JP2007143351A - Ac electric motor control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve accurate torque control in an AC electric motor control device. <P>SOLUTION: This control device is provided with a speed computation unit 12 that computes rotational speed based on a rotor phase from a rotational angle sensor 14 of a synchronous motor 13, a magnetic-flux estimate unit 10 that computes a magnetic-flux absolute value and a magnetic-flux phase from the rotational speed from the speed computation device 12 and a voltage command to an inverter 5, a coordinate converter 9 that computes a torque current feedback value from a current detection value and the magnetic-flux phase from a current sensor 8 of the synchronous motor 13, a current command computation unit 2 that computes torque current command from a torque command and the magnetic-flux absolute value, and a current controller 4 that controls an output voltage of the inverter 5 so that the torque current feedback value corresponds to the torque current command. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an AC motor control device using a power converter, and more particularly to an AC motor control device that controls an AC motor based on a torque command.

In the control of a power converter that converts power from a DC power source into AC by switching operation of a semiconductor element, when it is necessary to maximize the motor drive voltage with respect to the power supply voltage, a drive method using a rectangular wave voltage with a constant peak value Is used.
In rectangular wave drive, the voltage waveform by switching control is constant, and the torque generated by the motor can be manipulated by manipulating the phase of the voltage waveform. For example, in the case of a permanent magnet synchronous motor, the rotor position The torque can be manipulated by manipulating the voltage waveform phase for. On the other hand, the torque generated by the motor varies depending on the parameters of the motor (for example, in the case of a permanent magnet synchronous motor, the permanent magnet magnetic flux and inductance correspond), and the relationship between the voltage waveform phase and the torque variation is non-linear. Therefore, by estimating the torque using the motor power calculated from each phase voltage and current of the motor and performing feedback control using this estimated torque, the method of controlling the torque generated by the motor to a desired value is For example, it is proposed in Patent Documents 1 and 2.

JP 2000-050689 A (paragraphs 0020 to 0022, FIG. 1) Japanese Patent No. 3547117 (paragraphs 0011 to 0012, FIG. 1)

As described above, the conventional AC motor control device estimates the torque from the output power of the power converter and directly controls the torque based on the phase of the rectangular wave voltage, and the motor current is directly controlled. Absent. However, since the power output of the power converter includes converter loss and motor loss that do not contribute to torque, it has been difficult to accurately control torque with a conventional control device.
Further, in the conventional control device, since the motor current is not controlled, it is difficult to limit the motor current to a desired value, and an excessive current may flow. Driving was difficult.

The present invention has been made to solve the above-described problems, and an object thereof is to realize accurate torque control in an AC motor control device.
Another object of the present invention is to realize accurate torque control while making the best use of the power converter capability.
Another object of the present invention is to realize accurate torque control even in a control device that does not use a speed sensor of an electric motor.

An AC motor control device according to the present invention is an AC motor control device that controls an AC motor based on a torque command,
A magnetic flux estimator that calculates the magnetic flux absolute value and magnetic flux phase of the armature linkage flux of the AC motor, a coordinate converter that calculates the torque current feedback value from the current detection value and magnetic flux phase of the AC motor, torque command and magnetic flux absolute A current command calculator that calculates a torque current command from the value, and a current controller that controls the output voltage of the power converter that drives the AC motor so that the torque current feedback value matches the torque current command. is there.

  As described above, the AC motor control device according to the present invention controls the torque current, so that accurate torque control can be realized. In addition, since the motor current is a control target, it is possible to monitor the current value, and it is possible to realize accurate torque control while making the best use of the power converter capability.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of an AC motor control device according to Embodiment 1 of the present invention. In the figure, a control device 1 drives and controls a synchronous motor 13 that is an AC motor based on a torque command from a host controller (not shown).
As a main component, the control device 1 is synchronized with a speed calculator 12 that calculates a rotational speed from a detected rotor phase value from the rotational angle sensor 14 and a voltage command to the inverter 5 that is a rotational speed and a power converter. Coordinates for calculating the torque current feedback value from the magnetic flux estimator 10 for calculating the magnetic flux absolute value and magnetic flux phase of the armature interlinkage magnetic flux of the motor 13, and the current detection value and the magnetic flux phase of the synchronous motor 13 from the current sensor 8. A converter 9, a current command calculator 2 that calculates a torque current command from the torque command and the magnetic flux absolute value, and a current controller that controls the output voltage of the inverter 5 so that the torque current feedback value matches the torque current command. 4 is provided.

