JP2771191B2 - Control method of PWM converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a control method of a PWM converter, and is particularly suitable for continuously operating a system even at a momentary power failure.
The present invention relates to a method for controlling a PWM converter.

[Conventional technology]

The PWM converter is used as a DC power supply for an inverter for operating an AC motor at a variable speed, as described in Japanese Patent Application Laid-Open No. 61-244273. This method has a high power factor,
Moreover, since the electric and regenerative operations can be performed freely, the applicable range is wide. However, there is no mention of measures against overcurrent that occurs during a momentary power failure.

[Problems to be solved by the invention]

The above-mentioned prior art does not consider a method of suppressing an overcurrent generated at the time of recovery from an instantaneous power failure, and has a problem in continuously operating the system.

An object of the present invention is to prevent an overcurrent at the time of an instantaneous power failure and to safely continue operation.

[Means for Solving the Problems] To achieve the above object, in the control method of the PWM converter of the present invention, a pulse width modulation type converter for converting AC power to DC power, The capacitor connected to the output side, the current control circuit for controlling the current of the converter, and the detected value of the AC input side current of the converter or the detected value of the DC output side current of the converter has become a predetermined value or more. In this case, an overcurrent detection circuit that outputs an overcurrent detection signal, and, when the overcurrent detection signal is output from the overcurrent detection circuit, shuts off the gate of the converter and sets the output of the current control circuit to zero. It is like that.

[Action]

The overcurrent at the momentary power failure occurs as follows. That is, if an instantaneous power failure occurs during the reverse conversion of the PWM converter, the PWM operation continues in the PWM converter even after the instantaneous power failure, and the output voltage of the converter (regenerative AC voltage) is continuously induced on the AC power supply side. This voltage is controlled according to a PWM signal, which is also controlled according to a current command. Further, since this current command is formed from the regenerative AC voltage, the PWM converter is an AC oscillation source configured with a closed loop based on the current command and the regenerative AC voltage. A so-called self-excitation phenomenon occurs. "Thus, the regenerative AC voltage is induced by the self-excited phenomenon at the momentary power failure, but since the voltage is controlled according to the output value of the current control circuit (ACR), it is recovered at the momentary power failure recovery. A voltage difference occurs between the power supply line pressure and the regenerative AC voltage, which causes an overcurrent in the PWM converter.

Therefore, if an overcurrent occurs during recovery from a momentary power failure, the PW
By shutting off the gate of the M converter and resetting the output of the ACR, the ACR output disappears during the recovery from the momentary power failure, and the output voltage of the converter is controlled only by the power supply voltage detection signal added to the ACR output. There is no voltage difference in the output voltage, thus preventing overcurrent.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to FIG.

1 is a three-phase AC power supply, 2 is a three-phase transformer for insulating the three-phase AC power supply 1, 3 is a first PWM converter for converting a three-phase AC voltage to a DC voltage, and 4 is a three-phase transformer. Vessel 2 and the first P
Reactor connected between WM converter, 5 is the first PWM
6 is a smoothing capacitor for absorbing the pulsation of the output current of the converter 3, 6 is a second PWM converter for converting the DC voltage of the smoothing capacitor 5 into a three-phase variable voltage and a variable frequency AC, and 7 is An AC motor driven by a second PWM converter output (variable voltage, variable frequency). 8 is the first
A DC voltage command circuit for commanding the DC output voltage of the PWM converter, 9 a voltage detector for detecting the DC voltage of the smoothing capacitor 5, 10 amplifying the deviation between the DC voltage command signal and the output voltage of the voltage detector 9 A voltage deviation amplifier, 11 is a voltage detector for detecting the voltage of the three-phase AC power supply, and 12 is a voltage detector based on a signal corresponding to the voltage deviation from the voltage deviation amplifier 10 and a voltage detection signal from the transformer 11. An arithmetic circuit for generating a synchronized power supply current command pattern signal (sine wave signal),
13 is a current detector for detecting a power supply current, 14 is an amplifier for amplifying a difference between an output signal of the arithmetic circuit 12 and an output signal of the current detector 13 and outputting an AC three-phase voltage command of the first PWM converter 3. Current deviation amplifier. 15 is an adder for adding a voltage detection signal to the output of the current deviation amplifier 14, 16 is an oscillator for generating a triangular carrier signal, and 17 is a carrier signal and an adder 15.
A comparator 18 compares the output signals of the above and outputs a pulse width modulation signal (PWM signal). Reference numeral 18 amplifies the PWM signal output from the comparator 17, and outputs a transistor which is a switching element in the first PWM converter 3. This is a gate amplifier that controls the on / off of the device. 19 is a current detector for detecting a direct current on the output side of the first PWM converter 3, and 20 is an overcurrent for generating an output signal when the output signal of each of the current detectors 13 and 19 exceeds a predetermined value. The detector 21 is a mono-multi circuit that shuts off the output signal from the gate amplifier 18 for a predetermined time based on the output signal of the overcurrent detector 20 and further makes the output signal of the current deviation amplifier 14 zero.

