Research On LCL Type High Frequency Ice Melting Power Supply For Ice-Coated Transmission Line

Power grid accidents caused by natural disasters such as freezing rain,thunder and lightning,earthquakes are a worldwide problem.Among them,ice flashes,line disconnections,and towers(poles)caused by winter ice and snow are the most common power grid disasters.At present,although the power frequency AC and DC short-circuit ice melting technology mainly used for ice melting on transmission lines can achieve effective deicing within a certain range,the line needs to be shut down during the ice melting process,which has low thermal efficiency and has limitations in application.The high-frequency ice melting method is a new type of ice melting method with high ice melting efficiency.It can be used with special wave traps to realize the technical development prospects of online ice melting on transmission lines.In recent years,with the development of power electronics technology,high-frequency ice melting methods and devices R&D is receiving increasing attention.The thesis analyzes the high-frequency skin effect and ice-coated dielectric characteristics of the transmission line,establishes an equivalent circuit model of the ice-coated line,and analyzes the appropriate high-frequency excitation melting frequency under different ice dielectric loss angles based on the uniform transmission line theory And voltage;based on the principle of heat transfer,the high-frequency critical ice melting heat balance equation of the transmission line is established,the calculation method of the high-frequency ice melting critical current and the ice melting time is analyzed,and the finite element ANSYS analysis software is used to reveal the high-frequency ice melting critical current and ice melting The changing law of time with different environmental factors(wind speed,ambient temperature,ice thickness)provides a basis for the reasonable design of high-frequency ice melting power supply parameters;a cascaded inverter output type high-frequency ice melting power supply circuit is designed,and the input side LCL type PWM controllable rectifier based on space vector(SVM)modulation technology is adopted,inverter module side adopts converter cascade to realize high-power output,and carrier phase shift(CPS-SPWM)modulation technology is used to generate trigger signal control circuit;Obtain a stable voltage output,improve the system’s anti-periodical interference performance,design the voltage and current double closed loop plus repetitive control;design the parameters of the ice melting power circuit,including the LCL filter in the rectifier side,the DC side capacitor,and the inverter side RC damping LC filter parameters and repeated PI parameters in the double closed-loop control of ice melting power supply;considering the high-frequency electric field,the line inductance value is large,a method of using series capacitors for reactive power compensation to reduce the capacity of the power supply device is proposed;Taking 110kV transmission wire as an example,through MATLAB/Simulink simulation,the feasibility of the designed ice melting power circuit and control method is verified.The high-frequency excitation source studied in the thesis has an output of 1 kHz/10kV and a current amplitude of 554A,which can meet the frequency,voltage,and critical icemelting current value calculated by high-frequency ice melting theory.The simulation experiment has a good current and voltage waveform and low harmonic content.The grid side is controlled by LCL type PWM rectification,and the voltage and current phases have good homogeneity.The cascaded inverter adopts carrier phase shift technology to solve the problem of limited switching tube frequency.The research results provide a reference for the practical research and development of high-frequency ice melting devices.