ELECTRIC VEHICLE CONTROL DEVICE
Field
[0001] The present invention relates to an electric vehicle control device that includes a plurality of power conversion devices that drive a synchronous motor by using sensorless control.
Background
[0002] Sensorless control for a synchronous motor is a technique for controlling a synchronous motor by estimating the rotational speed of the rotor or the magnetic pole position of the rotor and then supplying a current from a power conversion device to the synchronous motor with the phase corresponding to the magnetic pole position, in order to control the synchronous motor with a desired torque and at a desired rotational speed, without using a position sensor or a speed sensor.
[0003] When such sensorless control is applied to a power conversion device, the rotational speed of the rotor or the magnetic pole position of the rotor can be detected only when the power conversion device is in operation, and the rotational speed or the magnetic pole position are unknown when the power conversion device is stopped. [0004] In an electric vehicle equipped with such a power conversion device that drives the synchronous motor by using sensorless control, there may be cases in which the electric vehicle is still moving even though the power conversion device is stopped. A case of decelerating on an upward slope, a case of accelerating on a downward slope, and a case of traveling with inertia due to the inertial

energy of the electric vehicle, i.e., a state called coasting, are examples of this. In these operating states, because the speed of the electric vehicle itself also changes, the rotational speed of the rotor or the magnetic pole position of the rotor cannot be determined. [0005] Therefore, in order to start the operation of a power conversion device by using sensorless control when the power conversion device is stopped, it is necessary to instantly set an initial value for detecting the rotational speed of the rotor or the magnetic pole position of the rotor.
[0006] Here, Patent Literature 1 below discloses a method for estimating an initial magnetic pole position by using magnetic saturation when the rotation of the rotor is stopped. In addition, Patent Literature 2 below discloses a method for estimating an initial speed and an initial magnetic pole position by using an induced voltage generated in a coil when the rotor is rotating. [0007] When sensorless control for a synchronous motor is applied to the electric vehicle control device, it is necessary to accurately detect the rotational speed or the magnetic pole position, and thus multiple estimation methods are often used in combination. For example, Patent Literature 3 discloses a technique for controlling the synchronous motor on the basis of an operation command value with the initial speed and the initial magnetic pole position being used as initial values.
Citation List
Patent Literature
[0008] Patent Literature 1: Japanese Patent No. 4271397 Patent Literature 2: Japanese Patent No. 5318286 Patent Literature 3: Japanese Patent No. 5291184

Summary
Technical Problem
[0009] However, in the case of an electric vehicle that includes a plurality of power conversion devices, because the diameters of the wheels to which respective synchronous motors are mechanically connected are not always the same in the electric vehicle, the rotational speeds of the rotors of the synchronous motors are also not always the same. A conventional sensorless-control technique used in such a state causes a variation in the operations of the power conversion devices. For example, when each power conversion device receives a re-power running command or a brake command in the coasting state, there are problems in that ride comfort is degraded due to the fact that, for each vehicle in a train, deviation occurs in the timing of the acceleration or deviation occurs in the timing of deceleration, and thus there is a concertina effect, in which the vehicles repeatedly approach and separate from each other.
[0010] The present invention has been made in view of the above, and it is an object to provide an electric vehicle control device capable of achieving an improvement in ride comfort by inhibiting the concertina effect associated with an electric vehicle control device that includes a plurality of power conversion devices that drive a synchronous motor by using sensorless control.
Solution to Problem
[0011] In order to solve the above problems and achieve the object, an aspect of the present invention is an electric vehicle control device including a plurality of power conversion devices that each drive a synchronous

motor by using sensorless control. The electric vehicle control device includes a start-up selector to select, on a basis of information on a vehicle speed obtained from a vehicle speed sensor, which control system starts the power conversion devices. Each of the power conversion devices starts an operation with an identical control system on a basis of the vehicle speed.
Advantageous Effects of Invention
[0012] The present invention has an effect of achieving an improvement in ride comfort by inhibiting a situation in which the electric vehicles experience a concertina effect associated with an electric vehicle control device that includes a plurality of power conversion devices that drive a synchronous motor by using sensorless control.
Brief Description of Drawings
[0013] FIG. 1 is a diagram of the configuration of an overall system that includes an electric vehicle control device according to a first embodiment.
FIG. 2 is a block diagram illustrating a detailed configuration of a power conversion device according to the first embodiment.
FIG. 3 is a flowchart illustrating the flow of processing performed by a signal selection unit according to the first embodiment.
FIG. 4 is a diagram of the configuration of an overall system that includes an electric vehicle control device according to a second embodiment.
FIG. 5 is a block diagram illustrating a detailed configuration of a power conversion device according to the second embodiment.
FIG. 6 is a diagram explaining a setting concept of a

