Abstract: Upon turn-off of IGBT, by suppressing variations in collector-emitter voltage between IGBTs connected in series, risk of breaking IGBT due to overvoltage breakdown can be reduced. In protection circuit provided for each of the plurality of IGBTs 50 connected in series, between collector and emitter of IGBT 50, avalanche elements D1˜D5, resistance R4 and avalanche element D6 are sequentially connected in series. Capacitor C1 and resistance R1 are connected parallel between both ends of the avalanche element D4, and capacitor C2 and resistance R2 are connected parallel between both ends of the avalanche element D5. Between a common connection point of the resistance R4 and the avalanche element D6 and gate of the IGBT 50, resistance R5, a parallel circuit of capacitor C3 and resistance R6, and a series component of Zener diodes ZD1 and ZD2 whose polarities are opposite to each other, are connected in series.

Abstract: A multilevel power conversion device includes: N (N?1) direct current voltage sources; a first flying capacitor; a second flying capacitor; and a phase module of a M phase (M?2) being configured to output, from the output terminal, a potential of one of the input terminals, or a potential obtained by adding or subtracting the voltage of the capacitor to or from the potential of the one of the input terminals, by selectively controlling the respective switching elements in an ON/OFF manner.

Abstract: Upon turn-off of IGBT, by suppressing variations in collector-emitter voltage between IGBTs connected in series, risk of breaking IGBT due to overvoltage breakdown can be reduced. In protection circuit provided for each of the plurality of IGBTs 50 connected in series, between collector and emitter of IGBT 50, avalanche elements D1˜D5, resistance R4 and avalanche element D6 are sequentially connected in series. Capacitor C1 and resistance R1 are connected parallel between both ends of the avalanche element D4, and capacitor C2 and resistance R2 are connected parallel between both ends of the avalanche element D5. Between a common connection point of the resistance R4 and the avalanche element D6 and gate of the IGBT 50, resistance R5, a parallel circuit of capacitor C3 and resistance R6, and a series component of Zener diodes ZD1 and ZD2 whose polarities are opposite to each other, are connected in series.

Abstract: A multilevel power conversion device includes: N (N?1) direct current voltage sources; a first flying capacitor; a second flying capacitor; and a phase module of a M phase (M?2) being configured to output, from the output terminal, a potential of one of the input terminals, or a potential obtained by adding or subtracting the voltage of the capacitor to or from the potential of the one of the input terminals, by selectively controlling the respective switching elements in an ON/OFF manner.

Abstract: There is provided a gap in a magnetic circuit of an iron core inductor, and a plurality of small size permanent magnet pieces are placed in the aforesaid gap, with the magnetizing directions thereof being provided in side-by-side relation. If the magnetizing direction of the permanent magnet pieces is opposed to that of a D.C. magnetic field which is produced in a magnetic circuit, yet in case D.C. and A.C. overlapping currents flow through the inductor, then the D.C. magnetic field produced in the magnetic circuit will be off-set thereby, providing a high inductance value, while eddy currents produced within the permanent magnet pieces due to the A.C. magnetic field will be reduced to a considerable amount, because the permanent magnet pieces are small in size, thus minimizing the heat to be produced in the permanent magnet pieces.

Abstract: There is provided a gap in a magnetic circuit of an iron core inductor, and a plurality of small size permanent magnet pieces are placed in the aforesaid gap, with the magnetizing directions thereof being provided in side-by-side relation. If the magnetizing direction of the permanent magnet pieces is opposed to that of a D.C. magnetic field which is produced in a magnetic circuit, yet in case D.C. and A.C. overlapping currents flow through the inductor, then the D.C. magnetic field produced in the magnetic circuit will be off-set thereby, providing a high inductance value, while eddy currents produced within the permanent magnet pieces due to the A.C. magnetic field will be reduced to a considerable amount, because the permanent magnet pieces are small in size, thus minimizing the heat to be produced in the permanent magnet pieces.