Performance of Active Power Filters and Their Applications for Power Generation Systems

Active filters have become a viable alternative for controlling harmonic levels in industrial and commercial facilities. However, there are many different filter configurations that can be employed and there is no standard method for rating the active filters. The compensation for harmonic and reactive currents becomes increasingly important owing to the wide use of power electronic equipment. Traditionally, passive LC filters have been used to eliminate line current harmonics and to increase the power factor. However, in practical applications these passive filters present many disadvantages, such as aging and tuning problems, series and parallel resonances and others. In order to overcome these problems, many compensated methods based on the technique of power electronics have been researched and developed recently, one of them is active power filters, which have gradually been recognized as a feasible solution to the problems created by nonlinear loads. They are used to eliminate the unwanted harmonics and compensate power factor by injecting equal but opposite compensation currents. An active power filter, a current source, connected in parallel with the nonlinear load, is controlled to generate the required compensation currents, so the main only needs to supply the fundamental current. Besides eliminate harmonic currents and compensate power factor, this kind of active power filter can keep the power system balanced under the condition of unbalanced and nonlinear loads simultaneously, if the compensation currents include harmonic, reactive, fundamental negative sequence and zero sequence currents. A detailed yet simple mathematical model of the active power filter, including the effect of the equivalent power system impedance, is derived and used to design the predictive control algorithm. The compensation performance of the proposed active power filter and the associated control scheme under steady state and transient operating conditions is demonstrated through simulations and experimental results.