Abstract
Discontinuous pulse width modulation (DPWM) strategies are usually adopted to reduce the switching loss and output current ripple of three-phase three-level traction inverters under three-phase load conditions. However, if there is a short circuit in any arbitrary phase or the inverter is used to feed a two-phase load, the output performance of conventional DPWM strategies will be deteriorated. Here, four improved DPWM (IDPWM) strategies for three-phase three-level neutral-point-clamped (NPC) traction inverter fed two-phase load are proposed. Unlike three-phase load conditions, the phase angle and the amplitude of each basic voltage vector in the space vector diagram are modified under two-phase load conditions. Consequently, sectors are re-divided and duty cycles of basic vectors during synthesis are recalculated. Clamping intervals of each phase for the four type discontinuous PWM (DPWM) strategies are rearranged according to the modified space vector diagram; then, the proposed DPWM strategies can be obtained. Compared with the conventional DPWM strategies, the output current waveform quality of the proposed strategy is significantly improved. Meanwhile, the amplitude of the neutral-point voltage ripple is also reduced.
Highlights
Multilevel inverters are more and more widely being used for high-voltage and medium-voltage applications, and low-voltage applications because of significantly high output waveform quality and low dV/dt [1,2,3]
The switching loss of three-level traction inverters can be considerably reduced by the use of Discontinuous pulse width modulation (DPWM)
Clamping intervals of each phase for the four types of DPWM strategies are rearranged according to the modified space vector diagram; the improved DPWM strategies can be obtained
Summary
Multilevel inverters are more and more widely being used for high-voltage and medium-voltage applications, and low-voltage applications because of significantly high output waveform quality and low dV/dt [1,2,3]. The switching loss of three-level traction inverters can be considerably reduced by the use of DPWM For this reason, DPWM is one of the preferred modulation strategies applied in EV applications. An adjustable DPWM strategy was presented in [11]; the discontinuous intervals are changed with the variation of power factor so as to reduce the switching loss in the whole power factor range These strategies are only suitable for three-phase inverter fed three-phase load. Based on the analysis above, a discontinuous modulation strategy for three-phase two-level inverter fed two-phase load was proposed to reduce the switching loss and current ripple [16]. A [P] means that the clamping phase is A and the clamping state is P, and C [N] means that the clamping phase is C and the clamping state is N
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