Generator system utilizing a fuel cell

In a generator system having a fuel cell and a battery to which the output current from the fuel cell can be supplied, in the case of a sudden variation in load, a battery supplies the power to the load until the fuel cell responds to the sudden variation in load. After the output power derived from the fuel cell itself becomes sufficient to be supplied to the load, an excess of the power supplied to the load is charged into the battery.

BACKGROUND OF THE INVENTION 
1.Field of the Invention 
The present invention relates to a generator system utilizing a fuel cell 
and more particularly to a generator system utilizing a fuel cell capable 
of controlling the output of the fuel cell in response to an amount of 
energy variations in load. 
2. Description of the Prior Art 
The conventional generator system utilizing a fuel cell is in general 
designed and constructed to deliver a constant output as shown in FIGS. 1 
or 2. 
FIG. 1 shows a conventional generator system utilizing a fuel cell which is 
driven while a fuel cell is connected to a power supply of a system. The 
generator system utilizing a fuel cell shown in FIG. 1 comprises a raw 
material tank 1 for storing therein a material to be reformed; 2, a 
reformer adapted to produce a reformed gas by reforming the raw material 
fed from the raw material tank 1; 4, a fuel cell; 10, a DC/DC converter; 
11, an inverter; 8A, a system power supply; 9, a load; 14B, a controller 
which is, for instance, in the form of a microprocessor and which controls 
all about the generator system utilizing a fuel cell; and 30 a generator 
system utilizing a fuel cell. 
The output power P.sub.F derived from the fuel cell 4 is applied through 
the DC/DC converter 10 to the inverter 11 so that the DC power is 
converted into the AC power. The inverter output power P.sub.I ; that is, 
the fuel cell output P.sub.F is delivered to the load 9. In this case, the 
AC power P.sub.L delivered to the load 9 is equal to P.sub.I. As the load 
9 is increased, the power supply must be increased accordingly, but when 
the output power P.sub.F delivered from the fuel cell is not sufficient, 
the power Ps from the power supply 8A must be combined with the output 
P.sub.I from the inverter 11 into the power P.sub.L which is supplied to 
the load 9. Therefore, the generator system utilizing a fuel cell is 
driven under the control of the controller 14B. 
FIG. 2 shows a system consisting of the combination of a fuel cell and a 
battery, thereby supplying the power to the load. Reference numeral 1 
represents a raw material tank; 2, a reformer; 4, a fuel cell; and 40 a 
generator system utilizing a fuel cell. The output P.sub.F derived from 
the fuel cell 4 is converted into a direct current by the DC/DC converter 
10, whereby the DC/DC converter output power Pc. 
The output Pc from the DC/DC converter 10 is constant and is delivered as 
the output P.sub.L and the output P.sub.B to the load 9 and the battery 8, 
respectively. It follows, therefore, when the value of the load 9 is 
light, an excess of the power P.sub.L delivered to the load 9 is supplied 
as the excess power P.sub.B to charge the battery 8. On the other hand, 
when the magnitude of the load 9 is heavy, the controller 14B operates in 
such a manner that in addition to the output power Pc from the DC/DC 
converter 10, the output power P.sub.B from the battery 8 is also 
delivered as the power P.sub.L to the load 9. 
However, the above-described conventional generator systems utilizing a 
fuel cell have a common problem that it is extremely difficult to control 
the magnitude of the fuel cell output immediately in response to the 
variations in load. 
This problem is caused by the characteristics of the reformer 2 shown in 
FIGS. 1 or 2. The reformer 2 evaporates a raw material to be reformed such 
as the mixture of water and methanol delivered from the raw material tank 
1 and produces the hydrogen gas, which is a fuel, by a chemical reaction 
utilizing a reforming catalyst. The response time required for the 
reforming the raw material into the hydrogen gas in response to the 
instruction from the controller 14B is of the order of 0.5-2 minutes so 
that it is impossible to produce the required volume of the hydrogen gas 
within a time less than above. On the other hand, the response time of the 
load is of the order of microseconds, so that the response of the fuel 
cell output power P.sub.F lags behind in time with respect to the 
variations in load. 
Then, in the case the generator system utilizing a fuel cell is driven, it 
is necessary to control the generator system utilizing a fuel cell by 
considering the response characteristic of the reformer 2 and the load 9. 
Therefore, both the conventional generator systems utilizing a fuel cell 
have a problem that the output power delivered from the fuel cell to be 
applied to the load 9 cannot be controlled in response to the variations 
in load 9. 
