Research On Control Strategy Of Permanent-magnet Direct-driven Wind Farm Connection Based On VSC-HVDC

With more emphasis put on the new energy increasingly,Wind power technology has been developed rapidly.Installed capacity of the wind power station is also more and more strong.Whether The network of wind farm is safe,reliable,efficient and economical depends on the network technology.For the long distance transmission network,the AC transmission and the traditional DC transmission all need to add reactive power compensation equipment.However,Flexible HVDC technology can provide reactive power support,so it is more applicable to wind farm networking.This paper focuses on research about control strategy of wind farm connection based on VSC-HVDC.In this paper,the permanent magnet direct drive wind turbine generator is used as the wind farm.The characteristics of permanent magnet generator and its vector control are studied.And the maximum wind energy tracking method is discussed.And in this paper,the mathematical model of VSC-HVDC in dq0two-phase synchronous rotating coordinate system is established.In the Matlab/Simulink platform,the VSC-HVDC system which is connected with two active communication networks is modeled and simulated.It is proved that the VSC can flexible independently regulate active power and reactive power at the same time.And the operation characteristics of VSC-HVDC system are obtained.According to the nonlinear characteristics of VSC-HVDC system,put forward a kind of VSC-HVDC control strategy that based on EL(Euder-Lagrange)model is suitable for wind farm networking.Firstly,the passivity of VSC is proved in theory,and the EL model of VSC is established in the dq0 two-phase synchronous rotating coordinate system.Finally,the EL passive controller is designed.According to the proposed control strategy,In order to maintain the stability of the AC bus voltage and ensure that the active power of the wind farm can be transmitted in time,converter for the wind farm side is controlled by constant active power and reactive power control;In order to ensure the stability of the DC side voltage and the transmission of reactivepower,Converter for the power grid side is controlled by constant DC voltage and constant reactive power.The whole simulation model of wind farm network system based on VSC-HVDC was built on Matlab/Simulink platform.Simulation results of steady-state performance show that the system has high robustness,and can flexibly regulate the active and reactive power;Simulation results of ground fault show that the system has strong anti-interference ability and can isolate the fault.So as to verify the control strategy proposed in this paper not only simplify the controller,but also have better dynamic and static performance.For the nonlinear VSC-HVDC system also has a strong pertinence,and it has high practical value in engineering application.