Research On Parameter Optimization Of PI Controller For Multi-terminal Hybrid HVDC Transmission System

LCC-HVDC transmission technology has the advantages of large capacity and low cost,while VSC-HVDC transmission technology has the advantages of flexible control and providing reactive power support.Combining the advantages of LCC and VSC,multiterminal hybrid HVDC transmission system has become an important development direction for the future multi-terminal HVDC transmission.PI controller has been widely used in HVDC transmission system because of its simple structure and great control effect.However,there is multiple PI controllers in the multi-terminal hybrid HVDC transmission system and the parameter configuration is complex.The trial-and-error method is usually used to select parameters in engineering,which will consume lots of time and resources.Therefore,this paper focuses on the parameter optimization of PI controller for multi-terminal hybrid HVDC transmission system.The main work is as follows.(1)Taking LCC-MMC-MMC hybrid HVDC transmission system as the research object,the corresponding simulation model is built in MATLAB/Simulink,which lays the foundation for the later research.The start-stop characteristics of the multi-terminal hybrid HVDC transmission system as well as the fault response characteristics of the multi-terminal hybrid HVDC transmission system with different control strategies when fault occurs at the AC side are analyzed by simulation.(2)Based on the small signal dynamic model,a method to analyze the impact of PI controller parameters on multi-terminal hybrid HVDC transmission system is proposed.The state space models of LCC,MMC and DC line are established,and the small signal dynamic model of multi-terminal hybrid HVDC transmission system is obtained by combining and linearizing the state space equations of each subsystem.The stability regions of PI controller parameters of LCC constant current control,MMC outer loop control and MMC loop suppression control are obtained by frequency domain analysis.And the influence of different PI controller parameters on the stability and dynamic response characteristics of multiterminal hybrid HVDC transmission system is studied by time domain analysis.Finally,the analysis results are verified by simulation.The proposed method can provide theoretical guidance for the control parameter selection of a single group of PI controller parameter.(3)An optimization strategy of PI controller parameters for the multi-terminal hybrid HVDC transmission system is proposed based on the established small signal model.The objective function of the optimization strategy is to increase the damping ratio of the system and keep the negative real eigenvalue away from the imaginary axis.The parameters of all PI controllers of the system are optimized by particle swarm optimization(PSO).And the dynamic response characteristics of the multi-terminal hybrid HVDC transmission system are improved under the condition of small disturbance stability.Finally,the optimization strategy proposed in this paper and the optimization strategy with ITAE criterion(error integral function)as the objective function are compared by simulationThis paper focuses on the parameter optimization of PI controller for multi-terminal hybrid HVDC transmission system,and the research results provide reference for the parameter design of PI controller in practical engineering..