Coordinated constant voltage control strategies of a battery-free medium-voltage direct current system incorporating distributed photovoltaic generation units

Traditional distributed photovoltaic generation units (DPVGUs) with maximum power point tracking (MPPT) control strategies are generally regarded as current sources without voltage regulation capability. Due to the lack of voltage regulation capability of DPVGUs, this paper proposes two control strategies to realise the voltage regulation capability of a battery-free medium-voltage DC (MVDC) system incorporating DPVGUs in the off-grid mode. A primary control strategy used on an individual DPVGU is proposed first, which is called an improved DC constant voltage control (CVC) strategy. Under this strategy, the maximum dynamic output characteristics of a photovoltaic (PV) panel and the boost capability of a DC/DC boost converter can be fully utilised to control the MVDC system bus voltage. Secondly, the sequential coordinated constant voltage control (SCCVC) strategy is then proposed on the condition that the limitation of the voltage regulation capability of an individual DPVGU is reached. Under the SCCVC strategy, according to the sequence of the voltage regulation capability of the DPVGUs from large to small, the DPVGUs take turns to operate in the improved DC CVC strategy to realise the voltage control function. Furthermore, simulations using the RTDS are conducted to verify the effectiveness of the proposed control strategies in actual applications.

Automated summary

This paper proposes two control strategies to achieve voltage regulation capability in a battery-free medium-voltage DC system with distributed photovoltaic generation units (DPVGUs). The first strategy is the improved DC constant voltage control strategy, utilizing the maximum output characteristics of a photovoltaic panel and the boost capability of a DC/DC boost converter to control the system voltage. The second strategy is the sequential coordinated constant voltage control strategy, where DPVGUs operate in turns using the improved DC constant voltage control strategy based on their voltage regulation capability.