JPS63171168A - Controller for flux control type pwm inverter - Google Patents

Abstract

PURPOSE:To prevent overcurrent on starting by setting a frequency of a flux control type PWM inverter at a value directly before its momentary stop when stopping momentarily and restarting said PWM inverter. CONSTITUTION:A control circuit for a flux control type PWM inverter 10 driving an induction motor 12 is composed of a frequency setter 1, a flux amplitude arithmetic circuit 2, a sine wave generator circuit 3, a multiplier circuit 4, a flux regulator 5, a comparison circuit 6, a carrier signal generator circuit 7, a flux detector 8 and a pulse distributor circuit 9 to turn ON-OFF a switching element for said in verter 10. In this case, said control circuit is also provided with a momentary stop detection circuit 20, a sequence circuit 21, slow-reset circuits 22 to 23 and limiting circuits 24 to 25. Thus, an undervoltage signal of supply voltage stops operation of the inverter 10 and, after said signal has disappeared, both an amplitude of flux command signal of the flux regulator 5 and a limiting value of output signal thereof are reduced to zero. Moreover, after the frequency has been fixed to a value at the time of generation of said undervoltage signal, said stop of operation is released and a voltage on restarting is made to start from zero.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a variable voltage/variable frequency inverter device (V
(VVF inverter), especially a control device for a magnetic flux-controlled voltage-type pulse width modulation (PWM) inverter. 1. [Prior art] Insufficient receiving voltage occurs and is resolved after a predetermined period of time.
When a so-called instantaneous power outage (hereinafter referred to as an instantaneous power outage) occurs, the inverter that is in operation is immediately stopped, and after the power outage, the inverter returns to the operating state before the instantaneous power outage, which is what is called a restart after the instantaneous power outage. However, conventionally, this has been done as follows, for example.

An example of a system for driving an induction motor at variable speed using a PWM inverter will be described below.

When a momentary power failure occurs, the inverter is first stopped immediately.

This can be easily done by stopping the ON signal of the switching element of the inverter. As a result, the induction motor enters a free-run state, and at that time, the terminals of the induction motor have a sine wave voltage (hereinafter referred to as residual voltage) whose frequency is commensurate with the number of rotations of the induction motor and whose magnitude decays exponentially. ) is induced.

After the power is restored, the frequency is measured from this residual voltage by H1, and the inverter is started with the same frequency as that frequency and the voltage at that time is a predetermined value for the frequency. (The stoppage of the ON signal is canceled) and then the frequency and output voltage of the inverter are returned to the values before the instantaneous power failure.

[Problem that the invention seeks to solve]

However, the above method has the following problems.

(1) A circuit that measures the frequency from residual voltage is generally expensive.

(2) When restarting the inverter after power is restored, an overcurrent may occur if the residual voltage has not attenuated by a minute.

(3) In order to avoid the above-mentioned overcurrent, the residual voltage must be maintained until it is sufficiently attenuated, so it takes time to restart after the power is restored. .

Therefore, it is an object of the present invention to realize the instantaneous restart function as described above at a low cost, and also to enable restarting in a relatively short time without causing overcurrent during restarting. And so.

[Means for solving problems]

Voltage monitoring means for monitoring the receiving power source voltage, limiting means for restricting the input and output of the magnetic flux regulator, and control means for controlling the operation of the inverter are provided, and the control means controls the power source voltage from the voltage monitoring means. When an undervoltage signal indicating a lack of voltage is output, the operation of the inverter is immediately stopped.However, when this undervoltage signal disappears, the amplitude of the magnetic flux command signal, which is the input signal of the magnetic flux regulator, and the After setting the limit values of the output signals to zero and fixing the frequency of the magnetic flux command signal to the value at the time the undervoltage signal was generated, the inverter is stopped, and the output signal of the magnetic flux regulator and the magnetic flux command are The amplitude values of both signals are gradually returned from 0 to the value at the time the undervoltage signal was generated, and the inverter is returned to its original operating state.

[Effect]

This invention performs the instantaneous restart function in a magnetic flux control type PWM inverter using the above-mentioned procedure.
By setting the frequency when restarting the inverter to the value immediately before the instantaneous power failure, an expensive frequency measurement circuit can be omitted, and by starting the voltage at restart from zero, overcurrent at startup is prevented, and restart is possible. This shortens the time required.

(Example) Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is an operation waveform diagram for explaining its operation, and Fig. 3 is a block diagram showing the principle configuration of a flux-controlled PWM inverter. be.

