Cooperative energy management for multi-microgrid systems

Abstract

Microgrids (MGs) bring considerable advantages in improving reliability, reducing cost, and integrating renewable energy to the future power systems. As distributed renewable generators (DRGs) will increase their penetrations in the power systems, the concept of multi-microgrid (MMG) system is proposed as a promising realization of the smart grid (SG). Due to the intermittent and fluctuant nature of renewables, the energy management of MMG systems with high renewable penetration is still challenging. Besides, as more DRGs are connected to SGs, the wide area measurement system (WAMS), which utilizes the phasor measurement units (PMUs) to provide real-time monitoring of MGs, becomes more critical. This thesis studies the energy management algorithms and the design of measurement system for the MMG systems with high-penetration of renewables so as to make the systems operate economically and reliably.

First, a cooperative MMG system framework has been proposed to exploit how MG cooperation, which aims to share energy and information to other MGs, would influence the system performance. We have proposed an adaptive energy scheduling scheme, known as on-line energy management algorithm (OEMA), for the cooperative MMG in order to reduce the time-averaged operation cost and improve the utilization of renewable energy resources. We have made use of Lyapunov optimization to design OEMA. We have proved that OEMA can achieve a near-to-optimal performance in terms of the system cost. Besides, a tradeoff between operation cost and battery size was derived. In the end, the simulation results show that the cooperation of MGs can help reduce the operation cost and improve the utilization of renewable energy resources dramatically.

Besides, we have addressed the selfishness issues of MGs in the MMG system by motivating the MGs to participate in MG cooperation. A Stackelberg game-theoretic framework to MG cooperation, called the MG energy trading game (MGETG), has been proposed. In the MGETG, an MMG center as the leader motivates and regulates the MG cooperation by setting the energy trading prices. Then, MGs as the followers determine their energy trading strategies so as to maximize their utilities. Nikaido-Isoda relaxation algorithm is applied to find the Nash equilibrium of MG actions and a pricing algorithm is devised to find the price of MMGC based on the golden section search. The simulation results show that the proposed algorithms can improve renewable utilization by 25.9% and reduce the total operation cost by 35.5% through MG energy trading.

Furthermore, the optimal PMU and communication link (CL) placement problem has been studied to ensure the system observability and timely data transmission. To meet the PMU data transmission requirements, the proposed model also considers the assignment of communication capacity on every CL. The numerical results show that, compared with the traditional optimal PMU placement model, OPLP can reduce the total installation cost of the measurement system in SG significantly.