JP2012065519A - Ac motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the correction performance of an offset error which a current sensor has.SOLUTION: The present invention provides an AC motor controller 10 which applies a multiphase AC voltage to a multiphase AC motor 90 for control. The AC motor controller 10 comprises: a current sensor 34; a control part 11 which generates a voltage command value of each phase for making a current of each phase follow up the current command value; a power amplification part 13 which applies a voltage of each phase to the multiphase AC motor in accordance with the voltage command value of each phase; a phase voltage offset correction part 17 which reduces a voltage offset value; and a phase current offset correction part 16 which reduces a current offset by correcting a current detection value of each phase. The AC motor controller 10 makes the phase voltage offset correction part 17 operate preferentially rather than the phase current offset correction part 16.

Description

  The present invention relates to a technique for correcting an offset error at the time of current detection of an AC motor control device.

  In AC motor drive control, vector control is generally performed in which a detected current follows a target current while a motor drive state is detected by a current sensor or position detector. Current sensors include current-to-voltage conversion devices such as current transformers and high-precision resistors, operational amplifiers that amplify voltages, and analog circuits such as AD converters. The analog circuit has a problem that an offset is generated due to its temperature characteristics and transient characteristics, and torque fluctuations (electrical angle primary component) synchronized with the electric angle period of the motor are caused. Many correction techniques for solving this problem have been proposed (Patent Documents 1 to 6).

JP 2006-121860 A JP 2006-149045 A JP-A-8-47280 JP-A-62-233084 JP 2001-186784 A Special table 2000-014866 gazette

  However, for example, in the techniques of Patent Documents 3 to 6, the timing at which the offset correction value can be learned is limited. In other words, the offset correction value is possible only in a specific state such as when the power is turned on, immediately before the start of energization, or in a special operation mode. On the other hand, in the techniques of Patent Documents 1 and 2, the present inventor has found a problem that the offset correction value is erroneously learned in a state where the offset error due to other factors is misidentified as the offset error of the current sensor. It was. The present inventor has found an offset error of a voltage generated due to an error of a position detector that detects the position of the motor as another factor.

  The present invention was created to solve the above-described conventional problems, and an object of the present invention is to provide a technique for improving the offset error correction performance of a current sensor.

  Hereinafter, effective means for solving the above-described problems will be described while showing effects and the like as necessary.

The invention of claim 1 is an AC motor control device that applies and controls a multiphase AC voltage to a multiphase AC motor,
A current sensor that detects a current of each phase supplied to the multiphase AC motor and outputs a current detection value of each phase;
A control unit that generates a voltage command value for each phase for causing the current of each phase to follow the current command value according to the given current command value and the current detection value of each phase;
A power amplifying unit that applies a voltage of each phase to the multiphase AC motor in accordance with a voltage command value of each phase;
A phase voltage for determining a voltage offset value representing a voltage offset of a voltage command value for each phase, and operating the current detection value for each phase according to the voltage offset value for each phase to reduce the voltage offset value An offset correction unit;
A phase current offset correction that determines a current offset value representing a current offset of a current detection value of each phase and corrects the current detection value of each phase according to the current offset value of each phase to reduce the current offset And
With
The AC motor control device operates the phase voltage offset correction unit with priority over the operation of the phase current offset correction unit.

  In the above invention, in the state where the offset value of each phase voltage of the applied voltage is sufficiently small (for example, almost zero), that is, in the state where the offset of each phase current of the multiphase motor (for example, three-phase motor) has theoretically disappeared. The detection error of the current sensor can be detected. In other words, in a state where the phase voltage offset is corrected to zero so that no offset occurs in the actual current of the multiphase motor, the offset value included in the detection value of the current sensor is obtained and corrected. It is said.

  This makes it possible to detect the offset error of the current sensor without being affected by other error factors even in a situation where multiple errors due to multiple errors occur, making it possible to perform accurate offset correction. Become. As another error factor, it has been found by the inventor's test and analysis that, for example, a position detection error of a three-phase motor is manifested as a current sensor error via a phase voltage offset.

  As described above, according to the present invention, it is possible to eliminate the influence of other error factors and to correct the offset due to the temperature characteristics and transient characteristics of the analog circuit constituting the current sensor. As a result, the offset of the current sensor can be accurately obtained and corrected, and torque fluctuation (electrical angle primary component) synchronized with the electric angle cycle of the motor can be suppressed. Further, the present invention has an advantage that the offset correction value learning can always be performed while the motor is being driven.

  Note that the determination of the voltage offset value and the current offset value includes not only calculating the voltage offset value and the current offset value quantitatively but also determining only the sign.

  In the invention of claim 2, the preferential operation is the operation of the phase current offset correction unit after the phase voltage offset correction unit is operated and the voltage offset value becomes smaller than a preset value. It is realized by starting.

  In the above invention, since the operation of the phase current offset corrector is started after the offset value of each phase voltage command value becomes smaller than a preset value, the current is checked after confirming the exclusion of the influence of other error factors. A detection error is detected. Thereby, the offset can be corrected in a state where the influence of other error factors is eliminated.

