Research On Active Optimization Of UPFC In Wind Power System And Its Engineering Application Design

As a FACTS device with excellent performance,unified power flow controller(UPFC)can not only fast regulate the power flow of the line and improve the transmission capacity of the power grid,but also provides series voltage compensation and parallel reactive power compensation.In response to large current shock when short-circuit fault occurs,Zhejiang University proposed a UPFC-FCL which combined UPFC with solid-state fault current limiter(SSFCL)and can effectively limit the amplitude and rising speed of short circuit current.In this paper,over-voltage protection strategies of capacitance in UPFC-FCL are proposed,active power optimization based on genetic algorithm in wind power system by controlling UPFC are discussed,and engineering application in intelligent distribution network with distributed power supply are designed.First,the mathematical model including static and dynamic models of traditional UPFC is established,and control strategies aimed at specific control objectives of converters are designed.Then,the working principle of UPFC-FCL and current limiting dynamic process during short-circuit fault are analyzed.To solve the problem of over-voltage of capacitance,a new protection strategy based on switchover of constant-current and constant-voltage are proposed,which can fed the energy of the DC capacitor back to the grid in an invert way.In addition,a overvoltage protection circuit triggered by BOD is designed,by which the discharge circuit can be formed immediately after the capacitance overvoltage is detected and auto recovery after fault removal.The simulation results show that the surge voltage of DC capacitor is smaller and time to afford is shorter under two improved protection strategies comparing to the conventional one,which prove the effectiveness of two strategies.Secondly,improving the distribution of power flow in wind power system by controlling UPFC is discussed.Considering the wind power output and the fluctuation characteristics of different types of load,the active power optimization strategy of wind power integrated system based on genetic algorithm is proposed.The fitness function is written according to the power flow calculation method and the injection voltage of UPFC is selected as a chromosome to code.Then optimize power flow by controlling UPFC aiming at the minimum peak regulating capacity required by the system.After that,a simulation model of 220 kV wind power integrated system with UPFC is built on PSCAD/EMTDC,and results show that the peak regulating capacity is significantly reduced in the example,which verifies the strategy helps to improve the power system peak load regulating capability and wind power accommodation.In addition,a power flow calculation method for wind power integrated system with UPFC under control of constant injection voltage is given.An additional node injection power algorithm is used to equivalue the UPFC to realize its decoupling with the system,then the power balance equations and the modified Jacobi matrices of the node are obtained which can conveniently combine with the traditional Newton-Raphson method.Thirdly,the application prospect of UPFC in intelligent distribution network with distributed power supply is analyzed,and it is considered that UPFC can satisfy the construction demand of intelligent distribution network well.Taking the 10 kV/1MVA UPFC prototype as an example,a brief introduction to the design of primary system and control system is given.And the access system solution,start-stop strategy and plane layout of UPFC in 10 kV distribution network are also designed.Under this project application,it will not affect the power supply of the system when UPFC is out of operation.Finally,the 380V and 10 kV test for the UPFC prototype was completed by the group,including starting and connecting test,power flow regulation test,compensation voltage test on series side and reactive compensation test on parallel side.The test waveforms are good,which verifies the working principle of UPFC and the effectiveness of the control strategy.