Optimal Design Of EMI Filters In Power Converters Based On Chaotic Pulse Width Modulation

Electricity is the core of the modern energy systems,and its efficient use is an important part of achieving "peak carbon dioxide emissions" and "carbon neutrality".As the core device of electric energy conversion,power converters have received extensive attention and research.However,the gradual application of silicon carbide and gallium nitride has brought about serious electromagnetic interference(EMI)problems while ensuring that power converters complete electric energy conversion with high frequency,high power and high-power density.The EMI generated by the rapid changes of voltages and currents caused by the switch actions affects the safe operation of itself and other equipment.Therefore,EMI filters are designed to suppress the EMI of power converters.In the face of increasingly severe EMI,it is very difficult but necessary to design passive EMI filters(PEF)while ensuring the power density of the systems.Although active EMI filter(AEF)can ensure small size,the gain bandwidth of the operational amplifier limits the high-frequency suppression effect.Therefore,it is important to optimize PEF and AEF so that they can better meet the development trend of power converters.Aiming at the problem of the large volume of PEFs,this thesis proposes the idea of combining chaotic pulse width modulation(CPWM)with PEF design to reduce the volume of PEFs.Firstly,based on the relationship between the spectral amplitude and the inductance and capacitance in PEFs,the mechanism of reducing the inductance and capacitance with CPWM is analyzed,and the common mode(CM)PEF is taken as an example to quantitatively analyze the relationship between the reduced spectrum amplitude and the change of CM inductance.Then the performance of CPWM in reducing CM inductance in low-switching-frequency and high-switching-frequency converters is analyzed respectively and verified in the experiments.Subsequently,the effect of the volume reduction of CM PEFs in the converters with different switching frequency is compared,then the trend of CM inductor volume changing with power is analyzed.Finally,the spectrum of the CM voltage is calculated and the results are compared with those in simulations and experiments.Aiming at the problem of the limited suppression effect of AEFs in high frequency,this thesis proposes the idea that using the CPWM reduces the gain of the operational amplifier to improve the high frequency suppression effect.Since the large operational amplifier gain in AEFs causes the deterioration of suppression effect in the high frequency band,the mechanism that CPWM reduces the operational amplifier gain with the reduced spectral amplitude is analyzed.A feedback current sense current compensation AEF is taken as an example to quantitatively analyze the relationship between the spectrum reduced by CPWM and the bandwidth of the operational amplifier in the AEF.Finally,the simulations and experiments are carried out based on the Boost converter and the results verify that CPWM can improve the suppression effect of AEFs in the high frequency band.The thesis combines the CPWM with the design of PEFs and AEFs to realize the volume reduction of PEFs and improvement of the suppression effect of AEFs in high frequency without changing the circuit structure,adding additional equipment or increasing the cost,which provides a new idea for the optimization of EMI filters.