  The invention according to claim 3 is characterized in that the preferential operation is realized by setting a time constant of the phase voltage offset correction unit smaller than a time constant of the phase current offset correction unit. To do.

  In the above invention, since the time constant of the phase voltage offset corrector is smaller than the time constant of the phase current offset corrector, the phase voltage offset correction precedes the phase current offset correction in terms of time. Even with such a configuration, the offset can be corrected in a state where the influence of other error factors is eliminated.

  According to a fourth aspect of the present invention, the phase voltage offset correction unit adds the voltage offset correction value generated according to the voltage offset value of each phase to the current detection value of each phase, so that the current of each phase The detection value is manipulated.

  In the above invention, since the output of the phase voltage offset correction unit is added to the detected current value, the current controller functions to cancel the added value. Thereby, the offset contained in each phase voltage command value can be suppressed. The addition to the current detection value may be before or after correction of the phase current offset.

In the invention of claim 5, the AC motor control device further includes a coordinate conversion unit that converts the coordinate system from a stationary coordinate system to a rotating coordinate system,
The current sensor outputs a current detection value of each phase as a value in the stationary coordinate system,
The control unit generates a voltage command value of each phase according to the current detection value of each phase converted by the coordinate conversion unit in the rotating coordinate system,
The phase voltage offset correction unit operates the current detection value of each phase converted into a value in the rotating coordinate system by the coordinate conversion unit.

  In the above invention, the phase voltage offset correction unit operates the current detection value of each phase converted into a value in the rotating coordinate system by the coordinate conversion unit. As described above, the operation of the current detection value of each phase may be performed in either the stationary coordinate system or the rotating coordinate system.

  According to a sixth aspect of the present invention, the phase voltage offset correction unit determines the voltage offset value by integrating the voltage command value of each phase with an integer multiple of an electrical angle.

  In the above invention, the offset value of each phase voltage command value is calculated by integrating each phase voltage command value with an integer multiple of the electrical angle. Therefore, even at high speed, integration is performed using sampling data of a plurality of cycles. The number of times can be secured. This is because sampling data of a plurality of cycles can be acquired as a value whose phase is shifted every cycle because the sampling cycle and the rotation cycle of the three-phase motor are asynchronous.

  The invention of claim 7 is characterized in that the phase current offset correction unit determines the current offset value by integrating the detected current value of each phase with an integer multiple of an electrical angle.

  In the above invention, since the offset value of each phase current detection value is calculated by integrating each phase current detection value with an integer multiple of the electrical angle, integration is performed using sampling data of a plurality of cycles even at high speeds. The number of times can be secured. The invention according to claim 6 is the invention in which the sampling target is replaced with each phase current detection value from each phase voltage command value.

  In the invention of claim 8, the phase voltage offset correction unit calculates a current correction amount corresponding to the voltage offset value by dividing the voltage offset value by a motor resistance value, and uses the current correction amount to calculate the current correction amount. The current detection value is manipulated.

  In the above invention, since the current offset value corresponding to the phase voltage offset value can be calculated by dividing the phase voltage integrated value by the motor resistance value, the calculation due to the calculation of the current offset value and the calculation time can be simplified. Shortening can be realized. The present invention was created by paying attention to the fact that an inductance component that is an AC component of the impedance of a three-phase motor can be omitted.

In the invention of claim 9, the AC motor control device further includes a position sensor that detects a rotational position of the AC motor and outputs rotational position information.
The phase voltage offset correction unit has a voltage integrator that integrates the voltage command value,
The voltage integrator multiplies the voltage command value by a position change amount between calculation periods of the rotational position information and integrates the voltage command value.

  In the above invention, since the position change amount during the calculation cycle of the rotational position information is multiplied by the input value of the voltage integrator, even if the rotation speed fluctuates within the calculation cycle, the integrated value of the voltage command value is affected. Can be calculated accurately without any problem.

In the invention of claim 10, the AC motor control device further includes a position sensor that detects a rotational position of the AC motor and outputs rotational position information.
The phase current offset correction unit includes a current integrator that integrates the current detection value,
The current integrator integrates the detected current value by multiplying a position change amount between calculation periods of the rotational position information.

  In the above invention, since the position change amount during the calculation cycle of the rotational position information is multiplied by the input value of the current integrator, even if the rotation speed fluctuates within the calculation cycle, the integrated value of the voltage command value is affected. Can be calculated accurately without any problem.

  The present invention can be embodied not only in the AC motor control device but also in the form of, for example, a computer program that embodies a control method or a control function, a program medium that stores the program, or a program product.

