U.S. patent application number 11/527480 was filed with the patent office on 2007-10-04 for fuel cell system.
Invention is credited to Hironori Sasaki, Kenji Yamaga.
Application Number | 20070231643 11/527480 |
Document ID | / |
Family ID | 38559461 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070231643 |
Kind Code |
A1 |
Yamaga; Kenji ; et
al. |
October 4, 2007 |
Fuel cell system
Abstract
The fuel cell system includes a fuel cell stack, a fuel cell
temperature sensor for measuring the internal temperature of the
fuel cell, a voltage sensor for measuring the power generation
voltage of the fuel cell, a current sensor for measuring the
current flowing from the fuel cell, a radiator for radiating heat
generated by the fuel cell, a fan attached to the radiator for
controlling the heat radiation amount, a cooling water pump for
increasing the pressure of a cooling fluid, a bypass valve for
controlling the cooling fluid amount entering the radiator, and a
controller, on the basis of the voltage information measured by the
voltage sensor, the temperature information measured by the
temperature sensor, and the current information measured by the
current sensor, for controlling at least one of the operation
amount of the cooling water pump, the operation amount of the fan,
and the cooling fluid amount flowing through the bypass valve.
Inventors: |
Yamaga; Kenji; (Hitachi,
JP) ; Sasaki; Hironori; (Hitachi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
38559461 |
Appl. No.: |
11/527480 |
Filed: |
September 27, 2006 |
Current U.S.
Class: |
429/431 ;
429/432; 429/437; 429/442; 429/454; 429/505 |
Current CPC
Class: |
H01M 8/04365 20130101;
H01M 8/04768 20130101; H01M 8/04589 20130101; Y02E 60/50 20130101;
H01M 8/04014 20130101; H01M 8/04559 20130101; H01M 8/04723
20130101 |
Class at
Publication: |
429/23 ; 429/24;
429/26 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2006 |
JP |
2006-092740 |
Claims
1. A fuel cell system comprising: a fuel cell stack; a fuel cell
temperature sensor for measuring an internal temperature of said
fuel cell; a voltage sensor for measuring a power generation
voltage of said fuel cell; a current sensor for measuring a current
flowing from said fuel cell; a radiator for radiating heat
generated by said fuel cell; a fan attached to said radiator for
controlling a heat radiation amount; a cooling water pump for
increasing pressure of a cooling fluid; a bypass valve for
controlling a cooling fluid amount entering said radiator; and a
controller, on the basis of voltage information measured by said
voltage sensor, temperature information measured by said
temperature sensor, and current information measured by said
current sensor, for controlling at least one of an operation amount
of said cooling water pump, an operation amount of said fan, and a
cooling fluid amount flowing through said bypass valve.
2. A fuel cell system comprising: a fuel cell stack formed by using
a metallic material for separators; a fuel cell temperature sensor
for measuring an internal temperature of said fuel cell stack; a
voltage sensor for measuring a power generation voltage of said
fuel cell; a current sensor for measuring a current flowing from
said fuel cell; a radiator for radiating heat generated by said
fuel cell; a fan attached to said radiator for controlling a heat
radiation amount; a cooling water pump for increasing pressure of a
cooling fluid; a bypass valve for controlling a cooling fluid
amount entering said radiator; a cathode line having an arranged
moistening device for adding water generated by power generation to
air; an anode line for supplying hydrogen; and a controller for
controlling an auxiliary device operation in said system; wherein:
said controller judges on the basis of voltage information measured
by said voltage sensor, temperature information measured by said
temperature sensor, and current information measured by said
current sensor, thereby controls at least one of an operation
amount of said cooling water pump, an operation amount of said fan,
and a cooling fluid amount flowing through said bypass valve.
3. The fuel cell system according to claim 1, wherein when: a
displacement amount dV/dt of a fuel cell stack voltage V to time t
is smaller than 0, a displacement amount dT/dt of a fuel cell stack
temperature T to time t is larger than 0, and a displacement amount
dI/dt of a fuel cell stack current I to time t is equal to or
larger than 0, said controller changes at least one of said
operation amount of said cooling water pump, said operation amount
of said fan, and said cooling fluid amount flowing through said
bypass valve and controls a quantity of heat discharged externally
from said fuel cell so as to increase.
4. The fuel cell system according to claim 1, wherein when: a
displacement amount dV/dt of a fuel cell stack voltage V to time t
is smaller than 0, a displacement amount dT/dt of a fuel cell stack
temperature T to time t is larger than 0, and a displacement amount
dI/dt of a fuel cell stack current I to time t is equal to or
larger than 0, said controller increases at least one of said
operation amount of said cooling water pump, said operation amount
of said fan, and a ratio of said cooling flow rate to said radiator
to said cooling fluid amount flowing through said bypass valve.
