This paper presents a typical topology of medium-power, active power filter that utilizes a one-step ahead current controller to improve the power quality of a four-wire, unbalanced nonlinear load without using an additional switching limb to regulate the neutral current. In contrast to commonplace control techniques of shunt active filters, the one-step ahead strategy, or predictive control method of the presented circuit, determines the switching of the active filter and, thereby, the generation of its currents, such that the supply current waveforms become virtually sinusoidal waves, being its THD -% when the filter is operated with a 2kW load. The principle of operation of the switching control scheme is analysed, using a space vector technique for simple implementation together with a description of its practical development, showing experimental results obtained with a 2kW prototype.