| Voltage source converter based high voltage direct current(VSC-HVDC)transmission technology has the advantages of control flexibly,environmental friendly,superior economic benefits and etc.It can alleviate the fluctuation and randomness of clean power generation connected to the grid,reduce the ripple of voltage and power caused by the grid disturbance,it is obviously more suitable for a large-scale of clean energy resources paralleled into the power grid and meet the electrical transmission demand,it is gradually becoming a hotspot in the area of transmission and distribution technology to relieve the energy crisis in the future.With a large great number of VSC-HVDC projects being constructed and have put into service,the power that the VSC-HVDC system transfers become higher,more and more attention have been paid on the transmission capacity of the VSC-HVDC system.Moreover,the primary goal for a power system is to keep it stable and safe operation,and small signal stability is one of the most important issues that will affect the reliable operation of a VSC-HVDC system.There is usually requirement that VSC-HVDC system should have ability to compensate the reactive power so that AC voltage can be adjusted.However,the inverter station with reactive power compensation may influence the stability of DC system.This paper establishes a VSC-HVDC terminal system small-signal input impedance model,making full use of VSC-HVDC system can absorb or issue reactive power while it is used to transmit active power so as to adjust the stability of the system.Based on small signal model of DC system,and then analyzed the impact of reactive power compensation characteristic of the inverter station on the DC system's voltage stability by using root locus.It is found that the inverter station with reactive power compensation will probably weaken the voltage stability of the DC system.Based on small signal stability constraints of the VSC-HVDC system,the calculation method for the reactive power compensation capacity that the inverter station can supply is proposed.Simulation is conducted by using PSCAD/EMTDC software.According to the control strategy proposed in this paper,the dynamic characteristics of the inverter station of VSC-HVDC system are simulated and analyzed.The simulation results are compared with the calculated results.It demonstrates the correctness of the mathematical model and the theoretical analysis.It provides a meaningful guidance to analyze the influence of the dynamic characteristics of the inverter station on the stability of the DC voltage and the DC transmission capacity. |
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