Balancing three-level neutral point clamped inverter DC bus using closed-loop space vector modulation: real-time implementation and investigation

In this study, a real-time controller implementing closed-loop space vector modulation (CLSVM) technique combined with DC bus voltage control is applied on a three-phase four-wire three-level neutral point clamped (NPC) inverter to be used in sustainable energy conversion systems with higher efficiency and lower switching frequency than conventional two-level inverters. The redundant switching states of CLSVM is dictated based on the voltage feedback obtained from DC link in order to constantly balance the DC bus capacitors voltages under various load conditions. The main feature of this technique is the use of only voltage sensors for balancing the DC capacitors voltages in four-wire system which makes the algorithm act fast, while permitting reduction of DC bus capacitors voltage ripple significantly and therefore smaller capacitors are used. The NPC inverter has been modelled and effects of redundant switching states have been analysed mathematically on DC capacitors voltages. Comprehensive experimental tests are conducted on a four-wire three-leg NPC operating as uninterruptible power supply application for sustainable energy conversion to validate the designed approach and the dynamic response under various load conditions including linear, non-linear, balanced, unbalanced and motor loads.