Research On Frequency Domain Modeling Analysis And Active Suppression Technology Of Conducted Electromagnetic Interference In Three-phase Two-level Inverter

With the wide application of pulse width modulation(PWM)based power converters,electromagnetic interference(EMI)problems caused by high-frequency switching actions of power electronic switches have become more and more serious.To avoid interference between different systems,the EMI noise emissions needed to be limited and complied with certain EMC regulations,so the researches on EMI issues are of great significance.The researches on conducted EMI problems includes two major categories,namely EMI prediction technology and EMI suppression technology.For the EMI prediction technique,the prediction accuracy of traditional frequency domain modeling methods is limited for neglecting the high-frequency resonances and the mixed-mode noises.For the EMI suppression technique,the active filtering technology can suppress the EMI noises of the system to a certain extent by restraining the EMI sources,but it only works in low-frequency range.To solve the above problems,this article focus on the EMI problems in three-phase two-level inverter system.The generation and propogation of the conducted EMI are analyzed and several suppression methods are proposed.To solve the prediction accuracy problems of the traditional frequency domain modeling methods,this article proposes a high-precisiion frequency domain modeling method.The proposed modeling method can implove the prediction accuracy from both the interference sources and the noise propagation.To predict the high-frequency resonances existing in the voltage waveforms of the switches,a high-frequency resonance function is introduced in the interference source.The stray capacitors of the swithes to the gound are took into consideration in the circuit model of the noise propagation to futher improve the prediction accuracy.A mixed-mode EMI nosie analytic method is proposed based on the equivalent modularterminal-behavioral model.The analytical results point out the affecting factors and mechanism of the mixed-mode EMI noise.The equivalent modular-terminal-behavioral model is derived based on the proposed frequency domain modeling method.All parameters in the model are obtained from the high-frequency equivalent circuit model of each component.The internal structure in the model is explicit,which is convenient for mixed-mode EMI analysis.Then,the quantitative analysis expression of the mixed-mode EMI noise is derived.The result points out that the mixed-mode EMI is the common-mode EMI caused by the differential-mode interference source.The stray capacitors of the swithes to the gound greatly affect the mixedmode EMI in the systm.The reason for the failure prediction of the traditional frequency domain models is explained when significant different exists between the two capacitance of the bus to the ground.To meet the special requirements of GJB 151 and GJB 152 standards,this article analyzes the low-frequency EMI in three-phase two-level inverter.The analysis results point out the influences of the load conditions on interference sources and noise propagation.Then,the lowfrequency EMI suppression technology based on DC-link capacitor design method is proposed.The analysis results of differential-mode EMI in the frequency range of 25 Hz ? 150 k Hz point out that unbalanced load condition causes double fundamental frequency harmonic.The analysis results of common-mode EMI in the frequency range of 25 Hz ? 150 k Hz point out that unbalanced load deteriorate the low-frequency characteristics of common-mode voltage interference source while the common-mode EMI noise propagation is unaffected.A lowfrequency EMI suppression technology based on the DC-link capacitor design is proposed through the above analysis.The technology can effectively suppress the low-frequency EMI caused by unbalanced load while avoiding over-design of the DC-link capacitor.An active suppression technology based on three-phase four-leg topology is proposed to suppress the common-mode EMI in three-phase two-level inverter.The action delay of the switches is analyzed through statistical methods.The analysis results show that the action delay of the switches depends only the direction of the currents flowing through the switches.Then a modulation optimization algorithm for compensating the action delay of the switches is proposed.The proposed algorithm can effectively improve the compensation effect.Finally,the active suppressin technology is combined with traditional passive EMI filtering technology.Thus,the EMI of the equipments can meet the requirements of the corresponding EMC standards.