JP2003230275A - Protection method for pwm cycloconverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection method for a PWM cycloconverter capable of suppressing a surge voltage generated in blocking the PWM cycloconverter, reducing the capacitance of a surge-absorbing capacitor and reducing applied voltages at both ends of a blocked two-way switch. <P>SOLUTION: When an abnormality occurs, a total output terminal of a motor 5 is connected to one arbitrary phase of a three-phase AC power supply 1 by a two-way switching group 4, to put the motor 5 in a state of an output being short-circuited, and an input part and an output part of the PWM cycloconverter are separated from each other. A short-circuited current is then made to flow to each output phase by an induced voltage of the motor 5. By blocking the two-way switch of a corresponding phase at a zero cross of each short-circuited current, a rise in voltage between terminals of a snubbering capacitor 6 is restrained, to enable the PWM cycloconverter to safely be stopped. Furthermore, with the one arbitrary phase of the three-phase AC power supply 1, which connects the total output terminal of the motor 5, as an intermediate voltage phase, the applied voltages at both the ends of the blocked two-way switch are reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection method for preventing a surge voltage higher than a motor induced voltage from being generated and safely stopping a PWM cycloconverter when an abnormal state occurs while driving a PWM cycloconverter. It is about.

[0002]

2. Description of the Related Art In a motor drive inverter,
If an abnormal condition that requires an emergency stop of inverter operation, such as overcurrent, overvoltage, momentary power failure, or external emergency stop command, occurs, even if the semiconductor switches are turned off at the same time, they are connected in parallel with the semiconductor switches. By the diode, the current flowing in the motor is three-phase full-wave rectified and flows into the DC link capacitor such as the smoothing capacitor. As a result, the energy existing in the inductance part of the motor is stored in the DC link capacitor, and a voltage higher than the motor induced voltage is not generated. However P
The WM cycloconverter is an AC-AC direct power converter that directly converts a three-phase AC power supply voltage into an arbitrary voltage / frequency, and therefore does not have a DC link capacitor in its circuit configuration. This eliminates the energy store,
Energy existing in the inductance part of the motor causes a surge voltage, which may cause overvoltage breakdown. As this overvoltage suppressing method, D shown in FIG.
When the C-clamp type snubber circuit is used, it is possible to suppress overvoltage by using a snubber capacitor having a large capacitance. Further, as another protection method, a method such as that disclosed in Japanese Patent Laid-Open No. 2000-139076 can be considered.

[0003]

However, when the above snubber capacitor is used, when the inductance value of the motor increases, it is necessary to increase the capacitance in proportion to it. In order to realize this, it is necessary to use a short-life component such as an electrolytic capacitor, which impairs the great advantage of the PWM cycloconverter. In general, the inductance value of the motor used is often unknown until it is energized. Therefore, when determining the capacitance of the snubber capacitor, it is necessary to consider the maximum inductance that can be assumed, and it is necessary to consider further increase of the capacitance. JP 20
When a method such as 00-139076 is used, the condition is that the input power supply is established, and if an instantaneous power failure or power interruption occurs, the surge voltage cannot be suppressed.

[0004]

