Research On Planning And Operation Of Microgrid Including CAES

Microgrids, as building blocks of Energy Internet, can be defined as small scale power systems which include distribution networks, distributed energy resources and local loads. With the penetration of renewable energy resources, energy storage systems are required to decouple the fluctuating energy supply from the fairly inelastic energy demand in microgrids. They are the central elements in microgrids which can improve system flexibility and safeguard the reliable operation of microgrids. Compressed air energy storage (CAES) has become a novel candidate for energy storage system in microgrids due to its salient features such as long cycle life, high ramp rate, quick start-up time and the ability of providing large scale storage capacities. To investigate the planning and operation of microgrids including CAES, the following work are carried on:(1) Configuration of Advanced Adiabatic Compressed Air Energy Storage and its thermal performance are discussed. The main components of CAES, i.e. the compressors, expanders and air containers are modeled in terms of power and energy in order to respect the flexibility in microgrid operation analysis.(2) To avoid suboptimal solution obtained by predetermined-dispatch-strategies-based sizing methods, a bi-level program is proposed for the microgrid planning problem. It considers optimization of operation at the design stage of microgrids. The sizing problem, which aims to search for the optimal capacity of microsources to minimize the total cost, is formulated on the upper level. The unit commitment problem with spinning reserve requirement for the microgrid, which determines the optimal unit schedule under the given capacities to minimize the operation and environmental cost, is described on the lower level. Compared with traditional methods, the model considers both planning and operation together and can obtain more economical results.(3) Considering the response characteristics of prime mover of electronically interfaced microsources, V/f control and droop control are studied for the operation of islanded microgrid. A first order lag transfer function is used to describe dynamic response of prime movers and its impacts on operation of inverters are analyzed as well. To improve the stability of islanded microgrid, a cooperative microgrid control strategy based on droop gain adjustment method is proposed. When the load is changed, the droop gain of CAES is decreased rapidly and increased slowly back to the initial value. By this means, CAES can absorb almost all demand variation and other controllable microsources change output slowly which matches their low response rate. The simulation results show that high response rate of CAES can help microgrids to achieve stable and secure operation.