Power delivery methods and power delivery systems

Abstract

Power supply method carried out in a system comprising a fuel cell (14), a secondary battery (12), a motor (18) and an auxiliary unit (15) for the fuel cell, wherein the method comprises: Control of an intermittent operation, whereby switching intermittently between execution and termination of power generation by the fuel cell in order to supply power to electrical power loads which include the motor and the auxiliary unit; Determine whether or not an abnormality occurs in the secondary battery during intermittent operation; Instructing the engine to regenerate power under the condition that, in determining whether or not an abnormality occurs, it is determined that the abnormality occurs in the secondary battery; and Supplying power obtained by performing regeneration to the auxiliary unit.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a power supply method and a power supply system. 2. Description of the related prior art

[0002] A power supply system built using a fuel cell has attracted attention. The fuel cell comprises an anode to which hydrogen-containing fuel gas is supplied and a cathode to which air is supplied, and generates electricity as a result of an electrochemical reaction between the fuel gas and oxidizer gas. Japanese patent application JP 2011-036101 A discloses a power supply system in which a fuel cell is used.

[0003] The electric vehicle in which the power supply system is installed is capable of switching between power supply from the fuel cell and a secondary battery as needed. For example, depending on the output requirements of a traction motor and auxiliary fuel cell components, as well as the charge level in the secondary battery, it is possible to switch between power supply from the fuel cell and the secondary battery, and power supply solely from the secondary battery. While power is supplied exclusively from the secondary battery, the fuel cell stops generating electricity. Thus, the fuel cell operates intermittently. This type of power supply is therefore referred to as intermittent operation.

[0004] Furthermore, DE 10 2014 224 890 A1 discloses an operating control system and method for a fuel cell system, wherein the operating control method comprises determining, by means of a control system, when a fuel cell stack has a water shortage, based on an oversupply of air to the fuel cell stack or a deterioration of the fuel cell stack. A diagnostic level is then assigned to the fuel cell system and at least one regeneration driving mode, which corresponds to the assigned diagnostic level, is carried out. SUMMARY OF THE INVENTION

[0005] There are instances where a malfunction occurs in the secondary battery during intermittent operation, rendering it unable to supply power. In such cases, it is necessary to power a traction motor using energy from the fuel cell. However, auxiliary components required to switch the fuel cell from a non-power-generating to a power-generating state also need to be supplied with power. Since the malfunction in the secondary battery prevents it from supplying power to these auxiliary components, the electric vehicle may be unable to continue its journey.

[0006] The invention provides a technology that enables a fuel cell to resume power generation even when an abnormality occurs in a secondary battery during intermittent operation.

[0007] A power supply method according to the first aspect of the invention is carried out in a system comprising a fuel cell, a secondary battery, a motor, and an auxiliary unit for the fuel cell. The power supply method includes controlling intermittent operation, by which the fuel cell intermittently switches between power generation and power generation to supply power to electrical loads, including the motor and the auxiliary unit; determining whether or not an abnormality occurs in the secondary battery during intermittent operation; instructing the motor to regenerate power if the abnormality is determined to be in the secondary battery; and supplying the power obtained by regeneration to the auxiliary unit.

[0008] In the foregoing aspect, the power supply method may further include calculating the power that can be generated by the regeneration carried out by the motor when, in determining whether an abnormality occurs or not, it is determined that the abnormality occurs in the secondary battery during intermittent operation, and the regeneration can be carried out when the power that can be generated is greater than or equal to a given value.

[0009] In the above aspect, the power supply method may involve measuring the velocity of a moving body to which the system is mounted, and the power that can be generated may be calculated based on the measured velocity.

[0010] In the foregoing aspect, the instruction to carry out regeneration may be given if the power obtained by subtracting at least one loss power from the regenerable power is greater than or equal to a power that allows the auxiliary unit to cause the fuel cell to commence operation, the loss power being necessary to obtain the regenerable power.

[0011] In the above aspect, power obtained by performing the regeneration can be stored in a capacitor.

[0012] A power supply system according to the second aspect of the invention is provided with a fuel cell, a secondary battery, a motor, an auxiliary unit for the fuel cell, and a controller. The controller is configured to manage intermittent operation, by which the fuel cell intermittently switches between executing and terminating power generation in order to supply power to electrical loads, which include the motor and the auxiliary unit. The controller is also configured to determine whether an abnormality occurs in the secondary battery during intermittent operation, to instruct the motor to regenerate power if the abnormality is determined to be present, and to supply the auxiliary unit with the power obtained by performing the regeneration.