According to the present invention, when an abnormal state such as an overcurrent occurs during driving of a PWM cycloconverter, first, all output phases of the PWM cycloconverter are connected to one input phase of an AC power supply. The output and short-circuit the output. In that case, a current flows due to the induced voltage of the motor, but this current is determined only by the induced voltage of the motor and the internal impedance of the motor. However, this current causes the motor to generate a braking torque. Therefore, when a short circuit occurs, first, at the moment when the output current for each phase becomes zero, in other words, at the time of zero crossing, all the bidirectional semiconductor switches connected to that output phase are shut off. As a result, the bidirectional semiconductor switch is cut off in the absence of the inductance energy of the motor, and a voltage higher than the motor induced voltage is not generated. Also, since the short-circuit current is a three-phase alternating current, when the zero crossing of the current is sequentially cut off from the bidirectional semiconductor switch connected to the output phase that came first,
In the worst case, the maximum value of the sum of the line voltage of the three-phase AC power supply and the motor line induced voltage may be applied to both ends of the interrupted phase switch. In order to avoid this, one input phase of the three-phase AC power supply connected for output short circuit is sequentially switched to the input phase which can minimize the voltage applied between both terminals of the interrupted bidirectional semiconductor switch. If it is possible, even if one phase is cut off, the previous maximum voltage application can be prevented.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific examples. FIG. 1 is a schematic diagram of a P for implementing the present invention.
1 shows a system configuration of a WM cycloconverter. FIG. 2 shows a current direction detection circuit for implementing the present invention. FIG. 3 shows current waveforms and switching patterns for carrying out the present invention. FIG. 4 shows voltage waveforms and switching patterns for implementing the present invention. First, referring to FIG. 1, the PWM cycloconverter directly connects the three-phase AC power supply 1 and the three-phase output that is an input to the motor 5 by using a total of nine bidirectional switch groups 4, and changes the AC power supply voltage to a direct current. It is possible to output an arbitrary frequency and voltage without converting to. However, in the input stage of the bidirectional switch group 4,
A pulsed current flows with the on / off operation of each bidirectional switch. Therefore, a filter is configured by using the three-phase AC reactor 2 and the three-phase AC capacitor 3. Further, as a protection circuit for the bidirectional switch group, the snubber diode group 7 and the snubber diode group 8 constitute a DC clamp type snubber circuit 13, and the DC current is absorbed by the snubber capacitor 6 to thereby create the bidirectional switch group. Protect.

In such a circuit configuration, the PWM cycloconverter is operated, and during the operation, overcurrent,
When an abnormal condition that requires an emergency stop of the inverter operation, such as an overvoltage, a momentary power failure, or an external emergency stop command, occurs, a protective operation is required to safely stop the device. First, a method that can be considered is a method of completely shutting off the bidirectional switch group 4 (hereinafter referred to as a base block). At this time, if a current is flowing through the motor 5, energy proportional to the square of the current is stored in the inductance portion of the motor 5. This energy is absorbed by the snubber capacitor 6 through the snubber diode group 7 when the bidirectional switch is cut off, that is, when the base block is performed. At this time, if the inductance of the motor 5 is large, or if the flowing current is large, the voltage across the terminals of the snubber capacitor 6 may significantly increase, possibly causing overvoltage breakdown. As a countermeasure against this, increasing the capacitance of the snubber capacitor 6 can be considered. However, to adopt a DC capacitor having a large capacitance, an electrolytic capacitor must be used. This impairs the great advantages of the PWM cycloconverter, such as small space and long life.

A method of regenerating an electric current in an AC power supply using a method such as that disclosed in Japanese Patent Laid-Open No. 2000-139076 is also conceivable. However, this method is based on the assumption that the AC power supply side is normal, and in the event of AC power supply interruption or momentary power failure, there is no path for current flow, and as a result, the DC clamp snubber circuit 13 receives current Flows in, causing overvoltage breakdown.

As a means for solving such a problem, in the present invention, the output current detector 10 used for normal current control is used.
Output current signals 9U, 9 obtained from U, 10V, 10W
Output current direction signal 12 in which the positive and negative of the current are converted into digital signals by using the comparator circuit as shown in FIG.
Create U, 12V, 12W. At the rising or falling edge of this signal, the output current is almost zero. Therefore, when shutting off the bidirectional switch, all the bidirectional switches connected to that phase are shut off by the edge of this output current direction signal (for example, all of S1, S2, and S3 in the bidirectional switch group 4 are shut off). If so, the energy is stored when the energy stored in the inductance part of the motor is small, so that the snubber capacitor 6 can be charged very little.

