Coordinated Control Strategy Between Large-scale Photovoltaic Power Stations And VSC-HVDC

Due to the characteristic of reverse distribution of energy resource and load in China,power collection in west region becomes a hot topic of the renewable energy integration.In order to realize the large-scale grid-connected photovoltaic(PV)generation,this thesis aims to study the solar energy concentration scheme of the Qinghai-Tibet Plateau.VSC-HVDC is superior to transfer large capacity energy over the traditional ac transmission technology in terms of transmission distance and therefore suitable for integrating multiple large-scale PV stations in a weak ac grid.However,the integrated PV stations and VSC-HVDC system should equip with the fault ride-through capability when the AC grid trips.This paper proposes a novel coordinated control strategy between VSC-HVDC and PV stations,which does not rely on communications and can maintain the balance of active power transmission quickly.Hence the proposed method can stabilize DC voltage and improve the fault ride through capability of the whole system even when the AC fault occurs in the sending grid.When multiple large-scale PV stations are integrated by voltage source converter based HVDC(VSC-HVDC)transmission,inertia response of VSC-HVDC is beneficial to enhance the transient stability of receiving end power grid.This paper analyzes the control strategy of VSC-HVDC and proposes a novel coordinated virtual synchronous generator(VSG)control strategy between PV stations and VSC-HVDC under the frequency variation of receiving end grid,which does not rely on communications.The coupling between the frequency of the receiving end power grid and the voltage amplitude of the sending end power grid was obtained through the variable voltage control of the sending end converter.PV stations will then change their output power reference in response to the voltage variation of the sending end converter of HVDC.As a result,the real power balance between the PV stations and HVDC is achieved and the HVDC system can keep its DC voltage unchanged under the steady state when assuming the VSG control scheme.This paper proposes a novel coordinated control strategy without communications between PV stations and VSC-HVDC in order to achieve fault ride-through capabilities.The receiving end converter(REC)adopts VSG control to provide frequency support to the AC grid,which would be switched to VCC control when receiving end AC grid faults occur,so that the REC could provide reactive power support to the AC grid.