Research On Microgrid Energy Management Strategy

A microgrid(MG) refers to the small power system, it is composed of the micro sources, energy storage system(ESS), power converter interface, different kinds of load and monitoring and protection device s. It has two operating modes, that is standalone and inter connected.T he long-term stable operation of the microgrid, need the energy management s ystem(EMS) to optimal arrange the start and shut, and power scheduling scheme of the micro sources and the ESS. In this way to maximize the service life of the ESS, to full consumption of the renewable energy, and minimize the MG total operation cost and improve the operation economics.As to the problem of MG EMS, first build the mathematical optimization models and the objective functions, according to the operating characteristics and limiting conditions of the micro sources and the ESS in the MG. Then use the commercial optimization software CPLEX, which use the branch and cut method as its kernel algorithm to solve the model, and get the optimal dispatch results of the micro sources and the ESS.In order to verify the effectiveness of the proposed EMS to full consumption of the renewable energy and improve the operation economics of the MG. Compare the total operation costs of the MG which use the proposed EMS to operate under different conditions and has a certain rate of renewable energy with the MG which has no renewable energy, the compare results show that the proposed EMS can effectively improve the operation economics.Currently the proposed EMS by may researchers to compute the optimal scheduling scheme, almost all of them use the forecast data of the renewable energy and the load directly, they have not take the renewable energy and the load power forecast errors and its bad effects on the operation of the MG into consideration.Analysis shows that the forecast errors can lead to the scheduling scheme of the micro sources and the ESS computed by the EMS to deviate from the actual operating point. With the MG operation contining, the errors will accumulate in the ESS and finally lead to the state of charge(SOC) of the ESS go beyond the limits. Under this condition the EMS has to shut the ESS to protect it, if at this time the operating state of the micro turbine(MT) is off, then during the shut period of the ESS the input and output power balance of the MG can’t guaranteed.If at this time the operating state of the MT is on, because of the ramp rate of its power output is far smaller than the ESS, the MG can’t ensure that the power input always balance with the big change rate loads, so the stable operation of the MG can’t guaranteed.Aimed at the problem of the forecast errors lead to the scheduling scheme of the micro sources and the ESS deviate from the actual operating point, which result in the ESS SOC go beyond the limits, and the stable operation of the MG can’t guarateed.Proposed the CRO(CPLEX Rolling Optimization) and KSO(Keep Stable Operation) strategies to deal with the problem of the ESS SOC go beyond the limits when the small or big forecast errors occur, respectively, and keep the SOC always in the allowable limits to improve the stablility of the MG.In this thesis, use the probability theory and the propagation of the errors theory to build the mathematical models of the stochastic forecast errors, to analyse the specific effects induced by the forecast errors to the operation of the micro sources and the ESS.Then simulate the real operation of the MG under the foercast errors, the simulation results verified the effectiveness of the proposed control strategies to keep the ESS SOC always in the limits, a nd prove that the strategies can help stable the MG.