Three-phase three-level one-cycle controlled bidirectional ac-dc neutral-point-clamped converter without having voltage sensors

Abstract

A three-phase three-level bidirectional ac-dc neutral-point-clamped converter (3 L-NPC) based on one-cycle control (OCC) is proposed in this study. It ensures that the 3 L-NPC converter operates stably during inverting mode of operation. A neutral point potential regulator is also presented which adds a dc offset to the three-phase modulating signals to nullify the deviation in the neutral point potential. First, a one-cycle controlled (OCC) 3 L-NPC converter which requires the sensing of instantaneous phase voltages of the utility is presented. Subsequently, a modified version of the OCC-based 3 L-NPC converter which does not requires sensing of the instantaneous phase voltages is proposed. The modified OCC-based 3 L-NPC estimates instantaneous phase voltages of the source from the pulse width modulation (PWM) switching sequence of the converter. The viability of the schemes is confirmed through a detailed simulation and experimental studies.