oa High-Voltage DC Integration of Photovoltaic Power by Front-End Isolated Quasi-Z-Source Converter Modules in Series

Considering dc characteristics of Photovoltaic (PV), a higher voltage dc integration of PV power is expected to inherit the PV power's natural dc property, replace the bulky line-frequency transformer as the central inverter, eliminate the dc-side low-frequency pulsating power as the cascade multilevel inverter, and reduce power loss in distribution and transmission. However, due to the PV panel insulation demand, the voltage of series connected PV panels is restricted to one kilovolt. To overcome that defect, a quasi-Z-source modular cascaded converter (qZS-MCC) is proposed by series connection of front-end isolated qZS half-bridge (HB) dc-dc converter submodules (SMs). The qZS-HB is able to handle PV voltage and power variations, dc-link voltage balance, and HV-side dc integration. Thus, there is no requirement to control the front-end isolation converter. It greatly reduces the complexity of control and implementation comparing to that without qZS network, where the front-end isolation converters of all SMs require separate control method and gate driving. Simulation investigations based on high-power qZS-HB SMs and experimental results on downscaled prototype validated the proposed solution, providing a promising approach for the future integration and transmission of high-power PV systems.