High efficiency, soft commutated power drive, for electrical vehicles (steady state operation)

In this paper, a new DC-AC-AC converter for variable AC drives using soft commutation technique is described. It consists of a dual-thyristor voltage inverter connected to cycloconverters. The realized intermediate alternative voltage link, allows to decouple the commutations of the two stages and to obtain nonresonant soft switching. It combines the advantages of a soft commutated converter and those of PWM control (constant commutation frequency, simple control). Experimental results of a three-phase 18 kW nominal power (450 V, 45 A) and 20 kHz chopping output frequency prototype are discussed. It is realized with IGBTs and it supplies trapezoidal currents to a brushless permanent magnet motor. 96% efficiency is measured at rated power.