Which is more suitable to a modular multilevel SDBC inverter for utility-scale PV applications, phase-shifted PWM or level-shifted PWM?

This paper discusses and compares phase-shifted pulsewidth modulation (PS-PWM) and level-shifted PWM (LS-PWM) in a modular multilevel single-delta bridge-cells (SDBC) inverter for utility-scale grid-tied photovoltaic (PV) applications. A unique characteristic of this inverter application is the capability to operate even under imbalanced power distribution among its bridge cells. An imbalanced energy distribution may degrade harmonic performance and limit the inverter operating range. The focus of this research lies in analyzing the following two fundamental properties; waveform quality and energy balancing capability when either PS-PWM or LS-PWM is applied. This paper highlights the benefits of LS-PWM over PS-PWM in this particular application, and demonstrates that the SDBC inverter is suitable for applications with imbalanced power distribution. Experimental results obtained from a three-phase 10-kW downscaled SDBC inverter with six bridge cells per cluster show good agreement with those from theoretical analysis.

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