Study On Improving Large-scale Thermal Power Plant Major Auxiliary Inverter High And Low Voltage Ride Through Capability

The faults of power system often cause power system voltage sags or swells.If the voltage swell or sag occur in the power supply system for the key equipment of large thermal power plant,such as vital auxiliary inverters,which may lead to the inverter stopped and then cause the boiler shutdown and the generator set take off from net.It will deteriorate the stability of the power grid,and threat the safe and reliable operation of power system seriously.So,to improve the high and low voltage ride through capability of the large thermal power plant auxiliary inverter is beneficial to improve the stability of power system,and is beneficial to avoid leading to losses of economic.The study of low voltage ride through at abroad began earlier,while in China started later.A lot of achievements have been made in the efforts of researchers.At present,there are many schemes to improve the frequency converter of high and low voltage ride through,such as DC/DC converter scheme,online UPS scheme,configuring battery in the inverter DC side program,dual power supply switching scheme,dynamic voltage restorer(DVR)programs.In this paper,the advantages and disadvantages of the existing technology are analyzed in details.In order to meet the needs of practical application and achieve the research goals of Chinese national grid,a scheme of paralleling super capacitors in the inverter DC link for low voltage ride through is presented,also a practical solution of paralleling batteries in the inverter DC link is designed;in order to improve the high voltage ride through ability of converter,the scheme of the configuring discharge resistance in the DC link of the inverter is presented.In the paper,the proposed high and low voltage schemes are analyzed,and the corresponding mathematical models are established.The simulation models are built by MATLAB/Simulink.A series of simulations have been finished and a lot of data for practical engineering applications are obtained.In order to prove the correctness and feasibility of the designed scheme in this paper,the measurement devices both for the high voltage and low voltage ride through are built,and a lot of experiments are carried out as well.The simulation results and experimental results show that the high and low voltage ride through schemes designed in this paper meet the requirements of the Chinese national power grid absolutely.The low voltage ride through device based on the battery supporting,has been applied to China Huaneng Yuhuan power plant,Liuheng power plant of China Zhejiang provincial energy group and other applications.