Direct power converting apparatus

A direct power converting apparatus, comprising:

• a positive-side DC power supply line;
• a negative-side DC power supply line to which a potential lower than a potential applied to said positive-side DC power supply line is applied;
• input capacitors each connected between ones of a plurality of input lines connected to a multi-phase AC power supply and functioning as a power supply;
• a current-source power converter converting a multi-phase AC voltage input from said input lines into a square-wave-shape DC voltage having two potentials, and supplying said positive-side DC power supply line and said negative-side DC power supply line with said DC voltage;
• a voltage-source power converter converting said DC voltage having two potentials between said positive-side DC power supply line and said negative-side DC power supply line into a square-wave-shape AC voltage, and outputting said square-wave-shape AC voltage to an inductive multi-phase load;
• a first capacitance device having one end connected to said positive-side DC power supply line;
• a second capacitance device connected to another end of said first capacitance device and said negative-side DC power supply line;
• a first diode device having, between said first capacitance device and said second capacitance device, an anode connected to said first capacitance device and a cathode connected to said second capacitance device;
• a second diode device having an anode connected to a point between said second capacitance device and said first diode device and a cathode connected to said positive-side DC power supply line;
• a third diode device having an anode connected to said negative-side DC power supply line and a cathode connected to a point between said first capacitance device and said first diode;
• a discharge resistor connected between said positive-side DC power supply line and said negative-side DC power supply line;
• and
• a switching device connected in series with said discharge resistor between said positive-side DC power supply line and said negative-side DC power supply line, being brought into conduction when a voltage between both ends of said first capacitance device or said second capacitance device exceeds a first predetermined value, and being interrupted when the voltage falls below a second predetermined value.