After being part of and contributing to the Epowerdrive project at the IRT Saint Exupéry, Hans Hoffmann Sathler defended his thesis on December 9, 2021, at the B612 in Toulouse. His work was supervised by the EOBE (Electrical, Optical, Bio-Physics, and Engineering) Doctoral School, the Paris-Saclay University, the SATIE Laboratory and the IRT Saint Exupéry.
ABOUT HIS THESIS
“Optimization of GaN-based Series-Parallel Multilevel Three-Phase Inverter for Aircraft applications”
The electrification of means of transport is a challenging reality that has taken over the scene over the years. The socio-environmental impact of burning fossil fuels and their future scarcity guided sustainable and versatile efforts of energy consumption development. The aerospace domain has set ambitious goals regarding gas emissions limitation, leading to new concepts and system architectures in several sectors. The replacement of heavy systems, such as mechanical, pneumatic, and hydraulic systems, reduces aircraft weight and fuel consumption with their electrical equivalents. Several projects have emerged in the last decades, aiming to replace these systems using new technologies.
This thesis presents an optimized design of a DC – AC converter (filters included) with gravimetric power density superior to 8 kW/kg and higher efficiency than 98.5 % for a 70 kVA MEA power drive system. Among different inverter topologies and semiconductors technologies, a 7-level flying capacitor three-phase inverter, composed of three paralleled legs of 3-level flying capacitor topology per phase with 4 GaNs in parallel per switch, was chosen to be built.
The prototype presented around 14 liters and 10.04 kg (it comprises filters, metallic structure, and control board). The measured weight is less than 4% superior considering the solution proposed in simulation, which corroborates the precision of the models used in the optimization procedure. A traditional 2-level converter using 1200 V for the same operating conditions shall be 74 % heavier than the 7-level inverter, with a power density 43.4% smaller than the multilevel topology. On three-level flying capacitor leg with 4 GaNs in parallel per switch was extensively explored, and the solution reached almost 99.2 % of measured efficiency, for 38 A/5.8 kW at the output of the converter (DC-DC Buck test) and 98.8 % in the monophase inverter test (42 A / 6.6 kW at the output of the converter), both 40 kHz with an RL load (resistor+inductor).
The experimental verification of the entire converter led to 98.6 % efficiency at 24.6 kVA (flf= 240 Hz, fsw= 40 kHz and Mi= 0.76). Due to circulating currents between paralleled legs, inverter safe operation was limited to 500 V/38 kVA/87 A (70 kVA/130 A nominal operation) with open-loop control. Regarding EMI modeling, this thesis proposed a generic model for multilevel converter equivalent circuit with good correspondence until 5 to 6 MHz (supported by experimental results) and can assist the predictive design of EMI filter.
- A. Piat, H. H. Sathler, F. Gallard and B. Cougo, “A Multidisciplinary Design Optimization Approach for EMC Filters Design For More Electric Aircraft Applications,” 2021 23rd European Conference on Power Electronics and Applications (EPE’21 ECCE Europe), 2021, pp. P.1-P.10.
- O. Mendes, H. H. Sathler, B. Cougo, M. M. Stopa, F. Costa and D. Labrousse, “Impact of PWM Techniques in Efficiency and Power Density of a 70kVA Multilevel Inverter for More Electric Aircrafts,” 2021 23rd European Conference on Power Electronics and Applications (EPE’21 ECCE Europe), 2021, pp. P.1-P.10.
- H. H. Sathler et al., “Design of three-level flying-capacitor commutation cells with four paralleled 650 V/60 A GaN HEMTs,” 2021 IEEE Applied Power Electronics Conference and Exposition (APEC), 2021, pp. 2277-2284, doi: 10.1109/APEC42165.2021.9487160.
- H. H. Sathler, B. Cougo, J. -P. Carayon, F. Costa and D. Labrousse, “Modeling of Common-Mode Voltage Source for Multilevel Inverter Topologies,” 2020 International Symposium on Electromagnetic Compatibility – EMC EUROPE, 2020, pp. 1-3, doi: 10.1109/EMCEUROPE48519.2020.9245681.
- B. Cougo, H. H. Sathler, R. Riva, V. D. Santos, N. Roux and B. Sareni, “Characterization of Low-Inductance SiC Module With Integrated Capacitors for Aircraft Applications Requiring Low Losses and Low EMI Issues,” in IEEE Transactions on Power Electronics, vol. 36, no. 7, pp. 8230-8242, July 2021, doi: 10.1109/TPEL.2020.3014529.
- H. H. Sathler, L. Nagano, B. Cougo, F. Costa and D. Labrousse, “Impact of multilevel converters on EMC filter weight of a 70 kVA power drive system for More Electrical Aircraft,” CIPS 2020; 11th International Conference on Integrated Power Electronics Systems, 2020, pp. 1-8.
THESIS DIRECTORS AND SUPERVISORS
|François COSTA||Thesis Director||ENS Paris Saclay University/SATIE|
|Bernardo COGO||Co-Supervisor||IRT Saint Exupéry|