The disturbances observed in the electrical system such as harmonics, asymmetry, flickers, voltage dips and swells, transients, are due to the type of connected devices. The nonlinear devices are the most common ones. Their connection to the electrical system without solution of mitigating their negative influence on supply network can be the cause of poor power quality. There are different types of solutions such as the passive harmonic filters (PHF), the active power filters (APF), the hybrid active power filters (HAPF). Each of those solutions presents some advantages and disadvantages. The chapter is focused on the HAPF, which is the combination of the PHF and shunt active power filter (SAPF) connected in series. Such topology is known in the literature, but still, there are certain problems that need more clarification through detailed studies. For instance, there are not enough recommendations on how to choose the PHF tuning frequency, when it is connected in series with SAPF. The investigations presented in this chapter are very detailed and based on a case study. The proposed control system algorithms of filters (SAPF and HAPF) are presented as well as formulated recommendations.