Research On Coordinated Control Strategy Of Multi HVDC Asynchronous Interconnected System

When the sending power grid is connected to the receiving end only by a series of HV/UHV DC or flexible DC to form an asynchronous interconnected power grid,large capacity DC blocking will lead to the problems of frequency and voltage in the sending and receiving end.In this paper,for the multi-DC island system after asynchronous networking,a coordinated control strategy for power support under DC blocking fault is proposed based on the fastness and controllability of DC system.Firstly,the research background and significance of this paper are introduced,and the research status of the stability and frequency control of asynchronous network back-end system at home and abroad are introduced.The mathematical model and control mode of DC system are introduced,and the influence of DC blocking fault on AC system is analyzed and verified by simulation.Simulation result shows that high frequency of sending system caused by large-capacity DC blocking in Yunnan power grid is more prominent.Subsequently,the frequency control measures of power plant and DC side are introduced.The advantages and disadvantages of RUN UP/BACK and FLC in power coordination control are compared and analyzed from the aspects of control structure,parameters and unit inertia time constant.It is pointed out that the power support via RUN UP/BACK channel can provide better support effect.Then,the DC power distribution factor is defined considering the effective short-circuit ratio of multi-infeed operation and the power transfer coefficient,and a set of active power distribution method considering the terminal voltage level is proposed.In addition,a coordinated control strategy for asynchronous interconnected power grids is proposed through coordination and cooperation of various measures of adjusting frequency,such as RUN UP/BACK,FLC,steady control and high-frequency cutting machine.Finally,a set of coordinated control system connected with RTDS of China Southern Power Grid was constructed.Taking Luo-ping conventional unit and Chu-sui bipolar locking experiment as an example,the effectiveness of this system is verified.The results show that the coordinated control measures proposed in this paper have a good supporting effect on the frequencies of the sending end and the receiving end system.The obtained results are consistent with the theoretical analysis.