Controlled Loss Redistribution, Thermal Equalization, and Capacitor Voltage Regulation Across the Full Operating Range of Neutral-Point-Clamped Converters

Neutral Point Clamped (NPC) converters are widely adopted in high-power wind energy conversion systems due to their ability to handle high voltages with reduced device stress. However, one of the main challenges of NPC topology is the unequal distribution of switching losses, which leads to thermal imbalances and reliability concerns. This paper proposes a modulation scheme for NPC converter in wind power applications, aiming to achieve active thermal control, loss balancing, and capacitor voltage regulation. The key idea is to reconstruct the middle voltage level of each phase through a linear combination of the three available levels, ensuring volt-second balance while reducing neutral-point current. This approach not only equalizes the switching losses among devices but also decreases the RMS current stress on DC-link capacitors, enabling the use of smaller and more cost-effective capacitors. Unlike conventional methods, the proposed scheme maintains its effectiveness across the entire range of modulation indexes, including those typical of low-voltage ride-through (LVRT) conditions in wind turbines. Importantly, all semiconductor devices operate at the same switching frequency, without a significant increase, ensuring equalized loss distribution. Experimental results validate that the applicability of the proposed method over the entire range of modulation indexes.