Cascaded five-level quasi-switched-boost inverter for single-phase grid-connected system

The quasi-switched boost inverter (qSBI) has the advantage over the quasi-Z-source inverter (qZSI) in reducing one capacitor and one inductor. The qSBI is applied to the cascaded H-bridge (CHB) topology to create a new cascaded single-phase five-level inverter. Besides, a PID controller for DC-link voltage of each module is proposed and implemented based on DSP TMS320F28335. Unlike the DC-link voltage controller in qZSI, the presented controller is directly controlled via controlling the capacitor voltage. By using this controller, the capacitor voltage is kept constant, even though the input voltage or the load is changed suddenly. As a result, the proposed cascaded system solves the imbalance problem of DC-link voltage in the traditional CHB inverters. Also, a grid-connected control strategy for modules in the cascaded five-level qSBI is presented. The proposed inverter offers much less total harmonic distortion of the output voltage. Simulation and experimental results are shown to verify the validity of the proposed control strategy.