Nowadays, switching power converters are massively used in almost any electrical and electronic equipment and appliances. This class of circuits are inherently time-varying systems that are characterized by the periodic activity of their internal switches which leads to discontinuous absorbed currents. The above currents, that play the role of high frequency noisy disturbances feeding the power distribution system, become a serious concern for designers that need to comply with the electromagnetic compatibility (EMC) regulation for the conducted emission (CE). In this frame- work, modeling and simulation tools for switching circuits are key resources in the early design phase for the prediction of the conducted emission and for the assessment of alternative design scenarios. The classical approach to CE prediction is via physical-based models and time-domain simulations. This solution, however, requires intimate knowledge of the internal device structure. Also, large simulation times are in general needed to avoid integration errors and to achieve accurate results (the CE are in fact computed by applying the Fourier transform on the steady-state portion of the current response of the circuit). As an alternative, frequency-domain behavioral approaches are available in literature. In the latter case, the proposed models are small-signal time-invariant approximations computed from the external observation of the circuit behavior. These approaches, that are based on simplified equivalents, do not take into account the internal time-varying nature of the circuit and in many cases unavoidably lead to a model accuracy that strongly depends on the operating condition of devices. To overcome the above limitations, this thesis proposes an alternative approach to CE assessment based on the mathematical framework developed for time-varying circuits and systems. The proposed method allows for the steady-state prediction of circuit responses directly in the frequency-domain. A topological approach is used, where the original time-varying circuit is suitably replaced by an augmented time-invariant equivalent solved via standard tools for circuit analysis. The new augmented variables in the above equivalent turn out to be the harmonic coefficients of the Fourier series expansion of the corresponding voltage and current variables in the original circuit. A second important contribution in this work is the application of the pro- posed mathematical tool to the modeling of a switching converter and of its CE disturbances from measured data. The converter is seen as a black-box element that is characterized via a limited set of port voltage and current observations, leading to an equivalent augmented admittance fully describing the time-varying nature of the system. Summarizing, this thesis provides a comprehensive theoretical discussion together with several tutorial examples. What is more important, it proposes a novel approach to CE prediction with improvements with respect to state-of-the-art approaches and linear time-invariant surrogates. A real application test case involving a dc-dc boost converter and real measured data is also used to validate the method and stress its features for both numerical simulation and black-box modeling.

EMI Analysis and Modeling of Switching Circuits / Trinchero, Riccardo. - (2015). [10.6092/polito/porto/2594555]

EMI Analysis and Modeling of Switching Circuits

TRINCHERO, RICCARDO
2015

Abstract

Nowadays, switching power converters are massively used in almost any electrical and electronic equipment and appliances. This class of circuits are inherently time-varying systems that are characterized by the periodic activity of their internal switches which leads to discontinuous absorbed currents. The above currents, that play the role of high frequency noisy disturbances feeding the power distribution system, become a serious concern for designers that need to comply with the electromagnetic compatibility (EMC) regulation for the conducted emission (CE). In this frame- work, modeling and simulation tools for switching circuits are key resources in the early design phase for the prediction of the conducted emission and for the assessment of alternative design scenarios. The classical approach to CE prediction is via physical-based models and time-domain simulations. This solution, however, requires intimate knowledge of the internal device structure. Also, large simulation times are in general needed to avoid integration errors and to achieve accurate results (the CE are in fact computed by applying the Fourier transform on the steady-state portion of the current response of the circuit). As an alternative, frequency-domain behavioral approaches are available in literature. In the latter case, the proposed models are small-signal time-invariant approximations computed from the external observation of the circuit behavior. These approaches, that are based on simplified equivalents, do not take into account the internal time-varying nature of the circuit and in many cases unavoidably lead to a model accuracy that strongly depends on the operating condition of devices. To overcome the above limitations, this thesis proposes an alternative approach to CE assessment based on the mathematical framework developed for time-varying circuits and systems. The proposed method allows for the steady-state prediction of circuit responses directly in the frequency-domain. A topological approach is used, where the original time-varying circuit is suitably replaced by an augmented time-invariant equivalent solved via standard tools for circuit analysis. The new augmented variables in the above equivalent turn out to be the harmonic coefficients of the Fourier series expansion of the corresponding voltage and current variables in the original circuit. A second important contribution in this work is the application of the pro- posed mathematical tool to the modeling of a switching converter and of its CE disturbances from measured data. The converter is seen as a black-box element that is characterized via a limited set of port voltage and current observations, leading to an equivalent augmented admittance fully describing the time-varying nature of the system. Summarizing, this thesis provides a comprehensive theoretical discussion together with several tutorial examples. What is more important, it proposes a novel approach to CE prediction with improvements with respect to state-of-the-art approaches and linear time-invariant surrogates. A real application test case involving a dc-dc boost converter and real measured data is also used to validate the method and stress its features for both numerical simulation and black-box modeling.
2015
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2594555
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