[0013] In the foregoing aspect, the controller can be designed to calculate power that can be generated by the regeneration carried out by the motor when, in determining whether an abnormality occurs or not, it is determined that an abnormality occurs in the secondary battery during intermittent operation, and can also be designed to cause the motor to carry out the regeneration when the generable power is greater than or equal to a given value.

[0014] In the aforementioned aspect, the power supply system can further include a vehicle speed sensor that measures the velocity of a moving body to which the power supply system is mounted. The controller can be designed to calculate the power that can be generated based on the measured velocity.

[0015] In the foregoing aspect, the controller may be designed to perform regeneration if the power obtained by subtracting at least one power loss from the generateable power is greater than or equal to a power that enables the auxiliary unit to cause the fuel cell to commence operation, wherein the power loss is required to obtain the generateable power.

[0016] In the above aspect, the power supply system may further include a capacitor that stores power obtained by performing the regeneration.

[0017] According to the first and second aspects, the invention provides a technology that enables the fuel cell to resume power generation even if an abnormality occurs in the secondary battery during intermittent operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Features, advantages, and the technical and economic significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, wherein identical reference numerals denote identical elements, and wherein: Fig. 1. A view showing a schematic structure of a power supply system according to one embodiment; and Fig. 2 is a flowchart showing a processing sequence carried out by the power supply system according to the embodiment. DETAILED DESCRIPTION OF EXECUTION FORMS

[0019] The embodiment of the invention is described in detail below with reference to the drawings. However, the scope of the invention is not limited to this embodiment. [Structure of a power supply system]

[0020] Referring to Fig. Figure 1 describes an example of a schematic structure of a power supply system according to the embodiment of the invention. The power supply system 1 is equipped with a controller 11, a secondary battery 12, a DC / DC converter 13, a fuel cell 14, auxiliary components 15, a DC / DC converter 16, an inverter 17, a motor 18, a vehicle speed sensor 19, a capacitor 20, a battery 21, a DC / DC converter 22, and a low-voltage load 23. The power supply system 1 can be mounted on a vehicle (a moving body), such as a fuel cell vehicle (FCV), an electric vehicle, and a hybrid vehicle. Fig. Figure 1 shows only one main structure included in the power supply system 1, and the power supply system 1 may also include other structures provided for in a general power supply system.

[0021] The secondary battery 12 is an electricity storage device capable of charging and discharging electricity. For example, the secondary battery 12 consists of a lithium-ion battery, a nickel-metal hydride battery, or a capacitor. The secondary battery 12 is integrated into a discharge path of the fuel cell 14 and connected to the fuel cell 14 in parallel with the inverter 17. The secondary battery 12 is also connected to the auxiliary equipment 15.

[0022] The DC / DC converter 13 is a DC voltage converter located between the secondary battery 12 and the inverter 17. The DC / DC converter 13 is, for example, a full-bridge converter that includes four power transistors and a dedicated drive circuit (both not shown). The DC / DC converter 13 steps up or down a DC voltage supplied by the secondary battery 12 and outputs it to the fuel cell 14 or to the inverter 17. The DC / DC converter 13 also steps up or down a DC voltage supplied by the fuel cell 14 and outputs it to the secondary battery 12. This means that the DC / DC converter 13 enables the secondary battery 12 to be charged and discharged.

[0023] Fuel cell 14 is constructed as a stack of solid polymer electrolyte cells, which is produced by laminating a plurality of cells (individual cells, each comprising an anode, a cathode, and an electrolyte (power generating body)) in series. During normal power generation, fuel cell 14 operates as follows: an oxidation reaction, expressed by formula (1), takes place in the anode, and a reduction reaction, expressed by formula (2), takes place in the cathode. Fuel cell 14 as a whole generates power as a result of an electrochemical reaction, expressed by formula (3). H2 → 2H + + 2e - Formula 1) (1 / 2) O2 + 2H + + 2e - → H2O Formula (2) H2 + (1 / 2) O2 → H2O Formula (3)

[0024] The auxiliary units 15 are various types of equipment used to operate the fuel cell 14. These auxiliary units 15 include, for example, a compressor and a pump for supplying fuel gas and oxidant gas to the fuel cell 14. The auxiliary units 15 use power supplied from the secondary battery 12 or the fuel cell 14 as their drive power. The power supply from the fuel cell 14 to the auxiliary units 15 is provided by the DC / DC converter 13 and the DC / DC converter 16.