However, in the actual operation, when an abnormality occurs, it is necessary to immediately start the protection operation. Therefore, in the present invention, when an abnormality occurs, first, all output terminals of the motor 5 are short-circuited by using the bidirectional switch group 4,
Input section of PWM cycloconverter (3-phase AC power supply 1
Side) and the output part (motor 5 side) are separated. Then, a short-circuit current flows for each output phase due to the induced voltage of the motor 5, and the bidirectional switch of each phase is cut off at the zero-cross of the output current of each phase, while suppressing the voltage rise between the terminals of the snubber capacitor 6. Can be safely shut down. This operation will be described with reference to FIG. It is assumed that an abnormal signal is generated while the motor 5 is being driven by performing normal switching. When the abnormal signal in FIG. 3 becomes High, first, R of the bidirectional switch group 4
The bidirectional switches S1, S4, S7 connected to the phase are always turned on, and the other bidirectional switches are turned off. As a result, all the output terminals of the motor 5 are short-circuited. In this embodiment, the short circuit of all the output terminals of the motor 5 is realized by turning on both of the two unidirectional semiconductor switches forming the bidirectional switch.
The same effect can be realized by turning on only one-way semiconductor switching corresponding to the direction of the output current detected by U, 12V, and 12W.

Next, due to the output short circuit, a short circuit current flows for each output phase due to the motor induced voltage. The zero cross of this current is detected, but in FIG. 3, the current of the U phase first changes from Low to High, and the zero cross is detected. At this moment, the bidirectional switch S1 is turned off. Then, the V-phase and W-phase currents become single-phase AC currents from that moment. Therefore, at the moment when the remaining two phase currents become zero, S4 and S7 are turned off at the same time. As a result, the PWM cycloconverter can be safely stopped without overcharging the snubber capacitor 6.

There are also some problems of concern when using this shutoff method. If only one phase is cut off at the first zero cross, the sum of the line voltage of the three-phase AC power supply 1 and the line induced voltage of the motor 5 is applied to both ends of the cut bidirectional switch, which may result in overvoltage. There is a nature. Therefore, when the output is short-circuited in the initial state, a short-circuit state is created in the input phase that can reduce the voltage applied to both ends of the shut-off bidirectional switch in the three-phase AC power supply 1 to shut off one-phase. Even in such a case, the voltage applied to both ends of the bidirectional switch according to the phase can be suppressed to be small. As the first method, when an abnormal state occurs, an output short-circuit state is created by connecting to the intermediate voltage phase of the phase voltage of the three-phase AC power supply 1. In this case, by setting the input phase of the three-phase AC power supply 1 to be short-circuited to be the intermediate voltage phase, the voltage applied across the interrupted bidirectional switch, that is, the line voltage of the three-phase AC power supply and the motor line Regarding the sum of induced voltages, 3
It is possible to reduce the line voltage of the phase alternating current power supply and suppress the applied voltage to a small value. This operation is further illustrated in FIG.
Described in. In the switching example (2) in FIG. 4, the intermediate voltage phase changes in the order of S → R → T → S → R → T. In that case, the bidirectional switch to be short-circuited is also S2.
・ S5 ・ S8 → S1 ・ S4 ・ S7 → S3 ・ S6 ・ S9 →
S2 ・ S5 ・ S8 → S1 ・ S4 ・ S7 → S3 ・ S6 ・ S
Change to 9. As a result, the input phase in which the output is always short-circuited becomes the intermediate voltage phase of the input voltage, so S2 is turned off at the zero crossing of the U-phase current, and S1, S2, and S3 are all turned off.
Even if it becomes the FF, it is possible to keep the voltage applied to both ends of each bidirectional switch of S1, S2 and S3 small. As the second method, first, the voltage between the output terminals of the PWM cycloconverter is measured at the moment when one phase is interrupted, and if the output terminal voltage of the interrupted phase is larger than that of the other phase, the three-phase AC power supply If the output terminal voltage of the interrupted phase is smaller than that of the other phases, the output short circuit condition is created in the phase with the smaller input phase voltage, and the output short circuit condition is created in the phase with the higher input phase voltage. In addition, the voltage applied to both ends of the bidirectional switch can be reduced. In addition, by continuously measuring the voltage between the output terminals of the PWM cycloconverter after shutting off one phase and switching the input phase of the three-phase AC power supply that creates a short-circuited state to the optimum input phase described above, It is possible to keep the voltage applied across the two-way switch small.

[0012]

As described above, by using the present invention, a snubber capacitor having a small capacitance can be used as a DC clamp snubber circuit even if an abnormal state such as an overcurrent occurs during driving of a PWM cycloconverter. It can be used and can suppress the generation of surge voltage when shutting off the bidirectional semiconductor switch, and can reduce the voltage applied to both ends of the bidirectional semiconductor switch during shutoff, and thus damage the device due to overvoltage. There is an effect that the operation can be stopped safely.

