JP2011008988A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the temperature of a secondary battery, using a simpler configuration in a fuel cell system.SOLUTION: The fuel cell system 10 is provided with the secondary battery 11 having an internal resistance; a step-up/down converter 12 connected in between the secondary battery 11 and a negative circuit; a fuel cell 13 that is connected in parallel to the negative circuit; and a control section 16 for controlling an action of the step-up/down converter 12. Here, the control section 16 has a charging/discharging means that allows charging and discharging to be repeated between the fuel cell 13 and the secondary battery 11, by raising/lowering the output voltage of the step-up/down converter 12.

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system including a secondary battery having an internal resistance.

  In recent years, fuel cell systems are mounted on hybrid vehicles and the like. When the fuel cell system is operated, the temperature of the secondary battery constituting the fuel cell system may be lowered. Therefore, it is desirable to raise the temperature of the secondary battery as necessary.

  As a technology related to the present invention, Patent Document 1 discloses, as a fuel cell system, a fuel cell, a power storage unit charged by the fuel cell, and a power generation control for controlling the power generation of the fuel cell so as to always have a constant output. The structure provided with a means and the temperature detection means which detects the temperature of an electrical storage means is disclosed. Then, it is described that the power generation control means performs control so as to generate a power generation amount corresponding to the load when the temperature of the power storage means detected by the temperature detection means exceeds a predetermined temperature.

  Patent Document 2 discloses, as a fuel cell system, a fuel cell that generates power by being supplied with fuel gas and oxidant gas, an oxidant gas supply unit that supplies oxidant gas to the fuel cell, and a fuel gas to the fuel cell. The fuel gas supply means for supplying the electric power, the secondary battery for charging and discharging the electric power, the generated electric power generated by the fuel cell is supplied to the load and consumed, and the secondary battery is supplied and charged. A configuration including a power distribution unit that discharges and supplies the load to a load is disclosed. Then, at the time of starting the system, the power distribution means is controlled so that the generated power of the fuel cell is supplied to the load and the secondary battery, and the generated power of the fuel cell and the discharged power of the secondary battery are supplied to the load. Thus, there is disclosed a configuration having control means for warming up the fuel cell and the secondary battery by repeating the process of controlling the power distribution means. Further, it is stated that the control means changes the determination value of the electric power that can be generated by the fuel cell for determining that the warm-up of the fuel cell is completed based on the operation state after the system startup is completed.

  Patent Document 3 discloses, as a fuel cell system, a fuel cell that is supplied with fuel gas and an oxidant gas to generate power, an oxidant gas supply unit that supplies an oxidant gas to the fuel cell, and a fuel gas to the fuel cell. The fuel gas supply means for supplying the power, the secondary battery for charging / discharging the power, the generated power generated by the fuel cell is supplied to the auxiliary equipment necessary for power generation of the fuel cell and consumed and supplied to the secondary battery. And a power distribution means for discharging the secondary battery and supplying it to the auxiliary machine. Then, at the time of starting the system, the power distribution means is controlled so that the generated power of the fuel cell is supplied to the auxiliary machine and the secondary battery, and the generated power of the fuel cell and the discharged power of the secondary battery are changed to the auxiliary machine. And a control means for warming up the fuel cell and the secondary battery by repeating the process of controlling the power distribution means so as to be supplied to the battery.

  Further, in Patent Document 4, in a hybrid vehicle equipped with a secondary battery and a power source capable of charging the secondary battery as a temperature increase control device, when the temperature of the secondary battery is low, The structure which discharges a secondary battery and raises temperature is disclosed. And it has the increase rate calculating means which calculates the increase rate of the dischargeable output of a secondary battery with respect to time passage of discharge, and a mode switching means, and the mode switching means responds to the calculated increase rate of the dischargeable output. And the structure which switches a secondary battery from discharge to charge is disclosed.

JP 2005-019033 A JP 2004-288530 A JP 2004-281219 A JP 2003-032804 A

  The configuration of Patent Document 1 only discloses that a fuel cell and a power storage unit are combined, the fuel cell intermittently generates power at a constant output, and the excess or deficiency of power is compensated by charging / discharging from the power storage unit. Thus, a specific configuration for raising the temperature of the secondary battery is not disclosed.

