Abstract: Reflux diode 5u.about.5w and 5x.about.5z are in anti-parallel connected to MOSFET 4u.about.4w and 4x.about.4z. When MOSFET 4u.about.4w and 4x.about.4z are turned OFF, an electric current flows in a forward direction to reflux diode 5u.about.5w and 5x.about.5z. In the case of this construction, when for example reflux diode 5u disconnects, a small inverse voltage is applied from inverse voltage applied circuit 7 to reflux diode 5u. For this reason, as the inverse recovery of reflux diode 5u is produced by low voltage direct current power source 8 of inverse voltage applied circuit 7, loss occurring at reflux diode 5u is reduced.

Abstract: A three-phase bridge rectifier includes three bidirectional switching circuits each including a single-phase rectifier circuit having four single-phase bridge-connected diodes and a semiconductor switching element connected between DC output terminals of the single-phase rectifier circuit, three AC side reactors each connected between one of two AC input terminals of each bidirectional switching circuit and each one of output terminals of a three-phase AC power supply, three positive side diodes each having an anode connected to a positive side DC output terminal of each one of the bidirectional switching circuits and a cathode connected to a positive side DC bus, three negative side diodes each having a cathode connected to a negative side DC output terminal of each one of the bidirectional switching circuits and an anode connected to a negative side DC bus, a smoothing capacitor including two capacitors series connected between the positive and negative side DC buses and a neutral terminal connected to the

Abstract: In the A.C. electric motor control device of this invention, with the object of improving response to abrupt speed adjustments and load fluctuations, and of improving stability of control under low speed operation, a prescribed current of the inverter circuit is detected and the power factor or power is controlled in accordance with the amount of change in this current.Specifically, a prescribed current of the inverter circuit is detected and the power factor or power is calculated from this detected current value. Using the result of this calculation, together with a command value, control quantities are calculated that determine the output voltage and output frequency of said inverter circuit. Control signals for the switching elements of said inverter circuit are then generated in accordance with these calculated control quantities.

Abstract: In an inverter in which six switching elements of an inverter main circuit is controlled to be turned on and off under a switching pattern in which a voltage space vector composed of adjacent two of six fundamental voltage vectors out of phase from one another by an electrical angle of .pi.