JP2006074951A - Controller for ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an offset of a current by reducing a deviation of a voltage SW timing caused by a detection error of a position detector in a controller for an AC motor driving with a rectangular wave voltage. <P>SOLUTION: This controller for the AC motor calculates an amount of phase correction corresponding to an offset of the current detected in a current sensor, calculates electrical angular speed by using an electrical angle θ detected in the position detector 6, converts a reference phase difference from the start to the last of a voltage SW pattern to a reference phase difference time t' by dividing it by the electrical angular speed ω, converts the value adding the amount of phase correction by the offset of the current to a phase error (θsw*-θnext) between an electrical angle target θsw* for switching the voltage SW pattern at the next control calculation and an estimated electrical angle at the next control calculation to a phase error time Δt by dividing it by the electrical angular speed ω, corrects the reference phase difference time by the phase error time, and set a carrier period according to the corrected value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an AC motor, and more particularly to a control device that controls an inverter with a rectangular wave voltage drive.

As a conventional control device for an AC motor, there is one described in Patent Document 1 below.
As a method for controlling the inverter that supplies current to the motor by such an AC motor control method, the PWM voltage drive method includes a rectangular wave voltage drive method that is used in an operation region where the output voltage is limited. In the rectangular wave voltage driving method described in Patent Document 1, a timer counter that operates with a clock at a fixed interval is used, and a voltage switching pattern (hereinafter abbreviated as a voltage SW pattern) is switched every time the count value reaches a target value. Is output. The phase difference target value from the start to the end of the voltage SW pattern is obtained as an ideal reference phase difference from the start to the end of one section of the voltage SW pattern, and the reference phase difference is determined by the phase error based on the deviation between the target torque and the estimated torque. It is obtained by correcting. The counter target value is determined according to a value obtained by time-converting the phase difference target value, and a position detector for obtaining the electrical angle θ is unnecessary.

JP 2002-359996 A

As described above, in the conventional example, the phase difference target value is calculated by correcting the phase difference reference value with the phase error based on the torque deviation. When performing control such that the phase difference target value is determined based on the detection amount of the detector, the voltage SW timing may be shifted due to the detection error of the position detector, and the current may be offset. was there.
The present invention has been made to solve the above-described problem, and in the rectangular wave voltage drive control, an AC motor in which a deviation in voltage SW timing caused by a detection error of a position detector is reduced and a current offset is suppressed. An object of the present invention is to provide a control device.

In order to achieve the above object, in the present invention, the offset of the current detected by the current detecting means is detected, the phase correction amount corresponding to the current offset is calculated, and the electrical angle θ detected by the position detector is calculated. Is used to calculate the electrical angular velocity ω, and the reference phase difference from the start to the end of one voltage SW pattern is divided by the electrical angular velocity ω to convert it into the reference phase difference time t ′, and the voltage at the next control calculation A value obtained by correcting the phase error (θsw ^* −θnext) between the SW angle switching electrical angle target value θsw ^* and the predicted electrical angle θnext at the next control calculation by the above phase correction amount is divided by the electrical angular velocity ω. Is converted into a phase error time Δt, the reference phase difference time is corrected with this phase error time, and the carrier period is set according to the corrected value.

By correcting the phase error between the electrical angle target value θsw ^* and the predicted electrical angle value θnext at the next control calculation by the phase correction amount corresponding to the current offset, the deviation of the voltage SW pattern switching timing due to the position detector error is corrected. This can reduce the current offset and suppress the current offset.

FIG. 1 is a block diagram of an embodiment showing a configuration of an AC motor control apparatus to which the present invention is applied.
In FIG. 1, the voltage phase generating means 1 outputs a voltage phase target value α ^* obtained by referring to a table using an externally input torque command value T ^* and the current rotational speed ω as indices. Specifically, for example, in the evaluation test of the electric motor to be controlled, the value of the voltage phase target value α ^* with respect to the torque command value T ^* and the rotational speed ω is obtained as table data. The value of the voltage phase target value α ^* corresponding to the torque command value T ^* and the rotation speed ω can be obtained by referring to the table.

