JPS5822960B2 - Inverter control circuit for motor drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter control circuit for controlling the speed of an induction motor.

Conventionally, when using an inverter, especially a current source inverter, and controlling the speed of an induction motor so that the ratio V/F of its output voltage V and frequency F is maintained at a constant value and the magnetic flux is constant, disturbance phenomena often occur. It is well known that it causes

To prevent this disturbance phenomenon, (a) connect a dummy reactor to the output side of the inverter, (b) use a motor with a large excitation current, and (c) increase the ratio of the motor voltage to frequency. Countermeasures are taken, such as using the device in a selectively over-excited state.

However, when these measures are taken, the power factor of the inverter output decreases, resulting in an increase in the capacity of the inverter and an increase in equipment costs.

As a result of extensive research, the inventors focused on the fact that the disturbance phenomenon is caused by fluctuations in the phase difference between the voltage and current of the inverter output. We have found that it is possible to prevent the disturbance phenomenon by taking compensation measures in the inverter control circuit to suppress changes in the phase difference.

In other words, the phase difference between the voltage and current of the inverter output is detected to find the amount of change in the phase difference over time, and the signal is supplied to the gate of the inverter so as to cancel out the change in phase angle corresponding to this amount of change. We have found that by configuring the inverter control circuit to adjust the phase of the pulse signal, fluctuations in the voltage and current phase angle of the inverter output can be compensated for, and the above-mentioned difficulties can be solved at once.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an impark control circuit for driving an electric motor 1 that can prevent disturbances and perform stable operation with a simple configuration.

In order to achieve this objective, the present invention provides electric motor 7
The output voltage and output current of the driving impark are passed through a voltage waveform pulsing circuit and a current waveform pulsing circuit, respectively, and a flip-flop circuit detects the phase difference between the voltage and current, and the pulse width of this phase difference output is A phase difference detector is provided which converts the phase difference output into an analog quantity having a magnitude proportional to , and an arithmetic unit that generates an output according to the amount of change or rate of change of the phase difference output of this phase difference detector is provided, and the output of this arithmetic unit is The present invention is characterized by providing a phase adjustment means for adjusting the phase of the gate pulse to the inverter in response to the change in phase difference between the voltage and current of the inverter output to compensate for the change. do.

Further, by providing a gain compensation circuit between the analog converter and the arithmetic unit, phase compensation for load fluctuations can be performed.

The phase shift adjusting means may be a phase angle adjuster inserted upstream of a ring counter that distributes pulses to individual controllable valves in the inverter.

In this case, the phase angle adjuster shifts the phase of the input pulse according to the output of the arithmetic unit and supplies it to the ring counter.

Alternatively, a voltage frequency converter that generates input pulses for a ring counter may be used as the phase adjustment means.

In this case, the voltage-frequency converter is supplied with an auxiliary input from the arithmetic unit superimposed on the original input that commands the inverter frequency.

Next, embodiments of an inverter control circuit according to the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 denotes an induction motor, and a frequency converter 18 consisting of a Cyrisk rectifier 12, a smoothing reactor 14, and a three-phase bridge-connected Cyrisk inverter 16 is connected to the power supply side of the induction motor 10. ing.

The output terminal of the frequency converter 18 is connected to each primary terminal of a voltage transformer 20 and a current transformer 22, and the secondary terminals of the voltage transformer 20 and current transformer 22 are connected to a voltage waveform pulsing circuit. 24, a current waveform pulsing circuit 26, and a flip-flop 28.

The output terminal of the phase difference detector 30 is connected to the input terminal of an analog converter 36 consisting of an integrating circuit 32 and an analog quantity holding circuit 34, and the output terminal of this analog converter 36 is connected to the input terminal of a differential calculator 38. do.

Furthermore, the output terminal of the differential calculator 38 is connected to the phase angle adjuster 40.
At the same time, a pulse signal having a frequency 6fl, which is six times the desired frequency f1, is connected to the other input terminal of the phase angle adjuster 40 according to a command signal from the frequency command terminal 42. The output terminal of the oscillator 44 that oscillates is connected.

