JP3864793B2 - PWM cycloconverter and PWM cycloconverter protection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a protection method for preventing the occurrence of a surge voltage higher than a motor induced voltage when an abnormal state occurs during driving of a PWM cycloconverter, and safely stopping the PWM cycloconverter.
[0002]
[Prior art]
In the motor drive inverter, if any abnormal condition that requires the inverter operation to be urgently stopped, such as overcurrent, overvoltage, instantaneous power failure, or emergency stop command from the outside, even if the semiconductor switch is turned OFF at the same time, A diode connected in parallel with the semiconductor switch causes the current flowing in the motor to be three-phase full-wave rectified and flows into a DC link capacitor such as a smoothing capacitor. As a result, the energy present in the inductance part of the motor is stored in the DC link capacitor, and no voltage higher than the motor induced voltage is generated.
However, the PWM 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. As a result, there is no energy storage part, and a surge voltage is generated by the energy present in the inductance part of the motor, and in some cases, an overvoltage breakdown occurs.
As the overvoltage suppressing method, when the DC clamp type snubber circuit shown in FIG. 1 is used, the overvoltage can be suppressed by using a snubber capacitor having a large capacitance.
As another protection method, a method as disclosed in JP 2000-139076 is also conceivable.
[0003]
[Problems to be solved by the invention]
However, when the above-described snubber capacitor is used, it is necessary to increase the capacitance in proportion to the increase in the inductance value of the motor. In order to realize this, it is necessary to use a short-life component such as an electrolytic capacitor, and the great advantage of the PWM cycloconverter is lost.
In general, the inductance value of the motor to be used is often unknown until energization. For this reason, when determining the capacitance of the snubber capacitor, it is necessary to consider the maximum possible inductance, and thus further increase in capacitance must be considered.
In the case of using a method such as Japanese Patent Laid-Open No. 2000-139076, it is a condition that an input power source is established. When an instantaneous power failure or power interruption occurs, the surge voltage cannot be suppressed.
[0004]
[Means for Solving the Problems]
In the present invention, when an abnormal state such as an overcurrent occurs when the PWM cycloconverter is driven, all the output phases of the PWM cycloconverter are first connected to one input phase of the AC power supply, and the output is short-circuited. In this 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 braking torque. Therefore, when a short circuit is first made, all bidirectional semiconductor switches connected to the output phase are shut off at the moment when the output current for each phase becomes zero, in other words, at the time of zero crossing. As a result, the bidirectional semiconductor switch is shut off in the absence of the inductance energy of the motor, and no voltage higher than the motor induced voltage is generated.
In addition, since the short-circuit current is a three-phase AC current, if the current is crossed sequentially from the bidirectional semiconductor switch connected to the output phase where the zero crossing came first, the worst-case There is a possibility that the maximum value of the sum of the line voltage of the three-phase AC power supply and the induced voltage between the motor lines is applied. To avoid this, one input phase of the three-phase AC power supply connected for output short-circuiting is sequentially switched to an input phase that can minimize the voltage applied between both terminals of the shut-off bidirectional semiconductor switch. If this is the case, the previous maximum voltage application can be prevented even when one phase is interrupted.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific examples.
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 carrying out the present invention. FIG. 3 shows a current waveform and a switching pattern for carrying out the present invention. FIG. 4 shows voltage waveforms and switching patterns for carrying out the present invention.
First, with reference to FIG. 1, the PWM cycloconverter directly connects the three-phase AC power source 1 and the three-phase output as the input to the motor 5 using a total of nine bidirectional switch groups 4, and the AC power source voltage is set to DC. Any frequency / voltage can be output without converting to. However, a pulsed current flows through the input stage of the bidirectional switch group 4 as each bidirectional switch is turned on / off. For this purpose, a filter is configured 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 bidirectional current switch is absorbed by the snubber capacitor 6 by absorbing the DC current. To protect.
[0006]
In such a circuit configuration, the PWM cycloconverter is operated, but during that operation, some abnormal condition such as overcurrent, overvoltage, instantaneous power failure, or emergency stop command from the outside needs to be stopped urgently. In such a case, a protective operation for safely stopping the apparatus is required. First, a method of completely blocking the bidirectional switch group 4 (hereinafter referred to as a base block) is conceivable. At this time, if a current flows through the motor 5, energy proportional to the square of the current is stored in the inductance part of the motor 5. This energy is absorbed by the snubber capacitor 6 via 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 between the terminals of the snubber capacitor 6 is remarkably increased, which may cause the worst overvoltage breakdown.
As a countermeasure for this, it is conceivable to increase the capacitance of the snubber capacitor 6. However, to employ a DC capacitor having a large capacitance, an electrolytic capacitor must be used. This detracts from the great advantage of the PWM cycloconverter, which is small space and long life.
[0007]
Further, a method of regenerating current in an AC power source using a method such as that disclosed in JP 2000-139076 is also conceivable. However, this method is based on the premise that the AC power supply side is normal, and when the AC power supply is cut off or an instantaneous power failure occurs, there is no path for current to flow. As a result, the current is supplied to the DC clamp type snubber circuit 13 in the same manner as described above. Flows in, causing overvoltage breakdown.
