|Title of Invention||
FUEL CELL BATTERY HYBRID POWER SOURCE FOR ELECTRIC VEHICLE
|Abstract||A fuel cell-battery hybrid power sourc comprising fuel cell stacks connected Iectrically in series; a battery bank connected in parallel thereto; a sub system for the supply of hydrog~n and a sub system for the supply of oxygeh constituting the fuel cell reactant feed system, the said feed system bein9 .controlled by a CPU; a PEMFC stack cooling system.|
This invention relates to a battery-fuel cell hybrid power source for electric vehicle application.
A fuel cell-battery hybrid electric vehicle, has many advantages compared to a battery powered electric vehicle. The invention disclosed in this patent includes a fuel cell-battery hybrid power source for electric vehicle, a novel reactant feed system for fuel cell stack, an integrated stack cooling system, hydrogen gas humidifying system, reactant re-circulation system for optimum use of the reactants, and a control system .
Electric Vehicles (EV) powered with batteries have certain disadvantages, such as limited range and long recharging time, due to the limitations of currently available batteries. A fuel cell power system, in principle, can to a large extent overcome the above problems and efforts are therefore being made through out the world to advance fuel cell technology and to develop Fuel Cell Electric Vehicles (FCEV).
Fuel cell generates electricity by the electrochemical combination of hydrogen and oxygen. It can provide power as long as the reactants are supplied to the invariant electrodes. The power available from the fuel cell is constant (power density is a function of state of charge in secondary batteries) and re-fuelling of fuel cell is rapid. Among the various types of fuel cells. Polymer Electrolyte Membrane Fuel Cell (PEMFC) is considered as the most suitable candidate for EV application. This fuel cell consists of a proton conducting polymer electrolyte membrane sandwiched between two electrodes, anode and the cathode, catalysed with precious metal (platinum) catalysts. Hydrogen gas is fed to the anode and oxygen or air is fed to the cathode. From a theoretical viewpoint, all hydrogen supplied may be used in the electrochemical reaction. In actual practice it is necessary to supply 1.2 to 1.5 times the stoichiometric quantity of reactant gases. The unused excess reactants have to be re-circulated. For
efficient working of the PEM fuel cell, the reactant gases have to be humidified. During the operation of fuel cell, considerable amount of heat is also generated. To ensure proper working condition of the PEM fuel cell, this heat has to be dissipated.
Fuel cells can be used in three different configurations in an electric vehicle. First option is an all fuel cell electric vehicle in which the entire power required is supplied by the fuel cell vehicle. However, this option will be very costly due to the high capital cost of currently available fuel cell stacks. A Hybrid Electric Vehicle (HEV) employing two power sources, battery and fuel cell system, will be more advantageous. Second option is a battery-fuel cell hybrid electric vehicle in which major power is supplied by the fuel cells and the batteries are used for peak power boost and often to store energy from a regenerative braking system. Third configuration is such a battery-fuel cell hybrid electric vehicle in which the fuel cell is used as a range extender of battery operated electric vehicle. In this, the major traction power comes from the batteries and the fuel cells are used to supply a portion of power required for traction and to recharge the batteries. This configuration has the advantage that it requires only a low power fuel cell stack, it can be incorporated in a well developed battery driven electric vehicle, and can provide extended range for the vehicle. This requires integration of fuel cell stack and battery bank, development of control system to draw power from battery and fuel cell-stack, charging of battery with fuel cell power, development of gas feed system, cooling system for fuel cell stack etc.
The present invention relates to a novel fuel cell-battery hybrid power source for electric vehicle consisting of PEM fuel cell stack, battery bank, DC-DC converter to boost the fuel cell voltage above the battery bank voltage, reactants (fuel and oxidant) supply system to the fuel cell stack, fuel cell stack cooling system, hydrogen gas humidifying system, reactant re-circulation system, and a hybrid control system.
Briefly described, the present invention comprises of two fuel cell stacks connected electrically in series and connected to the DC-DC converter. DC-DC converter steps up fuel cell voltage to >120V and the output are fed to hybrid controller. A 120V battery bank is connected in parallel to the fuel cell and the battery output is also fed to hybrid controller. The hybrid controller output is fed to drive controller, which supplies power to the DC motor depending on the speed/ commands from the driver. A diode is put in between fuel cell stack and hybrid controller, to avoid reverse flow of power from battery to fuel cell stack. A step down DC-DC converter is also connected to the battery bank, which provides output voltage of 12V DC for auxiliary power requirements for the control system, solenoid valves, pressure switch etc.
