| 摘要 |
A series circuit of capacitors 2 and 3 and a series circuit of semiconductor switches 4 and 5 such as SiC-MOSFETs are connected in parallel to a direct current power source 1, and one end of a bidirectional switch formed of semiconductor switches 12 and 13, such as IGBTs, and diodes 10 and 11, such as SiC-SBDs, is connected to a series connection point (an M point) of the capacitors 2 and 3, while the other end of the bidirectional switch is connected to a series connection point of the semiconductor switches 4 and 5, thereby configuring a three-level inverter which can output three voltage levels by operating the semiconductor switches 4, 5, 12, and 13. The three-level inverter is operated so as to satisfy at least one of the condition that the peak value of an alternating current output voltage V o is a value of 80% or more of the voltage of the capacitors 2 and 3 and the condition that an output power factor is 0.8 or more. By so doing, heretofore known inexpensive elements can be utilized for one portion of the semiconductor switches, thus achieving an increase in efficiency and a reduction in size while reducing cost. |