5. The fuel cell system according to claim 1, wherein when: a
displacement amount dV/dt of a fuel cell stack voltage V to time t
is larger than 0 and a displacement amount dT/dt of a fuel cell
stack temperature T to time t is smaller than 0, said controller
changes at least one of said operation amount of said cooling water
pump, said operation amount of said fan, and said cooling fluid
amount flowing through said bypass valve and controls a quantity of
heat discharged externally from said fuel cell so as to
decrease.
6. The fuel cell system according to claim 1, wherein when: a
displacement amount dV/dt of a fuel cell stack voltage V to time t
is larger than 0 and a displacement amount dT/dt of a fuel cell
stack temperature T to time t is smaller than 0, said controller
decreases at least one of said operation amount of said cooling
water pump, said operation amount of said fan, and a ratio of said
cooling flow rate to said radiator to said cooling fluid amount
flowing through said bypass valve.
7. The fuel cell system according to claim 1, wherein to a set
value Tc of said stack temperature at time of rated power
generation, when a present time T is within a range of T<Tc-5,
an operation of a cooling section is driven repeatedly.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese
application serial no. 2006-092740, filed on Mar. 30, 2006, the
content of which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a power generation system
using a fuel cell.
[0004] 2. Description of the Prior Art
[0005] A fuel cell is an electrochemical device for converting fuel
energy directly to electric energy by an electrochemical reaction.
The fuel cell, depending on a charge carrier used, is broadly
divided into a phosphoric fuel cell, a melt carbonate fuel cell, a
solid oxide fuel cell, a polymer electrolyte fuel cell
(hereinafter, abbreviated to PEFC), and an alkaline fuel cell.
[0006] Among these various fuel cells, the PEFC enables high
current density power generation and operation at a comparatively
low temperature, so that applications to various uses including a
power source for a mobile body are anticipated.
[0007] For an electrolyte of the PEFC, an ion exchange membrane
with a thickness of several tens .mu.m to hundred and several tens
.mu.m is used. The ion exchange membrane has a general structure
that a side chain having the sulfonic group is bonded to
fluorocarbon composing a main chain. The ion exchange membrane has
proton conductivity, thus the membrane material is required to
contain moisture. The reason is that the sulfonic group takes a
cluster structure in the material, and the clusters are connected
by a channel, and by conduction of protons (H.sub.3O.sup.+) in the
channel, the material shows proton conductivity, though to follow
this mechanism, existence of water is necessary.
[0008] Therefore, when operating the PEFC, a system that gas to be
supplied contains moisture for moistening the electrolyte is
general. When the PEFC generates power, it generates water by the
chemical reaction thereof. If collected generated water can be used
as moistening water, a system requiring no feed water from the
outside can be formed and the constituent devices can be
simplified.
[0009] When the constituent devices can be simplified, not only the
manufacturing cost can be reduced but also the system volume can be
made smaller, and particularly when the PEFC is used as a power
source for a mobile body, the advantage is increased.
[0010] To improve the operability of the fuel cell system, it is
preferable to realize a rapid start characteristic.
[0011] To start the system at high speed, it is necessary to
promptly increase the cell temperature to a preset temperature.
When separately installing a heater mechanism for increasing the
temperature of the cell, it is extremely inefficient in respect of
efficiency and volume, so that it is generally difficult to load it
in a power source for a mobile body. Therefore, in a system having
no special cell temperature rise mechanism, as a heat source for
increasing the temperature of the cell, heat generated by power
generation is used. To form the fuel cell, several hundreds
separators are generally used as one of the main materials. When
using carbon separators comparatively thick such as several mm or
more, the fuel cell is long in the lamination direction.
Simultaneously, in correspondence to an increase in the stack
volume, the heat capacity also increases. Namely, the temperature
rise speed at time of power generation is low and rapid start is
difficult.
[0012] Improvement of the start characteristic at low temperature
is described in Japanese Patent Laid-open No. 2005-190744.
SUMMARY OF THE INVENTION
[0013] The present invention proposes a fuel cell system having an
excellent start characteristic.
