Sensorless Dc-Link Auto Voltage Balancing for Five-Level NPC Inverter with Boosting Capability

Due to their simplicity and capacity to produce higher quality voltage with lower device ratings, Neutral-Point Clamped (NPC) multilevel inverters (MLIs) are widely employed in medium and high-power applications. However, dc-link capacitor voltage imbalance is the major issue with these inverters that adversely affects their performance and reliability. This paper proposes a very effective capacitor voltage balancing circuit suitable for five-level NPC MLI with four dc-link capacitors. By using proper switching states, the dc-link capacitor voltages are balanced automatically during charging and discharging cycles. As a result, no extra sensors or control circuitry is needed. A fundamental frequency-based Half-height (HH) method is utilized to produce the switching signals in order to improve voltage quality. It also features built-in double (200%) boosting capabilities without the use of a boost converter. The efficacy of the proposed voltage balancing circuit is verified through extensive simulation using Matlab/Simulink. Excellent dynamic performance is also observed under various loading scenarios. To assess the validity of the suggested topology and the correctness of the simulation findings, a small-scale 5-level single-phase laboratory prototype is developed.