Patent ID: 8450961

Claim:
A power converting apparatus, comprising: three input ends respectively receiving a phase voltage of three-phase AC; three output ends; first and second DC power supply lines; a current-source converter including a first switching device group including three switching devices connected between each of said input ends and said first DC power supply line and three switching devices connected between each of said input ends and said second DC power supply line; a voltage-source inverter including a second switching device group including three switching devices connected between each of said output ends and said first DC power supply line and three switching devices connected between each of said output ends and said second DC power supply line; and a clamp circuit including a clamp diode, a capacitor and a shorting switch, the clamp diode having an anode and a cathode connected to said first and second DC power supply lines, respectively, the capacitor being connected in series with said clamp diode between said first and second DC power supply lines, the shorting switch being connected in parallel with said clamp diode, wherein: said converter performs commutation in accordance with any of a first commutation mode and a 120-degree conduction mode determined by results of comparison between a carrier and three trapezoidal waves having a 360-degree cycle and a phase different from each other by 120 degrees; in said first commutation mode, each of said trapezoidal waves has a pair of flat sections continuous for a 120-degree section and a pair of slope areas linking the pair of flat sections for a 60-degree section; said converter performs commutation by comparison between said carrier and said trapezoidal waves changing between said pair of flat sections in said first commutation mode; said 120-degree conduction mode is employed at the timing when said shorting switch is rendered conductive in a state in which said first commutation mode is employed; and said first commutation mode is employed at and after the time when said shorting switching is rendered non-conductive.