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

An Enhanced Virtual Space Vector Modulation Scheme of Three-Level NPC Converters for More-Electric-Aircraft Applications

Multilevel converters have been used for aircraft electric starter/generator (ESG) systems due to their high power qualities. One of the desirable topologies is the three-level neutral-point-clamped (3L-NPC) converter. Our studied ESG system operates at a high speed during its generation mode, which results in high modulation index (MI) and puts some specific challenges on neutral-point (NP) voltage balance, especially under low power factor (PF) load conditions. Moreover, common-mode voltage (CMV) needs to be addressed properly as it leads to irreversible damage of motor shaft bearings, thereby degrading the efficiency and reliability of the entire system. Compared with the conventional nearest-three virtual space vector (NTV2) technique, the proposed modulation scheme employs three adjacent medium vectors to synthesize a new medium vector and two pairs of large vectors to compose new small vectors. This allows the presented modulation scheme to achieve balanced capacitor voltage and reduced CMV at the same time. In addition, the torque ripple of the proposed modulation strategy is thoroughly compared and analyzed. Meanwhile, in order to overcome the heavy computational burden, a fast calculation approach is adopted to simplify the algorithm. Simulation results obtained from Simulink/PLECS and experimental results obtained from a 45 kW, 32 krpm aircraft ESG system verify the effectiveness of the proposed strategy in more-electric-aircraft (MEA) applications