Fast Discrete-Time PID Controller for Current Servo

A tuning method for a discrete-time PID controller in a current sevro system was developed. The object is modelled by a double integrator. The method allows to obtain arbitrarily fast dynamics of the system, up to dead-beat control. Its use requires a four-parameter variant of the controller with a filtered derivative block. Analytical formulas were derived allowing the calculation of the controller settings based on simple basic design parameters: object gain, controller cycle time and settling time. The tuning method was verified by simulation and the relationship between the response dynamics and the sensitivity to deviation of the object gain from its design value was analyzed. In an experiment with a real object, the correct operation of the control system was confirmed for the settling time 5 and 10 times longer than the controller cycle time. The settings proposed in previous work allowed to obtain a settling time at least 25 times longer than the cycle time.