Multi Level Hysteresis Direct Power Control Strategy for Three-Level NPC Rectifier

Using the conventional look-up table-direct power control (LUT-DPC) strategy with its two-level hysteresis comparators and conventional switching table, poor regulation of active power (abnormal fluctuations appeared in reactive power waveform), non-sinusoidal input currents with a little high THD and depressed power factor are obtained. This study therefore set out to solve these problems; the conventional switching table and the two level hysteresis comparators are replaced respectively by a new switching table and three level hysteresis comparators. In this way, the influence of each voltage vectors are determined through utilizing the instantaneous power theory. Finally, the effectiveness of the proposed DPC strategy is verified, sinusoidal input currents with low high total harmonic distortion (THD), smooth regulation of both powers (active and reactive power) are achieved, and the simplicity of the conventional DPC is kept.