[0025] The DC / DC converter 16 is a DC voltage converter located between the fuel cell 14 and the inverter 17. The DC / DC converter 16 consists of a full-bridge converter or the like. The DC / DC converter 16 steps up or down the DC voltage of the power supplied from the fuel cell 14 and outputs it to the inverter 17.

[0026] Inverter 17, for example, is a PWM (pulse-width modulated) inverter that includes a number of switching elements. Inverter 17 converts direct current power supplied from the fuel cell 14 or the secondary battery 12 into three-phase alternating current power in accordance with a control command input from the controller 11 and supplies the converted power to the motor 18.

[0027] Motor 18 is a traction motor for driving the drive wheels and other components of the moving body to which the power supply system 1 is mounted. Motor 18 uses power supplied by inverter 17 from the fuel cell 14 or the secondary battery 12 as its driving force. The number of revolutions of motor 18 is controlled by inverter 17. Motor 18 is capable of regenerating power in accordance with its rotational speed. The regenerated power can be used to charge the secondary battery 12 and the capacitor 20.

[0028] The vehicle speed sensor 19 is a sensor that detects the speed of movement (vehicle speed) of the moving body on which the power supply system 1 is mounted and outputs the detected speed to the controller 11. The vehicle speed sensor 19 detects the speed of movement in accordance with the number of revolutions of the motor 18, the number of revolutions of the wheels of the moving body, and so on.

[0029] Capacitor 20 is an energy storage device that stores regenerated power from motor 18 (a connecting cable between capacitor 20 and motor 18 is not shown). Capacitor 20 also smooths the current output from DC / DC converter 13 and DC / DC converter 16 and supplies it to inverter 17. The remaining functions of capacitor 20 are described later. Capacitor 20 can be constructed from any type of energy storage device.

[0030] The battery 21 is an electrical storage device capable of being charged and discharged. For example, the battery 21 is a lithium-ion battery, a nickel-metal hydride battery, or a capacitor. The battery 21 is used as a power source for electrical equipment with a relatively low voltage (for example, 12 V), such as the low-voltage load 23 and the controller 11.

[0031] The DC / DC converter 22 is a DC voltage converter connected between the secondary battery 12 and the auxiliary equipment 15. The DC / DC converter 22 is a full-bridge converter or similar. The DC / DC converter 22 steps down a DC voltage of power supplied from the secondary battery 12 and delivers it to battery 21. Thus, battery 21 is charged.

[0032] The low-voltage load 23 is an auxiliary unit, such as an in-vehicle lighting system and an air conditioning system, which is powered by drive power at a relatively low voltage (for example, 12V).

[0033] Controller 11 comprises a computer equipped with a CPU (central processing unit), ROM (read-only memory), and RAM (random access memory). Controller 11 controls the processing and operation of each component of the power control system 1 based on signals input from other structures, programs stored in a memory component such as RAM, and so forth. Power to operate Controller 11 is supplied by battery 21 (a connecting cable between Controller 11 and battery 21 is not shown for the sake of simplicity).

[0034] For example, the controller 11 controls intermittent operation, in which the fuel cell 14 switches intermittently between executing and terminating power generation in order to supply power to electrical loads, which include the motor 18 and the auxiliary units 15. The intermittent operation is controlled according to the electrical power required by the electrical loads, a power accumulation ratio of the secondary battery 12, and so on. For example, the controller 11 first calculates the power required by the electrical loads, which include the motor 18 and the auxiliary units 15, and specifies a power accumulation ratio of the secondary battery 12.Next, the controller 11 determines whether the calculated power requirement is covered by a power supply from the secondary battery 12 and performs a control action so that power generation by the fuel cell 14 is stopped if it is covered, and the secondary battery 12 supplies power to the motor 18, the auxiliary units 15, and so on. If the power supply from the secondary battery 12 does not cover the required power, then the controller 11 performs a control action so that the fuel cell 14 generates power and both the fuel cell 14 and the secondary battery 12 supply power. A system-on-a-chip (SOC) can be used as a structure that determines whether the calculated power requirement is covered by the power supplied from the secondary battery 12 or not.

[0035] During intermittent operation, if an abnormality occurs in the secondary battery 12, the connection between the secondary battery 12 and the auxiliary units 15 may be interrupted, or the secondary battery 12 may be unable to supply power. In such a case, even if an attempt is made to control the fuel cell 14 from a non-power-generating state (non-operating state) to a power-generating state, it is not possible to supply power from the secondary battery 12 to the auxiliary units 15 to cause the fuel cell 14 to resume operation. Consequently, it is not possible to drive the auxiliary units 15, and the fuel cell 14 cannot be operated.If the fuel cell 14 is not operated, the motor 18 cannot be driven either, and further travel of the moving body on which the power supply system 1 is mounted becomes impossible.

