JPH1198840A - Pwm cyclo-converter and its drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cyclo-converter which is free of mis-commutation in the case that detection precision and time delay of a voltage comparison circuit, or waveform distortion in a power source voltage are present. SOLUTION: In this converter, each phase of an AC power source 1 is connected directly with each phase of the output side, by using bilateral switches 10-18 having self arc-extinguishing capability, an AC power source voltage is PWM-controlled in accordance with an output voltage command, and an arbitrary AC voltage and DC voltage are outputted. Each of the bilateral switches 10-18 is constituted by combining two single-direction semiconductor switches, and can be turned on and off independently of each other. A current direction detecting circuit 7 discriminates the direction of currents flowing in the bilateral switches 10-18. A commutation sequence switching circuit 5 changes over the arc-extinguishing sequence of the switches 10-18, in such a manner that the power source short-circuit and output opening are not generated, on the basis of the outputs of the current direction detecting circuit 7, a PWM command, and the logic state of other gate signals driving the forward direction semiconductor switches in the same output phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct connection between each phase of an AC power supply and each phase on the output side by a bidirectional switch having a self-extinguishing ability, and to change an AC power supply voltage to P in accordance with an output voltage command.
PWM that performs WM control and outputs arbitrary AC and DC voltages
The present invention relates to a cycloconverter and a driving method thereof.

[0002]

2. Description of the Related Art A first conventional PWM cycloconverter will be described with reference to FIG. In the figure, 1 is an AC power supply, 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, 9 is a bidirectional switch module, 10 to 18 are bidirectional switches, and 19 is a power supply voltage comparison circuit. When receiving the output voltage command, the controller 6 determines which bidirectional switch is to be fired while detecting the power supply voltage, and passes the PWM command to the commutation sequence switching circuit group 5. At this time, if the switching of the bidirectional switches 10 to 18 is performed at the same time, current spikes and voltage spikes do not occur. However, the switching is not actually performed at the same time due to variations in the bidirectional switches. Therefore, the power supply voltage comparator 19
The magnitude relation of each phase voltage is compared, classified into the maximum voltage, the intermediate voltage, and the minimum voltage, and the information is sent to the commutation sequence switching circuit group 5. According to the PWM command and the voltage comparison information, the commutation sequence switching circuit group 5 performs commutation from a phase with a large power supply voltage to a small phase (mode 1) or commutation from a phase with a small power supply voltage to a large phase (mode 2) ), And a gate signal is generated in the commutation sequence in each mode. The gate driver receives the gate signal and sends a signal insulated from the gate signal to the bidirectional switches 10 to 18 to drive the bidirectional switches 10 to 18. FIG. 7 shows a commutation sequence in each mode.

Next, as a second conventional example, Japanese Patent Publication No.
There is a cycloconverter described in JP-A-0312. This includes a first series circuit including, for each phase of the AC power supply, 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 series connected to the AC power supply and a second diode having a cathode connected to the anode of the second semiconductor control element and provided in parallel with the first series circuit in a reverse direction. And a load having a power receiving end connected to the cathode of the first diode of each phase, and a polarity inversion of a current of each phase flowing through the load by detecting a voltage across both diodes of each phase. A detection unit that detects a voltage pulse generated at the time and outputs a detection signal, and a switching unit 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]

However, in the first conventional example, the detection accuracy of the voltage comparison circuit and the time delay are disadvantageous.
In particular, commutation failure was likely to occur when the power supply voltage switched from negative to positive. In addition, commutation failure also occurs when the power supply voltage has a distorted waveform. Also, in the second conventional example, the direction of the current flowing through the element requires a PW
Not applicable for M cycloconverter. Therefore, the present invention can be applied to a cycloconverter which does not fail in commutation even when the detection accuracy and time delay of the voltage comparison circuit or the power supply voltage has a distorted waveform and further requires the direction of the current flowing through the element. It is an object to provide a converter and a driving method thereof.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method in which each phase of an AC power supply and each phase on the output side are directly connected by a bidirectional switch having a self-extinguishing ability, and an output voltage is controlled. In a PWM cycloconverter that performs PWM control of an AC power supply voltage in accordance with a command and outputs an arbitrary AC and DC voltage, the bidirectional switch has a configuration in which two one-way semiconductor switches are combined, and each is independently turned on. A configuration that can be turned off, a current direction detection circuit that determines a direction of a current flowing through the bidirectional switch, an output of the current direction detection circuit, a PWM command, and driving of a forward semiconductor switch in the same output phase. And a commutation switch for switching the firing order of the bidirectional switches based on the logic state of these signals so that power supply short circuit and output opening do not occur. It is obtained by a Nsu switching circuit. By the means described above, the direction of the current flowing through the switch is directly detected and the commutation sequence is switched, so that a drive system using a stable PWM cycloconverter without malfunction can be realized.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment 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 supply, 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 AC. An electric motor, 9 is a bidirectional switch module, and 10 to 18 are bidirectional switches. In this embodiment, each phase of the AC power supply 1 and each phase on the output side are directly connected by the bidirectional switches 10 to 18 having self-extinguishing ability, and the AC power supply voltage is PWM-controlled according to the output voltage command. This is a PWM cycloconverter that outputs arbitrary AC and DC voltages, and is one-way semiconductor switches Tr1 to Tr9, diodes D1 to D9 reversely connected thereto, and one-way semiconductor switches Tr1 ′ to Tr9 ′ and reversely connected thereto. It has bidirectional switches 10 to 18 in which diodes D1 'to D9' are connected in opposing series. In the present embodiment, the configuration of the bidirectional switch is as described above. However, as shown in FIG.
As shown in FIG. 2B, a diode having a reverse current blocking diode connected thereto, or a transistor having a transistor protection diode connected between an emitter and a collector as shown in FIG. 2C can also be used.

