Multiple Time Scale Control Scheme for the Power Distribution Network with DC Energy Balancing Interconnection

A multiple time scale interactive control scheme for distribution networks (DNs) with flexible direct current (DC) energy balancing interconnection is proposed, aiming to enhance the alternating current (AC) power system inertia and flexibility in diversified energy markets. The DC Energy Balancing interconnection (DEBI) framework consists of two back-to-back AC/DC converters and a hybrid energy storage (HES) unit is established. A bi-level multiple time scale control scheme is then developed to enable flexible energy interactions between the interconnected AC systems to attenuate power fluctuations and enhance energy profits. On the upper level for centralized control, a two-stage rolling model for energy optimization is proposed to guide energy interactions among interconnected AC Microgrids (MGs), and derive instructions as reference signals to the converters of the system. On the lower level for distributed local control, an improved virtual synchronous generator strategy with model predictive model control and fuzzy control (MPC-Fuzzy-VSG) is developed for the converters without frequency (derivative) measurement, and the control not need to switch control modes in case of grid fault. For the HES as power balancing unit on the DC side, an adaptive energy recovery (AER) control strategy is developed, the complementary properties of HES are utilized to provide balanced support for the system. Case studies show that, the presented multiple time scale control scheme is proven to be of great practical value in suppressing the power transfer fluctuations to the grid, which makes the demand side very friendly and helpful to the grid.