chr*_*892 12 c# embedded control-theory
我有一个在机器人上运行的PID控制器,旨在使机器人转向罗盘方向.以20Hz的速率重新计算/应用PID校正.
虽然PID控制器在PD模式下运行良好(IE,积分项为零),但即使是最轻微的积分也会迫使输出不稳定,使得转向执行器被推到左或右极限.
码:
private static void DoPID(object o)
{
// Bring the LED up to signify frame start
BoardLED.Write(true);
// Get IMU heading
float currentHeading = (float)RazorIMU.Yaw;
// We just got the IMU heading, so we need to calculate the time from the last correction to the heading read
// *immediately*. The units don't so much matter, but we are converting Ticks to milliseconds
int deltaTime = (int)((LastCorrectionTime - DateTime.Now.Ticks) / 10000);
// Calculate error
// (let's just assume CurrentHeading really is the current GPS heading, OK?)
float error = (TargetHeading - currentHeading);
LCD.Lines[0].Text = "Heading: "+ currentHeading.ToString("F2");
// We calculated the error, but we need to make sure the error is set so that we will be correcting in the
// direction of least work. For example, if we are flying a heading of 2 degrees and the error is a few degrees
// to the left of that ( IE, somewhere around 360) there will be a large error and the rover will try to turn all
// the way around to correct, when it could just turn to the right a few degrees.
// In short, we are adjusting for the fact that a compass heading wraps around in a circle instead of continuing
// infinity on a line
if (error < -180)
error = error + 360;
else if (error > 180)
error = error - 360;
// Add the error calculated in this frame to the running total
SteadyError = SteadyError + (error * deltaTime);
// We need to allow for a certain amount of tolerance.
// If the abs(error) is less than the set amount, we will
// set error to 0, effectively telling the equation that the
// rover is perfectly on course.
if (MyAbs(error) < AllowError)
error = 0;
LCD.Lines[2].Text = "Error: " + error.ToString("F2");
// Calculate proportional term
float proportional = Kp * error;
// Calculate integral term
float integral = Ki * (SteadyError * deltaTime);
// Calculate derivative term
float derivative = Kd * ((error - PrevError) / deltaTime);
// Add them all together to get the correction delta
// Set the steering servo to the correction
Steering.Degree = 90 + proportional + integral + derivative;
// We have applied the correction, so we need to *immediately* record the
// absolute time for generation of deltaTime in the next frame
LastCorrectionTime = DateTime.Now.Ticks;
// At this point, the current PID frame is finished
// ------------------------------------------------------------
// Now, we need to setup for the next PID frame and close out
// The "current" error is now the previous error
// (Remember, we are done with the current frame, so in
// relative terms, the previous frame IS the "current" frame)
PrevError = error;
// Done
BoardLED.Write(false);
}
有谁知道为什么会发生这种情况或如何解决它？
看起来你正在将你的时基用于积分三次.错误已经是自上一个样本以来的累积误差,所以你不需要将deltaTime乘以它.所以我会将代码更改为以下内容.
SteadyError += error ;
SteadyError是误差的积分或总和.
所以积分应该是SteadyError*Ki
float integral = Ki * SteadyError;
编辑:
我已经完成了你的代码,除了上面的修复之外,我还会修复其他几个项目.
1)您不希望以毫秒为单位的增量时间.在正常的采样系统中,delta项将是1,但是对于20Hz的速率,你输入的值为50,这具有通过该因子增加Ki并且还将Kd减小50倍的效果.如果您担心抖动,则需要将增量时间转换为相对采样时间.我会用这个公式代替.
float deltaTime = (LastCorrectionTime - DateTime.Now.Ticks) / 500000.0
500000.0是每个样本的预期滴答数,对于20Hz是50ms.
2)将积分项保持在一个范围内.
if ( SteadyError > MaxSteadyError ) SteadyError = MaxSteadyError;
if ( SteadyError < MinSteadyError ) SteadyError = MinSteadyError;
3)更改以下代码,以便当错误在-180左右时,您只需稍作更改就不会出错.
if (error < -270) error += 360;
if (error > 270) error -= 360;
4)验证Steering.Degree正在接收正确的分辨率和符号.
5)最后你可能只是将deltaTime放在一起并按以下方式计算差分项.
float derivative = Kd * (error - PrevError);
随着所有这些你的代码变成了.
private static void DoPID(object o)
{
// Bring the LED up to signify frame start
BoardLED.Write(true);
// Get IMU heading
float currentHeading = (float)RazorIMU.Yaw;
// Calculate error
// (let's just assume CurrentHeading really is the current GPS heading, OK?)
float error = (TargetHeading - currentHeading);
LCD.Lines[0].Text = "Heading: "+ currentHeading.ToString("F2");
// We calculated the error, but we need to make sure the error is set
// so that we will be correcting in the
// direction of least work. For example, if we are flying a heading
// of 2 degrees and the error is a few degrees
// to the left of that ( IE, somewhere around 360) there will be a
// large error and the rover will try to turn all
// the way around to correct, when it could just turn to the right
// a few degrees.
// In short, we are adjusting for the fact that a compass heading wraps
// around in a circle instead of continuing infinity on a line
if (error < -270) error += 360;
if (error > 270) error -= 360;
// Add the error calculated in this frame to the running total
SteadyError += error;
if ( SteadyError > MaxSteadyError ) SteadyError = MaxSteadyError;
if ( SteadyError < MinSteadyError ) SteadyError = MinSteadyError;
LCD.Lines[2].Text = "Error: " + error.ToString("F2");
// Calculate proportional term
float proportional = Kp * error;
// Calculate integral term
float integral = Ki * SteadyError ;
// Calculate derivative term
float derivative = Kd * (error - PrevError) ;
// Add them all together to get the correction delta
// Set the steering servo to the correction
Steering.Degree = 90 + proportional + integral + derivative;
// At this point, the current PID frame is finished
// ------------------------------------------------------------
// Now, we need to setup for the next PID frame and close out
// The "current" error is now the previous error
// (Remember, we are done with the current frame, so in
// relative terms, the previous frame IS the "current" frame)
PrevError = error;
// Done
BoardLED.Write(false);
}