1. A synchronous motor control device (1A) that includes: an inverter (14) including a plurality of switching elements; a current converting means (11) configured to convert a detected or estimated three-phase current of a synchronous motor (2) into a d-axis current and a q-axis current; a current feedback control calculating means (12) configured to calculate a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current, using current feedback control; and a voltage command value converting means (13) configured to convert the d-axis voltage command value and the q-axis voltage command value into a three-phase voltage command value, and sends an output to the synchronous motor (2) while controlling switching on and off of the switching elements on a basis of the three-phase voltage command value, characterized in that gain adjustment in the current feedback control is automatically performed while a winding inductance to be used in the current feedback control is estimated through calculation of a three-phase current, a three-phase voltage, and a rotation speed of the synchronous motor (2) as measurement parameters, the synchronous motor (2) in a constant rotating state being set as a measurement target.

2. The synchronous motor control device (1A) according to claim 1, characterized in that the three-phase current is converted into the d-axis current and the q-axis current in an orthogonal coordinate expression, the three-phase voltage is converted into a d-axis voltage and a q-axis voltage in an orthogonal coordinate expression, and the rotation speed of the synchronous motor (2) is converted into a mechanical angular velocity, each of which being used in the calculation.

3. The synchronous motor control device (1A) according to claim 2, characterized in that the winding inductance is expressed by a mathematical expression (5) obtained by modifying a mathematical expression (4) obtained by substituting a mathematical expression (2) into a mathematical expression (3), using the following mathematical expressions (1) to (6), [Math. 1] where · id and iq represent the d-axis current and the q-axis current, · vd and vq represent the d-axis voltage and the q-axis voltage, · Nr represents a motor rotation speed and is converted into a mechanical angular velocity ωr according to the mathematical expression (1), · R represents a motor one-phase resistance value, · L represents a motor one-phase inductance value, · Φm represents a magnet’s magnetic flux and is derived according to the mathematical expression (6), · P represents the number of motor poles, and the motor one-phase inductance (L) is estimated by substituting the mechanical angular velocity (ωr), the q-axis current (iq), the d-axis current (id), the q-axis voltage (vq), the d-axis voltage (vd), and the magnet’s magnetic flux (Φm) at the time of measurement into the mathematical expression (5).

Description:TECHNICAL FIELD
[0001]
The present invention relates to a synchronous motor control device, and more particularly, to a synchronous motor control device that has a function of automatically estimating a winding inductance as a parameter necessary for current feedback control of a synchronous motor.

BACKGROUND ART
[0002]
A synchronous motor is an electric motor that rotates at a synchronous speed determined by the frequency of an AC power supply, and performs a rotating operation following a rotating magnetic field formed by an input AC current while the rotor is attracted by the magnetic field. Normally, a synchronous motor is driven and controlled by a control system formed with a control device connected to the synchronous motor.
[0003]
FIG. 3 is a functional block diagram illustrating such a control system for a synchronous motor 2. In this system, in a control device 1B that performs the drive control of the synchronous motor 2, a three-phase current (iU, iV, iW) of the synchronous motor detected or estimated from a current sensor are used, or is represented by axes synchronized at an estimated motor position, so that the three-phase current is converted into a d-axis current (id) and a q-axis current (iq) by a current converting means 11.
[0004]
A current feedback control calculating means 12 calculates a d-axis voltage command value (Vdref) and a q-axis voltage command value (Vqref) by current feedback control so that the d-axis current (id) and the q-axis current (iq) match the input d-axis current command value (idref) and q-axis current command value (iqref), respectively. A voltage command value converting means 13 converts this voltage into a three-phase voltage command value (VUref, VVref, VWref) of the synchronous motor, and switching on and off of switching elements of an inverter are controlled, so that the three-phase voltage command value is output to the synchronous motor 2.
[0005]
A common method for measuring a winding inductance that is a parameter necessary for current feedback control in such a conventional control system for the synchronous motor 2 is now described with reference to FIG. 2. By this method, a winding inductance value in a resting state is measured with an LCR meter 3 or the like, a U-V interphase, a V-W interphase, and a W-U interphase in the synchronous motor 2 are measured, an average of each measured value is obtained, and the value obtained by halving the average is set as the winding inductance of one phase of the motor.
[0006]
Further, the current feedback control in the control system described above is expressed by the mathematical expressions shown below, and a proportional feedback gain is determined by the value of the winding inductance as shown below.
[Math. 1]

