether the amount of reactive power required QTMP is 0. When the amount of reactive power required QTMP=0 is satisfied (S206: Yes), the control device 4 determines that the required reactive power has been able to be supplied from the power converter 5B and proceeds to Step S209. [0063]
On the other hand, when the amount of reactive power required QTMP=0 is not satisfied (S206: No), the control device 4 determines that the required reactive power has not been able to be supplied from the power converter 5B and proceeds to Step S207. [0064]
In Step S207, the control device 4 calculates the reactive power command QREFC of the power converter 5C. The reactive power command can be calculated by Formula 9. [0065]
[Formula 9]

When the steel sheet arrival time estimated value tC and the current time t are different from each other (when the
27

roller 11C is not rolling), it can be assumed that the active power in the roller 11C is sufficiently low. Therefore, in Formula 9, the active power PC may be fixed to 0 without using the detection value of PC. [0066]
In Step S208, the control device 4 updates the amount of reactive power required QTMP. The control device 4 updates the amount of reactive power required QTMP according to Formula 10 such that the amount of reactive power required changes by the reactive power command calculated in Formula 9. [0067]
[Formula 10]

In Step S209, the control device 4 adjusts the reactive power command QREFC of the power converter 5C to be zero. [0068]
In Step S210, the control device 4 calculates the reactive power command QREFC of the power converter 5C. The reactive power command can be calculated by Formula 9. [0069]
In Step S211, the control device 4 updates the amount of reactive power required QTMP. The control device 4 updates the amount of reactive power required QTMP according to Formula 10 such that the amount of reactive power required changes by the reactive power command calculated in Formula 9.
28

[0070]
In Step S212, the control device 4 determines whether the amount of reactive power required QTMP is 0. When the amount of reactive power required QTMP=0 is satisfied (S212: Yes), the control device 4 determines that the required reactive power has been able to be supplied from the power converter 5C and proceeds to Step S215. On the other hand, when the amount of reactive power required QTMP=0 is not satisfied (S212: No), the control device 4 determines that the required reactive power has not been able to be supplied from the power converter 5C and proceeds to Step S213. [0071]
In Step S213, the control device 4 calculates the reactive power command QREFB of the power converter 5B. The reactive power command can be calculated by Formula 7. [0072]
In Step S214, the control device 4 updates the amount of reactive power required QTMP. The control device 4 updates the amount of reactive power required QTMP according to Formula 8 such that the amount of reactive power required changes by the reactive power command calculated in Formula 7 in Step S213. [0073]
In Step S215, the control device 4 adjusts the reactive power command QREFB of the power converter 5B to be zero. [0074]
29

In Step S216, the control device 4 determines whether the amount of reactive power required QTMP is 0. When the amount of reactive power required QTMP=0 is satisfied (S216: Yes), the control device 4 determines that the required reactive power has been able to be supplied from the power converter 5B and the power converter 5C and proceeds to Step S218. [0075]
On the other hand, when the amount of reactive power required QTMP=0 is not satisfied (S216: No), the control device 4 determines that the required reactive power has not been able to be supplied from the power converter 5B and the power converter 5C and proceeds to Step S217. [0076]
In Step S217, the control device 4 calculates the reactive power command QREFA of the power converter 5A. The reactive power command can be calculated by Formula 11. [0077]
[Formula 11]

In Step S218, the control device 4 adjusts the reactive power command QREFA of the power converter 5A to be zero. [0078]
A process of the reactive power command determination unit 16 when the number of power converters 5 is four or more
30

will be described using a flowchart of Fig. 7. [0079]
The control device 4 reads the reactive power detection
value QM, arrival time estimated values tB, tC, ..., and tN (N represents the number of power converters; hereinafter, the same shall be applied) of the steel sheet 13 at respective power converters 5A, 5B, ..., and 5N calculated by the arrival time estimation unit 17, rated apparent powers SA, SB, SC, ... and SN, and active powers PA, PB, PC, ..., PN (S301), and then proceeds Step S302. [0080]
The control device 4 calculates the amount of reactive power required QTMP (S302) and proceeds to Step S303. In order to adjust the power factor to "1", it is necessary to calculate the amount of reactive power required to cancel out the reactive power detection value. Therefore, the control device 4 calculates the amount of reactive power required by Formula 12. [0081]
[Formula 12]

In Step S303, the control device 4 sets an initial value. As the initial value, the control device 4 sets K=1 and N=the number of power converters.
31

[0082]
In Step S304, the control device 4 compares the arrival time estimated values of the load at the power converters 5B to 5N to each other and calculates a reactive power command QREFK of the power converter 5K having the K-th latest arrival time estimated value. The arrival time of the steel sheet 13 at the power converter 5A with which the steel sheet 13 comes into contact first cannot be estimated. Therefore, the power converter 5A is not included for the calculation of the power converter 5K having the K-th latest arrival time estimated value. The power converter reactive power command can be calculated by Formula 13. [0083]
[Formula 13]

In Step S305, the control device 4 updates the amount of reactive power required QTMP. The control device 4 calculates the amount of reactive power required QTMP by Formula 14 such that the amount of reactive power required changes by the reactive power command calculated in Formula 13. [0084]
32
[Formula 14]


In Step S306, the control device 4 determines whether the amount of reactive power required QTMP is 0. When the amount of reactive power required QTMP=0 is satisfied (S306: Yes), the control device 4 determines that the required reactive power has been able to be supplied from the power converter having the K-th latest arrival time estimated value and ends the process. [0085]
On the other hand, when the amount of reactive power required QTMP=0 is not satisfied (S306: No), the control device 4 determines that the required reactive power has not been able to be supplied from the power converter having the K-th latest arrival time estimated value and proceeds to Step S307. [0086]
In Step S307, the control device 4 compares K and N-1 to each other. When K < N-1 is satisfied (S307: Yes), the control device 4 proceeds to Step S308. On the other hand, when K < N-1 is not satisfied (S307: No), the control device 4 proceeds to Step S309. [0087]
In Step S308, the control device 4 updates the value of K by increasing the value of K by 1 and proceeds to Step S304. By updating K to K+1, the control device 4 can designate the power converter having the K+1-th latest arrival time estimated value in Step S304.
33

