JP3824189B2 - PWM cycloconverter and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention directly connects each phase of the AC power supply and each phase on the output side with a bidirectional switch having a self-extinguishing capability, and performs PWM control of the AC power supply voltage in accordance with the output voltage command, so that any AC and DC The present invention relates to a PWM cycloconverter that outputs a voltage and a driving method thereof.
[0002]
[Prior art]
A first conventional PWM cycloconverter will be described with reference to FIG. In the figure, 1 is an AC power source, 2 is an AC line filter, 3 is a power supply voltage detection circuit group, 4 is a gate drive circuit, 5 is a commutation sequence switching circuit group, 6 is a controller, 8 is an AC motor, and 9 is a bidirectional switch. Modules 10 to 18 are bidirectional switches, and 19 is a power supply voltage comparison circuit.
When the controller 6 receives the output voltage command, it determines which bidirectional switch to fire while detecting the power supply voltage, and passes the PWM command to the commutation sequence switching circuit group 5. At this time, if the bidirectional switches 10 to 18 are ideally switched at the same time, current spikes and voltage spikes are not generated, but actually there are variations in the bidirectional switches and the like, and switching is not performed simultaneously. Therefore, the power supply voltage comparator 19 compares the magnitude relationships of the phase voltages, classifies them into a maximum voltage, an intermediate voltage, and a minimum voltage, and sends the information to the commutation sequence switching circuit group 5.
The commutation sequence switching circuit group 5 is commutation from a phase having a larger power supply voltage to a smaller phase than the PWM command and voltage comparison information (mode 1), or commutation from a phase having a smaller power supply voltage to a larger phase (mode 2). ) To generate a gate signal in the commutation sequence in each mode. The gate driver receives the gate signal and sends a signal isolated from the gate signal to the bidirectional switches 10 to 18 to drive the bidirectional switches 10 to 18. The commutation sequence in each mode is shown in FIG.
[0003]
Next, as a second conventional example, there is a cycloconverter described in Japanese Patent Publication No. 4-10312. This comprises: a first series circuit comprising a first semiconductor control element having an anode connected to the AC power supply and a first diode having an anode connected to the cathode of the first semiconductor control element; A second semiconductor control element connected to the AC power source and a second diode connected to the anode of the second semiconductor control element and a cathode connected to the first series circuit in a reverse direction. A circuit having a power receiving end connected to the cathode of the first diode of each phase, and a polarity reversal of the current of each phase flowing through the load by detecting the voltage across both diodes of each phase A detection unit that detects a voltage pulse that is sometimes generated and outputs a detection signal, and a switch that alternately switches the conduction of the two semiconductor control elements of each phase by the detection signal of each phase. It is obtained by a part.
[0004]
[Problems to be solved by the invention]
However, in the first conventional example, because of the detection accuracy of the voltage comparison circuit, time delay, etc., commutation failure is likely to occur particularly when the power supply voltage is switched from negative to positive. Similarly, when the power supply voltage has a distorted waveform, a commutation failure occurs.
Further, the second conventional example cannot be applied to a PWM cycloconverter that requires the direction of current flowing through the element.
Therefore, the present invention can be applied to a cycloconverter that does not fail in commutation even when the detection accuracy of the voltage comparison circuit, the time delay, or the power supply voltage has a distorted waveform, and further requires the direction of the current flowing through the element. An object is to provide a converter and a driving method thereof.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention directly connects each phase of an AC power supply and each phase on the output side by a bidirectional switch having a self-extinguishing capability, and the AC power supply voltage is PWMed according to an output voltage command. In a PWM cycloconverter that controls and outputs an arbitrary AC and DC voltage, the bidirectional switch has a configuration in which two unidirectional semiconductor switches are combined and each can be turned on and off independently, and the bidirectional switch The current direction detection circuit for determining the direction of the current flowing through the switch, the output of the current direction detection circuit, the PWM command, and another gate signal for driving the forward semiconductor switch in the same output phase are fetched, and these signals And a commutation sequence switching circuit for switching the firing order of the bidirectional switches so that a power supply short circuit and an output opening do not occur based on the logic state of Than it is.