In this way, the output terminal of the phase angle regulator 40 is connected to the input terminal of the ring counter 46, and the output terminal of the ring counter 46 is connected to the input terminal of the ring counter 46.
The output terminal of is connected to the gate terminal of the thyrisk impulse 16 via a pulse amplifier 48.

Next, the operation of the circuit according to the present invention configured as described above will be explained.

When a three-phase AC voltage is applied to the frequency converter 18, the AC is converted into DC by the SiRIS rectifier 12, and this DC is supplied to the SiRIS impark 16 after the pulsation contained in the DC is removed by the smoothing reactor 14. is reconverted into an alternating current having a frequency corresponding to the gate signal of the thyristor inverter 16, so that the induction motor 10 is operated at the desired speed.

In this case, the output voltage of the frequency converter 18 is supplied to the voltage input terminal of the phase difference detector 30 via the potential transformer 20, and the output current of the frequency converter 18 is supplied to the voltage input terminal of the phase difference detector 30 via the current transformer 22. It is supplied to the current input terminal of the phase difference detector 30.

The voltage input (FIG. 2a) supplied to the voltage input terminal of the phase difference detector 30 is converted into a voltage pulse (FIG. 2b) by the voltage waveform pulsing circuit 24 and then sent to the flip-flop 28.
is supplied to the set input terminal of

Further, the current input (FIG. 2C) supplied to the current input terminal of the phase difference detector 30 is converted into a current pulse (FIG. 2D) by the current waveform pulsing circuit 26, and the flip-flop 28 is reset. Supplied to the input terminal.

Furthermore, a pulse signal having a pulse width equal to the phase difference ψ between voltage and current supplied from the set output terminal of the flip-flop 28 to the phase difference detector 30 (see e in FIG. 2) is sent to the input terminal of the analog converter 36 in the next stage. will be sent to.

This pulse signal (Fig. 3a) is supplied to the integration circuit 32, and the pulse width ψ is integrated over the period (Fig. 3b), and this integrated output is further supplied to the analog quantity holding circuit 34, and the pulse width ψ is integrated over the period (Fig. 3b). Analog amount ψ1 proportional to period pulse width ψ
(FIG. 3C), and the phase difference for each cycle is detected as an analog quantity.

In this case, the reference phase difference ψ is applied to the output of the analog quantity holding circuit 34.

By applying a bias value corresponding to the reference phase difference ψ, as shown in FIG.

The analog value in the case of is converted to an analog quantity ψ1 with the analog value as zero.

The phase difference converted into the analog quantity ψ1 is supplied to the differential calculator 38 and differentiated, and the temporal change amount dψ1/d
t and is supplied to one input terminal a of the phase angle adjuster 40.

Further, the other input terminal of the phase angle adjuster 40 is supplied with a pulse signal having a frequency 6fl that is six times the desired inverter output frequency f1.

However, in the phase angle adjuster 40, when the phase change amount dψ1/at supplied to the input terminal a has a positive sign, that is, when the phase difference increases, the phase angle adjuster 40 changes as shown in FIG. If dψ, /dt has a negative sign, that is, the phase difference decreases, the fluctuation in the phase difference can be counteracted by delaying the output of the phase angle adjuster 40 as shown in FIG. The phase angle adjuster 40 operates so as to erase the signal.

In this way, a pulse signal with a frequency of 6 fl whose phase angle has been adjusted is supplied from the output terminal of the phase angle adjuster 40 to the ring counter 46, and a pulse signal with an inverter output frequency fl is supplied from the output terminal of the ring counter 46 via the pulse amplifier 48. It is supplied to the gate of the silice inverter 16.

Therefore, fluctuations in the phase difference of the inverter output are canceled out, and the induction motor 10 operates stably.

In the above embodiment, the output of the differential calculator 38 is supplied to the phase angle adjuster 40, but if the oscillation frequency of the oscillator 44 can be changed freely based on a command, the phase angle adjuster 40 can be omitted. The same effect can be obtained by adding the output of the differential calculator 38 to the frequency command end 42.

