JP2006081322A - Ac motor control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an effect by delay in voltage switching timing arising from an detection error by a position transducer in an AC motor control unit that exercises rectangular wave voltage drive. <P>SOLUTION: In this AC motor control unit, electrical angular speed ω is calculated using an electrical angle θ detected by the position transducer 6. By dividing one cycle 2π of the electrical angle by the electrical angular speed ω, it is converted into a reference phase difference time t'. By dividing a phase difference (θsw<SP>*</SP>-θnext) between an electrical angle target value θsw<SP>*</SP>of voltage switching pattern change at the next control operation and an electrical angle expected value θnext at the time of the next control operation by the electrical angular speed ω, it is converted into a phase error time ▵t. The reference phase difference time is corrected by this phase error time. A value obtained by dividing the corrected value into six equal parts is used as each carrier cycle six times in the next one cycle. <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 provides a control device for an AC motor that reduces the effect of voltage SW timing shift caused by a detection error of a position detector in rectangular wave voltage drive control. The purpose is to do.

In order to achieve the above object, in the present invention, the electrical angular velocity ω is calculated using the electrical angle θ detected by the position detector, and one period 2π of the electrical angle is divided by the electrical angular velocity ω to thereby obtain a reference phase difference. Converted to time t ′, the phase error (θsw ^* −θnext) between the electric angle target value θsw ^{* for} switching the voltage SW pattern at the next control calculation and the predicted electric angle θnext at the next control calculation is calculated as the electric angular velocity ω. Is converted into a phase error time Δt, and the reference phase difference time is corrected by this phase error time, and the value obtained by dividing the corrected value into 6 equal parts is each of six carrier periods in the next period. It is constituted so that.

  In order to make the carrier period constant during one electrical angle period 2π, in the steady state, the voltage on time and the off time are equal during one electrical angle period, so the current offset due to the detection error of the position detector Can be suppressed. That is, if the resolver error is included in the electrical angle detected at the time of calculation of the carrier period, the voltage ON time and the OFF time are equal in one electrical angle cycle with a value including the error. Therefore, there is an error, but there is an effect that it is stable because it is always constant, and the influence of the error of the resolver can be reduced.

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 ^* .

Example 1
Hereinafter, the method for setting the carrier period in the first 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 at the valley of the carrier signal (triangular wave), and the voltage SW pattern is switched. 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”. In the Tonow interval, “Vu = 0 (−Vdc / 2), Vv = 0 (−Vdc / 2), Vw = 1 (+ Vdc / 2)”.

  In this calculation, that is, control calculation 1 (black arrow), the carrier cycle Tnext during the next electrical angle cycle 2π is set to the electrical angle θ at the start of the control calculation 1, the electrical angular velocity ω, and the current carrier cycle Tnow Is calculated as follows.

First, as shown in the following (Equation 1), an electrical angle period 2π [rad] is divided by an electrical angular velocity ω to be converted into time t ′ (reference phase difference time).
t ′ = 2π / ω (Equation 1)
Next, as shown in the following (Equation 2), the predicted electrical angle 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, when θnext is the closest value to (π−α ^* ), θsw3 ^* is selected as the electrical angle target value θsw ^* for the next voltage SW pattern switching, and the next voltage SW pattern is 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, + 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 ^* As shown in the following (Equation 3), the phase error (θsw ^* −θnext) is divided by the electrical angular velocity ω to be converted into time Δt (phase error time).
Δt = (θsw ^* −θnext) / ω (Equation 3)
Next, as shown in the following (Expression 4) and (Expression 5), t ′ obtained by the above (Expression 1) is corrected by Δt to obtain a time t, which is divided into 6 equal parts, Each carrier period Tnext in the next electrical angle period, that is, six carrier periods. Note that the above 6 equal divisions is a value obtained by dividing one period 2π by the reference phase difference π / 3 from the start to the end of one voltage SW pattern. That is, in FIG. 2, one period 2π means six carrier periods.
t = t ′ + Δt (Equation 4)
Tnext = t / 6 (Expression 5)
If the phase error (θsw ^* −θnext) is corrected by Δt converted to time as described above, the next voltage SW pattern switching timing can be controlled to coincide with the valley of the carrier signal.

  In the first embodiment, the carrier cycle is updated once every electrical angle cycle 2π, and the same carrier cycle Tnext = t / 6 is used during the electrical angle cycle 2π. In other words, after updating with the control calculation 1, the next update of the carrier cycle is the control calculation 3 after one electrical angle cycle 2π. Therefore, in the control calculation in the meantime, it is only necessary to select the next voltage SW pattern without calculating the carrier period.

  As described above, in the first embodiment, the carrier period is constant for one electrical angle period 2π. Therefore, in the steady state, the voltage on time and the off time are equal in one electrical angle cycle, and thus it is possible to suppress the offset of current due to the detection error of the position detector. In other words, if the resolver error is included in the electrical angle detected at the time of calculation of the carrier cycle (control computation 1), the voltage on time and the off time during one electrical angle cycle with the error included. Are equal. Therefore, although an error is included, it is stable because it is always constant, and the influence of the error of the resolver can be reduced. Further, the error can be corrected by a value such as torque control.

(Example 2)
As described above, in the first embodiment, basically, control is performed so that the carrier period is constant for one electrical angle period 2π. Therefore, when the rotation speed or the voltage SW pattern switching electrical angle target value θsw ^* greatly changes during one electrical angle cycle, the voltage SW pattern switching electrical angle until the next carrier cycle update becomes the target value. It will shift.
In order to cope with the above problem, in the second embodiment, the change in the rotation speed and the voltage SW pattern switching electrical angle target value θsw ^* since the last change of the carrier cycle is monitored. When the carrier cycle is updated, and the change of the rotation speed or the voltage SW pattern switching electrical angle target value θsw ^* exceeds the threshold value in the control calculation 2, the carrier cycle is updated in the control calculation 2 without waiting for the control calculation 3. Configure to do.
That is, the carrier in the next electrical angle cycle 2π is detected at the time of control calculation when it is detected that the change in the rotation speed or the voltage SW pattern switching electrical angle target value θsw ^* exceeds the threshold without waiting for the electrical angle cycle 2π. Calculate and update the period.

  By doing so, it is possible to prevent the voltage SW pattern switching electrical angle from deviating from the target value even in a transient state such as when the rotational speed is suddenly changed. However, in the case of the above configuration, the carrier period is changed during the transient state, so that the effect of the present invention does not occur in that section. As described above, the second embodiment reduces the influence of the resolver error in the steady state.

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. The signal waveform diagram for demonstrating the setting method of the carrier period in an Example. The figure which shows SW pattern of the voltage which should be input into an electric motor.

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

Claims (2)

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; and
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, converted to a reference phase difference time by dividing one cycle 2π of the electrical angle by the electrical angular velocity, and the voltage switching pattern switching at the next control calculation The phase error between the target electrical angle target value and the predicted electrical angle at the next control calculation is divided by the electrical angular velocity to convert it into a phase error time, and the reference phase difference time is corrected by this phase error time. A control apparatus for an AC motor, characterized in that a value obtained by dividing the subsequent value into six equal parts is defined as six carrier periods in the next one period. In the control apparatus for an AC motor according to claim 1,
Changes in the electrical angle target value for switching the rotational speed and the voltage switching pattern since the change of the carrier cycle was monitored, and the change in the electrical angle target value for switching the rotational speed or the voltage switching pattern exceeded a threshold value. When this is detected, the carrier motor is configured to calculate and update the carrier cycle at the time of the detected control calculation.

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