Seamless Dispatchable Grid Integration of an FPPT-Controlled PV System with Limited Local Energy Storage

With the proliferation of the photovoltaic (PV) power generation, dispatchability of the PV system is highly desirable to maintain the grid security. There is a requirement of the large local energy storage for the dispatchable grid connection of a maximum power point tracking controlled PV array. In contrast, no such local energy storage is, in principle, required in the case the maximum power point tracking is replaced with flexible power point tracking. However, since there may always be a power tracking error on the PV side because of the duty ratio quantization problem, it is not advisable to fully exclude the local energy storage so as to prevent the above power tracking error from propagating to the AC side. Instead, a low capacity local energy storage system may be used with an appropriate mechanism for its state-of-charge control. In the earlier control coordination methods for the above system configuration, the voltage-source converter was used to control the DC-link voltage, leading to unnecessary oscillations in the AC-side power output. In order to avoid the particular problem, the possibility of the DC-link voltage control by means a battery converter with very limited local energy storage is investigated in the present paper.