Digital control based on DPLL of an AC line conditioner

The goal of this work is to accomplish a study and design an indirect voltage conditioner controlled digitally through digital signal processor (DSP) based on digital PLL (phase locked loop). A digital PLL (DPLL) is proposed and implemented using the three-phase instantaneous power theory. The PLL used as reference signal does not contain harmonic distortions, and follows frequency variations in the power supply. The advantage of using PLL as reference lies in the immunity to variations and disturbances of the mains, besides being sensitive to the frequency variation, which make possible to follow the fundamental component of the voltage. For the digital control proposed in this work, two loops are used, one for input voltage feedforward, and the other one for controlling the effective output voltage. With the use of DSP, all the control algorithms can be developed in assembly language. Simulation and experimental results obtained on a 3 kVA conditioner are also presented. The ac-ac indirect conditioner does not use a dc link, as its weight and cost is reduced if compared with classical back-to-back topologies.