The design and implementation of active power filters based on variable structure system concepts

The authors consider the design and implementation of active power filter systems based on concepts from variable structure systems (VSSs) and sliding mode control. The equivalent control concept from VSSs proves to be a very useful tool in the design of the filter. It is shown how the power circuit parameters are integrally tied to the equivalent control, and how circuit performance can be likewise judged. A design procedure is outlined using this approach. In addition, the authors discuss a closed-loop control for an active power filter based on a three-phase switchmode voltage-source inverter. The controller is composed of an inner current control loop which utilizes a sliding-mode control law, and an outer linear control loop which regulates the average voltage across the DC bus of the inverter. Simulations are presented to document converter performance