Next, a detailed operation of the control system will be described. The magnetic flux estimator 10 estimates the magnetic flux absolute value Φa and the magnetic flux phase θφ of the armature linkage flux from the voltage commands Vu, Vv, Vw and the rotational speed ω of the rotor. The rotation speed ω is obtained by detecting the rotor phase θ of the synchronous motor 13 with the rotation angle sensor 14 and calculating the rate of change with the speed calculator 12.
FIG. 2 shows a vector diagram of the permanent magnet motor. The armature interlinkage magnetic flux Φa is the sum of the permanent magnet magnetic flux Φf created by the permanent magnet on the rotor and the armature reaction magnetic flux created by the armature current. If the voltage drop due to the resistance of the armature winding is ignored, the absolute value Va and the phase θv of the voltage vector can be expressed by the following equations (1) and (2).

  On the other hand, the absolute value Va and the phase θv of the voltage vector can be calculated by the following equations (3) to (6) from the voltage commands Vu, Vv, and Vw.

However, sign (ω) indicates either positive or negative sign of the rotational speed ω.
Using the above relationship, the magnetic flux absolute value Φa and the magnetic flux phase θφ of the armature linkage flux can be estimated from the voltage commands Vu, Vv, Vw and the rotational speed ω.

  Next, the coordinate converter 9 converts the motor currents Iu, Iv, and Iw detected by the current sensor 8 in the direction orthogonal to the magnetic flux phase θφ using the following equation (7). This current component in the direction perpendicular to the magnetic flux is hereinafter referred to as torque current.

  Here, the torque generated by the electric motor will be examined. For example, it is known that the torque τ generated by a permanent magnet motor having saliency is generally expressed by the following equation (8). Here, Ld and Lq are d and q-axis inductances, id and iq are d and q-axis currents, respectively, and Φf is a permanent magnet magnetic flux.

The rightmost side of the equation (8) can be considered to represent the torque generated by the permanent magnet motor as an outer product of the armature flux linkage on the d and q axes and the current vector. Since the value produced by the vector outer product does not depend on the observation coordinate system, the torque τ can be calculated by the outer product of the armature linkage magnetic flux and the current vector even in a coordinate system parallel and orthogonal to the armature linkage flux. Holds.
However, since the current vector component parallel to the armature interlinkage flux does not generate torque at this time, the torque τ generated by the motor is the magnitude Φa of the armature interlinkage flux as shown in the following equation (9). and it can be represented in the form of the product of the torque current i _T.

Based on equation (9), the current command calculator 2 calculates a torque current command i _T * from the torque command τ *. The adder 3 compares the torque current command i _T * with the actual torque current feedback value i _T obtained by the equation (7) to calculate a current error. The current controller 4 adjusts the voltage commands Vu, Vv, and Vw so that this current error becomes zero. The inverter 5 is driven in accordance with the voltage commands Vu, Vv, Vw generated in this way, and the synchronous motor 13 generates a desired torque corresponding to the torque command τ *.

  In the magnetic flux estimator 10 in the first embodiment, the influence of the resistance voltage drop of the armature winding of the synchronous motor 13 and the influence of the voltage error generated in the output voltage of the inverter 5 are not considered. If magnetic flux estimation is performed in consideration of these, more accurate torque control can be performed. Specifically, voltage values Vu ′, Vv ′, and Vw ′ corrected by the following equation (10) using the motor currents Iu, Iv, and Iw for magnetic flux estimation are expressed by equations (3) and (4). May be used instead of the voltage commands Vu, Vv, and Vw. In equation (10), R is the armature winding resistance, and Δv is the ON voltage drop of the inverter element.

  As described above, according to the first embodiment of the present invention, the torque current command is calculated based on the torque command, and the torque current feedback value based on the detected motor current is controlled to match the torque current command value. Since it did in this way, compared with the conventional control apparatus, a torque can be exactly matched by a torque command. In addition, since the motor current is to be controlled, specifically, it will be exemplified later, but it is possible to monitor the current value and realize accurate torque control while making the best use of the current capability of the inverter. it can.