  The control unit 2 includes a rectangular wave control unit 2-1 and a PWM control unit 2-2. Since the present invention relates to rectangular wave voltage driving, the rectangular wave control means 2-1 will be mainly described below, and only necessary portions of the PWM control means 2-2 will be described.

The rectangular wave control means 2-1 determines the voltage phase target value α ^* output from the voltage phase generation means 1, the electrical angle θ of the electric motor 5 detected by the position detector 6 (for example, a resolver), and the electrical angle θ. The electric angular velocity ω (rotational speed) obtained by the velocity calculating means 7 as an input is input, and the drive signal P of the on / off signal is calculated and output (details will be described later). The inverter 3 is controlled by this drive signal P, and three-phase rectangular wave voltages Vu, Vv, Vw having an amplitude of the power supply voltage Vdc or 0 (or + Vdc / 2 or −Vdc / 2) are output from the inverter 3, thereby The three-phase motor 5 is driven.

The voltage phase generation means 1 and the control means 2 are constituted by a computer or the like, and calculate the drive signal P by repeatedly performing calculations at a predetermined cycle.
The drive signal P is an on / off signal, and the output of the inverter 3 is output in synchronization with the drive signal P. That is, the timing at which the drive signal P is switched on / off is the timing at which the rectangular wave voltage is switched as it is (strictly speaking, on and off may be reversed). In the rectangular wave voltage drive, the applied voltage amplitude is the power supply voltage Vdc or 0 (+ Vdc / 2 or −Vdc / 2) and the amplitude cannot be controlled, so that the voltage phase follows the voltage phase target value α ^*. By controlling, the torque control of the electric motor 5 is performed so as to realize the given torque command value T ^* . That is, since there is a correlation between the torque and the voltage phase, the torque can be controlled by controlling the voltage phase. This voltage phase is controlled by switching a voltage SW pattern described later.

  Note that the PWM control means 2-2 in the control means 2 performs a general torque control calculation using the detected currents Iu and Iv detected by the current sensor 4 in the region where the PWM voltage drive is performed, and the inverter 3 outputs the PWM signal. The torque is controlled by changing the voltage value applied to each phase of the electric motor 5. The general torque control calculation in the above-described PWM control is, for example, calculating a d-axis current command value and a q-axis current command value based on the input torque command value and the rotation angle of the electric motor 5, and d-axis current command The proportional-integral calculation is performed based on the deviation between the value and the actual d-axis current value to calculate the d-axis voltage command value, and the q-axis is similarly calculated based on the deviation between the q-axis current command value and the actual q-axis current value. Calculate the voltage command value. The actual d-axis current value and q-axis current value are obtained by performing three-phase to two-phase conversion from the detected currents Iu and Iv (Iw can be calculated from Iu and Iv). Then, the d-axis voltage command value and the q-axis voltage command value are two-phase / three-phase converted to calculate a three-phase voltage command value. The drive signal P is obtained by calculating the duty command value of the PWM signal from the three-phase voltage command value and comparing the duty command value with a predetermined carrier signal (such as a triangular wave or a sawtooth wave).

  When the rectangular wave voltage drive used in the present invention is performed, the rectangular wave (Vdc or 0) is set by setting the duty ratio of the duty command value to be compared with the carrier signal to 0 [%] or 100 [%]. Drive signal P can be generated. In general, the rectangular wave voltage drive is used in a field weakening region where a high voltage is required, and PWM control is used in other regions.