A magnetic flux control type PWM inverter is disclosed in, for example, Japanese Patent Application Laid-Open No. 61-9
Although it is known from Japanese Patent Application No. 4585 (Japanese Patent Application No. 59-214218), it will be briefly explained with reference to FIG. In the figure, 1 is a frequency setting device, 2 is a magnetic flux amplitude calculation circuit, 3 is a sine wave generation circuit, 4 is a multiplication circuit, 5 is a magnetic flux regulator (AΦR), 6 is a comparison circuit, and 7 is a carrier wave signal ( carrier) generation circuit, 8 is a magnetic flux detection circuit, 9 is a pulse distribution circuit, 10 is a PWM inverter, 11 is a power supply, 12
is an induction motor.

A signal given from the frequency setter 1 is guided to a magnetic flux amplitude calculation circuit 2 and a sine wave generation circuit 3. The magnetic flux amplitude calculation circuit 2 generates the amplitude of the magnetic flux command value according to a predetermined relationship with respect to the input signal, and the sine wave generation circuit 3 generates a sine wave signal with an amplitude of ``1'' proportional to the input signal. , this is multiplied by the signal from the magnetic flux amplitude calculation circuit 2 in the S calculation circuit 4, and in AΦR5, the magnetic flux command signal and the magnetic flux detection signal from the magnetic flux detection circuit 8 are compared and adjusted, and the PWM
This becomes a voltage command signal for the inverter 10. This voltage command signal is compared with the carrier signal from the carrier signal generation circuit 7 in the comparison circuit 6, and then passed through the pulse distribution circuit 9 to the PW
This is a signal that turns the switching element of the M inverter 10 ON-OFF. Further, the power source 11 is, for example, a system power source such as a commercial power source, and as a load of the PWM inverter 10, induction lightning #ta12 is connected here.

Next, the embodiment will be described with reference to FIGS. 1 and 2. In addition, in FIG. 1, 20 is an instantaneous power failure detection circuit;
21 is a sequence circuit, 22゜23 is a slow return circuit, 24
．． ．． 25 is a limiting circuit, and the other parts are the same as in FIG. 3.

Now, when the power supply 1 momentarily fails at i=T+, the instantaneous failure detection circuit 20 immediately detects this and sends a signal to the sequence circuit 21 (corresponding to signal (b) in Fig. 2. a, b, ..., waveform r.

Q, . . . are written as the signals and waveforms shown in FIG. ). This signal causes the sequence circuit 2
1 acts on the pulse distribution circuit 9, and the PWM inverter 10
Stop the 011-OFF signal to (see signal (C)). As a result, the induction motor 12, which is the load, is disconnected from the PWM inverter 10, resulting in a free running state. At this time, residual voltage is generated in the induction motor 12 and the waveform (
0)), its magnitude and frequency decay according to a certain time constant.

On the other hand, from the sequence circuit 21, slow return circuits 22 and 23
A signal is also sent to The signal from the slow return circuit 22 (see signal (d)) acts on the limiting circuit 24 to limit the amplitude of the output signal of AΦR5 to ze[1. In addition, the slow return circuit 23
signal) 13 (see signal (e)) acts on the limiting circuit 25, and the amplitude of the output signal of the magnetic flux amplitude calculation circuit 2 (signal (e)
)) to zero. As a result, the amplitude (waveform (f)) of the magnetic flux command value that is input to AΦR5 also becomes zero.

The above is the instantaneous power failure (signal (a)) at t = 1-
This is an operation that moves I'J to +.

Next, when the power is restored at t=72, the instantaneous power failure detection circuit 20 immediately detects this. In response to this signal, the sequence circuit 21 acts on the pulse distribution circuit 9 at a timing of 1-T3 after a certain period of time, and releases the stopped ON-OFF signal to the PWM inverter 10. At this time, since the voltage command value which is the output signal of △ΦR5 is 10 (value of signal (d) at t=T3'), PW
The M inverter 10 starts operating with one output voltage.

that time,? :=At T30, the residual voltage of the induction motor 12 is short-circuited by the PWM inverter 10 whose output voltage is zero, so the residual voltage immediately becomes zero, and from then on the terminal f voltage of the induction motor 12 becomes the output of the PWM inverter 10. becomes equal to the voltage.

Note that at this time, a short circuit current will flow through the PWM inverter 10, but by adjusting the waiting time of the sequence circuit 21, it is possible to suppress the short circuit current to a level that does not pose a problem.

After j=73, according to the commands of the slow return circuits 22 and 23,
The limiting circuits 24 and 25 are activated, and the amplitude limits of the magnetic flux command value, which is the input signal of △ΦR5, and the voltage command value, which is the output signal, are gradually restored to the values before the instantaneous power failure, and the restart operation after the instantaneous power failure is completed. do. The waveform of the inverter output current is shown in waveform (h).

