JPH07123782A - Voltage source inverter device - Google Patents

Abstract

PURPOSE:To suppress an abrupt increase in a starting current generated due to a phase difference between an induced voltage and an output voltage when an induction motor is started by an inverter circuit in a rotating state. CONSTITUTION:The voltage type inverter comprises an inverter circuit for converting a DC voltage to an AC voltage of a phase responsive to a phase signal to drive an induction motor 5, and phase correcting means 15 for correcting the phase signal in response to an effective component current flowing to the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a voltage source inverter device which outputs an AC power of variable frequency and variable voltage to drive an induction motor.

[0002]

2. Description of the Prior Art As a voltage source inverter for outputting an AC power of variable frequency and variable voltage to drive an induction motor, V
It is generally known to perform constant / f control. When the induction motor is driven using this type of voltage source inverter, when the output of the voltage source inverter is stopped while the induction motor is rotating, and restart is performed before the induction motor is stopped. It is necessary to have a function of restarting with the inverter output voltage in which the amplitude, frequency and phase of the induced voltage of the induction motor are matched so that overcurrent does not occur. FIG. 5 shows the configuration of the main part of a conventional voltage source inverter having such a function.

In FIG. 5, 3 is a converter that outputs a constant DC voltage as a voltage source, and 4 is an inverter circuit that converts the DC voltage into an AC voltage, which outputs an AC voltage of a variable voltage and a variable frequency. Then, the induction motor 5 is driven. Reference numeral 6 is a speed setter that determines the target speed of the induction motor 5, and 7 is a change rate limiting circuit, and when the operation signal RUN is 1, the speed reference SP ^* on the input side is kept below a certain rate of change as a normal change rate limiting function. It is limited and output as the frequency reference f ^* . Also,
When the operation signal RUN is 0, the separately input frequency signal f _PLL is output as it is as the frequency reference f ^* without the change rate restriction. Reference numeral 8 is a function unit, which is a frequency reference f ^*
Outputs a voltage reference V ^* at a predetermined V / F ratio. A voltage controller 9 compares the voltage reference V ^* with the output voltage V of the inverter circuit 4 and outputs a control signal V _INV . The amplitude of the output voltage V of the inverter circuit 4 is controlled by V _INV so that the deviation from V ^* is reduced. 10 is an integrator, which is a frequency reference f
Integrate ^* and output the phase signal θ _INV . Reference numeral 11 denotes a PLL circuit which proportionally integrates the phase difference between the phase signal θ _INV and the AC output voltage V of the inverter circuit 4 and outputs the frequency signal f _PLL so that the phase difference disappears.

In the above structure, when the operation signal RUN becomes 1, the frequency reference f is caused by the action of the change rate limiting circuit 7.
^* Increases at a predetermined rate of change to the speed SP ^* set by the speed setter 6, and at the same time outputs a voltage reference V ^* of a predetermined V / F ratio via the function unit 8. The voltage controller 9 compares the voltage reference V ^* with the output voltage of the inverter circuit 4 and controls the inverter circuit 4 so as to eliminate the voltage deviation. On the other hand, the integrator 10 outputs a phase signal θ _INV according to the frequency reference f ^* to control the phase of the AC output voltage of the inverter circuit 4. As a result, the inverter circuit 4 converts a constant DC voltage output from the converter into an AC voltage having an amplitude according to the voltage reference V ^* and a frequency according to the frequency reference f ^* , and its phase is the phase. The induction motor 5 is synchronized with the signal θ _INV and the induction motor 5 has a set speed SP.
^Rotates at a speed according to ^* .

When the operation signal RUN becomes 0 while the induction motor 5 is rotating, the inverter circuit 4 and the voltage controller 9 stop operating, and the induction motor 5 decelerates depending on the inertia of the load and the load torque. The rotation speed decreases at a rate. On the other hand, when the RUN becomes 0, the rate-of-change limiting circuit 7 acts so as to output the output signal f _PLL of the PLL circuit 11 as it is as the frequency reference f ^* , so that the phase lock loop of the PLL circuit 11 is configured, Reference numeral 11 controls the frequency reference f ^* so that the phase signal θ _INV output from the integrator 10 matches the phase of the AC voltage induced in the induction motor 5. As a result, the frequency reference f ^* can follow the frequency corresponding to the rotation speed of the induction motor 5 and can match the phase of the phase signal θ _INV with the phase of the induced voltage.