The control block diagram of the power control device of a 1st embodiment. 5 is a flowchart showing a routine for offset correction of the power control apparatus 10; The time chart which shows the processing state of offset correction. The flowchart which shows the routine of the offset correction in 2nd Embodiment. The time chart which shows the processing state of offset correction. The graph which shows the sampling state of the phase voltage command value at the time of high speed rotation in 3rd Embodiment. The graph which shows the shift | offset | difference of the sampling position of the phase voltage command value at the time of high speed rotation. The graph which shows the pseudo increase method of the frequency | count of integration using the shift | offset | difference of a sampling position. The graph which shows the method of integrating in a motor position for calculation of the offset value of a phase voltage command value in 4th Embodiment. The control block diagram of the power control apparatus of a 1st modification. The control block diagram of the power control device of the 2nd modification. The control block diagram of the power control apparatus of a 3rd modification.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the present embodiment, a drive control device for a three-phase AC motor is embodied, and this will be described with reference to FIGS. 1 to 12.

(First embodiment)
FIG. 1 is a control block diagram of the power control apparatus 10 of the first embodiment. The first embodiment is configured as a power device including a three-phase motor 90 and a power control device 10 that controls the three-phase motor 90 by applying a voltage corresponding to each phase voltage command value. The power control device 10 includes a power amplifier 13, a current controller 11, a current sensor 15 for feeding back each phase current value of the three-phase motor 90 to the current controller 11, an inverse dq converter 12, and a dq conversion. A device 18, a position sensor 19, a phase current offset correction unit 16, and a phase voltage offset correction unit 17 are provided. The power amplifier 13 is an inverter that generates a three-phase alternating current from the direct-current power Vdc and supplies it to the three-phase motor 90. The current controller 11 is a controller that gives a voltage command value for each phase to the power amplifier 13. The current sensor 15 detects the current value in order to feed back the current value of each phase of the three-phase motor 90 to the current controller 11.

  The drive control device is also called an AC motor control device. The power amplifier 13 is also called a power amplification unit. The three-phase motor 90 is also called a multiphase AC motor. The dq converter 18 is also called a coordinate conversion unit. The current controller 11 is also called a control unit.

  The current controller 11 is a controller that executes PI control in a dq coordinate system that is an orthogonal biaxial rotational coordinate system. The current controller 11 outputs voltage command values Vd * and Vq * as control output signals in the dq coordinate system. The inverse dq converter 12 performs inverse dq transformation on the voltage command values Vd * and Vq * in the dq coordinate system to generate voltage command values Vu *, Vv * and Vw * in the three-phase stationary coordinate system. To the power amplifier 13. The power amplifier 13 applies a three-phase AC voltage corresponding to the three-phase voltage command values Vu *, Vv *, and Vw * to the three-phase motor 90.

  On the other hand, the current sensor 15 detects the current detection values Iu1, Iv1, Iw1 of the armatures of the respective phases of the three-phase motor 90 and feeds back to the current controller 11. The feedback values Iu, Iv, and Iw of each phase current are dq converted by the dq converter 18 into the current values Id and Iq of the dq coordinate system, and then fed back to the current controller 11. The feedback values Iu, Iv, and Iw of the phase currents are values obtained by correcting the current detection values Iu1, Iv1, and Iw1 by the phase current offset correction unit 16 and the phase voltage offset correction unit 17, respectively.

  The dq converter 18 converts the feedback values Iu, Iv, Iw of each phase current into current values Id, Iq in the dq coordinate system based on the rotational position information θ representing the rotational position detected by the position sensor 19. It is a coordinate converter. The inverse dq converter 12 is a coordinate converter that performs inverse dq conversion of the voltage command values Vd *, Vq * in the dq coordinate system into three-phase voltage command values Vu *, Vv *, Vw * based on the rotational position information θ + θe. is there. The rotational position information θ + θe is information representing a value obtained by adding the position sensor error θe to the actual position of the three-phase motor 90.

  As a result, the current controller 11 handles the voltage command values Vu *, Vv *, and Vw * that are sinusoidal voltages in the three-phase stationary coordinate system as DC voltages in the dq coordinate system that is an orthogonal biaxial rotational coordinate system. it can.

  The current controller 11 uses a voltage command value as a command value for reducing the deviations δId * and δIq * between the target values Id * and Iq * as current command values and the current values Id and Iq as feedback amounts. Vd * and Vq are generated. In the present embodiment, the feedback values Iu, Iv, and Iw of the phase currents are values obtained by adding the current offset correction value Ci and the voltage offset correction value Cv to the current detection values Iu1, Iv1, and Iw1.

  The phase current offset correction unit 16 generates intermediate feedback values Iu2, Iv2, and Iw2 in which the offset is suppressed from each phase of the current detection values Iu1, Iv1, and Iw1. The generation of the intermediate feedback values Iu2, Iv2, Iw2 is performed by individually adding the current offset correction value Ci to the current detection values Iu1, Iv1, Iw1 of each phase.

  The phase current offset correction unit 16 includes a current integrator 21 and an addition / subtraction unit 22. The current integrator 21 calculates an offset value by executing an integration operation for each phase of the intermediate feedback values Iu2, Iv2, and Iw2. For the calculation of the offset value, for example, as disclosed in JP-A-5-252785, the current offset value may be calculated by time-integrating one period of the electrical angle. The calculation may be performed with high accuracy. In the present embodiment, the offset value is generated as a positive or negative sign.