SUMMARY OF THE INVENTION 
In view of the above, the primary object of the present invention is to 
provide a generator system utilizing a fuel cell which substantially solve 
the abovementioned problem so that the output derived from the fuel cell 
is controlled immediately in response to the variations in load. 
In the first aspect of the present invention, in a method for controlling a 
generator system having the fuel cell and a battery to which the output 
current from the fuel cell is supplied, the method comprises the steps of: 
performing a first adjustment of adjusting the supply of the power to a 
load by the battery in response to the sudden variation in load until the 
fuel cell responds to the sudden variation in load; and 
controlling the power supplied from the fuel cell while performing a second 
adjustment of adjusting the supply of the power to the load by the fuel 
cell after the fuel cell responds to the sudden variation in load. 
Here, the step of performing the first adjustment may include a step of 
converting the DC power delivered from the battery into the AC power which 
is supplied to the load. 
The response of the fuel cell in the case of the sudden variation in load 
may be delayed in time by an integrator. 
The step of performing the second adjustment may include a step of 
detecting the power to be supplied to the load. 
The power to be supplied to the load may be detected by an AC transducer. 
The step of performing the second adjustment may include a step of setting 
the power to be charged into the battery. 
The step of performing the second adjustment may include a step of 
converting the DC power delivered from the battery into the AC power which 
in turn is supplied to the load. 
The control of the adjustment of the supply of the power to the load from 
the fuel cell may be accomplished by a controller for auxiliary devices. 
The controller for auxiliary devices may comprise an arithmetic unit, a 
pluse width modulator and power elements. 
The arithmetic unit may comprise a function generator in the form of a CPU, 
an operational amplifier and one or more resistors. 
In the second aspect of the present invention, a generator system having a 
fuel cell and a battery to which the output current from the fuel cell can 
be supplied, comprises: 
a first adjustment means for adjusting the output current derived from the 
fuel cell; 
a second adjustment means for adjusting the output current generated in the 
fuel cell; 
a converter means for converting the DC power supplied from the first 
adjustment means and the battery into the AC power to be supplied to a 
load; 
a first detector means for detecting the power supplied to the load from 
the converter means; 
a second detector means fcr detecting the power supplied to the second 
adjustment means from the output side of the first adjustment means; 
a setting means for setting a power to be charged to the battery; 
an arithmetic means for calculating the detection signal representative of 
the power to be supplied to the load from the first detector means into 
the value prior to be supplied to the converter means; 
an adder means for adding the output signal derived from the arithmetic 
means, the setting signal derived from the setting means and the detection 
signal derived from the second detector means; 
a first controll means for controlling the first adjustment means in 
response to the output derived from the adder by delaying a time interval 
corresponding to the delay in response of the fuel cell; and 
a second controll means for controlling the second adjustment means in 
response to the output from the adder means. 
Here, the second adjustment means may include an air blower for supplying 
reaction air to the fuel cell. 
The converter means may have an inverter. 
Each of the first and second detector means may have an AC transducer. 
The arithmetic means may have a function generator in the form of a CPU and 
a divider. 
The first control means may have a fuel cell current detector, an 
integrator and an adder. 
The fuel cell current detector may have a Hall current transformer. 
The second control means may comprise an arithmetic unit, a pluse width 
modulator and power elements. 
The arithmetic unit may have a function generator in the form of a CPU, an 
operational amplifier and one or more resistors. 
With the above-described construction, the present invention controls the 
output delivered from the fuel cell in response to the variations in load 
so that the power can be delivered to the load in a stable manner. 
Furthermore, in response to the sudden increase in load, the battery backs 
up the fuel cell to supply the power to the load until the reformer 
responds, whereby a slow response of the reformer is compensated and when 
the power output from the fuel cell becomes sufficient enough to supply 
the load, an excess of the output power to be supplied to the load is 
supplied to the battery to charge the same so that the stable power supply 
to the load is ensured. 
The above and other objects, effects, features and advantages of the 
present invention will become more apparent from the following description 
of embodiments thereof taken in conjunction with the accompanying drawings 
.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 3 is a block diagram of one embodiment of the present invention. In 
FIG. 3, reference numeral 1 designates a raw material tank which stores 
therein, for instance, methanol and water. Reference numeral 2 denotes a 
reformer for reforming the raw material delivered from the raw material 
tank 1 through a raw material feed pump 3 to produce the reformed gas 
H.sub.2. The reformed gas H.sub.2 is delivered to a fuel electrode 4A of a 
fuel cell 4. Reference numeral 5 denotes an air blower for combustion for 
feeding to the reformer 2 air sufficient volume to continue the reforming 
reaction in the reactor 2. Reference numeral 6 denotes an air blower for 
reaction for delivering air to an air electrode of the fuel cell 4. 
