Study On Mechanism And Characteristics Of HVDC System With The Absorb Shunt Capacitance Commutated Converter

China's energy and load are in reverse distribution,besides,energy development tends to be in the northwest direction.The development of long-distance high-voltage direct current(HVDC)transmission has more realistic meaning for China.It not only fits the implementation of China's energy development strategy,but also is an inevitable choice for China to insist on vigorously developing green energy.The inverter is a key device in the HVDC system.The device has a complex structure,is expensive,and consumes a large amount of reactive power during operation.Its technical performance is related to the safe and stable operation of the entire system.Therefore,how to reduce systems operating equipment,optimize the converters structures and innovate the devices commutation method are the problems in the development of HVDC systems that must be addressed timely and effectively.The application of power electronics in HVDC systems inevitably leads to various power quality problems,such as harmonic pollution,reactive loss and commutation failure,etc.To solve these issues,this paper proposes a novel absorb shunt capacitor commutated converters(ASCCC)to figure them out.A comparative analysis of the research status of domestic and foreign converters,combined with the theoretical research of traditional thyristor converters,the basic theory system and modeling analysis system of a new type absorb shunt capacitor commutation converter applied in the field of HVDC transmission is established.Comparing with the topology of the LCC-HVDC system,the topology characteristics of the new HVDC system with ASCCC are analyzed,and then,the system operating characteristics are presented.Moreover,the mathematical model for the ASCCC-HVDC system is established.The control strategy of ASCCC-HVDC system is studied,including the control strategy of the conventional HVDC transmission system and the packet switching control strategy of shunt capacitor C.At last,based on San-guang line actual HVDC engineering parameters set up the simulation on the MATLAB software to build ASCCC-simulation model of HVDC system through the simulation analysis ASCCC-steady transmission characteristic of the HVDC system and ac system fault transient characteristic curve,and compared with traditional HVDC system based on LCC comparative analysis.The feasibility of the proposed new topology is validated by simulation results.It manifests that the shunt capacitors not only greatly absorbs the high-order harmonic but also eliminates the commutation angle ? absolutely,hence,the commutation ability can be enhanced greatly.Besides,it also presents good filtering and reactive power compensating performances to public networks.