通过三、四两篇文章，基本上已经弄清楚了PID控制算法的最常规的表达方法。在普通PID控制中，引入积分环节的目的，主要是为了消除静差，提高控制精度。但是在启动、结束或大幅度增减设定时，短时间内系统输出有很大的偏差，会造成PID运算的积分积累，导致控制量超过执行机构可能允许的最大动作范围对应极限控制量，从而引起较大的超调，甚至是震荡，这是绝对不允许的。
为了克服这一问题，引入了积分分离的概念，其基本思路是 当被控量与设定值偏差较大时，取消积分作用; 当被控量接近给定值时，引入积分控制，以消除静差，提高精度。其具体实现代码如下：
pid.Kp=0.2;
pid.Ki=0.04;
pid.Kd=0.2; //初始化过程
if(abs(pid.err)>200)
{
index=0;
}else{
index=1;
pid.integral+=pid.err;
}
pid.voltage=pid.Kp*pid.err+index*pid.Ki*pid.integral+pid.Kd*(pid.err-pid.err_last); //算法具体实现过程
其它部分的代码参见《PID控制算法的C语言实现三》中的讲解，不再赘述。同样采集1000个量，会发现，系统到199所有的时间是原来时间的1/2,系统的快速性得到了提高。
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