  The addition / subtraction unit 22 adds / subtracts a certain correction amount according to the sign of the offset value to increase / decrease the current offset correction value Ci. As a result, the current offset correction value Ci is manipulated so that the offset of each phase of the intermediate feedback values Iu2, Iv2, and Iw2 converges to zero. When the offset of each phase of the intermediate feedback values Iu2, Iv2, and Iw2 converges to almost zero, the current offset correction value Ci is stabilized at a constant value. Note that the correction amount may be added or subtracted as a value obtained by multiplying a predetermined gain of the offset value instead of a constant value.

  The phase voltage offset correction unit 17 individually adds the voltage offset correction value Cv to each phase value of the intermediate feedback values Iu2, Iv2, and Iw2, thereby generating the feedback values Iu, Iv, and Iw of the respective phase currents. To do. The voltage offset correction value Cv is a correction value for suppressing the offset of the voltage command values Vu *, Vv *, Vw *.

  The phase voltage offset correction unit 17 includes a voltage integrator 24 and an addition / subtraction unit 23. The voltage integrator 24 calculates the voltage offset value by executing an integration operation of each phase of the voltage command values Vu *, Vv *, and Vw *. The offset value is calculated by the same method as that for the current integrator 21. The adder / subtractor 23 adds or subtracts a certain correction amount according to the sign of the offset value to increase or decrease the voltage offset correction value Cv.

  Thus, since the current controller 11 performs feedback control using the feedback values Iu, Iv, and Iw of each phase current including the voltage offset correction value Cv output from the phase voltage offset correction unit 17, As a result, control is performed to suppress the offset of the voltage command values Vu *, Vv *, Vw *. On the other hand, the phase current offset correction unit 16 functions to operate the current offset correction value Ci to converge the offset of each phase of the intermediate feedback values Iu2, Iv2, and Iw2 to zero.

  FIG. 2 is a flowchart showing an offset correction routine of the power control apparatus 10. FIG. 3 is a time chart showing the processing state of offset correction. The chart G1 shows the temporal change of the current offset correction value Ci. Chart G2 shows temporal changes in the phase voltage command value offset calculation value Cvc. The chart G3 shows temporal changes in the phase current detection value offset calculation value Cic that is the offset value of each phase of the intermediate feedback values Iu2, Iv2, and Iw2. In this time chart, in the power control device 10, the phase voltage offset correction unit 17 starts phase voltage offset correction at time A, and the phase current offset correction unit 16 starts phase current offset correction at time B.

  In step S11, the phase voltage offset corrector 27 (see FIG. 1) starts calculating the phase voltage command value offset calculated value Cvc at time A as shown in the chart G2. The phase voltage command value offset calculation value Cvc is an offset value of each phase of the voltage command values Vu *, Vv *, and Vw *. At the start of calculation of the phase voltage command value offset calculation value Cvc, the voltage command values Vu *, Vv *, and Vw * are not centered at zero and an offset occurs in each phase. Therefore, the phase voltage command value offset calculation value Cvc is a positive or negative value.

  In step S12, the phase voltage offset correction unit 17 performs an offset value correction process for the phase voltage command value. As described above, the offset value correction process is performed by increasing or decreasing the voltage offset correction value Cv of each phase in accordance with the sign of the phase voltage command value offset calculation value Cvc.

  As a result, the phase voltage command value offset calculation value Cvc converges to almost zero at time Tx1, and the voltage offset correction value Cv is also stabilized at a substantially constant value. On the other hand, the phase current detection value offset calculation value Cic fluctuates until time Tx1 due to the influence of the offset value correction processing of the phase voltage command value by the phase voltage offset correction unit 17.

  In step S13, power control device 10 determines whether or not phase voltage command value offset calculation value Cvc is smaller than a predetermined value as a preset threshold value. If it is determined that phase voltage command value offset calculation value Cvc is greater than or equal to a predetermined value, the process returns to step S11. On the other hand, if it is determined that phase voltage command value offset calculation value Cvc is smaller than the predetermined value, the process proceeds to step S14. Thus, the process proceeds to step S14 only when the phase voltage command value offset calculated value Cvc is smaller than a predetermined value as a preset threshold value. In this example, at time B, the process proceeds to step S14.

  In step S14, the phase current offset corrector 26 (see FIG. 1) starts calculating the phase current detection value offset calculation value Cic at time B. The calculation of the phase current detection value offset calculation value Cic is performed by the same method as the calculation of the phase voltage command value offset calculation value Cvc. In step S15, the phase current offset correction unit 16 performs an offset value correction process for the phase current detection value. This offset value correction process is performed by adding the current offset correction value Ci generated by the phase current offset corrector 26 to the current detection values Iu1, Iv1, and Iw1. The generation of the current offset correction value Ci is performed by the same method as the generation of the voltage offset correction value Cv using the phase current detection value offset calculation value Cic.

  Thereby, the phase current detection value offset calculation value Cic starts to change at time B. On the other hand, the voltage offset correction value Cv slightly varies under the influence of the operation of the current offset correction value Ci. This is because an offset is generated in the voltage command values Vu *, Vv *, and Vw * by operating the current offset correction value Ci.

