Networked-Based Hybrid Distributed 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-bandwidth communication 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 against communication 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.

I. Introduction

Driven by the economic, environmental, and technical reasons, the energy sector is showing increasing interest in adopting smart grid technologies (e.g., advanced communication, control, protection, and monitoring algorithms) to improve the efficiency and reliability of future power grids [1]. In particular, distributed generation (DG) microgrid systems are forming the building blocks for smart distribution grids. This vision is in line with the recently developed IEEE Std. 1547.6, which proposes microgrid clusters as building blocks of future distribution systems [2]. In this paradigm, networked control of microgrids is essential to optimize the microgrid performance in real-time, particularly under high penetration level of DG resources. An energy management controller can be implemented in the upper hierarchy of the microgrid system to optimize the energy flow in the microgrid system by controlling the set points of DG units and other controllable devices (e.g., energy storage devices, loads und the demand-side management program and reactive power sources). Wide band of energy management objectives can be considered in a typical microgrid depending on customer, and utility needs. For example, these objectives include minimizing the fuel cost in a microgrid, minimizing the emission and maximizing the network security [3]– [7]. The utilization of an energy management unit (EMU) brings more intelligence and efficiency to the microgrid system where more flexible operation is needed [8]. This is also in line with recent efforts carried out to adopt communication-based networked control systems in power systems [9]–[14] .