Power conversion device
The present invention aims to provide a power converter with an arm including switching devices connected in parallel, realizing long lifespans of switching devices. An inverter includes an upper and a lower arm, and gate drive circuits each driving the corresponding arm according to a gate control signal Gup_s indicating ON/OFF periods. Each arm includes switching devices connected in parallel. Each gate drive circuit includes: a switching gate control circuit 230 u bringing a switching device 210 u into conduction at the beginning of the ON period and bringing the same out of conduction within the ON period; and a conduction gate control circuit 231 u bringing switching devices 211 u and 212 u within a period from when the switching device 210 u is brought into conduction until the same is brought out of conduction, wherein the switching device 210 u has a lower parasitic capacitance than the switching devices 211 u and the 212 u.
1. A power converter comprising: an upper arm; a lower arm; and gate drive circuits each configured to drive a corresponding one of the arms according to a reference signal, the reference signal having a first-potential period and a second-potential period, wherein
each arm includes a set of switching devices connected in parallel,
each gate drive circuit includes:
a switching gate control circuit configured to bring a first switching device among the corresponding set of switching devices into conduction at the beginning of the first-potential period, and to bring the first switching device out of conduction at a point within the first-potential period;
a turn-off gate control circuit configured to bring a third switching device among the corresponding set of switching devices into conduction at the beginning of the second-potential period, and to bring the third switching device out of conduction at a point within the second-potential period; and
a conduction gate control circuit configured to bring a second switching device among the corresponding set of switching devices into conduction at a point within a period from when the first switching device is brought into conduction, which corresponds to the beginning of the first-potential period, until the first switching device is brought out of conduction, and to bring the second switching device out of conduction at a point within a period from when the third switching device is brought into conduction, which corresponds to the beginning of the second-potential period, until the third switching device is brought out of conduction, wherein
the first switching device has a smaller parasitic capacitance than the second switching device.
2. The power converter of claim 1 , wherein
the first switching device has a smaller switching loss than the second switching device, and
the second switching device has a smaller conduction loss than the first switching device.
3. The power converter of claim 2 , wherein
the first switching device is unipolar, and the second switching device is bipolar.
4. The power converter of claim 1 , wherein
each gate drive circuit further includes:
a primary voltage detection circuit configured to detect voltage between primary terminals of the switching devices; and
a primary voltage determination circuit configured to determine whether the first switching device has been brought into conduction by comparing the voltage detected by the primary voltage detection circuit with a predetermined voltage, and
the conduction gate control circuit brings the second switching device into conduction when the primary voltage determination circuit determines that the first switching device has been brought into conduction.
5. The power converter of claim 4 , wherein
each gate drive circuit further includes:
a switching termination primary voltage determination circuit configured to determine whether the second switching device has been brought into conduction by comparing the voltage detected by the primary voltage detection circuit with a second predetermined voltage, and
the switching gate control circuit brings the first switching device out of conduction when the switching termination primary voltage determination circuit determines that the second switching device has been brought into conduction.
6. The power converter of claim 1 , wherein
each gate drive circuit further includes:
a switching current detection circuit configured to detect current flowing between primary terminals of the first switching device; and
a switching current determination circuit configured to determine whether the first switching device has been brought into conduction based on the detection by the switching current detection circuit, and
the conduction gate control circuit brings the second switching device into conduction when the switching current determination circuit determines that the first switching device has been brought into conduction.
7. The power converter of claim 1 , wherein
a second threshold voltage of the second switching device is lower than a first threshold voltage of the first switching device.
8. The power converter of claim 1 , wherein
a potential difference between on-voltage and off-voltage output by the switching gate control circuit is larger than a potential difference between on-voltage and off-voltage output by the conduction gate control circuit.
9. The power converter of claim 1 , wherein
each gate drive circuit includes the same number of gate control circuits as the switching devices included in the corresponding one of the arms, including the switching gate control circuit and the conduction gate control circuit, and
the gate control circuits corresponding one-to-one to the switching devices, and each of the control circuits controls a corresponding one of the switching devices in the same manner as the switching gate control circuit or the conduction gate control circuit.
10. The power converter of claim 1 , wherein
a gate resistor is connected between a control terminal of each switching device and the gate control circuit controlling the switching device, and
the gate resistor connected to the control terminal of the second switching device is of higher resistance than the gate resistors connected to the control terminals of the rest of the switching devices.
11. The power converter of claim 1 , wherein
the first switching device has a lower threshold voltage than the third switching device.
12. The power converter of claim 1 , wherein
among the switching gate control circuit, the conduction gate control circuit, and the turn-off gate control circuit, the switching gate control circuit outputs on-voltage and off-voltage with the largest potential difference therebetween, followed by the conduction gate control circuit and the turn-off gate control circuit in this order.
13. The power converter of claim 1 , wherein
the first switching device is a metal-oxide-semiconductor field-effect transistor, and the second switching device is an insulated gate bipolar transistor,
each gate drive circuit further includes a low-current gate control circuit configured to bring the first switching device into conduction for a period in which the corresponding arm is required to be conductive, and
when the power converter is driven with current falling within a range where the metal-oxide-semiconductor field-effect transistor requires lower voltage than the insulated gate bipolar transistor to obtain a desired current value, the gate drive circuit drives the corresponding arm by using the low-current gate control circuit, and
when the power converter is driven with a current falling within a range where the insulated gate bipolar transistor requires lower voltage than the metal-oxide-semiconductor field-effect transistor to obtain the desired current value, the gate drive circuit drives the corresponding arm by using the switching gate control circuit and the conduction gate control circuit.
14. The power converter of claim 1 , wherein
the first switching device is a wide bandgap semiconductor.
15. The power converter of claim 1 , wherein
the first switching device has a smaller current carrying capacity than the second switching device.