Active Modulation Strategy for Capacitor Voltage Balancing of Three-Level Neutral-Point-Clamped Converters in High-Speed Drives

In this paper, the equivalent relationship between the nearest-three-virtual space vector (NTV2) and carrier-based pulse-width-modulation (CBPWM) scheme is established based on space vector coordinate for a three-level neutral-point-clamped (3L-NPC) converter. Moreover, to solve the neutral-point (NP) voltage imbalance problem of the studied 3L-NPC converter-fed high-speed drives, an active modulation strategy with the generalized bias-offset injection technique is proposed. Meanwhile, the excessive computational burden is significantly overcome by the fast calculation approach. The effectiveness of the proposed modulation algorithm is validated through both simulation and experimental results obtained from a 45 kW, 32 krpm aircraft electric starter/generator (ESG) prototype system.