Embodiment 2. FIG.
In the first embodiment, the general case where an arbitrary waveform can be handled for the output voltage of the inverter 5 has been described. However, in this second embodiment, the motor drive voltage is maximized with respect to the power supply voltage. A case will be described in which the present invention is applied when a rectangular wave voltage having a constant peak value is output to drive an electric motor, for example, when necessary. Hereinafter, the description will focus on the parts different from the first embodiment, and the description of the same parts will be omitted as appropriate.

3 is a diagram showing a configuration of an AC motor control device according to Embodiment 2 of the present invention. In FIG.
By the way, in the rectangular wave voltage drive of the synchronous motor, as shown in FIG. 4, a system is used in which each phase switch is driven at a predetermined electrical angle synchronized with the rotor phase θ. As shown in the upper half of FIG. 4, the potential of each phase switches between 0 and the voltage Vdc of the DC power supply 6 according to the rotor phase θ. When considered, each phase voltage is considered to have a stepped waveform as shown in the lower half of FIG.

In the second embodiment, as shown in FIG. 4, the output voltage waveform is a rectangular wave, so that the calculation of the magnetic flux estimation can be easily performed. That is, it is known that the effective value of the fundamental wave component of each step-like waveform is (√ (2) / π) * Vdc (see, for example, Patent Document 2).
Therefore, the absolute value Va of the voltage vector at the time of the rectangular wave voltage drive shown in FIG. 4 is (√ (6) / π) * Vdc, and the phase θv can be obtained as θ + φ + π / 2.
Where θ is the rotor phase, and φ is the voltage lead phase shown in FIG.

  As described above, in the case of the rectangular wave voltage drive, it is not necessary to calculate the voltage vector according to the above equations (3) to (6), and the voltage is determined from the DC power supply voltage Vdc, the rotor phase θ, and the voltage advance phase φ. The absolute value Va and the phase θv of the vector can be obtained. Then, by substituting the absolute value Va and the phase θv into the previous equations (1) and (2), the magnetic flux absolute value Φa and the magnetic flux phase θφ of the armature interlinkage magnetic flux can be obtained.

Next, the operation of the control system will be described with reference to FIG. The magnetic flux estimator 10 uses the DC power supply voltage Vdc from the voltage sensor 7, the rotor phase θ from the rotation angle sensor 14, and the voltage advance phase φ from the current controller 4 in the manner described above. The magnetic flux absolute value Φa and the magnetic flux phase θφ are calculated and estimated. The current controller 4 calculates a switching command to the inverter 5 so that the current error between the torque current command i _T * and the torque current feedback value i _T becomes zero. That is, control is performed by operating the voltage advance phase φ, and a voltage command is generated with reference to the rotor phase θ.
In particular, since the estimated magnetic flux value and the torque current feedback value at the time of driving the rectangular wave voltage include many pulsation components, a filter or the like may be used to remove these influences.

As described above, according to the second embodiment of the present invention, the torque current command is calculated based on the torque command, and the torque current feedback value based on the detected motor current is controlled to match the torque current command value. Since it did in this way, compared with the conventional control apparatus, a torque can be exactly matched by a torque command.
Moreover, since the rectangular wave voltage drive system is assumed, it is possible to easily calculate the magnetic flux absolute value and the magnetic flux phase of the armature interlinkage magnetic flux, and in particular, there is an advantage that the arithmetic processing is shortened.
Further, as in the case of the first aspect, the current value is monitored, and accurate torque control can be realized while maximizing the current capability of the inverter.

Embodiment 3 FIG.
FIG. 5 is a diagram showing a configuration of an AC motor control device according to Embodiment 3 of the present invention.
In the third embodiment, the current value is actually monitored, and the limit process is performed so that the current does not exceed the maximum current allowed for the inverter 5 and the synchronous motor 13, thereby maximizing the ability of these devices. Accurate torque control is realized with certainty. The following description will be focused on the parts different from those of the first embodiment, and the description of the same parts will be omitted as appropriate.

Specifically, a current component (flux direction current feedback value) iφ parallel to the armature flux linkage is obtained by the following equation (11) by the coordinate converter 9 of FIG. The maximum torque current calculator 16 obtains the maximum torque current i _T max that can be output by the following equation (12), and the limiter 15 limits the output from the current command calculator 2 based on this value.
In the equation (12), imax is an absolute value of an allowable maximum current vector of the inverter 5 or the synchronous motor 13.