second determination value.
Description of Embodiments
[0014] Hereinafter, an electric vehicle control device
according to embodiments of the present invention will be
explained with reference to the accompanying drawings. The
present invention is not limited to the following
embodiments.
[0015] First embodiment.
FIG. 1 is a diagram of the configuration of an overall system that includes an electric vehicle control device according to a first embodiment. FIG. 2 is a block diagram illustrating a detailed configuration of a power conversion device 1 according to the first embodiment. [0016] First, in FIG. 1, vehicles 40 (No. 1 car: 401, No.
2 car: 402, , No. N car: 40N) that constitute a train
50 are equipped with motors 2 (21, 22, , 2N) that
drive the train 50, and the power conversion devices 1 (11,
12, , 1N) that rotationally drive motors 2,
respectively. The motors 2 are synchronous motors driven by using sensorless control.
[0017] In addition, in FIG. 1, an operation support system 22 and a train information management device (Train Information Management System) 26 are illustrated, which are a system that supports the operation of the train 50. The main configuration of the operation support system 22 includes a control start operation unit 13, a train safety device 14, a handle 15, a kilometrage management device 16, a tacho-generator 17 that is a vehicle speed sensor, and an operation support device 23.
[0018] Among the components of FIG. 1, the electric
vehicle control device according to the first embodiment is
composed of the power conversion devices 1 (11, 12, ,

1N) that drive the motors 2 mounted on the train 50 by using sensorless control. In FIG. 1, a case is illustrated in which all of the illustrated vehicles are each equipped with the power conversion device 1 and the motor 2; however, this does not imply that there is never a vehicle on which neither of the power conversion device 1 nor the motor 2 is mounted. In addition, in FIG. 1, the control start operation unit 13, the train safety device 14, the handle 15, the kilometrage management device 16, the tacho-generator 17, the operation support device 23, and the train information management device 26 are illustrated outside the train 50, but are configured to be mounted on
any of the vehicles 40 (401, 402, , 40N) that
constitute the train 50. In particular, the tacho-generator 17 is in many cases installed so as to measure the rotational speed of a wheel shaft of a vehicle on which neither of the power conversion device 1 nor the motor 2 is mounted as described above.
[0019] In addition, the power conversion devices 1, as illustrated in FIG. 2, are each configured to include a power conversion unit 3 that takes in DC power or AC power supplied from an overhead wire 51 via a current collector 52 and supplies AC power for driving to the motor 2; a processing unit 4 that generates a switching signal SW for driving a switching device (not illustrated) that constitute the power conversion unit 3; and a storage unit 5 that stores an initial value generated by the processing unit 4.
[0020] A current detection unit 11 is provided between the power conversion unit 3 and the motor 2. The current detection unit 11 is a current sensor for detecting the current that flows between the power conversion unit 3 and the motor 2 and the current supplied from the power

conversion unit 3 to the motor 2. A detection value from the current detection unit 11 is input to a first start-up unit 6, a second start-up unit 7, and a motor control unit 8 that are described later. In the illustrated example, among the lines of the U, V, and W phases, sensors are disposed on the lines of the U phase and the W phase; however, the sensors may be disposed on the lines of the U phase and the V phase or may be disposed on the lines of the V phase and the W phase. The current of the phase on which the sensor is not disposed can be obtained by calculation from the equilibrium condition of the phase currents. In addition, the sensors may be disposed on the lines of all the three phases instead of any two phases. When the sensors are disposed on the lines of all the three phases, all the phase currents can be detected and therefore calculation processing is not necessary.
[0021] In addition, the power conversion unit 3 is provided with a voltage detector 3a for detecting the voltage of an intermediate link unit or a filter capacitor voltage. A voltage EFC detected by the voltage detector 3a
(hereinafter referred to as an "intermediate link voltage"), although not illustrated in FIG. 1, is input to the first start-up unit 6, the second start-up unit 7, and the motor control unit 8 that are described later, and is used for modulation rate calculation.
[0022] The processing unit 4 is configured to include the following functional components: the first start-up unit 6 that performs processing to estimate an initial magnetic pole position θ01 by using magnetic saturation; the second start-up unit 7 that performs processing to estimate an initial speed ω02 and an initial magnetic pole position θ02 by using an induced voltage; the motor control unit 8 that performs processing to drive the motor 2 with a