By the above means, the direction of the current flowing through the switch is directly detected and the commutation sequence is switched, so that a stable PWM cycloconverter drive system without malfunction can be realized.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the present invention. In the figure, 1 is an AC power source, 2 is an AC line filter, 3 is a power supply voltage detection circuit, 4 is a gate drive circuit, 5 is a commutation sequence switching circuit group, 6 is a controller, 7 is a current direction detection circuit group, and 8 is an AC current. An electric motor, 9 is a bidirectional switch module, and 10 to 18 are bidirectional switches.
In the present embodiment, each phase of the AC power supply 1 and each phase on the output side are directly connected by bidirectional switches 10 to 18 having a self-extinguishing capability, and the AC power supply voltage is PWM controlled according to the output voltage command, PWM cycloconverter that outputs arbitrary AC and DC voltage, and unidirectional semiconductor switches Tr1 to Tr9 and diodes D1 to D9 connected reversely thereto and unidirectional semiconductor switches Tr1 ′ to Tr9 ′ and reverse connected thereto Bidirectional switches 10 to 18 having diodes D1 ′ to D9 ′ connected in series are provided. In this embodiment, the configuration of the bidirectional switch is as described above. However, as shown in FIG. 2A, two transistors are simply reversely connected, and a reverse current blocking diode is connected as shown in FIG. Alternatively, a transistor protection diode connected between an emitter and a collector as shown in FIG. 2C can be used.
[0007]
The bidirectional switches 10 to 18 shown in FIG. 1 are connected to a current direction detection circuit group 7 for determining the direction of the current flowing through the bidirectional switches 10 to 18, and the output of the current direction detection circuit group 7 and the PWM The other gate signal for driving the forward semiconductor switch in the same output phase as the command is taken in, and the current direction detection circuit group 7 and the PWM command and other gate signals for driving the forward semiconductor switch in the same output phase are fetched. A commutation sequence switching circuit 5 that switches the firing order of the bidirectional switches 10 to 18 depending on the state is provided.
The current direction detection circuit group 7 includes current direction detection circuits 21a to 21c as shown in FIG. 3, and the cathode sides of the first and second diodes 30 at both ends of the bidirectional switches 10 to 18. The anode side of the first and second diodes 30 is connected to the + side of the isolated DC power source B via resistors R1 and R2, and the anode of the first diode 30 and the second diode are connected to each other. The potential difference of 30 anodes is detected, and the direction of the current flowing through the bidirectional switches 10 to 18 is determined.
[0008]
3, which is a circuit block diagram per output phase, 20a, 20b, 20c,... Are commutation sequence switching circuits, 21a, 21b, 21c,... Are current direction detection circuits, 22a, 22b, 22c. ... Are gate drive circuits per switch, and are provided in the same number as the bidirectional switches 10, 11, 12,.
The current direction detection circuit 21 is connected to both ends T1, T1 ′ of the bidirectional switch 10 and the connection point E1 of the transistors Tr1, Tr1 ′ in the bidirectional switch. The output Z1 of the current direction detection circuit 21 is input to the commutation sequence switching circuit 20. Further, the commutation sequence switching circuit 20 also receives the PWM command C1 from the controller 6 and gate signals G1, G2, G3 of other switches inputted to the forward transistors Tr1, Tr2, Tr3 in the same output phase. Switch the flow sequence. The commutation sequence switching circuit 20 outputs the gate signals G1 and G1 ′ for driving the forward and reverse transistors Tr1 and Tr1 ′ in the same bidirectional switch to drive the bidirectional switch 10. The other bidirectional switches 11 and 12 in the same output phase have the same circuit configuration.
[0009]
Next, a necessary commutation sequence will be described with reference to FIG. When the current flows from the power supply voltage 1 to the AC motor 8, the sequence shown in FIG. 5A is selected. When the current flows from the AC motor 8 to the power supply voltage 1, the sequence shown in FIG. 5B is selected. . At this time, when the bidirectional switch 10 is turned on, the current direction of the other bidirectional switches 11 and 12 in the same output phase, and when the bidirectional switch 10 is turned off, the current direction of the bidirectional switch 10 to be turned off. It turns out that information on is needed.