  The circuit shown in FIG. 5 is applied to the control device shown in FIG. 1 according to the first embodiment, but is applied to the control device shown in FIG. 3 according to the second embodiment that employs rectangular wave voltage driving. Can be applied in exactly the same way.

  As described above, according to the third embodiment, the torque current command as a control target is limited based on the allowable maximum current value of the device, so that stable operation while avoiding an overcurrent state is avoided. This makes it possible to make the most of the capabilities of these devices and ensure accurate torque control.

Embodiment 4 FIG.
FIG. 6 is a diagram showing a configuration of an AC motor control device according to Embodiment 4 of the present invention. Here, the present invention is applied to a sensorless control system for controlling a synchronous motor without using a rotation angle sensor. Since there is no rotation angle sensor, the speed calculator 12 calculates the rotational speed ω using the magnetic flux phase θφ instead of the rotor phase θ.
In the synchronous motor, since the magnetic flux phase θφ rotates in synchronization with the rotor phase θ, the value of the magnetic flux phase θφ estimated by the magnetic flux estimator 10 can be used instead of the rotor phase θ.

In the first embodiment, the current controller 4 refers to the rotor phase θ so that the current error between the torque current command i _T * and the torque current feedback value i _T becomes zero. Although Vv and Vw are adjusted, in the fourth embodiment, a voltage command is generated with reference to the magnetic flux phase θφ.
Although illustration is omitted, as described in the second embodiment, when a rectangular wave voltage is output by the inverter 5, control is performed by operating the voltage advance phase φ ′ with respect to the magnetic flux phase θφ. A voltage command is generated with reference to the phase θφ.
Further, in the case of this sensorless control method, the current value is actually monitored in the same manner as described in the third embodiment so that it does not exceed the maximum current allowed for the inverter 5 and the synchronous motor 13. By performing the limiting process, it is possible to make the most of the capabilities of these devices and to realize accurate torque control.

  As described above, according to the fourth embodiment of the present invention, even in a sensorless control method that does not use a rotation angle sensor, torque is estimated based on a torque command by using an estimated magnetic flux phase instead of a rotor phase. Since the current command is calculated and the torque current feedback value based on the detected motor current is controlled so as to coincide with the torque current command value, the torque can be calculated more accurately by the torque command than in the conventional control device. Can be matched. In addition, since the motor current is controlled, accurate torque control can be realized while maximally utilizing the current capability of the inverter by specifically monitoring the current value.

  Further, in each modification of the present invention, a speed calculator that calculates the rotational speed from the rotor phase detection value of the AC motor is provided, and the magnetic flux estimator includes the rotational speed from the speed calculator and a voltage command to the power converter. Thus, the absolute value of magnetic flux and the phase of magnetic flux necessary for calculating the torque current command and the torque current feedback value are reliably estimated based on the detected rotor phase. The

  When the power converter outputs a rectangular wave voltage with a constant peak value to drive the AC motor, the current controller detects the rotor phase detection value of the AC motor so that the torque current feedback value matches the torque current command. Since the phase of the rectangular wave voltage with respect to is controlled, current control is easily performed.

  The magnetic flux estimator calculates the magnetic flux absolute value and magnetic flux phase from the DC power supply voltage of the power converter, the rotor phase detection value of the AC motor, and the control phase of the rectangular wave voltage. Calculation is made simple.

  In addition, it has a speed calculator that calculates the rotational speed of the AC motor from the magnetic flux phase, and the magnetic flux estimator calculates the magnetic flux absolute value and magnetic flux phase from the rotational speed from the speed calculator and the voltage command to the power converter. As a result, the calculation of the magnetic flux estimation is reliably performed even in the speed sensorless control of the AC motor.

  Also, when the power converter outputs a rectangular wave voltage with a constant peak value to drive the AC motor, the current controller outputs the phase of the rectangular wave voltage with respect to the magnetic flux phase so that the torque current feedback value matches the torque current command. Therefore, even in the speed sensorless control of the AC motor, current control is easily performed.