[0088]
In Step S309, the control device 4 calculates the reactive power command QREFA of the power converter 5A and ends the process. The reactive power command QREFA of the power converter 5A can be calculated by Formula 11. [0089]
Fig. 8 is a schematic diagram illustrating a change over time in reactive power compensation in the related art prepared for a comparison to the example. Fig. 9 is a schematic diagram illustrating a change over time in reactive power compensation in the example. An actual relationship between active power, reactive power, and apparent power is represented by a vector sum, but it is difficult to illustrate this relationship with a drawing. Therefore, Figs. 8 and 9 schematically illustrate the relationship in one dimension. In Fig. 8, time td represents the response time required for the power converter 5 to supply reactive power from the transmission of the reactive power command to the power converter 5. In Figs. 8 and 9, the horizontal axis represents the time axis, and the vertical axis represents the power. [0090]
In Fig. 8, at time t11, t14, t15, when the steel sheet 13 arrives at the power converters 5A, 5B, and 5C such that the load increases, the sum of the active power and the reactive power command in the power converters 5A to 5C exceeds the rated
34

apparent power (hereinafter, also referred to as "rated
power").
[0091]
Here, in general, the power converter 5 has a function (limiter) of suppressing the current command so as not to exceed the rated power for device protection. Accordingly, when the load increases, the limiter acts such that the power converter 5 cannot supply reactive power as instructed by the reactive power command. [0092]
Further, the response time td is required for the power converter 5 to supply desired reactive power from the transmission of the reactive power command to the power converter 5. Therefore, as illustrated in Fig. 8, a period of time during which reactive power cannot be supplied as instructed by the reactive power command is generated corresponding to the response time td. [0093]
In the example illustrated in Fig. 9, the reactive power command is preferentially transmitted to the power converter having a slow arrival time estimated value of the steel sheet 13. Accordingly, even when the load rapidly increases, the power converter 5 can supply reactive power as instructed by the reactive power command. [0094]
35

For example, during a period between time t11 and time t14, the arrival time estimated value of the steel sheet 13 satisfies a relationship tB_EST < tC_EST. Therefore, the reactive power command is preferentially distributed to the power converter 5C prior to the power converter 5B. [0095]
During a period from the time at which the steel sheet 13 has passed through the gap between the rollers 11B and 12B corresponding to the electric motor 10B and time t15 at which the steel sheet 13 arrives at the next rollers 11C and 12C, the arrival time estimated value of the steel sheet 13 satisfies the relationship tB_EST > tC_EST. Accordingly, the control device 4 preferentially distributes the reactive power command to the power converter 5B prior to the power converter 5C. [0096]
According to the example having the above-described configuration, reactive power is preferentially supplied from the power converter 5 having a higher remaining current capacity. As a result, the distribution of reactive power to the electric motor having an early arrival time of the steel sheet 13 that causes an increase in load can be reduced. Accordingly, according to the example, the amount of reactive power required can be efficiently and stably supplied from the power converter 5, and the power factor of the plant power system 1 can be improved.
36

[0097]
In the example, the output of reactive power is assigned by estimating that the steel sheet 13 arrives at the rollers 11 and 12 based on the output state of the power converter 5. Therefore, a sensor for detecting the presence of the steel sheet 13 is unnecessary. Accordingly, the power control system of the plant can be simply improved at a relatively low cost. However, in the example, a high output of the reactive power cannot be assigned to the power converter 5A corresponding to the rollers 11 and 12 with which the steel sheet 13 comes into contact first. The reason for this is that the time at which the steel sheet 13 comes into contact with the rollers 11 and 12 is unclear. A configuration for accurately detecting the arrival of the steel sheet 13 will be described below. [0098]
In the above description, it is assumed that the length of one steel sheet is shorter than the distance between any rolling rollers. However, even when the length of one steel sheet is longer than the distance between any rolling rollers as illustrated in Fig. 10, reactive power can be output from the power converter 5 at an appropriate timing due to the same principle as that of Figs. 2, 5, and 7, and the overall power factor of the plant can be improved. [Example 2]
37

[0099]
A second example will be described with reference to Figs. 11 to 16. Examples described below including the second example correspond to modification examples of the first example, and thus differences from the first example will be mainly described. In the plant power control system according to the example, the sensors 21A to 21C that detect the steel sheet 13 are used. [0100]
Fig. 11 is a configuration diagram of the plant power control system according to the example. The overall configuration illustrated in Fig. 11 is different from the overall configuration according to the first example illustrated in Fig. 1, in that the sensors 21A, 21B, and 21C are added. Unless it is necessary to distinguish the sensors 21A, 21B, and 21C from each other, the sensors 21A, 21B, and 21C may be referred to as a "sensor 21". [0101]
The sensor 21 is not particularly limited as long as it can detect the presence of the steel sheet 13. The sensor 21 can also be referred to as, for example, a "steel sheet detector". The sensor 21 according to the example is configured as a sensor that detects the thickness of the steel sheet 13. Each of the sensors 21 is positioned at a position upstream of the corresponding rollers 11 and 12 and is arranged
38

in the vicinity of the upper roller 11. That is, the first sensor 21A is provided in the vicinity of a position upstream of the roller 11A, the second sensor 21B is provided in the vicinity of a position upstream of the roller 11B, and the third sensor 21C is provided in the vicinity of a position upstream of the roller 11C. A signal detected by each of the sensors 21 is input to the control device 4 through a communication network CN2. [0102]
Fig. 12 illustrates a configuration of a control device 4B. The configuration illustrated in Fig. 12 is different from the configuration according to the first example illustrated in Fig. 2, in that the reception unit 20C that receives a signal from the sensor 21 is added. [0103]
In the control device 4B according to the example, the signal of the sensor 21 arranged in the vicinity of a position upstream of the rollers 11 and 12 can be used. Therefore, the approaching of the steel sheet 13 to the initial rolling rollers 11A and 12A can be detected. Further, the accuracy of estimating the time at which the steel sheet 13 arrives at the next rolling rollers 11B, 11C, ..., and 11N and the rolling rollers 12B, 12C, ..., and 12N can be improved. [0104]
A process of the arrival time estimation unit 17 will
39

