An Overmodulation Algorithm With Neutral-Point Voltage Balancing for Three-Level Converters in High-Speed Aerospace Drives
Feng Guo, Tao Yang, Ahmed M. Diab, Seang Shen Yeoh, Chen Li, Serhiy Bozhko, Patrick Wheeler
Abstract
In this paper, a virtual space vector (VSV)-based overmodulation algorithm is presented for three-level neutral-point-clamped (3L-NPC) converters in high-speed aerospace motor drives. With the proposed inscribed polygonal-boundary compression technique, the output voltage capability is enhanced under a lower crossover angle and compression coefficient. As a result, it brings an opportunity for the operation of the studied aircraft electric starter/generator (ESG) systems easily extending from the linear modulation range into the overmodulation region. Furthermore, an active capacitor voltage balancing control method is investigated to recover neutral-point (NP) potential imbalance in the case of high modulation index and low power factor operating conditions. To simplify the digital implementation of the algorithm, a fast calculation approach is adopted in this work. The modulation performance of the proposed strategy is verified by both simulation and experimental results with a 45 kW, 32 krpm ESG prototype system.