Abstract
In this article, a virtual space vector based overmodulation algorithm is presented for three-level neutral-point (NP) clamped 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 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 k r/min ESG prototype system.
Highlights
T HE concept of more-electric-aircraft (MEA) is attracting more and more attentions in the aerospace industry due to higher fuel efficiency, better environmental impact, suppressed audible noise and lower maintenance cost [1]-[3]
Thu0.s02, the0.04Teimxe(ps)0e.06rime0.0n8 tal verifica0tions0.02main0.0l4Tyimef(so0).0c6 us on 0.08 the motor drives operating in the overmodulation region during the generation mode, in a light-load condition, whereas the results in the starter mode are not presented as it accounts for a short time compared with the whole operation time
Compared with existing NP control-based overmodulation strategies [25]-[31] for 3L-NPC converters, the proposed strategy embraces the following advantages: 1) As the configured switching patterns generate extra NP currents to realize net-zero NP current, the proposed capacitor voltage balancing control is effective for high modulation index and low power factor operating conditions
Summary
T HE concept of more-electric-aircraft (MEA) is attracting more and more attentions in the aerospace industry due to higher fuel efficiency, better environmental impact, suppressed audible noise and lower maintenance cost [1]-[3]. With respect to low power factor loads, the aforementioned methods pose a challenge for capacitor voltage balance, as well as elimination of low-frequency NP potential oscillation To address these deficiencies, a hybrid SVM strategy is introduced in [30] to operate a 3L-NPC inverter in the overmodulation region. The work reported in [32] discusses a novel overmodulation scheme that achieves the balanced capacitor voltages and alleviated low-frequency NP voltage fluctuation over the entire range of modulation indices and power factor angles, even for n-level NPC topologies. Compared with the prior method [32], the presented trajectory of the reference voltage vector contributes to a better overmodulation capability for converter-fed high-speed aerospace motor drives.
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