Design of space vector-based hybrid PWM techniques for reduced current ripple

Abstract

Switching sequence used by conventional space vector PWM (CSVPWM) involves equal division of zero vector time between the two zero states in every subcycle. The sequences employed by bus-clamping PWM involve use of only one zero state in a subcycle. This paper deals with two sequences, which use only one zero state and involve division of active vector time within a subcycle. A novel hybrid PWM technique, employing these two sequences in conjunction with the conventional sequence, is proposed. The proposed PWM technique is designed using the notion of stator flux ripple. A procedure is presented for designing hybrid PWM techniques involving multiple sequences for reduced current ripple. The proposed PWM technique results in reduced current ripple over CSVPWM at higher modulation indices. Experimental results on a 2hp prototype induction motor drive are presented.

Switching loss characteristics of sequences involving active state division in space vector based PWM

“…Stator flux ripple is the time integral of the error between the reference vector and the instantaneous applied voltage vector, and is a measure of the ripple in the line currents [4,6]. Based on this study, hybrid PWM techniques that use different sequences within a sector have been developed, with the objective to minimize THD.…”

“…The effect of different sequences on THD in line currents has been analyzed in [4,6] using the concept of stator flux ripple. Stator flux ripple is the time integral of the error between the reference vector and the instantaneous applied voltage vector, and is a measure of the ripple in the line currents [4,6].…”

“…Fig. 1, is generated by applying the active state 1, the active state 2 and the zero states 0 and/or 7 for durations T 1 , T 2 and T Z respectively [1][2][3][4][5]. For a given reference vector and Ts, the duration T 1 , T 2 and T Z are unique.…”

“…This freedom can be exploited to achieve reduction in the harmonic distortion (THD) in line currents and/or to reduce the switching losses in the inverter. The effect of different sequences on THD has been studied in [4,6], and a hybrid space vector PWM technique using sequences that involve active state division, in conjunction with the conventional sequence, has been proposed to reduce THD.…”

“…A significant, additional degree of freedom in space vector based PWM for three-phase, twolevel converters, compared to triangle comparison based PWM, is the division of active state time, and the choice in sequence of application of the different states in a sub-cycle [4][5][6]. This freedom can be exploited to achieve reduction in the harmonic distortion (THD) in line currents and/or to reduce the switching losses in the inverter.…”