  The configuration of Patent Document 2 described above includes a process for controlling the power distribution unit to supply the generated power of the fuel cell stack to the load and the secondary battery, and the generated power of the fuel cell stack and the discharged power of the secondary battery as the load. The fuel cell stack and the secondary battery can be warmed up by repeating the process of controlling the power distribution unit so as to be supplied. However, in the configuration of Patent Document 2, it is necessary to always use the power generated by the fuel cell stack.

  Patent Document 3 can also warm up the fuel cell stack and the secondary battery by repeating the same process as in Patent Document 2 above. However, even if the configuration of Patent Document 3 is used, it is necessary to always use the power generated by the fuel cell stack.

  The configuration of Patent Document 4 checks the dischargeable output of the secondary battery when driving the vehicle. If the output is smaller than the predetermined value A, the secondary battery is discharged at the maximum dischargeable output to increase the battery temperature. Can be made. However, in the configuration of Patent Document 4, it is necessary to check the increase rate of the dischargeable output that rises as the battery temperature rises, and when the increase rate becomes zero, it is necessary to perform charging by the engine.

  The objective of this invention is providing the fuel cell system which can raise the temperature of a secondary battery by simpler structure.

  A fuel cell system according to the present invention includes a secondary battery having an internal resistance, a buck-boost converter connected between the secondary battery and the load circuit, a fuel cell connected in parallel to the load circuit, and a buck-boost A control unit that controls the operation of the converter, and the control unit includes charging / discharging means that raises and lowers the output voltage of the buck-boost converter and repeats charging and discharging between the fuel cell and the secondary battery. Features.

  Further, in the fuel cell system according to the present invention, the charging / discharging means increases the output voltage of the step-up / step-down converter so that the electric charge discharged from the secondary battery is charged to the capacitor component of the fuel cell, and the output voltage of the step-up / down converter It is preferable to repeat the step of charging the secondary battery with the electric charge discharged from the capacitor component of the fuel cell by lowering the value.

  According to the fuel cell system having the above configuration, the output voltage of the buck-boost converter can be raised and lowered to repeat charging / discharging between the fuel cell and the secondary battery. Thereby, it can heat up using the internal resistance of a secondary battery. Therefore, the temperature of the secondary battery can be raised with a simpler configuration.

1 is a diagram showing a fuel cell system in an embodiment of the present invention. In embodiment of this invention, it is a figure which shows each element of a control part. In embodiment of this invention, it is a flowchart which shows the procedure for heating up the secondary battery of a fuel cell system. In embodiment of this invention, it is a figure which shows the change of the output voltage of a buck-boost converter at the time of heating up a secondary battery, and the change of the electric current value which flows into a secondary battery.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description, the same elements are denoted by the same reference symbols in all the drawings, and redundant description is omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a diagram showing a fuel cell system 10. The fuel cell system 10 includes a secondary battery 11, a buck-boost converter 12, a fuel cell 13, an inverter 14, a motor 15, and a control unit 16. The fuel cell system 10 is mounted on a hybrid vehicle that travels using an internal combustion engine (an engine not shown) and a rotating electrical machine (a motor 15).

  The secondary battery 11 is a battery for supplying power to a load circuit such as the inverter 14 and the motor 15. The secondary battery 11 is a DC power source that can be charged and discharged, and includes, for example, a negative electrode made of a carbon material, an electrolytic solution for moving lithium ions, and a positive electrode active that can reversibly take in and out lithium ions. A lithium ion secondary battery having a substance can be used. The secondary battery 11 has an internal resistance (not shown), and a temperature sensor (not shown) is attached to the secondary battery 11.

  The step-up / down converter 12 is configured using a coil, a transistor, and a capacitor (not shown). The buck-boost converter 12 has a function of boosting the DC voltage received from the secondary battery 11 using a coil or the like. Specifically, the step-up / step-down converter 12 stores a current flowing according to the switching operation of the transistor as electromagnetic energy, and further boosts the electromagnetic energy by storing electric charge in a capacitor.

  Further, the step-up / down converter 12 steps down the DC voltage received from the motor 15 or the DC voltage received from the fuel cell 13 and charges the secondary battery 11.

