This article focuses on reducing the harmonic distortion created by an uncontrolled three-phase rectifier bridge (non-linear load), using an active parallel filter (APF). Minimum adaptive variance control is used to regulate the continuous bus voltage dc voltage at the condenser limits and compared with the traditional proportional integral (PI) regulator. The minimum variance order for single-input single-output (SISO) systems is described by linear vector equations with constant but unknown parameters, a single-output, single-input, self-adaptive controller based on the minimum variance is then suggested, which uses a recursive least squares (RLS) estimator and a linear controller obtained directly from current estimates. By using for the extraction of the reference currents the theory active and reactive instantaneous powers (p-q), and the sinusoidal pulse width modulation (SPWM) technique for the control of the inverter. The results of simulations under the Matlab / Simulink environment show the effectiveness of the minimum variance control, whose goal is to improve the APF where we notice a significant reduction of the total harmonic distortion of the current (THDi) values below 5 % that meet the standards.

Keywords: Active parallel filter (APF), Sinusoidal pulse width modulation (SPWM), Total harmonic distortion (THD), p-q theory, Minimum variance control (MVC)