Power Sharing and Control for Islanded Microgrid Systems

Distributed generation (DG) microgrid systems are forming the building blocks for smart distribution grids. Enhanced networked-based control structure is needed not only to eliminate the frequency deviations, power-sharing errors, and stability concerns associated with conventional droop control in microgrids but also to yield: 1) improved microgrid dynamic performance, 2) minimized active/reactive power-sharing errors under unknown line impedances, and 3) high reliability and robustness against network failures or communication delays. This paper proposes a new hybrid distributed networked-based power control scheme that addresses the aforementioned problems in a distributed manner. The new method consists of a set of distributed power regulators that are located at each DG unit to ensure perfect tracking of the optimized set points assigned by the centralized energy management unit (EMU).

The average power measurements are transmitted to the EMU to calculate the share of each unit of the total power demand based on real-time optimization criteria; therefore, a low-bandwidthcommunication system can be used. In the proposed method, the distributed nature of the power regulators allows them to adopt the delay-free local power measurements as the required feedback signals. Therefore, the proposed structure provides great robustness againstcommunication delays. Further, this paper presents a generalized and computationally efficient modeling approach that captures the dominant dynamics of a microgrid system. The model can be used to study the impact of power-sharing controllers and delays in microgrid stability. Comparative simulation and experimental results are presented to show the validity and effectiveness of the proposed controller.