A single-phase five-level inverter with active power decoupling and voltage boosting for PV applications

Multilevel inverters (MLIs) with capabilities of voltage boosting and reactive power regulation have gained significant popularity in grid-connected photovoltaic (PV) applications. In this paper, a novel quasi-two-stage single-phase five-level inverter (FLI) with voltage boosting ability is proposed, where only single PV source, two capacitors and eight switches are employed. Compared to traditional single-phase two-stage T-type FLI, the proposed topology eliminates two switches and one capacitor. Moreover, there is no neutral-point voltage balance problem. To address the inherent double-line frequency (DLF) power pulsation problem in single-phase systems, a simple but robust active power decoupling (APD) control scheme is proposed. Thus, bulky dc-link electrolytic capacitors are removed and the required capacitance value is reduced by 93 %. Then, the system reliability and power density are enhanced. The working principles with the corresponding modulation method are discussed deeply. Moreover, the detailed controller parameter design is provided step-by-step. Comparisons between the proposed and the state-of-the art MLIs are exhibited in detail. Finally, a 2-kVA prototype was set up in laboratory to verify the feasibility of the proposed inverter. The experimental results show that the total harmonics distortion (THD) of grid current is 2.27 %, and the peak efficiency of the system reaches 96.2 % even with silicon (Si) semiconductor devices, which indicates that the system has good performance.