Reference numeral 7 represents a fuel cell current detector which is 
adapted to detect the direct current delivered to a battery 8 and a load 9 
and may be a shunt or a Hall current transformer. In this embodiment, the 
Hall current transformer is used. The battery 8 is interconnected between 
a DC/DC converter 10 and an inverter 11 which converts the DC output 
delivered from the DC/DC converter 10 into an alternating current. 
Reference numeral 12 denotes a load current detector to detect the value 
of the current to be supplied to the load 9. The value of the current thus 
detected and the value of the voltage v.sub.0 are delivered to a load 
power arithmetic unit 13 to detect the value of the load power W.sub.PL 
which in turn is delivered as a load power signal 204. 
When the output from the inverter 11 is a single phase alternating current, 
WTT2-83A-12 (the product of DAiichi Keiki Co., Ltd.) may be used, but when 
the output from the inverter 11 is a three phase alternating current, 
WTT2-83A-33 (also the product of the above-mentioned company) may be used. 
The load power signal 204 is supplied to the inverter efficiency arithmetic 
unit 14 which in turn delivers an inverter efficiency signal 203. In this 
case, the inverter efficiency signal 203 is equal to an input power signal 
103 applied to the inverter 11. 
As shown in FIG. 4, the inverter efficiency arithmetic unit 14 comprises, 
for instance, a function generator in the form of a CPU 14A and a divider 
14B. The function generator 14A is so designed and constructed the 
.eta..sub.INV +.intg.W.sub.PL is obtained in response to a predetermined 
efficiency curve or an efficiency curve obtained from the test data of the 
inverter 11, so that .eta..sub.INV is obtained in response to the load 
power W.sub.PL. Instead of obtaining .eta..sub.INV in the manner described 
above, it may be obtained in accordance with the sequence as shown in FIG. 
5. More particularly, when W.sub.PL (that is, the value represented by the 
signal 204) is detected to be higher than 1% in first step S1, the 
operation proceeds to the second step, but when it is 1% or less, 
.eta..sub.INV =0. Same steps are repeated to detect .eta..sub.INV until 
step S99. When W.sub.INV is detected to exceed 99% in step S99, 
.eta..sub.INV becomes 100%. 
.eta..sub.INV obtained from the function generator 14A is inputted to the 
divider 14B, so that an inverter efficiency signal 203 representative of 
W.sub.PL /.eta..sub.INV =P.sub.INV is obtained. Here, P.sub.INV represents 
the input power applied to the inverter 11. 
Again in FIG. 3, reference numeral 15 represents a device for setting a 
voltage to be applied to the battery and is composed of, for instance, a 
variable resistor to set the value of the power to be supplied to the 
battery; and 16, a power arithmetic unit for auxiliary devices to 
calculate the power which is delivered from the DC/DC converter 10 to the 
controller for auxiliary devices 21 to be described in more detail 
hereinafter. The value of the power for auxiliary devices is detected in 
response to the signals representative of the value of the current 
detected by the current detector for auxiliary devices 16A and the value 
of the voltage .sub.vB. The power arithmetic unit for the auxiliary 
devices 16 may be of the same type of the load power arithmetic unit 13. 
Applied to an adder 17 are the auxiliary power signal 302 derived from the 
arithmetic unit 16, an inverter efficiency signal 203 delivered from the 
inverter efficiency arithmetic unit 14 and the battery charging power 
signal 301 delivered from the device 15 for setting a voltage to be 
applied to the battery, so that an addition signal 202 is obtained and is 
equal to the output signal 102 representative of the voltage vB delivered 
from the DC/DC converter 10. In response to the addition signal 202, the 
stepped-up voltage efficiency arithmetic unit 18 calculates a stepped-up 
voltage efficiency signal 201 which is equal to the output signal 101 and 
is applied to a divider 19 and then an integrator 20, so that a fuel cell 
output current command signal I.sub.F is obtained. 
