JP5948210B2 - Fuel cell system mounted on vehicle - Google Patents

Description

  The present invention relates to a fuel cell system mounted on a vehicle.

  Industrial vehicles such as forklifts and passenger cars equipped with fuel cell systems are being put to practical use. In a general fuel cell system, fluctuations in the generated power cause deterioration of the fuel cell stack. Therefore, in order to prevent the deterioration of the fuel cell stack, it is necessary to generate power at a constant power while minimizing fluctuations in the generated power. preferable. For example, Patent Document 1 describes a fuel cell system that controls the generated power of a fuel cell stack in predetermined three stages without continuously changing the generated power. In such a system, a capacitor is connected in parallel with the load connected to the fuel cell stack, and when the generated power of the fuel cell stack exceeds the required power of the load, surplus power is charged to the capacitor, When the generated power is less than the required power, the insufficient power is discharged from the capacitor.

JP-A-64-38969

  In a system that controls the generated power of the fuel cell stack in three stages as in Patent Document 1, for example, when the generated power of the fuel cell stack is switched from predetermined intermediate power to maximum power, the generated power increases from the intermediate power to the maximum power. It takes a certain amount of time to do. For this reason, in order to maintain a stable power supply to the load, it is necessary to supplement the power shortage during this time with the discharge power from the capacitor. Ideally, if the amount of power that is insufficient when switching generated power is equal to the maximum amount of power that can be discharged from the capacitor at that time, the capacitor capacity is used to the maximum extent possible, and the capacitor is miniaturized. can do. However, there is no such technique in the past, and the current situation is that an excessively large capacitor is selected with a margin.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a fuel cell system capable of making maximum use of the capacity of a capacitor when switching generated power.

  In order to solve the above problems, a fuel cell system mounted on a vehicle according to the present invention includes a fuel cell stack electrically connected to a vehicle load, and an electrical connection to the fuel cell stack in parallel with the vehicle load. And a control means for switching the generated power of the fuel cell stack to three stages of a predetermined minimum power, a predetermined intermediate power and a predetermined maximum power based on the open circuit voltage of the capacitor, the control means comprising: When the open circuit voltage of the capacitor falls below a predetermined threshold when the fuel cell stack is generating with a predetermined intermediate power, the generated power of the fuel cell stack is switched from the predetermined intermediate power to a predetermined maximum power, The thresholds are: predetermined maximum power, predetermined intermediate power, capacitor capacity, allowable minimum voltage of capacitor, and generated power from predetermined intermediate power to predetermined maximum power Characterized in that it is determined based on the power increase rate at the time of raising.

によって定められる。 Preferably, the predetermined threshold value is V _TH1 , the predetermined maximum power is P _H , the predetermined intermediate power is P _M , the capacitance of the capacitor is C, the allowable minimum voltage of the capacitor is V _min , power If the rate of increase is α,

Determined by.

  The predetermined intermediate power can be set to the average power consumption of the vehicle calculated by using the vehicle for a predetermined period.

  According to the fuel cell system mounted on the vehicle according to the present invention, the capacity of the capacitor can be utilized to the maximum extent when switching the generated power.

It is a figure which shows the structure of the fuel cell system mounted in the vehicle which concerns on embodiment of this invention. It is a figure which shows the time transition of the open circuit voltage of the capacitor and the generated electric power of a fuel cell stack in the fuel cell system mounted on the vehicle according to the embodiment of the present invention. It is a figure which shows the detail of the time transition at the time of the switching of the electric power generation in the fuel cell system mounted in the vehicle which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment.
FIG. 1 shows the configuration of a fuel cell system 100 mounted on an industrial vehicle according to an embodiment of the present invention.

  The fuel cell system 100 includes a fuel cell stack 1, a hydrogen tank 2 that can supply hydrogen gas, and a compressor 3 that can supply air containing oxygen, and hydrogen supplied from the hydrogen tank 2 and the compressor 3. Electrical energy is generated by causing a chemical reaction in the fuel cell stack 1 with oxygen in the air supplied from the fuel cell stack 1. An electromagnetic valve 4 for adjusting the amount of hydrogen gas supplied to the fuel cell stack 1 is provided between the fuel cell stack 1 and the hydrogen tank 2, and the electromagnetic valve 4 and the compressor 3 are electronically controlled to be described later. Controlled by a unit (ECU) 8.