torque control command generated by using an initial speed and an initial magnetic pole position as initial values; a signal selection unit 9 that generates a selection signal SF for selecting the switching signal SW generated by any one of the first start-up unit 6, the second start-up unit 7, and the motor control unit 8 on the basis of a vehicle speed 14D and an operation command such as a power running command 11D and a brake command 12D; and a signal switch 10 that actually selects, in accordance with the selection signal SF output by the signal selection unit 9, any of the outputs of the first start-up unit 6, the second start-up unit 7, and the motor control unit 8. The signal selection unit 9 and the signal switch 10 constitute a start-up selector.
[0023] The signal switch 10 is provided with contacts 10a, 10b, 10c, 10d, and 10e. The contact 10a is an output terminal for outputting the switching signal SW to the power conversion unit 3. In addition, the contact 10b is connected to the output of the first start-up unit 6, and similarly, the contact 10c is connected to the output of the second start-up unit 7 and the contact 10d is connected to the output of the motor control unit 8. In addition, nothing is connected to the contact 10e. When the selection signal SF is input from the signal selection unit 9 to the signal switch 10 connected in this way, the following operation is performed.
[0024] First, when the selection signal SF that selects the first start-up unit 6 is input to the signal switch 10, a selector switch of the signal switch 10 is connected to the contact 10d. As a result, the switching signal SW output by the first start-up unit 6 is applied to the power conversion unit 3 via the contact 10a. [0025] When the selection signal SF that selects the

second start-up unit 7 is input to the signal switch 10, the selector switch of the signal switch 10 is connected to the contact 10c. As a result, the switching signal SW output by the second start-up unit 7 is applied to the power conversion unit 3 via the contact 10a. [0026] When the selection signal SF that selects the motor control unit 8 is input to the signal switch 10, the selector switch of the signal switch 10 is connected to the contact 10b. As a result, the switching signal SW output by the motor control unit 8 is applied to the power conversion unit 3 via the contact 10a.
[0027] The selection signal SF still has significance even if the selection signal SF does not select any of the first start-up unit 6, the second start-up unit 7, and the motor control unit 8. Specifically, such a signal means an all-gates off signal, i.e., a switching signal that does not operate any of the switching devices. When the selection signal SF is the all-gates off signal, the selector switch of the signal switch 10 is connected to the contact 10e. As a result, the contact 10a is not connected to any of the outputs of the first start-up unit 6, the second start-up unit 7, and the motor control unit 8, and even when the first start-up unit 6, the second start-up unit 7, or the motor control unit 8 operates, the switching signal is not applied to the power conversion unit 3. [0028] The processing unit 4, in terms of hardware, is configured to include a microcomputer or a processor logically configured as a hardware circuit such as a digital signal processor (DSP) or an FPGA. When the processing unit 4 includes the microcomputer, calculation processing in the first start-up unit 6, the second start¬up unit 7, and the motor control unit 8 can be realized by the microcomputer executing a program stored in the storage

unit 5. Multiple processors and multiple memories may cooperate to execute the above function. In addition, when a processor in which at least one of the DSP and the FPGA is logically configured as a hardware circuit is included, processing by a control system in the first start-up unit 6, the second start-up unit 7, and the motor control unit 8 may be realized by the processor. In such a case, the calculation processing portion may be processed by software in the microcomputer. The storage unit 5 stores the program and also stores the initial magnetic pole position θ01 estimated by the first start-up unit 6 and the initial speed ω02 and the initial magnetic pole position θ02 estimated by the second start-up unit 7. In addition, the storage unit 5 stores electric circuit constants of the motors 2 and parameters required for control.
[0029] Next, processing executed by the first start-up unit 6, the second start-up unit 7, and the motor control unit 8 will be described.
[0030] (Regarding the first start-up unit 6)
The first start-up unit 6 is a function unit that includes the control system that performs processing to estimate the initial magnetic pole position θ01 by using magnetic saturation as described above, and the method disclosed in Patent Literature 1 described above is used in the present embodiment. Details of the processing are disclosed in Patent Literature 1 in detail; therefore, detailed description is omitted here. All or some of the descriptions in Patent Literature 1 are incorporated herein, and they constitute a part of the present specification.
[0031] (Regarding the second start-up unit 7)
The second start-up unit 7 is a function unit that includes the control system that performs the processing to estimate the initial speed ω02 and the initial magnetic

pole position θ02 by using the induced voltage as described above, and the method disclosed in Patent Literature 2 described above is used in the present embodiment. Details of the processing are disclosed in Patent Literature 2 in detail; therefore, detailed description is omitted here. All or some of the descriptions in Patent Literature 2 are incorporated herein, and they constitute a part of the present specification.
[0032] (Regarding the motor control unit 8)
The motor control unit 8 is a function unit that includes the control system that uses, as an initial value, either the initial magnetic pole position θ01 estimated by the first start-up unit 6 or the initial speed ω02 and the initial magnetic pole position θ02 estimated by the second start-up unit 7, and performs the processing to drive the motor 2 with the torque control command generated by using the initial value, and the method disclosed in Patent Literature 3 described above is used in the present embodiment. Processing to operate the motor control unit 8 after the start of the first start-up unit 6 is a case where the motor 2 is stopped or considered to be stopped, and it is possible to perform processing with the initial speed set to zero. Details of the processing are disclosed in Patent Literature 3 in detail; therefore, detailed description is omitted here. All or some of the descriptions in Patent Literature 3 are incorporated herein, and they constitute a part of the present specification.
[0033] Next, the description refers back to FIG. 1. The function and role of each of the components of which the operation support system 22 is constituted and the flow of various types of information via the train information management device 26 will be described.
[0034] First, the control start operation unit 13 is

