Research On Reactive Power Compensation Coordination Strategy For Voltage Control Of AC-DC Hybrid Grid

China has a vast territory,and energy and main loads are concentrated in the west and east and are distributed in reverse.In recent years,due to the characteristics of long-distance and large-capacity transmission of HVDC power transmission,HVDC power transmission with the western energy center as the sending end and the east China and Guangdong load centers as the receiving end has been developed rapidly,forming our country's AC/DC hybrid power grid.During the construction period,the AC/DC hybrid power grid has problems such as high DC power receiving ratio and insufficient local power support.When the system fails,it may cause voltage drop or even commutation failure,which brings severe challenges to the voltage stability of the power grid.Dynamic reactive power compensation can quickly provide reactive power during system failures,meet the demand for DC to absorb reactive power from the AC system,and ensure the stability of the bus voltage.At this stage,important converter stations of AC and DC power grids are equipped with large-capacity new synchronous condensers,STATCOM and other dynamic reactive power compensation devices.Although they can provide dynamic reactive power support for the system,their capacity is limited,and there is a lack of coordination with the static reactive power compensation equipment in the station.The problem reduces the effect of dynamic reactive power support.Therefore,research on the coordination strategy of multi-reactive power source and reactive power compensation for the voltage stability of the hybrid power grid has important theoretical significance and great engineering value.Based on the above background and problems,thesis makes the following researches on the voltage control and multi-reactive equipment coordination of AC/DC hybrid power grids:Firstly,the influencing factors of the voltage stability of the AC/DC hybrid power grid is analyzed,and the voltage and reactive power characteristics of the system which provides a theoretical basis for subsequent control is analyzed.In order to accurately study the reactive power compensation coordination strategy for the busbar voltage control of the converter station,based on the actual engineering parameters,a typical line in the hybrid power grid is selected to establish a high-voltage DC transmission system including an AC system at the sending and receiving ends and a DC transmission system Electromagnetic transient simulation model.Under a variety of working conditions,the operating characteristics and voltage and reactive power problems are studied in detail,and it is concluded that the system is vulnerable to faults,resulting in voltage sag and commutation failure,and poor voltage transient stability.Combining with the characteristics of the established power grid model,it is pointed out that it is necessary to equip the converter stations on both sides with dynamic reactive power compensation.According to the actual needs of the project,electromagnetic transient simulation modeling of the new synchronous condenser and STATCOM dynamic reactive power compensation equipment,combined with the operation mode of the synchronous condenser,detailed design for the voltage and reactive power double closed loop excitation under steady state and transient conditions Control strategy,and design and analyze its voltage control strategy for voltage stabilization combined with the operation mode of STATCOM.Based on the above analysis and design and the built HVDC power transmission system,a power grid simulation model including a new type of synchronous condenser and STATCOM is established,and three schemes are set to analyze the reactive power control and operating characteristics under steady-state and transient system failures.The application characteristics,advantages and disadvantages of the two dynamic reactive power compensation equipment under fault conditions are compared and analyzed,which lays the foundation for the follow-up multi-reactive power reactive power compensation coordination strategy.Finally,in view of the above-mentioned research on the voltage stability of the AC-DC hybrid power grid and the multiple goals that need to be achieved in the coordinated control of reactive power compensation,this paper proposes a multi-mode multi-reactive source and reactive power coordinated control strategy based on the coordinated control of the new synchronous condenser,STATCOM and the reactive capacitor bank in the converter station,and proposes an overall control scheme.The control scheme includes a steady-state voltage regulation mode that keeps the voltage constant under steady-state conditions;and under transient conditions where voltage fluctuates greatly,the use of large-capacity synchronous condensers with superior sub-transient characteristics and strong overload capacity supports rapid recovery of the bus voltage and And the transient control mode that suppresses the failure of commutation;and the constant reactive voltage regulation mode that is convenient for the staff to manually control in emergency situations,and the overexcitation limit protection scheme for the synchronous condenser is designed.Based on the previously built LCC high-voltage DC transmission system simulation with static reactive power compensation in the station including large-capacity synchronous condenser,STATCOM and reactive power capacitor bank,a simulation including dynamic and static reactive power equipment and the use of reactive power compensation coordination strategies was established.The simulation records the reactive power control and voltage operation characteristics of the system under various fault conditions,including steady-state overvoltage at the sending end and transient voltage drop at the receiving end,to verify the effectiveness of the multi-reactive source reactive power compensation coordination strategy.The simulation results show that the use of a coordination strategy can quickly restore the bus voltage to the rated voltage under small steady-state fluctuations;under transient conditions,the commutation failure can be suppressed,and the voltage drop can be greatly reduced for reactive power support,making dynamic and static reactive power equipment The advanced phase and late phase compensation capabilities of the power supply can be maximized,and the recovery speed of the bus voltage after the fault is cleared will be accelerated.The multi-reactive power source and reactive power compensation coordination strategy proposed in this paper can improve the voltage stability of the AC/DC hybrid power grid under steady-state and transient conditions,and provide references for subsequent research and the safe and stable operation of the power grid.