Fuel cell system

Abstract

Fuel cell system comprising: a fuel cell (110); a secondary battery (120); a first converter (150) placed between the fuel cell (110) and a load (130); a second converter (180) placed between the secondary battery (120) and the load (130); and a controller (160), the controller (160) being configured: i) to temporarily stop the operation of the fuel cell system when an overvoltage is generated in a converter from the group of first converters (150) and second converters (180); ii) to maintain a stopped state of the fuel cell system when an overvoltage is generated in another converter from the group of first converters (150) and second converters (180) in a state in which the operation of the fuel cell system has been temporarily stopped;andiii) to restart the operation of the fuel cell system if no overvoltage is generated in the other converter in the state in which the operation of the fuel cell system was temporarily stopped, wherein the fuel cell system further comprises a voltage sensing unit (Sv) configured to detect a voltage of one converter if no overvoltage is generated in the other converter in the state in which the operation of the fuel cell system was temporarily stopped, wherein the controller (160) is configured to restart the operation of the fuel cell system using only a power output from the other converter if a voltage of one converter detected by the voltage sensing unit (Sv) is higher than a predetermined value.;

Description

1. Field of the invention The invention relates to a fuel cell system comprising a fuel cell and a battery as power sources. 2. Description of the state of the art Various fuel cell systems have been proposed for installation in motor vehicles or similar vehicles. These systems include a fuel cell and a battery as power sources to cope with sudden fluctuations in consumer demand that exceed the power generation capacity of the fuel cell. If, for example, a system component in such a fuel cell system, such as a drive motor powered by electricity from the fuel cell and battery, or an inverter controlling the drive motor, malfunctions, an unbalanced power output will result. Therefore, a system has been proposed that employs a function to cause individual system components to independently perform fault detection or to stop for self-protection (fail-safe) to prevent an unbalanced power output. However, in a system using such a function, it is likely that a so-called simultaneous or related fault will occur, in which another system component also malfunctions due to a defect in a particular system component. As a countermeasure against a simultaneous fault, the following technology is disclosed, for example, in WO 2014 / 013606 A1. In a system comprising a fuel cell converter (hereinafter referred to as the "fuel cell converter"), a battery converter (hereinafter referred to as the "battery converter"), and an inverter placed between the fuel cell converter and a load, and this inverter also placed between the battery converter and the load, fault information is transmitted between a first controller, which detects a fault in the fuel cell converter, and a second controller, which detects a fault in both the battery converter and the inverter. If either the first controller or the second controller detects the occurrence of a fault in one converter, the operation of the other converter and the inverter is stopped. Furthermore, DE 10 2009 042 901 A1 discloses a method for operating a fuel cell system to provide electrical power. In the event of a fault, the fuel cell system is switched off by control electronics that detect the fault. The fault that led to the shutdown is evaluated by the control electronics. The fuel cell system is automatically restarted by the control unit if the evaluation of the fault allows for this. Furthermore, JP 2013-112 098 A discloses that a hybrid vehicle controller performs the following processing. When a reading from a low-voltage-side voltage sensor falls below a threshold voltage, an EV mode is restricted, and a first inverter is controlled to balance inputs and outputs between the power generated by a first motor and the power consumption of electrical devices, including a second motor. A low-voltage and a high-voltage side of a converter are short-circuited, and when a reading from the low-voltage-side voltage sensor matches that of a high-voltage-side voltage sensor, the EV mode restriction is maintained.If the reading of the low-voltage side voltage sensor is lower than that of the high-voltage side voltage sensor, even though the low-voltage and high-voltage sides of the converter are short-circuited, the EV mode restriction is lifted. SUMMARY OF THE INVENTION However, if, as in the technology disclosed in WO 2014 / 013606 A1, a specific defect occurs in one converter (for example, if an overvoltage is generated), the other converter or inverter will also cease operation. Consequently, the entire system must be shut down, even if there is no problem in the other converter or inverter, and therefore the problem arises that the system cannot operate efficiently. Therefore, the invention provides a fuel cell system comprising a fuel cell and a battery, in which the entire system can continue to operate even if an overvoltage is detected in a converter. The foregoing problem is solved by the subject matter of claim 1. Advantageous embodiments of the invention are the subject matter of the dependent claims that follow. An