Comprehensive Analysis and Experimental Validation of 240$^\circ$-Clamped Space Vector PWM Technique Eliminating Zero States for EV Traction Inverters With Dynamic DC Link

Abstract

A bus-clamping space vector pulsewidth modulation (PWM) called 240 $^\circ$ -clamped PWM (240CPWM) is analyzed for three-phase converters that have a cascaded connection of a dc–dc stage and a dc–ac stage. A direct application of the proposed concept is electric vehicle (EV) traction inverters that employ a dc–dc stage to interface a relatively low-voltage battery to a high-voltage motor. The 240CPWM method has the major advantages of clamping a phase to the positive or negative rail for 240 $^\circ$ in a fundamental period, clamping of two phases simultaneously at any given instant, and use of only active states, completely eliminating the use of zero states. These characteristics lead to more than seven times reduction in switching losses of the inverter at unity power factor compared to CSVPWM, comparable or better total harmonic distortion (THD) performance, significant reduction in common-mode voltage and high efficiency. The THD of the line current is analyzed using the notion of stator flux ripple and compared with conventional and discontinuous PWM methods. The switching loss characteristics under different power factor conditions are discussed. Experimental results from a 10-kW hardware prototype are presented. The full load efficiency with the proposed 240CPWM for the dc–ac stage exceeds 99% even with Si insulated-gate bipolar transistors (IGBTs).