Research On The Relationship Between The Main Circuit Parameters And The Behaviour Of VSC-HVDC System

VSC-HVDC technology has been widely used in many fields such as offshore wind power integration,renewable energy integration,island power supply,distributed generation and integration,the parameters of the main circuit are closely related to the performance of the control system and the operation of VSC-HVDC system.As a result,it is important to study the relationship between the parameters of the main circuit and the operation behaviour of the system and to design the parameters of the main circuit.In this paper,the mathematical model of the VSC-HVDC system in the abc static coordinate system and the dq rotating system are established,the inner loop current controller,the outer loop voltage controller and the outer loop power controller are designed,the relationship between inductance and capacitance parameters of main circuit and behavior of VSC-HVDC system is studied.It mainly includes the following aspects:Based on the analysis of the operating principle of VSC-HVDC system,the mathematical model in abc static coordinate system is established,considering the difficulty of controller design in static coordinate system,the mathematical model of VSC-HVDC system in dq rotating coordinate is established in this paper.A dual closed-loop controller based on direct current control strategy is designed,according to the system transfer function,the PI parameters of the inner loop current controller,the outer loop voltage controller and the outer loop power controller are designed based on pole-assignment method.In order to improve the anti-disturbance performance of the system,load current feed-forward control strategy is introduced to improve the outer loop power controller.The relationship between the parameters of the main circuit and the operation behaviour of the system is studied.About the relationship between the inductance and the system performance,the influence of the inductance on four-quadrant operation of VSC,fast current tracking,harmonic current suppression and system power factor are analyzed,based on this,the range of inductance which satisfies these performance indexes is given.About the relationship between the capacitance and the system performance,the voltage loop tracking characteristics and the suppression of the DC voltage fluctuation are analyzed,based on this,the range of capacitance which satisfies these performance indexes is given.Finally,a VSC-HVDC system simulation model is built on the PSCAD/EMTDC platform,the inner loop part adopts a current controller,one end of the outer loop is controlled by constant active power and constant reactive power,and the other end is controlled by constant DC voltageand constant reactive power.According to the design method of main circuit inductance and capacitance,in the simulation model,the change of the system operating behavior index is analyzed when the main circuit parameters change.The simulation results after the selection of the main circuit parameters verify the correctness of the parameter selection method,which can meet the normal operation of the VSC and controller and lay a foundation for practical engineering application.