The SAVER project addressed the task of power conversion with battery charging.
To overcome the low power quality of passive converters, the SAVER concept consisted of two parts, an AC/DC converter and a Li-ion battery, and allowed key advantages such as smaller passive components, lower weight, higher efficiency and higher power density.
The converter moves from passive to high-frequency active switching with forced cooling. It also implemented zero current zero voltage switching instead of hard switching methods. Moving from passive to active switching also brings with it the ability to integrate other types of control within the embedded processing power, required for the control loop execution. This brought with it the opportunity of embedding battery constraints, such as battery charging and monitoring.
The other important development within SAVER was the Li-ion battery. Improving the power delivery capability of batteries is very important for the development of more electrical aircraft, and only Li-ion can deliver all of the requirements - but not without stringent safety measures. SAVER not only allowed the characterisation of Li-ion batteries for aerospace use, but also advised on all aspects regarding Li-ion usage such as safety, optimization, monitoring, battery management systems, simulation as well as testing (cycling, temperature and impedance analysis).
In addition to the hardware design and prototyping, the work included a detailed technology study, covering topics such as power converters, battery chargers and applicable aerospace standards. These results were used to deliver an architecture down-selection and help define specifications.
SAVER aided European aircraft manufacturers in testing and validating advanced power electronic converters and Li-ion technology for aerospace use; advancing more electrical aircraft and putting them at the forefront of industry.
SAVER "Smart Battery with Active Power Conversion" was developed as part of the Clean Sky 2 partnership between the European Commission and the European Aeronautical Industry, a partnership which is set up to bring significant innovations regarding the environmental impact of aviation by improving aircraft reliability and efficiency by contributing to the continuous development of More Electrical Aircraft (MEA).
SAVER delivered the 28Vdc active power conversion/energy storage architecture which is to be tested for MEAs. The multi-disciplinary nature of the project brought together three consortium partners, each with their own specialisation; UPJV (management, power electronics and battery simulation), SGTE (power electronics) and E4V (battery systems).
The main objective of SAVER was the delivery of a 28Vdc li-ion battery with its battery management system, together with its accompanying DC/DC converter for safe, accurate charging. This is to be used as a platform for developing li-ion technology for aerospace use.
The delivered battery is based on the LiFePO4 chemistry which trades power density for stability, ensuring safe operation - a critical aspect in aerospace use. Configured in 8s2p, the battery delivers 100Ah at 28Vnom.
The DC/DC buck converter powers the LVDC bus from the HVDC whilst also handling the battery charging. It makes use of soft-switching techniques in order to obtain high efficiency whilst keeping EMI at low levels.
Modelling and simulation activities produced high fidelity models of the both the battery and the converter. The battery model employs Kalman filters for state of charge (SOC) and temperature estimation, whilst the converter model aids in the development of control strategies.
SAVER test bench including the converters and the Li-Ion battery as well as the control system was tested and validated in April 2016 with the participation of all partners and the TM. It is ready to play its vital role in advancing li-ion battery architecture for use in aerospace applications.