Time-varying harmonic distortions in AC drives

A major part of the adjustable speed drive system is the converters fed by switched-mode power supplies with a bridge pulse topology. This bridge produces in the supply network currents with harmonic components. Thus, it is mandatory to map the time-varying harmonic distortion index caused by the controllers. This paper analyzes through computational simulations the influence of a sensor-less field-oriented control system in the generation of harmonics in time. Through the sliding window recursive-discrete, Fourier Transforms currents were decomposed into harmonic time-varying harmonics signals. Total time-varying harmonic distortions were calculated according to the IEEE 1459 standard. The total harmonic distortion function was obtained applying a curve fitting technique. Total harmonic distortion varying in time of grid currents showed values of less than 3%. The harmonic distortion increases in stator currents due to the action of the torque controllers. Engineers and researchers can use this total time-varying harmonic distortions to improve adjustable speed drive control systems minimizing the injection of harmonics the electric power system.