JP4973136B2 - Power converter - Google Patents

Description

  The present invention relates to a semiconductor power conversion device that has a current control system and performs power conversion, and more particularly to overshoot suppression when a power supply voltage recovers from an instantaneous drop.

  This type of power converter includes, for example, an inverter that performs motor vector control and torque control, a converter that obtains DC power controlled from a system power supply, and an active filter (power conditioner) that is linked to the system power supply.

In such a power converter, a current control system for controlling an output current is often provided as a control system. This current control system includes a proportional integration (PI) calculation unit 1 and a limiter unit 2 as shown in FIG. 6 as a current control amplifier in an equivalent block. The proportional integration calculation unit 1 detects a current command I * and output current detection. The deviation from the value _IDET is proportionally integrated, and the limiter unit 2 outputs the voltage command V * by limiting the calculation result to the positive / negative limiter values V _LIM and −V _LIM . The current of the motor 4 is controlled by controlling the output.

When a power supply control device having a current control system cannot secure a power supply voltage necessary for control, a so-called voltage saturation phenomenon occurs in which the output of the current control amplifier is limited by the power supply voltage. The occurrence of this voltage saturation prevents proper and stable control. As a countermeasure, voltage saturation is detected from the DC power supply voltage and output voltage command of the inverter controlled by the vector control method. A method has been proposed in which (update) is stopped, the output voltage is limited to the upper limit voltage or less, and the operation of the integral element is resumed when the voltage is recovered from saturation (see, for example, Patent Document 1).
JP 09-028099 A

  In the conventional voltage saturation countermeasure, since the integral element I of the current control amplifier holds the value up to the allowable value when the voltage saturation occurs, it prevents the output of the current control amplifier from quickly returning when the power supply voltage is restored. This causes the control current to overshoot.

FIG. 7 shows operation waveforms of the voltage command V * and the current I _DET when the power supply voltage V _DC once drops and then recovers after the instantaneous voltage drop. Limit value V _LIM of voltage set by the current control amplifier in order to effectively utilize the power supply voltage V _DC, is set to be larger than the supply voltage V _DC. In the figure, when the power supply voltage V _DC decreases to below the level required to flow a current I _DET, current I _DET begins to fall will not be able to maintain the current value. The output V * of the current control amplifier increases so as to increase the output in order to suppress a decrease in current, and finally outputs up to V _LIM . After that, when the power supply voltage V _DC is restored, the output V * clamped to the limit value of the current control amplifier is restored to the normal value, but in this process, the output V exceeding the level necessary to pass the current temporarily. * Is output and control current overshoot occurs.

  An object of the present invention is to provide a power conversion device capable of suppressing overshoot of a control current when a power supply voltage is restored from an instantaneous drop and quickly returning the control voltage.

  The present invention pays attention to the fact that the output of the current control amplifier cannot physically exceed the power supply voltage, and by adjusting the output limiter value of the current control amplifier according to the power supply voltage change, Is characterized by the following configuration.

(1) In a power conversion device that has a current control amplifier composed of a proportional integration (PI) calculation unit and a limiter unit and performs power conversion,
Positive and negative output limiter value of the current control amplifier when the power supply voltage is lowered and adjusted according to changes in the supply voltage advance, from a low limiter value output of the current control amplifier when the power supply voltage has returned to the correct voltage A limiter value adjuster that raises and returns to normal values;
Generates a voltage corresponding to the output of the proportional-plus-integral calculation unit obtained from the model to be controlled when the power supply voltage decreases, and adds this voltage as a feedforward voltage to the output of the proportional-integral calculation unit And
It is provided with.

  As described above, according to the present invention, since the output limiter value of the current control amplifier is adjusted according to the change in the power supply voltage, in the recovery operation from the undervoltage caused by the drop in the power supply voltage, the voltage is increased more than necessary. No output occurs, and overshoot of the control current can be suppressed. In addition, since the limit level of the voltage limiter is constantly optimized by the power supply voltage, the return operation from the limit level becomes faster.

(Embodiment 1)
FIG. 1 is an equivalent block diagram of a current control amplifier according to the present embodiment. 6 is different from FIG. 6 in that a limiter value adjusting unit 5 is provided.

The limiter value adjusting unit 5 adjusts the limiter value of the limiter unit 2 in accordance with the change in the power supply voltage level. The detection value of the DC voltage (or AC power supply voltage) of the inverter 3 is input to this limiter value adjusting unit 5. adjust the positive limit value + V _LIM of the limiter portion 2 at voltage V _DC which is proportional to, adjusting the negative limiter value -V _LIM of the limiter portion 2 at a voltage obtained by inverting the voltage V _DC by inverting amplifier 5A.

