Current Feedback Control Of VSC-HVDC System Applied To Passive Network

VSC-HVDC system is widely used in passive network access because of the good power quality,fast power regulation,no commutation failure and so on.Because of the complex interaction between the converter stations in VSC-HVDC system,the disturbance occurs in converter station or AC system will affect the stability of other converter stations and the AC systems connected to them through the interconnection of the DC system,especially to the common connection points(application to passive network)which have high requirement on the voltage stability.At present,there is no systematic study on this problem.It is very important for the controller design of system engineering and stable operation to clarify the interaction mechanism between the converter stations and take the corresponding suppression strategy.This paper which studies on the VSC-HVDC applied to passive network aims to clarify the interaction mechanism between the converter stations in VSC-HVDC system,and to reveal the causes and influencing factors of interaction mechanism.An improved control strategy based on DC side current feedback is studied in order to inhibit the effect of the interaction mechanism on passive network,to improve the anti-interference ability of passive network voltage and to ensure the normal operation of passive load.Small disturbance model is the basis of stability analysis,interaction mechanism and control strategy design.Firstly,the four small interference models of voltage source converter station,controller,DC circuit and AC filter are constructed under the absolutely stable synchronous rotating coordinate system through the reasonable selection and flexible transformation of synchronous rotating coordinate system.Then,the state space method is used to organize the small disturbance model,and the global improved small disturbance model of VSC-HVDC is built through the selection of reasonable state variables.The comparative analysis between small disturbance model simulation and electromagnetic transient simulation shows that the small disturbance model derived in this paper is more accurate.It lays the foundation for the construction of the object model of the converter stations.The interaction mechanism is the core of this paper and the controller design.Firstly,the object model of the converter station is constructed based on the small disturbance model of the system.The interaction mechanism between the converter stations is studied through the method of small disturbance analysis.Then,the transfer function of the DC current to the AC side voltage of the passive network is established.The related factors affecting interaction mechanism is researched through spectral characteristics.Lastly,an improved AC voltage control strategy based on DC side current feedback is proposed through interaction mechanism,which can be used to suppress the effect of disturbance on passive network.Ensuring system stability is the core of controller design.In this paper,the system state matrix eigenvalue of AC voltage controller based on DC current feedback is studied through small signal stability analysis.The small disturbance stability of the system is judged to prove the feasibility of the improved AC voltage controller in the system.Lastly,the spectrum characteristic of transfer function,the electromagnetic transient off-line simulation,real time simulation and experiment are analyzed in order to verify the effectiveness of the improved AC voltage controller based on DC side voltage feedback.It shows that AC voltage controller based on DC current feedback can effectively weaken the influence of other converter station disturbance on the passive network,improve the independent operation ability of converter stations,optimize system dynamic performance,improve the ability of passive network against voltage interference and ensure the normal operation of passive network load.