[0008]
As a means for solving such a problem, in the present invention, the output current signals 9U, 9V, and 9W obtained from the output current detectors 10U, 10V, and 10W used for normal current control are used by using a comparator circuit as shown in FIG. Output current direction signals 12U, 12V, and 12W are generated by converting the positive and negative currents into digital signals. At the rising edge 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 the phase are shut off by the edge of the output current direction signal (for example, all of S1, S2 and S3 in the bidirectional switch group 4 are shut off). If this is done, it will be cut off when the energy stored in the inductance part of the motor is small, so the snubber capacitor 6 needs to be charged very little.
[0009]
However, in actual operation, when an abnormality occurs, it is necessary to immediately perform a protective operation. Therefore, in the present invention, when an abnormality occurs, first, all output terminals of the motor 5 are short-circuited using the bidirectional switch group 4, and the input part (three-phase AC power source 1 side) and the output part (motor) of the PWM cycloconverter. 5 side). 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 shut off at the zero crossing of each phase output current, thereby suppressing the voltage increase between the terminals of the snubber capacitor 6. Can be safely shut down. This operation will be described with reference to FIG.
Assume that an abnormal signal is generated from a state in which the motor 5 is driven by performing normal switching.
When the abnormal signal in FIG. 3 becomes High, first, the bidirectional switches S1, S4, S7 connected to the R phase in the bidirectional switch group 4 are always turned on, and the other bidirectional switches are turned off. . As a result, all output terminals of the motor 5 are short-circuited. In this embodiment, a short circuit of all output terminals of the motor 5 is realized by turning on both of the two unidirectional semiconductor switches constituting the bidirectional switch, but this is detected by the output current direction signals 12U, 12V, 12W. A similar effect can be realized by turning on only one-way semiconductor switching corresponding to the direction of the output current.
[0010]
Next, when the output is short-circuited, a short-circuit current flows for each output phase due to the motor-induced voltage. The zero cross of this current is detected. In FIG. 3, first, the U-phase current 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 alternating current from that moment. Therefore, S4 and S7 are simultaneously turned OFF at the moment when the remaining two-phase current becomes zero. As a result, the PWM cycloconverter can be safely stopped without overcharging the snubber capacitor 6.
[0011]
When this blocking method is used, there is a problem that is a concern. When 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-off bidirectional switch. There is sex. Therefore, when the output short circuit is in the initial state, the one-phase circuit is cut off by creating a short circuit with the input phase that can reduce the voltage applied to both ends of the bidirectional switch of the three-phase AC power source 1. Even in this case, the voltage applied to both ends of the bidirectional switch related to the phase can be kept small.
As the first method, when an abnormal state occurs, an output short circuit state is created by connecting to an intermediate voltage phase of the phase voltage of the three-phase AC power source 1. In this case, by setting the input phase of the short-circuited three-phase AC power supply 1 as an intermediate voltage phase, the voltage applied to both ends of the blocked bidirectional switch, that is, the line voltage of the three-phase AC power supply and the motor line With respect to the sum of the induced voltages, the line voltage of the three-phase AC power supply can be reduced to keep the applied voltage small.
This operation will be further described with reference to FIG.
In the switching example (2) in FIG. 4, the intermediate voltage phase is changed from S → R → T → S → R → T. In this case, the bidirectional switch to be short-circuited also changes as S2, S5, S8, S1, S4, S7, S3, S6, S9, S2, S5, S8, S1, S4, S7, S3, S6, S9. As a result, the input phase in which the output is always short-circuited is the intermediate voltage phase of the input voltage. The voltage applied to both ends of each bidirectional switch can be kept small.
As a second method, the voltage between the output terminals of the PWM cycloconverter is first measured at the moment when one phase is interrupted. If the output terminal voltage of the interrupted phase is larger than the other phases, the three-phase AC power supply An output short circuit is created in the phase with a small input phase voltage, and if the output terminal voltage of the shut-off phase is small compared to the other phases, an output short circuit is created in the phase with a large input phase voltage, which is shut off. In addition, the voltage applied to both ends of the bidirectional switch can be kept small.
In addition, after one phase is shut off, the voltage between the output terminals of the PWM cycloconverter is continuously measured, and the input phase of the three-phase AC power supply that creates a short circuit is switched to the optimal input phase as described above. The voltage applied to both ends of the bidirectional switch thus made can be kept small.
[0012]
【The invention's effect】
As described above, by using the present invention, a snubber capacitor having a small capacitance can be used as a DC clamp type snubber circuit even if an abnormal state such as an overcurrent occurs when the PWM cycloconverter is driven. Surge voltage generation when the bidirectional semiconductor switch is shut off can be suppressed, and the voltage applied to both ends of the bidirectional semiconductor switch during shutdown can be reduced. Therefore, the operation can be safely stopped without damaging the device due to overvoltage etc. There is an effect that can be done.
