JP2000092899A - Controller of induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller of an induction motor whereby its torque is stabilized when an output voltage in its vector controlling device is saturated. SOLUTION: In a voltage-saturation compensating circuit 10 of this controller, an output V1 of a current controlling portion 5 is compared with an inverter DC-sensing voltage Vdc, and the difference voltage between them is integrated. Further, in the voltage-saturation compensating circuit 10, there is provided with a limiter 14 whereby the foregoing integrated voltage is subtracted from a magnetic-flux portion λd* of the current command of an induction motor when the inverter DC-sensing voltage Vdc exceeds the output V1 of the current controlling portion 5, and the subtraction quantity to be subtracted from the foregoing magnetic flux portion λd* is made zero when the voltage Vdc does not exceed the voltage V1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vector control device for a general-purpose induction motor, and more particularly to a method for stabilizing torque when output voltage is saturated.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional vector control device.
FIG. 3 is a diagram showing output current from the PWM inverter 1.
The induction motor 2 to be driven and the current i of the induction motor 2
_u, I _V, I_wAnd a detector 3 for detecting
Current i_u, I_V, I_wIs converted to flux and torque current.
The detected current converter 4 and the magnetic flux I of the current command_d ^*And Tor
Current I_q ^*And the magnetic flux component i from the detected current converter 4_dWhen
Torque i_qAnd add them so that
A current control unit 5 for performing integral (PI) control;
Output voltage v by control unit 5_d ^*, V_q ^*To three-phase conversion
Part 6 and limit the inverter DC detection voltage as the upper limit
And a voltage limiter. In FIG. 5, Kλ, K
_TIs the flux-current conversion gain and torque-current in the amplifier.
Indicates the flow conversion gain.

In the vector control having such a configuration as shown in FIG. 5, a voltage margin is required for controlling the current control unit 5 at a rated speed. In other words, if the inverter attempts to output a voltage exceeding the maximum voltage that the inverter can output due to fluctuations in the input power supply voltage or an increase in the output voltage during regenerative operation, that is, in a voltage saturation state, the current control unit cannot operate normally. This causes torque pulsation and torque reduction. For this purpose, the rated voltage of the induction motor is suppressed, for example, by about 10% from the power supply voltage to provide a voltage margin that does not cause voltage saturation.

Therefore, for example, when the AC input voltage is 400
Even if it is V, the inverter output voltage cannot output 400 V, and the rated voltage is about 10% lower.

[0005]

As described above, if voltage saturation occurs, the voltage cannot be increased by the voltage limiter process, the current control unit 5 cannot operate sufficiently, and a sinusoidal current cannot flow. When torque ripple occurs due to current pulsation and voltage saturation occurs in a state where a load is applied, a sufficient current for generating torque does not flow and torque is reduced. As a result, the rated voltage of the induction motor has been reduced to about 10% lower than the power supply voltage in practice.

When the rated voltage setting of the motor is equal to the input voltage setting as in a general-purpose induction motor, a slight power supply voltage fluctuation causes voltage saturation, so that a situation occurs in which a rated torque cannot be output at a rated speed. For this reason, the conventional vector control inverter cannot be applied to a general-purpose induction motor.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a control device for an induction motor which can maintain a constant output torque even when voltage saturation occurs and can be applied to a general-purpose induction motor.

[0008]

The present invention that achieves the above object has the following matters specifying the invention. A first invention is an induction motor, a detector for detecting a current of the induction motor, a detection current conversion unit for converting the current by the detector into a current for a magnetic flux and a torque, a magnetic flux for a current command, In a current control unit that controls the voltage of the induction motor so that the current of the torque and the current value of the detection current conversion unit match each other, and a control device of the induction motor that converts an output of the current control unit by an inverter. Comparing and integrating the output of the current control unit and the inverter DC detection voltage, and when the inverter DC detection voltage exceeds the output of the current control unit, the integrated output of the magnetic flux of the current command. And a voltage saturation compensating circuit for applying a limiter for setting the amount of subtraction of the magnetic flux to zero when the difference is smaller than zero.

According to a second aspect of the present invention, in the first aspect, the integration time constant is set to a different value by increasing or decreasing the integration output.

A third invention is the first invention, characterized in that the integral is a proportional integral process.

According to a fourth aspect of the present invention, in the first aspect, a limiter of a reduction amount is applied depending on a remaining amount of the compensation at the time of magnetic flux recovery.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to FIGS. In the present invention, when voltage saturation occurs in the block shown in FIG. 5, the secondary magnetic flux is reduced and the output voltage is reduced. However, in order to keep the output torque constant, the current limiter has a margin. In some cases, the same output can be obtained by increasing the current. That is, when the voltage is large and the current is small in the A characteristic as shown in FIG. 6, the voltage may be small and the current may be large as in the B characteristic in order to obtain the same output torque. By reducing the secondary magnetic flux, voltage saturation countermeasures can be realized.

Here, an example will be described with reference to FIG. In FIG. 1, the same parts as those in FIG. 5 are denoted by the same reference numerals. That is, in FIG. 5, 1 is a PWM inverter, 2 is an induction motor,
3 is a detector, 4 is a detected current converter, 5 is a current controller, 6
Is a conversion unit.