The stepped-up voltage efficiency arithmetic unit 18 may be composed of, 
for instance, a function generator 18A in the form of a CPU as shown in 
FIG. 4. The function generator 18A generates a function of .eta..sub.CH 
=.intg. (signal 202) based upon a predetermined efficiency curve or an 
efficiency curve obtained from the test data and in response to the value 
(202) of the signal 202.eta..sub.CH is obtained. Instead of obtaining the 
value .eta..sub.CH in the manner described above, it may be obtained in 
accordance with the flowchart as shown in FIG. 6. In the latter case, in 
step S1 when the value (202) of the signal 202 is detected to be 1% or 
less, the value of .eta..sub.CH becomes zero. If the value (202) exceeds 
1%, the program proceeds to the next step. The same operation is repeated 
until step S99 to detect the value (202) of the signal 202. In step S99, 
when the value (202) of the signal 202 is detected to exceed of 99%, the 
value of .eta..sub.CH is defined as 100 %. The value .eta..sub.CH thus 
obtained is delivered to a divider 19, so that the fuel cell output 
current signal 205 representing P.sub.CH /.eta..sub.CH =P.sub.F. 
The reason why the divider 19 is used is that the output delivered from the 
fuel cell 4 is dependent on the output current thereof. More particularly, 
the hydrogen gas produced in the reformer 2 is equal in volume to the 
hydrogen gas supplied to the fuel cell 4 and the output current derived 
from the fuel cell 4 is dependent on the volume of the hydrogen gas. 
It follows therefore that the signal 201 representative of the fuel cell 
output power is divided by a signal 303 representative of the fuel cell 
output voltage V.sub.F, the fuel cell output current signal 205 which is 
required for generating a fuel cell output current command signal I.sub.F 
can be obtained. The integrator 20 is provided in order to delay the 
signal 205 by an optimum time interval for generating the fuel cell output 
current command signal I.sub.F in response to the response time (of the 
order of 0.5-2 minutes) of the reformer 2. The function of the 
above-described circuits 13, 14, 16, 17, 18, 19 and 20 may be accomplished 
by the microprocessor. 
The fuel cell output current instruction signal I.sub.F thus obtained is 
applied to a controller 21 for the auxiliary devices 3, 5 and 6 which may 
be composed of a microprocessor and in response to the command signal 
I.sub.F, the raw material feed pump 3, the air blower for combustion 5 and 
the blower for reaction 6 are controlled so that the output current 
delivered from the fuel cell 4 itself can be controlled. 
FIG. 7 is a block diagram of the controller 21. Reference numerals 31, 32 
and 33 represent arithmetic units, respectively, which carry out the 
calculations in order to control the feed pump 3, the air blower for 
combustion 5 and the air blower for reaction 6, respectively. FIG. 8 is a 
block diagram of the arithmetic unit 31 and FIG. 9 shows the control 
procedure carried out by the arithmetic unit 31. 
In FIG. 8, reference numeral 31A denotes a function generator in the form 
of a CPU (Central Processing Unit); 31B, an operational amplifier; and 
31C, a resistor. The arithmetic unit 31 is so designed and constructed 
that the function generator 31A generates a desired function V.sub.P in 
response to the value of the I.sub.F delivered from the integrator 20. 
The mode of operation of the arithmetic unit 31 will be described with 
reference to the flowchart shown in FIG. 9. In first step S.sub.l, it is 
detected whether or not the value of the current I.sub.F derived from the 
integrator 20 is in excess of 1% and when the detected current is 1% or 
less, a voltage signal V.sub.P (=V.sub.P1) is supplied to a pulse width 
modulator 34 (FIG. 7). However, when the value of the current I.sub.F 
exceeds 1%, the operation proceeds to next step S2 in order to detect 
whether or not the value of the current I.sub.F is in excess of 2%. In 
like manner, the value of the current IF is sequentially detected until 
last step S(n-1). The detected voltage signals V.sub.P are applied to the 
pulse width modulator 34. 
So far the case of obtaining the voltage signal V.sub.P for energizing the 
feed pump 3 has been described, the voltage signal V.sub.B1 for energizing 
the air blower for combustion 5 and the voltage signal V.sub.B2 for 
energizing the air blower for reaction 6 are obtained in a manner 
substantially similar to that described above. 
The voltages V.sub.P, V.sub.B1 and V.sub.B2 are not linearly proportional 
to the value of the current I.sub.F and they can be calculated by the CPU 
31A as V.sub.P =f.sub.1.I.sub.F, V.sub.B1 =f.sub.2.I.sub.F and V.sub.B2 
=f.sub.3.I.sub.F. 
