Planning And Voltage Control Of Distribution Systems With Distributed Generation Integration

With the rapid development of renewable energy such as solar energy and wind energy,a large number of Distributed Generator(DG)emerges in urban and rural distribution network.DG completely changes the structure and operation status of the distribution network,which makes the distribution network change from single-power-source structure and one-way power flow to multi-power-source structure and frequently changing double-way power flow.The volatility of DG also brings great challenges to the reactive power / voltage control in distribution networks.This thesis focuses on the planning and voltage control of distribution network with high penetration of DG.Detailed works on the algorithms,rules and applications are as follows:(1)Based on the power flow equation of the distribution network,variation relationships of the network loss and voltage caused by DG along with the DG access location and capacity are studied and a group of analytical formulus to calculate these variations are derived.On the basis of the above analysis,the planning principles to instruct the optimal selection of the DG access location and capacity are summarized.The validity of the proposed analytical formulus and planning principle is verified by a practical example.(2)Based on the theories about solar radiation in the field of Meteorology and the monitoring data of actual PV station,a time series model for PV power is proposed in this paper,which is suitable for the long term operation analysis such as planning and reliability evaluation.The model takes account both the randomness and regularity of the PV output,and has the characteristics of low dependence on the historical data,few parameters and easy to obtain.The validity of the model is verified by comparison with the measured data from practical PV power station.A multi-objective optimization model for the planning of PV-grid-connection is then established.Two objective functions including the minimum network loss and the maximum voltage qualification rate are selected.The optimal location and capacity of PV can be calculated through solving of the model.The influence of load types on the planning results is also analyzed.(3)Towards the feeder voltage fluctuation problem caused by the PV,the fluctuation of PV power is simulated with the Beta-distribution based solar irradiance probabilistic model,considering three typical weather conditions,namely a low cloudiness day,a cloudless day and a partly cloudy day.The influence of grid-connected photovoltaic on the voltages of distribution system is analyzed.The strategys and rules for the allocation of dynamic reactive power compensation devices on the feeders are proposed to adapt to the integration of DG.(4)For the grid-connecting of the photovoltaic-energy storage hybrid systems in middle-voltage distribution network,the reactive power and voltage control problem is studied.A double-objective extended reactive power optimization model is proposed,which aims at minimum power loss and voltage violation risk.Both the active power of the energy storage equipment and power factor of the photovoltaic units are controlled in this model.The genetic algorithm NSGA-II is implemented to perform the optimization and the Pareto front of the objective function can be obtained.The best compromise solution is found through fuzzy theory to achive the reactive power and voltage optimization control in middle-voltage distribution network with photovoltaic.(5)For the reactive power and voltage control in the high-voltage distribution network with wind power integration,the loss characteristics of 110 kV branches with and without wind farms are analyzed.Settings of the gateway reactive power control band are derived using a slack optimal control theory.The getaway reactive power control bands are analyzed by a typical case under different loads and wind farm levels.The getaway reactive power control bands are improved by considering the intersection of the relevant constraints.Such obtained dispersed and slack optimal control can adapt to the variation of operation conditions in a high-voltage distribution network with wind power integration.Researches of the thesis provide models,algorithms and instruction rules for the planning and voltage control of distribution networks with high penetration of distributed generators.