JP2614788B2 - AC motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an AC motor, and more particularly to an AC motor control device for supplying AC power from a plurality of inverters to a polyphase AC motor.

[0002]

2. Description of the Related Art In order to increase the capacity of an inverter, switching elements are connected in series and in parallel, and multiple inverters are multiplexed and multi-phased. As one method of multiplexing and multi-phase, there is a method in which an AC motor is multi-phase winding and multiplexing is performed by a magnetomotive force.However, in a poly-phase AC motor, transient impedance is extremely large due to magnetic coupling between respective primary windings. There is a problem that the current control cannot be performed at a high speed because of the small size. Therefore, conventionally, a method of increasing the transient impedance by providing a reactor between the inverter and the polyphase AC motor is described in IEEJ Transactions on Volume 108, No. 2, 1988, pp. 137.

[0003]

The above prior art has a problem that an external reactor is required between the inverter and the polyphase AC motor. Further, in a system in which a series reactor is connected between a polyphase AC motor and an inverter, there is a problem that the maximum value of the voltage that can be supplied to the polyphase AC motor is reduced due to the voltage drop of the reactor, and the voltage utilization rate is deteriorated. SUMMARY OF THE INVENTION It is an object of the present invention to provide a system for supplying power to a polyphase AC motor using a plurality of inverters, by reducing or eliminating an external reactor to reduce the output current of a multiplex inverter or the winding of each phase of the polyphase AC motor. An object of the present invention is to provide a motor control device capable of stably balancing current.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-phase AC motor in which a plurality of inverters are connected in parallel to a representative current control system provided on a rotating coordinate system of the AC motor. This is achieved by setting the average value of the inverter output currents and the difference between the inverter output currents as the feedback signal to the unbalanced current control system provided on the rotating coordinate system of the AC motor.

[0005]

The current control system for suppressing imbalance acts so that the output currents of the inverters become equal, so that the currents of the windings of each phase of the polyphase AC motor can be balanced. Also, in an inverter connected in parallel using an external reactor, the unbalanced current can be similarly reduced by the operation of the current control system. As described above, by balancing the output currents of the inverters, the external reactor can be reduced or eliminated, and control capable of high-speed response can be realized.

[0006]