The basic operation of this embodiment is as follows. As is well known, a first PWM converter for converting AC voltage to DC,
A second method for supplying a variable voltage, variable frequency alternating current to the motor
An AC variable speed system using a PWM converter is well known as a control method of an AC motor. In particular, the first PWM converter can control the power factor of the AC power supply 1 to 1.0,
Moreover, since the forward conversion and the inverse conversion can be freely performed, the second
Most suitable as power supply for PWM converter.

By the way, the AC motor 7 can perform the acceleration / deceleration operation by controlling the second PWM converter 6, but when the AC motor 7 is decelerated or stopped from the constant speed operation state, the AC motor 7 Power is fed back to converter 6. Since the returned power charges the smoothing capacitor 5, the terminal voltage of the smoothing capacitor 5 increases. For this reason, the rise of the capacitor voltage is returned to the AC power supply 1 by the operation of the first PWM converter 3. In this way, the power of the AC motor 7 is returned (regenerated) to the AC power supply 1,
When an instantaneous power failure occurs during this return (regeneration) operation, as described above, the first voltage is generated by the voltage difference and phase difference between the voltage generated by the self-excitation phenomenon and the AC voltage of the AC power supply 1 when the instantaneous power failure is recovered. Overcurrent occurs in the converter. According to the present invention, when the current exceeds a predetermined level, the first
By shutting off the gate of the PWM converter 3 and resetting the output signal of the current deviation amplifier 14 to zero output, it is possible to prevent an overcurrent during a momentary power failure and at the time of recovery. By resetting the output signal of the amplifier 14 and setting the output to zero, the output voltage of the converter is controlled only by the power supply voltage detection signal added to the output of the amplifier 14 at the time of recovery from a momentary power failure. There is no voltage difference in the converter output voltage,
Therefore, overcurrent at the time of recovery is prevented. After a predetermined time, the reset is released and the operation is continued. If the overcurrent flows again after the reset is released, the above operation is repeated, and the operation is continued after the occurrence of the overcurrent is stopped. Thus, even if an overcurrent occurs during an instantaneous power failure, the operation can be continued without stopping the system.

FIG. 2 shows another embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The difference from FIG. 1 lies in that the first PWM converter is applied to an induction motor capable of secondary excitation. Reference numeral 30 denotes a wound-type induction motor (hereinafter referred to as IM), 31 denotes a speed generator directly connected to IM1, 32 denotes a forward converter (diode rectifier) that converts the secondary voltage of the wound-type induction motor 30 to DC, 33 Is a secondary chopper circuit that controls the secondary current of IM1 by this on / off operation, 34 is a diode for preventing backflow, 35 is a speed command circuit, 36
Amplifies the deviation between the speed detector 31 signal and the speed command signal.
A speed deviation amplifier that issues a secondary current command of IM1, 37 is a current detector for detecting the output current of the forward converter 32, and 38 compares the secondary current command signal from the speed deviation amplifier 36 with the current detection signal. The current deviation amplifier 39 outputs an on / off signal of the secondary chopper 33, and a pulse amplifier 39 supplies an on / off control signal to the secondary chopper 33. The operation of the induction motor capable of secondary excitation is as follows. The secondary current of the wound induction motor 30 and the torque proportional thereto in proportion to the output signal of the speed deviation amplifier 36 are controlled by the operation of the current deviation amplifier 38 and the like.
The rotation speed of 30 is controlled according to the speed command. On the other hand, while the secondary chopper 33 is off, the direct current is charged in the smoothing capacitor 5 via the diode 34. At this time, the secondary power of the wound induction motor 30 is converted into DC power and the smoothing capacitor 5 is charged. For this reason, the voltage of the smoothing capacitor 5 rises, but the first
The secondary power is regenerated by the PWM converter 3 into an AC power supply. Even in this case, if an instantaneous power failure occurs during the inverse conversion operation of the first PWM converter 3, the above-described problem occurs. However, by applying the present invention, this can be prevented, and the same effect as described above can be obtained. Is obtained.

〔The invention's effect〕

According to the present invention, even at the time of an instantaneous power failure, it is possible to prevent overcurrent by shutting off the gate of the PWM converter and making the output signal of the current control circuit zero, and to continue the operation without stopping the system. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a control device of a PWM converter according to the present invention, and FIG. 2 is a diagram showing another embodiment of the present invention. 1 ... three-phase AC power supply, 2 ... three-phase transformer, 3 ... first
PWM converter, 4 ... Reactor, 5 ... Smoothing capacitor, 6 ... Second PWM converter, 7 ... AC motor, 9 ...
... voltage detector, 14 ... current deviation amplifier, 15 ... adder,
16 ... Oscillator, 17 ... Comparator, 18 ... Gate amplifier,
13,19: Current detector, 20: Overcurrent detector, 21: Mono-multi circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 7/00-7/40

Claims (1)

(57) [Claims] A pulse width modulation type converter for converting AC power into DC power, a capacitor connected to a DC output side of the converter, a current control circuit for controlling a current of the converter, An overcurrent detection circuit that outputs an overcurrent detection signal when a detection value of an AC input side current of the converter or a detection value of a DC output side current of the converter becomes a predetermined value or more; A control method for a PWM converter, comprising shutting off the gate of the converter and setting the output of the current control circuit to zero when an overcurrent detection signal is output from a circuit.