U.S. patent application number 09/814827 was filed with the patent office on 2001-09-27 for control system and control method of combined system having secondary battery and generator.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Abe, Takaaki.
Application Number | 20010024105 09/814827 |
Document ID | / |
Family ID | 18601535 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024105 |
Kind Code |
A1 |
Abe, Takaaki |
September 27, 2001 |
Control system and control method of combined system having
secondary battery and generator
Abstract
A control system and a control method of a combined system
having a secondary battery 15 and a fuel cell power generation
system 12 are disclosed. wherein a vehicle controller 20 repeats a
secondary battery-charging running mode wherein electric power
output of the power generation system 12 is supplied to the
secondary battery 15 and a motor 11, and a secondary
battery-discharging running mode wherein electric power output of
the power generation system 12 and electric power output discharged
from the secondary battery 15 are supplied to the motor 11. In such
a control, the amounts of electric power output of the power
generation system 12 and electric power output discharged from the
secondary battery 15 are set to values to provide the maximum total
efficiency that is computed in conjunction with a charging
efficiency of the secondary battery 15 during the secondary
battery-charging running mode.
Inventors: |
Abe, Takaaki; (Kanagawa-ken,
JP) |
Correspondence
Address: |
Glenn Law
FOLEY & LARDNER
Suite 500
3000 K Street, N.W.
Washington
DC
20007-5109
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
18601535 |
Appl. No.: |
09/814827 |
Filed: |
March 23, 2001 |
Current U.S.
Class: |
320/132 |
Current CPC
Class: |
H02J 7/1415 20130101;
B60L 58/40 20190201; Y02T 90/40 20130101; H02J 7/1438 20130101;
Y02T 10/70 20130101; B60L 58/10 20190201; Y02T 10/72 20130101; B60L
2210/10 20130101 |
Class at
Publication: |
320/132 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2000 |
JP |
P2000-85155 |
Claims
What is claimed is:
1. A control system controlling a combined system having a
secondary battery and an electric power generator, and serving as a
power supply for a load, the secondary battery being charged by use
of the electric power generator, the control system comprising: a
charging efficiency calculating section calculating a charging
efficiency of the secondary battery in conjunction with an electric
power output of the electric power generator; a total efficiency
data calculating section calculating total efficiency data in
response to a demanded electric power of the load; and an electric
power supply controlling section controlling allocation of an
electric power output of the secondary battery and an electric
power output of the electric power generator both to be supplied to
the load; wherein the electric power supply controlling section
sets an electric power output of the secondary battery and an
electric power output of the electric power generator both to be
supplied to the load on the basis of the charging efficiency and
the total efficiency data.
2. A control system according to claim 1, wherein the total
efficiency data calculating section calculates the total efficiency
data in response to the demanded electric power of the load, on the
basis of an electric power generation efficiency of the electric
power generator and a discharging efficiency of the secondary
battery, for each charging efficiency of the secondary battery.
3. A control system according to claim 2, wherein the total
efficiency corresponds to a total operating efficiency obtained
when an electric power output is produced by the electric power
generator, the secondary battery is charged by the electric power
output, and the secondary battery is discharged.
4. A control system according to claim 1, wherein the electric
power supply controlling section sets the electric power output of
the secondary battery and the electric power output of the electric
power generator both to be supplied to the load so as to provide a
maximum total efficiency with respect to corresponding one of the
charging efficiency of the second battery while using the total
efficiency data.
5. A control system according to claim 1, wherein the charging
efficiency calculating section calculates the charging efficiency
of the secondary battery in such a manner that an average charging
efficiency of the secondary battery is obtained when the secondary
battery is charged with an electric power output of the electric
power generator.
6. A control system according to claim 1, wherein the secondary
battery and the electric power generator are installed in a vehicle
and the load includes an electric motor of the vehicle driving the
same, and wherein the electric power supply controlling section
controls the allocation of the electric power output of the
secondary battery and the electric power output of the electric
power generator in correspondence with a first running mode wherein
the electric power output of the electric power generator is
supplied to the load for driving the same and to the second battery
for charging the same, and with a second running mode wherein the
electric power output of the electric power generator and an
electric power output discharged from the secondary battery are
supplied to the load for driving the same.
7. A control system according to claim 6, wherein the electric
power supply controlling section sets the electric power output of
the secondary battery and the electric power output of the electric
power generator both to be supplied to the load on the basis of the
charging efficiency and the total efficiency data in the first
running mode.
