Terminal models have been used for various power electronic applications. In this work a two- and three-terminal black box model is proposed for electro-magnetic interference (EMI) characterization. The modeling procedure starts with a time-variant system at a particular operating condition, which can be a converter, set of converters, sub-system or collection of components. A unique, linear equivalent circuit is created for applications in the frequency domain. Impedances and current / voltage sources define the noise throughout the entire EMI frequency spectrum. All parameters needed to create the model are clearly defined to ensure convergence and maximize accuracy. The model is then used to predict the attenuation caused by a filter with increased accuracy over small signal insertion gain measurements performed with network analyzers. Knowledge of EMI filters interactions with the converter allows for advanced techniques and design constraints to optimize the filter for size, weight, and cost. Additionally, the model is also demonstrated when the operating point of the system does not remain constant, as with AC power systems. Modeling of a varying operating point requires information of all the operating conditions for a complete and accurate model. However, the data collection and processing quickly become unmanageable due to the large amounts of data needed. Therefore, simplification techniques are used to reduce the complexity of the model while maintaining accuracy throughout the frequency spectrum. The modeling approach is verified for linear and power electronic networks including: a dc-dc boost converter, phase-leg module, and a simulated dc-ac inverter. The accuracy of the model is confirmed up to 100 MHz in simulation and at least 50 MHz for experimental validation. / Ph. D.

This dissertation is to focus on the development of modeling and simulation methodology to predict conductive electromagnetic interference (EMI) for high power converters. Conventionally, the EMI prediction relies on the Fast Fourier Transformation (FFT) method with the time-domain simulation result that requires long hours of simulation and a large amount of data. The proposed approach is to use the frequency-domain analysis technique that computes the EMI spectrum directly by decomposing noise sources and their propagation paths. This method not only largely reduces the computational effort, but also provides the insightful information about the critical components of the EMI generation and distribution. The study was first applied to a dc/dc chopper circuit by deriving the high frequency equivalent circuit model for differential mode (DM) and common mode (CM) EMIs. The noise source was modeled as the trapezoidal current and voltage pulses. The noise cut-off frequency was identified as a function of the rise time and fall time of the trapezoidal waves. The noise propagation path was modeled as lumped parasitic inductors and capacitors, and additional noise cut-off frequency was identified as the function of parasitic components. . Using the noise source and path models, the proposed method effectively predicts the EMI performance, and the results were verified with the hardware experiments. With the well-proven EMI prediction methodology with a dc/dc chopper, the method was then extended to the prediction of DM and CM EMIs of three-phase inverters under complex pulse width modulation (PWM) patterns. The inverter noise source requires the double Fourier integral technique because its switching cycle and the fundamental cycle are in two different time scales. The noise path requires parasitic parameter extraction through finite element analysis for complex-structured power bus bar and printed circuit layout. After inverter noise source and path are identified, the effects of different modulation schemes on EMI spectrum are evaluated through the proposed frequency-domain analysis technique and verified by hardware experiment. The results, again, demonstrate that the proposed frequency-domain analysis technique is valid and is considered a promising approach to effectively predicting the EMI spectrum up to tens of MHz range. / Ph. D.

With GaN and SiC switching devices becoming more commercially available, higher switching frequency is being applied to achieve higher efficiency and power density in power converters. However, electro-magnetic interference (EMI) becomes a more severe problem as a result. In this thesis, the switching frequency effect on conducted EMI noise is assessed. As EMI noise increases, the EMI filter plays a more important role in a power converter. As a result, an effective EMI modeling technique of the power converter system is required in order to find an optimized size and effective EMI filter. The frequency-domain model is verified to be an efficient and easy model to explore the EMI noise generation and propagation in the system. Of the various models, the unterminated behavioral model can simultaneously predict CM input and output noise of an inverter, and the prediction falls in line with the measurement around 10 MHz or higher. The DM terminated behavioral model can predict the DM input or output noise of the motor drive higher than 20 MHz. These two models are easy to extract and have high prediction capabilities; this is verified on a 10 kHz-switching-frequency Si motor drive. It is worthwhile to explore the prediction capability of the two models when they are applied to a SiC-based power inverter with switching frequency ranges from 20 kHz to 70 kHz. In this thesis, the CM unterminated behavioral model is first applied to the SiC power inverter, and results show that the model prediction capability is limited by the noise floor of the oscilloscope measurement. The proposed segmented-frequency-range measurement is developed and verified to be a good solution to the noise floor. With the improved impedance fixtures, the prediction from CM model matches the measurement to 30 MHz. To predict the DM input and output noise of the SiC inverter, the DM terminated behavioral model can be used under the condition that the CM and DM noise are decoupled. With the system noise analysis, the DM output side is verified to be independent of the CM noise and input side. The DM terminated behavioral model is extracted at the inverter output and predicts the DM output noise up to 30 MHz after solving the noise floor and DM choke saturation problem. At the DM input side, the CM and DM are seen to be coupled with each other. It is found experimentally that the mixture of the CM and DM noise results from the asymmetric impedance of the system. The mixed mode terminated behavioral model is proposed to predict the DM noise when a mixed CM effect exists. The model can capture the DM noise up to to 30 MHz when the impedance between the inverter to CM ground is not balanced. The issue often happens in extraction of the model impedance and is solved by the curving-fitting optimization described in the thesis. This thesis ends with a summary of contributions, limitations, and some future research directions. / Master of Science

