Unified PWM algorithm based on effective time for four-switch three-phase inverter

A unified pulse-width modulation (PWM) algorithm is proposed for four-switch three-phase inverter (FSTPI) to reveal the essential relationship among different PWM algorithms. The FSTPI generates only four active vectors and the zero vector is absent, so the zero vector can be synthesised by two opposite active vectors or all four vectors. Effective time for different phase is derived for the proposed unified PWM. By altering the distribution of effective time in a PWM period, various PWM algorithms with different equivalent zero vectors are implemented. In the proposed algorithm, sector identification and trigonometric function calculation are not required and the voltage fluctuation across the two dc-link capacitors is also taken into account. Thus, the desired output voltage can be synthesised simply and precisely. Experimental results confirm the effectiveness of the proposed unified PWM algorithm.