Characterization of tracking performance for a three-phase reference signal generator for utility connected applications

Grid connected applications require the use of sinusoidal reference signals having low distortion and good frequency tracking performance. This paper presents a reference signal generator for use in three phase power electronics application where grid tracking must be provided. The proposed generator drift from the traditional DQ generator and is a hardware solution. The implementation is intended to be able of release digital control systems from the task of calculating the reference signals. Many control stages of three phase power electronics systems rely on DQ transformation operations to generate the low distorted reference signals. The major drawback of these transformations becomes clear when the grid is unbalanced or there is a frequency drift. A comparison between a DQ generator and the proposed scheme is presented; the testing conditions are severe sag ranging form 50% to 100% of nominal utility value, and frequency variations of around the nominal frequency value. The proposed scheme shows THD levels below 2% in every case simulated, a much lower value than the ones obtained with the classical approach. Experimental values are above 2%, but still below the maximum values of the DQ generator.