An embodiment of the present invention will be described below with reference to FIG. This figure is an embodiment applied to a polyphase AC motor having two sets of three-phase windings, and shows inverters 1A and 1B
Are directly connected to two sets of three-phase windings UA, VA, WA and UB, VB, WB of the electric motor 2 without passing through an external reactor. Current detectors 3A and 3B for detecting U-phase currents, current detectors 4A and 4B for detecting V-phase currents, and current detectors 5A and 5B for detecting W-phase currents are provided on the output sides of the inverters 1A and 1B. Are provided respectively. AC motor 2
Is detected by the speed detector 14, and the speed signal Wr is supplied to the adder 22. The torque current command signal Iq * is supplied to an adder 20A and a slip angular frequency calculator 21.
Supplied to The slip angular frequency calculator 21 generates a slip frequency command signal Ws * according to the torque current command signal Iq *, and outputs the generated signal to the adder 22. The adder 22 adds the speed signal Wr and the slip angular frequency command signal Ws * to generate a primary angular frequency command signal W1 *. The primary angular frequency command signal W1 * is supplied to the coordinate converters 15A, 15B, 16
A, 16B. The coordinate converter 16A detects the detection signals IUA, IVA, IA from the current detectors 3A, 4A, 5A.
WA is converted into an exciting current signal IdA and a torque current signal IqA in the rotating magnetic field coordinate system. The coordinate converter 16B converts the detection signals IUB, IVB, IWB from the current detectors 3B, 4B, 5B into an excitation current signal IdB and a torque current signal IqB in the rotating magnetic field coordinate system. The adder 24 adds the exciting current signals IdA and IdB, the adder 23 adds the torque current commands IqA and IqB, and the output signals of the adders are supplied to coefficient units 26 and 25, respectively. Coefficient unit 25,
26 has a gain of 0.5 (strictly speaking, inverters 1A and 1B
, And supplied to the subtracters 19A and 20A. In the subtractor 19A, the exciting current command signal Id * and the output signal of the coefficient unit 26 are subtracted. In the subtractor 20A, the torque current command signal Iq * and the output signal of the coefficient unit 25 are subtracted. The output signals are supplied to current controllers 17A and 18A, respectively. Current regulator 17A, 1
8A are voltage command signals Vd * and Vq * in the rotating magnetic field coordinate system according to signals from the subtracters 19A and 20A, respectively.
Generate The subtractor 46 subtracts IdB from the exciting current signal IdA, and the subtractor 47 subtracts IqB from the torque current signal IqA. In the subtractor 44, the output signal of the subtractor 46 is subtracted from the reference command signal I0 *,
In the subtractor 45, the subtractor 47 is derived from the reference command signal I0 *.
Are subtracted, and the output signals of the respective subtracters are supplied to the current regulators 30 and 31, respectively. Current regulator 3
0 and 31 are voltage command correction signals ΔVd in the rotating magnetic field coordinate system according to signals from the subtracters 44 and 45, respectively.
*, ΔVq *. The coefficient units 32A and 32B have gains of 0 to 1, multiply the voltage command correction signal ΔVd * by a gain, and supply them to the adder 40 and the subtractor 42, respectively. The coefficient units 33A and 33B have gains of 0 to 1, multiply the voltage command correction signal ΔVq * by a gain, and supply the multiplied signals to the adder 41 and the subtractor 43, respectively. In the adder 40, the voltage command signal Vd * and the output of the coefficient unit 32A are added, and the adder 41
In, the voltage command signal Vq * and the output of the coefficient unit 33A are added to generate respective voltage command signals VdA ** and VqA **. The coordinate converter 15A receives the voltage command signals VdA **, VqA
** is converted into three-phase AC output voltage command signals VUA **, VVA **, and VWA ** in the stator coordinate system of the AC motor 2, and the converted three-phase AC output voltage command is output to the inverter 1A.
In the subtractor 42, the voltage command signal Vd * is used to calculate the coefficient
The output of 2B is subtracted, and the output of the coefficient unit 33B is subtracted from the voltage command signal Vq * in the subtractor 43 to generate the respective voltage command signals VdB ** and VqB **. Coordinate converter 1
5B is a three-phase AC output voltage command signal VUB * in the stator coordinate system of the AC motor 2 for the voltage command signals VdB ** and VqB **.
*, VVB **, and VWB **, and outputs the converted three-phase AC output voltage command to the inverter 1B.

The operation of the coordinate converter 16A is as shown in FIG.
(1) of [Equation 1] shown in FIG. Also,
The operation of the coordinate converter 15A is represented by Expression (2) of [Equation 2] shown in FIG.

In the conventional method, the imbalance of the impedance of each main circuit including the inverter and the unbalanced current due to the difference between the output voltages of the inverters cannot be suppressed without providing an external reactor between the inverter and the AC motor. In the present invention, the average current (strictly speaking, the capacity distribution ratio of the inverters 1A and 1B) of an AC motor having two sets of three-phase windings is determined in the present invention. The current is controlled by the current regulators 17A and 18A,
An unbalanced current between one three-phase winding and the other three-phase winding is controlled by the current regulators 30 and 31 so that the difference becomes zero. As described above, in the present embodiment, the unbalanced current due to the impedance imbalance and the difference between the inverter output voltages in each main circuit including the inverter is:
Since the current can be suppressed by the current control system for suppressing the unbalance, the reactor can be eliminated.

FIG. 2 shows an embodiment in which the present invention is applied to a polyphase AC motor having six-phase windings. Here, what differs from FIG. 1 is that the AC motor is a six-phase winding or two sets of three-phase windings. The operation of each part is almost the same as that of the embodiment of FIG. 1, and the description is omitted here. However, the present invention
Even when applied to a phase winding AC motor, the unbalanced current due to the unbalance of each main circuit impedance including the inverter and the difference of each inverter output voltage can be suppressed by the unbalanced current control system. Can be eliminated.

