Generalized Direct Power Control for multilevel VSR converters

A fast and effective control of three-phase PWM-Rectifiers is presented in the paper, with reference to multilevel converter topologies. The presented strategy con be considered a “Direct Power Control” (DPC) because it is devoted to the direct control of active and reactive line-power, using a technique very similar to the well-known “Direct torque control” (DTC) of AC drives. An interesting aspect is the extension of the control technique to a generic m-level Voltage Source Rectifier (VSR). The converter architecture (diode-clamped, cascaded H-bridge, ...) has no influence on the proposed method. The selection of the most suitable converter voltage space-vector to follow the actual power reference values is made in each sampling interval using double-band hysteresis controllers. The outputs of these controllers allow us to quickly identify the most suitable voltage among properly ordered lists of the converter vectors, which can be dynamically built-on. The procedure is validated by means of numerical investigations in some relevant cases-study, with specific reference to the very reduced values of current distortion and asymmetry that can be obtained for fixed average value of the switching frequency.