Inverter

An inverter comprising:

• a d.c. voltage circuit with three potentials P, C, and N;
• “n” three-level inverter bridges (where “n” is an integer satisfying n≧1) which can selectively output any one of the potentials P, C, and N to an output terminal connected to a load, each of the “n” three-level inverter bridges including:
• first, second, third, and fourth self-arc-extinguishing semiconductor elements having respective anodes and cathodes and connected in series,
• first, second, third, and fourth free-wheeling diodes having respective anodes and cathodes and connected in reverse polarity in parallel and in parallel with the first second, third, and fourth self-arc-extinguishing semiconductor elements,
• a first coupling diode connected to a node between the potential C of the d.c. voltage circuit and the anode of the second self-arc-extinguishing semiconductor element,
• a second coupling diode connected to a node between the cathode of the third self-arc-extinguishing semiconductor element and the potential C of the d.c. voltage circuit,
• a first group of elements for suppressing current change rate connected to a junction between the potential P of the d.c. voltage circuit and the anode of the first self-arc-extinguishing semiconductor element,
• a second group of elements for suppressing current change rate connected to a junction between the potential N of the d.c. voltage circuit and the cathode of the fourth self-arc-extinguishing semiconductor element,
• a first serially-connected element connected to a node between the anode of the first self-arc-extinguishing semiconductor element and the potential C of the d.c. voltage circuit and including a first clamping diode having an anode and a cathode and a first clamping capacitor,
• a second serially-connected element connected to a node between the potential C of the d.c. voltage circuit and the cathode of the fourth self-arc-extinguishing semiconductor element and including a second clamping capacitor and a second clamping diode having an anode and a cathode,
• a third serially-connected element including a first recovery diode having an anode and a cathode and a first recovery capacitor for recovering energy from the first clamping capacitor and from the first group of elements current change rate, and
• a fourth serially-connected element including a second recovery diode and a second recovery capacitor for recovering energy from the second clamping capacitor and from the second group of element for suppressing the current change rate, the cathode of the first clamping diode and the anode of the first recovery diode being connected to a terminal of the first clamping capacitor which is not connected to the potential C of the d.c. voltage circuit, and the anode of the second clamping diode and the cathode of the second recovery diode being connected to terminal of the second clamping capacitor which is not connected to the potential C of the d.c. voltage circuit;
• a first energy regenerative circuit connected to the first recovery capacitor and feeding energy stored in the first recovery capacitor back to a node between the potential P and the potential C of the d.c. voltage circuit;
• and
• a second energy regenerative circuit connected to the second recovery capacitor and feeding energy stored in the second recovery capacitor back to a node between the potential C and the potential N of the d.c. voltage circuit.