Specifically, when current flows from the AC power source 1 to the AC motor 8 (FIG. 5A), first, Tr1 ′ is set to “OFF”. At this time, since the current flowing through the AC motor 8 flows through Tr1, the current is not interrupted. Next, Tr2 is set to “ON”. At this time, when the power supply voltage is V1> V2, a current flows through a solid loop through Tr1, and when V2> V1, a current flows through a broken loop through Tr2, and is commutated from Tr1 to Tr2. Next, Tr1 is turned “ON”. When V1> V2, the commutation from Tr1 to Tr2 occurs at this point. Finally, Tr2 ′ is set to “ON” to complete commutation.
Next, when current is flowing from the AC motor 8 to the AC power source 1 (FIG. 5B), first, Tr1 is set to “OFF”. At this time, since the current flowing through the AC motor 8 flows through Tr1 ′, the current is not interrupted. Next, Tr2 ′ is set to “OFF”. At this time, when the power supply voltage is V1 <V2, a current flows through a solid loop through Tr1 ′, and when V2 <V1, a current flows through a broken loop through Tr2 ′ and commutates from Tr1 to Tr2. To do. Next, Tr1 is set to “OFF”. When V1 <V2, commutation from Tr1 to Tr2 occurs at this point. Finally, Tr2 is set to “ON” to complete commutation.
By using the above commutation sequence, commutation can be performed without interrupting the current and without causing a power supply short circuit.
[0010]
Next, the current direction detection circuit 21 and the commutation sequence switching circuit 20 will be described with reference to FIG. 28 in the current direction detection circuit 21 is a photocoupler for insulating the control-side power supply from the main circuit, 29 is a comparator, 30 is a first and second diode, and 31 is an insulated power supply. The cathodes of the first and second diodes 30 are connected to both ends T1, T1 ′ of the bidirectional switch 10. The middle point of the insulated power supply 31 is connected to the connection point E1 of the bidirectional switch transistor. The anode sides of the first and second diodes 30 are connected to the + side of the insulated power supply 31 and the input of the comparator 29 through resistors. The output of the comparator 29 is connected to the cathode of the light emitting diode in the photocoupler 28. When the output of the comparator 29 is LO (low level), the transistor of the photocoupler 28 is in a conductive state and the output Z1 of the current direction detector 21 is LO.
In operation, when the bidirectional switch 10 is open, the anode potential of the first and second diodes 30 is fixed to the plus side potential of the insulated power supply 31, and the anode potential difference between the first and second diodes 30 is determined. Is zero. At this time, the output Z1 of the current direction detector 21 is HI (high level). When the bidirectional switch 10 is closed, the anode potentials of the first and second diodes 30 are fixed to the potentials of the terminals to which the respective cathodes are connected (the potentials at both ends T1 and T1 ′ of the bidirectional switch).
Since the polarity of the anode potential difference changes in the direction of current flow, the output Z1 of the current direction detector 21 becomes HI or LO, and the current direction can be detected. The output Z1 of the current direction detector 21 becomes LO when the current flows from the power supply voltage 1 to the AC motor 8, and conversely becomes HI when the current flows from the AC motor 8 to the power source side and when the bidirectional switch 10 is open. .
[0011]
Next, the commutation sequence switching circuit 20 will be described. In the commutation sequence switching circuit 20, 25 is a gate signal selection circuit, 26 is a mode switching circuit, and 27 is a delay signal generation circuit.
The mode switching circuit 26 receives the gate signals G1, G2, G3 of the forward transistors Tr1, Tr2, Tr3 of the bidirectional switches 10, 11, 12 in the same output phase, the current direction detection signal Z1, and the PWM command C1. . From the state of the gate signals G1, G2, G3 of the forward transistors Tr1, Tr2, Tr3 of the bidirectional switches 10, 11, 12 in the output same phase, the current direction of the bidirectional switches 10, 11, 12 in the output same phase is changed. to decide. When the PWM command C1 is HI, the current direction signal P selects the logical sum G of the gate signals G1, G2, G3 of the forward transistors Tr1, Tr2, Tr3 of the bidirectional switches 10, 11, 12 in the same output phase. When the PWM command C1 is LO, the current direction detection signal Z1 is selected.
