Patent ID: 8004317

Claim:
A method of controlling the commutation of a power semiconductor switching device and freewheel diode pair, the method comprising: applying, upon receipt of a switch-on command signal, a first waveform portion of a voltage function to a control terminal or the gate of the power semiconductor switching device, said first waveform portion of said voltage function allowing regulation of a current rise in the device whilst changing voltage across the device; and detecting a feature in a current or voltage sense signal of said pair, said feature substantially at the instant when the voltage across the diode begins to change from an on-state towards an off-state voltage during said applied first waveform portion of said voltage function; generating a reference function and producing a change in profile of said reference function responsive to said detection to thereby change said voltage function from said first waveform portion to a second waveform portion; applying substantially at said instant said second waveform portion of said voltage function to the control terminal or the gate of the power semiconductor switching device to enable the voltage change across the power semiconductor switching device to substantially track the voltage change across the diode; and controlling voltage change across the power semiconductor switching device during applying said first and second waveform portions, on the basis of comparison of said reference function and a scaled voltage of said semiconductor switching device.