说明：  基于平均法的buck型DC/DC建模步骤，包括电压模和峰值电流模。增加了误差放大器放大倍数的确定，电源调整率，负载调整率和三种变换器的一阶等效模型
(Based on the average of the buck-type DC/DC modeling steps, including the voltage mode and peak current mode. An increase of the error amplifier to determine the magnification, adjust the rate of power supply, load-adjusted factor and three first-order equivalent converter model)