An Improved Circuit for Accelerating Commutation in Current Source Inverters

The autosequential commutated current-fed inverter (ASCI) has found widespread application due to its simplicity and reliability. The simplest form of the power circuit is not well suited to high frequency operation at light load, because the duration of commutation is inversely proportional to the link current. The most commonly used modification to overcome this limitation is the diode ring-up circuit. The diode ring-up modification has some drawbacks, mainly a tendency to raise voltage and current stresses in the circuit. An improved ring-up circuit is described that greatly accelerates commutation in the ASCI, without increasing voltage and current levels at base speed and full load. The circuit operation will be described and analytical results presented to substantiate this claim. Some comparisons with the diode ring-up technique will be made. Finally experimental results will be presented to corroborate the theoretical analysis.