8. A control system according to claim 6, wherein the charging
efficiency calculating section calculates the charging efficiency
of the secondary battery in conjunction with the electric power
output of the electric power generator in the second running
mode.
9. A control system controlling a combined system having a
secondary battery and an electric power generator, and serving as a
power supply for a load, the secondary battery being charged by use
of the electric power generator, the control system comprising:
means for calculating a charging efficiency of the secondary
battery in conjunction with an electric power output of the
electric power generator; means for calculating total efficiency
data in response to a demanded electric power of the load; and
means for controlling allocation of an electric power output of the
secondary battery and an electric power output of the electric
power generator both to be supplied to the load, while setting an
electric power output of the secondary battery and an electric
power output of the electric power generator both to be supplied to
the load on the basis of the charging efficiency and the total
efficiency data.
10. A method of controlling a combined system having a secondary
battery and an electric power generator, and serving as a power
supply for a load, the secondary battery being charged by use of
the electric power generator, the method comprising: calculating a
charging efficiency of the secondary battery in conjunction with an
electric power output of the electric power generator; calculating
total efficiency data in response to a demanded electric power of
the load; and controlling allocation of an electric power output of
the secondary battery and an electric power output of the electric
power generator both to be supplied to the load, while setting an
electric power output of the secondary battery and an electric
power output of the electric power generator both to be supplied to
the load on the basis of the charging efficiency and the total
efficiency data.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a control system and
control method of a combined system having a secondary battery and
a generator and, more particularly, to allocation control of such a
combined system.
[0002] In recent years, various research and development have been
attempted to provide an electric vehicle installed with a secondary
battery and a generator (electric power generator) as a combined
power source for a drive motor and accessories with a view to
improving an energy efficiency of the combined power source.
[0003] In such an electric vehicle, a fuel cell power generation
system has been selected as an electric power generator to be
installed.
[0004] In vehicles equipped with fuel cell power generation systems
and secondary batteries, there are two types of running modes.
[0005] One typical example is a first mode wherein electric power
output of the fuel cell power generation system is supplied to the
drive motor, the accessories and the secondary battery, with the
first mode being substantially continued even when the vehicle
comes to a stop. This mode will be hereinafter referred to as a
secondary battery-charging running mode.
[0006] The other mode is to supply both electric power outputs of
the secondary battery and the electric power generator to the drive
motor and the accessories, while the secondary battery being not
charged by the electric power generator. This mode will be
hereinafter referred to as a secondary battery-discharging running
mode.
[0007] In such a vehicle having these two running modes, it is
required to increase a total efficiency of the fuel cell power
generation system and the secondary battery in respective running
modes with a view to improving an energy consuming performance.
SUMMARY OF THE INVENTION
[0008] In view of the investigation by the present inventor, the
secondary battery and the fuel cell power generation system have
operating efficiencies of which characteristics are shown in FIG.
4.
[0009] Since the secondary battery has a Joule's loss due to
internal resistance, the operating efficiency will decrease as the
amount of electric power output to be charged to or to be
discharged from the secondary battery increases as shown by a curve
a representing a case for discharging mode and a curve b
representing another case for charging mode.
[0010] The fuel cell power generation system also has a similar
characteristic in that it has the same Joule's loss as that of the
secondary battery and, in addition, it is suffered from the
operating efficiency of a compressor for supplying oxygen to the
fuel cell, with a resultant decrease in the operating efficiency
with the increase in the amount of electric power generation output
as shown by a curve c in FIG. 4.
[0011] For the above reasons, in the event that electric power is
supplied to the drive motor and the accessories at a constant rate
in the secondary battery-charging running mode, the amount of
electric power output of the fuel cell power generation system is
caused to increase with the increase in the amount of electric
power to be charged to the secondary battery, resulting in a
decreased total efficiency of the combined system.
[0012] Note should be undertaken here that the total efficiency is
typically meant by a total operating efficiency that is obtained
when the fuel cell power generation system is operated with fuel,
at least a part of the electric power output of the fuel cell power
generation system is used for charging the secondary battery, and
sequentially the secondary battery is discharged.
[0013] In order to avoid a decrease in the total efficiency, it has
heretofore been proposed to employ an operating method that
decreases the amount of electric power to be charged to the
secondary battery when demanded electric power is increased for the
drive motor and the accessories.
[0014] FIG. 8 shows the relationship between an electric power
generation efficiency of the fuel cell power generation system, a
discharging efficiency of the secondary battery and the total
efficiency with respect to electric power output of the fuel cell
power generation system (abscissas of FIG. 8). Here, various curves
are derived under a condition wherein demanded electric power for
the drive motor and the accessories is 60 KW.