With the development of power electronics, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) issues have become more and more important for both power converter designers and customers. This dissertation studies EMI noise emission characterization and modeling in power converters. A modular-terminal-behavioral (MTB) equivalent EMI noise source modeling approach is proposed. This work is the first to systematically develop a 3-terminal EMI noise source model for a switching phase-leg device module. Each module is modeled as pairs of equivalent noise current sources and source impedances. Although the proposed MTB modeling approach applies the linear circuit theory to a semiconductor switching device, which exhibits nonlinear behavior during switching transients, the analysis and experiments show that the nonlinearity has negligible practical effect on the modeling methodology. The validation range of the modeling methodology has been analyzed. One of the differences between the proposed MTB model and the other state-of-the-art models is that the MTB model characterizes and predicts the CM and DM noise simultaneously. The inseparable high-frequency CM and DM noise characteristics contributed by the source impedance and propagation path are analyzed. A comprehensive evaluation of different EMI noise source modeling approaches according to the criteria of accuracy, feasibility and generality has been presented. Results show that the MTB modeling approach is more accurate, feasible and general than other approaches. The modular and terminal characteristics of the MTB noise source model are verified in two more complicated cases. One example is the application of the MTB equivalent source model in a half-bridge AC converter with variable switching conditions. Although the MTB model is derived under a certain operating condition, the models under different conditions can be combined together to predict the EMI noise for the converter with variable switching conditions. Another example is the application of the MTB equivalent source model in multi-phase-leg converters. The EMI noise of a full-bridge converter is predicted based on the MTB equivalent source model of one phase-leg module. The implementation procedures and results for both applications are verified by the experiment. The applicability of the MTB model in different type of converters is discussed. Based on the MTB model, EMI noise management is explored. The parametric study based on the MTB model is demonstrated by selecting DC-link decoupling capacitors for voltage source converter (VSC). The EMI effect of a decoupling capacitor for a device s safe operation is analyzed, and this analysis shows the terminal characteristics of the MTB model. Both the EMI and voltage overshoot are predicted by the MTB model. A completed converter-level EMI model can be derived based on the noise source model and propagation path model. This model makes it possible to optimize the EMI filter design and study the EMI noise interactions between converters in a power conversion system. / Ph. D.

In this work, a modeling approach is delineated and described in detail; predominantly done in the time domain from low frequency, DC, to high frequencies, 100 MHz. Commercially available computer aided design tools will be used to determine the propagation path in a given structure. Next, an integrated transmission-line filter — fabricated using planar processing technologies — is modeled to accurately predict the EMI characteristics of the system. A method was derived to model the filter's performance in the time-domain while accurately depicting the highly frequency dependant transmission-line properties. A system model of a power factor correction (PFC) boost converter was completed by using active device models for diodes, MOSFETs, and the gate driver. In addition, equivalent circuits were used to characterize high frequency impedances of the passive components. A PFC boost converter was built and used to validate the model. The PFC operated at a peak output power of 1 kW, switching at 400 kHz, with a universal input ranging from 90-270 VRMS with unity power factor. The time-domain and EMI frequency spectrum waveforms are experimentally measured and agree very well with the simulated values; within 5 dB for EMI. The transmission-line filter was also manufactured for model verification, and it is tested for the first time with an operating converter: a PFC at 50 W output and 50 VDC input. The small signal characteristics match the model very well. In addition, impedance interactions between the filter, the converter, and the EMI measurement set-up are discussed, evaluated, measured, and improved to minimize undesired resonances and increase low-frequency EMI attenuation. Experimentally measured attenuation provided by the filter in the range from 100 kHz to 100 MHz was 20-50 dBμV. The simulation also shows a similar attenuation, with the exception of one key resonance not seen in the simulation. / Master of Science