Therefore, when restarting, the output voltage of the inverter circuit 4 is made to coincide with the phase, frequency and amplitude of the induced voltage of the induction motor 5 to suppress the current flowing at restarting and to restart stably. can do.

[0007]

However, in the above-mentioned conventional apparatus, it is difficult to make the phases completely coincide with each other at the time of restart due to a phase detection error of the phase lock loop, operation delay, etc., and a phase difference occurs. There's a problem. When the phase difference occurs, the error voltage of the vector difference between the induced voltage of the induction motor and the output voltage of the inverter circuit is applied to the low impedance of the main circuit, and a large starting current flows. This starting current may charge and discharge the capacitor provided on the output side of the converter 3 in a short time, cause resonance of the smoothing reactor and the capacitor, and may not be able to restart stably. In addition, there is a risk that the switching element of the inverter circuit may be damaged by the overcurrent.

The present invention has been made in order to solve the above problems, and its object is to provide a method in which there is a slight phase difference between the inverter output voltage at the time of restart and the induced voltage of the induction motor. An object is to provide a voltage source inverter device capable of stable restart.

[0009]

To achieve the above object, the present invention comprises an inverter circuit for converting a DC voltage into an AC voltage having a phase corresponding to a phase signal and driving an induction motor. Phase correction means for correcting the phase signal according to the effective component current flowing through the electric motor is provided.

Further, the phase correcting means corrects the phase signal to a delay side when the active component current has a positive polarity when the inverter circuit is started while the induction motor is rotating. When the effective component current has a negative polarity, the phase signal is corrected to the lead side.

Further, the phase signal is generated by an integrating means for integrating a frequency reference, and the phase correcting means is constituted by a frequency correcting means for correcting the frequency reference according to a rate of change of the effective component current.

Further, the frequency correction means reduces the frequency reference when the active component current increases in a positive polarity when the inverter circuit is started while the induction motor is rotating, The frequency reference is increased when the active component current increases negatively.

[0013]

In the above structure, when the induction circuit is started while the induction motor is rotating and there is a phase difference between the induction voltage of the induction motor and the output voltage of the inverter circuit, A large starting current is about to flow. The phase signal is modified according to the effective component current of the starting current, the phase of the output voltage of the inverter circuit is modified, and the phase difference is reduced. As a result, a rapid increase in the starting current is suppressed, and stable starting is possible.

[0014]

FIG. 1 shows an embodiment of the voltage source inverter of the present invention. In the figure, 12 is a current detector that detects the current flowing in the induction motor, 13 is a vector decomposer, and the current detector 12
Current I _M of the induction motor 5 detected via the
The effective component current I _R of the current I _M is detected from the phase signal θ _INV output from A frequency correction circuit 14 outputs a correction signal f _cmp according to the differential value of the signal I _R output from the vector decomposer 13 and adds it to the frequency reference f ^* for correction. Others are the same as the conventional one (FIG. 4), and are denoted by the same symbols.

In the above configuration, when the operation signal RUN is set to 0 while the induction motor 5 is rotating, the phase lock loop acts as in the conventional case, and the phase signal θ _INV matches the phase of the induced voltage. The follow-up control is performed as follows.

When restarting with the operation signal RUN set to 1 in this state, if a phase difference occurs between the output voltage of the inverter circuit 4 and the induced voltage of the induction motor 5, a large starting current tends to flow. . In this case, as shown in FIG. 2A, when the output voltage V of the inverter circuit 4 advances by a phase angle δ with respect to the induced voltage E of the induction motor 5 and starts in a phase, the resistance of the main circuit is changed to R and the reactance. The acceleration current I flows with X as X, and the error voltage is represented by a composite vector of RI and XI. The vector decomposer 13 detects the effective component current I _R of this acceleration current I. When the effective component current I _R increases, the frequency correction circuit 14 causes the correction signal f _cmp corresponding to the rate of change of I _R.
To act to reduce the frequency reference f ^* .
As a result, the phase signal θ _INV output from the integrator 10 is corrected to the delayed phase side, and the phase of the output voltage V of the inverter circuit 4 is also corrected to the delayed side. Therefore, the phase difference δ with the induced voltage E is reduced, the error voltage is reduced, and the sudden increase of the main circuit current I at the time of starting is suppressed. Further, as shown in FIG. 2 (B), when the output voltage V of the inverter circuit 4 is started in a phase delayed by the phase angle δ with respect to the induced voltage E of the induction motor 5,
A regenerative (braking) current I flows, and the error voltage is represented by a composite vector of RI and XI. In this case, the effective component current I _R of the regenerative current I has a phase difference of 180 degrees with respect to V, and is detected by the vector decomposer 13 as negative. Effective component current I _R
Is increased in the negative direction, the frequency correction circuit 14 outputs a correction signal f _cmp according to the rate of change of I _R , and acts to increase the frequency reference f ^* . As a result, the phase signal θ _INV output from the integrator 10 is corrected to the lead side, and the phase of the output voltage V of the inverter circuit 4 is also corrected to the lead side. Therefore, the phase difference δ with the induced voltage E is reduced, the error voltage is reduced, and the rapid increase of the main circuit current I at the time of starting is suppressed, and stable restart can be performed.