[0015] In the secondary battery-discharging running mode, since the
sum of electric power output of the fuel cell power generation
system and electric power discharged from the secondary battery is
supplied to the drive motor and the accessories, the fuel cell
power generation system will generate electric power output at a
reduced power generation efficiency with the increase in the amount
of electric power output produced by the fuel cell power generation
system, as shown by a curve a in FIG. 8. In contrast, since the
amount of electric power to be discharged from the secondary
battery decreases with the increase in the amount of electric power
output of the fuel cell power generation system, the discharging
efficiency of the secondary battery increases as shown by a curve b
in FIG. 8.
[0016] This causes the total efficiency of electric power outputs
to be supplied from the fuel cell power generation system and the
secondary battery to vary along a curve c shown in FIG. 8, with a
resultant maximum total efficiency owing to particular
relationships between the amount of electric power output of the
fuel cell power generation system and the amount of electric power
output to be discharged from the secondary battery.
[0017] Based on the above particular relationships, the amount of
each electric power output of the secondary battery and the fuel
cell power generation system is set to respective values for
achieving the maximum total efficiency.
[0018] The charging efficiency of the secondary battery varies in
the secondary battery-charging running mode as shown in FIG. 9 by
controlling the secondary battery. Also, the charging efficiency of
the secondary battery, which substantially corresponds to a more
actual charging efficiency of the secondary battery when the
secondary battery is charged in the combined system, is obtained by
multiplying the power generation efficiency of the fuel cell power
generation system and a charging efficiency of the secondary
battery, both of which are obtained based on actual measurements or
the like. The axis of abscissas represents the demanded electric
power of the drive motor and the accessories.
[0019] In FIG. 9, a curve a indicates the charging efficiency of
the secondary battery when the rate of charging the second battery
is held constant, a curve b indicates the charging efficiency of
the secondary battery when the rate of charging the secondary
battery is varied in proportionate to the amount of electric power
to be supplied to the drive motor and the accessories, and a curve
c indicates the charging efficiency of the secondary battery
wherein, when the charging efficiency of the secondary battery is
lowered to a given level, the amount of electric power to be
charged to the secondary battery is decreased to prevent the
charging efficiency of the secondary battery from being lower than
the given level.
[0020] Further, while the secondary battery is charged with
generative power produced by the drive motor during deceleration of
the vehicle, the power generation efficiency of the fuel cell power
generation system has no relation to the secondary battery and the
charging efficiency of the secondary battery to which the
generative power is charged varies along a curve d shown in FIG.
9.
[0021] In the secondary battery-charging running mode, it has been
attempted to combines various controls with a view to improving
both the energy consuming performance of the vehicle and the
performance of electric power.
[0022] By the way, a further research and development revealed
that, even when the control is set in a manner discussed above so
as to achieve the maximum total efficiency in the secondary
battery-discharging running mode, it is difficult to obtain the
maximum total efficiency throughout various running conditions of
the vehicle. That is, in the above propsed method, the maximum
total efficiency cannot be obtained throughout the whole operating
conditions wherein electrical energy is produced by the fuel cell
power generation system with the use of fuel and is charged to the
secondary battery, which subsequently discharges electric power
output.
[0023] Here, a reference will be given to FIG. 10, which shows
various curves for total efficiencies which are obtained when the
amount of electric power to be supplied to the drive motor and the
accessories in the secondary battery-discharging running mode is 60
KW. The axis of abscissas represents the electric power output of
the fuel cell power generation system and plural curves are plotted
for each efficiency in cases where the secondary battery is charged
in the secondary battery-charging running mode.
[0024] As will be apparent from FIG. 10, the total efficiency with
respect to electric power output of the fuel cell power generation
system (abscissas of FIG. 10) varies responsive to the efficiencies
attained when the secondary battery is charged. For example, in the
event that the efficiency is 70% when the secondary battery is
charged, the maximum level of the total efficiency becomes 65% as
shown by the curve B.
[0025] In the case that in a control system where a charging
efficiency of the secondary battery is not considered, it is
required for the charging efficiency of the secondary battery to
reach 100% on a characteristic curve such that the maximum total
efficiency is obtained when electric power output of the fuel cell
power generation system is 20 KW and electric power output
discharged from the secondary battery is 40 KW (i.e., 60 KW-20
KW).