[0007]
By the method for measuring the winding inductance with the LCR meter 3 or the like, however, measurement is performed while the synchronous motor 2 is in a resting state. Therefore, the winding inductance value depending on current characteristics is not accurately measured, and an error tends to be large. Therefore, it is difficult to perform accurate control in the current feedback control described above. Further, it is also necessary to perform parameter measurement and an adjustment operation each time the specification of the synchronous motor 2 to be controlled is changed.
[0008]
On the other hand, claim 16 of WO 2009/144957 (Patent Literature 1) proposes a method for calculating a winding inductance value of a pair of adjacent stators from a current change rate of the three-phase alternating current applied from a three-phase inverter corresponding to each stator winding. Further, claim 8 of WO 2011/024935 (Patent Literature 2) proposes a method by which a storage unit that stores a map indicating a relationship between d-axis and q-axis currents and a winding inductance value, and calculating the winding inductance value from a current command value calculated by a current command value calculating unit and the map in the storage unit.
[0009]
However, even by the methods proposed in Patent Literatures 1 and 2 described above, the control device connected to the synchronous motor cannot accurately measure the winding inductance value in the synchronous motor being driven. Therefore, it has to be said that it is difficult for the control device to automatically perform the current feedback control with high accuracy in cases including a case where the specification of the synchronous motor is changed.

CITATION LIST
PATENT LITERATURE
[0010]
Patent Literature 1: WO 2009/144957 A
Patent Literature 2: WO 2011/024935 A

SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0011]
The present invention is to solve such problems as described above, and aims to enable a synchronous motor control device to accurately estimate a winding inductance of a synchronous motor, and automatically perform gain adjustment in current feedback control with high accuracy.

SOLUTION TO PROBLEM
[0012]
Therefore, the present invention provides a synchronous motor control device that includes: an inverter including a plurality of switching elements; a current converting means configured to convert a detected or estimated three-phase current of a synchronous motor into a d-axis current and a q-axis current; a current feedback control calculating means configured to calculate a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current, using current feedback control; and a voltage command value converting means configured to convert the d-axis voltage command value and the q-axis voltage command value into a three-phase voltage command value, and sends an output to the synchronous motor while controlling switching on and off of the switching elements on the basis of the three-phase voltage command value, the synchronous motor control device being characterized in that gain adjustment in the current feedback control is automatically performed while a winding inductance to be used in the current feedback control is estimated through calculation of a three-phase current, a three-phase voltage, and a rotation speed of the synchronous motor as measurement parameters, the winding inductance being obtained by setting the synchronous motor in a constant rotating state as a measurement target.
[0013]
As described above, a method for automatically performing gain adjustment in current feedback control while estimating a winding inductance by calculating a three-phase current, a three-phase voltage, and a motor rotation speed as measurement parameters, with a synchronous motor in a constant rotating state being set as a measurement target, is adopted, to enable the connected control device to estimate the winding inductance of the operating synchronous motor online, and automatically perform gain adjustment in the current feedback control with high accuracy.

[0014]
In the present invention, in a case where the three-phase current is converted into a d-axis current and a q-axis current in an orthogonal coordinate expression, the three-phase voltage is converted into a d-axis voltage and a q-axis voltage in an orthogonal coordinate expression, and the rotation speed of the synchronous motor is converted into a mechanical angular velocity, each of which is to be used in the above-described calculation, it is possible to easily and accurately estimate the winding inductance in the control device.
[0015]
In the present invention, the winding inductance is expressed by a mathematical expression (5) formed by modifying a mathematical expression (4) obtained by substituting a mathematical expression (2) into mathematical expression (3), mathematical expressions (1) to (6) being used:
[Math. 2]

[0016]
Here,
· id and iq represent the d-axis current and the q-axis current,
· vd and vq represent the d-axis voltage and the q-axis voltage,
· Nr represents a motor rotation speed and is converted into a mechanical angular velocity ωr according to the mathematical expression (1),
· R represents a motor one-phase resistance value,
· L represents a motor one-phase inductance value,
· Φm represents a magnet’s magnetic flux and is derived from the mathematical expression (6),
· P represents the number of motor poles, and
the motor one-phase inductance (L) is estimated by substituting the mechanical angular velocity (ωr), the q-axis current (iq), the d-axis current (id), the q-axis voltage (vq), the d-axis voltage (vd), and the magnet’s magnetic flux (Φm) at the time of measurement into the mathematical expression (5). In this case, winding inductance estimation and gain adjustment in the control device can be performed without fail.