A second embodiment of the present invention is shown in FIG. The second embodiment is an example in which the current detector 12 is provided on the DC side of the inverter circuit 4 and the vector decomposer 13 is omitted. The effective component current I _R on the AC side of the inverter circuit 4 and the current (average value) I _DC on the DC side are almost equivalent, and if the pulse width modulation frequency of the inverter circuit 4 is set appropriately high, the DC average will be obtained. The time constant of the filter that obtains the value I _DC can be shortened, and the same effect can be obtained.

A third embodiment of the present invention is shown in FIG. In the third embodiment, 15 is a phase correction circuit, which is a correction signal θ corresponding to the effective component current I _R detected by the vector decomposer 13.
_It outputs _cmp and corrects the phase signal θ _INV and performs proportional operation. In this arrangement, the effective component current I _R is corrected phase signal theta _INV when the positive polarity to the delay side, I _R is corrected to the advanced side of the theta _INV for a negative polarity.
As a result, the phase difference between the induced voltage of the induction motor 5 and the output voltage of the inverter circuit 4 is reduced, and the error voltage is reduced. Therefore, the sudden increase in the starting current caused by the phase difference is suppressed, and the restart is smoothly performed. can do. Even in the case of this embodiment, the vector decomposer 13 is omitted, and the current on the DC side of the inverter circuit 4 is detected as in the second embodiment of FIG. 3 and its average value is used as the effective component current. be able to.

[0019]

According to the present invention, when the inverter circuit is started while the induction motor is rotating, there is a slight phase difference between the induced voltage of the induction motor and the output voltage of the inverter circuit. Even if occurs, the phase of the output voltage of the inverter circuit is modified so that the phase difference decreases when the current begins to flow, so a voltage that can start stably without passing an excessive starting current. A shaped inverter device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of essential parts of an embodiment of claims 3 and 4 of the present invention.

FIG. 2 is a vector diagram for explaining the operation of the present invention.

FIG. 3 is a main part configuration diagram of a second embodiment of claims 3 and 4 of the present invention.

FIG. 4 is a main part configuration diagram of an embodiment of claims 1 and 2 of the present invention.

FIG. 5 is a configuration diagram of a main part of a conventional voltage source inverter device.

[Explanation of symbols]

3 ... Converter as DC voltage source 4 ... Inverter circuit 5 ... Induction motor 6 ... Speed setting device 7 ... Change rate limiter 8 ... Function device 9 ... Voltage controller 10 ... Integrator 11 ... PLL circuit 12 ... Current detector 13 ... Vector decomposer 14 ... Frequency correction circuit 15 ... Phase correction circuit

Claims (4)

[Claims] 1. An inverter circuit for converting a DC voltage into an AC voltage having a phase corresponding to a phase signal and driving an induction motor, and correcting the phase signal according to an effective component current flowing in the induction motor. A voltage source inverter device characterized in that phase correction means is provided. 2. The voltage source inverter device according to claim 1, wherein the phase correction means causes the effective component current to be positive when the inverter circuit is started while the induction motor is rotating. The voltage source inverter device corrects the phase signal to the delay side when the active component current is negative, and corrects the phase signal to the advance side when the effective component current is negative. 3. The voltage source inverter device according to claim 1, wherein the phase signal is generated by an integrating means for integrating a frequency reference, and the phase correcting means is responsive to a rate of change of the effective component current. A voltage source inverter device comprising frequency correction means for correcting the frequency reference. 4. The voltage source inverter device according to claim 3, wherein the frequency correction means causes the effective component current to be positive when the inverter circuit is started while the induction motor is rotating. Voltage source inverter device, wherein the frequency reference is reduced when the active component current increases with a negative polarity, and the frequency reference is increased when the active component current increases with a negative polarity.