be described with reference to Figs. 13 and 14. The flowchart of Fig. 13 illustrates the process on the power converter 5A. The flowchart of Fig. 14 illustrates the process flow on the power converter 5B. [0105]
Fig. 15 illustrates an example of a positional relationship between the steel sheet 13, the rollers 11 and 12, and the sensor 21 for the explanation of Figs. 13 and 14. [0106]
In Fig. 15, the rolling rollers 11A and 12A are arranged at the position XA, the rolling rollers 11B and 12B are arranged at the position XB, and the rolling rollers 11C and 12C are arranged at the position XC. The sensor 21A is arranged at a position XAS, the sensor 21B is arranged at a position XBS, and the sensor 21C is arranged at a position XCS. In Fig. 15, the left side represents an upstream side, and the right side represents a downstream side. It is assumed that the steel sheet 13 moves from the upstream side to the downstream side. [0107]
Time t31 represents a state where the steel sheet 13 arrives at the sensor 21A. Time t32 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is started. Time t33 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is completed and the steel sheet 13 is positioned at a
40

position downstream of the rolling rollers 11A and 12A. Time t34 represents a state where the steel sheet 13 arrives at the sensor 21B. Time t35 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11B and 12B is started. [0108]
Returning to Fig. 13, the description will be made. In Fig. 13, the control device 4B reads the electric motor
arrangement XA, the torque TA(t), and the speed command VA(t) of the power converter 5A at time t and a detection value DSTA (t) of the sensor 21A (S401). [0109]
The control device 4B compares the torque TA(t) and a threshold TH1A to each other (S402) . When the torque TA(t) is higher than the threshold TH1A (S402: Yes) , the control device 4B determines that the steel sheet 13 is being rolled and proceeds to Step S403. On the other hand, when the control device 4B determines that the torque xA(t) is higher than the threshold TH1A (S402: No), the control device 4B proceeds to Step S404. [0110]
In Step S403, the control device 4B updates the arrival time estimated value of the steel sheet 13. At time t, the steel sheet 13 is moving to the rolling rollers 11A and 12A. Therefore, the control device 4B updates an arrival time estimated value tAEST(t) of the steel sheet 13 from the
41

following Formula 15. [0111]
[Formula 15]

wherein t represents the current time.
[0112]
In Step S404, the control device 4B compares the detection value DSTA(t) of the sensor 21 and a threshold TH2A to each other. When DSTA > TH2A is satisfied (S404: Yes), the control device 4B determines that the sensor 21 recognizes the presence of the steel sheet 13 at time t and thus proceeds to Step S405. On the other hand, when DSTA > TH2A is not satisfied (S404: No), the control device 4B determines that the sensor 21 does not recognize the presence of the steel sheet 13 at time t and thus ends the process. [0113]
In Step S405, the control device 4B compares a detection value DSTA(t-tCAL) of the sensor at time (t-tCAL) and the predetermined threshold TH2A to each other. When DSTA(t-tCAL) > TH2A is satisfied (S405: Yes), the control device 4B ends the process. On the other hand, when DSTA(t-tCAL) > TH2A is not satisfied (S405: No), the control device 4B determines that the steel sheet 13 arrives at the sensor 21B at time t and proceeds to Step S406.
42

[0114]
In Step S406, the control device 4B updates the time at which the steel sheet 13 arrives at the rolling rollers 11A and 12A from the following Formula 16. [0115]
[Formula 16]

wherein tSETAS represents a period of time required for the steel sheet 13 to arrive at the rolling rollers 11A and 12A after the sensor 21A recognizes the steel sheet 13. Time tSETAS can be estimated from the following Formula 17 using a distance (XA-XAS) between the sensor 21A and the rolling rollers 11A and 12A and the speed VA(t) of the rolling rollers 11A and 12A. [0116]
[Formula 17]

wherein tSETAS may be a predetermined value. [0117]
In Fig. 14, the control device 4B reads the electric motor
arrangement XA, the torque TA(t), and the speed command VA(t) of the power converter 5A, a detection value DSTB(t) of the sensor 21B, and the electric motor arrangement XB and the torque
43

TB(t) of the power converter 5B (S501). [0118]
Since Steps S502 to S506 are the same as Steps S202 to S206 in Fig. 6, the description thereof will not be made. [0119]
In Step S507, the control device 4B compares the torque xA (t-tCAL) of the sensor at time (t-tCAL) and the threshold TH1A to each other. When TA (t-tCAL) > TH1A is satisfied (S507 : Yes) , the control device 4B determines that the rolling by the rollers 11A and 12A is completed at time t and proceeds to Step S508. On the other hand, when TA (t-tCAL) > TH1A is not satisfied (S507: No), the control device 4B proceeds to Step S509. [0120]
In Step S508, the control device 4B stores time tENDA at which the rolling of the steel sheet 13 by the rollers 11A and 12A is completed and an electric motor speed VA (tENDA) . Next, the control device 4B proceeds to Step S509. [0121]
In Step S509, the control device 4B compares the detection value DSTB(t) of the sensor 21 and the predetermined threshold TH2B to each other. When DSTB > TH2B is satisfied (S509: Yes), the control device 4B determines that the sensor 21B recognizes the presence of the steel sheet 13 at time t and thus proceeds to Step S510. On the other hand, when DSTB > TH2B is not satisfied (S509: No), the control device 4B
44

determines that the sensor 21 does not recognize the presence of the steel sheet 13 at time t and thus proceeds to Step S512. [0122]
In Step S510, the control device 4B compares a detection value DSTB (t-tCAL) of the sensor 21B at time (t-tCAL) and the predetermined threshold TH2B to each other. When DSTB (t-tCAL) > TH2B is satisfied (S510: Yes), the control device 4B proceeds to Step S512. On the other hand, when DSTB (t-tCAL) > TH2B is not satisfied (S510: No), the control device 4B determines that the steel sheet 13 arrives at the sensor 21B at time t and proceeds to Step S511. [0123]
In Step S511, the control device 4B calculates and updates the time at which the steel sheet 13 arrives at the rolling rollers 11B and 12B from the following Formula 18. [0124]
[Formula 18]

wherein tSETBS represents a period of time required for the steel sheet 13 to arrive at the rolling rollers 11B and 12B after the sensor 21B recognizes the steel sheet. Time tSETBS can be estimated by Formula 19 using a distance (XB-XBS) between the sensor 21B and the rolling rollers 11B and 12B and the speed VA (tENDA) at the end of the rolling by the rolling rollers 11A and 12A.
45

