A Jitter Compensating PID Controller to Mitigate the Detrimental Effects of Software Induced Jitter in Digital Control Systems

Abstract

Software induced delays in a digital control system can lead to degradation in performance and as a result plant response characterizing performance requirements such as percent overshoot, rise time, and settling time can be violated. In the worst case the digital control system can become unstable. These delays can be constant or varying from one period to the other. The latter type of delay is known as jitter. Existing solutions attempt to improve the performance of digital control systems in the presence of software induced delays notwithstanding shortcomings. These include but are not limited to, a lack of regard for satisfying plant response characterizing performance requirements, implementation complexity, and an increase in the runtime overhead to execute the solution. In addition, a solution to compensate for inputoutput and output jitter for proportional integral derivative (PID) controllers is not available in the literature. Taking the problem to be solved and shortcomings in the literature into account, this paper proposes method to design a discrete-time PID controller that compensates for sampling, input-output, and output jitter. The solution initially models the worst case delay between input to output and then places it in a model of the digital control system in the forward loop between the PID controller and plant. Subsequently, the PID controller is tuned to satisfy plant response characterizing performance requirements. The two main advantages of this solution is that plant response characterizing performance requirements are satisfied and the execution time of the PID controller remains unchanged. An evaluation of the performance using a step input experiment validate that the proposed solution is capable of satisfying plant response characterizing performance requirements whereas the uncompensated counterpart failed to satisfy one requirement. A square wave tracking experiment also demonstrated that the proposed solution improved performance.