In FIG. 7, reference numerals 34, 35 and 36 designate pulse width 
modulators, respectively, each comprising an oscillator 34A (35A, 36A) for 
generating the saw tooth waveform signal, a comparator 348 (358, 36B) and 
a pulse generator 34C (35C, 36C). The comparator 34B (35B, 36B) is adapted 
to deliver the comparison output signal when the level of the saw tooth 
waveform signal exceeds the voltage signal derived from the arithmetic 
unit 31, (32, 33). Each of the pulse generators 34C, 35C and 36C generates 
a rectangular pulse in response to the output from its corresponding 
comparator. 
Reference numerals 37, 38 and 39 represent high power bipolar transistors 
or power elements in the form of a power MOS FET and are driven in 
response to the output pulses derived from the pulse generators 34C, 35C 
and 36C. 
The voltage signals V.sub.P, V.sub.B1 and V.sub.B2 derived from the 
arithmetic units 31, 32 and 33, respectively, are applied to the 
comparators 348, 358 and 36B, respectively. The pulse width derived from 
each of the pulse generators 34C, 35C and 36C is determined in response to 
the level of each corresponding voltage signal. The pulses generated by 
the pulse generators 34C, 35C and 36C are applied as the PWM signals to 
the corresponding power elements 37, 38 and 39, respectively. The 
frequency of the saw tooth waveform signal derived from each oscillator 
becomes a switching frequency of each corresponding power element 37 (38, 
39). 
The pulse generated by the pulse generators 34C, 35C and 36C have a narrow 
pulse duration when the output power delivered from the fuel cell 4 is 
low; that is, when the value of the current I.sub.F is low, so that the 
time interval when the power elements 37, 38 and 39 are on is short. As a 
result, the rotational speeds of the motors (not shown) for driving the 
feed pump 3, the air blower for combustion 5 and the air blower for 
reaction 6 become slower so that it suffices to supply the raw material 
and air in small amounts. On the other hand, when the output power derived 
from the fuel cell 4 is high, the pulse width of the pulses generated by 
the pulse generators 34C, 35C and 36C are increased, so that the 
rotational speeds of the motors for driving the feed pump 3, the air 
blower for combustion 5 and the air blower for reaction 6 becomes faster 
and the amounts of the raw material and air to be supplied are increased. 
Therefore, because of the switching operations by the power elements in 
response to the PWM signals delivered from the pulse width modulators 34, 
35 and 36, the voltage v.sub.P, v.sub.B1 and v.sub.B2 applied to the 
driving motors for driving the feed pump 3, the air blower for combustion 
5 and the air blower for reaction 6 are varied so that it becomes possible 
to control the feed pump 3, the air blower for combustion 5 and the air 
blower for reaction 6. 
The fuel cell output current command signal I.sub.F derived from the 
integrator 20 and the output signal i.sub.F derived from the fuel cell 
current detector 7 are added by an adder 22 and the resultant signal or 
the control signal 105 is applied to the DC/DC converter 10 through the 
fuel cell current regulator 23 in the form of an amplifier. The DC/DC 
converter 10 is interconnected between the fuel cell 4 and the battery 8 
and in response to the control signal 105, determines the optimum values 
of the output currents supplied from the fuel cell 4 to the battery 8 and 
the load 9. 
In the embodiment just described above, the power from the battery 8 
discharges the power to the load 9 in response to the increase in load 9 
and the discharged direct current is inverted into the AC by the inverter 
11 and then applied to the load 9. During the power is derived from the 
battery 8 to the load 9 in the manner described above, the integrator 20 
responds to determine an optimum time delay so that the output current 
from the fuel cell 4 is controlled in response to the variation in the 
load 9. When the supply of the power to the load 9 reaches the steady 
state, the power is derived from the fuel cell 4 to the auxiliary devices 
such as the battery 8, the raw material feed pump 3 and so on and to the 
load 9. 
As described above, according to the present invention, in response to the 
variations in load, the output from the fuel cell is controlled so that 
the stable output can be supplied to the load. 
Furthermore, in response to the sudden increase in load, the back-up by the 
battery is available so that until the reformer responds, the battery 
supplies the power to the load, thereby compensating for a slow response 
to the reformer. After the output from the fuel cell itself to be supplied 
to the load 9 reaches a sufficient level, an excess of the output power to 
be delivered to the load is supplied to the battery to charge the same. As 
a result, the stable output can be always supplied to the load. 
The invention has been described in detail with respect to preferred 
embodiments, and it will now be apparent from the foregoing to those 
skilled in the art that changes and modifications may be made without 
departing from the invention in its broader aspects, and it is the 
invention, therefore, in the appended claims to cover all such changes and 
modifications as fall within the true spirit of the invention.