In this case, when advancing the output phase of the phase angle adjuster 40, the output of the differential calculator 38 is added to the frequency command end 42 so as to increase the output frequency of the oscillator 44, and the output phase of the phase angle adjuster 40 is When delaying, the output of the differential calculator 38 is added to the frequency command end 42 so as to decrease the output frequency of the oscillator 44.

In addition, if the load on the induction motor 10 always fluctuates greatly, a gain compensation circuit (not shown) may be provided between the analog converter 36 and the differential calculator 38 in the above embodiment to achieve optimal phase compensation. It can be carried out.

Note that although the above-described embodiments were mainly directed to current-source inverters, a voltage-source inverter can also be controlled in the same way.

However, in the case of a voltage source inverter, control is performed by changing the voltage phase, and if the phase difference increases, the gate pulse phase is delayed to delay the inverter output voltage phase, and if the phase difference decreases, the gate pulse phase is configured to advance the impark output voltage phase by advancing the impark output voltage phase.

According to the circuit of the present invention, it is possible to prevent the occurrence of disturbances in the induction motor by suppressing fluctuations in phase difference with a simple configuration, and it is extremely effective in improving performance and reducing manufacturing costs.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the inverter control circuit according to the present invention, FIG. 2 is a waveform diagram showing the operation of the phase difference detector shown in FIG. 1, and FIG. 3 is the waveform diagram shown in FIG. 1. A waveform diagram showing the action of the analog converter, Figure 4 shows the relationship between the input pulse width and the converted analog value when a bias value corresponding to the reference phase difference is applied to the analog converter shown in Figure 1. FIG. 5 is a curve diagram showing the characteristics of the phase angle adjuster shown in FIG. 1. 10... Induction motor, 12... Cyrisk rectifier,
14... Smoothing reactor, 16... Sirisk inverter, 18... Frequency converter, 20... Instrument transformer, 22... Current transformer, 24... Voltage waveform pulsing circuit, 26...Current waveform pulsing circuit, 28...
Flip-flop, 30... Phase difference detector, 32...
・Integrator circuit, 34...Analog amount holding circuit, 36...
・Analog converter, 38... Differential calculator, 40...
Phase angle adjuster, 42... Frequency command end, 44... Oscillator, 46... Ring counter, 48... Pulse amplifier.

Claims (1)

[Claims] 1. The output voltage and output current of an inverter for driving a motor are passed through a voltage waveform pulsing circuit and a current waveform pulsing circuit, respectively, and a flip-flop circuit detects the phase difference between the voltage and the current. A phase difference detector is provided that converts the pulse width of the phase difference output into an analog quantity proportional to the pulse width, and an arithmetic unit is provided that generates an output according to the amount of change or rate of change in the phase difference output of the phase difference detector. Furthermore, a phase adjustment means is provided to adjust the phase of the gate pulse to the impark corresponding to the output of this arithmetic unit, so that when the phase difference between the voltage and current of the inverter output changes, the change is compensated for. An inverter control circuit for driving an electric motor, characterized by comprising: 2. The inverter control circuit for driving the electric motor 1 as set forth in claim 1, wherein a gain compensation circuit is provided between the analog converter and the arithmetic unit. 3. In the impark control circuit for driving an electric motor according to claim 1, the phase adjustment means is a phase angle adjustment means inserted into the input side of a ring counter that distributes pulses to individual controllable valves in the inverter. 1. An inverter control circuit for driving a motor, characterized in that the inverter control circuit is a regulator, and the input pulse is phase-shifted by the phase angle regulator according to the output of the arithmetic unit and is applied to a ring counter. 4. In the motor drive inverter control circuit according to claim 1, the phase adjustment means is a voltage frequency converter that provides input pulses to a ring counter that distributes pulses to individual controllable valves in the inverter; An impark control circuit for driving an electric motor, characterized in that the output of the arithmetic unit is added to the original input for commanding the frequency of the inverter and applied to the voltage frequency converter.