explanatory aspect of the present disclosure relates to a fuel cell system comprising a fuel cell, a secondary battery, a first converter placed between the fuel cell and a load, a second converter placed between the secondary battery and the load, and a controller. The controller is configured to temporarily halt the operation of the fuel cell system when an overvoltage is detected in one converter, either the first converter or the second converter. The controller is also configured to maintain a halted state in the fuel cell system when an overvoltage is detected in another converter, either the first converter or the second converter, in a state where the operation of the fuel cell system has been temporarily halted.The controller is configured to restart the operation of the fuel cell system if no overvoltage is detected in the other converter in a state where the operation of the fuel cell system has been temporarily stopped. According to this principle, if an overvoltage is generated in one converter but not in the other, the system as a whole can continue to operate. Therefore, compared to a prior art scenario where one converter must also cease operation if an anomaly (occurrence of an overvoltage or similar) is detected in the other converter, it is possible to operate the system more efficiently. The fuel cell system further includes a voltage sensing unit configured to detect a voltage from one converter when no overvoltage is detected in the other converter during the state in which the operation of the fuel cell system has been temporarily halted. The controller is configured to restart the operation of the fuel cell system using only one power output from the other converter if a voltage detected by the voltage sensing unit from one converter exceeds a predefined value. The first converter can be a fuel cell converter that includes a first overvoltage detection circuit. The second converter can be a battery converter that includes a second overvoltage detection circuit. The controller can be configured to temporarily halt the operation of the fuel cell system if the first overvoltage detection circuit detects an overvoltage in the fuel cell converter. The controller can be configured to maintain the halted state of the fuel cell system if the second overvoltage detection circuit detects an overvoltage in the battery converter, in the state to which the operation of the fuel cell system was temporarily halted.The controller can be configured to restart the operation of the fuel cell system if no overvoltage is detected in the battery converter by the second overvoltage detection circuit in the state where the operation of the fuel cell system was temporarily stopped. The fuel cell system may further include a voltage sensing unit configured to detect a voltage from the fuel cell converter when no overvoltage in the battery converter is detected by the second overvoltage detection circuit in the state where the operation of the fuel cell system is temporarily suspended. The controller may be configured to restart the operation of the fuel cell system using only one power output from the battery converter if a voltage from the fuel cell converter detected by the voltage sensing unit is higher than a preset value. The controller may be configured to override the first overvoltage detection circuit and restart the operation of the fuel cell system if the voltage from the fuel cell converter detected by the voltage sensing unit is lower than the preset value. The fuel cell system may further include a relay configured to control the connection between the fuel cell converter and the battery converter. The relay may be located between the fuel cell converter and the battery converter. The controller may be configured to determine that a circuit break occurs in the relay when the voltage of the fuel cell converter, as detected by the voltage sensing unit, is higher than the preset value. According to the invention, in a fuel cell system comprising a fuel cell and a battery as power sources, it is possible to cause the entire system to operate continuously, even when an overvoltage is detected in a converter. BRIEF DESCRIPTION OF THE DRAWINGS Features, advantages, and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements, and wherein: Fig. 1 is a diagram representing a configuration of a fuel cell hybrid vehicle system (FCHV system) according to one embodiment, mounted in a motor vehicle; Fig. 2 is a diagram representing a circuit diagram of a basic circuit of a fuel cell converter according to the embodiment; Fig. 3 is a flowchart representing a control program for overvoltage determination according to the embodiment; and Fig. 4 is a diagram representing a type table for overvoltage determination according to the embodiment. DETAILED DESCRIPTION OF EXECUTION FORMS (Embodiment) A fuel cell system according to one embodiment of the invention is described below with reference to the accompanying drawings. In this embodiment, a fuel cell system according to the invention is used as an onboard power generation system (FCHV system) of a fuel cell vehicle (a fuel cell hybrid vehicle (FCHV)), but it can be applied to various other movable objects (for example, a ship, an aircraft, or a robot) in addition to a motor vehicle, a stationary power supply device, or a mobile fuel cell system. An FCHV system 100 comprises, for example, a polymer electrolyte fuel cell 110 and a battery 120 as a power supply source for a consumer 