Patent ID: 6563723
Filing Date: 2003-05-13
Classification: H02M,H03K

Abstract:
A fault tolerant power supply, the supply comprising a dc power source having a dc output with a positive and a negative de bus; an inverter leg, the inverter leg comprising a pair of switch modules; each one of the pair of switch modules comprising a di/dt reactor in series connection with a switch circuit; each of the switch circuits comprising a switching device connected anti-parallel with an antiparallel diode, the first of the pair of switch modules having the anode of the switching device commonly connected to the di/dt reactor in the first of the pair of switch modules, the second of the pair of switch modules having the cathode of the switching device commonly connected to the di/dt reactor in the second of the pair of switch modules, the first of the pair of switch modules having the di/dt reactor connected to the positive dc bus, the second of the pair of switch modules having the di/dt reactor connected to the negative dc bus, the pair of switch modules having a switch common connection, the common switch connection connecting together the cathode of the switching device in the first of the pair of the switch modules and the anode of the switching device in the second of the pair of the switch modules; a first and a second commutation capacitor connected in series across the dc output of the dc power source, the first and second commutation capacitors connected together at a capacitor common connection; a load induction coil connected between the switch common connection and the capacitor common connection; the improvement comprising:a protective circuit comprising: a protective capacitor; a blocking diode having its cathode connected in series with the protective capacitor, the series combination of the blocking diode and protective capacitor connected across the anode of the switching device in the first of the pair of switch circuits and the cathode of the switching device in the second of the pair of switch circuits; and a discharge resistor connected in parallel with the protective capacitor, whereby the protective capacitor charges to a voltage less than the peak allowable voltage of the switching devices, and absorbs additional charge from the first and second commutation capacitors when the load induction coil is at least partially short-circuited to increase the charge on the protective capacitor to a voltage less than the peak allowable voltage of the switching devices so that the voltage applied across a non-conducting switching device at the time of the short circuit is less than the peak allowable voltage of the non-conducting switching device.