  Since the phase voltage offset correction unit 17 continues to operate even after the phase current offset correction unit 16 starts operating, the phase voltage command value offset calculation value Cvc converges to almost zero, and the voltage offset correction value Cv is also substantially constant. It becomes stable at the value of. On the other hand, the phase current detection value offset calculation value Cic converges slowly after the phase voltage command value offset calculation value Cvc converges. At this time, the current offset correction value Ci converges toward the target value Ic as shown in the chart G3.

  The target value Ic is a value having the same magnitude as the current sensor error Ie but having a different sign. Since the target value Ic is a value when the current sensor error Ie (see FIG. 1) is canceled, the target value Ic results in a current value having the same magnitude with a sign different from the current sensor error Ie as an offset error.

  In step S16, power control device 10 determines whether or not phase current detection value offset calculation value Cic is smaller than a predetermined value as a preset threshold value. If it is determined that the phase current detection value offset calculation value Cic is greater than or equal to the predetermined value, the process returns to step S11. On the other hand, if it is determined that the phase current detection value offset calculation value Cic is smaller than the predetermined value, the process is terminated.

  Thus, according to the offset correction routine of the power control apparatus 10 of the first embodiment, it is confirmed that the phase voltage command value offset calculation value Cvc is smaller than a predetermined value as a preset threshold value. (Step S13), the phase current detection value offset calculation value Cic can be corrected so as to be smaller than a predetermined value.

  In the flowchart of FIG. 2, the calculation of the phase current detection value offset calculation value Cic is started at time B, but in the chart G3, the calculation of the phase current detection value offset calculation value Cic is performed at the time for ease of understanding. It starts with A.

  In the prior art, a method of correcting an offset error of one of the phase current detection value and the phase voltage command value has been proposed (Patent Documents 1 to 6). Since this correction method assumes only the offset error of the current sensor 15, if one of the offset errors is corrected, both offset errors are eliminated and the detection error of the phase current detection value can be learned. It was based on that.

  However, the present inventor has found that such a premise is not necessarily established. Specifically, for example, even if the offset of the phase current detection value has been eliminated, the offset remains in the phase voltage command value, and it is found that the phase current offset correction unit 16 may learn incorrectly. It was. As a specific example, the inventor has clarified a mechanism of occurrence of erroneous learning that occurs when a combined error between the position sensor 19 and the current sensor 15 occurs.

  In this mechanism, a position sensor error θe (see FIG. 1), which is a detection error of the position sensor 19, causes an error including an offset error in the dq converter 18 and the inverse dq converter 12 to be generated in the phase voltage command value. The inventor has clarified this as a new finding. According to this mechanism, the offset error caused by the detection error of the position sensor 19 is mistakenly recognized as the offset error of the phase current detection value and learned.

The inventor of the present invention has newly created a method for solving such a problem of erroneous learning extremely easily by the following two-step process.
(1) In the first step, correction is performed so that the phase voltage offset that is the source of the current actually flows in the three-phase motor 90 is zero so that no offset occurs.
(2) In the second step, after confirming that there is no offset in the current that actually flows through the three-phase motor 90, the offset value generated by the current sensor 15 is obtained and corrected using that value. To do.

  In this method, since it is possible to obtain the offset value generated in the current sensor 15 after ensuring that no offset is generated in the current that actually flows through the three-phase motor 90, it is possible to prevent mixing of errors from other sensors. The current sensor error Ie as the offset error of the current sensor 15 can be acquired with certainty. Eventually, the phase voltage offset corrector 27 suppresses the offset error caused by the detection error of the position sensor 19 by operating the voltage offset correction value Cv, and the phase current offset corrector 26 corrects the current offset correction value Ci. The offset error of the current sensor 15 is suppressed by the operation.

  As described above, the power control apparatus 10 according to the first embodiment can eliminate the offset error due to the detection error of the position sensor 19 and can accurately learn the offset error of the current sensor 15 to realize the offset correction. it can.

(Second Embodiment)
FIG. 4 is a flowchart showing an offset correction routine in the second embodiment. In step S21, the phase voltage offset corrector 27 (see FIG. 1) calculates an offset value of the phase voltage command value. In step S22, the phase voltage offset correction unit 17 performs an offset value correction process for the phase voltage command value. In step S23, the phase current offset corrector 26 calculates an offset value of the phase current detection value. In step S <b> 24, the phase current offset correction unit 16 executes an offset value correction process for the phase current detection value.

  Thus, in the second embodiment, the offset value correction process for the phase voltage command value and the phase current detection are performed without determining whether or not the voltage offset correction value Cv is smaller than a predetermined value as a preset threshold value. The value offset value correction processing is executed in parallel. However, in the second embodiment, the phase voltage command value offset value correction process (step S22) is configured to have a smaller time constant than the phase current detection value offset value correction process (step S24). Therefore, the offset value correction process for the phase voltage command value converges in preference to the offset value correction process for the phase current detection value.