[0125]
[Formula 19]

wherein tSETBS may be a predetermined value. [0126]
Since Steps S512 to S515 are the same as Steps S207 to S210 in Fig. 6, the description thereof will not be made. [0127]
Fig. 14 illustrates the example of estimating the arrival time estimated value tB at the rolling rollers 11B and 12B. The arrival time estimation unit 17 relating to the rolling rollers 11C and 12C can also be implemented by performing calculation according to the same flowchart as that of Fig. 14. [0128]
A process of the reactive power command determination unit 16 will be described with reference to Fig. 16. Since Steps S601 to S603 are the same as Steps S301 to S303 in Fig. 7, the description thereof will not be made. [0129]
In Step S604, the control device 4B compares the arrival time estimated values of the load at the power converters 5 to each other and calculates the reactive power command QREFK of the power converter 5K having the K-th latest arrival time estimated value. The reactive power command can be calculated
46

by Formula 13. [0130]
Since Steps S605 and S606 are the same as Steps S305 and S306 in Fig. 7, the description thereof will not be made. [0131]
In Step S606, the control device 4B determines whether the amount of reactive power required QTMP is 0. When the amount of reactive power required QTMP=0 is satisfied (S606: Yes), the control device 4B determines that the required reactive power has been able to be supplied from the power converter 5K having the K-th latest arrival time estimated value and ends the process. [0132]
On the other hand, when the amount of reactive power required QTMP=0 is not satisfied (S606: No), the control device 4B determines that the required reactive power has not been able to be supplied from the power converter 5K having the K-th latest arrival time estimated value and proceeds to Step S607. [0133]
In Step S607, the control device 4B compares "K" and "N" to each other. When K < N is satisfied (S607: Yes), the control device 4 proceeds to Step S608. When K < N is not satisfied (S607: No), the control device 4 ends the process. [0134]
The sensor 21 is not necessarily the detector that
47

detects the thickness of the steel sheet and is not particularly limited as long as it can determine whether the steel sheet is present. When whether the steel sheet is present is detected as "1 (Steel Sheet Present) " or "0 (Steel Sheet Not Present) ", thresholds TH2A, TH2B, ..., and TH2N are a value more than 0 and may be set to be less than 1.
[0135]
The example having the above-described configuration exhibits the same effects as those of the first example. Further, in the example, the signal of the sensor 21 that detects the steel sheet 13 can be used. Therefore, a change in the state of the power converter 5 can be estimated more accurately than the first example, and the output of reactive power can be efficiently distributed at an appropriate timing.
[Example 3]
[0136]
A third example will be described with reference to Figs . 17 to 19. Fig. 17 illustrates a control device 4C of the plant power control system according to the example. The configuration illustrated in Fig. 17 is different from the configuration according to the second example illustrated in Fig. 12, in that a steel sheet speed estimation unit 23 is added. Hereinafter, the steel sheet speed estimation unit 23 may be abbreviated as a "speed estimation unit 23".
[0137]
48

The steel sheet speed estimation unit 23 is a function provided for reducing a difference between an actual value and an estimated value of the moving speed of the steel sheet 13. Since slipping or the like occurs between the steel sheet 13 and the rollers 11 and 12. Therefore, there may be a difference between the actual value and the estimated value of the speed of the steel sheet 13. The speed estimation unit 23 calculates the estimated value of the speed based on the angular velocity information from the power converter 5 and the signal from the sensor 21. [0138]
Fig. 18 illustrates a configuration of the speed estimation unit 23. The speed estimation unit 23 includes, for example, a sensor detection value storage device 29, an actual speed calculation unit 24, a speed correction coefficient learning unit 25, a speed correction coefficient storage unit 26, a steel sheet speed estimated value calculation unit 27, a speed information storage device 30, and a torque information storage device 31. The names of the configuration are appropriately omitted in Fig. 18. [0139]
The sensor detection value storage device 29 stores the detection value of the sensor 21 and outputs the detection value to the actual speed calculation unit 24. The speed information storage device 30 stores the speed information and outputs the
49

speed information to the speed correction coefficient learning unit 25. The torque information storage device 31 stores the torque information and outputs the torque information to the speed correction coefficient learning unit 25. The speed correction coefficient storage unit 26 stores a speed correction coefficient input from the speed correction coefficient learning unit 25 and outputs a response speed estimation unit. [0140]
A process of the actual speed calculation unit 24 will be described. On the other hand, the actual steel sheet speed between the roller 11A and the roller 11B is calculated based on Formula 20 using time t34 at which the detection of the sensor 21B is started and time t35 at which the rolling of the steel sheet by the roller 11B is started. [0141]
[Formula 20]

A process of the speed correction coefficient calculation unit 25 will be described. An estimated value VEST_AB0 of the steel sheet speed before correction can be considered as the speed of the roller 11A when t=t33 in Fig. 15 (t=tENDA in the flowchart of Fig. 14) and can be calculated by Formula 21.
50

[0142]
[Formula 21]

When a ratio between the estimated value of the steel sheet speed and the actual steel sheet speed is represented
by a correction coefficient a, the correction coefficient a
is represented by Formula 22.
[0143]

[Formula 22]

