Battery management system and method
A battery management system is disclosed for control of individual cells in a battery string. The battery management system includes a charger, a voltmeter, a selection circuit and a microprocessor. Under control of the microprocessor, the selection circuit connects each cell of the battery string to the charger and voltmeter. Information relating to battery performance is recorded and analyzed. The analysis depends upon the conditions under which the battery is operating. By monitoring the battery performance under different conditions, problems with individual cells can be determined and corrected.
1. A battery management system for monitoring and recording a plurality of conditions in a battery having a string of units electrically connected in series, each of the units having positive and negative terminals, the system comprising:
a voltage detector circuit for measuring the voltage across the terminals of a unit of the battery;
a charge circuit for selectively supplying charge to the terminals of an individual unit of the battery;
a selector for selectively coupling the terminals of unit to one of the voltage detector circuit and the charge circuit; and
a microprocessor for controlling the selector to couple the terminals of each of the units to one of the voltage detector and the charge circuit and for recording the state of the selector and an output of the voltage detector,
wherein the microprocessor includes means for detecting a discharge knee characteristic of the battery and wherein the means for detecting the discharge knee characteristic includes:
means for periodically sampling a voltage of each unit in the battery;
means for summing together the sampled voltages over a selected time interval;
means for storing a sum of sampled voltages for a selected time interval; and
means for comparing a current sum of sampled voltages to a stored sum of sampled voltages and indicating the knee discharge characteristic if the difference between the compared sums exceeds a threshold value.
2. A method for managing a battery having a string of units electrically connected in series, each of the units having positive and negative terminals, the method comprising the steps of:
selectively connecting a unit to a voltage detector circuit for measuring the voltage across the terminals of the unit;
selectively connecting a unit to a charge circuit for supplying charge to the terminals of a unit of the battery;
recording an output of the voltage detector at selected time intervals; and
detecting a discharge knee characteristic of the battery, wherein step of detecting the discharge knee characteristic includes the steps of:
periodically sampling a voltage of each unit in the battery;
summing together the sampled voltages over selected time intervals;
comparing a sum of sampled voltages for a first selected time interval to a sum of sampled voltages for a second selected time interval; and
determining a knee discharge characteristic if the difference between the compared sums exceeds a threshold value.