[Brief description of drawings]

FIG. 1 shows a system configuration of a PWM cycloconverter for carrying out the present invention.

FIG. 2 shows a current direction detection circuit for implementing the present invention.

FIG. 3 shows current waveforms and switching patterns for implementing the present invention.

FIG. 4 shows voltage waveforms and switching patterns for implementing the present invention.

[Explanation of symbols]

1 Three-phase AC power supply 2 Three-phase AC reactor 3 Three-phase AC capacitor 4 bidirectional switch group 5 motor 6 Snubber capacitors 7 Snubber diode group 1 8 Snubber diode group 2 9U output current signal 1 9V output current signal 2 9W output current signal 3 10U, 10V, 10W output current detector 11U Comparator 1 11V comparator 2 11W comparator 3 12U output current direction signal 1 12V output current direction signal 2 12W output current direction signal 3 13 DC clamp type snubber circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Keisuke Sonoda             2-1, Kurosaki Shiroishi, Hachiman Nishi-ku, Kitakyushu City, Fukuoka Prefecture               Yasukawa Electric Co., Ltd. F term (reference) 5H750 AA10 BA01 BA06 BB04 BB12                       CC01 CC02 CC14 DD05 DD14                       DD18 EE04 FF02 FF05 GG02                       GG04 GG14 GG17

Claims (6)

[Claims] 1. A unidirectional semiconductor switch in which each phase of an AC power source and each phase output of an M-phase (M is 2 or more) output power converter can be energized in only one direction is bidirectionally energized. Two bidirectional semiconductor switches are connected in parallel and are directly connected by bidirectional semiconductor switches configured so that each of the unidirectional semiconductor switches can be turned on and off independently, and each bidirectional semiconductor switch is controlled to be turned on and off according to an output voltage command. In the PWM cycloconverter that is the power converter that outputs the AC and DC voltages, when an abnormal state occurs, the bidirectional semiconductor switch is used to output all the phases of the PWM cycloconverter to any of the AC power supplies. A method for protecting a PWM cycloconverter, which is characterized in that the PWM cycloconverter is connected to the first phase to be in a short-circuited state. 2. When an abnormal state occurs, all of the output phases of the PWM cycloconverter are connected to the phase in which the phase voltage value of the AC power supply is in the intermediate state by using the bidirectional semiconductor switch to make a short-circuit state. The method for protecting a PWM cycloconverter according to claim 1, wherein: 3. In the short-circuited state, the middle of the phase voltage value of the AC power supply is synchronized with the sequential switching,
The method for protecting a PWM cycloconverter according to claim 2, wherein the short-circuit state is switched to a short-circuit state in the phase. 4. In the short circuit state, a zero cross of the output current is detected for each output phase of the PWM cycloconverter, and the bidirectional semiconductor switch connected to the output phase where the zero cross is detected is cut off. The method for protecting the PWM cycloconverter according to claim 1 to claim 3. 5. A zero cross of the output current is detected for each output phase of the PWM cycloconverter in the short-circuited state, and the bidirectional semiconductor switch connected to the output phase in which the zero cross is detected is cut off, and In the beginning of the PWM cycloconverter, the inter-terminal voltage generated between the output terminal related to the interrupted output phase and another output terminal is detected, and the uninterrupted output phase is short-circuited and connected by the bidirectional semiconductor switch. 2. The PWM according to claim 1, wherein as the one phase of the power supply, one phase of the AC power supply that can reduce the voltage applied between both terminals of the cut off bidirectional semiconductor switch is selected and connected. Cycloconverter protection method. 6. The non-interrupted output phase is short-circuited by the bidirectional semiconductor switch in synchronism with switching of a phase capable of reducing a voltage applied between both terminals of the interrupted bidirectional semiconductor switch. 6. The protection of the PWM cycloconverter according to claim 5, wherein, as one phase of the AC power supply, the connection is switched to a phase in which the voltage applied between both terminals of the interrupted bidirectional semiconductor switch can be reduced. Method.