On the discrete-time implementation of resonant controllers for active power filters

Current control is crucial in active power filters. The current controller should provide perfect tracking of reference and total rejection of disturbance (grid voltage). The use of resonant controllers has been often proposed as one of the highest performance alternatives for alternating current and voltage control. In this work it is studied the effect of the discrete-time implementation of resonant controllers in their performance, specially when tracking high order components. It is proved that some methods cause a displacement of the resonant peaks, so infinite gain is not located at the desired frequencies. On the other hand, other options, such as impulse invariant, maintain the resonance at the design location, allowing for a superior performance. It is also studied the effect of zeros distribution on the behavior. A single-phase active power filter laboratory prototype has been built. The theoretical analysis is validated by experimental results, demonstrating the importance of the discrete-time implementation and the superiority of the impulse invariant method.