  FIG. 5 is a time chart showing the processing state of offset correction. The chart G1a shows the temporal change of the current offset correction value Ci. Chart G2a shows temporal changes in the phase voltage command value offset calculation value Cvc. The chart G3a shows temporal changes in the phase current detection value offset calculation value Cic. In the second embodiment, both the phase voltage offset correction and the phase current offset correction are started at time A.

  The current offset correction value Ci temporarily swings immediately after the time A to the side opposite to the target value Ica. This fluctuation is an erroneous correction due to the offset of the phase voltage command value. However, the phase voltage command value offset value correction process has a smaller time constant than the phase current detection value offset value correction process, so it converges rapidly and the phase current detection value has a large time constant. It can be seen that the current offset correction value Ci gradually approaches the target value Ica by the offset value correction process. Specifically, the offset correction process for the phase voltage command value has substantially converged at time Tx2, as can be seen from the chart G2a, whereas the offset value correction process for the phase current detection value is performed from the chart G3. As can be seen, the correction value converges to the target value Ica relatively slowly.

  In step S25, it is determined whether or not the phase voltage command value offset calculation value Cvc is smaller than a predetermined value as a preset threshold value. If it is determined that phase voltage command value offset calculation value Cvc is equal to or greater than a predetermined value, the process returns to step S21. On the other hand, if it is determined that phase voltage command value offset calculation value Cvc is smaller than the predetermined value, the process proceeds to step S26. Thus, the process proceeds to step S26 only when the phase current detection value offset calculation value Cic becomes smaller than a predetermined value as a preset threshold value.

  In step S26, it is determined whether or not the current offset correction value Ci has become smaller than a predetermined value as a preset threshold value. If it is determined that the current offset correction value Ci is equal to or greater than the predetermined value, the process returns to step S21. On the other hand, when it is determined that the current offset correction value Ci is smaller than the predetermined value, the learning is completed and the process ends.

  As described above, the offset correction process routine of the second embodiment is configured such that the offset value correction process for the phase voltage command value converges in preference to the offset value correction process for the phase current detection value by setting the time constant. Therefore, the offset error of the phase voltage command value caused by the detection error of the position sensor 19 can be eliminated. Thereby, since the offset error of the current sensor 15 can be accurately learned, an accurate and highly reliable offset correction can be realized. The time constant has a broad meaning and does not assume only the time constant as a value of the first-order lag system, but includes what is widely defined as the length of the transient response state.

(Third embodiment)
FIG. 6 to FIG. 8 are graphs showing a method of integrating for each of a plurality of periods of electrical angles in order to calculate the offset value of the phase voltage command value in the third embodiment. According to this method, the number of integrations can be increased in a pseudo manner by increasing the number of integrations in a pseudo manner. 6 to 8, sampling of the phase voltage command value of the six-pole pair three-phase motor 90 is performed at a constant time cycle (200 μsec).

  FIG. 6 is a graph showing the sampling state of the phase voltage command value during high-speed rotation. During high-speed rotation, for example, at 8000 rpm, the number of samplings in each electrical angle cycle is as small as 6 or 7. As a result, the inventor has found that the integration error becomes excessively large. The electrical angle cycle is 360 ° electrical angle.

  FIG. 7 is a graph showing the deviation of the sampling position of the phase voltage command value during high-speed rotation. In the first cycle (0 ° to 360 °) of the electrical angle, sampling is performed at seven sampling positions S1 to S7 in the first cycle. In the second period (360 ° to 720 °) of the electrical angle, sampling is performed at six sampling positions S8 and the like in the second period. The deviation of the sampling position means a deviation of the sampling position in each cycle of the electrical angle. Specifically, for example, it means that the sampling position S8 does not coincide with any of the sampling positions S1 to S7.

  FIG. 8 is a graph showing a method for artificially increasing the number of integrations using a sampling position shift. In the example of FIG. 6, the first period (0 ° to 360 °), the second period (360 ° to 720 °), the third period (720 ° to 1080 °), and the fourth period (1080 ° to 1440 °). An example in which the sampling at is superimposed on the first period (0 ° to 360 °) as one period is shown in the enlarged window W. As can be seen from the sampling state of the enlarged window W, the number of sampling positions has increased to 26.

As described above, in the second embodiment, the sampling position of the phase voltage command value at the time of high-speed rotation is reduced by superimposing the sampling positions of a plurality of periods by superimposing the sampling positions in a plurality of periods. The increase of integration error is suppressed. This method is based on the premise that the fluctuation of the rotation speed of each cycle to be superimposed is small, but at the time of high-speed rotation, the ratio of the fluctuation of the rotation speed in a continuous cycle is small, so this method is extremely practical. . Note that the present method can also be applied to sampling of the current detection value.

(Fourth embodiment)
FIG. 9 is a graph showing a method of integrating at the motor position in order to calculate the offset value of the phase voltage command value in the fourth embodiment. According to this method, it is possible to suppress the occurrence of an integration error due to the fluctuation of the rotational speed. Since the calculation of the offset value is based on the premise that the phase voltage command value is a sine wave, the fact that the integral value of each period becomes zero is used.

