Research Of High Voltage High Power Medium-frequency ESP Power Supply

Prevention and control of air pollution is an important goal of environmental protection in China.One of the main sources of air pollutants is a large number of harmful emissions in the production process of electric power,cement and other industries.Therefore,it is necessary to adopt effective industrial dust removal technology to control the emission of air pollutants.Among many industrial dust removal technologies,electrostatic dust removal technology has been widely used and occupies a larger market share especially in the field of coal-fired power plants.The key part of electrostatic precipitator is its high voltage power supply.Because of the shortcomings of traditional power supply,such as low dust removal efficiency and high energy consumption,it can't meet the current environmental protection requirements.Further improving the dust removal efficiency,reducing energy consumption and optimizing the control strategy of electrostatic precipitator have become the research hotspot of electrostatic precipitation technology.In this thesis the research goal is the high-voltage high-power medium-frequency power supply and the research work are focused on the technology of high-power inverter,the design of high-voltage high-power medium-frequency transformer and the controller system.First of all,during the operation of electrostatic precipitator power supply in cement industry,voltage flashover is very easy to occur,resulting in severe load fluctuation.In this thesis,the PWM hard switch circuit and the resonant circuit are analyzed theoretically.It is pointed out that the electrostatic precipitator composed of PWM hard switch circuit has the advantages of simple control principle,excellent dynamic performance and high dust removal efficiency under light load and heavy load conditions.The above advantages overcome the defects of complex control and poor characteristics with light load of high frequency power supply.Combined with the equivalent load of electrostatic precipitator,the PWM hard switching circuit is simulated and analyzed by PSIM simulation software.The simulation results verify the correctness of the conclusion.Also a control algorithm of the energy feedback converter is researched in this thesis.Secondly,the calculation of winding loss of medium and high frequency transformer is one of the difficulties in transformer theoretical research.It can't be ignored of winding high frequency effect in medium-frequency transformer working non-sinusoidal excitation.Focusing on the high frequency effect of medium-frequency transformer,the harmonic model of AC winding combined skin effect and proximity effect is established and analyst by using Dowell's calculation principle of AC winding resistance.And according to the characteristics of customized core of high power medium-frequency transformer,the design principle of transformer winding independent of the number of winding layers m is put forward.Based on the above principles,the winding design principle and realization method of copper foil,rectangular conductor and circular conductor are given when AC loss of medium-frequency transformer is optimal.The correctness of harmonic model of AC winding and winding design principle is verified by small power medium-frequency transformer prototype.Thirdly,According to the harmonic model and winding design method of medium-frequency transformer proposed above,the thesis uses the AP method to carry out the preliminary design of the amorphous core medium-frequency transformer and optimizes design with the constraint conditions of AC loss,temperature rise and transformer cost.Then the high-voltage high-power medium-frequency transformer with the capacity of 96 k KA is developed and the distribution parameters and transformer losses of the prototype are calculated and analyzed.On the basis of the development of the prototype,a long-time load experiment is carried and the experimental results verify the correctness of the design method.This thesis also studies a new sensor for large transformer on-line fault detection.Fourthly,Voltage flashover often occurs in the operation of medium-frequency transformer,which may result in winding deformation and structure damage.In this thesis,the simulation model of high-voltage high-power medium-frequency transformer is established by using the field circuit coupling method of time domain finite element.Based on the model above,the electromagnetic transient characteristics of transformer under the two working conditions of unsaturated core,sinusoidal excitation and saturated core,non-sinusoidal excitation are analyzed.Those transient characteristics include voltage/current of transformer primary and secondary sides,core and winding force of transformer under starting,steady state and short-circuit condition.Considering magnetic core saturation characteristics and load characteristics of transformer,the voltage/current of transformer in primary and secondary sides and core and winding force characteristic values of transformer are reduced compared with sinusoidal excitation and unsaturated core.The simulation results of overcurrent and overvoltage of transient state in the working process of transformer verify the great negative effects to thermal and structure design of transformer.At last,according to the simulation results the structure optimization of medium-frequency transformer is completed.Finally,according to the operating characteristics of high-voltage high-power electrostatic precipitation medium-frequency power supply in cement industry,a peak current control method is designed and a prototype of medium-frequency power supply is trial-produced.The prototype experiment shows that the peak current control method effectively controls the over-current and protection restart and effectively solves the problem of dust removal efficiency decline.At the same time,PID control algorithm is used to realize the load control strategy of electrostatic precipitator medium-frequency power supply.The high-voltage high-power electrostatic precipitator medium-frequency power supply researched in this thesis has been widely used in cement industry with good dust removal effect and high social economic benefits.