  The output of the fuel cell stack 1 is connected to the vehicle load 20 via the DC / DC converter 5, and the DC power generated by the fuel cell stack 1 is stepped down to a predetermined voltage by the DC / DC converter 5. Then, it is output to the vehicle load 20.

  The vehicle load 20 is specifically a cargo handling motor for driving a cargo handling device of an industrial vehicle, a travel motor for driving an axle, or the like. The cargo handling motor or the travel motor is driven by electric power supplied from the fuel cell system 100. By being driven, a cargo handling operation and a traveling operation of the vehicle are performed.

A capacitor 6 is connected to the output of the DC / DC converter 5 in parallel with the vehicle load 20. If the generated power P _G of the fuel cell stack 1 exceeds the required power P _W of the vehicle load 20, when surplus power is charged in the capacitor 6, the generated power P _G is below the required power P _W is insufficient The minute power is discharged from the capacitor 6. A voltage estimator 7 is attached to the capacitor 6. The voltage estimator 7 obtains a charge amount of the capacitor 6 by integrating currents input to and output from the capacitor 6, and estimates an open circuit voltage (OCV) of the capacitor 6 based on the charge amount.

Furthermore, the fuel cell system 100 includes an electronic control unit (ECU) 8 constituted by a microcomputer. ECU8 is hydrogen based on the open circuit voltage V _C of the capacitor 6 which are estimated by the voltage estimator 7, supplied by controlling the discharge amount of the opening and the compressor 3 of the solenoid valve 4, the fuel cell stack 1 the amount of oxygen was adjusted to control the generated power P _G of the fuel cell stack 1.

As described above, in order to prevent deterioration of the fuel cell stack 1 is preferably generated by a constant power while suppressing maximize the variation of the generated power P _G. Therefore, ECU 8 is the generated power _{P G} of the fuel cell stack 1, to control a predetermined minimum power _{P L,} the intermediate power _{P M,} the three stages of the maximum power _{P H.} Here, the maximum power P _H is defined as the maximum value of power required by the vehicle load 20 when the industrial vehicle operates at the maximum high load, and the minimum power P _L is not accompanied by deterioration of the fuel cell stack 1. The intermediate power P _M is defined as a predetermined value between the maximum power P _H and the minimum power P _L.

The ECU 8 constantly monitors the open circuit voltage V _C of the capacitor 6 estimated by the voltage estimator 7, and as shown in FIG. 2, the open circuit voltage V _C of the capacitor 6 has a predetermined first threshold value V _TH1 and a first threshold voltage V _TH1 . during normal lying between 2 threshold V _TH2, setting the generated power P _G of the fuel cell stack 1 to the intermediate power P _M. Further, ECU 8 decreases the amount of charge of the capacitor 6 due to an increase in required power P _W of the vehicle load 20, when the open-circuit voltage V _C detects that below a predetermined first threshold value V _TH1 When the generated power P _G is switched from the intermediate power P _M to the maximum power P _H and it is detected that the open circuit voltage V _C rises and exceeds the first threshold value V _TH1 , the generated power P _G is changed to the intermediate power P _M again. Switch to. Further, ECU 8, when the open circuit voltage _{V C} charge amount of the capacitor 6 is increased it is detected that exceeds a predetermined second threshold value _{V TH2,} the generated power _P minimum power _G from the intermediate power _{P M P L} the switching, the open circuit voltage V _C detects that falls below the second threshold value V _TH2 decreases, switching the generated power P _G again to the intermediate power P _M.

Here, how to determine the predetermined first threshold value V _TH1 will be described. When switching the generated power P _G of the fuel cell stack 1 from the intermediate power P _M to the maximum power P _H is ECU 8 by controlling the discharge amount of the opening and the compressor 3 of the solenoid valve 4, the fuel cell stack 1 increase the amount of hydrogen and oxygen supplied to raise the generated power P _G to a maximum power P _H. At this time, as shown in detail in FIG. 3, also started to switch at time t _0, takes a certain time τ is in generated power P _G is increased from the intermediate power P _M to the maximum power P _H. Therefore, in order to request power P _W of the vehicle load 20 is to maintain a stable power supply to the vehicle load 20 even in critical cases equal to the maximum power P _H is the amount of power (in the figure the missing during the predetermined time τ not a shown is area) W _a by hatching, not supplemented by electric power discharged from the capacitor 6 to.