FIG. 2 shows operation waveform diagrams of current and voltage in the present embodiment. Normally, the detection current I _DET coincides with the current command I *, the output voltage V * is lower than the power supply voltage V _DC (limiter value V _LIM ), and is not limited by the limiter value. When the power supply voltage decreases (undervoltage detection), the voltage V _DC (limiter value V _LIM ) decreases as the voltage decreases, the output voltage V * is limited to this voltage, and the current output I _DET also decreases. After that, when the power supply is restored and the power supply voltage returns from the undervoltage to the normal voltage, the output V * starts to rise from the low limiter value and returns to the normal value.

  Therefore, when the power supply voltage returns from the undervoltage to the normal voltage, the voltage V * is not output more than necessary, and the overshoot of the control current can be suppressed. Further, by constantly optimizing the voltage limit level in accordance with the power supply voltage, the return operation from the limit level can be accelerated and the early return to normal operation can be performed.

(Embodiment 2)
Although the first embodiment is applied to a speed-type current control amplifier, this embodiment is applied to a position-type current control amplifier.

  FIG. 3 is an equivalent block diagram of the current control amplifier according to the present embodiment. The position type current control calculation is a method of adding the integral calculation output to the previous calculation output, and in FIG. 3, only the integration elements according to the present embodiment are shown by the position type calculation block.

1 is different from FIG. 1 in that a limit operation determination unit 6 and a changeover switch 7 are provided. The limit operation determination unit 6 determines the presence or absence of the limiter operation based on whether or not the difference between the output V ₀ of the proportional integration calculation unit 1 and the output V * of the limiter unit 2 is greater than or equal to a certain value. The changeover switch 7 is switched according to the determination result of the limit operation determination unit 6, and continues position type integration calculation by the integral calculation element (I) in the determination state without the limit operation, and integration calculation in the determination with the limit operation. The integration calculation of element (I) is set to “0” and the previous value is held.

  Also in the present embodiment, when the power supply voltage returns from the undervoltage to the normal voltage, the voltage V * is not output more than necessary, and the control current overshoot can be suppressed. Further, by constantly optimizing the voltage limit level in accordance with the power supply voltage, the return operation from the limit level can be accelerated and the early return to normal operation can be performed.

(Embodiment 3)
In this embodiment, a feedforward voltage based on the model to be controlled is added to the output of the current control amplifier.

  FIG. 4 is an equivalent block diagram of the current control amplifier according to the present embodiment. 1 is different from FIG. 1 in that a model voltage calculation unit 8 is provided.

  When the power supply voltage decreases (undervoltage detection), the model voltage calculation unit 8 generates a voltage corresponding to the output of the proportional integration calculation unit 1 obtained from the model to be controlled, and outputs this voltage from the proportional integration calculation unit 1 To the input of the limiter unit 2.

  Also in this embodiment, when the power supply voltage returns from the undervoltage to the normal voltage, by applying the model voltage, the return operation from the limit level is accelerated while the control current overshoot is suppressed, and the normal operation is performed. An early return to

(Embodiment 4)
As shown in the equivalent block diagram of the current control amplifier in FIG. 5, the present embodiment is in that the model voltage calculation unit 8 in the third embodiment is added to the position type current control amplifier in the second embodiment.

  In the present embodiment as well, for the position-type proportional integral calculation, when the power supply voltage returns from the insufficient voltage to the normal voltage, the model voltage is applied to suppress the control current overshoot while limiting the limit level. It is possible to quickly return to normal operation by speeding up the return operation.

The equivalent block diagram of the current control amplifier which shows Embodiment 1 of this invention. FIG. 3 is an operation waveform diagram of current and voltage in the first embodiment. The equivalent block diagram of the current control amplifier which shows Embodiment 2 of this invention. The equivalent block diagram of the current control amplifier which shows Embodiment 3 of this invention. The equivalent block diagram of the current control amplifier which shows Embodiment 4 of this invention. The equivalent block diagram of the conventional current control amplifier. The operation waveform figure of the current at the time of the conventional instantaneous voltage drop, and a voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Proportional integral calculation part 2 Limiter part 3 Inverter 4 Motor 5 Limiter value adjustment part 6 Limit action determination part 7 Changeover switch 8 Model voltage calculation part

Claims (1)

In a power conversion device that has a current control amplifier composed of a proportional integration (PI) calculation unit and a limiter unit and performs power conversion,
Positive and negative output limiter value of the current control amplifier when the power supply voltage is lowered and adjusted according to changes in the supply voltage advance, from a low limiter value output of the current control amplifier when the power supply voltage has returned to the correct voltage A limiter value adjuster that raises and returns to normal values;
Generates a voltage corresponding to the output of the proportional-plus-integral calculation unit obtained from the model to be controlled when the power supply voltage decreases, and adds this voltage as a feedforward voltage to the output of the proportional-integral calculation unit And
A power conversion device comprising:

Images