Asymmetrical Level-Shifted PWM-Based Power Distribution Control of Single-Stage Multiport Inverter-Connected Islanded Microgrids

The single-stage multiport inverter (SSMPI) is a cost-effective and high-efficiency solution for multisource integration in islanded microgrids because the energy storage components can connect to the ac microgrid directly without intermediate dc-dc converters. However, it is challenging to design the modulation scheme for SSMPI due to the time-varying dc input voltages and requirement for power distribution between the energy storage components. To this end, this article proposes an asymmetric level-shifted pulsewidth modulation (ALSPWM) scheme for flexible power distribution of the SSMPI under time-varying dc input voltage. In the proposed ALSPWM scheme, proportional variation and asymmetric carriers are defined to ease system modeling under the time-varying dc input voltage in SSMPI. Besides, an instantaneous power model based on non-negative three-phase modulation waves is derived, and a zero-sequence voltage injection method is proposed for desired power distribution control. With the proposed ALSPWM, the flexible power distribution between the energy storage components and superior grid current control of the SSMPI under time-varying dc input voltages, along with reduced computational burden, are realized. Finally, the effectiveness of the proposed ALSPWM scheme is verified on an SSMPI-connected islanded microgrid platform.