摘要
由于三电平直流变换器可以降低开关管的电压应力，实现主开关管的软开关，近年来逐渐成为电力电子技术的一个研究热点。本文在前人的研究成果基础上，提出了基本三电平单元的概念，并将之应用到所有的直流变换器中，由此得到一族的三电平直流变换器，使三电平直流变换器的研究走向系统化。在这些变换器中，如果采用适当的控制方案，除了可以降低变换器开关管电压应力外，部分变换器还可以在输出滤波器上得到三电平电压波形，大大改善了滤波器的工作条件。
本文以Buck三电平变换器和复合式全桥三电平变换器为例作了细致的分析。Buck三电平变换器具有将开关管电压应力减小一半，大大改善输出滤波器工作条件的优势，论文详细分析它的工作原理、参数设计和外特性。复合式全桥三电平变换器不仅可以将开关管电压应力减小一半，大大改善输出滤波器工作条件的优势，还可实现所有开关管的全负载范围软开关，本文详细分析该变换器的工作原理、参数设计、控制方案，并进行实验验证。
针对传统(半桥)三电平直流变换器的一些不足，本文提出一种倍流整流方式PWM零电压开关三电平直流变换器，可以使开关管在全负载范围内实现零电压开关，副边整流二极管无电压尖峰，无占空比丢失。文牛以一个540W的原理样机对该变换器进行验证。
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.
引文
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