Optimal design of current and voltage controllers for a distributed energy resource

This paper presents optimal design of controllers of the general type of proportional-integrating-derivative (PID) for achieving optimal tracking of a constant or slow-changing set-point. The design method is developed for the first- and second-order plants (with or without zero) in which only an output signal is used for the feedback. A generalization of the proposed method for higher-order plants with state-feedback is also introduced. The method is based on formulating the design objectives as a minimization problem with a suitable form which can be solved by the linear quadratic regulation (LQR) technique. Various controller structures are described and their advantages and drawbacks are explained. The method is applied to the design of current and voltage controllers in a grid-connected distributed energy resource, demonstrating the optimal tracking of real and reactive power set-points.