Analysis And Suppression Of Common-mode Electromagnetic Interference In PWM Inverter

The rapid development of power electronics technology enables a comprehensive improvement in the performance of PWM inverter, which hsa made a wide range of applications. Using high-frequency power switching devices in the inverters will speed up the response rate and reduce the volume of the converter. However, the high-frequency converter power at high speed switching process will produce fast voltage transitions, and cause severe electromagnetic interference(EMI). The EMI includes conducted interference and radiated interference. Common-mode interference is more serious and outstanding in the conducted interference problems. Therefore, the common-mode EMI becomes the main target of the inverter EMI governance. In this thesis, the research contents are divided in two parts: the analysis and the suppression of common-mode EMI in inverter.In this thesis, the principle of common-mode interference in single-phase full-bridge inverter is analyzed. Then, the sources of common-mode interference are obtained and the propagation paths of interference are abstracted. This thesis includes the analysis of the equivalent circuit of interference sources in series based on existing literatures, the finding that the equivalent circuit is in deficiency, the proposition of the equivalent circuit of interference sources in parallel for common-mode EMI, the analysis of the common-mode current from time domain and the frequency spectra from frequency domain. Then, there is a contrast of the common-mode interference in single-phase full-bridge inverter under various modulation strategies, and an analysis of common-mode current characteristic under a variety of different interference sources. Through the theoretical analysis and simulation analysis, it can be verified that the equivalent circuit of interference sources in parallel for analysis of common-mode interference is correct.According to the theoretical analysis and simulation analysis of common-mode conducted interference in single-phase full-bridge inverter, this thesis presents the suppression program of common-mode EMI under the circumstances of different sources. When the common-mode interference source is not complementary symmetry, using external compensation circuit can suppress the common-mode EMI effectively, but when the common-mode noise sources are complementary symmetry, through the use of bipolar SPWM modulation strategy, the complementary symmetry in two bridge arms can be used to reduce common-mode EMI, and through additional compensation devices, common-mode EMI can be reduced. Through the simulation experiments, the common-mode current spectrum in inverter has been reduced greatly under the two cases and the common-mode EMI has been well suppressed, which shows the feasibility of the suppression method.