[0014] The fuel cell system includes:
[0015] a fuel cell stack, a fuel cell temperature sensor for
measuring the internal temperature of the fuel cell, a voltage
sensor for measuring the power generation voltage of the fuel
cell,
[0016] a current sensor for measuring the current flowing from the
fuel cell,
[0017] a radiator for radiating heat generated by the fuel cell, a
fan attached to the radiator for controlling the heat radiation
amount,
[0018] a cooling water pump for increasing the pressure of a
cooling fluid,
[0019] a bypass valve for controlling the cooling fluid amount
entering the radiator, and
[0020] a controller, on the basis of the voltage information
measured by the voltage sensor, the temperature information
measured by the temperature sensor, and the current information
measured by the current sensor, for controlling at least one of the
operation amount of the cooling water pump, the operation amount of
the fan, and the cooling fluid amount flowing through the bypass
valve.
[0021] According to the present invention, a fuel cell system
having an excellent start characteristic can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a drawing showing a part of the power generation
system configuration of Embodiment 1 relating to the present
invention,
[0023] FIG. 2 is a drawing showing a part of the power generation
system configuration of Comparison Examples 1 and 2 relating to the
present invention,
[0024] FIG. 3 is a drawing showing the power generation test
results at start time of Embodiment 1 relating to the present
invention,
[0025] FIG. 4 is a drawing showing the power generation test
results at start time of Comparison Example 1 relating to the
present invention, and
[0026] FIG. 5 is a drawing showing the power generation test
results at start time of Comparison Example 2 relating to the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The embodiments relating to the present invention will be
explained.
[0028] Firstly, a fuel cell system including a fuel cell stack
formed by using a metallic material for separators, a fuel cell
temperature sensor for measuring the internal temperature of the
fuel cell, a voltage sensor for measuring the power generation
voltage of the fuel cell, a current sensor for measuring the
current flowing from the fuel cell, a radiator for radiating heat
generated by the fuel cell, a fan attached to the radiator for
controlling the heat radiation amount, a cooling water pump for
increasing the pressure of a cooling fluid, a bypass portion for
controlling the cooling fluid amount entering the radiator, a
cathode line having an arranged moistening device for adding water
generated by power generation to air, an anode line for supplying
hydrogen, and a controller for controlling the auxiliary device
operation in the system, wherein the controller judges on the basis
of the voltage information measured by the voltage sensor, the
temperature information measured by the temperature sensor, and the
current information measured by the current sensor, thereby
controls the cooling fluid amount flowing through the cooling water
pump, fan, and bypass portion is proposed.
[0029] The fuel cell has a characteristic that due to the property
of the electrolytic membrane, when moisture in the cell is reduced,
the cell performance is lowered. Even at start time when the
temperature is changed particularly terribly, by use of a system
having the aforementioned constitution, the cell temperature can be
controlled finely, and the vapor pressure in the cell is
controlled, thus the cell characteristic can be stabilized without
excessively reducing moisture in the electrolytic membrane.
[0030] Secondly, a system that the controller, when the
displacement amount dV/dt of the fuel cell stack voltage V to the
time t is smaller than 0, and the displacement amount dT/dt of the
fuel cell stack temperature T to the time t is larger than 0, and
the displacement amount dI/dt of the fuel cell stack current I to
the time t is equal to or larger than 0, changes the cooling fluid
amount flowing through the cooling water pump, fan, and bypass
portion, and controls the quantity of heat discharged externally
from the fuel cell so as to increase is proposed.
[0031] As an embodiment, the controller increases at least one of
the operation amount of the cooling water pump, the operation
amount of the fan, and the ratio of the cooling flow rate flowing
to the radiator to the cooling flow rate flowing through the bypass
valve.
[0032] By use of this control method, the temperature is controlled
at the very early timing when the internal drying condition of the
cell affects the cell characteristic, and the moisture content in
the cell can be controlled, so that particularly even when the cell
temperature is changed greatly at start time, the cell
characteristic is hardly lowered and the cell behavior is
stabilized.
[0033] Furthermore, thirdly, when the displacement amount dV/dt of
the fuel cell stack voltage V to the time t is larger than 0 and
the displacement amount dT/dt of the fuel cell stack temperature T
to the time t is smaller than 0, it is proposed to control the
cooling fluid amount flowing through the cooling water pump, fan,
and bypass portion. By use of this method, the cell temperature is
judged to be lowered as required, and the cooling effect is
regulated by changes in the operation amounts of the pump and fan,
thus without unnecessarily lowering the cell temperature, that is,
without generating condensed water causing flooding, minimal
cooling necessary for stabilization of the cell performance is
executed, thus the system can be started at high speed.
[0034] As an embodiment, the controller decreases at least one of
the operation amount of the cooling water pump, the operation
amount of the fan, and the ratio of the cooling flow rate flowing
to the radiator to the cooling fluid amount flowing through the
bypass valve.
[0035] Furthermore, fourthly, to the set value Tc of the stack
temperature at time of rated power generation, when the present
time T is within the range of T<Tc-5, it is proposed to drive
repeatedly the operation of the cooling section.