FIG. 3 shows an embodiment in which the present invention is applied to a three-phase AC motor. The operation of each part is almost the same as that of the embodiment of FIG. 1, and only the differences will be described. Inverter 1
A and 1B have a plurality of switching elements, and when each switching element operates, it is not shown in the drawing,
The input DC voltage is converted into a three-phase AC voltage and supplied to both ends of the reactors 27U, 27V, and 27W with intermediate taps. A voltage obtained by averaging the three-phase AC voltages of the inverters 1A and 1B is supplied to the AC motor 2 from the intermediate tap of the reactor with the intermediate tap. As a conventional multiplexing method, even if inverters are connected in parallel via a reactor with an intermediate tap, there remains a problem that an imbalance in output current occurs due to a difference in inverter output voltage. However, in the present embodiment, since the unbalanced current can be suppressed by the current control system for unbalance correction, the size of the reactor with the intermediate tap can be reduced.

FIG. 4 shows another embodiment in which the present invention is applied to a polyphase AC motor having two sets of three-phase windings. The operation of each part is almost the same as that of the embodiment of FIG. 1, and only the differences will be described. The coordinate converter 15A receives the voltage command signal VdA
*, VqA * are converted into voltage command signals VU *, VV *, VW * in the stator coordinate system of the AC motor 2. Subtractor 50A, 5
At 0B and 50C, the detection signals IUB, IVB and IWB are subtracted from the detection signals IUA, IVA and IWA. Subtractor 51
In A, 51B, and 51C, the output signals of the subtractors 50A, 50B, and 50C are subtracted from the reference command signal I0 *, and the output signals of the respective subtracters are used as current controllers 60A and 60C, respectively.
B, 60C. Current regulators 60A, 60B,
60C generates voltage command correction signals ΔVU *, ΔVV *, ΔVW * in the stator coordinate system according to signals from subtracters 51A, 51B, 51C, respectively. Coefficient unit 54A,
54B has a gain of 0 to 1 and a voltage command correction signal ΔV
The gain of U * is multiplied by an adder 52A and a subtractor 53A, respectively.
To supply. The coefficient units 55A and 55B have gains of 0 to 1, multiply the voltage command correction signal ΔVV * by a gain, and supply the multiplied signals to the adder 52B and the subtractor 53B, respectively. Coefficient unit 56
A and 56B have gains of 0 to 1 and multiply the voltage command correction signal ΔVW * by a gain.
Supply to 3C. In the adders 52A, 52B, 52C, the voltage command signals VU *, VV *, VW * and the coefficient units 54A,
The outputs of 55A and 56A are added, and 3
Generate phase AC voltage command signals VUA **, VVA **, VWA **,
Output to inverter 1A. Subtractors 53A, 53B, 5
In 3C, the outputs of the coefficient units 54B, 55B, 56B are respectively subtracted from the voltage command signals VU *, VV *, VW * to generate respective voltage command signals VUB **, VVB **, VWB **, Output to inverter 1B. Also in this embodiment,
As in the embodiment of FIG. 1, the unbalanced current between the three-phase windings can be suppressed, and the external reactor can be eliminated.

FIG. 5 shows another embodiment in which the present invention is applied to a three-phase AC motor. The operation of each part is almost the same as that of the embodiment of FIG. 4, and only the differences will be described. The inverters 1A and 1B have a plurality of switching elements,
When each switching element operates, although not shown, the input DC voltage is converted into a three-phase AC voltage,
It is supplied to both ends of reactors 27U, 27V and 27W with intermediate taps. A voltage obtained by averaging the three-phase AC voltages of the inverters 1A and 1B is supplied to the AC motor 2 from the intermediate tap of the reactor with the intermediate tap. As a conventional multiplexing method, even if inverters are connected in parallel via a reactor with an intermediate tap, there remains a problem that an imbalance in output current occurs due to a difference in inverter output voltage. However, in the present embodiment, since the unbalanced current can be suppressed by the current control system for unbalance correction, the size of the reactor with the intermediate tap can be reduced.

