An Advanced Dual-Carrier-Based Multi-Optimized PWM Strategy of Three-Level Neutral-Point-Clamped Converters for More-Electric-Aircraft Applications

Since three-level neutral-point-clamped (3L-NPC) power generation units bring much competitiveness to the next-generation electric starter/generator (ESG) system for more-electric-aircraft (MEA) applications, the versatile multi-optimized pulse-width-modulation (PWM) becomes a key enabler to this technology. Regarding the mission profile of the state-of-art ESG, the operating points at the cruise feature a high modulation index and low power factor. This means that the neutral-point potential (NPP) fluctuation becomes severe. Besides, if switching states are not configured properly, not only could the lifetime of capacitors be threatened but also irreversible damage to bearing insulation occurs due to the common-mode voltage (CMV), followed by devastating effects on the reliability of other avionic facilities. Given the limitations of the 270VDC unipolar dc-bus structure, deep flux-weakening currents are constantly required for the high speed, resulting in more machine copper losses. To address these issues without any hardware-level efforts, an advanced PWM strategy with dual-carrier-based implementation is proposed in this article, which achieves boosted dc-link voltage utilization, CMV reduction and balanced NPP at the same time. Simulation results obtained from Simulink/PLECS and experimental results obtained from a 45 kW, 32 krpm ESG prototype system verify the effectiveness and feasibility of the proposed algorithm.