Research On Micro-grid System Energy Optimal Scheduling Strategy

ABSTRACT:With effective integration of distributed generations (DGs), Micro-grid not only solves the harmonic problem caused by DG decentralized accessing to the utility grid, but also greatly enhances the flexibility and reliability of power system. The energy optimal strategy of Micro-grid system is very important for the Micro-grid system in improving power supply reliability and economical operation. One Micro-grid energy optimal strategy proposed in this paper can guarantee the security, stability, economical operation of Micro-grid system. The main research contents are as follows:Aiming at unit level control for Micro-grid system, firstly establish the mathematical model of each DG and analyze the different control strategy for distributed generation, including constant power control, constant voltage constant frequency control and droop control. Finally, the validity and effectiveness of control strategy for each DG has been verified based on Beijing Jiaotong University Micro-grid experimental platform.Take converter control strategy for Micro-grid unit as foundation, this chapter further studies the upper level control of Micro-grid system. Aiming at grid-connected operation mode, a Real-time Micro-grid energy optimal management strategy is proposed. It divides the load demand into peak, flat, valley period at first. Secondly, different optimization strategy is determined according to different period and state of charge (SOC) of storage battery. Finally, power instruction is transferred to each DG to ensure the optimal operation of Micro-grid. Energy optimal scheduling model based on optimal strategy is established and battery discharge penalty function is added to the objective function to ensure battery always maintaining a certain energy reserves. A simulation example programmed with Matlab validates the rationality and validity of the control strategy.Aiming at the islanded mode of Micro-grid energy optimal management, the problems of energy optimization is divided into previous planning and real-time scheduling. In previous planning, optimal on/off state of each controllable DG is determined with the help of uncontrollable sources output power and load demands forecasting. In real-time scheduling, the result of optimal on/off states for DG is adopted, and two different real-time energy management strategies are proposed according to whether Micro-grid system includs energy storage device or not. For the Micro-grid system including energy storage device, different strategy is determined by the state of energy (SOE) of the battery, load demand and on/off state of each DG. Load shedding and excess-power dissipationg are considered in Micro-grid operation, too. Finally, a simulation example implements the proposed scheduling strategy. Results show that the proposed micro-grid energy management optimization strategy can not only ensure the security, reliability, long-term operation, but also can reduce the energy storage capacity requirements, save investment cost.