Novel six-step and twelve-step current source inverters with DC-side commutation and energy rebound

Abstract

New six-step and twelve-step current source inverters (CSI) with novel features of DC-side commutation and energy rebound are proposed with detailed analysis and explanation of the circuit operation. The proposed inverters operate over very wide range of frequency and load variation due to the DC-side commutation. Optimum design of the commutating circuit has been achieved through computer simulation and four different types of energy rebound circuits are proposed. The energy rebound scheme has made the use of low voltage SCR``s possible and contributed to an increase in inverter efficiency and reliability. Also, a method to determine the amount of rebounding energy and the rating of the rebound circuit is presented for the specified operating condition of the inverter drive system. An auxiliary inverter with a power requirement of about one-half of that of the main inverter is added to the six-step CSI to obtain a twelve-step CSI. This is to be contrasted with the twelve-step dual current source converter which is composed of two six-step CSI``s. Full four quadrant motor operation has been possible with both the new sixand twelve-step inverters. Experimental results tested with a laboratory prototype have shown good agreement with theoretical expectations.