In FIG. 1, a voltage saturation compensation circuit 1
0 has been added. In this voltage saturation compensation circuit 10,
First, the magnitudes of the output voltage vectors v _d ^* and v _q ^* of the current control unit 5 are calculated by the calculator 11, and the obtained value V 1 is compared with the DC detection voltage V _dc by the adder 12, and the output is calculated. If the voltage V1 exceeds the DC detection voltage V _dc, the integral gain K _i and sample e - obtaining a compensation amount at the output of the integrator 13 to fit plus the previous output by field Z ^-1. And the magnetic flux command λ
By subtracting this compensation amount from _d ^{*, the} magnetic flux is reduced based on the excess output voltage of the current control unit 5. When the output voltage V1 falls below the DC detection voltage _Vdc , the integration operation is continued until the amount of compensation becomes zero, and the limiter 14 applies a zero limiter so that the amount of compensation does not become negative.

As described above, the voltage saturation compensation circuit 10
Even at the time of voltage saturation, the same torque as in the case where voltage saturation does not occur can be obtained unless the current is applied to the limiter. In addition, since the voltage limiter is not applied at the same time, it is possible to realize control that does not cause current ripple (torque ripple) due to the voltage limiter.

FIG. 2 shows a modification of FIG. That is, at the time of voltage saturation, characteristics such as torque reduction and torque ripple are deteriorated. Conversely, when the voltage is recovered from the voltage saturation state, it is desired to return the magnetic flux quickly. However, if the voltage is recovered too quickly, torque pulsation may occur or stability at the time of voltage saturation may be impaired. As a result, the integration time constant is changed when the voltage saturation compensation amount increases and decreases. That is, as shown in FIG. 2, in the voltage saturation compensating circuit 10, when the value is positive, the integral gain _Ki1 is selected, and when the value is negative, the integral gain _Ki2 is selected. The selection is made by a switch.

FIG. 3 is a block diagram when it is desired to speed up the compensation response. That is, when it is desired to speed up the regenerative compensation response, the response can be sped up by replacing the integral control (I control) in FIG. 2 with the proportional integral control (PI control) in FIG. _Ki1 and _Ki2 are integral gains _Kp1 and _Kp2 are proportional gains.

FIG. 4 is a block diagram when it is desired to slowly reduce the compensation amount. The block shown in FIG. 3 is further provided with a limiter. In other words, when the magnetic flux is recovered, the amount of compensation is desired to be reduced slowly, and when the amount of compensation is reduced, a limiter process of the amount of reduction is performed based on the remaining amount of compensation. That is, it has a limiter 15 for reducing the amount of compensation by the remaining amount and a limiter 16 for limiting the output of the proportional integration control by the limiter 15.

[0019]

According to the present invention as described above, the following effects can be obtained. A first invention is an induction motor, a detector for detecting a current of the induction motor, a detection current conversion unit for converting the current by the detector into a current for a magnetic flux and a torque, a magnetic flux for a current command, In a current control unit that controls the voltage of the induction motor so that the current of the torque and the current value of the detection current conversion unit match each other, and a control device of the induction motor that converts an output of the current control unit by an inverter. Comparing and integrating the output of the current control unit and the inverter DC detection voltage, and when the inverter DC detection voltage exceeds the output of the current control unit, the integrated output of the magnetic flux of the current command. And a voltage saturation compensating circuit that applies a limiter that reduces the amount of subtraction of the magnetic flux to zero when the voltage falls below the threshold value. If no voltage saturation unless applied to the limiter same torque can be obtained and, also it is possible to control that does not cause current ripple due to the voltage limiter for not applied to the voltage limiter at the same time.

Further, by setting the integration time constant to a different value depending on the increase or decrease of the integration output, high-speed response, reduction of torque pulsation, and increase of voltage saturation stability between regeneration and magnetic flux recovery can be achieved.

Furthermore, the speed can be increased by employing the proportional and integral control, and the slow operation can be achieved by employing the reduction limiter at the time of voltage recovery.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example according to the present invention.

FIG. 2 is a block diagram showing a modification of the voltage saturation compensation circuit.

FIG. 3 is a block diagram showing another example of the voltage saturation compensation circuit.

FIG. 4 is a block diagram showing another example of the voltage saturation compensation circuit.

FIG. 5 is a block diagram showing a conventional example of vector control.

FIG. 6 is an explanatory diagram showing a current vector at the time of voltage saturation.

[Explanation of symbols]

 Reference Signs List 10 voltage saturation compensation circuit 11 arithmetic unit 12 adder 13 integration amount 14 limiter

Claims (4)

[Claims] 1. An induction motor, a detector for detecting a current of the induction motor, a detection current converter for converting a current by the detector into a current for a magnetic flux and a torque, a magnetic flux and a torque for a current command A current control unit that controls the voltage of the induction motor so that the current of the current and the current value of the detection current conversion unit match each other, and a control device of the induction motor that converts an output of the current control unit by an inverter. The output of the current control unit and the inverter DC detection voltage are compared and integrated, and when the inverter DC detection voltage exceeds the output of the current control unit, the integrated flux component of the current command is converted to the integrated output. A control device for an induction motor, comprising: a voltage saturation compensating circuit for applying a limiter for setting the amount by which the magnetic flux is subtracted to zero when the difference is smaller than zero. 2. The control device for an induction motor according to claim 1, wherein the integral time constant is set to a different value depending on the increase or decrease of the integral output. 3. The induction motor control device according to claim 1, wherein the integral is a proportional integral. 4. The control device for an induction motor according to claim 1, wherein a limiter of a reduction amount is applied according to a remaining amount of the compensation when the magnetic flux is recovered.