Disturbance Rejection Enhancement for Three-Phase Converters by Active Inductance

The current control has an important impact on the performance of three-phase voltage source converters. A common approach is to adopt a two-degree-of-freedom scheme by which the reference-tracking and disturbance-rejection response are independently adjusted. On the one hand, a conventional current controller, such as a proportional-integral or resonant controller, is tuned to optimize the reference-tracking dynamics. On the other hand, an active resistance is selected to improve the disturbance rejection without altering the reference tracking. There are methods to further enhance the disturbance rejection by, e.g., adding extra selective controllers, but this increases complexity and requires the knowledge of the frequencies to be compensated. Therefore, it is still desirable to ameliorate the disturbance rejection to a greater extent, in a simple manner and without a priori information about the disturbance frequencies. This paper proposes to improve the disturbance rejection by means of an active inductance, without affecting the optimum reference tracking. Concerning the transient response, the overshoot (and hence, the integrated error) is significantly reduced. Furthermore, the steady-state attenuation of harmonics becomes larger in the lower part of the spectrum, where the harmonic disturbances usually arise. Simulation results supporting the functionality of the proposal are provided.