Research On Coordinated Control Of High Frequency Isolated Variable Frequency Speed Regulation In Underground Coal Mine

China is actively promoting the implementation of the “energy conservation and emission reduction” plan to meet the challenges posed by the global energy strategy.Electric traction shearer is an important equipment of comprehensive working face.In the work,in order to adapt to different geological coal seams,frequent acceleration and deceleration will occur,and when the load changes suddenly,it will lead to DC bus voltage fluctuations.In the medium or high voltage and limited space occasions of coal mine,the traction frequency converter of shearer mostly adopts power frequency transformer to connect to the power grid and the controlled motor mostly adopts open-loop control.Which has the problems of narrow working space,complex structure and poor robustness of motor control.Whether the static and dynamic performance of the traction inverter is good and the control accuracy of the motor will influence the stability and efficiency of the system and increase energy waste.Therefore,it is of great significance to reduce the complexity of the system structure,improve the anti-interference ability of the system and improve the control accuracy of the motor.In view of the above problems,a coordinated control strategy based on a topology of high frequency isolated variable frequency speed regulation in coal mine is proposed.Including,AC input stage three-phase voltage type PWM rectifier link based on grid voltage oriented vector control strategy;isolated transmission stage high frequency isolated bidirectional full bridge DC-DC conversion link single phase shift closed-loop control strategy;a speed sensorless vector control strategy for three-phase inverter link of AC output stage is proposed.In this method,model reference adaptive system is used to estimate the speed of asynchronous motor.The feasibility and effectiveness of the proposed coordinated control strategy are verified by Simulink.The results show that the coordinated control strategy has good static and dynamic performance and anti-load disturbance ability.Finally,the experimental platform of high frequency isolated variable frequency speed regulation coordinated control system is built.Adopting 0.75 k W three-phase asynchronous motor as the tested motor,the coordinated control strategy of high frequency isolated variable frequency speed regulation in coal mine is verified by experiments.The results are as follows.(1)The DC bus voltage fluctuation on both sides of the isolated transmission stage is small.The voltage of the primary single-phase inverter square wave and the high-frequency transformer coupled phase-shifted high-frequency square wave is equal,the waveform is smooth and the voltage peak is small.(2)The output voltage and current waveforms of the three-phase inverter link have good sinusoidality and smoothness,symmetrical waveforms,small total harmonic distortion and good power quality.The change of excitation current is relatively stable,and the torque current responds quickly when starting,and the torque current is large in the starting stage,which can produce large torque.(4)The motor can start and stop smoothly,and the model reference adaptive speed identification accuracy is good.(5)The motor torque of this scheme can reach more than three times the stable torque,which is better than the traditional open-loop control scheme.In summary,the high frequency isolated variable frequency speed regulation coordinated control strategy in coal mine is correct and feasible.