The fuel cell requires continuous feeding of hydrogen and oxygen gas for the production of electricity. Compressed oxygen and hydrogen gas, stored in metal cylinders are used. Double stage gas regulators are fitted to the cylinders for setting the required gas feed pressure. The gas regulators are connected to rotameter/ mass flow controller and their outlets were connected to the fuel cell stack. A humidification system is introduced in the gas feed line to humidify the hydrogen gas before it enters the stack. The gas outlets from the fuel cell stacks are connected to a gas pump/compressor operating on 12VDC, for pumping the excess un-reacted gases from the fuel cell stack to the fuel cell stack inlet feed port. A pressure transducer is used to monitor the gas pressures and a solenoid valve is introduced to open/ close gas supply to fuel cell stacks. The PEMFC stack temperature is maintained by circulation of distilled water using a double-headed peristaltic pump. The outlet of the two stacks is fed to a radiator where the heat exchange with the environment takes place. A fan sucking air through the cooling fins further enhances this. A heat sensor placed at the water outlet of the stacks triggers the fan on. A hybrid power source controller is installed between the hybrid power source and motor drive controller. This controller enables drawing power simultaneously from the fuel cell and battery, connected in parallel. It enables to alter/set the fuel cell output current to a desired value,
using a potentiometer knob. The control unit also enable to cut off the gas supply and fuel cell load in case the fuel cell operating parameters such as voltage, gas pressure and temperature, deviate from the set values. The hybrid controller also enables the charging of battery using the fuel cell power when the vehicle stops, even for a very short duration. The controller also ensures that reverse flow of current from battery to fuel cell does not take place. A monitoring system installed in the electric vehicle, indicates status information on various parameters. The display in the instrument panel include fuel cell stack voltages, temperatures, hydrogen and oxygen gas pressures, fuel cell stack current/ DC-DC input voltage & current, DC-DC output voltage & current, battery voltage & current, drive output voltage & current. Display also includes green and red indicator lights to show whether the system is operating within the set limits. An electric vehicle fitted with this type of hybrid power source does not have to depend on external grid power for battery charging and provides higher range compared to a battery powered electric vehicle.
The characteristics and advantages of the invention will be evident from the following drawings.
FIG. 1 is a block-schematic drawing of the Battery - Fuel Cell Hybrid Power Source in accordance with the present invention.
FIG. 2 is a schematic diagram of the Hydrogen gas supply system.
FIG. 3 is the schematic diagram of the Oxygen/(Oxygen from air) gas supply system.
FIG. 4 is the schematic diagram for the integrated stack cooling system.
FIG. 5 is the block diagram of a central processing unit of the systems in Fig. 2, 3 and 4.
FIG. 6 is a flow diagram of the unit in Fig. 5 for control and operation of the PEMFC stack
The power system includes two PEM fuel cell stacks connected electrically in series and a battery bank connected parallel to the above. It also includes a subsystem for the supply of hydrogen, a subsystem for the supply of oxygen, which constitutes the fuel cell reactants feed system. In addition we have the PEMFC stack cooling system. The other components include the integrated battery-fuel cell hybrid control system, vehicle drive system and the auxiliary power system. FIG. 1 gives a comprehensive picture of the battery-PEMFC hybrid power source for electric vehicle.
FIG. 2 presents the hydrogen feed sub system. This sub system consists of a hydrogen storage tank with a gas regulator. Alternately the hydrogen can be obtained from a storage system like a metal hydride or hydrogen may be generated by a reforming system. The hydrogen delivery line is connected to humidification system, where the hydrogen supplied to the PEMFC stacks is humidified and heated. The temperature, T4, of the hydrogen fed into the supply line is monitored through the CPU. A pressure gauge PH in the hydrogen supply line monitors the hydrogen gas pressure. Two valves, V1, a manual valve and V2, a solenoid valve, operating at a voltage VH, monitored through the CPU, supplies or cuts off the supply of gas to the PEMFC stacks. The valve V2 is controlled by the CPU, which governs the whole system in accordance with commands, received from a master controller. The gas fed to the PEMFC stack is governed by a mass flow controller MH. The gas flow stochiometry for different currents drawn from the PEMFC stacks is controlled by the mass flow controller and monitored by the CPU. The outlet of the PEMFC stacks is connected to the atmosphere through a non-return valve NRV, V3, This valve releases the gas to the atmosphere if and when the line pressure exceeds 2psi. For effective use of the gas the excess gas in the outlet line is re-circulated to the PEMFC stacks by a re-circulation pump, CH. The unidirectional nature of the NRV, V3, also ensures
that the pump CH does not suck in air from the atmosphere into the hydrogen line, which could have an explosive effect. The CPU controls the pump CH. The CPU switches it on in conjunction with the solenoid V3 after a small delay. The flow from the pump is monitored by a flow controller and fed into the inlet line. This enables optimum use of the reactant gas. The hydrogen gas is introduced into the stacks at temperatures of about 50*^C. All parts of the hydrogen supply sub-system, which are in contact with hydrogen, are of heavy-duty material in order to minimizing contamination of the gas. Also all the electrical units in contact with the hydrogen supply system have in built safety features to guard against explosion.
FIG. 3 presents the oxygen feed sub-system. The description of this system is as in the hydrogen gas feed system. In this figure, T5 denotes the temperature of the oxygen feed. Po is the pressure of the oxygen feed. Vo, is the operating voltage of the solenoid valve V2. Mo is the oxygen mass flow controller. Co is the oxygen re-circulation pump.