[0036] To avoid this situation, in this embodiment, the controller 11 first determines whether or not an abnormality occurs in the secondary battery 12 during intermittent operation. If an abnormality is determined to be present, the controller 11 is able to perform a control action such that the motor 18 is instructed to regenerate power. In accordance with this instruction, the motor 18 regenerates power. The controller 11 then performs a control action such that the capacitor 20 is charged with regenerated power received from the motor 18. Consequently, the auxiliary units 15 are activated by power supplied by the capacitor 20 (a connecting cable between the capacitor 20 and the auxiliary units 15 is not shown), and it is possible to begin driving the fuel cell 14 by driving the auxiliary units 15.

[0037] An abnormality of the secondary battery 12 is detected in accordance with a control signal received by the controller 11 from the secondary battery 12 or the DC / DC converter 13, or by the fact that the control signal is not received.

[0038] As previously explained, according to this embodiment, the motor 18 begins to regenerate power if an abnormality occurs in the secondary battery 12 during intermittent operation. This means that even in a state where power regeneration is not intended (for example, when a vehicle is traveling downhill), the motor 18 begins to regenerate power if an abnormality occurs in the secondary battery 12 during intermittent operation. Therefore, according to this embodiment, even if an abnormality occurs in the secondary battery 12 during intermittent operation, regenerated power obtained from the motor 18 is supplied as drive power to the auxiliary units 15, thus enabling the fuel cell 14 to resume operation.

[0039] Depending on the number of revolutions of the motor 18 or the speed of the moving body to which the power supply system 1 is mounted, there are cases in which the regeneration process does not generate enough power to operate the fuel cell 14. If, even after performing a regeneration as described above, insufficient power is generated to operate the fuel cell 14 while the moving body is in motion, then the inertial travel distance will be short. Consequently, the distance the moving body can travel to reach a safe location will be short. Considering these points, the controller 11 is able to perform a control operation such that regeneration is carried out when it is possible to generate sufficient power to operate the fuel cell 14 from the regeneration process described below.

[0040] First, if an abnormality occurs in the secondary battery 12 during intermittent operation, the controller 11 calculates the power that can be generated by the regeneration performed by the motor 18. The power that can be generated by regeneration is calculated, for example, based on the vehicle speed (vehicle speed) detected by the vehicle speed sensor 19. In this case, the controller 11 stores a formula to calculate the power that can be generated by regeneration based on the vehicle speed, or a map that represents a relationship between vehicle speed and generateable power, and the controller 11 is able to use the formula or the map to calculate the generateable power.

[0041] The controller 11 performs a control operation such that the motor 18 regenerates power when the generateable power is greater than or equal to a given value. The given value is set to a value greater than the power required by the auxiliary units 15 to start the operation of the fuel cell 14. For example, it is possible to set the given value to a value greater than the power obtained by adding the power loss to the power required to start the operation of the fuel cell 14. The power loss is the power required to generate the power necessary to start the operation of the fuel cell 14.This means that the controller 11 is capable of performing a control operation such that the motor 18 regenerates power when the power obtained by subtracting at least one power loss from the power that can be generated through regeneration is greater than or equal to the power that allows the auxiliary units 15 to start the operation of the fuel cell 14. The power loss is the power required to obtain the power that can be generated through regeneration.

[0042] As previously explained, according to this embodiment, the controller 11 is capable of performing a control operation to initiate regeneration when the regeneration generates sufficient power to start operation of the fuel cell 14. Consequently, by performing power regeneration, it is possible to prevent the inertial travel distance from becoming short even if insufficient power is generated to start operation of the fuel cell 14. [Control sequence of a power supply]

[0043] Referring to Fig. Section 2 describes the processing sequence of a power supply carried out by the power supply system 1. This processing is controlled by the controller 11. The details of the processing are omitted, as they have already been explained.

[0044] Initially, in step S11, the controller 11 starts an intermittent operation, in which it switches intermittently between the execution and termination of power generation by the fuel cell 14 in order to supply power to the electrical power loads, which include the motor 18 and the auxiliary units 15.

[0045] In step S12, the controller 11 determines whether or not an abnormality occurs in the secondary battery 12. For example, an abnormality in the secondary battery 12 is detected in accordance with a control signal received by the controller 11 from the secondary battery 12 or the DC / DC converter 13, or by the fact that the control signal is not received. If an abnormality is determined to occur, processing continues with step S13.