130. The fuel cell 110 is a solid polymer electrolyte cell stack in which a plurality of cells are stacked in series. The fuel cell 110 includes a channel for supplying fuel gas to an anode, a channel for supplying oxidation gas to a cathode, and a channel for supplying coolant (none of which are shown) and can generate a desired electrical current by controlling the quantity of supplied fuel gas or oxidation gas by a controller 160 according to a control signal. The fuel cell 110 and the consumer 130 are connected to each other via a power line A. In the power line A, a fuel cell converter (hereinafter referred to as the "fuel cell converter") 150, a fuel cell relay 155 and an inverter 140 are positioned sequentially on the side of the fuel cell 110. The fuel cell converter 150 serves to control an output voltage of the fuel cell 110 and is a unidirectional voltage converter that increases the output voltage of the fuel cell 110, which is supplied on one input side (i.e., on the side of the fuel cell 110), and outputs the increased output voltage as the output voltage of the fuel cell converter 150 on one output side (i.e., to the side of the inverter 140). The control is performed by the fuel cell converter 150 such that the output voltage of the fuel cell 110 reaches a voltage corresponding to a target output. An overvoltage detection circuit (hereinafter referred to as the "fuel cell overvoltage detection circuit") 151 and a voltage sensor Sv, which detects an overvoltage on the output side of the fuel cell converter 150, are arranged on the output side of the fuel cell converter 150.When an overvoltage is detected on the output side of the fuel cell converter 150, the fuel cell overvoltage detection circuit (a first overvoltage detection circuit) 151 outputs a fuel cell overvoltage detection signal Sov1 to the controller 160. A power line B is connected to power line A. A connection point X between power line A and power line B is located between the fuel cell converter 150 and the inverter 140. The battery 120 is connected to one end of power line B, and a battery converter 180 is located between the battery 120 and connection point X. The connection between the fuel cell converter 150 and the battery converter 180 is switched between ON and OFF by the fuel cell relay 155, which is controlled by the controller 160. Battery 120 is connected in parallel to the fuel cell 110 and the consumer 130. It serves as a storage device for excess electricity, as a regenerative energy storage system during regenerative braking, and as an energy buffer when the load changes due to acceleration and deceleration of the fuel cell vehicle. For example, a secondary battery, such as a nickel-cadmium battery, a nickel-hydride battery, or a lithium secondary battery, is used as battery 120. The battery converter 180 serves to control an output voltage of the battery 120 (an input voltage Vin of the inverter 140). An overvoltage detection circuit (hereinafter referred to as the "battery overvoltage detection circuit") 181, which detects an overvoltage on an output side of the battery converter 180, is arranged on an output side of the battery converter 180. When the overvoltage on the output side of the battery converter 180 is detected, the battery overvoltage detection circuit (a second overvoltage detection circuit) 181 outputs a battery overvoltage detection signal Sov2 to the controller 160. The circuit diagram of the battery converter 180 can have the same arrangement as the fuel cell converter 150, but is not limited to this and can use any arrangement as long as it can control the input voltage Vin of the inverter 140. The inverter 140, for example, is a PWM inverter driven by pulse width modulation. It converts the direct current output from the fuel cell 110 and / or the battery 120 into three-phase alternating current according to a control command from the controller 160 and supplies the three-phase alternating current to the load 130. Examples of loads 130 include an air compressor or a drive motor, but the load is not limited to these examples. Although not shown in the drawings, in this embodiment, on a low-voltage side (the side of battery 120) of the power line B, an auxiliary motor is provided which drives a hydrogen pump for returning hydrogen-containing gas, which has been expelled from a hydrogen gas passage of the fuel cell 110, an auxiliary motor which drives a coolant pump for circulating a coolant which is used to adjust the temperature of the fuel cell 110, an auxiliary inverter which converts a direct current into three-phase alternating current and supplies the three-phase alternating current to the auxiliary motors (none of which are shown) and the like. Fig. 2 is a diagram showing a circuit diagram of a basic circuit of the fuel cell converter 150. In Fig. 2, for the purpose of a simpler description, an unboosted voltage supplied to the fuel cell converter 150 is defined as the input voltage VI, and a boosted voltage output from the fuel cell converter 150 is defined as the output voltage Vh. The fuel cell converter 150 comprises a reactor (inductor) L1, a rectifying diode D1, a switching element SW1 formed from an insulated-gate bipolar transistor (IGBT), and a smoothing capacitor C1. One end of the reactor (inductor) L1 is connected to an output terminal of the fuel cell 110, and the other end is connected to the collector of the switching element SW1. The switching element SW1 is connected between a power line of