Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – Having variable number of cells or batteries in series
Reexamination Certificate
2002-07-24
2003-11-11
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
Having variable number of cells or batteries in series
C320S121000
Reexamination Certificate
active
06646418
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to fuel cells and more specifically to fuel cell protection means.
BACKGROUND OF THE INVENTION
Fuel cells provide clean, direct current (DC) electricity. Fuel cells convert reactants, namely fuel and oxidant (air or oxygen), to generate electric power and reaction products. A typical fuel cell power source is constructed from a stack of cells coupled in series as shown in FIG.
1
. For a series electrical connection
100
, the same amount of current is drawn from each cell
102
. In practice, each cell
102
has slightly different performance characteristics.
Fuel cells exhibit a decreasing output voltage as the current output is increased. This curve is not linear and tends to drop off faster at higher currents. Consequently, as can be seen in
FIG. 2
, the power vs. current characteristic
200
generally has a peak
202
at mid-current levels and then rolls off. Below the “peak power” point
202
, as more current is drawn, the power increases. Above the “peak power” point
202
, as more current is drawn, the power decreases. The region in which the slope of power vs. current is negative is referred to as negative dP/dI region
204
. Beyond point
202
, if the system tries to draw more power from the fuel cell, it quickly goes to low power (low voltage) and typically the support circuitry shuts off and the whole system stops working. In some cases, one of the cells may fail to work properly because of a temporary problem within the cell, such as a blocked micro-channel caused by particles or carbon dioxide bubbles. Therefore, it is desirable to monitor the system operation and avoid this condition.
Prior art fuel cell systems have included systems that monitor and compare the fuel cell voltage to a reference fuel cell voltage (Vfc), activating an alarm when the Vfc is exceeded. However, this type of system only provides for monitoring and alarm activation. Other systems have utilized a high power resistor and thermistor in conjunction with monitoring a voltage, and still other systems have used optoisolators. Again, these systems focus on monitoring the cell voltage and lack any constructive means of circuit protection.
Accordingly, a need exists for a protection apparatus and technique to prevent any cells from operating in the negative dP/dI region.
REFERENCES:
patent: 4931947 (1990-06-01), Werth et al.
patent: 4962462 (1990-10-01), Fekete
patent: 5170124 (1992-12-01), Blair et al.
patent: WO 02/03086 (2002-01-01), None
Hallmark Jerald A.
Xie Chenggang
Doutre Barbara R.
Gilmore Douglas W.
Motorola Inc.
Tso Edward H.
LandOfFree
Method and apparatus for fuel cell protection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for fuel cell protection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for fuel cell protection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3120858