1. Field of the Invention
The present invention is a method and apparatus for implementing smart management of a rechargeable battery. The invention uses the operation data of the rechargeable battery including the voltage, temperature and current flow to manage charging and discharging of the battery in an intelligent manner. The method is a dynamic technique for the management of the rechargeable battery that is able to make appropriate adjustments in response to any change in parameter values of the battery.
2. Description of Related Art
Use of high performance and long life batteries, low power consumption and product miniaturization are on-going objectives in the design of portable electronic devices such as notebook computers, personal digital assistants (PDA) and mobile phones. To further enhance the portability of an electronic product, the first thing a product designer must do is to find a long-life rechargeable battery that is capable of supporting the operation of the product for ten hours or more. However, the miniaturization of electronic products has severely constrained the storage capacity for a battery without sufficient space to accommodate additional rechargeable cells. In addition, designers are trying to package more functions in existing products to make them super versatile. Such devices with increased complexity after incorporating all the additional functions definitely need larger load current than their conventional counterparts. Developing a smart battery management system for rechargeable batteries to cut down unnecessary power loss has become imperative.
Portable electronic products such as notebook computers usually have a built-in battery control circuit to optimize and adjust the current flow during the charging and discharging of the battery. In the conventional method, the control circuit in portable devices works in conjunction with a signal I/O interface to retrieve the parametric values from the battery. These periodically collected data relating to the battery operation are shown to the user of a portable device to make him or her aware of the current operational status of the battery.
The control circuit in conventional battery management is set up with predetermined values for the battery operation parameters. These parameters may be the lower or upper reference voltage, or lower or upper reference temperature. The control circuit then uses the data to control the charge and discharge of the battery. However, a rechargeable battery is usually made of chemical compounds such as a lithium-polymer or nickel-metal. During the operation of a battery, electrochemical reaction takes place simultaneously inside the battery. In the electrochemical process, the basic elements often exhibit non-linear characteristics. Simply by presetting the values of the external control factors such as operating temperature, flow of current during charge or discharge, and the time the battery being used is not adequate to control the operation characteristics of the battery with the design specs.
Specifically, changing in temperature affects the internal ohmic resistance of an electrode in the battery. Higher temperature could cause an increase of internal ohmic resistance, and vice versa, leading to unpredictable variation of the terminal voltage of the battery. Furthermore, longer battery use time could cause an increase in internal ohmic resistance, resulting in improper estimates of the upper and lower voltage limits.
In conventional methods, constant current flow is often used in the process of charging or discharging a battery. According to the charge/discharge characteristic curve of a battery, using a small current to charge a battery is more efficient than a high constant current. Also, using a large current to charge/discharge a battery could produce early saturation or depletion. This phenomenon can be explained by an increasing amount of electric energy being transformed to thermal energy as the battery approaches saturation. It is not economical to charge a battery with a constant current, since this electric energy cannot be efficiently saved in the storage battery. Besides, low ambient temperature or long idling of the battery could cause the electrolyte in the battery to coagulate or produce sedimentation. Under such conditions, charging with excessive current flow could easily damage the battery.
In the conventional method, if the battery is close to depletion in a discharge mode, only a message is issued by the control system to warn users of impending depletion, but the discharging process continues without interruption. As a result, the battery could be over discharged and create irreversible damage, such that the battery cannot be used anymore.
The main objective of the present invention is to provide a method and apparatus for implementing a smart battery management system on a rechargeable battery. The charging of a battery is carried out in two stages with the assistance of an optimizing charge controller. In the first stage, charging a battery is conducted in the normal mode with a constant flow of current. As the charging of the battery approaches saturation, the charge controller is switched to pulsation-charge mode to charge the battery intermittently. With the smart control, the charging efficiency of a rechargeable battery is improved notably.
The second objective of the present invention is to provide a trickle charger. If the ambient temperature of the battery is below a predetermined lower temperature limit or the terminal voltage is below a predetermined voltage lower limit, the trickle charger is enabled to slowly charge with a small current. The trickle charger serves to activate the electrolyte in the battery in preparation for a normal charge. These control methods can prevent possible harmful charging of the battery with excessive current.
The third objective of the present invention is to provide a discharge controller to protect the battery against over discharge. If the central processing unit detects that the voltage of the battery is below a predetermined lower voltage limit, representing excessive discharge from a battery, it automatically turns off the discharge controller to stop the discharging of the battery and cuts off all load supply current from the battery control circuit, entering a self-cutoff mode.
The fourth objective of the present invention is to provide a cutoff switch. If the central processing unit detects that the battery is not active, it cuts off the load current to the temperature detector to reduce power loss from the battery.
The apparatus necessary for implementing smart management of the rechargeable battery includes a central processing unit, a charge controller, trickle charger, a discharge controller, a cutoff switch and an economizer switch.
The central processing unit is respectively connected to a current flow detector for sensing charge/discharge current flow, a temperature detector for sensing the surface temperature of the battery, and a voltage detector for sensing the terminal voltage across the battery. These parametric values relating to the operational status of the battery collected by the above detectors are saved in an EEPROM.
The optimizing charge controller is connected across the central processing unit and the rechargeable battery. If the battery operates within the normal range of terminal voltage and temperature, the central processing unit activates the charge controller to carry out normal-charge of a battery with a constant current.
The trickle charger is connected across the central processing unit and rechargeable battery. In the charge mode, it can provide slow charge of the battery with a small current to activate the electrolyte in the battery before the normal charging process is initiated.
The discharge controller is connected across the central processing unit and the rechargeable battery. If the terminal voltage of the battery is below a predetermined lower voltage limit during discharging, the central processing unit hereupon issues a control signal to turn off the discharge controller stopping the discharging and turns off the voltage regulator entering a self-cutoff mode.
The cutoff switch is connected to the temperature detector and central processing unit. If the central processing unit detects that the battery is idling, the processor turns off the temperature detector to reduce power loss.
The economizer switch is connected to the rechargeable battery and the central processing unit through the voltage regulator. If the battery is connected to an external power source for recharging, the economizer switch activates the voltage regulator which in turn supplies normal operating voltage to force the system to return to normal operation from the previous self-cutoff mode.
The features and related techniques of the present invention will become more apparent from the description of the preferred embodiment when taken with the FIGS. of the invention.