used when a constant speed operation is started. A crew member operates the control start operation unit 13, whereby a control start command 1D that indicates the start of the constant speed operation can be output. [0035] The train safety device 14 can receive speed-limit information 2D that indicates an ATC speed limit from an automatic train control (ATC) device (not illustrated). The handle 15 can output handle operation information 3D when acceleration or brake operation is performed by a crew member. The ATC device is exemplified as the train safety device 14; however, it is not limited thereto and it is possible to use an operation safety device such as an automatic train stop (ATS).
[0036] The kilometrage management device 16 can manage the kilometrage of the train and can output kilometrage information 4D, which is used when performing, for example, a scheduled operation in accordance with traveling reference time between stations.
[0037] The tacho-generator 17 is a vehicle-speed sensor, and can output a detected speed as a speed signal 5D. Regarding the tacho-generator 17, due to differences in wheel diameter, the values are usually different from each other for each axle or vehicle. For this reason, it is preferable to manage the average of the values obtained from the tacho-generator 17 as the speed signal 5D; to manage a value obtained from the tacho-generator 17 provided on an axle with the smallest wheel diameter as the speed signal 5D; or to manage by receiving only the speed signal 5D of the lead vehicle. In this way, the speed signal 5D managed by the train information management device 26 has a unique value, and variation can be avoided in the operation of the power conversion devices 1. In addition, the tacho-generator 17 is installed so as to

measure the rotational speed of the wheel shaft of the vehicle on which neither of the power conversion device 1 nor the motor 2 is mounted as described above. A wheel shaft equipped with the motor 2 accelerates or decelerates the vehicle by transmitting the rotation force of the motor 2 to the rail via the wheel; however, the wheel may, for example, easily idle/glide (slip/slide) when the rail is wet on a rainy day. When such idling/gliding occurs, the vehicle speed cannot be correctly detected. Therefore, it is preferable to receive and manage only the speed signal 5D of a wheel shaft not equipped with the motor 2. [0038] The operation support device 23 is configured to include a travel management unit 25 and a speed regulation section storage unit 24. The operation support device 23 is normally mounted on the lead vehicle or the like; however, it is not limited thereto.
[0039] The speed regulation section storage unit 24 stores in advance speed-regulation information 17D for a speed regulation section and the like. The information stored in the speed regulation section storage unit 24 is not limited thereto. For example, an estimated arrival time may be calculated for each kilometrage in advance by using a train speed, a remaining distance based on the travelled distance, a route gradient, and the like, and then the estimated arrival time may be stored in the speed regulation section storage unit 24 before starting an operation and used for a constant speed operation. [0040] When receiving the control start command 1D, the travel management unit 25 sets the target speed required for performing a constant speed operation in accordance with the speed-regulation information 17D or the speed-limit information 2D. The target speed is indicated by a value obtained by subtracting approximately 3 km/h from the

speed-limit information 2D or the speed-regulation information 17D; however, it is not limited thereto. This constant speed operation control is realized by adjusting a notch such that the train speed follows the target speed described above. Because information on this notch is recorded in the travel management unit 25 as notch information that enables travel at a constant speed for the kilometrage, a notch corresponding to the kilometrage information is derived from the travel distance and the like, and the operation speed is finely adjusted by raising or lowering the notch from the following speed, which is the center notch so that the train speed follows the target speed, whereby a constant speed operation is realized. Here, the speed-regulation information 17D is read from the speed regulation section storage unit 24 and used; however, it is not limited thereto. For example, the speed-regulation information 17D and the kilometrage information may be recorded in a portable storage medium or the like in advance, handed over before the train operation, and externally connected to the operation support device 23. [0041] In order to bring the current train speed closer to the target speed on the basis of the speed signal 5D, the travel management unit 25 can output a power running command 6D or a brake command 7D. When a vehicle speed 9D approaches a target speed 10D, the travel management unit 25 can output a constant speed operation command 8D and switch to the constant speed operation. When the travel management unit 25 receives the handle operation information 3D during the constant speed operation, the travel management unit 25 can stop the output of the constant speed operation command 8D and switch to the manual operation. When the travel management unit 25 receives the control start command 1D after switching to

