Research On Differential Mode And Common Mode Passive Filter For PWM Inverter

Because of the continuous improvement of switching frequency and output power of power electronic devices,the output voltage of PWM inverter contains a large number of high-frequency harmonic components,and the negative effects such as electromagnetic interference are becoming more and more serious.In addition to LC filters and second-order RLC low-pass filters which are commonly used to eliminate differential mode high-frequency voltage components,the structure of common-mode high-frequency voltage filters has been continuously improved.This paper first introduces the research status of PWM inverter output filter at home and abroad,analyzes the working principle of PWM inverter,and expounds the mechanism of PWM inverter output harmonic voltage.The main components of the output differential mode harmonic voltage and common mode harmonic voltage of PWM inverter are analyzed through the derivation of mathematical formula,which provides a theoretical basis for the design of passive low-pass filter.Secondly,in order to solve the negative effect of PWM inverter,two new passive filter structures are proposed in this paper.The differential mode filter inductors are integrated into the common mode transformer to reduce the size of the filter.The differential mode and common-mode harmonic voltage of PWM inverter can be suppressed simultaneously.Through the study of circuit topology,the filter differential mode and common-mode single-phase equivalent circuit are analyzed in detail,and the possible unstable states of filter circuit are studied and demonstrated in detail,and the limiting conditions of filter parameter selection are given.Finally,the effectiveness and feasibility of the differential common-mode passive filters are proved by the comparison of different types of passive filters.This paper also focuses on the topology of the differential common-mode passive filter and the design of the common-mode transformer.By analyzing the working state of common-mode transformer in the circuit,the selection of magnetic core material and shape is given,and the size structure of magnetic core of common-mode transformer is determined according to AP method.A new winding method for common mode transformer is proposed to solve the problem of unbalanced coupling coefficient between the windings.The simulation analysis of the common mode transformer is carried out by using ANSYS software,which verifies the effectiveness of the new winding method.At last,a simple experimental platform is built to verify the difference common mode passive filter,and the experimental results of the new filter show the validity of the differential common mode passive filter and the correctness of the previous theoretical analysis.