Research On Reactive Characteristics Of HVDC Absorption And Shunt Capacitance Commutated Converter

HVDC transmission project has obvious advantages in high-capacity,long-distance transmission of electrical energy.To save the national land resources and promote the rapid economic development,HVDC transmission project has been widely used in China in recent years,which has played an indelible role in achieving the great rejuvenation of China.Most of the existing HVDC transmission project converter stations used Line Commutated Converter(LCC).If the commutation supply provided by the AC system is relatively weak,the commutation failure of the inverter is likely to occur.In order to prevent commutation failure on the inverter side,the extinction angle of the converter is generally set at about 15-17°.Considering the influence of the converter inductor,the trigger control angle of the inverter becomes larger,so the AC side needs to provide a large amount of reactive power to the converter during operation.It is easy to cause over-voltage of the converter bus due to excessive reactive power when the system is operating under the load rejection,in severe cases,the system will be shut down and bring greater harm to the power grid.In order to avoid the commutation failure and improve the reactive power balance,the paper depicts a new type of HVDC system Absorption and Shunt Capacitor Commutation Converter,and has carried out a series of studies.The main contents of the thesis include the following aspects:This paper summarizes the research status and application fields of HVDC transmission project,explains the reasons of the commutation failure,and analyzes the harmonics generated during the commutation.The reactive power characteristics of the HVDC transmission system using the Line Commutated Converter(LCC),Capacitor Commutated Converter(CCC),and Controlled Series Capacitor Converter(CSCC)on the inverter side were separately studied,which is,the relationship between the reactive power of the above-mentioned commutation converter and the firing angle,the extinction angle and direct current is studied.Based on the topology of HVDC Absorption and Shunt Capacitance Commutated Converter,the mathematical model and working mechanism are given.The reactive characteristics of the Absorption and Shunt Capacitance Commutated Converter were studied,and the method for calculating the reactive power of the Absorption and Shunt Capacitance Commutated Converter was deduced.Comparing the reactive characteristics of the Line Commutated Converter,the Capacitor Commutated Converter,the Controlled Series Capacitor Converter,and the Absorption and Shunt Capacitance Commutated Converter,the paper introduces the reactive power compensation device and its configuration.Based on the operation of Goose City Inverter Station,the capacitors with ASCCC structure are grouped to study the reactive power compensation strategy,and the economical efficiency of reactive power compensation for the Absorption and Shunt Capacitance Commutated Converter is described.Taking the actual parameters of the unipolar operation of the Sanxia-Guangzhou DC Transmission Project as the research background,and the 500 kV Goose City Inverter Station of Huizhou,Guangdong Province as the research object,and the Absorption and Shunt Capacitance Commutated Converter is adopted.After simulating the system through MATLAB,the prototype experiment was conducted in the laboratory.The results analyzed and proved that the Absorption and Shunt Capacitance Commutated Converter not only has the advantage of reducing the commutation failure of the inverter,but also can optimize the converter transformer and even the operating status of the entire system.