Research On Frequency Conversion System For Power Electronic Transformer Mine

Mine frequency converter is the main carrier for realizing frequency conversion and speed regulation of underground electromechanical equipment in coal mines,which can save energy and reduce consumption for coal mine enterprises.However,the current mine frequency converter itself cannot isolate the voltage transformation,and it is separated from the bulky power frequency transformer and takes up too much underground working space,which cannot be well adapted to the special narrow working environment in the coal mine.In addition,in actual work,the input stage of the mining inverter mostly uses diodes for rectification,which reduces the power factor and efficiency of the inverter and the energy can only flow in one direction.At the same time,the three-phase AC voltage output by the traditional frequency conversion algorithm has high harmonic content and poor waveform quality,which cannot efficiently realize the frequency conversion speed control of the underground motor.In response to the above problems,this thesis takes the mining inverter and power electronic technology as the research background.Firstly,it combines the power electronic transformer on the basis of the traditional AC-DC-AC inverter topology,and proposes the power electronic transformer mining inverter system topology,including Input stage three-phase voltage type PWM rectifier,intermediate stage DAB converter and output stage three-phase frequency conversion circuit.The DAB converter is used to replace the intermediate DC link of the current inverter topology,and the high-frequency transformer,the core component of DAB,is used to replace the power frequency transformer to reduce the overall volume and quality of the transformer and the inverter,and improve the working efficiency and power of the inverter system Utilization rate.Secondly,this thesis uses a three-phase voltage type PWM rectifier instead of the diode uncontrolled rectifier unit as the input stage of the mine variable frequency system,and uses the voltage and current double closed loop algorithm based on the grid voltage oriented vector for control,which has low harmonic content and power factor.Tune and other advantages.At the same time,a single phase-shift algorithm is used to control the DAB converter,which realizes the two-way flow of energy between the primary and secondary sides of the transformer,electrical isolation,and voltage level conversion.And use Matlab/Simulink to simulate the three-phase voltage-type PWM rectifier under double closed-loop control and the forward working waveform of DAB converter under single-phase shift control.Then,it analyzes the basic principle of SPWM and traditional SVPWM algorithm,the realization process and the essential connection between the two.A new SVPWM variable frequency control algorithm based on 120°coordinate system is introduced.Simultaneously,the feasibility of the new algorithm to output three-phase variable frequency AC power is verified by simulation.Finally,the corresponding hardware circuit and software program are designed,and the experiment platform of the power electronic transformer mine variable frequency system is built,and the feasibility of the proposed system to output three-phase variable frequency AC power is further verified through the experiment.The experimental results prove that the frequency conversion system proposed in this thesis can realize isolated voltage transformation,the output three-phase frequency conversion voltage is symmetrical in phase,and the waveform quality is good.