Finite control set model predictive control with reduced switching frequency applied to multi-cell rectifiers

The utilization of multi-cell converters, through the use of low voltage semiconductors, has permitted to implement medium and high voltage applications as PV farms and AC drives. In conventional AC drives, this converter requires an input multipulse transformer, which allows the low frequency harmonic cancellation that are generated by the three-phase diode rectifiers included in each cell. This multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells, making the transformer topology dependent. This work proposes and evaluates a harmonic minimization strategy based on a Finite Control Set — Model Predictive Control (FCS — MPC), which emulates the harmonic cancellation of a multi-pulse transformer. This feature allows the minimization of the Total Harmonic Distortion (THD) of the AC grid current of the multi-cell converter. The evaluation is focused in one disadvantage of the FCS — MPC which is its high switching frequency that causes high losses in the semiconductors. To overcome this disadvantage, an additional objective function is proposed. Simulation results prove the theory, with satisfactory results.