JP2017027669A - On-board fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce frequency of charging/discharging a secondary cell and thereby to reduce a load on the secondary cell.SOLUTION: A fuel cell system includes: a power source having a fuel cell and a secondary cell; and a control unit which acquires required output power required for the power source by using an amount of depression of an accelerator pedal of a vehicle and controls power to be output from the respective fuel cell and secondary cell by using the required output power and speed of the vehicle. The control unit performs: (i) when the speed is a predetermined value or less, output of electric power according to the required output power from the fuel cell; (ii) when the speed is larger than the predetermined value, output of electric power determined according to the speed from the fuel cell. Further, in the case of (ii), the control unit performs: (iia) when the electric power determined according to the speed is larger than the required output power, charge of the secondary cell with electric power exceeding the required output power; and (iib) when the electric power determined according to the speed is the required output power or less, output of electric power that is short of the required output power from the secondary cell.SELECTED DRAWING: Figure 2

Description

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

  Patent Document 1 describes a technique for cooling a fuel cell so that the fuel cell is not intermittently operated in a fuel cell system mounted on a vehicle by intermittently operating the fuel cell with a constant output. . It also describes controlling the coolant temperature so that the power generation efficiency of the fuel cell is maximized.

JP 2005-044533 A

  However, the system of Patent Document 1 is configured to travel with the power from the secondary battery and to replenish the shortage from the fuel cell when the power is insufficient. Since the fuel cell of the fuel cell system does not always generate power but intermittently generates power as necessary, the number of times the secondary battery is charged and discharged increases, and the load on the secondary battery is large.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.

(1) According to one aspect of the present invention, a fuel cell system mounted on a vehicle is provided. The fuel cell system obtains a required output required for the power source using a power source having a fuel cell and a secondary battery, and a depression amount of an accelerator pedal of the vehicle, and the required output and the vehicle And a control unit that controls electric power output from the fuel cell and the secondary battery using speed. (I) When the speed is equal to or lower than a predetermined value, the control unit causes the fuel cell to output electric power corresponding to the required output, and (ii) the speed is higher than a predetermined value. In this case, the fuel cell is caused to output electric power determined according to the speed, and (iii) when the electric power determined according to the speed is larger than the required output, the electric power exceeding the required output is The secondary battery is charged, and (iib) When the power determined according to the speed is equal to or lower than the required output, the power required for the required output is output from the secondary battery. According to this aspect, the control unit causes the fuel cell to generate electric power corresponding to the required output when the vehicle speed is equal to or less than a predetermined value, so that the number of times of charging and discharging to the secondary battery is reduced. The load on the secondary battery can be reduced.

  Note that the present invention can be realized in various modes. For example, in addition to the fuel cell system mounted on the vehicle, it can be realized in the form of a vehicle mounted with a fuel cell, a moving body, a fuel cell system control method, a fuel cell mounted vehicle, a mobile body control method, and the like. .

Explanatory drawing which shows the fuel cell mounting vehicle carrying a fuel cell system. The control flowchart of the fuel cell system in a 1st embodiment. The map which shows the relationship between the speed of a vehicle and the target output of a fuel cell. Explanatory drawing which shows the preparation method of the map shown in FIG. Explanatory drawing which shows the relationship between the output of a vehicle and a power source, and a cooling loss. The control flowchart of the fuel cell system in 2nd Embodiment.

Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing a fuel cell-equipped vehicle 10 (also referred to as “vehicle 10”) equipped with a fuel cell system. The vehicle 10 includes a fuel cell 100, a control unit 110 (also referred to as an ECU (Electronic Control Unit)), an accelerator pedal 120, an accelerator pedal sensor 125, a secondary battery 130, a power distributor 140, and a wheel drive. A motor 150, a drive shaft 160, a power distribution gear 170, wheels 180, and a speedometer 190 are provided. The fuel cell 100, the secondary battery 130, and the power distributor 140 are collectively referred to as a “power source 200”.