  Also, a speed calculator that calculates the rotational speed of the AC motor from the magnetic flux phase is provided, and the magnetic flux estimator calculates the absolute magnetic flux from the DC power supply voltage of the power converter, the rotational speed from the speed calculator, and the control phase of the rectangular wave voltage. Since the value and the magnetic flux phase are calculated, the magnetic flux estimation is easily calculated even in the speed sensorless control of the AC motor.

  Also, the maximum torque current is calculated from the maximum current allowed for the magnetic flux direction current feedback value and the coordinate converter that calculates the magnetic flux direction current feedback value from the current detection value and the magnetic flux phase of the AC motor, and the AC converter. A maximum torque current calculator that can be operated and a limiter that limits the output from the current command calculator so that the torque current command does not exceed the maximum torque current. Therefore, accurate torque control can be reliably realized by making full use of the capabilities of the equipment.

It is a figure which shows the structure of the control apparatus of the alternating current motor in Embodiment 1 of this invention. It is a vector diagram of a permanent magnet motor. It is a figure which shows the structure of the control apparatus of the alternating current motor in Embodiment 2 of this invention. It is a figure which shows the voltage waveform in the rectangular wave voltage drive of a synchronous motor. It is a figure which shows the structure of the control apparatus of the alternating current motor in Embodiment 3 of this invention. It is a figure which shows the structure of the control apparatus of the alternating current motor in Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus, 2 Current command calculator, 3 Adder, 4 Current controller, 5 Inverter, 6 DC power supply, 7 Voltage sensor, 8 Current sensor, 9 Coordinate converter, 10 Magnetic flux estimator, 12 Speed calculator, 13 Synchronous motor, 14 rotation angle sensor, 15 limiter,
16 Maximum torque current calculator.

Claims (8)

A control device for an AC motor that controls the AC motor based on a torque command,
A magnetic flux estimator that calculates the magnetic flux absolute value and magnetic flux phase of the armature linkage magnetic flux of the AC motor, a coordinate converter that calculates a torque current feedback value from the current detection value of the AC motor and the magnetic flux phase, and the torque A current command calculator that calculates a torque current command from the command and the magnetic flux absolute value, and an output voltage of a power converter that drives the AC motor so that the torque current feedback value matches the torque current command. An AC motor control device comprising a current controller. A speed calculator for calculating the rotational speed from the rotor phase detection value of the AC motor;
2. The control of an AC motor according to claim 1, wherein the magnetic flux estimator calculates the magnetic flux absolute value and the magnetic flux phase from a rotational speed from the speed calculator and a voltage command to the power converter. apparatus. When the power converter drives the AC motor by outputting a rectangular wave voltage having a constant peak value,
The said current controller controls the phase of the said rectangular wave voltage with respect to the rotor phase detection value of the said AC motor so that the said torque current feedback value may correspond with the said torque current command. AC motor control device. The magnetic flux estimator calculates the magnetic flux absolute value and the magnetic flux phase from a DC power supply voltage of the power converter, a rotor phase detection value of the AC motor, and a control phase of the rectangular wave voltage. The control apparatus for an AC motor according to claim 3. A speed calculator that calculates the rotational speed of the AC motor from the magnetic flux phase;
2. The control of an AC motor according to claim 1, wherein the magnetic flux estimator calculates the magnetic flux absolute value and the magnetic flux phase from a rotational speed from the speed calculator and a voltage command to the power converter. apparatus. When the power converter drives the AC motor by outputting a rectangular wave voltage having a constant peak value,
2. The control apparatus for an AC motor according to claim 1, wherein the current controller controls the phase of the rectangular wave voltage with respect to the magnetic flux phase so that the torque current feedback value matches the torque current command. A speed calculator that calculates the rotational speed of the AC motor from the magnetic flux phase;
The magnetic flux estimator calculates the magnetic flux absolute value and the magnetic flux phase from a DC power supply voltage of the power converter, a rotational speed from the speed calculator, and a control phase of the rectangular wave voltage. Item 7. A control device for an AC motor according to Item 6. A coordinate converter for calculating a magnetic flux direction current feedback value from the detected current value of the AC motor and the magnetic flux phase, a maximum torque current from the maximum current allowed for the power converter and the AC motor and the magnetic flux direction current feedback value. 8. A maximum torque current calculator for calculating the torque torque, and a limiter for limiting an output from the current command calculator so that the torque current command does not exceed the maximum torque current. A control device for an AC motor according to claim 1.

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