Modeling And Parameter Optimization Of Hybrid HVDC Transmission System Based On PSCAD

It is estimated that China's generator installed capacity will reach 2 billion kilowatts in 2020,and the "West-to-East Power Transmission" project will deliver 270 million kilowatts through the UHV transmission system.UHV transmission lines connect the regional grids.A large-scale AC/DC hybrid system is formed.The operating characteristics of the power system have changed dramatically.Power system transient processes are becoming more complex.It is necessary to study the transient process of the power system.Firstly,this paper refers to the actual DC engineering parameters to model the primary equipment and control system of the traditional HVDC transmission system.Based on PSCAD,a transient simulation model of high-voltage direct current transmission system was built.The research focuses on the control structure,control mode and coordinated operation strategy of the HVDC transmission system.Based on the model,the step response of the system is studied and analyzed.Meanwhile,the transient process of three faults overhead line ground short circuit fault and single pole blocking fault is studied.Secondly,combined with light-duty direct current transmission technology,the topology and control strategy of LCC-VSC hybrid HVDC transmission system are studied.In the PSCAD,the model and the controller of LCC-VSC hybrid DC transmission system are built.Through this model,the transient process of three faults which single pole blocking fault,AC grid single phase grounding and AC grid three-phase grounding is studied.And compared with the transient process of traditional DC transmission technology.The simulation results show that the control performance of LCC-VSC hybrid HVDC transmission system is better than that of traditional HVDC system,which can effectively reduce the voltage and frequency fluctuation of AC system.Finally,combined with SOM neural network algorithm and particle swarm optimization algorithm,the faults of high-voltage direct current transmission system are clustered based on SOM neural network algorithm.According to the clustering result,particle swarm optimization algorithm is used to optimize PI parameters of DC controller.The simulation results show that selecting the corresponding PI control parameters for different faults can improve the stability of the system and reduce the time for fault recovery.