In addition, in order to control the voltage phase to follow the voltage phase target value α ^* in the rectangular wave control means 2-1, the voltage SW pattern (detailed later) is determined at a timing determined according to the voltage phase target value α ^*. Do by switching.
The setting of the voltage SW pattern and the carrier cycle is effective at the trough of the triangular wave or sawtooth wave of the carrier signal, and at the same time, an interrupt for starting the control calculation is generated. The timing at which the rectangular wave pattern (voltage SW pattern) is switched is adjusted by changing the carrier cycle so that the voltage SW pattern switching timing is appropriate. In other words, the voltage phase is set to voltage by controlling the period of the carrier signal (for example, triangular wave) for creating the rectangular wave so that the switching point of the voltage SW pattern coincides with the valley of the carrier signal (at the start of the interrupt calculation). Control is performed to follow the phase target value α ^* .

The detected currents Iu and Iv of the current sensor 4 are input to the current offset detector 8, and the current offset detector 8 outputs offset amounts Iu0, Iv0, and Iw0 of each phase current. Note that Iw is calculated from Iw = −Iu−Iv.
The PI controllers 9 to 11 receive the offsets Iu0, Iv0, and Iw0 and amplify them with PI (proportional and integral) gains to obtain phase correction amounts Δθu0, Δθv0, and Δθw0, which are rectangular. Send to wave generator 2.
In the rectangular wave generator 2, the rectangular wave control means 2-1 calculates the voltage SW pattern switching electrical angle based on the phase correction amounts Δθu0, Δθv0, Δθw0 in the calculation of the voltage SW pattern switching electrical angle. Correct (details will be described later).

(Example)
Hereinafter, the carrier period setting method in the embodiment will be described in detail.
FIG. 2 is a signal waveform diagram showing a carrier period setting method.
In FIG. 2, the control calculation is interrupted and the voltage SW pattern is switched at the valleys (time points t ₀ and t ₁ ) of the carrier signal (triangular wave). The voltage SW pattern is a voltage pattern applied to each of the three phases U, V, and W, that is, a pattern of which one of the three phases is set to “1”, that is, Vdc, and which is set to “0”. ₀ in ~t ₁ is in a "Vu = 1 (Vdc), Vv = 0, Vw = 0 ".

In the control calculation 1 performed at the time point t ₀ , the carrier cycle Tnext of one section of the next voltage SW pattern is used as follows using the electrical angle θ and the electrical angular velocity ω at the start of the control calculation 1 and the current carrier cycle Tow. To calculate.

First, as shown in Equation 1, time t ′ (reference phase difference time) is obtained by dividing the reference phase difference π / 3 [rad] from the start to the end of one voltage SW pattern by the electrical angular velocity ω. ).
t ′ = π / 3ω (Equation 1)
Next, as shown in the equation (2), an electrical angle predicted value θnext at the time of switching the next voltage SW pattern is calculated.
θnext = θ + ωTnow (Equation 2)
The current carrier cycle Tow corresponds to the next carrier cycle Tnext calculated in the previous carrier cycle setting.

The electrical angle target value of the next voltage SW pattern switching .theta.sw ^*, based on FIG. 3 showing the electrical angle theta, the voltage phase target value alpha ^*, the relationship between the SW pattern of voltage to be input to the motor, θsw0 ^* ~ The electrical angle closest to θnext is selected from θsw5 ^* , and the voltage SW pattern output after the next voltage SW pattern switching is determined from the current rotation direction. For example, in FIG. 3, if θnext is the closest value to (2π / 3) −α ^* , θsw2 ^* is selected as the electrical angle target value θsw ^* for the next voltage SW pattern switching, and the next voltage SW The pattern is “Vu = −Vdc / 2, Vv = −Vdc / 2, Vw = + Vdc / 2”.

  In FIG. 3, each voltage SW pattern is a binary rectangular wave of + Vdc / 2 and −Vdc / 2 with 0 as the center. This is because, when the three-phase winding of the motor is Y-connected, any two of the three phases U, V, and W are connected in series between the power supply voltage Vdc terminal and the ground terminal. If the neutral point is set to 0, + Vdc / 2 is applied to the phase connected to the Vdc terminal side, and -Vdc / 2 is applied to the phase connected to the ground terminal side. It is because it can be displayed. Therefore, as shown in FIG. 2, + Vdc / 2 may be represented by “1” (Vdc) and −Vdc / 2 may be represented by “0”.

