PI vs fractional PI for the control of a shunt active power filter

Nonlinear loads connected to electric power systems lead to distortions in the source current waveform. One solution to improve power quality is the use of Shunt Active Power Filters (SAPF), which are able to correct both the harmonics and the unbalance in the load current. Two of the most commonly used control strategies for these devices are the so-called Unity Power Factor (UPF) strategy and the Voltage Synchronization (VS) strategy. In these, the reference currents are obtained by multiplying the source voltages by the equivalent conductance. In VS strategy this conductance is obtained from the tracking error between the measured dc bus voltage and a reference value. To minimize this tracking error, linear controller structures, as PI are used. In the last three decades, Fractional Order Control (FOC) has been used in many robust control problems, and has been applied recently to the control of a Power Electronic Buck Converter. In this line, we here consider the use of a fractional PI controller to obtain the reference current in a SAPF under the VS strategy. Simulation results are given comparing the PI and Fractional PI controllers in order to minimize the ISE and IAE cost functions of the tracking error. They show the improved performance obtained with the PI fractional controller.