JP2018121375A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus capable of improving controllability of a discharge circuit discharging a smooth capacitor.SOLUTION: An power conversion apparatus according to this invention comprises an inverter circuit for converting power, a smooth capacitor for smoothing the power input to the inverter circuit, a discharge resistor for discharging a charge stored in the smooth capacitor, a switching element connected in series with the discharge resistor, a current detection resistor connected in series with the switching element, and a clamp circuit which is constructed to be connected in parallel to the current detection resistor and increase a voltage between a gate and a source of the switching element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device that supplies power to a motor for driving a vehicle.

  The power converter is provided with a smoothing capacitor connected in parallel with an inverter circuit that converts a direct current and an alternating current. After the power converter is stopped, a discharge circuit may be provided for removing charges accumulated in the smoothing capacitor from the viewpoint of safety.

  Patent Document 1 describes that the discharge circuit includes a discharge resistor, a discharge switch element, and a current detection resistor, which are connected in series.

  However, in the discharge circuit described in Patent Document 1, when the discharge current of the smoothing capacitor is large, the voltage drop of the current detection resistor is increased, which may make it difficult to control the discharge switch.

Japanese Patent Laid-Open No. 2006-86492

  Therefore, the problem to be solved by the present invention is to improve the controllability of the discharge circuit for discharging the smoothing capacitor.

  The power conversion device according to the present invention includes an inverter circuit that converts power, a smoothing capacitor that smoothes power input to the inverter circuit, a discharge resistor that discharges electric charge stored in the smoothing capacitor, and the discharge A switch element connected in series to a resistor, a current detection resistor connected in series to the switch element, and a clamp circuit connected in parallel with the current detection resistor and configured to increase a gate-source voltage of the switch element And comprising.

  According to the present invention, the controllability of the discharge circuit can be improved.

1 is a system configuration diagram of a vehicle driving motor 104 including a power conversion device 100 according to the present embodiment. 2 is a graph showing a discharge current and a source voltage of a discharge switch 132 in the conventional circuit and the circuit of FIG. 2 is a graph showing a discharge current and a gate-source voltage of a discharge switch 132 in the conventional circuit and the circuit of FIG.

  An embodiment according to the present invention will be described with reference to FIGS.

  FIG. 1 is a system configuration diagram of a vehicle driving motor 104 including a power conversion device 100 according to the present embodiment.

  The power conversion apparatus 100 includes a smoothing capacitor 102, an inverter circuit 101, and a discharge circuit 103.

  The smoothing capacitor 102 stabilizes the DC side voltage of the inverter circuit 101. The inverter circuit 101 is configured by a three-phase output circuit in which three circuits in which a switching element 112 and a switching element 122 are connected in series are connected in parallel.

  A diode 113 is connected to the switching element 112 connected to the positive electrode side of the smoothing capacitor 102, and a diode 123 is connected to the switching element 122 connected to the negative electrode side in antiparallel.

  The midpoints of the three circuits formed by connecting the switching elements 112 and 113 in series are connected to the three terminals of the motor 104 as output terminals on the AC side.

  The current sensor 106 detects the current flowing through the motor of each phase.

  Based on the current sensor 106, the control circuit 105 outputs voltages for driving the six switching elements of the inverter circuit 101 to the control terminals of the six switching elements.

  The discharge circuit 103 includes a discharge resistor 131, a discharge switch 132, a current detection resistor 133, a diode 134, a voltage source 135, a buffer 136, a reference voltage 137, and a comparator 138.

  The discharge resistor 131 consumes energy stored in the smoothing capacitor 102.

  The discharge switch 132 discharges based on a discharge signal transmitted from the control circuit. Although MOSFETs are used in FIG. 1, other switching elements such as IGBTs can be substituted.

  When the discharge signal is on, the buffer 136 connects the gate terminal of the discharge switch 132 and the voltage source 138 to turn on the discharge switch 132. When the discharge signal is off, the buffer 136 connects the gate terminal of the discharge switch 132 to the ground potential. The switch 132 is turned off.

