Demand for electric vehicles with hybrid drive has soared worldwide due mainly to a recent sharp increase in fuel prices. Conventional battery management systems for electric vehicles (EVs), however, are designed in an ad hoc way, causing the supply of electric vehicles to fall behind the market demand.
Cost-effective electric vehicles require not only development of high energy density battery cells, but also efficient management of large-scale battery packs, each consisting of a large number of battery cells. In particular, a battery management system (BMS) that monitors and controls battery cells in a pack, must cope with heterogeneous batterycell characteristics. That is, even if characteristics of all battery cells in a battery pack are initially identical, as they are charged and discharged repeatedly, each cell will exhibit different characteristics. A weak cell—hat is (charged and/or) discharged faster than others—is likely to be (over-charged and/or) deep-discharged, i.e., the battery cell continues to be discharged even when its terminal voltage falls below a certain threshold called a cutoff voltage. This weak battery cell can eventually become faulty, and will, if not managed properly, cause the whole pack to be dysfunctional.
A battery management system should be able to cope with weak/faulty cells in such a way that faulty cells are bypassed to keep the pack operational. Bypassing certain cells inside a pack, however, requires switches by which the connection arrangement of battery cells can be changed. Switches are placed around battery cells, regulating the battery supply power. Furthermore, a reconfigurable battery system may offer a way to alter battery connectivity and dynamically adjust supply power to meet application demands. All of these systems require careful system specification, cost-effective incorporation and control of system components, such as switches and battery cells.
There are two main challenges in developing a battery management architecture. First, there is a tradeoff between the minimum number of hardware components to use and maximum reconfigurability in a BMS. Key components therein are switches that allow a battery-cell array to be reconfigurable. The more switches around cells, the more reconfigurable the array becomes, but the costlier. Also, individual components affect directly system reliability. System reliability should be assessed based on the reliability of components and their connections. At the same time, since the cost is the major consideration in realizing a reconfigurable architecture, the components count should be minimized. Second, to maximize both system reconfigurability and reliability, a reconfigurable architecture should be specified with respect to software/hardware components and their inter-relationship. An application (software) may require various battery (hardware) conditions from a BMS. Also, a BMS may request subsystem/local BMSs, if any, for the information on the status of individual battery cells in the case of modular management architecture. Upon receipt of this request, individual local BMSs periodically monitor their battery-cell arrays and reconfigure them, if necessary, in accordance with individual cell characteristics. This interaction between local BMSs also depends upon the underlying hardware system design. A well-designed, combined hardware-software battery management architecture will provide high reliability, cost-effectiveness, and scalability.
This section provides background information related to the present disclosure which is not necessarily prior art.