Patent ID: 7577009

Claim:
A PWM cycloconverter that is an electric power converter directly connected by a two-way semiconductor switch having two one-way semiconductor switches combined and respectively independently turned on and off, in which a current can be supplied only in one direction between each phase of a three-phase ac power source and each phase of the electric power converter with three-phase outputs, the on/off time of the two-way semiconductor switch being determined in accordance with a voltage command applied to a load connected to the output side of the two-way semiconductor switch, the PWM cycloconverter comprising: an input voltage phase detector for detecting the phase of the voltage of the three-phase ac power source; a current detector for detecting the direction of the current supplied to the two-way semiconductor switch; and a commutation compensator for receiving the outputs of the input voltage phase detector and the current detector as inputs to compensate for the voltage command; wherein output voltage commands are obtained by the commutation compensator from following formulas (1), (2) and (3): Vu _ref2= Vu _ref1 ΔV (1) Vv _ref2= Vv _ref1 ΔV (2) Vw _ref2= Vw _ref1 ΔV (3) under conditions that when the phases of the three-phase ac power source are respectively defined as Vr=Vin*sin θin, Vs=Vin*sin(θin−120) and Vt=Vin*sin(θin−240), if the output of the current detector is positive in sections of 0°≦θin≦60°, 120°≦θin≦180° and 240°≦θin≦300°, and if the output of the current detector is negative in sections of 60°≦θin≦120°, 180°≦θin≦240° and 300°≦θin≦360°, ΔV represents a negative fixed value, and if the output of the current detector is negative in the sections of 0°≦θin≦60°, 120°≦θin≦180° and 240°≦θin≦300°, and if the output of the current detector is positive in the sections of 60°≦θin≦120°, 180°≦θin≦240° and 300°≦θin≦360°, ΔV represents a positive fixed value, and in this case, a calculation is carried out to obtain output voltages by defining Vu_ref 2 , Vv_ref 2 and Vw_ref 2 as output voltage command values of a U-phase, a V-phase and a W-phase respectively commuted by commutation compensator; Vu_ref 1 , Vv_ref 1 and Vw_ref 1 as output voltage command values of a U-phase, a V-phase and a W-phase; Vr, Vs and Vt as input voltage values of an R-phase, an S-phase and a T-phase; Vin as a peak value of an input voltage and θin as a phase of the input voltage.