TECHNOLOGIES TO IMPROVE GAN-BASED LLC RESONANT CONVERTER FOR WIDE INPUT VOLTAGE, HIGH OUTPUT CURRENT AC-DC AND DC-DC APPLICATIONS

Abstract

The industry driving toward smaller, and more efficient electronics has led to the development of Switch Mode Power Supply (SMPS) in today’s most popular industrial applications. Resonant converters, among a variety of mainstream power converter topologies, are receiving more and more attention owing to their features of high efficiency and high power density. This thesis discusses several challenges to apply LLC resonant converter in industrial applications, including wide input voltage range, poor feedback performance, output current unbalance among multiply phases, and double line frequency ripple with power factor correction (PFC). Aiming at these issues, several solutions have been proposed. A single-stage LLC converter is used in power adapter applications. Voltage doubler circuit is added to reduce the rectified DC bus voltage range. Thus, the LLC converter can be designed with narrow input voltage range, and large magnetizing inductor can be used, which reduces the rms current and the turn-off current. A frequency modulation with nonlinear voltage-controlled-oscillator (VCO) is proposed to improve the feedback performance of LCLC converter in data center applications. Conventional linear VCO may cause oscillation at low inputs or poor dynamic response at high inputs. However, the proposed nonlinear VCO could achieve better feedback performance. A three-phase interleaved LLC converter is proposed for high output current EV low voltage DC-DC charger (LDC) applications. With proposed three-phase interleaved topology, the conduction loss and copper loss can be reduced significantly. In addition, the switches current rating is reduced. Due to the resonant component tolerance, severe current unbalance happens in three-phase interleaved LLC converter. To achieve current sharing, full-wave switch-controlled capacitor (SCC) circuit is added into the resonant tank to compensate the tolerance. In addition, a digital comparison control strategy is proposed to control the SCC switches for current sharing. A single-stage LLC converter with PFC is applied in EV AC-DC on-board charger (OBC) application. A power converter-controlled capacitor (PCCC) is proposed to eliminate the double line frequency voltage ripple on LLC PFC converter output side. The average power handled by the PCCC is zero. In this thesis, the proposed theories are verified by mathematical analysis, computer simulation and experimental testing.