Voltage Control Algorithm Of OLTC In Wind Power Systems Considering Discontinuity Of Tap Changers

With large-scale wind power penetration, random variation of wind speed makes the problem of voltage control more prominent. The on-load tap changer (OLTC) can flexibly switch the tap changers under load and adjust bus voltages without additional investment effectively. The algorithms for guiding the adjusting of tap changers have optimization algorithm and sensitivity algorithm, but both can not avoid the difficulty of discrete tap changers. The voltage control algorithm of OLTC in wind power system considering discontinuity of tap changers is investigated. The main content is as below.(1) Voltage control to wind power system with OLTC based on improved genetic algorithm1) The multi OLTCs coordinated optimization model for the target of voltage security and the optimization of power loss and tap changer margin is established. The active output of the wind turbine generators is divided into several sections and the corresponding sectional mean model is established. For analyzing the voltage security probability of OLTC regulating based on the optimization model, the method that applies the sectional mean to calculating the optimization model and then employs the interval limits to estimate voltage security probability is suggested. Finally, the effect of target weight and divided intervals on the optimization model is discussed.2) The genetic algorithm is chose to solve optimization model. The genetic algorithm is improved for enhancing the ability to deal with discrete variables and seek the global excellent result. The integer coding is adopted. The crossover for individuals is based on random coordination array. The mutation operation is carried out by a random number within variables’ limits. The selection operation is improved by combining the probabilistic survival with the optimal reservation strategy.The results show that:improved genetic algorithm effectively decreases the control error of the canonical genetic algorithm to the nearest integer. The smaller weight coefficient of voltage security and the less number of divided intervals yield the lower probability of voltage security. The suggested method can be used for the probabilistic analysis to voltage security of discrete equipments regulating in wind power system.(2) Sensitivity algorithm of OLTC for voltage control to wind power system based on transforming tap changers to continuous variables.1) The Sigmoid function, NCP function and binary entropy function’s properties and their mechanisms for transforming 0-1 variables to continuous variables are analyzed. The canonical sensitivity algorithm of bus voltage to tap changer is investigated, and then is applied to guide the voltage control of OLTC in wind power system. The cause of control errors is also discussed.2) With binary encoding, the tap changers are described by linear combination of 0-1 variables, and then transformed to continuous variables by introducing Sigmoid function, NCP function and binary entropy function respectively, thus three sensitivity algorithms by transforming tap changes to continuous variables are newly derived. The effect of every algorithm’s initial values and parameter on the algorithm’s error, iterations and OLTC regulating is analyzed, and that how to select the values of every algorithm’s initial values and parameter is investigated.The results show that:The proposed algorithms are effective, and provide new solutions for sensitivity analysis to the discrete variables with equal interval. When the effect of initial values and parameter on corresponding algorithm is avoided, the proposed three algorithms all can be quickly and accurately applied to guide the adjusting of tap changers in wind power system.