the manual operation, the travel management unit 25 can output the constant speed operation command 8D and switch to the constant speed operation again.
[0042] The train information management device 26 can collectively managing information transmitted from the travel management unit 25. In FIG. 1, only one train information management device 26 is illustrated; however, it is not limited thereto. By mounting the train information management device 26 on each vehicle and connecting them to a transmission line laid between the vehicles, pieces of information such as the power running command 11D, the brake command 12D, a constant speed operation command 13D, the vehicle speed 14D, and a target speed 15D can be relayed from the train information management device 26 of the lead vehicle to the train information management devices 26 mounted on vehicles other than the lead vehicle, for example. The train information management device 26 of each vehicle transmits information such as the power running command 11D, the brake command 12D, the constant speed operation command 13D, the vehicle speed 14D, and the target speed 15D to the corresponding
power conversion device 1 (11, 12, , 1N). Such a
transmission form is only an example and other transmission forms may be adopted. For example, without using the train information management device 26 of each vehicle, the information may be transmitted from the train information management device 26 of the lead vehicle directly to the
power conversion devices 1 (11, 12, , 1N) of the
vehicles.
[0043] When accelerating the train, the power conversion
devices 1 (11, 12, , 1N) control the rotations of the
motors 2 (21, 22, , 2N) on the basis of the target
speed 15D, the vehicle speed 14D, and the power running

command 11D transmitted from the train information management device 26.
[0044] When the vehicle speed 14D approaches the target speed 15D, in order to switch to the constant speed
operation, the power conversion devices 1 (11, 12, ,
1N) control the rotations of the motors 2 (21, 22, ,
2N) on the basis of the constant speed operation command 13D. In addition, when the train decelerates, the
rotations of the motors 2 (21, 22, , 2N) are
controlled on the basis of the brake command 12D and a braking device (not illustrated) is also controlled. [0045] Next, the operation of the signal selection unit 9 will be described with reference to FIG. 3. FIG. 3 is a flowchart illustrating the flow of processing that is performed by the signal selection unit 9 and that changes depending on the operation command and the vehicle speed. In FIG. 3, the operation command includes the constant speed operation command, the power running command, and the brake command. Hereinafter, the three commands, i.e., the constant speed operation command, the power running command, and the brake command, are collectively referred to as an operation command.
[0046] First, in step S101, it is determined whether there is an operation command or not. Here, when an operation command has been input, the processing proceeds to step S102, and when an operation command has not been input, the processing proceeds to step S111. In step S102, it is determined whether the vehicle speed is equal to or greater than a first determination value. When the vehicle speed is less than the first determination value, the selector switch of the signal switch 10 is connected to the contact 10d, and the processing proceeds to step S103 and the first start-up unit is operated. In step S104, it is

determined whether the processing performed by the first start-up unit 6 has terminated. When the processing performed by the first start-up unit 6 has terminated, i.e., when the processing to estimate the initial magnetic pole position θ01 has terminated, the selector switch of the signal switch 10 is connected to the contact 10b, and the processing proceeds to step S107.
[0047] The description refers back to step S102, in which, when the vehicle speed is equal to or greater than the first determination value, the selector switch of the signal switch 10 is connected to the contact 10c and the processing proceeds to step S105, in which the second start-up unit 7 is operated. In step S106, it is determined whether the processing performed by the second start-up unit 7 has terminated. When the processing performed by the second start-up unit 7 has terminated, i.e., when the processing to estimate the initial speed ω02 and the initial magnetic pole position θ02 has terminated, the selector switch of the signal switch 10 is connected to the contact 10b and the processing proceeds to step S107.
[0048] In step S107, the motor control unit 8 is operated, and in step S108, it is determined whether there is an operation command. When there is an operation command, i.e., when the operation command has been input, the operation in step S107 and the determination processing in step S108 are repeated. Conversely, when there is no operation command, the processing proceeds to step S109, where it is determined whether the vehicle speed is equal to or greater than a second determination value. When the vehicle speed is equal to or greater than the second determination value, the processing returns to step S107. After that, the operation in step S107 and determination processing in each of step S108 and step S109 are executed.

The second determination value is greater than the first determination value.
[0049] In addition, in step S109, when the vehicle speed is less than the second determination value, the processing proceeds to step S110 and all the gates are turned off, i.e., switching control for the power conversion unit 3 is stopped, and the processing returns to step S101. After that, the processing from step S101 is repeated. [0050] The description refers back to the processing in step S111, where it is determined whether the vehicle speed is equal to or greater than the second determination value. When it is equal to or greater than the second determination value, the processing proceeds to step S105 and the second start-up unit 7 is operated. After that, the processing in step S106 and subsequent steps are executed.
[0051] In addition, in step S111, when the vehicle speed is less than the second determination value, the processing proceeds to step S112, an all-gates off operation that stops switching control for the power conversion unit 3 is performed, and the processing returns to step S101. After that, the processing from step S101 is repeated. [0052] Here, a supplementary description of the above processing will be given. In step S102, the vehicle speed is compared with the first determination value, where the first determination value is the vehicle speed at which it is possible to determine that the motors 2 have stopped rotating. When it is possible to determine that the motors 2 have stopped rotating, processing that uses magnetic saturation is possible, and the motor control unit 8 can be started after starting the first start-up unit 6. In addition, when it is possible to determine that the motors 2 have not stop rotating by using the first determination

