Nonlinear Inductors in Power Electronics: Modeling, Design, and Control

Inductors that operate in partial magnetic saturation are increasingly attracting the interest of the scientific community in the attempt of enhancing the power density of switched-mode power supplies. Designing and simulating converters that use nonlinear magnetic components need accurate models capable of predicting their voltage and current characteristics, as well as power losses under various operating conditions. Typically, inductor datasheets do not provide comprehensive information regarding inductance and losses related to partial magnetic saturation. Furthermore, the data usually applies only to sinusoidal excitation waveforms. However, the voltage across inductors is often nonsinusoidal. In the case of DC-DC converters, the inductor voltage typically resembles a square wave, with varying frequency, amplitude, and duty cycle. The inductor current is approximately a biased triangular wave, which can become significantly distorted as magnetic saturation occurs. This thesis is focused on circuit models for inductors that account for partial magnetic saturation and power losses. These models are validated using inductors with cores made of ferrite – the most widely used core material – and amorphous alloys. The models operate across various frequencies with sinusoidal, square, and triangular waveforms, while also considering the influence of inductor design parameters such as the number of turns and any air gaps in the core. Temperature effects are accounted for as well. One of the developed circuit models is exploited for an embedded control based on model predictive control of a boost converter. With an accurate model, the predictive control enables the control of converters while enforcing constraints, even when the inductors operate under conditions of partial magnetic saturation. An analysis of the effects of magnetic saturation in the inductor of a buck converter is carried out using a circuit model validated against experimental measurements. This study provides a proof of concept for switching converters that exploit saturable inductors. In the test case, using inductors that operate in partial magnetic saturation can lead to an increase in power density, with only a slight reduction in efficiency.