Coordinated and Voltage Sharing Control for Input-Parallel and Output-Series Connected PV DC Boost Converter

PV system integration with VSC-HVDC technology has been significantly developed in the past decades. The photovoltaic DC boost integration and grid-connected system (PV-HVDC) is composed of DC boost converter and modular multi-level converter(MMC). Input-parallel and output-series(IPOS) connected DC/DC converter is adapted to increase the output voltage of PV plants. As there are multiple operation modes of the system, the DC/DC converter should be controlled coordinately to assure stable operation of system. A communication-less coordinated control strategy that the DC boost converter can switches the control mode according to the variation of DC bus voltage is proposed in this paper. When the error between the DC bus voltage and the rated value exceeds the dead zone, DC boost switches to constant output voltage mode, and the stability of DC bus voltage can be maintained. In addition, an output voltage sharing control strategy is designed for the IPOS connected converter to achieve coordinated and stable operation between sub modules. The proposed control strategy is evaluated based on time-domain simulation studies in PSCAD using a 1MW PV-HVDC system. The results show that the proposed strategy enables the stable operation of the system in various conditions.