Nonlinear Control and Model Predictive Control Applied to a Multi – Cell AFE Rectifier
Sr. Eduardo E. Espinosa N.
Alumno de Doctorado en Ingeniería Eléctrica, LCDA – DIE
The utilization of multi-cell converters, based on low voltage semiconductors, has allowed the implementation of AC drives and PV farms in medium and high voltage levels. The conventional converter uses in the grid side a multipulse transformer that performs the cancellation of low frequency current harmonics, which are generated by the three-phase diode-based rectifiers included in the power cells. This multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells (in order to achieve the harmonic cancellation), which does not permit to have a total modularity of the equipment. This work evaluates a harmonic
minimization strategy based on a Finite Control Set – Model Predictive Control (FCS - MPC), which emulates the harmonic cancellation of a multipulse transformer. The strategy allows the minimization of the Total Harmonic Distortion (THD) of the overall input current and lets the use of a standard transformer, thus incorporating the modularity at the transformer level. This feature permits the interconnection of an arbitrary number of power cells by just stacking power cells up to achieve the desired voltage and power levels. The DC voltage regulation in each power cell is done by the Active Front End (AFE) converter, which uses a nonlinear control scheme for ensuring the stable operation of the system. Simulated and experimental results show the correct performance of proposed scheme.