Electricity: battery or capacitor charging or discharging – One cell or battery charges another – Vehicle battery charging
Reexamination Certificate
2002-09-17
2004-08-17
Luk, Lawrence (Department: 2838)
Electricity: battery or capacitor charging or discharging
One cell or battery charges another
Vehicle battery charging
C320S103000
Reexamination Certificate
active
06777909
ABSTRACT:
The invention relates to a method and apparatus for generating electrical power using a fuel cell in a vehicle which has at least one drive motor that can be connected via a converter to the fuel cell, with auxiliary units for the starting phase and the continuous operation after the starting phase also assigned to the fuel cell.
A circuit for supplying electrical power to a power system containing a fuel cell and an accumulator circuit in which the accumulator supplies power during the starting process is disclosed in German patent document DE 198 104 685. In this arrangement, the accumulator circuit is connected to the fuel cell power system via at least one d.c./d.c. converter. The drives of auxiliary units and a compressor for feeding the fuel and/or air are also connected to the fuel cell power system. At the beginning of a starting process, the accumulator supplies power for the auxiliary units. After the starting process (that is, during rated operation), the accumulator is charged via the d.c./d.c. converter.
A method for starting a fuel cell vehicle which is driven by an electrical drive unit fed by fuel cell is also known. The fuel cell vehicle contains a fuel cell to which a fuel (for example, hydrogen) is fed via a line in which a valve and a pressure regulator are arranged. An oxidant (for example, air) is fed to the fuel cell via a further line in which an air filter, an air flow rate meter and a compressor are arranged. To drive the compressor, an electric starter motor which is supplied with 12 V from a starter battery and a further electric motor which is configured for the voltage of the fuel cell are provided. To start the fuel cell, the starter motor is supplied with current by the starter battery. During normal operation, the fuel cell supplies the power required to operate the further electric motor. By means of a potentiometer, the rotational speed of the electric motor (and thus that of the compressor for influencing the oxidant mass flow rate) are set in order to influence the power of the fuel cell (German patent document DE 43 22 767 A1).
At higher drive powers of the vehicle, a correspondingly dimensioned fuel cell is necessary, whose auxiliary and supplementary units also require large powers in the starting phase. When a 12 V starter battery is used, it must therefore output large currents in the starting phase, which is unfavorable for the charge state and also for the service life. The large currents also require large conductor cross sections. In vehicles supplied with electrical power from fuel cells it is desirable to brake them recuperatively. However, a conventional starter battery of 12 V can only partially absorb the fed-back power so that a large amount of the power has to be converted into heat. This degrades the overall efficiency of the fuel cell system.
German patent document DE 197 31 250 A1 discloses a power supply system with a fuel cell stack, storage battery, drive motor and auxiliary machinery, as well as a method for charging the storage battery. The storage battery is connected to the fuel cell stack via a switching contact. The auxiliary machinery is connected to the fuel cell stack and to the storage battery via a d.c./d.c. converter. The drive motor is connected via a switching contact to the fuel cell stack and to the storage battery. A residual charge-sensing device is used to sense residual charge of the storage battery by measuring voltage or current. When the power supply system starts, both the storage battery and the fuel cell stack output electrical power to a load until the heating of the fuel cell stack is terminated.
A device for generating electrical power in a modern motor vehicle must be able to cope with an increasing number of electrical loads, which leads to a rising demand for electrical power. In particular, the number of high-power low-voltage loads is continuously increasing. The vehicle's onboard power system and the power supply or power distribution in the vehicle's onboard power system must be appropriately adapted. Furthermore, it is necessary to ensure readiness to drive even when the primary power source (that is, the fuel cell) fails.
One object of the invention is therefore to provide a device for generating electrical power with a fuel cell and with the auxiliary or supplementary units necessary for the starting and the continuous operation of the fuel cell, such that a storage battery which is present in the vehicle's onboard power system with loads such as lamps is relieved of loading in the starting phase of the fuel cell.
Another object of the invention is to provide a fuel cell system that is composed of the fuel cell and its auxiliary or supplementary units, and has a high level of efficiency in the various operating states of the vehicle, in particular even under partial load of the vehicle drive, during idling or when braking, if appropriate even when the vehicle is at a standstill.
Still another object of the invention is to provide a fuel cell system that can provide power which is necessary for rapid acceleration of the vehicle in addition to the fuel cell power.
Finally, yet another object of the invention is to provide a method for operating such a fuel cell system.
These and other objects and advantages are achieved according to the invention by a fuel cell system of the type described above, in which the converter and auxiliary or supplementary units for the starting and the operation of the fuel cell as well as one end of a bidirectional d.c./d.c. converter can be connected to the electrical outputs of the fuel cell via at least one switching contact. An electrical temporary power store can be connected to the other end of the d.c./d.c. converter via at least one further switching contact; and a controller is provided which controls the release of the power flux via the d.c./d.c. converter and the direction of the power flux as a function of the operating state of the fuel cell and of the temporary power store. The auxiliary units for the starting of the fuel cell can be supplied with power in the starting phase from the temporary power store which has an appropriate capacity. When the switching contact is closed, the power flux then flows between the temporary power store and the d.c./d.c. converter in the direction of the auxiliary units. After the starting phase, the switching contact which is connected downstream of the outputs of the fuel cell is closed. The starting phase is terminated when the fuel cell has reached its predefined operating voltage. This state can be defined by the controller which brings about the closing of the switching contact between the outputs of the fuel cell and the further loads, such as auxiliary units, converters and the d.c./d.c. converter, which are connected to the fuel cell power system.
When the direction of the flow of current in the d.c./d.c. converter is reversed in this switched state, the temporary power store can be charged either by the fuel cell or by the converter in the operating mode of the vehicle. The charging of the temporary power store can be expedient for absorbing a part of the electrical power from the fuel cell if the drive operates in the partial load mode, but in order to achieve a high level of efficiency the fuel cell outputs a higher level of power. In the braking mode, the power which is fed back by the converter of the drive is fed to the temporary power store. If the power which is required by the vehicle drive drops very quickly (for example, when there is a rapid transition from the driving mode into the stationary state), the fuel cell can be adjusted back to a low power level more slowly in order to utilize the combustion gas, the power which is no longer required by the drive being conducted into the temporary power store. The switching contact is, in particular, a component of a battery protection switch, for example power contactor, which is connected to the controller.
In one preferred embodiment, a diode whose polarity is in the forward direction with respect to the polarity of the out
Aberle Markus
Sonntag Josef
Ballard Power System AG
Luk Lawrence
Seed IP Law Group PLLC
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