[0026] However, assuming that the charging efficiency of the
secondary battery is 70%, the maximum total efficiency is obtained
at a point B in FIG. 10 under the conditions wherein electric power
output of the fuel cell power generation system is 36 KW and
electric power output discharged from the secondary battery is 24
KW (i.e., 60 KW-36 KW). In this event, the total efficiency at the
point A, wherein electric power output of the fuel cell power
generation system is 20 KW and electric power output discharged
from the secondary battery is 40 KW, becomes smaller than the
maximum total efficiency that would be expected.
[0027] Thus, the charging efficiency of the secondary battery
varies in the secondary battery-charging running mode responsive to
the running conditions of the vehicle and the total efficiency has
the maximum point that varies responsive to the charging efficiency
of the secondary battery in the secondary battery-discharging
running mode.
[0028] It is therefore an object of the present invention to
overcome the above situations investigated by the present inventor
and to provide a control system and a control method of a combined
system having a secondary battery and an electric power generator
to provided the maximum total efficiency at substantially all times
throughout operating conditions wherein, even when a charging
efficiency of the secondary battery varies, the electric power
generator generates electric energy that is charged to the
secondary battery which then discharges electric power output.
[0029] In the present invention, a control system controls a
combined system having a secondary battery and an electric power
generator, and serving as a power supply for a load, wherein the
secondary battery is charged by use of the electric power
generator. The control system is provided with: a charging
efficiency calculating section calculating a charging efficiency of
the secondary battery in conjunction with an electric power output
of the electric power generator; a total efficiency data
calculating section calculating total efficiency data in response
to a demanded electric power of the load; and an electric power
supply controlling section controlling allocation of an electric
power output of the secondary battery and an electric power output
of the electric power generator both to be supplied to the load.
The electric power supply controlling section sets an electric
power output of the secondary battery and an electric power output
of the electric power generator both to be supplied to the load on
the basis of the charging efficiency and the total efficiency
data.
[0030] In other words, a control system controlling such a combined
system of the present invention is provided with: means for
calculating a charging efficiency of the secondary battery in
conjunction with an electric power output of the electric power
generator; means for calculating total efficiency data in response
to a demanded electric power of the load; and means for controlling
allocation of an electric power output of the secondary battery and
an electric power output of the electric power generator both to be
supplied to the load, while setting an electric power output of the
secondary battery and an electric power output of the electric
power generator both to be supplied to the load on the basis of the
charging efficiency and the total efficiency data.
[0031] Besides, a method of controlling such a combined system of
the present invention calculates a charging efficiency of the
secondary battery in conjunction with an electric power output of
the electric power generator, calculates total efficiency data in
response to a demanded electric power of the load, and controls
allocation of an electric power output of the secondary battery and
an electric power output of the electric power generator both to be
supplied to the load, while setting an electric power output of the
secondary battery and an electric power output of the electric
power generator both to be supplied to the load on the basis of the
charging efficiency and the total efficiency data.
[0032] Other and further features, advantages, and benefits of the
present invention will become more apparent from the following
description taken in conjunction with the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a block diagram for illustrating a preferred
embodiment of a control system according to the present invention,
with the control system being shown as applied to a fuel cell
powered vehicle;
[0034] FIG. 2 is a general flow diagram for illustrating the basic
sequence of control achieved by the control system shown in FIG.
1;
[0035] FIG. 3 shows a flow diagram for illustrating the basic
sequence for computing electric power output discharged by a
secondary battery and electric power output produced by a fuel cell
power generation system;
[0036] FIG. 4 is a graph for illustrating the characteristic of
charging and discharging efficiencies of an secondary battery and
an efficiency of electric power output of an fuel cell power
generation system investigated by the present inventor;
[0037] FIG. 5 is a graph for illustrating the characteristics of
total efficiencies plotted for respective charging efficiencies of
the secondary battery in conjunction with the amounts of electric
power output of the fuel cell power generation system;
[0038] FIG. 6 is a graph for illustrating the characteristics of
total efficiencies plotted for respective charging efficiencies of
the secondary battery in conjunction with the amounts of electric
power outputs from the fuel cell power generation system;
[0039] FIG. 7 is a graph for illustrating the characteristics of
total efficiencies plotted for respective charging efficiencies of
the secondary battery in conjunction with the amounts of electric
power outputs from the fuel cell power generation system;
[0040] FIG. 8 is a graph for illustrating the characteristics of an
efficiency of electric power output of a fuel cell power generation
system, and a charging efficiency and the total efficiency of a
secondary battery during a secondary battery-discharging running
mode investigated by the present inventor;
[0041] FIG. 9 is a graph for illustrating the characteristics of
the charging efficiencies of the secondary battery for each control
mode during the secondary battery-charging running mode
investigated by the present inventor; and
[0042] FIG. 10 is a graph showing the characteristics for
illustrating influences of the charging efficiencies of the
secondary battery with respect to the respective total efficiencies
during the secondary battery-discharging running mode investigated
by the present inventor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Hereinafter, a control system and control method of a
combined system having a secondary battery and an electric power
generator according to one embodiment of the present invention will
be described in detail in reference to the attached drawings.
