The aviation industry is increasingly interested in high-efficiency and high-density electric propulsion systems enabled by high-power Silicon Carbide (SiC) modules. However, designing a high-power SiC-based multi-level inverter for aircraft faces several challenges, including high loop inductance, bulky current sensors, high-bandwidth sampling of device current, partial discharge (PD) at high altitudes, and shorter short-circuit withstanding time of SiC MOSFETs. To address these challenges, this paper proposes an ultra-compact multi-functional gate driver that integrates the driving circuit, Rogowski coil current sensor (RCCS), and commutation path for a 211-kW SiC-based three-level (3-L) propulsion inverter. The optimized commutation path and RCCS provide multiple functions, including suppressing overshoot voltage, ultra-fast short-circuit protection, and ac load current sampling. The gate driver’s electric-field can be controlled by PCB-based shielding and shaping to eliminate the PD at high altitudes, thereby improving power density and reducing insulation risk. The paper presents the design methodology of the multi-functional ultra-compact gate-driver and the board-level to system-level common-mode (CM) noise modeling and suppression. The performance of the gate driver is verified on a 211-kW 3-L altitude-ready SiC propulsion inverter system, achieving a power density of 19.5 kW/kg and 7.1 kW/L.

Thermal management is important since it determines the reliability and robustness of power inverters. It becomes more critical for high-altitude motor drives due to the reduced air density. This paper provides a design process of thermal management for high-density high-power inverters. Thermal models for different scenarios are derived, and the hotspot temperature can be estimated under different cooling conditions. To demonstrate the proposed design process, a 200 kW three-level T-Type propulsion inverter designed for altitude of 7,620 m (25,000 ft) is used to present the thermal designs. Several thermal mitigation techniques are also introduced. In addition, it is discovered that the stagnating air space can create hotspots and have detrimental effect on the thermal performances. To address the thermal issue of stagnating air space, several solutions are proposed in which the forced cooling air duct solution is selected in this work. By optimizing both internal and external airflow, the hotspot temperature in the stagnating air space is reduced by 41 % using designed air duct. Furthermore, based on full-power experimental thermal tests, the hotspot temperature of inverter within sealed enclosure can be maintained lower than 130 °C at the ambient of 75 °C and altitude of 7,620 m. The final thermal design verifies the feasibility of the proposed design process.

In this paper, a 200-kW SiC-based high-speed motor drive system for electric aircraft propulsion is investigated. The focus is on maximizing power density while conforming to stringent aerospace electromagnetic interference (EMI) standards, fitting the special load characteristics of high-speed propeller, addressing the challenges posed by low air pressure conditions, and mitigating motor bearing current. To achieve this goal, a comprehensive set of weight models and design tools is developed, considering the impact of voltage, switching frequency, and topologies on system density. To mitigate EMI noise and bearing current issues, a three-level (3-L) T-Type inverter is employed, and a 200-kW (300 Arms ac torque current) prototype is designed. A seamless integration of short-circuit protection, gate driver, commutation loop and sensors is proposed while ensuring insulation integrity and optimal heat transfer capability, even in challenging conditions of altitudes up to 25,000 ft. Furthermore, the challenge posed by breakaway torque of propeller on low-speed operation is solved by introducing a novel loss-balance modulation for the 3-L T-Type inverter to reduce the weight and cost of power devices. The hardware achieves a thermally verified power density of 19.7 kW/kg, meeting DO-160 EMI emission and motor bearing current requirements, making it suitable for operation at 25,000 ft altitude.

This paper presents the full-scale high power inverter design considerations that are needed for minimum conducted noise propagation throughout the system. Specifically, system design issues pertaining to high current and high altitude, high switching transients during commutation process, ribbon cables for high-speed signal transmission, strict conducted emissions requirements and motor side bearing/leakage currents are discussed. Based on the underlying deficits for high power motor drives, layout and circuit design methodologies are proposed to tackle such problems, while keeping costs at a bare minimum. Subsequently, modeling and prediction of common-mode (CM) and differential-mode (DM) noise is made possible using accurate lumped inverter and filter models, allowing for a better understanding of the sensitive components contributing to peak CM-DM noise. A high power (211 kW) rated three level T-type inverter prototype is used to demonstrate the viability of the proposed design techniques for reliable system operation and conducted electromagnetic interference (EMI) emissions mitigation.

The advent of SiC devices which results in lower rise times and steep $\text{d}v/\text{d}t$ at the inverter terminal can compromise the common mode (CM)-conducted emissions’ compliance, motor peak ac -CM currents, and leakage currents. Consequently, this results in a high ac and dc side CM filter weight. AC filters at the inverter output terminal are effective in reducing the slew rate of inverter voltage thereby reducing the peak CM current. However, a special case with high $\text{d}v/\text{d}t$ arising from low duty cycles is found to increase the peak ac-CM current significantly. Reduced CM voltage (CMV) schemes are popular pulsewidth modulation (PWM) methods to minimize the peak CMV but suffer from high $\text{d}v/\text{d}t$ under this special case as well. In this article, a staggered PWM scheme to minimize such peak ac -CM currents for a high-speed variable frequency drive (VFD) is evaluated using a three-level SiC-based T-type inverter as a demonstrator. From the analysis, the proposed switching pattern shows benefits over conventional sinusoidal PWM (SPWM) scheme and is found to be scalable to other PWM schemes and voltage levels. Simulation and experimental results are shown to validate the performance of the proposed switching pattern.

The multilevel T-type inverter exhibits an inherent challenge of unbalanced power loss distribution among switches. This discrepancy in loss distribution is greatly influenced by the modulation index and the power factor, leading to increased system costs due to the overdesign of power devices and cooling systems based on worst-case scenarios. Furthermore, this loss imbalance will cause uneven device lifetimes, ultimately compromising the overall reliability of the converter system. To address the issue of loss imbalance, this article proposes a comprehensive and generic modulation scheme for the multilevel T-type inverter. The proposed scheme enables the balancing of switching and conduction losses for all switches in the inverter, regardless of the power factor and modulation index, as long as the modulation index is below a specific threshold. Importantly, the proposed scheme ensures that the losses of each individual device and the total converter loss are independent of the power factor and modulation index, which only requires knowledge of the on -resistance of the power mosfet . Additionally, the proposed modulation scheme effectively reduces the total loss of the inverter and naturally balances the neutral point potential. The proposed modulation scheme is validated in a 200 kW SiC-based three-level T-type inverter.