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In a two-stage photovoltaic (PV) system, batteries are generally connected to the DC-link via a converter for buffering the power imbalance induced by the grid supportive services of grid-side inverter and the maximum power point tracking (MPPT) of PV source. Considering the limited battery capacity, the MPPT operation is easily compromised to avoid over-energizing the batteries in the conventional virtual synchronous generator (VSG) control, degrading the energy efficiency and extending the payback period. To concurrently achieve grid supporting and maximum PV power harvesting without increasing batteries, a coordinated VSG control for the photovoltaic/battery (PV/Bat) system is proposed in this paper. In the proposed strategy, the DC-link voltage level is segmented to differentiate the operations of converters. When the DC-link voltage is within the safety margin, the PV source operates at MPPT mode and the inverter output frequency is programmed proportionally to the DC-link voltage deviation. Meanwhile, droop control is implemented to associate the battery power with the DC-link voltage. When the DC-link voltage goes beyond the safety margin, PV de-loading and inverter rectification will be adaptively activated to restore DC-link voltage within the predefined range. The effectiveness and advantages of the proposed strategy are eventually verified by simulations and experiments.
Liu et al. (Fri,) studied this question.