For example, the correction coefficient a is learned according to each of the torque information stored in the torque information storage device 31 and the speed information stored in the speed information storage device 30. In this case, the
correction coefficient a is provided through a two-dimensional
table of the torque and the speed.
[0144]
The information used for the learning of the correction
coefficient a is not limited to the torque and the speed. For example, at least one kind of information of the torque, the speed, the thickness of the steel sheet, the temperature of the steel sheet, and the component ratio of the steel sheet may be acquired from an external device, and the correction coefficient a may be learned according to the acquired
51

information. [0145]
For example, when the correction coefficient a is learned according to the torque, the speed, and the thickness of the steel sheet, a configuration may be added such that the thickness of the steel sheet 13 can be input to the speed correction coefficient learning unit 25 of Fig. 18, and the
correction coefficient a may be provided through a
three-dimensional table.
[0146]
A process of the steel sheet speed estimated value calculation unit 27 will be described. The estimated value of the steel sheet speed after correction can be calculated by Formula 23 using the correction coefficient a. [0147]
[Formula 23]

An example of the speed command correction using Formulae 20 to 23 will be described with reference to Fig. 19. By considering an average speed VACT_AB during a period between t34 and t35 as the actual steel sheet speed and correcting a ratio between the average speed VACT_AB and the estimated value VEST_AB0 of the steel sheet speed before correction obtained from the speed of the roller 11A, the actual steel sheet speed can be estimated.
52

The example having the above-described configuration exhibits the same effects as those of the second example. Further, in the example, a difference between the actual moving speed and the estimated speed of the steel sheet 13 can be corrected. Therefore, a change in the state of the power converter 5 can be estimated more accurately than the second example, and reactive power can be output from each of the power converters 5 at an appropriate timing. [Example 4] [0148]
A fourth example will be described with reference to Fig. 20. Fig. 20 illustrates a configuration of a control device 4D used in the plant power control system according to the example. The control device 4D according to the example is different from the control device 4C illustrated in Fig. 17, in that a stored data change unit 32 and an external interface 33A for changing data of the stored data change unit 32 from an external device are added in Fig. 20. In Fig. 20, the electric motor arrangement storage unit 18 is abbreviated as "M", and the rated apparent power storage unit 19 is abbreviated as "S". [0149]
The stored data change unit 32 has a function of changing each of the electric motor arrangement stored in the electric motor arrangement storage unit 18, the rated apparent power
53

stored in the rated apparent power storage unit 19, and stored data including the speed command value, the torque command value, the rolling time, and the speed correction coefficient stored in the steel sheet speed estimation unit 32. [0150]
The example having the above-described configuration exhibits the same effects as those of the third example. Further, in the example, a user such as a system manager can change some or all the parameters based on which the value of reactive power to be output from each of the power converters 5 and the timing thereof can be calculated. Accordingly, according to the example, in a case where the arrangement of the electric motor 10 is changed, for example, when the facility of the plant is updated, the user can change the information of the electric motor arrangement and the rated apparent power using the stored data change unit 32. As a result, even after updating the facility of the plant, required reactive power can be compensated for using the reactive power command determination unit 16. [Example 5] [0151]
A fifth example will be described with reference to Figs. 21 to 24. Fig. 21 is an overall configuration diagram of the plant power control system according to the example. The fifth example is different from the first example, in that a
54

transformer 34 and a power factor adjustment device 35 are
added.
[0152]
The power factor adjustment device 35 is connected to the plant power source 1 through the transformer 34. In addition, the power factor adjustment device 35 is connected to a control device 4E through a communication path CN3. [0153]
Fig. 22 is a configuration diagram illustrating the power factor adjustment device 35. The power factor adjustment device 35 includes, for example, a plurality of capacitors 37A, 37B, and 37C and switches 36A, 36B, and 36C that are connected in series to the capacitors 37A, 37B, and 37C, respectively. The power factor adjustment device 35 turns on or off the switches 36A, 36B, and 36C such that the capacitors 37A, 37B, and 37C can be connected to or separated from the system. The configuration of the power factor adjustment device 35 is limited to the example illustrated in Fig. 22. For example, as the power factor adjustment device, for example, a reactive power compensation device (Static Var Compensator) may be used. [0154]
Fig. 23 illustrates a configuration of the control device 4E according to the example. The control device 4E according to the fifth example is different from the control device 4 according to the first example, in that a reception unit 20D
55

that receives a reactive power supply plan from the power factor adjustment device 35 and a function 38 that calculates the distribution of reactive power are added to the control device 4E according to the fifth example. [0155]
The control device 4E receives the reactive power supply plan, which is to be performed by the power factor adjustment device 35, from the power factor adjustment device 35 through the reception unit 20D. The control device 4E distributes the amount of reactive power required to the power factor adjustment device 35 and each of the power converters 5. [0156]
The reactive power distribution calculation unit 38 calculates reactive power to be compensated for by the reactive power command determination unit 16 of the control device 4E by obtaining a difference between the reactive power detection value of the reactive power detection device 2 received through the reception unit 20A and the reactive power supply plan of the power factor adjustment device 35 received through the reception unit 20D. [0157]
Fig. 24 illustrates an example in which the power factor adjustment device 35 and the group of power converters are used in combination to compensate for reactive power. The upper section in Fig. 24 illustrates a change over time in the
56

reactive power detected by the reactive power detection device 2. The middle section in Fig. 24 illustrates a state where the power factor adjustment device 35 compensates for the reactive power. The lower section of Fig.24 illustrates a state where the reactive power is output from each of the power converter 5. [0158]
As illustrated in Fig. 24, the power factor adjustment device 35 controls reactive power by turning on and off the capacitor 37. Therefore, reactive power cannot be completely compensated for by using only the capacitor 37 of the power factor adjustment device 35. [0159]
Therefore, in the example, the compensation of reactive power by the power factor adjustment device 35 and the power factor compensation function of each of the power converters 5 are combined. As a result, the overall power factor of the plant power control system can be compensated for. Further, in the example, the power factor compensation function of the power converter 5 is used. Therefore, the capacitor capacity required for the power factor adjustment device 35 can be reduced, and the costs of the power factor adjustment device 35 can be reduced. [Example 6] [0160]
57

