Publication: Modified five-level resonant DC-DC boost converter for high voltage application
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Date
2024-07
Authors
Lim, Zhan Hong
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Abstract
Due to the increasing need for efficient and modular DC-DC voltage conversion for high-voltage applications, multilevel LLC boost DC-DC resonant converter (RC) is used extensively to handle wide input voltage ranges and generate desired constant output voltage by stepping up or stepping down voltage based on frequency control. A Cascaded H-Bridge Multilevel Inverter (CHBMLI) is one of the most used inverter topologies for the LLC RC to achieve a multilevel voltage waveform because of its lower switch count requirement. Although MLIs have more advantages than other inverters, extensive tests and developments have been conducted to improve MLI's efficiency based on size and cost consideration for different voltage levels. This shows the need to reduce the switch count of MLI, thereby reducing the size and cost of MLI. Therefore, to further improve the efficiency of a five-level LLC boost RC, this project aims to design a reduced switch five-level LLC boost DC-DC RC for high voltage applications. The voltage gain of resonant tank is selected to generate an output voltage of 1000V from input voltage from 200V to 300V. The switching frequency is limited to a range between 57.10kHz and 158.22kHz. The proposed converters’ behaviour is simulated and verified using MATLAB/Simulink features. It was observed that the resonant converter with a five level diode-bypassed inverter, has switching frequency always lower than the resonance frequency under all the input and load conditions. This behaviour is the same with five-level cascaded H-bridge inverters. The deployed frequency controller achieves the targeted specifications against input and load variation at maintaining 1000V output, achieving a full load efficiency of 93.66%. The diode-bypassed DC link inverter is chosen instead of the diode-bypassed neutral-point inverter because it achieves higher
efficiencies for load currents below 3A and similar efficiencies for load currents above 3A, all with a lower switch count of five. The results demonstrate a switch reduction of 37.5%, a power loss reduction of 45% and a 5% efficiency improvement using a diode-bypassed DC-link inverter.