value, the motor control unit 8 can be started after starting the second start-up unit 7. With these controls, determining whether to start sensorless control can be unified across the power conversion devices 1 (11,
12, , 1N). As a result, because the timing of
outputting torque from the motors 2 (21, 22, , 2N) can
be synchronized; therefore, a concertina effect between the vehicles can be inhibited and thus ride comfort in the electric vehicle can be improved.
[0053] In addition, in step S111 and step S109, the vehicle speed is compared with the second determination value, where the second determination value is a vehicle speed at which it is possible to determine whether the motors 2 are rotating at a high speed. Here, a case is considered where the motors 2 are permanent magnet type motors and the motors 2 are rotating at a high speed. In such a situation, it is assumed that the induced voltage of each of the motors 2 generated by the rotation of the permanent magnet (specifically, the voltage across terminals of each of the motors 2) exceeds the filter capacitor voltage. In such a case, when the power conversion unit 3 does not perform any operation in an all-gates off state and the induced voltage of each of the motors 2 exceeds the filter capacitor voltage, each of the motors 2 becomes a generator and supplies electricity to the overhead wire 51 via a diode (not illustrated) in the power conversion unit 3. Therefore, in such a high-speed rotation range, it is necessary to perform control such that the induced voltage of each of the motors 2 does not exceed the filter capacitor voltage by operating the power conversion unit 3 and performing field-weakening control. In addition, because it is necessary to perform the control as described above even in a state in which the vehicle is

traveling with inertia due to only the inertial energy thereof (referred to as coasting) in a state in which the operation command is not input, the control is referred to as coasting control in the present invention. The torque command during the coasting control is zero. This does not imply that, even during such coasting control, the vehicle speed at which the coasting control is required varies for
each of the power conversion devices 1 (11, 12, , 1N)
because of the effect of the wheel diameter difference as described above.
[0054] The description refers back to FIG. 3 of the present invention. The processing in step S111 and step S109 determines whether the coasting control described above is to be performed by comparing the vehicle speed with the second determination value. With such a configuration, the power conversion devices 1 (11,
12, , 1N) simultaneously start the coasting control,
and thus variation in operations among the power conversion
devices 1 (11, 12, , 1N) can be eliminated and any
increase in the induced voltage of each of the motors 2 can be suppressed.
[0055] Further, even when a re-power running command or a brake command is input in such a coasting state, the timing of outputting torque from the motors 2 (21,
22, , 2N) can be synchronized; therefore, the
concertina effect between the vehicles can be inhibited and thus ride comfort in the electric vehicle can be improved. [0056] Here, a supplementary description of the above timing of outputting torque will be given. As illustrated in FIG. 3, during sensorless control of the synchronous motor, in order to operate the power conversion devices 1 from a state where the power conversion devices 1 are stopped (all-gates off state, which corresponds to step

S112 and step S110 in FIG. 3) and shift each device to a state of sensorless control of the motor (this corresponds to S107 in FIG. 3), it is necessary to execute the processing as illustrated in FIG. 3. Here, during coasting, in which an operation of the power conversion devices 1 is stopped, it is in a state of waiting in a loop that returns to the processing in step S101 via step S111 and step S112, and the coasting control in which the power conversion devices 1 are operated is in a state of controlling the motor in a loop that returns to step S107 via step S108 and step S109. In addition, a state of controlling the motor on the basis of the operation command is a loop that returns to step S107 via the processing in step S108. Here, when the re-power running command or the brake command is input in the coasting state as described above, in order to shift to the state of controlling the motor on the basis of the operation command, different processing is required for the shift "during coasting in which an operation of the power conversion devices 1 is stopped" compared to that required for "the coasting control in which the power conversion devices 1 are operated", and the timing of outputting torque from each of the motors 2 differs. The present invention solves such a problem, and it is configured to determine whether the coasting control is to be performed by comparing the vehicle speed with the second determination value, whereby the power conversion devices 1
(11, 12, , 1N) simultaneously start the coasting
control, the variation in operations among the power
conversion devices 1 (11, 12, , 1N) can be eliminated,
and the timing of outputting torque from the motors 2 (21,
22, , 2N) can be synchronized.
[0057] In addition, for variation in operations caused by the wheel diameter difference as described above,

reducing the variation in operations caused by the wheel diameter difference by positively managing the wheel diameter difference can also be considered. However, in order to unify the variation in operations in sensorless control for the synchronous motor as described in the problem of the present invention across the power
conversion devices 1 (11, 12, , 1N), because it is
necessary to manage the wheel diameter of the wheels of the electric vehicle to which the motors 2 are mechanically connected with tolerance equal to or less than several millimeters, the maintenance cost of electric vehicle may increase. This is a unique problem with electric vehicles that have multiple power conversion devices that each drive the synchronous motor by using sensorless control. The present invention is also obviously effective with regard to such a maintenance cost problem. [0058] Second embodiment.
FIG. 4 is a diagram of the configuration of an overall system that includes an electric vehicle control device according to a second embodiment, and FIG. 5 is a block diagram illustrating a detailed configuration of a power conversion device according to the second embodiment. The configuration of the power conversion devices 1 according to the first embodiment illustrated in FIGS. 1 and 2 differs from the power conversion devices 1 in the second embodiment as follows: the signal selection unit 9 is not included; the intermediate link voltage EFC, which is a detection voltage detected by the voltage detector 3a, is input to the processing unit 4 and also to the outside of the power conversion device 1 (more specifically, it is input to the train information management device 26 as illustrated in FIG. 5); although not illustrated, the second determination value is varied in accordance with the