the inverter 140 and a ground line. Specifically, the collector of the switching element SW1 is connected to the power line, and its emitter is connected to the ground line. In this configuration, when the switching element SW1 is switched on, current first flows from the fuel cell 110 to the inductor L1, then to the switching element SW1, and the inductor L1 is excited by a direct current at this time and stores magnetic energy. Subsequently, when the switching element SW1 is switched off, an induced voltage resulting from the magnetic energy stored in the inductor L1 is superimposed on the output voltage of the fuel cell 110 (i.e., the input voltage VI of the fuel cell converter 150). An operating voltage (i.e., the output voltage Vh of the fuel cell converter 150), which is higher than the input voltage VI smoothed by the capacitor C1, is output by the inductor L1, and an output current is passed through the diode D1. The controller 160 obtains a desired output voltage Vh by appropriately varying the ON / OFF duration of the switching element SW1.If a circuit break occurs in the fuel cell relay 155, which connects the fuel cell converter 150 and the battery converter 180, electrical current whose output destination has disappeared is stored in the capacitor C1 in the fuel cell converter 150 and eventually an overvoltage (a voltage higher than a nominal voltage) is generated in the capacitor C1. Referring back to Fig. 1, the controller 160 is a computer system for controlling the FCHV system 100 and includes, for example, a CPU, RAM, and ROM. The controller 160 receives input values ​​from various signals supplied by a sensor group 170 (for example, a signal indicating the degree of accelerator pedal opening, a signal indicating vehicle speed, and a signal indicating an output current or voltage at the output terminal of the fuel cell 110) and calculates the power required for the consumer 130 (that is, the power required for the entire system). The power required for consumer 130, for example, is the sum of the vehicle's driving power and auxiliary machine power. Auxiliary machine power includes electrical power consumed in onboard auxiliary machines (such as a humidifier, air compressor, hydrogen pump, and coolant circulation pump), electrical power consumed by devices required for driving a motor vehicle (such as a gearbox, wheel steering, steering system, and suspension), and electrical power consumed by devices located in the passenger compartment (such as an air conditioner, lighting system, and audio system). The controller 160 determines a distribution rate of the output power of the fuel cell 110 and the battery 120 and calculates a power generation command value. Once the required power for the fuel cell 110 and the battery 120 has been calculated, the controller 160 controls the operation of the fuel cell converter 150 and the battery converter 180 in such a way that the required power is obtained. The controller 160 according to this embodiment has an overvoltage detection function for the converters (the fuel cell converter 150 and the battery converter 180). Specifically, when a fuel cell overvoltage detection signal Sov1 is received from the fuel cell overvoltage detection circuit 151, the controller 160 determines that an overvoltage is generated on the output side of the fuel cell converter 150. When a battery overvoltage detection signal Sov2 is received from the battery overvoltage detection circuit 181, the controller 160 determines that an overvoltage is generated on the output side of the battery converter 180. If a voltage value V1, detected by a voltage sensor Sv located on the output side of the fuel cell converter 150, is higher than a predetermined voltage level limit Lmax, the controller 160 determines that an overvoltage is generated.A specific process for determining an overvoltage by the controller 160 is described in detail below with reference to Fig. 3. Figure 3 is a flowchart illustrating an overvoltage detection control process performed by the controller 160. When an overvoltage is detected on the output side of the fuel cell converter 150, the fuel cell overvoltage detection circuit 151 outputs a fuel cell overvoltage detection signal Sov1 to the controller 160. When the fuel cell overvoltage detection signal Sovl is received, the controller 160 determines that an overvoltage is being generated on the output side of the fuel cell converter 150 (step S1) and temporarily shuts down the FCHV system 100 as a whole (step S2). The controller 160 then also determines whether an overvoltage is generated on the output side of the battery converter 180 (step S3). If a battery overvoltage detection signal Sov2 is received from the battery overvoltage detection circuit 181, the controller 160 also determines that an overvoltage is generated on the output side of the battery converter 180 (YES in step S3).In this way, when an overvoltage is detected in the same way by the overvoltage detection circuits of both converters (i.e., the fuel cell overvoltage detection circuit 151 and the battery overvoltage detection circuit 181) connected to the inverter 140, the controller 160 determines that the relay (i.e., the fuel cell relay 155) located between the fuel cell 110 and the inverter 140 is normally connected and maintains the suspended state of operation of the FCHV system 100 until the overvoltage is released (step S4). If, on the other hand, a battery overvoltage detection signal Sov2 is not received