CONTROLSUITE的PID相关例程

#ifndef __PI_H__
#define __PI_H__

typedef struct {  _iq  Ref;      // Input: reference set-point
      _iq  Fbk;      // Input: feedback
      _iq  Out;      // Output: controller output      _iq  Kp;    // Parameter: proportional loop gain
      _iq  Ki;       // Parameter: integral gain
      _iq  Umax;   // Parameter: upper saturation limit
      _iq  Umin;   // Parameter: lower saturation limit
      _iq  up;    // Data: proportional term
      _iq  ui;    // Data: integral term
      _iq  v1;    // Data: pre-saturated controller output
      _iq  i1;    // Data: integrator storage: ui(k-1)
      _iq  w1;    // Data: saturation record: [u(k-1) – v(k-1)]
    } PI_CONTROLLER;

Ref是给定值，Fbk是反馈，out是PID的输出，关于Up,ui,v1,i1,w1具体指的是什么不清楚，有谁知道的可以具体解释一下吗，谢谢。