ADVANTAGEOUS EFFECTS OF INVENTION
[0017]
According to the present invention in which a synchronous motor in a constant rotating state is set as the measurement target, and a control device performs winding inductance estimation online while calculating a three-phase current, a three-phase voltage, and a rotation speed of the synchronous motor as measurement parameters, the winding inductance of the synchronous motor can be accurately estimated, and gain adjustment in current feedback control can be automatically performed with high accuracy.

BRIEF DESCRIPTION OF DRAWINGS
[0018]
FIG. 1 is a functional block diagram illustrating a processing situation during winding inductance estimation and automatic gain adjustment by a synchronous motor control device according to an embodiment of the present invention;
FIG. 2 is an explanatory diagram illustrating an outline of a method for estimating a winding inductance of a synchronous motor according to a conventional example;
FIG. 3 is a functional block diagram illustrating an outline of a control system in a conventional synchronous motor control device; and
FIG. 4 is a chart showing a process of deriving each mathematical expression in the present invention.

DESCRIPTION OF EMBODIMENTS
[0019]
In the description below, embodiments of the present invention will be explained with reference to the drawings. Note that, in the present invention, “online” refers to a state in which a synchronous motor connected to a control device is being driven.
[0020]
FIG. 1 is a functional block diagram illustrating the processing details at a time of winding inductance estimation and at a time of automatic gain adjustment, which are characteristic parts of the details of control to be performed on a synchronous motor 2 by a control device 1A of the present embodiment. The basic configuration and the basic functions of the control device 1A are the same as those of a conventional control device 1B illustrated in FIG. 3.
[0021]
The basic configuration of the control device 1A according to the present embodiment is now described with reference to FIGS. 1 and 3. The control device 1A includes an inverter 14 including a plurality of switching elements, and a computer 10 including a storage means, a CPU, and the like. As the means functionally formed by the computer 10, the control device 1A includes; a current converting means 11 that converts a detected or estimated three-phase current of the synchronous motor 2 into a d-axis current and a q-axis current; a current feedback control calculating means 12 that calculates a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current, using current feedback control; and a voltage command value converting means 13 that converts the d-axis voltage command value and the q-axis voltage command value into a three-phase voltage command value. On the basis of the converted three-phase voltage command value, the control device 1A sends an output to the synchronous motor 2 while controlling switching on and off of the switching elements of the inverter 14. The above components are the same as those of the control device 1B according to the conventional example.
[0022]
Further, the present embodiment is characterized in that the control device 1A performs gain adjustment in the above-mentioned current feedback control while estimating the winding inductance by calculating the three-phase current, the three-phase voltage, and the rotation speed of the synchronous motor as measurement parameters to obtain the winding inductance to be used in the current feedback control, the measurement target being the synchronous motor 2 in a constant rotating state.
[0023]
That is, the winding inductance, which is a parameter necessary for the current feedback control on the synchronous motor 2, can be estimated online from the outer product of the current value and the voltage value at a time of constant rotation, and the control device 1A can automatically and accurately perform gain adjustment in the current feedback control.
[0024]
The processing details are now described in detail with reference to FIG. 1. Although measurement of a winding inductance is performed for the synchronous motor 2 in a stationary state in conventional cases as illustrated in FIG. 2, the control device 1A of the present embodiment sets, as the measurement target, the synchronous motor 2 put in a constant rotating state under drive control of the inverter 14.
[0025]
The measurement parameters do not include the winding inductance, but include a three-phase current (iU, iV, iW), a three-phase voltage (VU, VV, VW), and the rotation speed (Nr) of the synchronous motor. Note that the rotation speed (Nr) of the synchronous motor is converted into a mechanical angular velocity (ωr) according to the mathematical expression (1) shown below.
[Math. 3]

[0026]
By calculating these measurement parameters with the computer 10 in the control device 1A, the winding inductance estimation and the gain adjustment in the current feedback control can be automatically performed. That is, as illustrated in FIG. 1, a winding inductance estimating means 10a functionally formed by the computer 10 automatically estimates the winding inductance, and a control gain automatic adjusting means 10b formed in the same manner automatically adjusts the gain.
[0027]
Next, the principles of a method for measuring the above-mentioned winding inductance is described, using a voltage equation and an outer product equation in the synchronous motor 2.
[0028]
The voltage equation and the outer product on the d-axis and the q-axis of the synchronous motor 2 are expressed by the mathematical expressions (2) and (3) shown below. Here, an equation is shown using a motor one-phase resistance (R), a motor one-phase inductance (L), the mechanical angular velocity (ωr), and a magnet’s magnetic flux (Φm).

