UBC Theses and Dissertations
Investigation of bridgeless single-phase solutions for ac-dc power factor corrected converters Alam, Md. Muntasir Ul
In modern power supplies and battery chargers, a front-end power factor correction (PFC) AC-DC converter is used to comply with regulatory requirements for input current harmonics. The prevalence of standards and recommended practices to meet harmonic current limits has gained, and continues to gain, momentum over recent years. Additionally, the improvement of overall converter efficiency is critical for the emergence and acceptance of these converter technologies, to meet the standard of efficiency and power factor requirements. This dissertation presents some innovative solutions for bridgeless non-isolated and isolated PFC AC-DC converters. All proposed converter solutions realize bridgeless converter operation to reduce conduction losses and operate in hybrid resonant pulse-width-modulation (HRPWM) mode. The PWM switches share the same gating signal, so the converter does not need extra circuitry to sense the positive and negative ac input line-cycle operation. The first contribution is a non-isolated bridgeless AC-DC converter, which has inherent inrush current-limiting capabilities. The converter architecture also enables simple implementation of lightning and surge protection systems. Moreover, this converter can survive sustained over-voltage events and can limit the voltage stress on the converter and downstream components. The second contribution is a non-isolated bridgeless AC-DC converter, which realizes soft-switching operation to reduce switching losses. This converter can operate at high switching frequency to increase power density. The third contribution is a three-level non-isolated bridgeless AC-DC converter, which has high voltage gain. This converter also provides soft-switching operation of all the power devices. Due to the three level architecture, all commutations occur with a voltage level equivalent to half the output voltage, which further reduces switching losses. This converter can utilize lower voltage rated devices, which reduces system cost. The final contribution is a single-stage bridgeless isolated AC-DC converter. This converter shows low conduction loss due to bridgeless operation and low voltage stress of the secondary diodes, low switching loss due to soft-switching operation, and a transformer that has no dc magnetizing current and does not store energy. These characteristics minimize the transformer size and increases transformer efficiency.
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