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UBC Theses and Dissertations

High-order resonant power converters for battery charger applications Shafiei, Navid


The demand for electric vehicles has expanded rapidly for both industrial and transportation applications. In parallel, new battery technologies have been introduced which are capable of deep-discharge and powering electric vehicles for long periods of time. Due to the increasing complexity of charging algorithms, battery chargers are exposed to demanding operating requirements. In battery charger applications, power converters should not only regulate the battery voltage and power over a wide range, all the way from complete discharge up to the charged floating voltage but also respond to the input voltage variation period. It is also important to work at high efficiency and with low switching noise and charging current ripple. This work studies different problems regarding DC-DC power converters with wide voltage regulation as battery chargers and investigates the application of novel high-order resonant power converters (fourth and fifth-order) and modulation strategies at various power levels. As a solution for high power applications, this work first introduces a modified full bridge LLC resonant power converter driven by both variable frequency and phase shift modulation. The proposed modulation strategy along with the modified resonant circuit exhibits excellent performance for a 3kW resonant power converter, without taking advantage of burst mode strategy. The second part of this work introduces a novel fifth-order L3C2 resonant converter for medium power level applications, that can regulate the battery voltage from near zero output voltage, zero output current to maximum output power. A 950W design example demonstrates a wide output voltage regulation with maximum efficiency of 96%. Finally, a fourth order L3C resonant converter is proposed for electric vehicles with roof-top solar photovoltaic panels, which can not only regulate the battery voltage in a wide range but also track the input voltage variation for extracting the maximum available power from the PV panel. All results from this work have been confirmed experimentally, which highlight the exceptional regulation capability of the proposed resonant power converters and modulation techniques.

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