Voltage Optimization And Correction Method In Three-phase Active Distribution Network

Renewable energy generations,including wind power generation and photovoltaic generation,are promising solutions to release the energy crisis and environment pollution.Compared with the centralized generation,distributed generation is more flexible and efficient,which is becoming a sustainable energy pattern of sustainable development.However,due to the constant access of the distributed generators,on the one hand,voltage amplitude in distribution network fluctuates more and more obviously and over limited easier;On the other hand,single-phasing or biphase distributed generators and loads enhance the three-phase voltage unbalanced degree,affectting the power quality.In this paper,we study the voltage optimization and correction technology in three-phase active distribution network,putting forward the strategy of centralized optimization in the whole network and local correction.In the long period,a voltage optimization model for three-phase active distribution network based on the semi-definite programming theory is established to realize the optimization of the entire network,Coordinating active and reactive power resources.The reactive power optimization in distribution networks with distributed generators is a complex mixed integer non-convex nonlinear problem.Considering semi-definite programming(SDP)model has excellent mathematical properties,this paper applies it to voltage optimization for distribution network.First,we establish a mathematical model of voltage optimization for three-phase distribution network taking interphase mutual inductance of each branch into consideration.Without considering discrete variables,the original model is transformed and relaxed into a SDP model to guarantee the global optimal solutions within the polynomial times.In dealing with discrete variables,we use sensitivity analysis method combined with branch and bound method.The sensitivity analysis method is used to linearize the original model,transfering the original problem into a first order optimization problem.Then we use branch and bound method to determine the discrete variables in the next iteration.In the short period,a voltage phasor correction quadratic programming model is set up to realize voltage correction,using the sensitivity of voltage phasor to nodal injection power.,which can use adjustable distributed generators and reactive power equipment to correct grid fluctuation quickly.Simulation of three-phase IEEE33 node standard testing system shows that the optimization in the entire network can reduce the network loss effectively,while local correction can correct the over limited voltage amplitude and reduce the three-phase imbalance degree with the least power adjustment amount.