| MS Seminar

Name of the Speaker: Ms. Kalyani Vasantrao Lande (EE21S092)
Guide: Dr. Arun Karuppaswamy B
Venue: CSD-308 (Conference Hall)
Date/Time: 30th October 2024 (Wednesday), 3:30 PM
Title: Conducted EMI in Grid-Connected Inverters: Sources Identification, Parasitic Estimation and High-Frequency Modelling

Abstract :

Electromagnetic interference (EMI) in power electronic converters is a significant challenge. Poor EMI performance can result in unintended interference with other equipment in the network or with sensitive subsystems, such as control circuits, affecting the normal operation of the converter and potentially causing damage. To ensure the satisfactory and reliable operation of any converter in an electromagnetically active environment, it must comply with EMI requirements directed by international standards.

This work focuses on identifying the dominant sources of conducted EMI and conduction paths, high-frequency modelling of filter inductors, and estimating the parasitic capacitance offered by thermal interface material (TIM) in a three-phase grid-connected inverter system. The literature reports that the primary source of EMI is the high-speed switching of power semiconductor devices, such as IGBTs and MOSFETs, which generate trapezoidal voltage and current waveforms with steep transients. In addition, high-frequency ringing resulting from L and C parasitic elements within the circuits significantly contributes to EMI. This work highlights the use of Fourier-based spectral analysis to characterize EMI sources and their dominant spectral components, emphasizing the influence of key parameters such as DC bus voltage, rise and fall times of power devices, switching frequency and PWM technique on emissions.

Conducted EMI, ranging from 150 kHz to 30 MHz, is classified into common mode (CM) and differential mode (DM) noise. Extensive literature has acknowledged that CM currents leak through the parasitic capacitance provided by the TIM mounted between the device tab and the heatsink. Accurate prediction of these currents depends on the precise value of the parasitic capacitance. However, theoretical estimates of capacitance tend to be inaccurate under varying temperature and frequency conditions. This work introduces an experimental method to estimate the parasitic capacitance of the TIM under realistic operating conditions using a double pulse test (DPT) circuit. Apart from a more accurate estimation, the experimental method helps in understanding the CM current flow path in a grid-connected inverter in detail.

The output filter inductors are part of the CM and DM noise paths. At conducted EMI frequencies, their impedance behaviour is influenced by high-frequency phenomena such as skin effect, proximity effect, inductances due to eddy currents and parasitic capacitances. These effects lead to alternate parallel-series resonances, as observed in impedance analyzer plots. This work proposes a simplified high-frequency model incorporating these effects for amorphous core filter inductors. The proposed model is easy to simulate and provides good accuracy without the need for complex numerical methods.

The high-frequency models, identified sources and high-frequency current flow paths are expected to be useful in designing the EMI filters for grid-connected inverters.