  The current detection resistor 133 detects the presence or absence of a discharge current. The voltage of the current detection resistor 133 and the reference voltage 137 are compared by a comparator 138. When the former is large, the discharge current flows. If it is larger, it is determined that the discharge current is not flowing.

  When the voltage of the smoothing capacitor 102 decreases, the discharge current decreases, and the voltage of the current detection resistor 133 becomes equal to or lower than the reference voltage 137, a signal is transmitted to the control circuit so as to end the discharge.

  The diode 134 is for clamping the voltage of the current detection resistor 133, and can reduce the risk of the discharge switch 132 being erroneously turned off due to an increase in the current detection resistance voltage due to an increase in the discharge current. Since the reference voltage 137 is small and susceptible to noise, a diode 134 may be connected in series in order to increase the reference voltage 137.

  A plurality of diodes 134 connected in parallel to the current detection resistor 133 are connected in series. As a result, the voltage applied to the current detection resistor 133 increases, so that the voltage input to the negative terminal of the comparator 138 that compares the voltage of the current detection resistor 133 with the reference voltage 137 increases, and the reference voltage 137 increases. can do.

  Therefore, it is possible to reduce the possibility that noise is mixed in the voltage applied to the current detection resistor 133 and the comparator 138 malfunctions.

  FIG. 2 is a graph showing the discharge current and the source voltage of the discharge switch 132 in the conventional circuit and the circuit of FIG.

  The horizontal axis represents the discharge current, and the vertical axis represents the source terminal voltage of the discharge switch 132. The voltage of the voltage source 135 is Vcc, and the maximum value of the forward voltage of the diode 134 is Vf.

  A solid line indicates a case where only the current detection resistor is provided, and a broken line indicates a case where a diode is connected in parallel to the current detection resistor.

In the case of only the current detection resistor, the voltage increases in proportion to the current as shown by the solid line. The voltage increases,
As the forward voltage is approached, the slope becomes smaller and eventually clamps at the forward voltage.

  FIG. 3 is a graph showing the discharge current and the gate-source voltage of the discharge switch 132 in the conventional circuit and the circuit of FIG.

  The horizontal axis represents the discharge current, and the vertical axis represents the gate-source voltage of the discharge switch 132.

  The voltage of the voltage source 135 is Vcc, and the maximum value of the forward voltage of the diode 134 is Vf.

  A solid line indicates a case where only the current detection resistor is provided, and a broken line indicates a case where a diode is connected in parallel to the current detection resistor. In the case of only the current detection resistor, the gate-source voltage decreases as the current increases as indicated by the solid line.

When diodes are connected in parallel, the gate-source voltage decreases as the current increases in the region where the current is small, as with the resistance characteristics.
Since the source terminal voltage is clamped by the forward voltage of the diode, even if the discharge current increases, the gate-source voltage can be reduced by the forward voltage at most.

DESCRIPTION OF SYMBOLS 100 ... Power converter device 101 ... Inverter circuit, 102 ... Smoothing capacitor, 103 ... Discharge circuit, 104 ... Motor, 105 ... Control circuit, 106 ... Current sensor, 112 ... Switching element, 113 ... Diode, 122 ... Switching element, 123 DESCRIPTION OF SYMBOLS ... Diode ... 131 ... Discharge resistor, 132 ... Discharge switch, 133 ... Current detection resistor, 134 ... Diode, 135 ... Voltage source, 136 ... Buffer, 137 ... Reference voltage, 138 ... Comparator

Claims (3)

An inverter circuit for converting power;
A smoothing capacitor for smoothing the power input to the inverter circuit;
A discharge resistor for discharging the charge stored in the smoothing capacitor;
A switch element connected in series to the discharge resistor;
A current sensing resistor connected in series to the switch element;
And a clamp circuit connected in parallel with the current detection resistor and configured to expand a gate-source voltage of the switch element. The power conversion device according to claim 1,
A comparison circuit that inputs a voltage applied to the current sensing resistor and compares it with a reference voltage;
A power conversion device comprising: a diode connected in parallel with the current detection resistor. The power conversion device according to claim 2,
The diode is a power conversion device configured by connecting a plurality of diode elements in series.

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