Analysis of time‐frequency characteristic parameters of electromagnetic interference sources in the basic commutation unit

Establishing accurate electromagnetic interference (EMI) sources of the basic commutation unit is the key to accurately predicting the EMI of the converter equipment. To compensate for the insufficiency of the reported works, that is to use asymmetric trapezoidal waveforms (ATW) as common mode (CM) and differential mode (DM) EMI sources, this paper analyzed the switching transient process of insulated gate bipolar transistor (IGBT) device in the basic commutation unit, and then proposed the equivalent waveform of EMI sources with multi-polylines-damped oscillation waveform (MP-DOW). The spectrum envelop characteristic parameters of MP-DOW were obtained by the frequency domain analysis method, and its correctness was experimentally verified. Comparison with the reported works shows that the proposed spectrum envelope of MP-DOW can take into account the voltage and current overshoot during the switching transients of IGBT devices, and the spectrum characteristic parameters are more accurate. This paper is beneficial to the prediction of EMI for the converter already in operation, and can also provide theoretical guidance for the converter to be designed in conjunction with the analytical formula of the EMI source.