  The integration error due to the fluctuation of the rotational speed occurs due to the calculation method using time integration. Graphs T1, T2, and T3 show the rotational speed (deg / sec), the phase voltage command value (V), and the integral value (V · sec) when rotating at a constant rotational speed, respectively. . The graph T1 indicates that the three-phase motor 90 is rotating at a constant rotation speed (deg / sec). The graph T2 indicates that a sine wave phase voltage command value is output according to the rotation of the three-phase motor 90. The reason why the sine wave shape of the phase voltage command value is maintained with respect to the time axis is that the three-phase motor 90 is rotating at a constant rotational speed (deg / sec).

  The graph T3 shows that the integrated value of the phase voltage command value increases from time 0 to time t when the phase voltage command value has a positive value, and the phase voltage command value has a negative value from time t to time 2t. It shows how the integral value of the voltage command value decreases and the closing price is zero. The closing price of zero means that the area of the positive region of the sine wave is equal to the area of the negative region in the graph T2. The rotation angle of the three-phase motor 90 is 180 ° at time t and 360 ° at time 2t within this period.

  Thus, when the three-phase motor 90 is rotating at a constant rotational speed, the shape of the sine wave of the voltage command value is maintained, so that by time integration of the phase voltage command value having a sine wave waveform An offset value can be calculated.

  However, it can be seen that if the rotational speed of the three-phase motor 90 fluctuates as can be seen from the graphs T1a, T2a, and T3a, the waveform of the sine wave collapses, and it is difficult to calculate an accurate offset value. The graph T1a shows how the rotational speed of the three-phase motor 90 varies within the cycle. Specifically, the rotational speed of the three-phase motor 90 is half of the speed from time 0 to time t from time t to time 3t. Accordingly, the rotation angle of the three-phase motor 90 is the same as that of the graph T1 in that the rotation angle is 180 ° at the time t in this cycle, but at the time 2t and 3t, the rotation angle is 270 ° and 360 °, respectively. Yes.

  A graph T2a shows a state in which the shape of the sine wave of the phase voltage command value is broken. The sine wave of the phase voltage command value is in a state in which the area of the negative region of the sine wave is enlarged on the time axis due to the speed reduction from time t (180 °) to time 3t (360 °). As a result, as shown in the graph T3a, the final value of the integral value of the phase voltage command value is negative even though the phase voltage command value has no offset.

  The three graphs R1, R2, and R3 show the rotation speed (deg / sec) and the phase voltage command value when the integration based on the rotation angle is used instead of the time integration in calculating the integral value of one electrical angle cycle. (V) and an integral value (V · sec) are shown. The graph R1 shows how the rotational speed of the three-phase motor 90 varies within a cycle. The graph T2 indicates that a sine wave phase voltage command value is output according to the rotation of the three-phase motor 90. The reason why the shape of the sine wave of the phase voltage command value is maintained with respect to the horizontal axis is that the horizontal axis is not affected by the speed fluctuation because it is the rotation angle. As a result, as shown in the graph R3, the final value of the integrated value of the phase voltage command value is zero even though the rotational speed of the three-phase motor 90 varies within the cycle.

As described above, the offset value calculation method of the fourth embodiment can accurately calculate the offset value regardless of fluctuations in the rotational speed of the three-phase motor 90. This method has a remarkable effect at the time of low-speed rotation in which an offset value calculation error due to fluctuations in the rotation speed of the three-phase motor 90 is likely to occur.

The offset value calculation method of the third embodiment and the fourth embodiment may be switched according to the rotation speed at the time of learning. Furthermore, the offset value calculation method according to the fourth embodiment adjusts the sampling position and performs sampling at a position where a deviation occurs in each cycle (for example, every angle that is not divisible by 360 °). A combination with the method of the third embodiment is also possible. Thereby, for example, it is possible to cope with a case where it is necessary to reduce the sampling frequency due to a problem of processing time during high-speed rotation. Note that the present method can also be applied to sampling of the current detection value.

(Other embodiments)
The embodiment is not limited to the above contents, and may be implemented as follows, for example.

  (1) In each of the embodiments described above, the phase voltage offset correction unit 17 uses the voltage offset correction value Cv of the voltage command value of the three-phase stationary coordinate system as the feedback value Iu, Iv of each phase current of the three-phase stationary coordinate system. , Iw is included in phase voltage offset correction. However, the present invention is not limited to such a configuration. For example, the voltage offset correction value Cv of the voltage command value of the three-phase stationary coordinate system is converted by the dq converter 28 like the phase voltage offset correction unit 17a of the first modified example of FIG. It may be converted and included in the feedback amount in the dq coordinate system which is the orthogonal biaxial rotational coordinate system which is the rotational coordinate system.

  (2) In each of the above-described embodiments, the sign is determined using the time integral value of the phase voltage command value offset calculation value Cvc and the phase current detection value offset calculation value Cic. However, for example, if the timing at the time of zero crossing is detected, the positive side time and the negative side time of the sine wave can be detected. Therefore, based on the comparison, it is determined which side is positive or negative. You can also.

