【作者】 马柏平；

【导师】 吴建强；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2007， 硕士

【摘要】 近年来,开关型功率变换器得到了广泛的应用。科研人员通过分析、研究开关功率变换器的工作原理,设定有效的控制策略,提高变换器性能。研究表明,如果变换器工作在电流连续状态(CCM),将导致轻载时电感电流变负,引起循环能量增大、导通损耗增加、变换效率降低。为提高轻载时的变换效率,必须使变换器工作在电流断续模式(DCM)。DCM的优点是控制简单,成本低廉,且具有自然的零电流关断特性,二极管反向恢复电流所引起的开关关断损耗也较小。一些PFC电路甚至在设计时就让其在整个周期中工作在DCM下,以简化控制。因此研究DCM下工作的变换器模型具有重要的意义。首先,对全桥零电压不连续导电模式下变换器电路拓扑进行了工作模态的分析,在此基础上,对电路中各个开关管的零电压条件进行了分析,从而确定出整个电路的零电压实现条件。依照实际技术指标,对电源的主回路、控制回路进行了详尽的设计,对主要元件,如高频变压器,进行设计和参数计算。对移相控制芯片UC3875进行了介绍和应用设计。同时分析了其零电压开关条件、副边占空比丢失以及整流二极管的换流情况。二次侧采用桥式整流方式,在DCM模式下可解决变换器高压输出带来的整流管寄生振荡和电压过冲。其次,对不连续导电模式下的移相全桥ZVS DC-DC变换器进行了详细的建模。利用FB ZVS变换器和BUCK变换器的相似性,简化了全桥变换器的建模。通过分析占空比丢失造成的影响,建立了移相全桥ZVS DC-DC变换器的大信号模型和小信号模型。该模型具有比较直观的物理意义,且为下面的分析做好了准备。最后,通过仿真软件Orcad建立全桥零电压DC-DC变换器的仿真电路,结果表明该变换器各部分电路工作正常,实现了设计目标,证明了原理分析的正确性,电路主要波形和理论分析保持一致,在轻载时也能实现开关管的零电压导通。根据全桥零电压DC-DC变换器的小信号模型及其传递函数,对闭环系统的补偿网络进行了设计,使变换器具有良好的稳态和暂态性能。更多还原

【Abstract】 Recently, switch power converters are applied broadly. It is very necessary to analyze switch power converter. It can help us to find out work principium of the switch power converter and enactment effective control strategy to improve the performance. If the converter works in CCM at all times, the inductance current will become negative, circle energy will become more, waste will be more and transform efficiency will be reduced when the load is light. The converter must work in DCM for improving the transform efficiency when the load is light. The advantages of DCM are that the control mode is simple and the cost is low. Otherwise DCM has zero current switch-on characteristic in natural. And it’s waste of breaking off which is evocable by the reverse comeback current of diode is low. Some PFC circuit is designed to work in DCM in the entire cycle to predigest the control mode. So it is important to research the converter model in DCM.Firstly, the work mode of FB ZVS-PWM converter in DCM is analyzed. The work process of this circuit topology which works in phase shift mode is known deeply. The ZVS condition of every switch in circuit is analyzed based on the analyses of the work mode. Then ZVS conditions of the whole circuit are confirmed. The main circuit, control circuit, drive circuit and protect circuit are designed exhaustively. The main elements such as high frequency transformer are designed. And their parameters are calculated. UC3875 is introduced and designed. Meanwhile the duty cycle loss of secondary side and the change of current of the commutate diode are analyzed. The secondary side is adopted in bridge commutate mode. Thus it can solve the parasitic oscillation of rectifiers and the clash of voltage by the high voltage output of converter.Secondly, FB ZVS-PWM DC-DC converter is modeled exhaustively. The model of FB converter is predigested because of the comparability of the FB ZVS converter and BUCK converter. The small signal model and large signal model of FB ZVS DC-DC converter is set up by analyzing the effect of the duty cycle loss. This model has the intuitionist physics meaning. And it makes the next analyses easy. Finally the simulation circuit of FB ZVS DC-DC converter is constituted by Orcad. The simulation results indicate that the whole circuit works in gear. The design target is come true. The correctness of the analyses of principle is proved. The main waveforms are consistent with the analyses of principle. ZVS of switch is come true in light load. The closed loop system is designed Based on the small signal model and the transfer function of FB ZVS DC-DC converter. The closed loop system makes the converter have the well transient and steady performance.更多还原