A Stochastic Stability Enhancement Method of Grid-Connected Distributed Energy Storage Systems

Integrating distributed energy storage systems (DESSs) into the distribution system can facilitate the high-level penetration of renewable energy source-based distributed generations (RES-DGs). To mitigate irregularly time-varying power outputs from RES-DGs, supervisory controllers of DESSs need to allocate corresponding power set points for DESS inverter primary controllers. Consequently, operating conditions of DESS inverters determined by allocated power set points could suddenly change over a wide range and seriously threaten the stability of DESSs. To guarantee DESSs operate stably over a wide range of conditions, this paper proposes a stochastic stability enhancement method embedded in the DESS grid-connected dc-ac inverter controllers. Specifically, by considering the stochastic change of DESS operating conditions as a Markov chain process, the small-signal expression of the distribution system is modeled as a Markov jump linear system (MJLS). Based on this MJLS model, a mode-dependent supplementary controller is developed for the DESS grid-connected dc-ac inverter by solving a set of linear matrix inequalities. This controller can adjust its control gains according to the measured real-time operating mode to enhance the stochastic stability of the distribution system. Studies of the Canadian urban benchmark distribution system have shown the proposed controller can enable the distribution system operate in a stable manner when its operating condition stochastically varies.