  The fuel cell 13 is a fuel cell that is connected in parallel to a load circuit including an inverter 14 and a motor 15 and generates electric power using an electrochemical reaction between hydrogen and oxygen. Further, the fuel cell 13 generates power by receiving supply of air and hydrogen from an air supply device and a hydrogen supply device (not shown), and supplies the generated power to a load circuit including the inverter 14 and the motor 15. . And the hydrogen side electrode and the oxygen side electrode are each provided in the both ends of the electrolyte of the fuel cell 13 via the platinum catalyst. Here, the fuel cell 13 is preferably a solid polymer electrolyte fuel cell. A solid polymer electrolyte type fuel cell has advantages that it can be started at room temperature and therefore has a short start-up time and a high current density at room temperature. In addition, the solid polymer electrolyte type fuel cell has the advantages that it can be operated at a low load and can be reduced in size and weight, and has excellent characteristics as a fuel cell for a hybrid vehicle. The fuel cell 13 is not limited to a fixed polymer electrolyte fuel cell, but may be an alkaline electrolyte fuel cell, an acidic electrolyte fuel cell, a molten salt electrolyte fuel cell, a solid electrolyte fuel cell, a phosphoric acid fuel cell, or the like. Can be used.

  Here, the fuel cell 13 has a capacitance component that accumulates the electric charge discharged from the secondary battery 11. The fuel cell 13 includes, for example, a capacitance component formed between the hydrogen side electrode and the electrolyte (in other words, a capacitor component) or a capacitance component formed between the electrolyte and the oxygen side electrode. (In other words, a capacitor component) or a capacitance component (in other words, a capacitor component) that takes in and releases charges when the platinum catalyst is oxidized or reduced.

  The inverter 14 converts the DC voltage from the step-up / down converter 12 into an AC voltage and supplies it to the motor 15 during powering of the hybrid vehicle, whereby the motor 15 is rotationally driven. Further, the inverter 14 converts the AC voltage generated by the motor 15 into a DC voltage during regeneration of the hybrid vehicle and supplies the DC voltage to the secondary battery 11, whereby the secondary battery 11 is charged.

  The motor 15 is a rotating electrical machine that functions as an electric motor that rotates and outputs a driving force when the hybrid vehicle is powered, and functions as a generator that is driven to rotate and generate electric power when the hybrid vehicle is regenerated.

  FIG. 2 is a diagram illustrating each element of the control unit 16. The control unit 16 is a control device that controls the entire fuel cell system 10. The control unit 16 includes a storage unit 108, a temperature determination processing unit I / F 110, a switching control processing unit I / F 112, and a CPU 100. Each element is connected to each other through an internal bus. The control unit 16 can use a computer suitable for the fuel cell system 10.

  The temperature determination processing unit I / F 110 is an interface circuit connected to the temperature sensor of the secondary battery 11. The switching control processing unit I / F 112 is an interface circuit connected to the buck-boost converter 12 and the inverter 14.

  The CPU 100 includes a temperature determination processing unit 102, a duty ratio determination processing unit 104, and a switching control processing unit 106. Each of these functions can be realized by executing software, specifically, by executing a secondary battery temperature increase program stored in the storage unit 108. Further, some of these functions may be realized as hardware.

  The temperature determination processing unit 102 acquires the temperature information of the secondary battery 11 detected by the temperature sensor of the secondary battery 11 via the temperature determination processing unit I / F 110, and the temperature of the secondary battery 11 is equal to or lower than the threshold temperature. It has a function of determining whether or not there is.

  When the temperature determination processing unit 102 determines that the temperature of the secondary battery 11 is equal to or lower than the threshold temperature, the duty ratio determination processing unit 104 determines the transistor of the buck-boost converter 12 according to the temperature of the secondary battery 11. Has a function of determining the duty ratio when performing the switching operation.

  The switching control processing unit 106 has a function of switching the transistors of the buck-boost converter 12 based on the duty ratio determined by the duty ratio determination processing unit 104. The switching control processing unit 106 has a function of performing control for stopping the switching operation of the inverter 14 when the temperature determination processing unit 102 determines that the temperature of the secondary battery 11 is equal to or lower than the threshold temperature. .