A sixth example will be described with reference to Figs. 25 to 27. Fig. 25 is an overall configuration diagram of the plant power control system according to the example. The configuration of the sixth example illustrated in Fig. 25 is different from the configuration of the fifth example illustrated in Fig. 21, in that in the example, a signal flows from a control device 4F to the power factor adjustment device 35. [0161]
Fig. 26 illustrates a configuration of the control device 4F according to the example. The control device 4F illustrated in Fig. 26 and the control device 4 illustrated in Fig. 2 are different from each other, in that the control device 4F according to the example includes a transmission unit 15A. [0162]
A process of the reactive power command determination unit 16 including the control device 4F according to the example will be described with reference to Fig. 27. [0163]
Since Steps S701 and S706 are the same as Steps S601 and S606 in Fig. 16, the description thereof will not be made. [0164]
In Step S707, the control device 4F compares "K" and "N" to each other. When K < N is satisfied (S707: Yes), the control device 4F determines that the power converter 5 having the
58

latest K+1-th arrival time estimated value is present and
proceeds to Step S708.
[0165]
On the other hand, when K < N is not satisfied (S707: No), the power converter 5 having the latest K+1-th arrival time estimated value is not present. Therefore, the control device 4F determines that the reactive power compensation by the power factor adjustment device 35 is necessary and proceeds to Step S709. [0166]
In Step S708, the control device 4F updates the value of K and returns to Step S704. By increasing the value of the variable K by one, the control device 4F can designate the power converter having the K+1-th latest arrival time estimated value in Step S704. [0167]
In Step S709, the control device 4F transmits a reactive power output command QTMAPREF to the power factor adjustment device 35. [0168]
The example having the above-described configuration exhibits the same effects as those of the fifth example. In the example, when reactive power cannot be compensated for by using only the power converter 5, reactive power is compensated for in cooperation with the power factor adjustment device 35.
59

As a result, the overall power factor of the plant can be
improved.
[Example 7]
[0169]
A seventh example will be described with reference to Figs. 28 and 29. Fig. 28 is a configuration diagram illustrating a control device 4G included in the plant power control system according to the example. The control device 4G according to the example is different from the control device 4 according to the first example illustrated in Fig. 2, in that the control device 4G includes an alarm display unit 39. The alarm display unit 39 is connected to the reactive power command determination unit 16 and outputs an alarm according to an instruction from the reactive power command determination unit 16. [0170]
The flowchart of Fig. 29 illustrates a process of the reactive power command determination unit 16 included in the control device 4G. Since Steps S801 and S808 are the same as Steps S701 and S708 in Fig. 27, the description thereof will not be made. [0171]
In Step S809, the control device 4G displays a predetermined alarm on the alarm display unit 39. As the predetermined alarm, for example, the message "in an N number
60

of power converters, reactive power cannot be compensated for as requested" is displayed on a display. Instead of or in addition to displaying a message on the display, an alarm sound may be output. The predetermined alarm is not necessarily character information. For example, an indicating lamp may be turned on to attract the attention of the user. [0172]
The predetermined alarm may include a suggestion from the plant power control system. This suggestion includes at least either a short-term suggestion or a long-term suggestion. The short-term suggestion includes contents that can be executed to compensate for reactive power within a relatively short period of time. Examples of the short-term suggestion include a change of the reactive power supply plan of the power factor adjustment device 35. That is, the control device 4G calculates whether reactive power can be compensated for by changing at least either the number of capacitors 37 to be turned on and off or a timing at which the capacitor 37 is turned on and off. When the control device 4G determines that reactive power can be compensated for, a change of the reactive power supply plan of the power factor adjustment device 35 is suggested to the user. The long-term suggestion is a suggestion executed for a longer period of time than the short-term suggestion. The long-term suggestion includes an update suggestion relating to the power facility of the plant,
61

for example, replacement or addition of the power converter 5 or replacement or addition of the power factor adjustment device 35. [0173]
The example having the above-described configuration exhibits the same effects as those of the first example. Further, in the example, when reactive power cannot be compensated for, the alarm is output. Therefore, the user recognizes the alarm, and can take countermeasures according to the alarm. As a result, the convenience of the user is improved. [Example 8] [0174]
An eighth example will be described with reference to Figs. 30 and 31. Fig. 30 is a configuration diagram illustrating a control device 4H included in the plant power control system according to the example. The control device 4H according to the example is different from the control device 4 according to the first example, in that a reactive power comparison unit 40, a log data storage unit 41, and an external interface 33B for inputting and outputting data of the log data storage unit 41 from or to an external device are added. [0175]
The reactive power comparison unit 40 receives the reactive power detected by the reactive power detection device
62

2 through the reception unit 20A and receives the information of the reactive power to be output from each of the power converters 5 through the reception unit 20B. The reactive power comparison unit 40 compares the reactive power received from the reception unit 20A and the reactive power received from the reception unit 20B to each other. When the control device 4H determines that reactive power cannot be compensated for, the control device 4H stores predetermined log data in the log data storage unit 41. [0176]
A process of the reactive power comparison unit 40 included in the control device 4H will be described using the flowchart of Fig. 31. [0177]
The control device 4H reads the reactive power detection value QM from the reception unit 20A and reads the reactive
powers QA, QB, QC, •••, and QN from the reception unit 20B (S901) . [0178]
The control device 4H calculates a total amount of reactive power required QREF0 (S902) . The total amount of reactive power required QREF0 can be calculated from the following Formula 24. [0179]
63
[Formula 24]


The control device 4H calculates a sum QTOTAL of the reactive powers QA, QB, QC, ..., and QN (S903) . QTOTAL is represented by the following Formula 25. As described above, N in QN represents the number of power converters. [0180]
[Formula 25]