by the battery overvoltage detection circuit 181 and it is determined that an overvoltage is not being generated on the output side of the battery converter 180 (NO in step S3), the controller 160 causes the sequence to proceed to step S5. Then, the controller (the voltage detection unit) 160 measures a voltage value V1 on the output side of the fuel cell converter 150 using the voltage sensor Sv located on the output side of the fuel cell converter 150. The controller 160 determines whether the voltage value V1, detected by the voltage sensor Sv located on the output side of the fuel cell converter 150, is lower than a predetermined voltage level limit Lmax (step S6).If the voltage value V1 detected by the voltage sensor Sv is lower than the specified voltage level limit Lmax (JA in step S6), the controller 160 determines that a specific fault (an anomaly) exists in the overvoltage detection circuit (i.e., in the fuel cell overvoltage detection circuit 151) located in the fuel cell converter 150, disables the fuel cell overvoltage detection circuit 151, continues the operation (including driving the fuel cell vehicle) of the FCHV system 100 (restarts it) (step S7) and terminates the control program for an overvoltage determination. On the other hand, if the voltage value V1 detected by the voltage sensor Sv is higher than the voltage level limit Lmax (NO in step S6), the controller 160 determines that a circuit breaker (an open circuit fault) is occurring in the fuel cell relay 155, which connects the fuel cell converter 150 and the battery converter 180, continues to operate the FCHV system 100 as a whole using only the battery 120 as the power source (step S8) and terminates the control program for an overvoltage determination. Fig. 4 is a diagram representing a type table for overvoltage determination TB1, in which overvoltage determination results of the controller 160 are compiled. As shown in Fig. 4, the overvoltage determination results are differentiated between three types, Type 1 to Type 3. Type 1 is a case in which an overvoltage is not actually generated, but it is determined that an overvoltage is generated in the fuel cell converter 150 because the overvoltage detection circuit of the fuel cell converter 150 (the fuel cell overvoltage detection circuit 151) has a fault (step S1 → S2 → S3 → S5 → S6 → S7). In this case, since an overvoltage is not actually generated, the overvoltage detection circuit of the fuel cell converter 150 is overridden and the operation of the FCHV system 100 as a whole is carried out continuously. Type 2 is a case in which an overvoltage is actually generated due to a circuit breaker in the relay (the fuel cell relay 155) that connects the two converters, and it is determined that an overvoltage is generated in the fuel cell converter 150 (step S1 → S2 → S3 → S5 → S6 → S8). In this case, since an overvoltage is indeed generated in the fuel cell converter 150, but there is no anomaly in the power line B of the battery 120, the operation of the FCHV system 100 as a whole is carried out continuously using only the battery 120 as the power source. Type 3 is a case where a fault in the relay (the fuel cell relay 155) connecting the two converters is not confirmed, but the generation of an overvoltage by the overvoltage detection circuits (the fuel cell overvoltage detection circuit 151 and the battery overvoltage detection circuit 181) of both converters is detected (step S1 → S2 → S3 → S4). In this case, since an overvoltage is not actually generated in the fuel cell converter 150 and the battery converter 180, the suspended operating state of the FCHV system 100 is maintained until the overvoltage is released. As described above, according to this embodiment, if an overvoltage is generated in one of the converters (in the example above, the fuel cell converter 150) and no overvoltage is generated in the other converter (in the example above, the battery converter 180), it is possible to allow the entire system to operate continuously (see Type 1 and Type 2 in Fig. 4). Accordingly, compared to a prior art case in which one converter must also cease operation when an anomaly is detected in the other converter (occurrence of an overvoltage or the like), it is possible to operate the system more efficiently. If an overvoltage is generated in one converter (in the example above, in the fuel cell converter 150) and an overvoltage is not generated in the other converter (in the example above, in the battery converter 180), it is possible to determine whether the cause of the overvoltage is an open circuit of the relay (in the example above, the fuel cell relay 155) that connects both converters, or a defect in the overvoltage detection circuit (in the example above, the fuel cell overvoltage detection circuit 151) of one converter, and to perform appropriate system control measures. In this embodiment, a configuration is used in which one converter is the fuel cell converter 150 and the other converter is the battery converter 180, but a reverse configuration can also be used. That is, a configuration in which one converter is the battery converter 180 and the other converter is the fuel cell converter 150 can be used. In this embodiment, an overvoltage generated in the fuel cell converter 150 is detected first; however, the same applies if an overvoltage generated in the battery converter 180 is detected first. The invention can be applied to various systems comprising two or more converters.