  The fuel cell 100 is a power generator for taking out electric power by electrochemically reacting a fuel gas and an oxidant gas. The secondary battery 130 is used as a power source for moving the vehicle 10 together with the fuel cell 100. As the secondary battery 130, for example, a nickel metal hydride battery or a lithium ion battery can be adopted. The secondary battery 130 is charged by, for example, directly charging using the power output from the fuel cell 100. It is also possible to regenerate and charge the kinetic energy of the vehicle 10 by the wheel drive motor 150 when the vehicle 10 decelerates. The wheel drive motor 150 functions as an electric motor for moving the vehicle 10. The wheel drive motor 150 functions as a generator that regenerates the kinetic energy of the vehicle 10 into electrical energy when the vehicle 10 decelerates. The drive shaft 160 is a rotating shaft for transmitting the driving force generated by the wheel drive motor 150 to the power distribution gear 170. The power distribution gear 170 distributes the driving force to the left and right wheels 180. The speedometer 190 acquires the speed SPD of the vehicle 10 using the rotation speed of the power distribution gear 170.

  The control unit 110 acquires the amount of depression of the accelerator pedal 120 using the accelerator pedal sensor 125, and acquires the required output Preq to the power source 200 using the amount of depression of the accelerator pedal 120. The control unit 110 controls the operation of the fuel cell 100, the secondary battery 130, and the power distributor 140 using the requested output Preq and the speed SPD of the vehicle 10. In response to an instruction from the control unit 110, the power distributor 140 switches between the power output from the fuel cell 100 to the wheel drive motor 150 and the power output from the secondary battery 130 to the wheel drive motor 150. When the vehicle 10 is decelerated, the power distributor 140 receives a command from the control unit 110 and sends the power regenerated by the wheel drive motor 150 to the secondary battery 130 to be charged.

First embodiment:
FIG. 2 is a control flowchart of the fuel cell system according to the first embodiment. In step S <b> 100, control unit 110 acquires speed SPD of vehicle 10 using speedometer 190. In step S <b> 110, the control unit 110 acquires the depression amount of the accelerator pedal 120 using the accelerator pedal sensor 125. In step S120, control unit 110 calculates a required output Preq to power supply 200 using the amount of depression of accelerator pedal 120. The control unit 110 may acquire either the speed SPD or the request output Preq first.

  In step S130, control unit 110 determines whether or not speed SPD is greater than a predetermined low speed threshold value SPD_low. When the speed SPD is equal to or lower than the low speed threshold SPD_low, the control unit 110 proceeds to step S210. In step S210, the control unit 110 controls the fuel cell 100 so that the power FCout to be output from the fuel cell 100 matches the required output Preq. In this case, the control unit 110 does not output power from the secondary battery 130 toward the wheel drive motor 150 and does not charge the secondary battery 130 with the power from the fuel cell 100.

  In step S130, when the speed SPD is larger than the low speed threshold value SPD_low, the control unit 110 proceeds to step S140. In step S140, control unit 110 determines target output Pfc_aim to be output from fuel cell 100 according to speed SPD.

  FIG. 3 is a map showing the relationship between the speed SPD of the vehicle 10 and the target output Pfc_aim of the fuel cell 100. In this example, the target output Pfc_aim increases from Pfc_al to Pfc_ah as the speed SPD increases from the low speed threshold SPD_low to the high speed threshold SPD_hi. When the speed SPD is equal to or higher than the high speed threshold value SPD_hi, the target output Pfc_aim is maintained at Pfc_ah. When the speed SPD of the vehicle 10 is equal to or lower than the low speed threshold value SPD_low, as described in step S210 (FIG. 2), the control unit 110 matches the power FCout to be generated by the fuel cell 100 with the required output Preq. The fuel cell 100 is controlled. Therefore, the map shown in FIG. 3 is not used. The control unit 110 can select, for example, a range of 50 km / h or more and 100 km / h or less as the low speed threshold SPD_low, and a range of 100 km / h or more and 150 km / h or less as the high speed threshold SPD_hi (however, SPD_low < SPD_hi) can be selected. Note that. The relationship between the speed SPD and the target output Pfc_aim may not be linear, but normally, a relationship is set in which the target output Pfc_aim monotonously increases as the speed SPD increases.