[0044] Referring to FIG. 1, there is shown a preferred embodiment
of a control system and control method of a combined system having
a secondary battery and an electric power generator according to
the present invention, with the control system being shown as
applied to a fuel cell powered vehicle FV.
[0045] In FIG. 1, the fuel cell powered vehicle FV includes an
electric motor 11 that serves as a drive source for driving wheels
10, an electric power supply including a fuel cell power generation
system 12 and a secondary battery 15, and a vehicle controller 20
that controls the fuel cell power generation system 12 and the
secondary battery 15 responsive to running conditions of the
vehicle.
[0046] The fuel cell power generation system 12 operates such that
it produces hydrogen gas by reforming fuel composed of methanol and
hydrogen is reacted with oxygen in a fuel cell to produce electric
power output.
[0047] The fuel cell power generation system 12 is connected
through a DC/DC converter 13 to an inverter 14, which converts a DC
output to an AC output which is applied to the electric motor 11
and auxiliary equipments or accessories 16 and is also connected
through the DC/DC converter 13 to the secondary battery 15.
[0048] The DC/DC converter 13 is connected to and controlled by a
vehicle controller 20, which serves to produces command signals to
switch-over between a first operating mode wherein electric power
output of the fuel cell power generation system 12 is supplied to
the electric motor 11, accessories 16 and the secondary battery 15
and a second operating mode wherein both electric power output of
the fuel cell power generation system 12 and electric power output
discharged from the secondary battery 15 are supplied to the
electric motor 11 and the accessories 16.
[0049] With such a control of power delivery, electric power output
of the fuel cell power generation system 12 is raised or lowered in
voltage and is supplied to the secondary battery 15 and to the
electric motor 11 and the accessories 16 through the inverter
14.
[0050] Electric power of the secondary battery 15 is supplied
through the DC/DC converter 13 to the inverter 14, from which AC
power output is supplied to the electric motor 11 and the
accessories 16. When the electric motor 11 generates generative
power output during deceleration of the vehicle, generative power
output is charged to the secondary battery 15 through the inverter
14 and the DC/DC converter 13.
[0051] The vehicle controller 20 is connected to an accelerator
pedal sensor 28 that detects a depressed displacement of an
accelerator pedal to produce an output signal indicative thereof,
and a rotation speed sensor 29 that detects rotational speed of the
electric power 11 to produce an output signal indicative thereof.
Thus, the vehicle controller 20 computes demanded amount of
electric power responsive to operating parameters such as depressed
displacement of the accelerator pedal and the rotational speed of
the motor 11.
[0052] The vehicle controller 20 is also connected to a voltage
sensor 21 that detects the total amount of output voltage of the
second battery 15 to produce a detection signal indicative thereof,
an electric current sensor 22 that detects electric current to
produce a detection signal indicative thereof, and a temperature
sensor 23 that detects temperature of the secondary battery 15 to
produce a detection signal indicative thereof. The vehicle
controller 20 computes the remaining capacity (state of charge) SOC
charged in the secondary battery 15, the amount of electric power
to be discharged, the amount of electric power to be charged, an
electrical discharging efficiency and an electrical charging
efficiency responsive to these detection signals.
[0053] Further, the vehicle controller 20 is also connected to a
voltage sensor 25 that detects the total voltage of electric power
output of the fuel cell power generation system 12 to produce a
detection signal indicative thereof, and an electric current sensor
26 that detects electric current of the fuel cell power generation
system 12 to produce a detection signal indicative thereof. The
vehicle controller 20 computes electric power generation efficiency
responsive to these detection signals.
[0054] Incidentally, a charging efficiency calculating section C1
of the vehicle controller 20 calculates the charging efficiency of
the secondary battery 15, a total efficiency data calculating
section C2 of the vehicle controller 20 calculates the total
efficiency data of the combined system having the secondary battery
15 and the fuel cell power generation system 12, and an electric
power supply controlling section C3 of the vehicle controller 20
controls the allocation of the electric power output of the
secondary battery 15 and the electric power output of the fuel cell
power generation system 12 as an electric power generator.
