Project Duration: May 2011 – October 2014

The project ESTRELIA provides building elements contributing to enhanced reliability and safety at lowered costs for smart energy storage for FEVs.

Objectives

• New BMS ICs for cell monitoring and autonomous cell balancing for ultra capacitors and Li-Ion cells with the goal to reduce electric component costs by 1/3^rd
• New gas sensors and spark detection sensors to improve safety monitoring of energy storage systems
• Ultra capacitor cell with 40% higher energy density
• HV testing capabilities to verify safe galvanic isolation up to 2.5kV
• Cost effective power antifuse for dynamical configuration of energy storage units

The first samples of the Battery Management System BMS IC are available and have been used to build-up the demonstrators of a Li-Ion cell based Energy pack and an Ultra-capacitor based Power pack.

These ICs provide for the first time full monitoring functions together with a flexible passive or active cell balancing in one single integrated circuit perfectly suited for the high accuracy demanding monitoring of Li-Ion batteries and ultra capacitors.

 Cell balancing and monitoring of 7 cells with one BMS IC

The BMS IC provides the following key features:

• Simultaneous cell voltage capture for balancing and safe operating area (SOA) monitoring.
• Autonomous balancing and SOA monitoring strongly reduces data communication and data processing, and thereby improves EMC robustness.
• All shuttle switches integrated to enable 100 mA of active or passive balancing current.
• Active balancing with true energy re-distribution, if energy is taken from entire pack;
• Absolute cell voltage read out through EMC robust 3 wire daisy chain communication. Chained direct action pins for fast SOA diagnosis.

Test boards for autonomous cell balancing with stackable daisy chain function 

A new ultracapacitor power pack has been developed. High-energy density ultracapacitor samples have been assembled integrating the BMS ICs. These ultracapacitor samples demonstrate an average capacitance greater than 2800F. This compares to commercial cells in the same form factor of 2000F hence confirming the > 40% improvement in energy density. Initial cell level testing has demonstrated good reliability performance for both steady state (maximum temperature and voltage) and current cycling operation across the full temperature range.

High energy density ultracapacitor cell samples

Measured cell characteristic providing >40% higher energy density

Safety sensors for EVs

ESTRELIA has shown successful progress with development of new spark detection sensors based on silicon MEMS approaches. In order to perform spark detection a new architecture of ultra-sonic acoustic sensors using Silicon piezo-resistive nanogauges as detection principle has been implemented as it exhibits high sensitivity with low voltage and high adaptability.

The new spark detector concept will enable general safety functions by spark detection from hazardous events in and around a FEV battery.

The gas sensor has been integrated into the battery pack demonstrator and monitors changes of combustible gases in battery cycling experiments. In all experiments the sensor has shown a stable baseline and high sensitivity for alarm threshold levels.

Temperature variations result in gas sensor signal fluctuation from outgassing of polymers. High gas sensor signals have been measured from outgassing of a pouch cell in an overcharging experiment when the cell did not blow the safety relief valve.

Newly developed high voltage testers enable the verification of the reliability of galvanic isolation technology and have successfully been used to evaluate the isolation function of BMS communication ICs. Thereby test isolation protections in the environment of several hundred volts as present in FEVs have been proofed.

Finally, the completely new concept for the development of low cost power antifuses together with the new energy management hardware (BMS IC) and software enables dynamic reconfigurable topologies in the energy storage unit, thus providing limp-home functionality to the FEV despite single cell failures. Experimental results show that this is a first step to provide a cost effective solution to bypass single cell failure for the future.

All these components are evaluated on energy storage prototypes based on Li-Ion cells and ultra capacitors. For the final evaluation also cooperation synergies with project SuperLIB are utilized.

Although the technical approach for Estrelia and SuperLIB is different, many synergies have been achieved. Both teams exchanged and reflected regularly state-of the art and technical solutions in battery technology, the same HW for cell monitoring was used in both projects and same reference cycles are now used to assess the different system and identify the advantages of each solution.

For more information please refer to the ESTRELIA webpage http://www.estrelia.eu