Gestion de batteries par cellules commutées

International audienceAs opposed to the first battery technologies (Pb, Ni-Mh…), whose protection and management required simple electronic circuits, today's Li-ion batteries need to be precisely supervised during all their working cycles to limit their charges and discharges, to ensure their security and improve their lifetime. Battery management is currently performed by monitoring battery cell voltages: charging is interrupted when the voltage of the first cell of the serial arrangement exceeds a threshold value (charging then goes forward with a lower current for the remaining cells). Battery discharge is managed similarly and is interrupted when the voltage of first battery cell falls below a threshold value. The remaining energy in the other cells of the serial arrangement is not used. Hence, the energy stored into the battery is not fully exploited, which limits the autonomy of the supplied system. Non-dissipative solutions to exchange energy between cells so as to maintain the cells balanced have been reported; yet, they require a large number of DC/DC converters with associated size, weight and price drawbacks. To overcome these limitations and to remove the battery charger and output converter (DC/DC or DC/AC converter to supply the load), we propose a full converter based on battery cell switching, to adjust the battery pack output voltage to the effective need in real time and maintain the battery cells balanced. The architecture we developed consists in connecting or disconnecting in real time each cell placed in the serial arrangement. In the case of an electrical vehicle with 30kWh on board, by using battery cells of 3.3V, the output voltage can be adjusted by steps of 3.3V from-60V to +60V. We show that it is possible to directly drive a three-phase electric motor with an efficiency up to 98% from few Hz to 400Hz, while maintaining the cells balanced. Moreover, this is achieved with a transistor cost lower than 300€ (consumer prices, expectedly 10 times lower for large quantities). For the transistor driving part, a distributed electronic is placed in front of each cell of the serial arrangement. Each distributed electronic circuit is able to drive up to 14 transistors, to carry out local measurements (temperature, current, voltage) and to calculate the estimated State of Charge of the local cell. Distributed electronic circuits communicate with an electronic advisor by using galvanically isolated a common serial communication bus. SWITCHED BATTERY STRUCTURE Standard battery architectures for electric vehicles are based on a battery arrangement of s battery levels connected in series, and battery levels are composed of p cells connected in parallel. This battery pack is connected on one side to a charger (to recharge the battery on the electrical network) and on the other side to the electric motor by an inverter (DC/DC or DC/AC electrical converter depending on the type of the motor to supply)