[0046] In step S13, the controller 11 calculates the power that can be generated by a regeneration performed by the motor 18 and determines whether the generateable power is greater than or equal to a given value. For example, the power that can be generated by the regeneration is calculated based on a movement speed detected by the vehicle speed sensor 19. If it is determined that the generateable power is greater than or equal to the given value (Yes in step S13), then the processing continues with step S14. Otherwise (No in S13), the processing ends in Fig. 2 shown processing methods.

[0047] In step S14, the controller 11 performs a control operation such that an instruction is issued to the motor 18 to generate power. The processing then continues with step S15. If, in step S13, it is determined that the generateable power is less than the given value, then regeneration does not occur. In step S15, regenerated power is supplied to the auxiliary units 15, and the auxiliary units 15 initiate the operation of the fuel cell 14.

[0048] As explained above, according to this embodiment, even if an abnormality occurs in the secondary battery 12 during intermittent operation, regenerated power obtained from the motor 18 is supplied as drive power for the auxiliary units 15, and the power supply continues to initiate operation of the fuel cell 14.

[0049] Furthermore, according to this embodiment, the controller 11 is capable of performing control such that regeneration occurs when sufficient power can be generated from the regeneration to start operation of the fuel cell 14. Consequently, by regenerating power even if insufficient power is generated to start operation of the fuel cell 14, a short inertial travel distance can be prevented.

[0050] The embodiment of the invention has been explained with reference to the drawings. However, the scope of the invention is not limited to this embodiment. It is obvious that a person skilled in the art will arrive at various changes and modifications within the category described in the claims, and those changes and modifications fall within the scope of protection of the invention.

Claims

A power supply method carried out in a system comprising a fuel cell (14), a secondary battery (12), a motor (18), and an auxiliary unit (15) for the fuel cell, wherein the method comprises: controlling intermittent operation by which the fuel cell intermittently switches between performing and terminating power generation in order to supply power to electrical power loads comprising the motor and the auxiliary unit; determining whether or not an abnormality occurs in the secondary battery during intermittent operation; instructing the motor to regenerate power under the condition that, in determining whether or not an abnormality occurs, it is determined that the abnormality occurs in the secondary battery; and supplying power obtained by performing the regeneration to the auxiliary unit. Power supply method according to claim 1, further comprising calculating power that can be generated by the regeneration carried out by the motor when, in determining whether an abnormality occurs or not, it is determined that the abnormality occurs in the secondary battery during intermittent operation, wherein the regeneration is carried out when the power that can be generated is greater than or equal to a given value. Power supply method according to claim 2, further comprising measuring the speed of movement of a moving body on which the system is mounted, wherein the power that can be generated is calculated based on the measured speed of movement. Power supply method according to claim 2 or 3, wherein the instruction to carry out the regeneration is given when the power obtained by subtracting at least one loss power from the generateable power is greater than or equal to a power that allows the auxiliary unit to cause the fuel cell to commence operation, wherein the loss power is required to obtain the generateable power. Power supply method according to one of claims 1 to 4, wherein power obtained by performing the regeneration is stored in a capacitor. Power supply system comprising: a fuel cell (14); a secondary battery (12); a motor (18); an auxiliary unit (15) for the fuel cell; and a controller (11), wherein the controller is configured to control intermittent operation by which the fuel cell intermittently switches between performing and terminating power generation in order to supply power to electrical power loads which include the motor and the auxiliary unit, the controller is configured to determine whether or not an abnormality occurs in the secondary battery during intermittent operation, to instruct the motor to regenerate power under the condition that the abnormality is determined to occur, and to supply power to the auxiliary unit obtained by performing the regeneration. Power supply system according to claim 6, wherein the controller is configured to calculate power that can be generated by the regeneration performed by the motor when, in determining whether or not an abnormality occurs, it is determined that the abnormality occurs in the secondary battery during intermittent operation, and is also configured to cause the motor to perform the regeneration when the generateable power is greater than or equal to a given value. Power supply system according to claim 7, further comprising a vehicle speed sensor that measures the speed of movement of a moving body on which the power supply system is mounted, wherein the controller is configured to calculate the power that can be generated based on the measured speed of movement. Power supply system according to claim 7 or 8, wherein the controller is configured to perform regeneration when the power obtained by subtracting at least one power loss from the generateable power is greater than or equal to a power that allows the auxiliary unit to cause the fuel cell to commence operation, wherein the power loss is required to obtain the generateable power. Power supply system according to claims 6 to 9, further comprising a capacitor (20) which stores power obtained by performing the regeneration.

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