FIG. 4 presents the integrated stack cooling system. The water from a water tank is fed into the PEMFC stacks S1 and S2 by a double-headed peristaltic pump. The two heads P1 and P2 supply distilled water to the stacks S1 and S2. These pumps ensure that a constant flow is maintained to the stacks. The pump is controlled by the CPU via the supply voltage E1 to the pump. The water outlet of the stacks is fed in to a radiator fan assembly where the excess heat is removed to the atmosphere. The fan is controlled by the CPU via the supply voltage E2 to the fan. The water temperature T1 at the outlet of the stacks helps us monitor and control the stack temperature T2 and T3. The CPU maintains temperature T1 at a set value namely 50 ° C. When this temperature is exceeded the CPU automatically turns the fan on. Thus, the radiator fan assembly helps us maintain the stacks at a constant working temperature. In order to bring the stacks rapidly to the working temperature a heating element can be introduced in
the cooling circuit to circulate preheated water through the staks. This can reduce the startup time of the PEMFC unit.
FIG. 5 is the block diagram of the CPU for controlling the reactant gas feed system. The CPU is the unit to which the various pressure, temperature, and flow sensors, T1 to T5, PH, PO, MH, MQ send signals which they generate. These signal being converted, in case of analog signals, into binary code by means of analog-digital converters incorporated in the CPU. These components are displayed for reference. A suitable program is loaded in the EPROM of the CPU that does the switching on and off of the various components by supplying voltages VH and Vo to the solenoids V2, voltages E1, E2, E3, Co and CH to the pumps, fan heater and oxygen and hydrogen gas circulation pumps, respectively.
FIG. 6 is the flow diagram showing several significant aspects of the control process developed to put the system into operation.
The starting process is initiated by a start command by the operator: START.
Following the start command the solenoids Vo and VH, mass flow controllers Mo and MH, the cooling pumps E1, heater E3 are triggered: POWER Vo, VH, MQ, MH, E1,E3.
When the temperature of the stack and the reactant feed reaches operating temperatures the PEMFC stacks is at a temperature ready for start up. The heater E3 is switched off: SW-OFF E3.
The control unit checks the temperature of the cooling fluid by sensor T1: T1 The fan is switched on to maintain constant cooling fluid temperature and thereby maintain constant stack temperature: START E2.
The fan is switched off when the temperature T1 is less than the set operating temperature: SW-OFF E2.
At this stage the reactant circulating pumps are enabled: START CH, CQ.
A stop procedure may be instigated to any moment in the flow process as result of a stop command which may be effected by the operator or by emergency signals: STOP
Stop command is activated under any pre set conditions of Temperature T1, T2 and T3 and pressure Po and PR. This triggers switching off CH, CO, VH, VO, MH, MO, E1 and E3: SW-OFF CH, CO, VH, VO, MH, MO, E1, and E3
1. A fuel cell battery hybrid power source comprising fuel cell stacks connected electrically in series; a battery bank connected in parallel thereto; a subsystem for the supply of hydrogen and a subsystem for the supply of oxygen constituting the fuel cell reactant feed system, the said feed system being controlled by a hybrid controller CPU; a PEMFC stack cooling system.
2. A fuel cell battery hybrid power source as claimed in Claim 1 wherein the hydrogen feed subsystem comprises means for humidifying and heating hydrogen for supply to the PEMFC stacks; the said CPU for supplying and cutting off hydrogen to the said stacks, the outlet of the said stacks being connected to the atmosphere through a non return valve.
3. A fuel cell battery hybrid power source as claimed in Claim 2 wherein a recirculation pump controlled by the said CPU is provided for recirculating the excess hydrogen in the outlet line to the said stacks.
4. A fuel cell battery hybrid power source as claimed in any one of the preceding Claims wherein the oxygen feed subsystem comprises means for humidifying and heating oxygen for supply to the PEMF stacks, the said CPU supplying and cutting off oxygen to the said stacks, the outlet of the said stacks being connected to atmosphere trough a non-return valve.
5. A fuel cell battery hybrid power source as claimed in Claim 4 wherein a recirculation pump controlled by the said CPU is provided for recirculating the excess oxygen in the outlet line to the said stacks.
6. A fuel cell battery hybrid power source as claimed in any one of the preceding Claims provided with a double headed peristaltic pump , controlled by the said CPU, for
supply of constant flow distilled water to the said stacks; a radiator fan assembly, controlled by the said CPU, for receiving the water outlet from the stacks and removing excess heat to atmosphere
7. A fuel cell battery hybrid power source substantially as herein described with reference to, and as illustrated in. Figs 1 to 6 of the accompanying drawings
|Indian Patent Application Number||592/MAS/2001|
|PG Journal Number||26/2007|
|Date of Filing||19-Jul-2001|
|Name of Patentee||SPIC SCIENCE FOUNDATION|
|Applicant Address||111 MOUNT ROAD ,GUINDY CHENNAI 600 032|
|PCT International Classification Number||H01M 8/00|
|PCT International Application Number||N/A|
|PCT International Filing date|