Evaluation of stationary frame and fixed switching frequency digital current control techniques for power active filters

In this paper two stationary frame digital current control techniques, the RST and the multi-resonant controller, are analysed and experimentally tested in an active filter application. The RST controller has been tuned in order to obtain a deadbeat response. The method used to tune the multi-resonant controller is based on a frequency response approach that guarantees the stability and robustness of the system. It is well-known that the performance of deadbeat controllers is constrained to the accuracy of the plant model as well as the accuracy of the reference and disturbance predictions. The accuracy of the multi-resonant controller is guaranteed as long as the system is stable and the harmonics of the reference and the disturbance coincide with the resonance frequencies of the controller. Theoretically the main advantages of the deadbeat controller are its simplicity and its dynamics. However, in a complex application such as the active filtering the intrinsic delay of the controller is unacceptable and therefore it is necessary to use reference (and eventually disturbance) prediction techniques. The use of these techniques can have a non-negligible effect on the characteristics of the system and can be detrimental for both the dynamics and the simplicity of the system. In this paper two different prediction techniques have been implemented: periodicity and resonant. It is shown that the steady-state performances in both cases are satisfactory and similar to those obtained with the multi-resonant controller. Nevertheless, the first of the prediction techniques deteriorates significantly the dynamic performance of the system while the second one increases considerably its complexity, showing that the multi-resonant controller is better adapted for this kind of applications than the studied deadbeat controller