Novel control algorithm for a unified power quality conditioner connected to a radial grid

This paper addresses a novel control algorithm for a three-phase Unified Power Quality Conditioner (UPQC), connected to a radial grid with widespread nonlinear loads. Based on the proposed control algorithm, the shunt converter acts as a selective active filter and compensates the power factor. On the other hand, the series converter compensates voltage sags or swells, harmonic- and unbalanced-voltages, and, also, improves the overall power system stability once it damps possible low-frequency resonances involving the UPQC passive filters with the system impedance. All of the control algorithms are in dq system-coordinates, through the synchronous reference frame concepts, together with a synchronizing PLL circuit. It is worth to comment a decrement of the number of input signals to determine the current- and voltage-references, in comparison with ordinary UPQC control algorithms, once the load- and grid-currents are no longer used. To evaluate the UPQC performance, with the proposed control algorithms, simulation results involving transient- and steady-state conditions are presented.