Power converting apparatus
A power converting apparatus includes a main inverter having a high-voltage DC power supply that operates at a low frequency employing SiC MOSFETs having a high withstand voltage exceeding 600 V and a sub-inverter having a low-voltage capacitor that operates through high-frequency PWM employing Si MOSFETs having a low withstand voltage. With AC sides of the main inverter and the sub-inverter connected in series, the power converting apparatus outputs AC power having a prescribed voltage waveform by adding voltages individually generated by the main inverter and the sub-inverter. Specifically, the SiC MOSFETs are used only in the main inverter of which devices are required to have a high withstand voltage and the Si MOSFETs are used in the sub-inverter of which devices may have a relatively low withstand voltage, whereby conduction loss is reduced with an inexpensive circuit configuration.
1. A power converting apparatus comprising:
a first inverter circuit including a first DC voltage source and a plurality of semiconductor switching devices; and
a second inverter circuit including a second DC voltage source having a lower voltage than the first DC voltage source and a plurality of semiconductor switching devices;
wherein
all of the semiconductor switching devices of said first inverter are wide band gap semiconductor switching devices made of semiconductor material having a wider band gap than silicon, and all of the semiconductor switching devices of said second inverter are silicon semiconductor switching devices, and
AC-side output terminals of said first inverter circuit and AC-side output terminals of said second inverter circuit are connected in series and said power converting apparatus supplies AC power having a prescribed voltage waveform obtained by combining outputs of said first and second inverter circuits to a load.
2. The power converting apparatus according to claim 1 , wherein a switching frequency used for driving said first inverter circuit is lower than a switching frequency used for driving said second inverter circuit.
3. The power converting apparatus according to claim 2 , wherein only said second inverter circuit among said first and second inverter circuits is controlled by high-frequency pulse-width modulation.
4. The power converting apparatus according to claim 1 , wherein each of said first inverter circuit and said second inverter circuit is configured with a single-phase inverter.
5. The power converting apparatus according to claim 1 , wherein said first inverter circuit is configured with an n-phase multiphase inverter and said second inverter circuit is configured with at least n number of single-phase inverters, and wherein AC-side output terminals of the individual single-phase inverters of said second inverter circuit are connected to AC output terminals for individual phases of said first inverter circuit in series, whereby said power converting apparatus combines output voltages of said first and second inverter circuits for the individual phases and supplies n-phase AC power having the prescribed voltage waveform to an n-phase load.
6. The power converting apparatus according to claim 1 , wherein said load is connected in between an AC-side output terminal of said first inverter circuit and an AC-side output terminal of said second inverter circuit, the AC-side output terminal of said first inverter circuit and the AC-side output terminal of said second inverter circuit are electrically connected to each other only through the load, and said first inverter circuit and said second inverter circuit together supply the AC power to said load from both sides thereof.
7. The power converting apparatus according to claim 1 , wherein said first inverter circuit includes at least one pair of series-connected units each configured with two wide band gap semiconductor switching devices, and one of the wide band gap semiconductor switching devices of each series-connected unit is turned on during a period from a point of completion of turn-off of the other of the wide band gap semiconductor switching devices to a point immediately preceding a next turn-on action thereof.
8. The power converting apparatus according to claim 1 , wherein SiC MOSFETs are used as the wide band gap semiconductor switching devices provided in said first inverter circuit.
9. The power converting apparatus according to claim 1 , wherein unipolar devices are used as the wide band gap semiconductor switching devices provided in said first inverter circuit and as the silicon semiconductor switching devices provided in said second inverter circuit.
10. The power converting apparatus according to claim 1 , wherein said first inverter circuit includes the plurality of semiconductor switching devices and a plurality of diodes made of semiconductor material having a wider band gap than silicon.
11. The power converting apparatus according to claim 10 , wherein the plurality of diodes are SiC Schottky barrier diodes.
12. The power converting apparatus according to claim 1 , wherein said second inverter circuit includes the plurality of semiconductor switching devices and a plurality of diodes made of semiconductor material having a wider band gap than silicon.
13. The power converting apparatus according to claim 1 , wherein a wiring inductance between the second DC voltage source and each of the semiconductor switching devices of said second inverter circuit is smaller than a wiring inductance between the first DC voltage source and each of the semiconductor switching devices of said first inverter circuit.
14. The power converting apparatus according to claim 1 , wherein the plurality of semiconductor switching devices provided in said first inverter circuit and the plurality of semiconductor switching devices provided in said second inverter circuit are incorporated in a common module.