JP3791393B2 - Inverter circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inverter circuit that converts DC power into AC power, and relates to an inverter circuit that prevents oscillation when a control signal is interrupted.
[0002]
[Prior art]
An inverter circuit that performs power conversion includes a combination of a plurality of semiconductor switches. By sequentially turning on and off the semiconductor switches, a DC voltage is converted into an arbitrary frequency and an arbitrary voltage. Some semiconductor switches use an insulated gate bipolar transistor (hereinafter referred to as IGBT).
[0003]
The IGBT contributes to the improvement of the control performance due to the high speed and the reduction of the loss due to the low saturation voltage. On the other hand, electromagnetic noise (including conduction noise and radiation noise) generated by high-speed switching causes a problem that causes electronic devices such as computers to malfunction. Electromagnetic noise is largely caused by the reverse recovery period of the freewheeling diode when the IGBT is turned on and the high-frequency current associated with the voltage and current change rate (dv / dt, di / dt) in the current decay feedback when the IGBT is turned off. . Thus, for example, JP-A 2000-22513 discloses connecting a capacitor between the gate and emitter of IGBT, there is a circuit as shown in JP-A-9-51068 JP.
[0004]
FIG. 3 is a circuit diagram showing a conventional inverter circuit. The conventional inverter circuit includes transistors Tr7 to Tr12 which are IGBTs, capacitors C9 to C14, free wheel diodes D7 to D12, and control circuits 30 to 35. Control circuits 30 to 35 are inserted into the gates of the transistors Tr7 to Tr12, and capacitors C9 to C14 are connected between the gate and the emitter. Free wheel diodes D7 to D12 are connected between the collectors and emitters of the transistors Tr7 to Tr12.
[0005]
Control signals are sequentially input to the VinU terminal, VinV terminal, VinW terminal, VinX terminal, VinY terminal, and VinZ terminal shown in FIG. A high potential side of a DC power source (not shown) is input to the P terminal, and a low potential side is input to the N terminal. The voltage of the DC power supply is converted to an arbitrary frequency by a control signal and output to the U terminal, V terminal, and W terminal to which a load is connected.
[0006]
By the way, when a control signal is simultaneously input to the VinU terminal and the VinX terminal, the transistors Tr7 and Tr10 are simultaneously turned on, and a short-circuit current flows between the P terminal and the N terminal. The emitter of the transistor Tr10~Tr12 constituting the lower arm, since a common ground, short-circuit current flows through the transistor Tr10, via a potential emitter of another transistor Tr11, Tr 12 is connected to the N-terminal And flow.
[0007]
The control circuits 30 and 33 detect this short-circuit current and cut off the output of the input control signal. By this interruption, the transistors Tr7 and Tr10 are turned off, and the short-circuit current flow between the P terminal and the N terminal is interrupted.
[0008]
[Problems to be solved by the invention]
In this way, the short-circuit current flowing in the lower arm bypasses the common ground of the lower arm and flows to the low voltage side of the DC power supply, so the potential of the common ground becomes unstable and the switching element of the lower arm oscillates. There is a problem that the voltage is output to the load output terminal even after the control signal is cut off.
[0009]
The present invention has been made in view of the above points, and an object of the present invention is to provide an inverter circuit that stably stops even when a control circuit cuts off a control signal due to a short circuit of a DC power supply.
[0010]
[Means for Solving the Problems]
In the present invention, in order to solve the above problem, in an inverter circuit that converts DC power to AC power, a short-circuit current of a DC power source that supplies the DC power to the upper arm and the lower arm is detected, and the upper arm and the Between a control circuit that cuts off a control signal for converting the DC power input to the lower arm into the AC power, and between each upper control terminal and each phase output terminal of the upper switch element constituting the upper arm to the upper capacitor element connected respectively, and the lower capacitance elements each connected between each lower control terminals of the lower switch elements constituting the lower arm and the common ground, is connected in series with the lower capacitance element, There is provided an inverter circuit comprising a resistor for suppressing oscillation of the lower arm when the control signal is interrupted.
[0011]
In such an inverter circuit, even if the control circuit cuts off the control signal due to a short-circuit current of the DC power supply, a condition in which oscillation occurs due to the resistance connected to the lower arm is avoided and the lower arm does not oscillate.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an inverter circuit according to the present invention will be described in detail with reference to the drawings, taking as an example the case of applying to an inverter circuit.
[0013]
FIG. 1 is a circuit diagram showing a three-phase inverter circuit of the present invention.
The three-phase inverter circuit shown in the figure includes control circuits 10 to 12, transistors Tr1 to Tr3, which are IGBTs, capacitors C1 to C3, freewheel diodes D1 to D3, control circuits 13 to 15, and Tr4 which is an IGBT. To Tr6, capacitors C4 to C6, and a lower arm composed of freewheel diodes D4 to D6.
[0014]
First, the upper arm will be described.