The control device 4 compares QTOTAL and QREF0 to each other (S904). When QTOTAL < QREF0 is satisfied (S904: Yes), the control device 4H proceeds to Step S905. On the other hand, when QTOTAL < QREF0 is not satisfied (S904: No), the control device 4H ends the process. [0181]
The control device 4H stores the predetermined log data in the log data storage unit 41 (S905). The predetermined log data includes, for example, the reactive power detection value received by the reception unit 20A, at least one of the active power, the reactive power, the torque, and the speed of each of the power converters 5 received by the reception unit 20B, and a time stamp at the time of storing the log data. Instead, any data at a plurality of time points may be stored in the log data storage unit 41. [0182]
The user can extract the log data stored in the log data
64

storage unit 41 through the external interface 33B and can use the extracted log data. The log data can contribute to, for example, improvement of a reactive power distribution method by changing a threshold or the like or determination of a rated apparent capacity of the power converter 5 at the time of the future facility update. [0183]
The example having the above-described configuration exhibits the same effects as those of the first example. Further, in the example, when reactive power cannot be compensated for, the predetermined log data is stored. Therefore, the log data can contribute to cause analysis, future facility update, or the like, and the convenience of the user is improved. [Example 9] [0184]
A ninth example will be described with reference to Figs. 32 to 35. Fig. 32 is a configuration diagram illustrating a control device 4J included in the plant power control system according to the example. The control device 4J according to the example is different from the control device 4 according to the first example, in that an active power estimation unit 42, a reactive power shortfall estimation unit 43, a reception unit 20E, and a transmission unit 15A are added, the power factor adjustment device 35 is connected to the transmission
65

unit 15A, and the reactive power estimated value 44 is connected
to the reception unit 20E.
[0185]
Fig. 33 is a configuration diagram illustrating the active power estimation unit 42. Fig. 34 illustrates an example of a positional relationship between the steel sheet 13, the rollers 11 and 12, and the sensor 21. [0186]
In Fig. 34, the rolling rollers 11A and 12A are arranged at the position XA, the rolling rollers 11B and 12B are arranged at the position XB, and the rolling rollers 11C and 12C are arranged at the position XC. The sensor 21A is arranged at the position XAS, the sensor 21B is arranged at the position XBS, and the sensor 21C is arranged at the position XCS. In the description of Fig. 34, it is assumed that the left side represents an upstream side, the right side represents a downstream side, and the steel sheet 13 moves from the upstream side to the downstream side. [0187]
Time t41 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is started. Time t42 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11A and 12A is completed and the steel sheet 13 is positioned at a position downstream of the rolling rollers 11A and 12A. Time t43 represents a state where the
66

rolling of the steel sheet 13 by the rolling rollers 11B and 12B is started. Time t44 represents a state where the rolling of the steel sheet 13 by the rolling rollers 11B and 12B is completed and the steel sheet 13 is positioned at a position downstream of the rolling rollers 11B and 12B. [0188]
Returning to Fig. 33, the description will be made. The active power estimation unit 42 includes, for example, an arrival time storage device 44, an active power storage device
45, the speed information storage device 30, the torque
information storage device 31, an active power learning unit
46, and an active power estimated value calculation unit 47.
In the drawing, the names of the respective configurations are
appropriately omitted.
[0189]
The active power learning unit 46 is a function that learns active power of each of the power converters 5 at any time in the future. For example, in Fig. 34, it is assumed that active power of the power converter 5A when one steel sheet 13 passes through the power converter 5A (during a period from time t41 to time t42) is represented by PA_DB, and active power of the power converter 5A when the same steel sheet 13 passes through the power converter 5B (during a period from time t43 to time t44) is represented by PB_DB. When a ratio between the active power PA_DB of the power converter 5A and the active power
67

PB DB of the power converter 5B is represented by a correction coefficient |3, the correction coefficient |3 is represented by the following Formula 26. [0190]
[Formula 2 6]
P=PB_DB^"A_DB
By learning the correction coefficient |3 illustrated in Formula 26 in association with the speed information, the torque information, or the like, active power PB PRED when the steel sheet 13 is rolled in the power converter 5B can be estimated by Formula 27 based on active power information PA, speed information, torque information, and the correction
coefficient |3 when the steel sheet 13 is being rolled in the power converter 5A. [0191]
[Formula 27]
■B_PRED~PX "A
The active power estimated value calculation unit 47 is
a function of estimating active power at any time in the future. An estimated value PPRED of active power at any time t+tARB in the future can be calculated from the following Formula 28. tARB represents any time. [0192]
[Formula 28]

N
i=l
Pi PRED (t + tARB) in Formula 28 is determined as follows. That is, any time t+tARB and arrival time estimated values (tA EST/ tB EST/ -i and tN EST) stored in the arrival time storage device 44 are compared to each other, and when it is estimated that the steel sheet 13 has arrived at any time t+tARB/ the active power estimated value learned by the active power learning unit 46 is set as Pi PRED (t_tARB) • When it is estimated that the steel sheet 13 has not arrived at any time t+tARB/ the active power under no load is set as the active power estimated value Pi PRED
( t_tARB ) •
[0193]
A process to be performed by the reactive power shortfall estimation unit 43 will be described using the flowchart of Fig. 35. [0194]
The control device 4J reads estimated values PA (t+tARB) , PB (t+tARB) i -i PN (t + tARB) of active power from the active power estimation unit 42, reads an estimated value QREFO (t+tARB) of the total amount of reactive power required from the reception unit 20D, and reads rated apparent powers SA, SB, ..., SN from the rated apparent power storage unit 19 (S1001) . [0195]
The control device 4J calculates an estimated value of

reactive power that can be supplied at any time in the future (S1002) . An estimated value QPRED (t + tARB) of reactive power that can be supplied at any time t+tARB in the future can be calculated from the following Formula 29. [0196]
[Formula 2 9]
N
QpRED(t + tARB) = SSQRKS^-PLppE^t + t^)2)
i=l
The control device 4J compares the estimated value QPRED
(t+tARB) of reactive power that can be supplied at any time in the future and the estimated value QREFO (t+tARB) of the total amount of reactive power required to each other (S1003) . When QPRED (t + tARB) > QREFO (t + tARB) is satisfied (S1003: Yes), the control device 4J proceeds to Step S1004. On the other hand, when the control device 4J determines that QPRED (t + tARB) > QREFO
(t+tARB) is not satisfied (S1003: No), the control device 4J ends the process.
[0197]
In Step S1004, the control device 4J transmits the reactive power output command QTMAPREF to the power factor adjustment device 35.
[0198]
The example having the above-described configuration exhibits the same effects as those of the first example. Further, in the example, a command can be transmitted to the

power factor adjustment device 35 according to the total amount of reactive power required before the remaining capacity of reactive power of each of the power converters 5 becomes insufficient. As a result, in the example, the power factor adjustment device 35 can be rapidly operated such that a decrease in power factor caused by response time lag of the power factor adjustment device 35 can be suppressed. [Description of Reference Numerals and Signs] [0199]
1: power source
2: reactive power detection device
3: lagging power factor load facility
4: control device
5: power converter
6: transformer for power converter
7: transformer for lagging power factor facility
8: current detector
9: power source voltage detector
10: electric motor
11: roller upper portion
12: roller lower portion
13: steel sheet
15: transmission unit
16: reactive power command determination unit
17: arrival time estimation unit