[Math. 4]

[0029]
The motor one-phase inductance (L) is derived according to the following mathematical expression (4) formed by substituting the mathematical expression (2), which is a voltage equation of VdVq, into the mathematical expression (3), which is an outer product equation.
[Math. 5]

[0030]
The motor one-phase inductance (L) is then deformed so as to shift to the left side, so that the mathematical expression (5) shown below is obtained.
[Math. 6]

[0031]
The motor one-phase inductance (L) can be estimated by substituting the mechanical angular velocity (ωr), the q-axis current (iq), the d-axis current (id), the q-axis voltage (vq), the d-axis voltage (vd), and the magnet’s magnetic flux (Φm) at the time of measurement into the mathematical expression (5).
[0032]
FIG. 4 illustrates a process of deriving the above mathematical expressions (1) to (5).
[0033]
Note that the q-axis current (iq) and the d-axis current (id) are obtained by converting the three-phase current (iU, iV, iW) into an orthogonal coordinate expression, and the q-axis voltage (vq) and the d-axis voltage (vd) are obtained by converting the three-phase voltage (VU, VV, VW) into an orthogonal coordinate expression. The magnet’s magnetic flux (Φm) can be estimated from the mechanical angular velocity (ωr) and the q-axis voltage (vq) at a time of no-load driving of the synchronous motor 2, according to the mathematical expression (6) shown below.
[Math. 7]

[0034]
In this manner, the winding inductance estimation that takes into account the frequency and the current characteristics at a time of driving the synchronous motor 2 can be performed online, which greatly contributes to improvement of controllability in the current feedback control. Also, optimum control gain adjustment can be performed without being affected by any change in the specification of the synchronous motor 2.
[0035]
As described so far, the synchronous motor control device according to the present invention is capable of accurately estimating the winding inductance of a synchronous motor, and thus, the gain adjustment in the current feedback control can be automatically performed with high accuracy.

REFERENCE SIGNS LIST
[0036]
1A Control device
2 Synchronous motor
10 Computer
10a Winding inductance estimating means
10b Control gain automatic adjusting means
11 Current converting means
12 Current feedback control calculating means
13 Voltage command value converting means
14 Inverter
, Claims:1. A synchronous motor control device (1A) that includes: an inverter (14) including a plurality of switching elements; a current converting means (11) configured to convert a detected or estimated three-phase current of a synchronous motor (2) into a d-axis current and a q-axis current; a current feedback control calculating means (12) configured to calculate a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current, using current feedback control; and a voltage command value converting means (13) configured to convert the d-axis voltage command value and the q-axis voltage command value into a three-phase voltage command value, and sends an output to the synchronous motor (2) while controlling switching on and off of the switching elements on a basis of the three-phase voltage command value, characterized in that
gain adjustment in the current feedback control is automatically performed while a winding inductance to be used in the current feedback control is estimated through calculation of a three-phase current, a three-phase voltage, and a rotation speed of the synchronous motor (2) as measurement parameters, the synchronous motor (2) in a constant rotating state being set as a measurement target.

2. The synchronous motor control device (1A) according to claim 1, characterized in that
the three-phase current is converted into the d-axis current and the q-axis current in an orthogonal coordinate expression,
the three-phase voltage is converted into a d-axis voltage and a q-axis voltage in an orthogonal coordinate expression, and
the rotation speed of the synchronous motor (2) is converted into a mechanical angular velocity, each of which being used in the calculation.

3. The synchronous motor control device (1A) according to claim 2, characterized in that
the winding inductance is expressed by a mathematical expression (5) obtained by modifying a mathematical expression (4) obtained by substituting a mathematical expression (2) into a mathematical expression (3), using the following mathematical expressions (1) to (6),
[Math. 1]

where
· id and iq represent the d-axis current and the q-axis current,
· vd and vq represent the d-axis voltage and the q-axis voltage,
· Nr represents a motor rotation speed and is converted into a mechanical angular velocity ωr according to the mathematical expression (1),
· R represents a motor one-phase resistance value,
· L represents a motor one-phase inductance value,
· Φm represents a magnet’s magnetic flux and is derived according to the mathematical expression (6),
· P represents the number of motor poles, and
the motor one-phase inductance (L) is estimated by substituting the mechanical angular velocity (ωr), the q-axis current (iq), the d-axis current (id), the q-axis voltage (vq), the d-axis voltage (vd), and the magnet’s magnetic flux (Φm) at the time of measurement into the mathematical expression (5).