Design of resonant current regulation for discrete frequency tuning active filter

Harmonic resonances of the distribution power system have become a significant issue in recent years, due to extensive use of either nonlinear loadings or inverter-based distributed generation systems. This paper presents resonant current regulation to enhance the damping capability of the discrete frequency tuning active filter for suppressing power system harmonics. The resonant current regulator, which is composed of various parallel band-pass filters tuned at harmonic frequencies, is implemented so that the active filter can operate as variable conductance for each harmonic frequency without increasing overall gain of controller. Compared to the active filter with proportional control, the current tracking capability and the associated damping performances can be improved in the proposed method, especially for higher order harmonics due to severe phase lagging. Therefore, harmonic resonances can be definitely avoided and voltage distortion for each harmonic frequency can be separately suppressed to conform with harmonic regulation. The required damping conductance to maintain the harmonic voltage at an allowable level is also significantly reduced. Operation principles are explained and test results validate the effectiveness of the proposed approach.