A novel carrier-based PWM strategy for hybrid multilevel inverters

The hybrid multilevel power conversion has achieved attention in resent years for minimizing the cascaded cells number for given output voltage levels. However, the equipment complexity is not really decreased due to the adopting of PWM rectifier and this restrains its industry utilization. In order to avoid using controlled rectifier, the hybrid frequency carrier-based PWM (HFPWM) control strategy adapted to hybrid power cells is presented in this paper. In comparison with the general scheme, this proposed strategy is able to make each cell of the hybrid inverter participate PWM modulation and have the same output voltage polarity. Thus the reverse current of the low-voltage cell is not present and this power cell can also be fed by diode rectifier. The hybrid multiply connecting approach of the transformer secondary windings feed for the three-phase diode rectifiers with different input voltages is illustrated in this paper. The driving approach of each power cell is derived from this strategy and realized on the hybrid seven-level adjustable-speed drive laboratory system. This control strategy will benefit the energy saving applications such as speed control of pumps and blowers.