Study On Distribution Network Optimal Operation And Distributed Generation Hosting Capacity

With the rapid increasing of renewable distributed generation(DG)penetration,the integration of high penetration DG has brought various impacts on distribution network,including voltage rise,loss increase,power quality decline,etc.In order to solve the issues caused by high penetration DG,a series of research has been carried out,which focuses on power flow algorithm for distribution network with DGs,control method of step voltage regulator(SVR),economic dispatch of hybrid AC/DC distribution network,and DG hosting capability.The main contributions of this dissertation are as follows.1.Three-phase transformer model of the grounded wye-delta connection is developed on the basis of the equivalent transformer impedance matrix,and a three-phase power flow program is realized,which takes into account various three-phase transformer connections.Based on the sensitivity impedance matrix of PV nodes,a modified three-phase backward/forward sweep algorithm is developed for radial distribution networks containing DGs which are modeled by PV nodes.By means of simulation,two kinds of PV nodes are compared to explore their impact on voltage level of distribution networks.2.The shortcoming of the voltage control method based on line drop compensator(LDC)and the reason that it failed are analyzed.To address this issue,a fuzzy control method based on communication is proposed to regulate SVRs,and a fuzzy logic controller considering active and reactive power synthetically is designed to mitigate the pressure of frequent action of SVRs.3.A security-constrained coordinated economic dispatch method of energy storage systems and converter stations for hybrid AC/DC distribution networks is proposed.By means of optimizing reactive power adjustment of converter station and charging/discharging of ESS,power supply companies can ensure safe operation of distribution networks,and minimize the total cost of energy purchase from the upper grid in transmission and distribution separated electricity market.In addition,this is a mixed integer nonlinear programming problem and is difficult to solve.In order to improve the computing speed,the original model is transformed into a mixed integer linear programming problem by linearization technique.4.A DG hosting capacity evaluation method based on robust optimization(RO)is presented.It models uncertainty of DG power output and load level by means of interval theory.This evaluation method can take into consideration all possible scenarios caused by the uncertain DG power output and load level in the predefined intervals.Coordinated voltage control and reactive power compensation are integrated into the proposed RO-based framework,which affects the ability of a distribution system to accommodate DGs.The parameter that represents the level of conservativeness is introduced into the proposed RO-based evalution method,and the DG hosting capacities can be determined corresponding to different conservative levels.