98ba591357
If you want to use derivative-on-measurement, you will need to negate the 'D'-gain you would typically use in a 'standard derivative-on-error' PID controller - I did not mention that in the video. Since the 'error signal' effectively going into the differentiator does not depend on the setpoint: e[n] = 0 - measurement, and therefore (e[n] - e[n - 1]) = (0 - measurement) - (0 - prevMeasurement) = -Kd * (measurement - prevMeasurement). So, for example, if you require a controller with a D-gain of 10, you would set pid->Kd = -10. This is a slight quirk of the derivative-on-measurement form - however, the code can of course be adapted to include the minus sign.
44 lines
926 B
C
44 lines
926 B
C
#ifndef PID_CONTROLLER_H
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#define PID_CONTROLLER_H
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typedef struct {
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/* Controller gains */
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float Kp;
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float Ki;
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float Kd; /* Note: since using derivative-on-measurement, Kd needs to be negative (in contrast to conventional 'derivative-on'error') */
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/* Derivative low-pass filter time constant */
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float tau;
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/* Output limits */
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float limMin;
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float limMax;
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/* Integrator limits */
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float limMinInt;
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float limMaxInt;
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/* Sample time (in seconds) */
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float T;
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/* pid coefficient offset for start pid */
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float offset;
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/* Controller "memory" */
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float integrator;
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float prevError; /* Required for integrator */
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float proportional;
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float differentiator;
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float prevMeasurement; /* Required for differentiator */
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/* Controller output */
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float out;
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} PIDController;
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void PIDController_Init(PIDController *pid);
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float PIDController_Update(PIDController *pid, float setpoint, float measurement);
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#endif
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