As described above, the electrical angle target value of the next voltage SW pattern switching θsw ^*, θsw0 ^* ~θsw5 ^* calculated by selecting those electrical angle prediction value θnext is closest to the phase error a difference θnext and .theta.sw ^* And the phase error (θsw ^* −θnext) corrected by the above-described phase correction amounts Δθu0, Δθv0, Δθw0 is divided by the electrical angular velocity ω to be converted into a phase error time Δt. At that time, as shown in the following formulas (3) to (8), depending on which of the electrical angle target values θsw ^* is close to θsw0 ^{* to} θsw5 ^* , the phase correction amounts Δθu0, Δθv0, Correction is performed at any one of Δθw0.

When θsw ^* is θsw0 ^* Δt = (θsw ^* −θnext + Δθiu) / ω (Equation 3)
When θsw ^* is θsw1 ^* Δt = (θsw ^* −θnext−Δθiw) / ω (Equation 4)
When θsw ^* is θsw2 ^* Δt = (θsw ^* −θnext + Δθiv) / ω (Equation 5)
When θsw ^* is θsw3 ^* Δt = (θsw ^* −θnext−Δθiu) / ω (Equation 6)
When θsw ^* is θsw4 ^* Δt = (θsw ^* −θnext + Δθiw) / ω (Equation 7)
When θsw ^* is θsw5 ^* Δt = (θsw ^* −θnext−Δθiv) / ω (Equation 8)
However, as shown in FIG.
θsw0 case of A ^*, θsw ^* If the electrical angle θ is the case θsw1 ^* close to 0-α ^* and is of, θsw ^* of the electrical angle θ is (1/3) π-α case θsw2 ^* close to the ^* If a, θsw ^* If the electrical angle θ is the case θsw3 ^* close to (2/3) π-α ^* and is of, in the case θsw ^* of the electrical angle θ is the case θsw4 ^* close to the π-α ^* is When the electrical angle θ of θsw ^* is close to (4/3) π-α ^* , the case of θsw5 ^{* corresponds to} the case where the electrical angle θ of θsw ^* is close to (5/3) π-α ^* , respectively. .

Next, as shown in the following (Expression 9) and (Expression 10), t ′ (Expression 1) obtained by converting the reference phase difference π / 3 into time is corrected by the above Δt. Time t, and this is the next carrier cycle Tnext.
t = t ′ + Δt (Equation 9)
Tnext = t (Equation 10)
Further, the next voltage SW pattern is selected based on FIG. 3 from the electrical angle target value θsw ^* of the next voltage SW pattern switching and the rotation direction.

If the value obtained by correcting the phase error (θsw ^* −θnext) with the phase correction amount corresponding to the current offset as described above is converted into time, and t ′ is corrected by the converted value Δt, the error of the position detector is obtained. It is possible to correct the current offset due to the above and control the next voltage SW pattern switching timing to coincide with the valley of the carrier signal.

Next, detection of current offset in the current offset detection means 8 of FIG. 1 will be described.
FIG. 4 is a block diagram showing the configuration of the current offset detection means 8.
In FIG. 4, reference numerals 8-1, 8-2, and 8-3 are low-pass filters having sufficiently large time constants, and the DC component of each phase current is detected using these low-pass filters. The DC component of each phase current thus obtained corresponds to the offset.

For these low-pass filters, for example, a general first-order lag filter is used. Further, instead of the low-pass filter, a time average value for one electrical angle cycle may be obtained.
In FIG. 4, the case where the W-phase current Iw is obtained from the U-phase current Iu and the V-phase current Iv is illustrated as an example. However, a current sensor is provided for each phase, and a current value is measured for each phase. May be.