intermediate link voltage EFC; and the train information management device 26 includes a calculation unit 26a. Other configurations are the same or equivalent to those of the first embodiment; therefore, the same or equivalent components are denoted by the same reference numerals and redundant descriptions are omitted.
[0059] The electric vehicle control device according to the second embodiment is configured such that the calculation unit 26a illustrated in FIG. 4 executes the processing performed by the signal selection unit 9 in each
of the power conversion devices 1 (11, 12, , 1N) in
the first embodiment.
[0060] In addition, as illustrated in FIG. 4 and FIG. 5,
the intermediate link voltages EFC detected by the
respective power conversion devices 1 (11, 12, , 1N)
are input to the train information management device 26. Because each of the intermediate link voltages EFC is detected by the voltage detector 3a provided in a corresponding one of the power conversion devices 1 (11,
12, , 1N), the intermediate link voltages EFC are not
necessarily the same value due to tolerance of the voltage detectors 3a. Therefore, in the second embodiment, the intermediate link voltages EFC are aggregated and collected in the train information management device 26, an average value EFCmean or a minimum value EFCmin of the intermediate link voltages EFC is calculated by the calculation unit 26a of the train information management device 26, and a unified value is used for the entire train formation. In the second embodiment, the selection signal SF generated by the signal selection unit 9 in FIG. 2 is fed to a transmission line and transmitted to each of the power
conversion devices 1 (11, 12, , 1N). Such a
configuration causes the processing executed by each of the

power conversion devices 1 (11, 12, , 1N) to be
reduced and can contribute to a cost reduction of the power conversion devices 1. In FIG. 4, information on the intermediate link voltages EFC and the selection signal SF is transmitted through the transmission line of the train information management device 26; however, the transmission may be realized by using other transmission lines, and the processing performed by the signal selection unit 9 is also not limited to that executed by the calculation unit 26a. [0061] Next, a signal switching operation performed by the signal switch 10 in the second embodiment will be described. In the second embodiment, the signal switching operation is also executed in accordance with the flowchart in FIG. 3. In the processing in the second embodiment, the second determination value that is used when the flowchart in FIG. 3 is executed is changed in accordance with the intermediate link voltage EFC. The intermediate link voltage EFC used in the following description is the average value EFCmean or the minimum value EFCmin of the intermediate link voltages EFC detected by the respective
power conversion devices 1 (11, 12, , 1N).
Hereinafter, this point will be described.
[0062] First, the second determination value can be
formulated as the following equation.
[0063] Second determination value = intermediate link
voltage EFC × proportionality factor K - control margin
G (1)
[0064] The proportionality factor K indicated in the above equation (1) is a value uniquely determined due to the proportional relationship between the vehicle speed and the voltage across the terminals of the motor 2 connected to the axle with the minimum wheel diameter (hereinafter, referred to as a "minimum wheel-diameter motor-voltage" for

convenience), and it can be expressed by the following
equation.
[0065] Proportionality factor K = vehicle speed V /
minimum wheel-diameter motor-voltage (2)
[0066] The control margin G indicated in the above equation (1) is a design value for making adjustments such that the second determination value becomes a value smaller than the value determined by the intermediate link voltage EFC × the proportionality factor K. A purpose of providing the control margin G is to avoid having an intermediate link voltage EFC that is less than the voltage across the terminals of each of the motors 2 due to the fluctuation in the proportionality factor K or a steep fluctuation in the intermediate link voltage EFC.
[0067] FIG. 6 is a diagram explaining the setting concept of the second determination value. In FIG. 6, the horizontal axis indicates the vehicle speed and the vertical axis indicates the relationship between the intermediate link voltage and the voltage across the terminals of each of the motors 2. In addition, a straight line Ka represents the voltage across the terminals of a motor a and a straight line Kb represents the voltage across the terminals of a motor b. Here, the motor a denotes a motor connected to an axle with a wheel diameter a, and the motor b denotes a motor connected to an axle with a wheel diameter b. Here, there is a relationship where wheel diameter a < wheel diameter b, and it is assumed that the wheel diameter a is the minimum wheel diameter within the train formation. That is, the motor a is a motor connected to an axle having the minimum wheel diameter within the train formation, and the motor b denotes one of the motors connected to an axle not having the minimum wheel diameter.

