Three-level Dc-dc Converter

Because the switches suffer only the half of the input voltage, the Three-Level (TL) converters have been attracting more and more attentions. In this thesis, the TL cells are proposed and applied to all dc/dc converter, thus a family of TL converters are derived. Besides the reduction of the voltage stress of the switches, by adopting proper control strategy, some TL converters have the TL waveforms across the filter, so the filter can be significantly reduced.Buck TL converter and Hybrid Full-Bridge (HFB) TL converter are taken as the examples to illustrate the operation of the TL converter. The operation of Buck TL converter are analyzed as well as parameter design and input/output characteristics.HFB TL converter has two phase legs, one is Three-Level leg, the other is Two-Level leg. The switches of the Three-Level leg suffer only the half of the input voltage and can realize Zero-Voltage-Switching (ZVS) in a wide load range, so the MOSFET can be adopted. The switches of the Two-Level leg suffer the input voltage and can realize Zero-Current-Switching (ZCS) in a wide load range, so the IGBT can be adopted. The voltage across the output filter is a TL waveforms, which reduces the output filter. The input current of HFB TL converter is nearly a dc current, which reduces the input filter. The operation and parameter design are discussed and verified by a 2.7kW prototype converter.A Current-Doubler-Rectifier (CDR) ZVS PWM (Half-Bridge) three-level converter is proposed in this paper. ZVS can be achieved for all the switches in a wide load range with the use of the energy stored in the output filter inductances. The output rectifier diodes commutate naturally without voltage oscillation and voltage spike. Due to very small leakage inductance, the duty cycle loss is very little. A 540W prototype converter is built in the lab to verify the effectiveness of the proposed converter.