The harmonic problem in power systems is gaining more attention as incidences correlated with harmonics increase. Conventional passive filtering techniques for harmonic mitigation have inherent problems, and purely active filters have the disadvantages of higher costs and ratings. Hybrid active filters inherit the efficiency of passive filters and the improved performance of active filters, and thus constitute a viable improved approach for harmonic compensation. To date, there have been several literature works comparing passive and active filters for harmonic mitigation. However, there are currently no comparisons of possible hybrid active filters. This thesis presents an assessment and comparison of hybrid active filters, including their topologies and control algorithms. Three different topologies of hybrid active filters are simulated in PSpice version 9.0 to verify their feasibility for harmonic compensation. From the simulations, all three topologies have better performance over passive filters for harmonic compensation and are insensitive to parameter variations. In addition, the simulated hybrid active filter ratings are lower than can be achieved with purely active filters. A modified "p-q" theory is introduced for control strategy, which is more feasible for extracting harmonic components for distorted load voltages. This thesis concludes with a comprehensive comparison of the hybrid active filter characteristics. / Graduation date: 2001