In the above embodiment, the description has been given of the case where the inverter output current is detected for three phases. However, the present invention is also applied to the case of detecting and controlling two phases because the combination of three phase currents is zero. be able to. Further, the present invention can be applied to a polyphase AC motor including two or more sets of three-phase windings. Further, the present invention can naturally be applied to a polyphase AC motor in which a plurality of sets of three-phase windings are wound with different geometric shapes. It is also apparent that the same effects can be obtained by applying the present invention to a voltage-type inverter based on space vector control that selects an output voltage vector based on an output voltage command and an output phase command.

[0014]

As described above, according to the present invention,
In the case of one set of three-phase winding three-phase induction motors, the unbalanced current can be suppressed, and the external reactor can be reduced. Further, even with a polyphase AC motor composed of two or more three-phase windings, unbalanced current can be suppressed, and inverters can be multiplexed without providing an external reactor.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention.

FIG. 2 shows a second embodiment of the present invention.

FIG. 3 shows a third embodiment of the present invention.

FIG. 4 shows a fourth embodiment of the present invention.

FIG. 5 is a fifth embodiment of the present invention.

FIG. 6: Numerical expressions (1) and (2)

[Explanation of symbols]

 1A, 1B Inverter 2 Polyphase AC motor 17A, 18A, 30, 31 Current controller 15A, 15B, 16A, 16B Coordinate converter 40, 41 Adder 42, 43, 44, 45, 46, 47 Subtractor

Claims (6)

(57) [Claims] 1. A DC power supply and an AC motor control device for supplying a voltage of the DC power supply to a polyphase AC motor via a plurality of power converters, wherein output currents of the plurality of power converters are detected. Detection means, first coordinate conversion means for converting one current detection value of the power converter into rotation coordinates, and second coordinate conversion means for converting the other current detection value of the power converter into rotation coordinates. Average value calculating means for calculating an average output current value from output signals of the first and second coordinate conversion means; and a representative two-phase signal based on an output of the average value calculating means, an exciting current command value and a torque current command value. Voltage command generation means for generating a voltage command value, correction signal generation means for generating a correction signal from the outputs of the first and second coordinate conversion means,
Voltage command correction means for generating a plurality of two-phase voltage command values from the output of the correction signal generation means and the output of the voltage command generation means; and a plurality of voltage command correction means for generating a three-phase voltage command from the output of the voltage command correction means. An AC motor control device comprising: command coordinate conversion means for reducing unbalanced current of a polyphase AC motor. 2. The subtraction means according to claim 1, wherein said correction signal generation means calculates a difference between an output of said first coordinate conversion means and an output of said second coordinate conversion means. An AC motor control device comprising current adjusting means for setting the output to zero. 3. The voltage command correcting means according to claim 1, wherein said voltage command correcting means adds a gain converting means of an output of said correction signal generating means and one of an output of said gain converting means and an output of said voltage command generating means. An AC motor control device, comprising: an adding unit that performs subtraction; and a subtraction unit that subtracts the other. 4. A DC power supply and an AC motor control device for supplying a voltage of the DC power supply to a polyphase AC motor via a plurality of power converters, wherein output currents of the plurality of power converters are detected. Detection means, first coordinate conversion means for converting one current detection value of the power converter into rotation coordinates, and second coordinate conversion means for converting the other current detection value of the power converter into rotation coordinates. Average value calculating means for calculating an average output current value from output signals of the first and second coordinate conversion means; and a representative two-phase signal based on an output of the average value calculating means, an exciting current command value and a torque current command value. Voltage command generating means for generating a voltage command value;
A plurality of command coordinate conversion means for generating a phase voltage command; a correction signal generation means for generating a correction signal from an output of the current detection means; an output of the correction signal generation means and an output of the plurality of command coordinate conversion means. And a voltage command correcting means for generating a plurality of three-phase voltage command values from the AC motor control device. 5. The correction signal generating means according to claim 4, wherein said correction signal generating means obtains a difference for each phase from an output signal of said current detecting means, and current adjusting means sets an output of said subtracting means to zero. An AC motor control device, comprising: 6. The voltage command correcting means according to claim 4, wherein said voltage command correcting means adds a gain converting means of an output of said correction signal generating means and one of an output of said gain converting means and an output of said voltage command generating means. An AC motor control device, comprising: an adding unit that performs subtraction; and a subtraction unit that subtracts the other.