[0055] With such a structure of the fuel cell powered vehicle FV,
the control system of the invention repeatedly controls the fuel
cell power generation system 12 and the secondary battery 15 in "a
secondary battery-discharging running mode" wherein both electric
power output of the fuel cell power generation system 13 and
electric power output discharged from the secondary battery 15 are
supplied to the electric motor 11 and the accessories 16, while the
secondary battery 15 being not charged by the fuel cell power
generation system 12, and "a secondary battery-charging running
mode" wherein electric power output of the fuel cell power
generation system 12 is supplied to the electric motor 11 and the
accessories 16 and is also supplied to the secondary battery 15 for
charging the same, responsive to running conditions of the
vehicle.
[0056] Further, during deceleration of the vehicle, the electric
motor 11 produces generative power that is supplied to and charged
in the secondary battery 15.
[0057] Now, a control sequence of the vehicle controller 20 will be
described with reference to FIG. 2 which illustrates a general flow
diagram for illustrating the basic sequence of operation of the
vehicle controller 20.
[0058] At the start, i.e., when a key (not shown) is turned on in
step S101 for beginning operation of the vehicle, remaining
capacity SOC of the secondary battery 15 is computed on the basis
of the total output voltages of the secondary battery 15 in step
S102.
[0059] In step 103, "the secondary battery-discharging running
mode" is set in the vehicle controller 20.
[0060] In step 104, the running mode is again checked whether the
current running mode is in "the secondary battery-discharging
running mode" or in "the secondary battery-charging running
mode".
[0061] When the vehicle controller 20 is set in "the secondary
battery-discharging running mode", the operation goes to step 111
wherein it is checked whether the remaining capacity SOC of the
secondary battery 15 is greater than a lowermost preset value
SOC1.
[0062] When the remaining capacity SOC of the secondary battery 15
is greater than the lower limit SOC1, the operation goes to step
112 while continuously maintaining the vehicle controller in the
"secondary battery-discharging running mode", and electric power
output to be discharged from the secondary battery 15 and electric
power output to be generated by the fuel cell power generation
system 12 are computed on the basis of the demanded electric power
and the charging efficiency of the secondary battery 15 last
obtained in "the secondary battery-charging running mode". Note
should be undertaken that the charging efficiency of the secondary
battery 15 in an initial sequential flow is set to an initial
preset value of for, example, 90%.
[0063] In step 113, the DC/DC converter 13 is controlled such that
both electric power output discharged from the secondary battery 15
and electric power output of the fuel cell power generation system
12 are supplied to the electric motor 11 and the accessories
16.
[0064] In the next step 114, the remaining capacity SOC of the
secondary battery 15 is computed by calculating the total voltages
of the secondary battery 15 or total values of the discharged
electric current thereof, and the operation returns to the step
111.
[0065] In the step 111, when the remaining capacity SOC of the
secondary battery 15 is below the lower limit SOC1 of the preset
value, the operation returns to step 115 to prevent further
discharging of the secondary battery 15.
[0066] In step 115, the running mode is switched over to the "the
secondary battery-charging running mode", and the operation returns
to step 104.
[0067] In step 104, when the running mode is confirmed in "the
secondary battery-charging running mode", the operation goes to
step 121, wherein it is checked whether the remaining capacity of
the secondary battery 15 is below the upper limit SOC2 of the
preset value.
[0068] When the remaining capacity SOC of the secondary battery 15
is below the upper limit SOC2, "the secondary battery-charging
running mode" is continued and the operation goes to step 122.
[0069] In step 122, allocation of electric power output of the fuel
cell generation system 12 is set in electric power output demanded
by the electric motor and the accessories, and electric power to be
supplied to the secondary battery 15, within an allowable range
determined by given electric power generation efficiency of the
fuel cell generation system 12. In step 123, also, electric power
output is supplied to the electric motor 11 and the accessories 16
responsive to allocation of electric power generation and is also
supplied to the secondary battery 15 that is charged.
[0070] In step 124, the charging efficiency of the secondary
battery 15 is computed in a predetermined time sequence during a
time period when the secondary battery 15 is charged and, in step
125, an average charging efficiency of the secondary battery 15 is
obtained in correspondence with the predetermined time
sequence.
[0071] In step 126, further, remaining capacity SOC of the
secondary battery 15 is computed and the operation returns to step
121.