  FIG. 4 is an explanatory diagram showing a method of creating the map shown in FIG. The control unit 110 acquires the frequency of the output Pfc of the fuel cell 100 when the vehicle 10 is driven at the low speed threshold SPD_low using only the power from the fuel cell 100 without using the secondary battery 130. Even when the vehicle 10 is driven at the same speed, for example, the fuel cell 100 may be changed depending on the road gradient (up or down), the direction of wind (whether it is tailwind or headwind), and the operating state of auxiliary equipment such as an air conditioner. This is because the output Pfc changes. The control unit 110 calculates an average value Pfc_al of the output Pfc of the fuel cell 100 when running at the low speed threshold value SPD_low. Similarly, the control unit 110 acquires the frequency of the output Pfc of the fuel cell 100 when the vehicle 10 is driven at the high speed threshold SPD_hi using only the electric power from the fuel cell 100 without using the secondary battery 130, An average value Pfc_ah of the output Pfc is obtained. The controller 110 interpolates the average output of the fuel cell 100 at a speed between the low speed threshold value SPD_low and the high speed threshold value SPD_hi. In addition, the control unit 110 similarly uses several powers between the low speed threshold value SPD_low and the high speed threshold value SPD_hi when only the electric power from the fuel cell 100 is used without using the secondary battery 130. The frequency of the output Pfc of the fuel cell 100 may be acquired to calculate an average value, and the target output Pfc_aim at those speeds may be obtained.

  In the above embodiment, the control unit 100 acquires the frequency for each output Pfc of the fuel cell 100 when the vehicle 10 is driven only by the electric power from the fuel cell 100 without using the secondary battery 130 and obtains the average value. Although the target output Pfc_aim is calculated, the median value or mode value of the output Pfc may be used as the target output Pfc_aim. Note that the map of FIG. 3 is preferably created in advance before the start of the process of FIG.

  In step 150 of FIG. 2, control unit 110 determines whether or not required output Preq to power supply 200 is greater than target output Pfc_aim of fuel cell 100. When the required output Preq is larger than the target output Pfc_aim, the control unit 110 outputs the target output Pfc_aim from the fuel cell 100 and outputs the shortage (Preq−Pfc_aim) from the secondary battery 130 (discharge) in step S160. Let On the other hand, if the required output Preq is smaller than the target output Pfc_aim, the target output Pfc_aim is output from the fuel cell 100 in step S180, and the secondary battery 130 is charged with the excess (Pfc_aim-Preq).

  In addition, in the said flowchart, although the charge amount of the secondary battery 130 is not demonstrated, when the secondary battery 130 is not fully charged, it cannot discharge from the secondary battery 130. FIG. In this case, in step S <b> 160, the control unit 110 only outputs the target output Pfc_aim from the fuel cell 100 and does not have to discharge from the secondary battery 130. Further, when the secondary battery 130 is fully charged, it cannot be charged any more. In this case, the control unit 110 may lower the target output Pfc_aim to the required output Preq in step S180.

  FIG. 5 is an explanatory diagram showing the relationship between the output of the vehicle 10, the power source, and the cooling loss Qw. In FIG. 5, the fuel cell 100 and the gasoline engine are compared. The cooling loss Qw of the fuel cell 100 is a ratio of energy that cannot be used as electric energy of the fuel cell 100 in the combustion enthalpy ΔH. The energy that cannot be used as electric energy is a loss that cannot be used to drive the vehicle 10, and is generated as heat and is cooled by the cooling system, so it is called a cooling loss.

The cooling loss of the fuel cell 100 can be expressed by the following formula (1).
Qw = a × P ² + b (1)
In Expression (1), P is an output, and a and b are coefficients. As can be seen from Equation (1), the cooling loss Qw is a power of the output P, and the cooling loss Qw is expected to increase in a high load region where the output P is large. In the fuel cell 100, this heat (cooling loss Qw) is exhausted in a concentrated manner in the cooling water.

On the other hand, in the gasoline engine, the cooling loss Qw is expressed by the following equation (2).
Qw = P × (1 / r ^(κ−1) ) (2)
It becomes. In the formula (2), r is a compression ratio, and κ is [constant molar specific heat (also referred to as “constant specific heat”)] / [constant molar specific heat (also referred to as “constant specific heat”)]. The cooling loss Qw of the gasoline engine is linear with respect to the output P. Further, since the heat of the gasoline engine can be discharged out of the system as high-temperature exhaust gas, the heat discharged out of the system as high-temperature exhaust gas does not have to be cooled with cooling water.

