Comparison of PQ, PQR, and SRF Methods for Reference Current Extraction in Active Power Filtering Systems

This paper is aiming to compare three most used techniques in generating reference currents for active power filters: the traditional pq theory, its extension pqr, and the SRF (Synchronous Reference Frame) approach. In electrical grid it is mostly observed a voltage distortions and a harmonic distortions that can be reduced by those methods and determine its efficacity. The evaluation is implemented via MATLAB/Simulink simulations founded on a two-level inverter model, investigated under several representative operating conditions, extending from ideal balanced voltages to highly distorted and unbalanced cases. We evaluated each approach based on three principal indicators: total harmonic distortion (THD), the injected current waveform quality, and the active and reactive power exchange stability. We conclude from simulation that the SRF method achieved the best overall performance results by maintaining a stable operation and low harmonic content in all tested scenarios, that motivates to apply it in future medium-voltage systems using modular multilevel converters (MMCs).