Smart Control Strategy
Another challenge will be a correct and timely estimation of the SoC level since the voltage level of the HE and HP cell might be different during fast charge or discharge. Thus, new SoC and state of health (SoH) estimation algorithms must be developed and implemented. The SoH calculation should be done on cell level in order to detect defects in a very early stage. Once the faults have been detected the balancing circuit will help to optimise current/power flow in the battery and thus increase the lifetime and reliability of the whole system.
The energy and charge distribution will be controlled by the smart control algorithm for the DC-DC converter. The decision for the energy distribution will be based on accurate estimations of the battery state. Thus, precise SoC estimations by the battery management system (BMS) are required as an accurate and reliable indication for the vehicle control system. The SoC is not directly measurable on board, since it is related to the concentration of ions inside the battery cells. The coulomb-counting procedure is not reliable for a precise SoC determination in traction batteries, since not all the supplied current goes to the charging of the cell. However SoC estimations mostly rely on a book keeping method derived from Coulomb counting. In the SuperLIB project, HE and HP cell models will be used to design an Extended Kalman Filter or Unscented Kalman Filter and provide a more accurate indication of the battery SoC. In addition algorithms will be developed, which control the charge-equalization circuit.
These control algorithms are designed using a modelling and control tool (e.g. Matlab-Simulink™) and validated by co-simulation on different European driving cycles at 20°C. In a second step, the algorithms to be used in BMS algorithms will be tested in a HIL environment under dynamic current solicitation to assess its performances under representative conditions.
The SuperLIB project focuses on smart control system solutions for traction batteries. The general concept consists of a combination of measures for
- a dual-cell battery concept comprising high-power and high-energy cells,
- including an electronic architecture for an efficient energy and current distribution,
- managed by a smart control strategy, and
- monitored by cell integrated temperature sensors