Penalty-Based Distributed Optimal Control of DC Microgrids With Enhanced Current Regulation Performance

Abstract

Steady-state optimization and real-time controls are conventionally achieved by separate controllers acting at different timescales in dc microgrids. The separation between them not only lowers the overall energy efficiency but also can cause the line currents and the output currents of distributed generators (DGs) to exceed their limits. Targeting these issues, an optimal controller for dc microgrids is proposed in this article to simultaneously achieve the real-time minimization of operating losses (converter losses and line losses) and the regulation of line currents and DG output currents. First, the optimization problem is established, then converted to an optimal control problem by a designed penalty function. Thereafter, the necessary and sufficient optimality conditions of the problem are derived, based on which a distributed controller is proposed to dynamically track the optimal operating point. Driven by the proposed optimal controller in real-time, line current and DG output current regulations are ensured with greatly enhanced performance. Finally, the closed-loop system stability is analyzed rigorously through Lyapunov stability synthesis. Simulations based on a switch-level microgrid model validate the performance of the proposed control solution.