Next, the PWM signal C1 is input to the delay signal generation circuit 27, and the first and second gate signals A and B are generated as outputs. The first gate signal A is delayed by 3ΔT with respect to the PWM command C1 at the time of rising, and is synchronized with the PWM command C1 at the time of falling. Further, the second gate signal B is delayed by ΔT with respect to the PWM command C1 at the time of rising, and delayed by 2ΔT at the time of falling. The gate signal selection circuit 25 receives the first and second gate signals A and B and the mode switching signal P, and receives the gate signal G1 of the forward direction transistor Tr1 and the gate signal G1 ′ of the reverse direction transistor Tr1 ′. Output. Depending on the mode switching signal P, the gate signal G1 of the forward direction transistor Tr1 and the gate signal G1 ′ of the reverse direction transistor Tr1 ′ are selected as the first gate signal A or the second gate signal B. To do.
As described above, the commutation sequence is determined. By using such a commutation sequence, it is possible to perform commutation without interrupting the current and without causing a power supply short circuit.
[0012]
【The invention's effect】
As described above, according to the present invention, since the direction of the current flowing in the bidirectional switch is directly detected and the commutation sequence is switched, a drive system using a stable PWM cycloconverter without malfunction can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing various examples of bidirectional switches.
FIG. 3 is a block diagram showing an embodiment of the present invention.
FIG. 4 is a circuit diagram showing an embodiment of the present invention.
FIG. 5 is an operation principle diagram showing a commutation sequence.
FIG. 6 is a block diagram showing a conventional example.
FIG. 7 is a diagram illustrating a conventional commutation sequence operation principle.
[Explanation of symbols]
1 AC power supply, 2 AC line filter, 3 power supply voltage detection circuit, 4 gate driver, 5 commutation sequence switching circuit group, 6 controller, 7 current direction detection circuit group, 8 AC motor, 9 bidirectional switch module, 10 to 18 Bidirectional switch, 19 Power supply voltage comparison circuit, 20 Commutation sequence switching circuit, 21 Current direction detection circuit, 22 Gate drive circuit per switch, 23 delay circuit (2ΔT), 24 delay circuit (ΔT), 25 Gate signal selection Circuit, 26 mode switching circuit, 27 delay signal generation circuit, 28 photocoupler, 29 comparator, 30 first and second diode, 31 isolated power supply, Tr1 to Tr3 forward transistor, Tr1 ′ to Tr3 ′ reverse transistor, T1 -T3 Bidirectional switch power supply terminal, T1 'to T3' Bidirectional switch load side Terminals, E1 to E3 forward and reverse transistor connection points, P mode switching signals, Z1 to Z3 current direction detection signals, G1 to G3 forward transistor gate signals, G1 ′ to G3 ′ reverse transistor gate signals, C1 to C3 PWM command, G OR of gate signals of forward transistors in the same output phase, A first gate signal, B second gate signal

Claims (2)

Each phase of the AC power supply and each phase on the output side are directly connected by a bi-directional switch with self-extinguishing capability, and the AC power supply voltage is PWM controlled according to the output voltage command to output any AC and DC voltage In PWM cycloconverter,
The bidirectional switch has a configuration in which two unidirectional semiconductor switches are combined, and each can be independently turned on / off,
A current direction detection circuit for determining a direction of a current flowing through the bidirectional switch;
The output of the current direction detection circuit, the PWM command, and other gate signals for driving the forward direction semiconductor switch in the same output phase are taken in, and based on the logical state of these signals, the power supply short circuit and the output release do not occur. And a commutation sequence switching circuit for switching the firing order of the bidirectional switches. Each phase of the AC power supply and each phase on the output side are directly connected by a bi-directional switch with self-extinguishing capability, and the AC power supply voltage is PWM controlled according to the output voltage command to output any AC and DC voltage In the driving method of the PWM cycloconverter,
The PWM cycloconverter includes two unidirectional semiconductor switches and a bidirectional switch configured to be turned on and off independently, and a current direction detection circuit that determines the direction of current flowing through the bidirectional switch,
Capture other gate signals that drive the forward direction semiconductor switch in the same output phase as the output of the current direction detection circuit and the PWM command, and based on the logical state of these signals, power supply short circuit and output opening do not occur, A method of driving a PWM cycloconverter, wherein the firing order of the bidirectional switches is switched.

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