Design Methodology for Improved Electromagnetic Compatibility of Switched-Mode Power Converters

Electromagnetic compatibility is one of the most critical challenges when designing switched-mode power converters. Due to printed circuit board layout requirements imposed by electromagnetic compatibility and thermal issues, efficient analysis and optimization of the printed circuit board layout with general purpose electromagnetic solvers is practically impossible. 

The objective of this dissertation is to simplify the electromagnetic analysis of switched-mode power converters by introducing improved algorithms for a specific set of problems typically occurring in the switched-mode power converter design and to develop a design methodology for switched-mode power converters with an improved electromagnetic compatibility. The ability to improve the electromagnetic compatibility early in the design stage reduces the design cost and time to market.

The developed methodology consists of the decoupled electromagnetic and circuit simulations of the analyzed converter. The electromagnetic simulation results in the radiation characteristics of the parasitic antenna of the analyzed converter for the unity current excitation. The steady-state time-domain circuit simulation results in the actual current excitation of the parasitic antenna of the analyzed converter. A mathematical combination of the two results gives the predicted radiated emissions of the analyzed converter. Decoupled electromagnetic and circuit simulations allow simplifying the simulation domains, which speeds up the simulations and enables parametrized analysis of the converter. The method for the design of the input decoupling network, which is the critical part of the electromagnetic compatibility of the converters, is developed. Radiation characteristics of the converters are modeled by a small loop above finite image plane and the image theory is extended to finite square image planes. A modular board system for positioning of the converters inside the transverse electromagnetic cell in three orthogonal orientation relative to the septum and a procedure for calculation of radiated emissions from the measurements performed by a transverse electromagnetic cell and a hybrid coupler is developed. Impedance mismatch between the transverse electromagnetic cell and the hybrid coupler is analyzed and the procedure for correcting the mismatch is developed. The 62-pin high-current card-edge connectors, which are used in the modular board system, are modeled by a generalized capacitance matrix of widely separated conductors.

The application of the methodology is demonstrated on the example of a synchronous buck converter. The converter is based on the integrated circuit NCP5369 from ON Semiconductor. The predicted radiated emissions of the converter are compared to the radiated emissions calculated from the measurements performed by a transverse electromagnetic cell and a hybrid coupler and a good agreement is obtained.