1. Field of the Invention
This invention relates generally to a system and method for charging a battery and, more particularly, to a system and method for charging a vehicle battery that employs both a voltage control mode and a current control mode.
2. Discussion of the Related Art
Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV) that combine a battery and a main power source, such as an internal combustion engine, fuel cell system, etc., and electric only vehicles, such as the battery electric vehicles (BEV). All of these types of electric vehicles employ a high voltage battery that includes a number of battery cells. These batteries can be different battery types, such as lithium-ion, nickel metal hydride, lead acid, etc. A typical high voltage battery for an electric vehicle may include 196 battery cells providing about 400 volts. The battery can include individual battery modules where each battery module may include a certain number of battery cells, such as twelve cells. The individual battery cells may be electrically coupled in series, or a series of cells may be electrically coupled in parallel, where a number of cells in the module are connected in series and each module is electrically coupled to the other modules in parallel. Different vehicle designs include different battery designs that employ various trade-offs and advantages for a particular application.
There is a need in the art to reliably charge batteries, particularly vehicle batteries, to accurately and reliably provide a full battery charge without damaging the battery. Currently, battery charging algorithms may attempt to charge the battery to a particular battery voltage within a certain period of time. Once the battery is charged to that voltage level, then the charging algorithm may go into a sustaining charging mode, where a trickle current is provided to maintain the battery at the charge voltage. The algorithms that control the battery charger would need to control the amount of current being provided to the battery to control heat, over-charging, etc., so that the battery and other components would not be damaged. These different types of chargers have different goals where they may be over-night chargers or fast chargers depending on the charging situation. The battery charger may be on the vehicle or may be separate from the vehicle where an electrical cord from the battery charger is plugged into the vehicle or the vehicle is plugged directly into an AC wall outlet.