The Research Of Coordinated Control Strategy Of Large-Scale Wind Power HVDC Sending System Under Mono-Polar Block Fault

The Chinese special condition that the wind energy resources and load centers are in reverse distribution decides the wind power utilization model having the characteristic of large-scale and long-distance transmission.Meanwhile,the high voltage direct current(HVDC)transmission system having the unique advantage in terms of large-scale and long-distance power transmission,it has been widely applied in the large-scale power transmission system.However,HVDC transmission system might introduce the new fault behaviors in the real industry application.As a kind of typical HVDC transmission system fault,the mono-polar block fault has been concerned by people.When the HVDC transmission system occurs mono-polar block fault,the reactive power of the alternating current(AC)sending system will be surplus,which leads to the swell of the voltage of the AC sending system and results in a serious threat to the system's safe and stable operation.On the other hand,because of the equipment in AC sending system has flexible reactive power adjustment ability,this paper combines the mechanism of the AC sending system's overvoltage caused by mono-polar block fault and the operation characteristics of the equipment in AC transmission system under mono-polar block fault,the corresponding fault ride-through control strategy has been investigated.The main research contents in this paper include:Firstly,the equivalent mathematical models of the line commutated converter based high voltage direct current(LCC-HVDC)transmission system,double fed induction generator(DFIG)and wind power HVDC transmission system are built.Based on this,the voltage characteristic of AC sending system under mono-polar block fault is analyzed.Furthermore,the reason of AC sending system's overvoltage caused by mono-polar block fault is revealed.Secondly,under mono-polar block fault condition,the operation characteristic of the convertor station,additional reactive power compensator and DFIG wind farm in AC sending system is researched.The short-time overload capacity of the convertor at the sending side and the power controllable operation area of the DFIG-based wind farm are specifically analyzed.Furthermore,the control strategy of the convertor and DFIG-based wind farm under mono-polar block fault is presented.Meanwhile,in order to enhance the dynamic reactive power reserve,the operating principle and response characteristics of the synchronous condenser(SG)and STATCOM are compared.The analytical results show that the SG is more suitable for HVDC transmission system.Finally,the coordinated control strategy combining DFIG-based wind farm,the convertor and reactive power compensator under mono-polar block fault is designed,and it's verified by Matlab/Simulink.Also,the synchronous condenser is built based on the above model.The coordinated operation of the equipments in the AC sending system under mono-polar block fault is simulated and verified.The work of this dissertation will provide the theoretical basis for enhancing the stability and the fault ride-through capability of the wind power HVDC sending system under mono-polar block fault,which will provide a certain technical support to help the construction and development of the large-scale wind power HVDC sending system.