| Every year,the power system has the harm of line icing,which causes all kinds of power faults.In particular,the southern region was hit by a rare ice disaster in 2008,causing multiple lines to be suspended.A great deal of research has been done on the melting ice of the line at home and abroad.Various different ice melting techniques and de-icing techniques have been studied.But there are some defects in various methods.At present,Joule thermal melting technology is the most widely used,mainly DC and AC short-circuit ice melting technology.Different from the traditional thermal ice-melting technology,the high-frequency excitation ice-melting method has the advantages of low current,high efficiency,and on-line ice-melting with the combination of wave blocker and other devices.In the future the direction of ice melting has certain potential for development,and its related theories and key technologies need to be studied.The method of high frequency excitation melting ice is further studied,The basic principle of high frequency excitation ice melting method is analyzed.The dielectric characteristics of ice under high frequency and conductor skin effect on line impedance value were studied,and the equivalent model of transmission line icing is established.The determination method of melting ice voltage and frequency of high frequency melting ice excitation electric source is analyzed.A topology structure of ice melting excitation power supply is proposed.The working principle of the power supply and the characteristics of the topology are analyzed.The AC-DC-AC voltage source inverter topology is used as the basic power unit,and the capacity of the power supply is increased by cascaded multi-level mode.The parameters of the main circuit are designed,including AC side inductance,DC side capacitance and power switch selection.Considering the large inductance value of the line at high frequency,the inductance value of the line is reduced by series compensation capacitance and the capacity of the ice melting excitation source is reduced.PWM rectifier is used in the front end of the power supply to supply DC power.Based on the instantaneous power theory,a direct power control strategy is designed in two-phase static coordinates,and the switching signal is generated by space vector control.Cascaded H-bridge inverters are used to realize the output of high-voltage and high-frequency parameters,double closed-loop control strategy and high-frequency output filter are designed.Carrier phase shift modulation technology is used to solve the problem of low switching frequency of high-power devices,which can not output high-frequency voltage,and reduce the output harmonic content.Several connection schemes of excitation power supply are discussed.According to the design method and control strategy of excitation power supply,a simulation model is built by MATLAB/Simulink to verify the feasibility of the design and control method of excitation power supply.The proposed ice-melting excitation power supply can output high-frequency voltage that meets the requirements of ice-melting.The rectifier side can realize the input of unit power factor.The harmonic content of output voltage and current is low and the power supply capacity is large.The switching frequency of power supply can be reduced by carrier phase shift.The research results have certain significance for realizing high-frequency ice-melting excitation in practice. |
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