说明：  spwm正弦表有很多，但不知怎样调用它，有了这个脉宽计算器 直接调用，不同的定时器频率生成不同的spwm 还附带有定时器周期设置计算值，对正弦波开发很有帮助
(SPWM sine table has a lot of, but I do not know what to call it, the pulse width calculator direct calls, timer frequency of different generation of the SPWM also comes with a cycle timer setting calculation, very helpful for sine wave development)