The dual PWM variable frequency speed regulation system applied to scraper conveyors, coal shearers and other mechanical equipments needs to be installed a filter on the rectifier grid-side to suppress harmonic currents. The existing LCL filter design method relies on experience and has low efficiency, and the damping loss problem is not considered enough. It is easy to cause device heating and the design is not suitable for underground applications. By analyzing the LCL filter model of the rectifier of the double PWM variable frequency speed regulation system, the mathematical relationship among the inductance ratio, damping resistance and current attenuation coefficient, resonance frequency, and damping loss is derived, and then a PWM rectifier LCL filter design method suitable for underground coal mines is proposed. In order to reduce the volume of the rectifier, a smaller total inductance should be selected on the basis of considering the filtering effect, the current fast tracking ability, and the fast response ability of the system. On the premise of ensuring the filtering effect, it is suggested to increase the filter capacitance. Within the allowable range of total harmonic distortion rate of the current, it is proposed to select the minimum value of inductance ratio and damping resistance. A three-phase voltage PWM rectifier control model is built in Matlab/Simulink for simulation and verification. The results show that the LCL filter designed by this method can make the PWM rectifier have a small overshoot, fast response and low total harmonic distortion rate. The prototype experiment verifies that the LCL filter can better suppress the grid-side current of the PWM rectifier and improve the quality of the grid-connected current waveform. It is verified by comparison that the filter inductance and damping resistance designed by this method are significantly smaller than those designed by the traditional method, which can reduce the size of the filter and reduce the cost effectively.
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