Claims

Fuel cell system comprising: a fuel cell (110); a secondary battery (120); a first converter (150) placed between the fuel cell (110) and a load (130); a second converter (180) placed between the secondary battery (120) and the load (130); and a controller (160), the controller (160) being configured: i) to temporarily stop the operation of the fuel cell system when an overvoltage is generated in a converter from the group of first converters (150) and second converters (180); ii) to maintain a stopped state of the fuel cell system when an overvoltage is generated in another converter from the group of first converters (150) and second converters (180) in a state in which the operation of the fuel cell system has been temporarily stopped;andiii) to restart the operation of the fuel cell system if no overvoltage is generated in the other converter in the state in which the operation of the fuel cell system was temporarily stopped, wherein the fuel cell system further comprises a voltage sensing unit (Sv) configured to detect a voltage of one converter if no overvoltage is generated in the other converter in the state in which the operation of the fuel cell system was temporarily stopped, wherein the controller (160) is configured to restart the operation of the fuel cell system using only a power output from the other converter if a voltage of one converter detected by the voltage sensing unit (Sv) is higher than a predetermined value.; Fuel cell system according to claim 1, wherein: the first converter (150) is a fuel cell converter comprising a first overvoltage detection circuit (151); the second converter (180) is a battery converter comprising a second overvoltage detection circuit (181); and the controller (160) is configured: i) to temporarily halt the operation of the fuel cell system when an overvoltage is detected in the fuel cell converter by the first overvoltage detection circuit (151); ii) to maintain the halted state of the fuel cell system when an overvoltage is detected in the battery converter by the second overvoltage detection circuit (181) in the state in which the operation of the fuel cell system was temporarily halted;andiii) to restart the operation of the fuel cell system if no overvoltage is detected in the battery converter by the second overvoltage detection circuit (181) in a state in which the operation of the fuel cell system has been temporarily stopped.; Fuel cell system according to claim 2, wherein the voltage sensing unit (Sv) is configured to detect a voltage of the fuel cell converter when no overvoltage in the battery converter is detected by the second overvoltage detection circuit (181) in the state in which the operation of the fuel cell system has been temporarily stopped, wherein: the controller (160) is configured to restart the operation of the fuel cell system using only a power output from the battery converter if a voltage of the fuel cell converter detected by the voltage sensing unit (Sv) is higher than a predetermined value; and the controller (160) is configured to override the first overvoltage detection circuit (151) and restart the operation of the fuel cell system if the voltage of the fuel cell converter detected by the voltage sensing unit (Sv) is lower than the predetermined value. Fuel cell system according to claim 3, which further comprises a relay (155) configured to control the connection between the fuel cell converter and the battery converter, wherein the relay (155) is placed between the fuel cell converter and the battery converter, wherein the controller (160) is configured to determine that a circuit break in the relay (155) takes place when the voltage of the fuel cell converter detected by the voltage sensing unit (Sv) is higher than the predetermined value.

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