[0068] In FIG. 6, the voltage across the terminals of the motor increases as the vehicle speed increases, and the voltage across the terminals of the motor a, which has the minimum wheel diameter, increases the most for the same vehicle speed. Therefore, it can be seen that the second determination value only needs to be made variable on the basis of the minimum wheel-diameter motor-voltage. Therefore, the second determination value illustrated in FIG. 6 is made to be variable depending on the intermediate link voltage on the basis of the straight line Ka, which is the minimum wheel-diameter motor-voltage. [0069] Further, because the DC voltage value of an intermediate link may greatly fluctuate when used for example in general electric railways, as indicated in the above equation (1), when the control margin G is adjusted such that a second predetermined value is a lower value than the DC voltage value of the intermediate link × a proportionality constant while taking these conditions into consideration, it is possible to reliably avoid a situation in which the intermediate link voltage EFC is smaller than the voltage across the terminals of the motor, i.e., a situation in which the motors 2 are brought into a regenerate state; therefore, torques generated by the
motors 2 (21, 22, , 2N) can be reliably equalized, and
thus the concertina effect between the vehicles can be inhibited and improvement in the ride comfort in the electric vehicle can be achieved.
[0070] The proportionality factor K may fluctuate a little depending on the temperatures of the magnets in each of the motors 2. Accordingly, when the effect of the temperatures of the magnets in each of the motors 2 is large, each of the motors 2 may be provided with a temperature sensor, and the proportionality factor K may be

made variable depending on the detection information on the temperature sensor. In addition, the magnet temperature may be estimated from the currents that flow through the motors 2, and the proportionality factor K may be made variable depending on the estimation result, or the control margin G may be adjusted while taking these influences into consideration.
[0071] The configurations described in the above embodiments describe examples of the content of the present invention, and can be combined with other known techniques. Furthermore, a part of each of the configurations can be omitted or modified without departing from the gist of the present invention.
Reference Signs List
[0072] 1(11, 12, , 1N) power conversion device,
2(21, 22, , 2N) motor, 3 power conversion unit, 3a
voltage detector, 4 processing unit, 5 storage unit, 6 first start-up unit, 7 second start-up unit, 8 motor control unit, 9 signal selection unit (start-up selector), 10 signal switch (start-up selector), 11 current detection unit, 13 control start operation unit, 14 train safety device, 15 handle, 16 kilometrage management device, 17 tacho-generator, 22 operation support system, 23 operation support device, 24 speed regulation section storage unit, 25 travel management unit, 26 train information management device, 26a calculation unit, 40 vehicle, 50 train, 51 overhead wire, 52 current collector.

CLAIMS
1. An electric vehicle control device including a
plurality of power conversion devices that each drive a
synchronous motor by using sensorless control, the electric
vehicle control device comprising:
a start-up selector to select, on a basis of information on a vehicle speed obtained from a vehicle speed sensor, which control system starts the power conversion devices, wherein
each of the power conversion devices starts an operation with an identical control system on a basis of the vehicle speed.
2. The electric vehicle control device according to claim
1, wherein
a first determination value to determine a magnitude of the vehicle speed is set, and
each of the power conversion devices switches the control system of a corresponding one of the power conversion devices in accordance with presence or absence of an operation command and a magnitude relationship between the vehicle speed and the first determination value.
3. The electric vehicle control device according to claim
2, wherein
a second determination value to determine a magnitude of the vehicle speed is set,
the second determination value is greater than the first determination value, and
each of the power conversion devices stops switching control for a power conversion unit in accordance with a magnitude relationship between the vehicle speed and the second determination value.

4. The electric vehicle control device according to claim
3, wherein
each of the power conversion devices is configured to include
a first start-up unit to perform processing to estimate an initial magnetic pole position by using magnetic saturation,
a second start-up unit to perform processing to estimate an initial speed and an initial magnetic pole position by using an induced voltage, and
a motor control unit to perform processing to drive the motor with a torque control command generated by using, as an initial value, one of the initial magnetic pole position estimated by the first start-up unit and the initial speed and the initial magnetic pole position that are estimated by the second start-up unit.
5. The electric vehicle control device according to claim
4, wherein, in a case where an operation command is input,
each of the power conversion devices operates the first
start-up unit when the vehicle speed is less than the first
determination value and operates the second start-up unit
when the vehicle speed is equal to or greater than the
first determination value.
6. The electric vehicle control device according to claim
4, wherein, in a case where an operation command is not
input, each of the power conversion devices operates the
second start-up unit when the vehicle speed is equal to or
greater than the second determination value and stops
switching control for a power conversion unit when the
vehicle speed is less than the first determination value.

7. The electric vehicle control device according to claim 3, wherein the second determination value is adjusted depending on an intermediate link voltage of each of the power conversion devices.
8. The electric vehicle control device according to claim 3, wherein the second determination value is adjusted depending on a temperature of a magnet in the synchronous motor.