[Brief description of the drawings]
1 shows a system configuration of a PWM cycloconverter for carrying out the present invention. FIG. 2 shows a current direction detection circuit for carrying out the present invention. FIG. 3 implements the present invention. FIG. 4 shows a voltage waveform and a switching pattern for carrying out the present invention. [Description 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 capacitor 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

Claims (8)

Two unidirectional semiconductor switches that can be energized in only one direction are connected in parallel with each phase of the AC power supply and each phase output of the power converter with M (M is 2 or more) phase output. In addition, each unidirectional semiconductor switch is directly connected by a bidirectional semiconductor switch configured to be able to be turned on / off independently, and each bidirectional semiconductor switch is controlled to be turned on / off in accordance with an output voltage command to output an arbitrary voltage . In the PWM cycloconverter that is the power converter,
When an abnormal state occurs, the bidirectional semiconductor switch is used to connect all phases of the output of the PWM cycloconverter to a phase in which the phase voltage value of the AC power supply is in the middle,
A method of protecting a PWM cycloconverter, characterized in that, in the short-circuit state, the short-circuit state is switched to a short-circuit state in the phase in synchronization with the phase that is intermediate between the phase voltages of the AC power supply being sequentially switched. . Two unidirectional semiconductor switches that can be energized in only one direction are connected in parallel with each phase of the AC power supply and each phase output of the power converter with M (M is 2 or more) phase output. In addition, each unidirectional semiconductor switch is directly connected by a bidirectional semiconductor switch configured to be able to be turned on / off independently, and each bidirectional semiconductor switch is controlled to be turned on / off in accordance with an output voltage command to output an arbitrary voltage. In the PWM cycloconverter that is the power converter,
When an abnormal state occurs, the bidirectional semiconductor switch is used to connect all phases of the output of the PWM cycloconverter to a phase in which the phase voltage value of the AC power supply is in the short-circuit state, and the short-circuit state The PWM cycloconverter is characterized in that the short circuit state is switched to the short circuit state in the phase in synchronization with the phase that is intermediate between the phase voltage values of the AC power supply being sequentially switched. (The M 2 or more) phases and M of the ac power source and each phase output of phase output of the power converter, two parallel-connected in a direction unidirectional semiconductor switches which can be energized in one direction only is possible bidirectional energization And each unidirectional semiconductor switch is directly connected by a bidirectional semiconductor switch configured to be able to be turned on / off independently, and each bidirectional semiconductor switch is controlled to be turned on / off in response to an output voltage command to output an arbitrary voltage. In the PWM cycloconverter that is the power converter,
When an abnormal state occurs, all the bidirectional semiconductor switches connected to any one phase of the AC power supply are turned on,
Detect zero crossing of output current for each output phase,
PWM cycloconverter protection method, characterized by interrupting said bidirectional semiconductor switch connected to an output phase of detecting the zero crossing. The method of protecting a PWM cycloconverter according to claim 3,
When an abnormal state occurs, only the unidirectional semiconductor switch on the side corresponding to the direction of the output current among the bidirectional semiconductor switches connected to any one phase of the AC power supply is turned on,
Detect zero crossing of output current for each output phase,
A method for protecting a PWM cycloconverter , comprising: cutting off the one-way semiconductor switch connected to an output phase in which a zero cross is detected . Blocking the bidirectional semiconductor switch connected to an output phase of detecting the zero Rokurosu, and inter-terminal voltage generated between the output terminal and the other output terminal of the output phase is interrupted at the beginning of the PWM cycloconverter Detect
As one phase of the AC power supply that short-circuits the output phase that is not cut off by the bidirectional semiconductor switch, the voltage applied between both terminals of the cut-off bidirectional semiconductor switch can be reduced. 4. The method of protecting a PWM cycloconverter according to claim 3 , wherein the phases are selected and connected.   In synchronization with the switching of the phase that can reduce the voltage applied between the two terminals of the blocked bidirectional semiconductor switch, the output phase of the AC power supply is short-circuited by the bidirectional semiconductor switch. 6. The method of protecting a PWM cycloconverter according to claim 5, wherein the connection is switched to a phase that can reduce a voltage applied between both terminals of the blocked bidirectional semiconductor switch as a phase. Two unidirectional semiconductor switches that can be energized in only one direction are connected in parallel with each phase of the AC power supply and each phase output of the power converter with M (M is 2 or more) phase output. In addition, each unidirectional semiconductor switch is directly connected by a bidirectional semiconductor switch configured to be able to be turned on / off independently, and each bidirectional semiconductor switch is controlled to be turned on / off in accordance with an output voltage command to output an arbitrary voltage. In the PWM cycloconverter that is the power converter,
When an abnormal condition occurs, all the bidirectional semiconductor switches connected to any one phase of the AC power supply are turned on, and the output current is detected by detecting the zero cross of the output current for each output phase. A PWM cycloconverter characterized in that the bidirectional semiconductor switch connected to a phase is cut off. The PWM cycloconverter according to claim 7,
When an abnormal state occurs, only the unidirectional semiconductor switch on the side corresponding to the direction of the output current among the bidirectional semiconductor switches connected to any one phase of the AC power supply is turned on, and each output phase A PWM cycloconverter characterized by detecting a zero crossing of the output current and shutting off the one-way semiconductor switch connected to the output phase where the zero crossing is detected.

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