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 another gate signal for driving the forward direction semiconductor switch in the same output phase as the PWM command, and the current direction detection circuit group 7 and another signal for driving the forward direction semiconductor switch in the same output phase as the PWM command. A commutation sequence switching circuit 5 that switches the firing order of the bidirectional switches 10 to 18 according to the state of the gate signal. The current direction detection circuit group 7 includes current direction detection circuits 21a to 21c... As shown in FIG. And the first and second
The anode side of the diode 30 is connected to the + side of the insulated DC power supply B via the resistors R1 and R2, and the potential difference between the anode of the first diode 30 and the anode of the second diode 30 is detected. The direction of the current flowing through the direction switches 10 to 18 is determined.

In FIG. 3 which is a circuit block diagram for one output phase, reference numerals 20a, 20b, 20c... Denote 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 and T1 'of the bidirectional switch 10 and a connection point E1 of the transistors Tr1 and Tr1' in the bidirectional switch. Current direction detection circuit 21
Is input to the commutation sequence switching circuit 20. The commutation sequence switching circuit 20 also receives the PWM command C1 from the controller 6 and the gate signals G1, G2, G3 of the other switches input to the forward transistors Tr1, Tr2, Tr3 in the same output phase. Switch the flow sequence. The commutation sequence switching circuit 20 outputs a gate signal G for driving the forward and reverse transistors Tr1 and Tr1 'in the same bidirectional switch.
1, G1 'is output to drive the bidirectional switch 10.
The other bidirectional switches 11 and 12 in the same output phase have the same circuit configuration.

Next, a necessary commutation sequence will be described with reference to FIG. The current is changed from the power supply voltage 1 to the AC motor 8
5A when the current is flowing from the AC motor 8 to the power supply voltage 1 when the current is flowing from the AC motor 8 to the power supply voltage 1.
(B) The sequence is selected. At this time, when turning on the bidirectional switch 10, the current directions of the other bidirectional switches 11 and 12 in the same output phase and the bidirectional switch 10
Bi-directional switch 1 to be turned off when flipping
It can be seen that information on the current direction of 0 is required.
Specifically, when a current is flowing from the AC power supply 1 to the AC motor 8 (FIG. 5A), Tr1 'is first set to "OF".
F ". At this time, the current flowing through AC motor 8 is T
Since the current flows through r1, the current is not interrupted. Next, Tr2 is turned “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 commutates from Tr1 to Tr2. Next, Tr1 is turned “ON”. When V1> V2, commutation from Tr1 to Tr2 occurs at this time. Finally Tr
The commutation is completed by setting 2 ′ to “ON”. Next, when a current flows from the AC motor 8 to the AC power supply 1 (FIG. 5).
In (b)), Tr1 is first turned “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, if the power supply voltage is V1 <V2, a current flows through a solid line loop via Tr1 ′, and
When 2 <V1, a current flows through a loop indicated by a broken line via Tr2 ′ and commutates from Tr1 to Tr2. Next, Tr1 is set to “OFF”. When V1 <V2, T1 is set at this time.
A commutation from r1 to Tr2 occurs. Finally, change Tr2 to "O
N ”to complete the commutation. By using the above commutation sequence, commutation can be performed without interrupting a current and without causing a power supply short circuit.

Next, the current direction detecting circuit 21 and the commutation sequence switching circuit 20 will be described with reference to FIG.
Reference numeral 28 in the current direction detection circuit 21 denotes a photocoupler for insulating the control-side power supply from the main circuit, 29 denotes a comparator, 30 denotes first and second diodes, and 31 denotes an insulated power supply. The cathodes of the first and second diodes 30 are connected to both ends T1 and T1 'of the bidirectional switch 10. The middle point of the insulated power supply 31 is the connection point E of the transistor in the bidirectional switch.
Connected to 1. The anode side of the first and second diodes 30 is connected to the + side of the insulated power supply 31 and the comparator 2 via a resistor.
9 inputs. 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 conductive and the output Z1 of the current direction detector 21 is It becomes LO. In operation, when the bidirectional switch 10 is open, the potentials of the anodes of the first and second diodes 30 are fixed to the positive potential of the insulated power supply 31, and the potential difference between the anodes of the first and second diodes 30 is set. 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 in which the current flows, 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 becomes HI when the current flows from the AC motor 8 to the power supply side and when the bidirectional switch 10 is opened. .