  As described above, in the fuel cell 100, the cooling loss Qw rapidly increases in the high load region as compared with the gasoline engine. The heat generated by the cooling loss Qw is cooled by the cooling water. Therefore, in the high load region, the target output Pfc_aim obtained from the speed SPD of the vehicle 10 is set to an operation that suppresses the output of the fuel cell 100 from being increased or decreased rather than the output of the fuel cell 100 being increased or decreased according to the load. The operation in which the output of the battery 100 is insufficient from the secondary battery 130 can reduce the cooling loss Qw of the fuel cell 100 as a whole.

  As described above, according to the present embodiment, when the speed SPD of the vehicle 10 is equal to or lower than a predetermined value (low speed threshold value SPD_low), that is, when the air resistance is small and the load is small, the power corresponding to the required output Preq is obtained. When the speed SPD is larger than a predetermined value (low speed threshold SPD_low), that is, when the air resistance is large, the fuel cell 100 outputs a predetermined power based on the speed SPD. Let At this time, when the predetermined output Pfc_aim based on the speed SPD is larger than the required output Preq, the power exceeding the required output Prec is charged to the secondary battery 130, whereas when it is less than the required output Preq Then, the electric power that is insufficient for the required output Preq is output from the secondary battery 130. Therefore, the load of the secondary battery 130 can be reduced by reducing the number of times the secondary battery 130 is charged.

  Further, when the speed SPD of the vehicle 10 is larger than the low speed threshold value SPD_low and equal to or less than the high speed threshold value SPD_hi, the target output Pfc_aim for the fuel cell 100 is used to output the speed SPD of the vehicle 10 without using the secondary battery 130. It is set to the required average output. Therefore, even if the speed SPD of the vehicle 10 is larger than the low speed threshold value SPD_low, if the driver does not accelerate the vehicle 10 and the road is not an uphill road, the vehicle 10 can travel with an average output. The load on the secondary battery 130 can be reduced by reducing the number of times the secondary battery 130 is charged and discharged.

Second embodiment:
FIG. 6 is a control flowchart of the fuel cell system according to the second embodiment. The difference from the flowchart shown in FIG. 2 is the operation of steps S160a and S180a. The second embodiment is different from the first embodiment in that the SOC, discharge power Wo, and charge power Win of the secondary battery 130 are taken into consideration in steps S160a and S180a.

  The SOC is an index indicating how much power is charged in the secondary battery 130 with the fully charged state being 100% and the fully discharged state being 0%. If the SOC is too high, there is a possibility that the secondary battery 130 may be deteriorated quickly, and regenerative power may not be charged during regeneration. On the other hand, if the SOC is too low, it may not be used when it is desired to use the power of the secondary battery 130. Therefore, the SOC is controlled to be within a predetermined allowable range, the lower limit value SOC_l to the upper limit value SOC_h, for example, a range of 30% to 70%. There are also restrictions on the discharge power Wo and the charge power Win. If these values are large, the secondary battery 130 generates a large amount of heat, which may cause the secondary battery 130 to deteriorate.

  Hereinafter, differences from the first embodiment will be described. In step S165, it is determined whether or not the SOC of secondary battery 130 is greater than lower limit SOC_l. When the SOC of the secondary battery 130 is equal to or lower than the lower limit SOC_l, it is not preferable to discharge the secondary battery 130 any more. Therefore, even when the required output Pfc to the fuel cell 100 is larger than the target output Pfc_aim of the fuel cell 100, the control unit 110 performs control to compensate the difference by outputting from the secondary battery 130. Absent. In this case, the control unit 110 proceeds to step S200 and sets the output FCout of the fuel cell 100 as the target output Pfc_aim. In this case, the output FCout of the fuel cell 100 is smaller than the required output Preq. However, the control unit 110 is disadvantageous in terms of cooling loss, but the output FCout of the fuel cell 100 may be set to be equal to or less than the required output Preq although it is larger than the target output Pfc_aim.