A control circuit 10 is connected to the gate of the transistor Tr1, and a capacitor C1 is connected between the gate and emitter of the transistor Tr1. A free wheel diode D1 is connected between the collector and emitter of the transistor Tr1. The free wheel diode D1 has a cathode connected to the collector and an anode connected to the emitter.
[0015]
The control circuit 10 supplies a voltage to the VccU terminal, thereby converting a control signal input from the VinU terminal into a gate drive voltage for the transistor Tr1 and outputting the same. Further, the control circuit 10 detects that an overcurrent has passed through the transistor Tr1 and cuts off the output of the control signal. The GNDU terminal is a ground for the VccU terminal and the VinU terminal.
[0016]
The capacitor C1 charges and discharges when the control signal input to the gate of the transistor Tr1 is switched. This charging / discharging prolongs the switching time of the control signal, reduces dv / dt and di / dt, and reduces electromagnetic noise.
[0017]
The control signal input to the VinU terminal is converted by the control circuit 10 into a voltage that can drive the gate of the transistor Tr1, and input to the gate of the transistor Tr1. The transistor Tr1 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. By this on / off, the voltage of the DC power source E input to the P terminal is generated at the U terminal.
[0018]
In the transistor Tr2, the control circuit 11 is connected to the gate, and the capacitor C2 is connected between the gate and the emitter. A freewheel diode D2 is connected between the collector and the emitter. Further, the P terminal and the collector of the transistor Tr2 are connected.
[0019]
The control signal input to the VinV terminal is converted by the control circuit 11 into a voltage that can drive the gate of the transistor Tr2, and input to the gate of the transistor Tr2. The transistor Tr2 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. By this on / off, the voltage of the DC power source E input to the P terminal is generated at the V terminal.
[0020]
In the transistor Tr3, the control circuit 12 is connected to the gate, and the capacitor C3 is connected between the gate and the emitter. A free wheel diode D3 is connected between the collector and the emitter. The P terminal and the collector of the transistor Tr3 are connected.
[0021]
The control signal input to the VinW terminal is converted into a voltage that can drive the gate of the transistor Tr3 by the control circuit 12, and input to the gate of the transistor Tr3. The transistor Tr3 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. Voltage of the DC power source E, which is input to the terminal P by the on-off occurs W pin.
[0022]
Next, the lower arm will be described.
A control circuit 13 is connected to the gate of the transistor Tr4, and a capacitor C4 and a resistor R1 are connected in series between the gate and emitter of the transistor Tr4. A freewheel diode D4 is connected between the collector and emitter of the transistor Tr4. The free wheel diode D4 has a cathode connected to the collector and an anode connected to the emitter. The collector of the transistor Tr4 is connected to the U terminal, and the emitter is connected to the N terminal.
[0023]
When the voltage is supplied to the Vcc terminal, the control circuit 13 converts the control signal input from the VinX terminal into the gate drive voltage of the transistor Tr4 and outputs the converted signal. Further, the control circuit 13 detects that an overcurrent has flowed through the transistor Tr4 and cuts off the output of the control signal. The GND terminal is a ground for the Vcc terminal and the VinX terminal. The GND terminal is connected to the emitters of the transistors Tr5 and Tr6, and is a common ground for the VinY terminal and the VinZ terminal.
[0024]
The capacitor C4 is charged and discharged when the control signal input to the transistor Tr4 is switched. This charging / discharging prolongs the switching time of the control signal, reduces dv / dt and di / dt, and reduces electromagnetic noise. The resistor R1 connected in series with the capacitor C4 is a resistor for suppressing the collector current of the transistor Tr4 from oscillating when an overcurrent flows through the transistor Tr4 and the input of the control signal is interrupted.
[0025]
The control signal input to the VinX terminal is converted by the control circuit 13 into a voltage that can drive the gate of the transistor Tr4 and input to the gate of the transistor Tr4. The transistor Tr4 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. Voltage of the DC power source E, which is input to the N terminal by the on-off (0V) is generated in the U terminal.
[0026]
In the transistor Tr5, the control circuit 14 is connected to the gate, and a resistor R2 and a capacitor C5 connected in series are connected between the gate and the emitter. A freewheel diode D5 is connected between the collector and the emitter. The collector is connected to the V terminal, and the emitter is connected to the N terminal.
[0027]
The control signal input to the VinY terminal is converted by the control circuit 14 into a voltage that can drive the gate of the transistor Tr5 and input to the gate of the transistor Tr5. The transistor Tr5 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. This on-off, the voltage of the DC power source E, which is input to the N terminal occurs in V pin.
[0028]
In the transistor Tr6, the control circuit 15 is connected to the gate, and a resistor R3 and a capacitor C6 connected in series are connected between the gate and the emitter. A freewheel diode D6 is connected in parallel between the collector and the emitter. The collector is connected to the W terminal, and the emitter is connected to the N terminal.
[0029]
The control signal input to the VinZ terminal is converted by the control circuit 15 into a voltage that can drive the gate of the transistor Tr6 and input to the gate of the transistor Tr6. The transistor Tr6 turns on and off between the collector and the emitter in accordance with a control signal input to the gate. As a result of this on / off, the voltage of the DC power source E input to the N terminal is generated at the W terminal.
