Research In Rectifier Control For High Voltage Direct Current Transmission Systerm Based On Adaptive Dynamic Programming

High voltage direct current transmission(HVDC)system is convenient for large capacity and long distance power transmission,which has been developed rapidly in our country.And it will be conducive to promoting the power grid interconnection.HVDC system is a highly controllable complex nonlinear system,the performance of the controller of which is a strong guarantee that the direct current transmission system can operate normally.The traditional PI or PID controller has the advantages of simple structure,easy realization,quick adjustment and others,which can effectively control the HVDC system to some extent,but it will be lack of adaptive and other issues when HVDC system suffers from a large perturbation,so it is often difficult to achieve the expected response speed and robustness.In view of the features of the traditional controller,this paper has designed the rectifier controller on the basis of action dependent heuristic dynamic programming(ADHDP)of approximate dynamic programming(ADP)to control the HVDC system,and what the approximate structure of function uses is BP(Back Propagation)neural network,the research work of this paper is as follows:First,this paper has studied the theoretical system provided by HVDC system,mainly including the basic principles,structure and connecting mode;and then focused on the analysis of the working principles of the converter and its control mode,laying the theoretical foundation for the design of the rectifier controller below;and established the mathematical model of the system by DC transmission line equivalent circuit.Second,the basic principles of BP neural network,RBF(Radial Basis Function)neural network,PID and ADHDP are studied deeply.The ADHDP rectifier controller based on BP neural network,RBF neural network PID rectifier controller and PID rectifier controller are designed.The control algorithms of three controllers above are researched and deduced.Then,the program flowcharts of three control algorithms are given,and they are written by using S function and M language in MATLAB software.Finally,based on the MATLAB/Simulink simulation platform,this paper has built a 12-pulse wave simulation model of HVDC system,and adopted the basic control mode that rectifier-side uses constant-current control and inverter-side uses constant-voltage control.The algorithms program of ADHDP,RBF-PID and PID rectifier controller are embedded in simulation model.The simulation is carried out according to the three control methods,which are as follows:(1)both of the rectifier side and inverter side adopt PID controller;(2)rectifier side uses RBF-PID controller,and inverter side uses PID controller;(3)rectifier side uses ADHDP controller,and inverter side uses PID controller.When the HVDC system is in steady state,single-phase grounding short circuit,two-phase short circuit,three-phase grounding short circuit and direct current transmission line grounding short circuit faults occur,and then simulation results are compared and analyzed in detail.The simulation results show that ADHDP rectifier controller can effectively improve the transient performance of the HVDC system and is with good robustness and adaptability.