Parasitic capacitance has a considerable impact on conductive electromagnetic interference (EMI), especially on the common mode (CM) noise. In vehicular applications, such as more electric aircraft and electrical vehicles, the value of CM stray capacitance can vary during the drive cycle, due to some change in environmental, and operating conditions, resulting in fluctuations in EMI level. Designing EMI filters according to potentially overestimated CM capacitance results in additional weight, volume, and cost which should be avoided. In this paper, for the first time, the parasitic capacitance relevant to CM noise is estimated in real-time using unscented Kalman filter (UKF). The UKF is employed due to its ability in dealing with nonlinearity and stochastic nature of the EMI as well as the measurement noises. The proposed method is tested on a typical dc–dc buck converter in different operating conditions. The effectiveness of the proposed method is tested using some hardware-in-the-loop experiments using dSPACE1104 development platform.

Estimation of Parasitic Capacitance of Common Mode Noise in Vehicular Applications: An Unscented Kalman Filter-Based Approach

A review on recent effort of conductive EMI suppression methods in high‐frequency power converters

Inter-winding parasitic capacitances of the transformer in LLC resonant DC-DC converters have a considerable impact on conductive electromagnetic interference, especially on the common-mode (CM) noise. The variations of environmental and operating conditions such as temperature, vibrations, and humidity can change the dielectric constant, which increases the value of parasitic capacitances. The real-time estimation of the parasitic capacitance is a nice solution to study CM parasitic capacitance and EMI emission in real operating conditions. In this paper, the parasitic capacitance relevant to the CM noise is estimated in real-time using unscented Kalman filter. Different simulation results are provided and discussed to demonstrate the correct performance of the proposed method in different operating conditions.

Estimation of CM Parasitic Capacitances in Front-end LLC Resonant DC-DC Converters

This article analyzes various strategies and implementation techniques in detail for complex receiver system design to qualify Environmental Stress Screening (ESS) especially EMI/EMC tests for airborne system applications. Isolation of leakage energy between various RF/DC-DC converters/regulators/pulsing blocks are the key target of this design to keep conductive and radiative emission to a minimum. Hence, complex receiver design has been segregated into various modules. Then they are stacked together very tactfully within the specified area without compromising inter-channel/module interference between them and the form factor, respectively. The super compact stacks are further channelized for RF, DC supply, controls etc. and protected from any kind of interference. Low cost flexi interconnects are made to interface various stacks to arrest unwanted high/low frequency leakages. Proper layout, component placement, layer specific signal routing, and wire shielding have been used to protect low/high frequency reference clock, control signals, switching pulses, etc. from mixing. Processor boards with a DC supply unit are also integrated into the receiver as another stack and have been isolated from each other to qualify emission tests. Finally, four modules are developed and tested over temperatures of -40°C to +71°C (ESS) and EMI/EMC successfully to establish the methodology for mass production.

Improved Complex Receiver System Design Strategies to Overcome EMI/EMC Challenges

This article analyzes various strategies and implementation techniques in detail for complex receiver system design to qualify Environmental Stress Screening (ESS) especially EMI/EMC tests for airborne system applications. Isolation of leakage energy between various RF/DC-DC converters/regulators/pulsing blocks are the key target of this design to keep conductive and radiative emission to a minimum. Hence, complex receiver design has been segregated into various modules. Then they are stacked together very tactfully within the specified area without compromising inter-channel/module interference between them and the form factor, respectively. The super compact stacks are further channelized for RF, DC supply, controls etc. and protected from any kind of interference. Low cost flexi interconnects are made to interface various stacks to arrest unwanted high/low frequency leakages. Proper layout, component placement, layer specific signal routing, and wire shielding have been used to protect low/high frequency reference clock, control signals, switching pulses, etc. from mixing. Processor boards with a DC supply unit are also integrated into the receiver as another stack and have been isolated from each other to qualify emission tests. Finally, four modules are developed and tested over temperatures of -40°C to +71°C (ESS) and EMI/EMC successfully to establish the methodology for mass production. 

Critical conduction mode (CRM) boost power factor correction (PFC) converter is widely used in ac–dc power supplies to achieve high power factor. The switching frequency varies in a half-line cycle. In this article, both the differential-mode (DM) and common-mode (CM) electromagnetic interference (EMI) noises below 1 MHz from the ac–dc power supply in a LED TV are analyzed and modeled. The power supply consists of two parts: CRM boost PFC converter and LLC resonant converter. The conducted EMI noise and noise source voltages are measured in the time domain and then converted to the frequency domain via short-time fast Fourier transform (STFFT). Through the joint time-frequency analysis using STFFT, the drain-to-source voltage of the power MOSFET in the PFC converter is identified as the dominant noise source of both CM and DM EMI noises below 1 MHz from the power supply. The EMI current path is different during different periods of a cycle of the line voltage. During most time of a cycle, two diodes of the bridge rectifier are forward biased, and the bridge rectifier can be treated as short circuit. The current paths of DM and CM EMI noises are explained and modeled by a linear equivalent circuit model. Three parasitic capacitances need to be considered to model the CM EMI noise in this device under test. From the circuit model, transfer functions relating DM and CM EMI spectra to noise source voltage spectrum are obtained. The conducted EMI spectra are predicted by multiplying the spectrum of noise source voltage by the transfer functions. The prediction matches with measurement. The effects of parasitic capacitances on CM EMI noise are analyzed by simulation and then validated by measurement. The analysis results can help with EMI design to reduce the CM EMI.

Sangho Cho

Papers

Analysis and Modeling of Conducted EMI from an AC–DC Power Supply in LED TV up to 1 MHz