[0030]
That is, by sequentially switching the voltage of the control signal input to the VinU terminal, VinV terminal, VinW terminal of the upper arm, the VinX terminal, VinY terminal, and VinZ terminal of the lower arm, the voltage of the DC power supply E at the arbitrary frequency is the U terminal. , V terminal and W terminal.
[0031]
Here, for example, when a control signal is simultaneously input to the VinU terminal of the upper arm and the VinX terminal of the lower arm, a short-circuit current of the DC power source E flows between the P terminal and the N terminal. The short-circuit current flows from the P terminal between the collector and emitter of the transistor Tr1 and between the collector and emitter of the transistor Tr4. The short-circuit current that has flowed through the emitter of the transistor Tr4 bypasses the common ground of the transistors Tr4 to Tr6 and flows to the terminal N, but oscillation is suppressed by the capacitor C4 and the resistor R1 connected in series between the gate and emitter of the transistor Tr4. .
[0032]
Here, the principle of suppressing oscillation will be described.
FIG. 2 shows an equivalent circuit diagram for one phase of the lower arm. The equivalent circuit for one phase of the lower arm connects the control circuit 20, the wiring pattern of the printed circuit board, and the aluminum wire inductors L1 and L2 that connect the printed circuit board and the IGBT, and the wiring pattern of the printed circuit board and the printed circuit board and the IGBT. It consists of resistors R4 and R5 of aluminum wires, a capacitor C7 which is an input capacitance between the gate and emitter of the IGBT, and a capacitor C8 for reducing dv / dt.
[0033]
Here, the inductance values of the inductors L1 and L2 are L ₁ and L ₂ , the resistance values of the resistors R4 and R5 are R ₁ and R ₂ , and the capacitance values of the capacitors C7 and C8 are C ₁ and C ₂ . The conditional expression that causes oscillation is R ² <(4L / C). Here, R = R ₁ + R ₂ , L = L ₁ + L ₂ , and C = C ₁ + C ₂ .
[0034]
In order to prevent oscillation, it is only necessary to increase R, decrease L, and increase C in the conditional expression in which oscillation occurs. In order to reduce L, it is necessary to make the wiring of the printed circuit board short and thick, which is difficult due to structural limitations. In order to increase C, it is necessary to increase C ₁ or C _2. However, C ₁ needs to change the internal structure of the IGBT, and if C ₂ is increased, switching loss increases. However, it is not preferable. Increasing R ₁ and R ₂ is not desirable because L ₁ and L ₂ increase simultaneously. Therefore, oscillation is suppressed by inserting a resistor in series with C8 in FIG.
[0035]
That is, after the control circuits 10 and 13 detect the short-circuit current and cut off the short-circuit current, the inverter circuit does not oscillate, so that the control signal can be cut off stably.
[0036]
By the way, in the above description, the case where the control signal is simultaneously input to the VinU terminal and the VinX terminal has been described. However, the transistor having the upper arm and the transistor having the lower arm are simultaneously turned on, and the short-circuit current of the DC power supply E is reduced. Similarly, the control signal can be shut off stably in the combination in the case of flowing.
[0037]
In the above three-phase inverter circuit, the control circuits 10 to 15 may be configured by discrete components, or all functions may be integrated into an IC.
Further, the switching element is not limited to the IGBT, and a self-extinguishing element such as a MOSFET may be used.
[0038]
【The invention's effect】
As described above, in the present invention, since the lower capacitance element and the resistor are connected between the lower control terminal and the common ground, the short circuit current of the DC power source is detected by the control circuit, and the control signal is cut off. However, oscillation caused by a short-circuit current flowing in the common ground of the lower arm can be prevented, and the inverter circuit can be stably stopped.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a three-phase inverter circuit of the present invention.
FIG. 2 shows an equivalent circuit diagram for one phase of the lower arm.
FIG. 3 is a circuit diagram showing a conventional inverter circuit.
[Explanation of symbols]
10 to 15, 20, 30 to 35 Control circuits Tr1 to Tr12 Transistors R1 to R5 Resistors C1 to C14 Capacitors L1 to L2 Inductors

Claims (2)

In an inverter circuit that converts DC power into AC power,
A short-circuit current of a DC power source that supplies the DC power to the upper arm and the lower arm is detected, and a control signal for converting the DC power input to the upper arm and the lower arm into the AC power is cut off. A control circuit;
An upper capacitive element connected between each upper control terminal and each phase output terminal of the upper switch element constituting the upper arm ; and
A lower capacitive element connected between each lower control terminal of the lower switch element constituting the lower arm and a common ground;
And suppress resistance to oscillation of the lower arm when connected in series, wherein the control signal is cut off before SL under capacitive element,
An inverter circuit comprising: 2. The inverter circuit according to claim 1, wherein when the short circuit current is not detected, the control circuit converts the control signal into a voltage for driving the upper switch element and the lower switch element and outputs the converted voltage.

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