Patent Application
20070284166
The following discussion of the embodiments of the invention directed to a system and method for controlling the power output of a fuel cell stack and battery in a hybrid fuel cell system is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
The power system 50 also includes a battery SOC controller 62 that attempts to maintain the SOC of the battery 14 at a predetermined or optimal value. This value should be set as the mean value between the minimum and maximum of the allowed battery SOC. For example, the battery 14 may have an acceptable state of charge range of 50%-80%, and an optimal SOC of 65%. The optimal battery state of charge or set-point signal is provided to a subtractor 56 at node 58. The SOC set-point may be 65% where there is room to charge the battery 14, such as during regenerative braking, or discharge the battery 14 when extra power is required to supplement the stack power. The actual battery SOC is provided to the subtractor 56 at node 60.
The SOC set-point signal and the battery SOC signal are subtracted by the subtractor 56 and the difference is provided to the battery SOC controller 62. The battery SOC controller 62 processes the difference signal to provide a battery SOC control signal representative of the battery SOC. In one embodiment, the controller 62 is a Pi controller. Because of the SOC controller 62, the battery 14 can be charged and discharged over a wider range.
The damped driver power request signal from the power damping processor 58 is added to the battery SOC control signal from the controller 62 by an adder 64. The output of the adder 64 is a power demand signal for both the fuel cell stack 12 and the battery 14 that will identify how much of the battery power will be used for operating the vehicle and how much of the fuel cell stack power will used for recharging the battery 14. The signal from the adder 64 is sent to a power balancing module 70 that provides a power demand signal for the stack 12 on line 72 and a power demand signal for the battery 14 on line 74. The module 70 distributes the power demand between the stack 12 and the battery 14 based on the discussion above. Particularly, if the damped power request signal commands more energy from the stack 12 than is required during low power transients, the supplemental energy is used to charge the battery 14. The battery SOC controller 62 determines whether additional stack power will be commanded to provide more battery charging. During a high power transient, the damped power request signal will be lower than what is requested by the vehicle operator, where the extra power will be satisfied by the battery 14. As the vehicle accelerates and decelerates, the SOC controller 62 operates to attempt to maintain the battery SOC at the optimal level.
During acceleration, the battery power is used to fulfill the power request and the battery SOC decreases. When the required vehicle speed is reached, the SOC controller 62 starts to charge the battery 14 until the SOC set-point is reached. If a relationship between the SOC set-point and an aggression index is generated, for example, a damped derivative of the acceleration pedal, an adaptive algorithm is possible.
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