FIG. 4 is a block diagram showing another embodiment of the present invention. The difference from Fig. 1 is that when the output current of the PWM inverter 10 exceeds the current limit level during restart operation after an instantaneous power failure, the output frequency of the PWM inverter 10 is lowered and the induction motor 12 is halted. It is something to avoid. Physically, elements 30 to 33 are added to deal with this problem.

That is, the PWM detected by the current detection circuit 30
A limit current detection circuit 31 determines whether the output current of the inverter 10 is below or above a preset limit level. During restart operation after instantaneous power failure, when the output current of the PWM inverter is equal to or higher than the set level, that is, equal to or higher than the current limit value, a signal is generated from the limit current detection circuit 31, and while this signal is generated, the integrator circuit 32 The set frequency that provides the output frequency of the PWM inverter 10 is lowered via the reduction circuit 33 according to a certain deceleration gradient.

Also, if the output current of the PWM inverter becomes less than the current limit level during this operation, the limit current detection circuit 31
There is no signal from the integration circuit 32. and the set frequency is changed to the integration circuit 32. It is returned to the original value via the subtraction circuit 33 according to a certain acceleration gradient.

〔Effect of the invention〕

According to this invention, when restarting a magnetic flux control type PWM inverter after an instantaneous interruption, the frequency is set to the value immediately before the instantaneous interruption, which eliminates the need for an expensive frequency counting circuit, thereby making it possible to reduce costs. Instead, the voltage at restart is started from zero, which prevents overcurrent at startup and provides the advantage of shortening the time required for restart.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an operation waveform diagram for explaining its operation, Fig. 3 is a block diagram showing the principle structure of a flux-controlled PWM inverter, and Fig. 4 is a block diagram showing the principle structure of a flux-controlled PWM inverter. It is a block diagram which shows another Example of this invention. Code explanation 1... Frequency setter, 2... Magnetic flux amplitude abstract circuit, 3
... Sine wave generation circuit, 4 ... @ calculation circuit, 5 ... Magnetic flux regulator (AΦR), 6 ... Comparison circuit, 7 ... Carrier generation circuit, 8 ... Magnetic flux detection circuit, 9... Pulse distribution circuit, 10... PWM inverter, 11... Power supply, 12... Induction motor, 20... Momentary power failure detection circuit,
21... Sequence circuit, 22.23... Slow return circuit, 24.25... Limiting circuit, 30... Current detection circuit, 31... Limiting current detection circuit, 32... Integrating circuit, 33...Subtraction circuit.

Claims (1)

[Scope of Claims] 1) A flux-controlled PWM inverter that includes at least a magnetic flux regulator and drives a motor at variable speed by being supplied with power from an AC power source, comprising: voltage monitoring means for monitoring a receiving power supply voltage; and an input of the magnetic flux regulator. and a control means for controlling the operation of the inverter. While immediately stopping the undervoltage signal, after the undervoltage signal disappears, the amplitude of the magnetic flux command signal, which is the input signal of the magnetic flux regulator, and the limit value of the output signal of the magnetic flux regulator are both set to zero, and the magnetic flux command is After fixing the signal frequency to the value at the time the undervoltage signal was generated, the inverter is stopped, and both the output signal of the magnetic flux regulator and the amplitude value of the magnetic flux command signal are changed from zero to the value when the undervoltage signal is generated. A control device for a magnetic flux control type PWM inverter, characterized in that the inverter is returned to its original operating state by slowly returning the inverter to the value of . 2) The control device for a magnetic flux controlled PWM inverter according to claim 1, characterized in that the return of the amplitude value of the magnetic flux command signal is slower than the return of the limit value of the output signal of the magnetic flux regulator. A control device for a magnetic flux controlled PWM inverter. 3) In the control device for a magnetic flux controlled PWM inverter according to claim 1 or 2, when the output current of the inverter exceeds a preset limit value during the gradual return operation, A control device for a magnetic flux controlled PWM inverter, which is characterized by lowering the output frequency of the inverter. 4) In the control device for a magnetic flux controlled PWM inverter according to claim 3, when lowering the output frequency, the reached value of the amplitude value of the magnetic flux command value during the slow return operation is set to correspond to the output frequency. A control device for a magnetic flux control type PWM inverter, characterized in that the magnetic flux control type PWM inverter is set to a preset value. 5) In the control device for a magnetic flux controlled PWM inverter according to claim 3 or 4, when the inverter output current becomes below a limit value, the output frequency is changed to the value at the time when the undervoltage occurred. A control device for a magnetic flux control type PWM inverter characterized by gradual return.