  When the SOC is larger than the lower limit SOC_l, in step S170, the control unit 110 calculates the discharge power Wo of the secondary battery 130, outputs the target output Pfc_aim from the fuel cell 100, and discharges from the secondary battery 130. Electric power Wo is output. The discharge power Wo is a smaller value of the shortage of output (Preq−Pfc_aim) and the allowable maximum value Wo_max of the discharge power. When the shortage (Preq−Pfc_aim) is equal to or smaller than the allowable maximum value Wo_max, the control unit 110 causes the secondary battery 130 to output the shortage (Preq−Pfc_aim). The sum of the output Pfc_aim from the fuel cell 100 and the output (Preq−Pfc_aim) from the secondary battery 130 is equal to the required output Preq. On the other hand, when allowable discharge power maximum value Wo_max is smaller, control unit 110 causes target output Pfc_aim to be output from fuel cell 100, and allows secondary battery 130 to output power of allowable maximum value Wo_max. In this case, the sum of the output Pfc_aim from the fuel cell 100 and the output Wo_max from the secondary battery 130 is smaller than the required output Preq. The control unit 110 may be disadvantageous in terms of cooling loss, but may cause the secondary battery 130 to output the power of the allowable maximum value Wo_max and the fuel cell 100 to output the shortage (Preq−Wo_max). .

  In step S185, it is determined whether or not the SOC of secondary battery 130 is less than upper limit value SOC_h. When the SOC of the secondary battery 130 is not less than the upper limit SOC_h, it is not preferable to charge the secondary battery 130 any more. Therefore, even when the required output Preq to the fuel cell 100 is smaller than the target output Pfc_aim of the fuel cell 100, the control unit 110 does not charge the secondary battery 130. In this case, the control unit 110 proceeds to step S205 and causes the fuel cell 100 to operate at the target output Preq.

  In step S190, control unit 110 calculates charging power Win for secondary battery 130, causes target output Pfc_aim to be output from fuel cell 100, and causes secondary battery 130 to be charged with charging power Win. The charging power Win is a larger one of the charging power (Preq−Pfc_aim) corresponding to the excess of the output and the allowable maximum value Win_max of the charging power. Here, the discharge power from the secondary battery 130 is positive, the charge power to the secondary battery 130 is negative, and the charge power (Preq-Pfc_aim) and the charge power corresponding to the excess output in step S190 The allowable maximum value Win_max is a negative value. In other words, in step S190, the smaller one of the absolute value | Preq-Pfc_aim | of the charging power corresponding to the excess of the output and the absolute value | Win_max | Adopted as power Win.

  When the output excess (Preq−Pfc_aim) ≧ allowable maximum value (Win_max), the value obtained by subtracting the charging power [− (Preq−Pfc_aim)] to the secondary battery 130 from the output Pfc_aim of the fuel cell 100 is the required value. Equal to output Preq. On the other hand, when the allowable maximum value (Win_max)> the excess of output (Preq−Pfc_aim), the control unit 110 cannot charge all the power obtained by subtracting the required output Preq from the output Pfc_aim of the fuel cell 100. The fuel cell 100 may be operated at an output not less than the required output Preq and not more than the required output Preq + allowable maximum value (Win_max).

  As described above, also in the second embodiment in which the SOC of the secondary battery 130, the charging speed Win to the secondary battery 130, and the discharging speed Wo are taken into account, the secondary battery 130 is reduced in the number of times of charging and discharging. Can be reduced.

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Vehicle with fuel cell 100 ... Fuel cell 110 ... Control part 120 ... Accelerator pedal 125 ... Accelerator pedal sensor 130 ... Secondary battery 140 ... Electric power distributor 150 ... Wheel drive motor 160 ... Drive shaft 170 ... Power distribution gear 180 ... Wheel 190 ... Speedometer 200 ... Power supply

Claims (1)

A fuel cell system mounted on a vehicle, wherein the power source includes a fuel cell and a secondary battery;
Electric power to be output from the fuel cell and the secondary battery using the required output and the speed of the vehicle, respectively, while obtaining the required output required for the power source using the depression amount of the accelerator pedal of the vehicle A control unit for controlling
With
The controller is
(I) When the speed is equal to or lower than a predetermined value, power corresponding to the required output is output from the fuel cell;
(Ii) When the speed is greater than a predetermined value, the fuel cell is caused to output electric power determined according to the speed,
(Iii) If the power determined according to the speed is larger than the required output, the secondary battery is charged with power exceeding the required output,
(Iib) When the power determined according to the speed is equal to or lower than the required output, the power required for the required output is output from the secondary battery.
Fuel cell system.

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