Electric power architectures for hybrid-electric aircraft
Electric energy and power systems for future transport aircraft propulsion systems require an optimised electric power architecture (EPA) design with regard to efficiency and mass. A typical EPA for power trains consists of electric motors, power sources, like batteries, and power electronics, including converters or inverters, transmission cables, protection devices and cooling systems.
Increased system voltages may help to reduce overall system mass on transport aircraft level, but can cause arcing at typical cruise altitudes. Investigations indicate that high voltages are also preferable from a transmission efficiency point of view. Especially power electronics show the highest sensitivity in choosing the system voltage with regard to conduction and switching losses, leading to an optimisation between these losses at a required design power. An additional degree of freedom also offers the architectural layout. Two architecture design philosophies, the constant system voltage (CSVA) and the variable system voltage (VSVA) architecture, have been studied. The CSVA maintains a constant system voltage over the entire operation, while the VSVA allows for variations in the voltage level caused, for example, by a battery. For both architectures an optimum system voltage was identified near the operating voltage of the electric motor, which was, in this scenario, in the low kilovolt range.
At this voltage level and with state-of-the-art technologies, overall system efficiencies of 90 % to 95 % can be achieved. From this study, it can be concluded that, from an efficiency point of view, it is not necessary to increase the voltage to higher levels.
- Architecture options: Two different design strategies connecting the components have been investigated. The constant system voltage and the variable system voltage architecture.
- Voltage impact: Loss contribution of the single components installed in the constant system voltage architecture at different design voltages