[0072] In step 121, when remaining capacity SOC of the secondary
battery 15 exceeds the upper limit SOC2, further charging of the
secondary battery 15 is not required and the operation returns to
step 127 wherein the running mode is set to "the secondary
battery-discharging running mode". Thereafter, the operation
returns to step 104.
[0073] FIG. 3 is a flow diagram for illustrating the basic sequence
of computing electric power output discharged from the secondary
battery 15 and electric power output generated by the fuel cell
power generation system 12 in step 112, in detail.
[0074] In initial step 131, the vehicle controller 20 computes
electric power output demanded by the electric motor 11 and the
accessories 16 on the basis of running conditions estimated by
calculating given operating parameters such as the depressed
displacement value detected by the accelerator pedal sensor 28.
[0075] In the next step 132, the total efficiency (total efficiency
data)in conjunction with the amount of electric power output
generated by the fuel cell power generation system 12 is computed
from demanded electric power output. Here, the total efficiency in
conjunction with the amount of electric power generation output of
the fuel cell power generation system 12 is derived as shown in
FIG. 5, while the charging efficiency of the secondary battery 15
being treated as the parameters, on the basis of the relationship
between electric power output discharged from the secondary battery
15 and an efficiency as shown by a curve a in FIG. 4 and the
relationship between electric power output of the fuel cell power
generation system 12 and an efficiency as shown by a curve c if
FIG. 4. Also, FIG. 5 shows the same characteristic curves for the
charging efficiencies, when the demanded electric power is 60 KW,
as shown in FIG. 10, with respect to electric power output of the
fuel cell power generation system (abscissas of FIG. 10).
[0076] In the succeeding step 133, electric power output to be
generated by the fuel cell power generation system 12 and electric
power output to be discharged from the secondary battery 15 are
computed to obtain the maximum total efficiency. This is obtained
by computing electric power output to be generated by the fuel cell
power generation system 12 to provide the maximum value in the
characteristic curve which corresponds to average charging
efficiency of the secondary battery 15 that has been obtained in
the secondary battery-charging running mode as shown in FIG. 5.
Also, it is to be noted that electric power output to be discharged
from the secondary battery 15 equals to the sum wherein electric
power output of the fuel cell power generation system 12 is
subtracted from demanded electric power output.
[0077] With such a computation, when demanded electric power is 60
KW and charging efficiency is 70%, the total efficiency is improved
from a point A of 62%, which is obtained in a control method
disregarding charging efficiency of the secondary battery, to a
point B of 65% as viewed from graph of FIG. 5.
[0078] Similarly, FIGS. 6 and 7 show the total efficiencies of a
case wherein demanded electric power is 40 KW and a case wherein
demanded electric power is 20 KW, with respect to electric power
output of the fuel cell power generation system (each abscissas
thereof) respectively. As seen in FIG. 6, when the charging
efficiency of the secondary battery 15 is 70%, the total efficiency
is improved from a point C of 62% to a point D of 69%. As shown in
FIG. 7, the total efficiency is improved from a point E of 65% to a
point F of 73%. In the event that the charging efficiency of the
secondary battery 15 is below 70%, the total efficiency is improved
in a further wide range.
[0079] Incidentally in the illustrated embodiment, the
characteristic data as shown in each of FIGS. 4 to 7 have been
stored in memories (not shown) in the controller 20 as a table or
the like.
[0080] The aforesaid steps 124 and 125 are executed by the charging
efficiency computing section C1, the steps 131 and 132 are executed
by the total efficiency data computing section C2 and the steps 133
and 113 are executed by the electric power supply controlling
section C3.
[0081] With such a structure of the preferred embodiment discussed
above, the secondary battery-discharging running mode and the
secondary battery-charging running mode are alternately repeated so
as to maintain the remaining capacity of the secondary battery 15
in a range between the preset values SOC1 and SOC2 and, during this
time interval, electric power output of the fuel cell power
generation system 12 and electric power output discharged from the
secondary battery 15 are set to respective values so as to maintain
the efficiency computed in conjunction with charging efficiency of
the secondary battery 15 in the secondary battery-charging running
mode at the maximum level. Accordingly, it is possible to highly
improve the total efficiency throughout the whole operating
conditions wherein electric power output generated by the fuel cell
power generation system 12 using fuel is charged to the secondary
battery 15 and, in subsequent step, the secondary battery 15
discharges electric power output, to a higher level.
[0082] While, in the illustrated embodiment, the load has been
shown and described as comprising the electric motor 11 and the
accessories 16, the load is not limited hereto.