Next, the commutation sequence switching circuit 20 will be described. 25 in the commutation sequence switching circuit 20 is a gate signal selection circuit, 26 is a mode switching circuit,
7 is a delay signal generation circuit. The mode switching circuit 26 has a gate signal G of the forward transistors Tr1, Tr2, Tr3 of the bidirectional switches 10, 11, 12 in the same output phase.
1, G2, G3, current direction detection signal Z1, PWM command C
1 is input. Bidirectional switch 10 in the same output phase,
11, 12 forward transistors Tr1, Tr2, Tr
The current direction of the bidirectional switches 10, 11, and 12 in the same output phase is determined from the states of the gate signals G1, G2, and G3 of the third. When the PWM command C1 is HI, the current direction signal P is the gate signal G of the forward transistors Tr1, Tr2, Tr3 of the bidirectional switches 10, 11, 12 in the same output phase.
The logical sum G of 1, G2 and G3 is selected, and the current direction detection signal Z1 is selected when the PWM command C1 is LO. Next, the PWM command C1 is input to the delay signal generation circuit 27, and first and second gate signals A and B are generated as outputs. The first gate signal A is delayed by 3ΔT from the PWM command C1 at the time of rising, and the PWM command C1 is delayed at the time of falling.
Sync with Also, the second gate signal B is delayed by ΔT from the PWM command C1 at the time of rising,
Delay by ΔT. The first and second gate signals A and B and the mode switching signal P are input to the gate signal selection circuit 25, and the gate signal selection circuit 25 converts the gate signal G1 of the forward transistor Tr1 and the gate signal G1 'of the reverse transistor Tr1'. Output. The mode switching signal P selects whether the gate signal G1 of the forward transistor Tr1 and the gate signal G1 ′ of the reverse transistor Tr1 ′ are the first gate signal A or the second gate signal B. I do. The commutation sequence is determined as described above. By using such a commutation sequence, commutation can be performed without interrupting a current and without causing a power supply short circuit.

[0012]

As described above, according to the present invention, since the direction of the current flowing through the bidirectional switch is directly detected and the commutation sequence is switched, a stable PW without malfunction is provided.
A drive system using an M cyclo converter 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 a bidirectional switch.

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 the principle of operation of a conventional commutation sequence.

[Explanation of symbols]

REFERENCE SIGNS LIST 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 (Δ
T), 25 gate signal selection circuit, 26 mode switching circuit, 27 delay signal generation circuit, 28 photocoupler, 2
9 comparators, 30 first and second diodes, 31 insulated power supply, Tr1 to Tr3 forward transistors, Tr1 'to
Tr3 'Reverse transistor, T1-T3 Power supply side terminal of bidirectional switch, T1'-T3' Load side terminal of bidirectional switch, E1-E3 Connection point of forward and reverse transistors, P mode switching signal, Z1 Z3 current direction detection signal, G1 to G3 forward transistor gate signal, G1 'to G3' reverse transistor gate signal, C1 to C3 PWM command, GOR of gate signals of forward transistors in the same output phase, A First gate signal, B Second gate signal

Claims (2)

[Claims] An AC power supply is directly connected to each phase of an AC power supply with a bidirectional switch having a self-extinguishing ability, and the AC power supply voltage is PWM-controlled according to an output voltage command. In a PWM cycloconverter that outputs a DC voltage, the bidirectional switch has a configuration in which two one-way semiconductor switches are combined, and each of the bidirectional switches can be turned on and off independently. A current direction detection circuit for determining, an output of the current direction detection circuit, a PWM command, and another gate signal for driving a forward semiconductor switch in the same output phase; A commutation sequence switching circuit for switching a firing order of the bidirectional switch so that a short circuit and an output open do not occur. Cyclo converter. 2. An AC power supply and each phase on the output side are directly connected by a bidirectional switch having a self-extinguishing ability, and the AC power supply voltage is PWM-controlled in accordance with an output voltage command. A method of driving a PWM cycloconverter that outputs a DC voltage, comprising: a bidirectional switch configured to combine two unidirectional semiconductor switches with the PWM cycloconverter and to be able to be turned on and off independently; A current direction detection circuit for discriminating the direction, taking in the output of the current direction detection circuit and another gate signal for driving the forward direction semiconductor switch in the same output phase as the PWM command, based on the logic state of these signals. Cycloconverter for switching the firing order of the bidirectional switch so that power supply short-circuit and output opening do not occur. Method of driving a motor.