  (3) In each of the above-described embodiments, the phase current offset correction unit 16 operates the current offset correction value Ci by integrating the values of the intermediate feedback values Iu2, Iv2, and Iw2 after the offset correction. However, the present invention is not limited to this method. For example, a current offset correction value corresponding to the current sensor error Ie is directly generated and corrected from the integrated value of the current detection values Iu1, Iv1, and Iw1 before the offset correction. You may do it.

  (4) In each of the embodiments described above, the phase voltage offset correction unit 17 adds or subtracts a fixed correction amount by the addition / subtraction unit 23 according to the sign of the phase voltage command value offset calculation value Cvc, thereby obtaining the voltage offset correction value Cv. It is operating. However, the present invention is not limited to such a configuration. For example, a current correction amount corresponding to the phase voltage offset value is obtained by dividing the phase voltage integrated value by the motor resistance value as in the phase voltage offset correction unit 17b of the second modification of FIG. And the voltage offset correction value Cv may be manipulated by adding and subtracting the calculated value.

  In this way, the convergence time of the phase voltage offset correction can be shortened, so that a control system having a small time constant can be easily configured for the phase current offset correction. In addition, it is good also as a structure which combined the 1st modification and the 2nd modification like the 3rd modification of FIG.

  DESCRIPTION OF SYMBOLS 10 ... Power control apparatus, 11 ... Current controller, 12 ... Inverse dq converter, 13 ... Power amplifier, 15 ... Current sensor, 16 ... Phase current offset correction part, 17, 17a, 17b ... Phase voltage offset correction part, 18 ... dq converter, 19 ... position sensor, 21 ... current integrator, 22 ... adder / subtractor, 23 ... adder / subtractor, 24 ... voltage integrator, 28 ... dq converter, 90 ... three-phase motor.

Claims (10)

An AC motor control device that controls by applying a polyphase AC voltage to a multiphase AC motor,
A current sensor that detects a current of each phase supplied to the multiphase AC motor and outputs a current detection value of each phase;
A control unit that generates a voltage command value for each phase for causing the current of each phase to follow the current command value according to the given current command value and the current detection value of each phase;
A power amplifying unit that applies a voltage of each phase to the multiphase AC motor in accordance with a voltage command value of each phase;
A phase voltage for determining a voltage offset value representing a voltage offset of a voltage command value for each phase, and operating the current detection value for each phase according to the voltage offset value for each phase to reduce the voltage offset value An offset correction unit;
A phase current offset correction that determines a current offset value representing a current offset of a current detection value of each phase and corrects the current detection value of each phase according to the current offset value of each phase to reduce the current offset And
With
The AC motor control device operates the phase voltage offset correction unit with priority over the operation of the phase current offset correction unit.   The preferential operation is realized by operating the phase voltage offset correction unit and starting the operation of the phase current offset correction unit after the voltage offset value becomes smaller than a preset value. The AC motor control device according to claim 1.   3. The AC motor control according to claim 1, wherein the preferential operation is realized by setting a time constant of the phase voltage offset correction unit to be smaller than a time constant of the phase current offset correction unit. apparatus.   The phase voltage offset correction unit operates the current detection value of each phase by adding a voltage offset correction value generated according to the voltage offset value of each phase to the current detection value of each phase. 4. The AC motor control device according to any one of 1 to 3. The AC motor control device further includes a coordinate conversion unit that converts the coordinate system from a stationary coordinate system to a rotating coordinate system,
The current sensor outputs a current detection value of each phase as a value in the stationary coordinate system,
The control unit generates a voltage command value of each phase according to the current detection value of each phase converted by the coordinate conversion unit in the rotating coordinate system,
5. The AC motor control device according to claim 1, wherein the phase voltage offset correction unit operates a current detection value of each phase converted into a value in the rotating coordinate system by the coordinate conversion unit. 6. .   6. The AC motor control according to claim 1, wherein the phase voltage offset correction unit determines the voltage offset value by integrating the voltage command value of each phase at an integer multiple of an electrical angle. apparatus.   The AC motor control according to any one of claims 1 to 6, wherein the phase current offset correction unit determines the current offset value by integrating the detected current value of each phase with an integer multiple of an electrical angle. apparatus.   The phase voltage offset correction unit calculates a current correction amount corresponding to the voltage offset value by dividing the voltage offset value by a motor resistance value, and operates the current detection value using the current correction amount. Item 8. The AC motor control device according to any one of Items 1 to 7. The AC motor control device further includes a position sensor that detects a rotational position of the AC motor and outputs rotational position information.
The phase voltage offset correction unit has a voltage integrator that integrates the voltage command value,
9. The AC motor control device according to claim 1, wherein the voltage integrator integrates the voltage command value by multiplying a position change amount during a calculation cycle of the rotational position information by the voltage command value. The AC motor control device further includes a position sensor that detects a rotational position of the AC motor and outputs rotational position information.
The phase current offset correction unit includes a current integrator that integrates the current detection value,
10. The AC motor control device according to claim 1, wherein the current integrator multiplies the current detection value by a position change amount during a calculation cycle of the rotational position information and integrates the current detection value.

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