Front-End Isolated Quasi-Z-Source DC-DC Converter Modules in Series for High-Power Photovoltaic Systems-Part II: Control, Dynamic Model, and Downscaled Verification

This paper is the continuation of Part I in which a quasi-Z-source modular cascaded converter (qZS-MCC), comprising front-end isolated qZS half-bridge dc-dc converter submodules (SMs), for dc integration of high-power photovoltaic (PV) systems is proposed. The qZS-MCC-based PV system features modular structure, high-voltage dc collection of PV power, simple control with a unified and constant duty cycle for the front-end isolation converter of all SMs, and low qZS impedance due to no double-line-frequency pulsating power. Here, control scheme of the qZS-MCC PV system integrated into the dc collection grid is investigated. Dynamic model of the system is established for controllers design and time-domain transient simulation. Experimental tests are carried out on the downscaled prototype as a proof-of-concept of the proposed control and modeling, demonstrating the validity of the proposed approaches.