  Next, the operation of the fuel cell system 10 having the above configuration will be described with reference to FIGS. FIG. 3 is a flowchart showing a procedure for raising the temperature of the secondary battery 11 in the fuel cell system 10. FIG. 4 is a diagram illustrating the relationship between the output voltage of the fuel cell 13 and the current value flowing through the secondary battery 11 when the temperature of the secondary battery 11 is raised in the fuel cell system 10. First, the secondary battery temperature increase program stored in the storage unit 108 is executed in the control unit 16.

  It is determined whether or not the temperature of the secondary battery 11 is lower than a threshold value (S10). Specifically, the control unit 16 acquires the temperature of the secondary battery 11 detected by the temperature sensor of the secondary battery 11 via the temperature determination processing unit I / F 110, and the temperature of the secondary battery 11 is determined in advance. It is determined whether the temperature is lower than the given threshold temperature. This process is executed by the function of the temperature determination processing unit 102 of the CPU 100. When it is determined that the temperature of the secondary battery 11 is higher than the threshold temperature, the process proceeds to return processing.

  When it is determined that the temperature of the secondary battery 11 is lower than the threshold temperature, the duty ratio of the buck-boost converter 12 is determined (S12). Specifically, according to the temperature of the secondary battery 11, the duty ratio for switching the transistor of the buck-boost converter 12 is calculated and determined. This step is executed by the function of the duty ratio determination processing unit 104 of the CPU 100.

  After S12, switching control is performed for a predetermined number of times (S14). Specifically, the transistor of the buck-boost converter 12 is switched at the duty ratio determined in the step S12. As a result, as shown in FIG. 4A, the output voltage of the buck-boost converter 12 (in other words, the output voltage of the fuel cell 13) can be raised or lowered by a predetermined number of times. This process is executed by the function of the switching control processing unit 106 of the CPU 100. After S14, the process returns to S10 again.

Thus, according to the configuration of the fuel cell system 10, when the temperature of the secondary battery 11 becomes lower than the threshold temperature, the output voltage of the buck-boost converter 12 is set as shown in FIG. Can be moved up and down. At this time, as shown in FIG. 4B, the value of the current flowing through the secondary battery 11 is a negative value from time t ₀ to time t ₁ and from time t ₁ to time t ₂ . It becomes a positive value, becomes a negative value from time t ₂ to time t ₃ , and is repeated as a positive value from time t ₃ to time t ₄ . Here, when the current value of the secondary battery 11 shows a negative value, the electric charge discharged from the secondary battery 11 is charged to the electrostatic capacity component of the fuel cell 13, and the current value of the secondary battery 11 becomes a positive value. Is charged in the secondary battery 11, that is, charging / discharging is repeated between the secondary battery 11 and the fuel cell 13. Thereby, since heat is radiated by the internal resistance of the secondary battery 11, the temperature of the secondary battery 11 can be raised.

  DESCRIPTION OF SYMBOLS 10 Fuel cell system, 11 Secondary battery, 12 Buck-boost converter, 13 Fuel cell, 14 Inverter, 15 Motor, 16 Control part, 100 CPU, 102 Temperature judgment processing part, 104 Duty ratio determination processing part, 106 Switching control processing part , 108 Storage unit, 110 Temperature determination processing unit I / F, 112 Switching control processing unit I / F.

Claims (2)

A secondary battery having an internal resistance;
A buck-boost converter connected between the secondary battery and the load circuit;
A fuel cell connected in parallel to the load circuit;
A control unit for controlling the operation of the buck-boost converter;
With
The control unit includes a charging / discharging unit that increases / decreases the output voltage of the step-up / down converter and repeats charging / discharging between the fuel cell and the secondary battery. The fuel cell system according to claim 1, wherein
Charging / discharging means
By increasing the output voltage of the buck-boost converter, the electric charge discharged from the secondary battery is charged to the capacitor component of the fuel cell,
A fuel cell system characterized by repeating a step of charging a secondary battery with electric charges discharged from a capacitor component of the fuel cell by lowering an output voltage of the buck-boost converter.

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