说明：  本方法的基本思想就是利用单片机具有的PWM端口，在不改变PWM方波周期的前提下，通过软件的方法调整单片机的PWM控制寄存器来调整PWM的占空比，从而控制充电电流
(The basic idea of this method is the use of microcontroller has the PWM ports, without changing the PWM square wave cycle, under the premise of the method to adjust by software MCU PWM control registers to adjust the PWM duty cycle and thus control the charge current)