Compensating Capacitor Voltage Fuzzy Hysteresis Control for a Direct Current Controlled Active Filter

The regulation of the dc-link voltage for the shunt active power filters is typically done by a proportional integrative controller. The use of a fuzzy controller for this job eliminates the laborious tuning process, which is replaced by the membership functions definition. To validate the results, a comparative study was done between the fuzzy controller and the reference proportional-integrative controller performance. The fuzzy voltage controller has an aperiodic response, with good voltage regulation, but because of the high output ripple, a first order, low pass filter is necessary. The low pass filter reduces the ripple to a level at which the distortion produced to the compensated current becomes insignificant, without noticeable affecting the controller performance. On the other hand, the filter presence changes the fuzzy controller response from aperiodic to oscillatory, but the created oscillation is low, lower than the PI controller corresponding oscillation. A comparative study was also done between the unfiltered fuzzy controller and the filtered fuzzy controller performance. For the case of the fuzzy controller a compromise must be made between high output ripple and poor regulation. Although, for the direct current control, the active charging current is low, so the output ripple can be reduced without visibly affecting the voltage regulation.