[0083] Further, although the secondary battery-discharging running
mode and the secondary battery-charging running mode have been
described as being alternately repeated so as to maintain the
remaining capacity of the secondary battery 15 within a range
between the preset values SOC1 and SOC2, the aforesaid two running
modes may be switched over in suitable sequences, if desired, as
long as the remaining capacity is maintained in the range between
the capacity levels SOC1 and SOC2.
[0084] Also, although the fuel cell power generation system has
been described as the type wherein methanol is reformed to produce
hydrogen which is supplied to the fuel cell, the fuel cell power
generation system is not limited thereto but may be modified such
that gasoline is used or hydrogen gas is directly supplied to the
fuel cell to produce electrical power output.
[0085] In addition, although the remaining capacity SOC of the
secondary battery 15 has been described as being computed in steps
102, 114 or 126 in the flow chart, the remaining capacity may be
computed on the basis of the total voltage of the secondary battery
15 or may be read out from the remaining capacity of the secondary
battery 15 that has been stored in a memory (not shown) in the
controller 20 when the key is off from the fuel cell powered
vehicle.
[0086] Further, the initial value of the charging efficiency of the
secondary battery 15 in initial sequences from the key-on operation
to step 112 may be similarly read out from the charging efficiency
of the secondary battery 15 that has been stored in the last
key-off operation in a memory (not shown) in the controller 20.
[0087] Further, although parameters such as the remaining capacity
SOC of the secondary battery 15 and the temperature of the
secondary battery 15 are omitted from the charging and discharging
efficiencies of the secondary battery 15 in FIG. 4, since the
charging and discharging efficiencies vary responsive to the
remaining capacity SOC and the temperature of the secondary battery
15, characteristic curves for the charging and discharging
efficiencies of the secondary battery 15 may be prepared in
conjunctions with the remaining capacity SOC and the temperature,
respectively, resulting in a further improved precise control.
[0088] While the electric power generation system has been shown
and described, in the illustrated embodiment, as comprising the
fuel cell power generating system, the present invention is not
limited thereto and the present invention may also be applied to a
case wherein the electric power generator comprises an electrical
power generator of the type driven by an engine.
[0089] According to a feature of the present invention, since the
amounts of electric power outputs of the secondary battery and the
electric power generator to be supplied to the load are set in
conjunction with the charging efficiency of the secondary battery
in the secondary battery-charging running mode, allocation of
electric power of the secondary battery and electric power of the
electric power generator with respect to the demanded electric
power is determined so as to improve the total efficiency
throughout the operating conditions wherein the secondary battery
is charged and is then discharged. With this determination, energy
consuming efficiency is improved even when the electric power
generator includes any types of electric power generators such as a
fuel cell power generation system or an electric power generator
driven by an engine.
[0090] According to another feature of the present invention, since
the total efficiency data is computed for each charging efficiency
responsive to the demanded electric power and respective electric
power outputs of the secondary battery and the electric power
generator are set to respective values to provide the maximum total
efficiency in the whole total efficiency data corresponding to the
actual charging efficiencies, it is possible to provide the maximum
total efficiency throughout an operating sequence wherein the
secondary battery is charged and is then discharged.
[0091] According to another feature of the present invention, since
the control system employs an average value of charging
efficiencies obtained when the secondary battery is charged with
electric power generated by the electric power generator, it is
possible to reduce in load for computing the amounts of electric
power of the secondary battery and electric power of the electric
power generator to be supplied to the load responsive to the
charging efficiencies as compared to a case wherein a computing
step is achieved by directly using efficiencies that varies with
variations in time.
[0092] According to another feature of the present invention, in a
vehicle having a drive motor adapted to be driven by electric power
outputs of the secondary battery and the electric power generator,
it is possible to maintain the remaining capacity of the secondary
battery within a suitable range for thereby improving the total
efficiency by alternately repeating the first running mode wherein
the vehicle runs during charging the secondary battery and the
second running mode wherein the vehicle runs during discharging the
secondary battery. With such operation, the secondary battery is
effectively utilized and deterioration of the secondary battery is
prevented, with a resultant decrease in fuel consumption.
[0093] The entire content of a Patent Application No. TOKUGAN
2000-85155 with a filing date of Mar. 24, 2000 in Japan is hereby
incorporated by reference.
[0094] Although the invention has been described above by reference
to a certain embodiment of the invention, the invention is not
limited to the embodiment described above. Modifications and
variations of the embodiment described above will occur to those
skilled in the art, in light of the teachings. The scope of the
invention is defined with reference to the following claims.
* * * * *