Next, the operation will be described.
FIG. 5 is a diagram illustrating an example of an error of the position detector.
As shown in FIG. 5, the detected electrical angle 2 of the position detector indicated by the solid line has a sinusoidal error having substantially the same period as the electrical angular period, with respect to the actual electrical angle 1 indicated by the broken line. . If there is such an error, for example, when the U-phase voltage is switched at an electrical angle of 0 [rad] and π [rad] as shown in the target voltage waveform 3, current offset correction is not performed. Since the ON section is shortened and the OFF section is lengthened as in the actual voltage waveform 4, the U-phase current is offset in the negative direction.

  However, in the calculation of Δt (phase error time), if the U-phase current Iu is corrected as shown in the equations (3) and (6), the U-phase current is offset in the negative direction. As shown in the actual voltage waveform 5, the voltage ON section is lengthened and the OFF section is shortened according to the current offset amount, so that the voltage on section and the off section are not detected due to the detection error of the position detector. The balance is suppressed and the current offset can be reduced. The same applies to the V-phase current and the W-phase current.

The block diagram of one Example which shows the structure of the control apparatus of the alternating current motor to which this invention is applied. FIG. 4 is a signal waveform diagram for explaining a carrier period setting method in the first embodiment. The figure which shows SW pattern of the voltage which should be input into an electric motor. FIG. 3 is a block diagram showing the configuration of current offset detection means 8. The figure which showed an example of the error of a position detector, and the shift | offset | difference of the voltage SW pattern by it.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Voltage phase generation means 2 ... Control means 2-1 ... Rectangular wave control means 2-2 ... PWM control means 3 ... Inverter 4 ... Current sensor 5 ... Electric motor 6 ... Position detector 7 ... Speed calculation means 8 ... Current offset detection Means 8-1, 8-2, 8-3 .. Low pass filter

Claims (3)

In a control device for an AC motor that performs rectangular wave voltage drive that applies the highest value and the lowest value of the power supply voltage to each phase of the motor winding in a predetermined voltage switching pattern,
Voltage phase generation means for outputting a voltage phase target value according to a torque command value given from the outside and the current rotation speed;
A position detector for detecting the electrical angle of the electric motor;
Rectangular wave control means for calculating a drive signal of a rectangular wave for driving the electric motor from the voltage phase target value, the electric angle of the electric motor, and the electric angular velocity of the electric motor;
An inverter that drives the electric motor by applying a rectangular wave voltage corresponding to the rectangular wave driving signal to each phase of the motor winding;
Current detecting means for detecting a current flowing in each phase of the motor winding;
Current offset detection means for detecting an offset of the current detected by the current detection means;
Phase correction amount calculation means for calculating a phase correction amount corresponding to the current offset detected by the current offset detection means,
The rectangular wave control means repeatedly generates an interrupt for starting a control calculation for each valley position of the carrier signal and performs setting of the voltage switching pattern and setting of a carrier period of the carrier signal,
In addition, the electrical angular velocity is calculated from the electrical angle detected by the position detector, and the reference phase difference from the start to the end of one voltage switching pattern is divided by the electrical angular velocity to be converted into a reference phase difference time. The phase error between the target value of the electrical angle for switching the voltage switching pattern at the time of control calculation and the predicted value of the electrical angle at the time of the next control calculation is converted to the phase error time by dividing the value corrected by the phase correction amount by the electrical angular velocity. The control apparatus for an AC motor is configured to correct the reference phase difference time with the phase error time and set a next carrier cycle according to the corrected value.   The phase correction amount calculation means calculates a phase correction amount for each phase of the U-phase current, V-phase current, and W-phase current, and is determined according to the electrical angle target value for voltage switching pattern switching at the next control calculation. 2. The control apparatus for an AC motor according to claim 1, wherein the phase error is corrected by any one of the phase correction amounts.   2. The AC motor according to claim 1, wherein the current offset detection unit includes a low-pass filter that smoothes a current of each phase, and outputs a direct current component of each phase current as a current offset. Control device.

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