[0036] At start time, it is natural that the stack and auxiliary
device are greatly changed in temperature, though when power is
generated under the rated condition and then power is generated
under the partial load condition, the heat value is reduced, so
that the temperature set by Tc cannot be maintained, and the stack
temperature lowers. Furthermore, thereafter, when power is
generated again under the rated condition, the stack temperature
rises greatly, so that the condition coincides with the condition
at start time. By this proposal, not only at start time but also in
correspondence to sudden temperature change of the stack due to
change in the power generation condition, the cell can be operated
stably.
[0037] In a system using a self moistening method using generated
water accompanying power generation of the fuel cell, immediately
after start, the collection amount of generated water is small, and
self moistening is not executed sufficiently, so that the cell
performance may be lowered or may become unstable. According to the
embodiment of the present invention, even a fuel cell power
generation system using the moistening method for collecting
generated water at time of power generation and adding it to gas to
be supplied can be started in a short time and can perform an
operation at a stable power generation voltage.
[0038] Hereinafter, the embodiment of the present invention will be
explained with reference to the accompanying drawings.
Embodiment 1
[0039] The basic constitution of the power generation cell is that
around an electrode electrolytic membrane composed of
perfluorocarbon sulfonic acid based electrolytic membrane and an
electrode having a catalyst of platinum particles carried by a
carbon carrier as a main component which are united with each
other, on the front and rear surfaces thereof, a cathode diffusion
layer and an anode diffusion layer which are carbon paper that
polytetrafluoroethylene (PTFE) is dispersed on the surface and the
water repellency is controlled are arranged, and furthermore
metallic separators are arranged on both sided thereof. By
combining 120 power generation cells and 60 cooling cells for
passing cooling water and lowering the cell temperature, one stack
is prepared.
[0040] The cooling line including an anode line 2 for supplying
hydrogen, a cathode line 4 having a moistening device 5 composed of
a water penetration membrane for collecting generated water and
moistening, a cooling water pump 10 for sending cooling water, a
radiator 7 with a fan 8 attached, a bypass portion 11, and a bypass
valve 9 for controlling the flow rate thereof is connected to a
stack 1. To an output line 16 taking out output from the stack 1, a
current sensor 14 is attached. To measure the voltage of the cell
composing the stack, a voltage sensor 12 is connected to a
separator for each 10 cells. A temperature sensor 13 is arranged at
the central part of the electrode almost at the central position of
the stack so as to detect the maximum temperature in the stack
during power generation. Here, the voltage sensor 12 measures the
voltage of all 10 cells together. However, even if all the cells
are measured individually and even if more than 10 cells, for
example, 20 or more cells are measured together, no problems are
imposed. Each sensor information is connected to a controller 15
and the controller 15, on the basis of the information from the
sensors, controls the operations and operation amounts of the
cooling water pump, bypass valve, and fan. The block diagram of
this system is shown in FIG. 1.
[0041] The operation instruction contents of the controller are
indicated below.
[0042] When the displacement amount dV/dt of the stack voltage V
when the power generation is started to the time t is smaller than
0, and the displacement amount dT/dt of the stack temperature T to
the time t is larger than 0, and the displacement amount dI/dt of
the stack current I to the time t is equal to or larger than 0, the
operation or operation amount of the cooling water pump is
increased to increase the sending amount of cooling water, and when
the displacement amount dV/dt of the stack voltage V to the time t
is larger than 0 and the displacement amount dT/dt of the stack
temperature T to the time t is smaller than 0, the cooling water
pump 10 is stopped or the operation amount thereof is lowered to
reduce the sending amount of cooling water.
[0043] Further, when the set value TC of the stack temperature at
time of rated power generation is set to 70.degree. C. and on the
other hand, the present temperature T is 65.degree. C., it is set
to execute temperature control only by the operation of the
fan.
[0044] The aforementioned contents are stored in the controller,
and when the stack temperature is equal to the room temperature,
hydrogen controlled at a fixed pressure of 45 kPa and air of 250
L/min are supplied, and when it is confirmed that the stack voltage
increases to 110 V or higher, a rated current load of 55 A is
added, and the system is started. The current is kept constant, and
assuming the moment the current starts to flow as t1, the time
after t1, stack voltage, and stack temperature are measured.
Further, at the point of time when the current starts to flow, no
cooling operation is performed.
COMPARISON EXAMPLE 1
[0045] The system constitution of Comparison Example 1 is shown in
FIG. 2. Comparison Example 1 has an almost similar constitution to
that of Embodiment 1, though the controller 15 for controlling the
cooling water pump, bypass valve, and fan judges on the basis of
the stack temperature T measured by the temperature sensor and
controls the operation and operation amount thereof.