18: electric motor arrangement storage unit
19: rated apparent power storage unit
20: reception unit
21: sensor
23: steel sheet speed estimation unit
24: actual speed calculation unit
25: speed correction coefficient learning unit
26: speed correction coefficient storage unit
27: steel sheet speed estimated value calculation unit
29: sensor detection value storage device
30: speed information storage device
31: torque information storage device
32: stored data change unit
33: external interface
34: transformer for power factor adjustment device
35: power factor adjustment device
36: switch
37: capacitor
38: reactive power distribution calculation unit
39: alarm display unit
40: reactive power comparison unit
41: log data storage unit
42: active power estimation unit
43: reactive power shortfall estimation unit
44: reactive power estimated value

Claims

[Claim 1]A plant power control system comprising:
a power converter positioned between a power system of a plant and each of electric motors to be provided for each of the electric motors;
a reactive power load facility connected to the power system;
a control device that generates a predetermined command for instructing each of the power converters to supply reactive power to the power system; and
a reactive power detection device that detects reactive power at a power receiving point between the reactive power load facility and the power system, wherein
the control device:
calculates an amount of reactive power required to allow the reactive power supplied from each of the power converters to the power system to cancel out the reactive power detected by the reactive power detection device; and
calculates a command value for distributing the calculated amount of reactive power required to each of the power converters for each of the power converters according to a remaining capacity of the power converter based on the amount of reactive power required and predetermined information relating to each of the electric motors.

[Claim 2] Claim 1
The plant power control system according to claim 1, wherein
as the predetermined information, the control device uses electric motor arrangement information which shows an installation position relationship between the respective electric motors, either torque information or active power information output from each of the power converters, angular velocity information of each of the electric motors output from each of the power converters, and rated apparent power of the power converter.
[Claim 3] Claim 2
The plant power control system according to claim 2, wherein
as the predetermined information, the control device uses the electric motor arrangement information, either the torque information or the active power information, the angular velocity information, and load increase time information that shows a time at which a load of each of the power converters increases.
[Claim 4] Claim 2
The plant power control system according to claim 3,

wherein
the control device calculates the load increase time based on either the active power information or the torque information and the angular velocity information and determines a predetermined timing based on the calculated load increase time.
[Claim 5] Claim 3
The plant power control system according to claim 4, wherein
each of the electric motors performs a predetermined process on a target,
a target detector is further provided to detect a position of the target, and
the control device calculates the load increase time based on either of the active power information or the torque information, the angular velocity information, and an output of the target detector.
[Claim 6] Claim 4
The plant power control system according to claim 5, wherein
the control device further includes an angular velocity information storage unit that stores the angular velocity information and time information in association with each other,

and
the control device corrects the angular velocity information based on the angular velocity information stored in the angular velocity information storage unit.
[Claim 7] Claim 5
The plant power control system according to claim 1, wherein
the control device rewrites all or a part of parameters used to calculate at least one of the amount of reactive power required, the command value, the load increase time, and the predetermined timing from an external device.
[Claim 8] Claims 6 to 8
The plant power control system according to claim 7, wherein
the control device is capable of rewriting all or a part of at least one kind of information of the electric motor arrangement information, the rated apparent power, and the angular velocity information from an external device.
[Claim 9] Claim 9
The plant power control system according to any one of claims 1 to 8, wherein
the control device calculates the command value for each

of the power converters based on a reactive power supply plan of a reactive power compensation device connected to the power system, the electric motor arrangement information, either of the torque information or the active power information, the angular velocity information, the rated apparent power, and the amount of reactive power required.
[Claim 10] Claim 10
The plant power control system according to any one of claims 1 to 8, wherein
the control device instructs a reactive power compensation device connected to the power system to output a shortfall of reactive power supplied from each of the power converters to the power system.
[Claim 11] Claim 11
The plant power control system according to any one of claims 1 to 8, wherein
the control device outputs an alert when determining that the reactive power supplied from each of the power converters to the power system is not balanced with the reactive power detected by the reactive power detection device.
[Claim 12] Claim 12
The plant power control system according to any one of

claims 1 to 8, wherein
the control device stores predetermined log data when determining that the reactive power supplied from each of the power converters to the power system is not balanced with the reactive power detected by the reactive power detection device .
[Claim 13]
The plant power control system according to any one of claims 1 to 8, wherein
the control device further includes:
an active power estimation unit that estimates active power of each of the power converters; and
a reactive power shortfall estimation unit that estimates a shortfall of reactive power using an estimated value of reactive power at the power receiving point, the rated apparent power, and the active power estimated by the active power estimation unit.
[Claim 14]
A control method of a plant power control system,
the plant power control system including:
a power converter positioned between a power system of
a plant and each of electric motors to be provided for each
of the electric motors;
a reactive power load facility connected to the power

system;
a control device that generates a predetermined command for instructing each of the power converters to supply reactive power to the power system; and
a reactive power detection device that detects reactive power at a power receiving point between the reactive power load facility and the power system, and
the control device being configured to:
calculate an amount of reactive power required to allow the reactive power supplied from each of the power converters to the power system to cancel out the reactive power detected by the reactive power detection device;
calculate a command value for distributing the calculated amount of reactive power required to each of the power converters for each of the power converters based on the amount of reactive power required and predetermined information relating to each of the electric motors; and
transmit the calculated command value to each of the power converters corresponding to the command value.