At this time, from the definition of the first threshold value V _TH1 , the open circuit voltage of the capacitor 6 at the switching start time t ₀ is V _TH1 , the allowable minimum voltage of the capacitor 6 is V _min , and the capacitance of the capacitor 6 is C, capacitor 6 is dischargeable power amount W _C is

It is expressed. To compensate for the lack power amount W _A by the dischargeable power amount W _C,

It is necessary to satisfy the relationship. Furthermore, as mentioned in the description of the background art, in order to maximize effective use of the capacity of the capacitor 6, the dischargeable power amount W _C insufficient power amount W _A is equal,

It is ideal to satisfy this relationship.

Substituting equation (1) into equation (3) and organizing V _TH1 ,

The relationship is obtained.

Further, in FIG. 3, the generated power P _G is the change in time of rising from the intermediate power P _M to the maximum power P _H is assumed to be linear, the power shortage amount W _A

By substituting this equation (5) into equation (4),

The relationship is obtained. Moreover, the power increase rate α when generated power P _G is increased from the intermediate power P _M to the maximum power P _H

によって定義して式（６）に代入すると、

And substituting it into equation (6)

The relationship is obtained. That is, when the maximum power P _H , the intermediate power P _M , the capacitor capacitance C, the capacitor allowable minimum voltage V _min , and the power increase rate α are given, the first threshold value V _TH1 is determined according to the equation (8). The capacity of 6 can be used as much as possible.

As described above, in the fuel cell system 100 is mounted to the industrial vehicle according to this embodiment, ECU 8, when the fuel cell stack 1 is generated by the predetermined intermediate power P _M, the opening of the capacitor 6 When the circuit voltage _{V C} falls below a predetermined first threshold value _{V TH1,} it performs control for switching the generated power _{P G} of the fuel cell stack 1 from the intermediate power _{P M} to the maximum power _{P H,} the first threshold value _{V TH1} of the predetermined is Is determined according to the above equation (8). Thereby, the capacity | capacitance of the capacitor 6 can be utilized effectively to the maximum, and the capacitor 6 can be reduced in size.

Other embodiments.
In the above embodiment, in order to further prevent the deterioration of the fuel cell stack 1, it is preferable to reduce maximize the number of times of switching the power generation electric power P _G. Studies by the inventors of this application, the industrial vehicle for example, using the actual work over a predetermined period such as one week or one month to calculate the average power consumption, calculate the predetermined intermediate power P _M by setting the average power consumption that is, it has been found that the number of switching times in the generated power P _G can be greatly reduced.
In the above-described embodiment, the industrial vehicle having the cargo handling device has been described. However, the vehicle is not particularly limited as long as the above-described invention is applicable. For example, a passenger car, a forklift, or a tow truck may be used.

100 fuel cell system, first fuel cell stack, 6 capacitors, 8 ECU (control means), _{P G} generated power, _{P H} maximum power, _{P M} intermediate power, _{P L} minimum power, open circuit voltage _{V C capacitor, V TH1} First threshold (threshold), allowable minimum voltage of V _min capacitor, capacity of C capacitor, α power increase rate.

Claims (3)

A fuel cell system mounted on a vehicle,
A fuel cell stack electrically connected to a vehicle load;
A capacitor electrically connected to the fuel cell stack in parallel with the vehicle load;
Control means for switching, based on the open circuit voltage of the capacitor, the generated power of the fuel cell stack into three stages of a predetermined minimum power, a predetermined intermediate power, and a predetermined maximum power;
When the fuel cell stack generates power with the predetermined intermediate power and the open circuit voltage of the capacitor falls below a predetermined threshold, the control means converts the generated power of the fuel cell stack to the predetermined intermediate power. Switch to the predetermined maximum power from
The predetermined threshold is determined when the predetermined maximum power, the predetermined intermediate power, the capacity of the capacitor, the allowable minimum voltage of the capacitor, and the generated power increase from the predetermined intermediate power to the predetermined maximum power. A fuel cell system mounted on a vehicle, characterized in that the fuel cell system is determined based on a power increase rate. The predetermined threshold is V _TH1 , the predetermined maximum power is P _H , the predetermined intermediate power is P _M , the capacitance of the capacitor is C, the allowable minimum voltage of the capacitor is V _min , If the power increase rate is α,

The fuel cell system mounted on a vehicle according to claim 1, wherein the fuel cell system is defined by:   The vehicle according to claim 1 or 2, wherein the predetermined intermediate power is set to an average power consumption of the vehicle calculated by using the vehicle for a predetermined period. Fuel cell system.

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