[0046] For the system of Comparison Example 1, the power generation
test is executed according to the same contents as those of
Embodiment 1.
COMPARISON EXAMPLE 2
[0047] Comparison Example 2 has the same constitution as that of
Comparison Example 1 and a system in which the control method for
increasing the stack temperature up to the set operation
temperature TC at a predetermined temperature rise rate at start
time is stored in the controller 15 is used as Comparison Example
2.
[0048] For the system of Comparison Example 2, the power generation
test is executed according to the same contents as those of
Embodiment 1. The predetermined temperature rise rate used in the
power generation test of Comparison Example 2 is set to the same
value as the time required for Embodiment 1 from the start up to
the temperature TC.
[0049] FIG. 3 shows the relationship between the stack voltage and
the time at start time when the power generation test is executed
using the system of Embodiment 1. The point of time when hydrogen
and air are supplied to the system of Embodiment 1 and the rated
load is applied to it is t1 and at this time, the voltage is
lowered according to the current due to various resistance
components. Further, due to generation of heat accompanying start
of power generation, the stack temperature rises slowly. At t2, the
stack voltage is lowered from the preceding one, so that the
controller judges that due to a cell temperature rise accompanying
power generation, the relative humidity in the stack is lowered and
it starts cooling to wet the electrolytic membrane. At t3, the
voltage increases due to the effect of cooling, so that the
controller judges that a minimum cooling step is completed and it
stops cooling. Between t2 and t3 during which the cooling is
executed, it can be confirmed that the stack temperature is also
lowered. The interval between t3 and t4 is a time zone that the
temperature rises again due to generation of heat and at the point
of time when the stack voltage is lowered at t4, the cooling is
restarted by the judgment of the controller. As a result, the stack
temperature is lowered, and the controller detects an increase of
the stack voltage at t5, thereby stops the cooling operation. At
t6, the controller repeats the similar control, though at this
point of time, the temperature approaches sufficiently the set
value of the power generation temperature, and the cooling water
temperature also increases, so that at t6 and thereafter, even if
the stack voltage increases, the cooling operation is executed
continuously. At the time ts, the temperature reaches the set
temperature TC. In this experiment, the interval between t1 and ts
is 480 seconds. The stack temperature rises furthermore and at t7,
the operation to lower the water temperature, in this constitution,
the fan installed on the radiator starts operation. At t8, the fan
continues the operation up to the point of time when the
temperature is lowered sufficiently and thereafter, this process is
repeated.
[0050] In FIG. 4, the start data when the power generation test is
executed using the system of Comparison Example 1 is shown.
Comparison Example 1 is a control method for taking in temperature
information and increasing the temperature up to the set
temperature in a shortest time, so that the arrival time (from t1
to ts2) from start to TC (70.degree. C.) is 175 seconds and the
temperature can be raised rapidly. However, during this period,
moisture supply corresponding to the cell temperature rise is
insufficient, so that the relative humidity in the cell is lowered
greatly. Thereby, it seems that moisture in the electrolytic
membrane is taken away outside the cell system, and the cell
voltage is lowered greatly to zero or below it. When the
temperature rises to 70 .degree. C. or higher, the cooling
operation is started, and the stack temperature is also lowered,
and the voltage is recovered temporarily, though in the situation
of temperature rise, the voltage is lowered again to zero or below
it. Namely, in Comparison Example 1, the rising time to the set
temperature is short, though the power generation cannot be
continued.
[0051] In FIG. 5, the start data when the power generation test is
executed using the system of Comparison Example 2 is shown. In
Comparison Example 2, the cooling system operation is controlled so
as to keep the temperature rise rate constant from start, thus the
time ts required to reach the power generation set temperature is
480 seconds similarly to Embodiment 1. However, in Comparison
Example 2, as the time elapses, the voltage is changed little by
little. The reason is that the cell temperature is suppressed
excessively by cooling, so that moistening water or generated water
is condensed in the cell, and reaction gas is prevented from
diffusion, thus the voltage of several single cells composing the
fuel cell is lowered greatly. Namely, in Comparison Example 2,
although the start time is the same as that of Embodiment 1, it
cannot be said that the power generation stability is sufficient
and the start characteristic is not satisfactory.
[0052] From the above-mentioned, in Embodiment 1 in which the
system constitution and control of this proposal are executed, it
is proved that regardless of the simple system constitution, the
start time from the stop state to the set temperature can be
shortened, and the stability of the power generation voltage during
the period is high, and the start characteristic is excellent.
* * * * *