The Research On Reactive Power Planning For AC/DC Hybrid System

With a certain scale of HVDC projects and the development of ultra-high voltage AC(UHV-AC)system,a cross-regional large scale AC/DC hybrid system will come into being in the future in China.So the identification of weak buses in AC/DC hybrid system and the reactive power planning methodology considering voltage stability have a very important significance for the safety and stability of the power system in China.The research findings in this paper are presented as following:(1)A candidate location selection approach for reactive power planning which considers the static voltage stability is proposed.A good reactive power planning methodology needs not only an accurate voltage stability assessment index but also the analysis on candidate planning locations.Thus,the extended voltage sensitivity factor(EVSF)index is proposed.Compared with the common static voltage stability indexes,EVSF index considers the voltage regulation of HVDC,generator,excitation,dynamic reactive power compensation devices and so on.EVSF index can be used to identify the buses with weak static voltage stability.And it can determine the candidate locations for the reactive power planning which considers the static voltage stability.(2)A reactive power planning model considering the static voltage stability is proposed.It's a new situation that several HVDC converters locate at an area,which makes some influences on HVDC with each other.Then,based on quantitative voltage interaction influence factor(MIIF),a reactive power planning model considering the mutual influences is proposed.The objectives of the model are to decrease MIIF between HVDC,system power loss and investment cost of static reactive power devices.The proposed methodology can enhance the static voltage stability and increase the economy of the reactive power planning.(3)A candidate location selection approach for reactive power planning which considers the transient voltage stability is proposed.Transient voltage recovery index(TVRI)and transient voltage fluctuation index(TVFI)can be used in the transient voltage stability assessment.And the proposed transient voltage stability indexes can search the best candidate locations for reactive power planning which considers transient voltage stability.In addition,a candidate locations combination method based on compensation sensitivity is presented to avoid excess candidate locations.(4)A reactive power planning model considering the transient voltage stability is proposed.The proposed methodology can enhance the transient voltage stability,decrease power loss cost and dynamic reactive power compensation investment cost.And it can satisfy the need of generator rotor angle stability and obtain the least compensation amount to satisfy the transient voltage stability.(5)A comprehensive reactive power planning methodology considering static and transient voltage stability is proposed.The comprehensive reactive power planning methodology considers MIIF,static and transient voltage stability,investment cost and operation cost.Compared with the methodology considering the static voltage stability only,the reactive power devices investment of the comprehensive methodology is a little higher.But the comprehensive methodology can satisfy the static and transient voltage stability meanwhile.Compared with the methodology considering the transient voltage stability only,the comprehensive methodology can also improve the static voltage stability with more economic investment.(6)A comprehensive reactive power planning methodology based on multi-stage programming for AC/DC hybrid system is proposed.The comprehensive reactive power planning is divided as several planning stages,which considers the reactive power amount coordination between the around stages.The comprehensive reactive power planning methodology based on multi-stage programming not only can enhance the static and transient voltage stability for AC/DC hybrid system and obtain the best planning amount for reactive power planning,which satisfies the reactive power demand at different planning stages,but also can raise the utilization of the reactive power devices.The reactive power planning methodology for AC/DC hybrid system proposed in this paper can improve the static and transient voltage stability well.And it can be a reference means for the safety and stability of the AC/DC hybrid system.