Software-based digital hysteresis-band current controller

A hysteresis-band current controller for voltage-source invertors (VSI) is presented. The current trajectories of the three-phase system are transformed into the static alpha-beta frame, which enables the current-error components to be decoupled, facilitates the application of different shapes for the current-error boundaries and leads to a simple digital implementation. This new technique, which has been verified experimentally, is based on the use of a second input, the current-error derivative for the selection of the zero-voltage vectors. This greatly reduces the invertor switching frequency and avoids the use of a second hysteresis band, which limits the current-error excursion. The paper proposes a software implementation for the controller, as this simplifies the control calculations and takes advantage of digital techniques. Computer simulations and laboratory tests have been carried out to investigate the performance of the regulator, and the results have shown the effectiveness of the proposed control scheme.