Research On The Coordination Control And Capacity Optimization Method Of Extended Energy Storage Systems In Microgrid

Microgrid (MG) is an efficient structure to integrate distributed generators (DGs),energy storage systems (ESS) and loads, which can supply flexible, reliable andeconomic power to local customers. The key point to the reliable operation of MG isto achieve self-control, protection and management by reasonable planning andcoordination control of its internal units. As an important part of MG, ESS can adjustthe power distribution, maintain power balance and improve the power quality. In thisdissertation, ESS is extended to include the load demand response in MG. And, mainworks of this dissertation focus on its coordination control and capacity optimizationas follows:1. Various DG models suitable for stability simulation of MG are developed,including wind turbine, solar array, battery, supercapacitor, family-friendlycontrollable loads and power electronic converters. These models will be used in thefollowing studies.2. A double-layer voltage control strategy is developed to mitigate the voltagefluctuations and flickers at the gird-connected point (GCP) in MGs. It coordinates theautomatic voltage control and the battery energy storage control (BESC) by setting avoltage switching threshold so as to mitigate the voltage fluctuations and flickers atthe GCP and reduce the charging/discharging cycles of battery energy storage system(BESS) at the same time.3. According to the frequency issue of autonomous MG (AMG), novel frequencyregulation strategies are developed from the views of hybrid energy storage system(HESS) and family-friendly controllable loads.1) A frequency regulation strategy based on a frequency hysteresis loop isdeveloped to the battery-supercapacitor HESS (abbr. strategy I). Hysteresis loop isintroduced to the control strategy, and frequency regulation accuracy and BESS’scharging/discharging cycles are coordinated so as to avoid some small, meaninglesscharging/discharging actions.2) Based on strategy I, a new frequency regulation strategy (abbr. strategy II) isdeveloped. Priorities of BESS and supercapacitor are optimized in the strategy.Utilization ratio and service life of the battery-supercapacitor HESS can also beimproved while maintain the frequency control accuracy.3) A novel decentralized demand control (DDC) strategy for family-friendlycontrollable loads is proposed to regulate the AMG’s frequency in coordination with ESS, in which a variable participation degree proportional to the frequency deviationis introduced. DDC strategy not only can guarantee the customer comforts andimprove the capability of frequency regulation, but also can reduce the ESS’s capacity.Compared with the centralized based demand-side control methods, DDC strategy cansignificantly reduce the investment cost and improve the frequency control efforts.4. A probabilistic capacity optimization method is developed to determine theoptimal capacity of HESS in AMG. It combines the probability analysis andtime-domain simulation to generate probability distributions of HESS. Optimalobjective is obtained using a new area planning algorithm.