中文摘要：

为了分析工作在断续导通模式下的Buck变换器因负载变化而产生的分岔现象，首先建立了闭环脉宽调制Buck变换器的离散迭代映射．基于此映射绘制了输出电压随负载变化的分岔图．然后利用MATLAB仿真绘制了输出电压、电感电流波形及相应的相图．与分岔图相互印证并直观地反映了系统以倍周期分岔至混沌的过程。为了保证变换器工作的稳定性．根据滑模控制的基本思想，采用了自适应滞环调制策略，使系统稳定工作在单周期态。仿真结果表明，用滑模变结构法可以有效地避免因负载变化所产生的混沌态，使控制过程具有良好的动态响应特性及鲁棒性，且算法简单。易于实现。

英文摘要：

In order to analyze the bifurcation phenomenon caused by load variation of Buck converter operating in discontinuous conduction mode,the discrete iterative map of closed-loop PWM Buck converter is derived and its voltage-load bifurcation diagram is then obtained. The output voltage and inductor current waveforms and corresponding phase diagram are plotted by MATLAB simulation,which are consistent with the bifurcation diagram and reveal directly the process of system from double-period bifurcation to chaos. To ensure the stable operation of converter,a strategy of adaptive hysteresis-band modulation based on the sliding mode control is adopted to make the system operating stably in single-period state. Simulative results show that,the sliding mode control with simple algorithm is easy to realize,which improves system dynamic response and robustness and effectively prevents the chaos caused by load variation.