JP2018032554A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which suppresses erroneous determination in welding detection. A fuel cell system according to the present invention includes a secondary battery 109, an output control unit 105, a battery relay unit 108, a fuel cell 102, and a control device 101. Then, the control device 101 raises the voltage V2 of the capacitor 105c to a voltage higher than the maximum voltage of the secondary battery 109 when the fuel cell 102 is not generating power, and one of the relays included in the battery relay unit 108 Welding of relay terminals is detected by connecting one of the relays, disconnecting the other relays, and discharging the capacitor at a predetermined rate. The discharging speed at this time is slower than the charging speed at which the capacitor 105c is charged by the secondary battery 109 when the battery precharge relay is connected. [Selection diagram] Figure 2

Description

  The present invention relates to a fuel cell system.

  In recent years, systems using fuel cells that generate electricity by mixing fuel gas and oxidizing gas have been developed. Patent Document 1 discloses a fuel cell system in which a relay is provided between a fuel cell stack and a boost converter. In such a system, when the relay is turned on from off, the relay terminal may be welded by arc discharge. Therefore, the fuel cell system includes means for detecting welding of the relay terminal.

JP 2013-247084 A

  As a means for detecting the welding of the relay terminal, a method of detecting a change in voltage generated between the terminals of the relay by discharging a capacitor connected to the boost converter can be considered. However, in a system having a precharge relay connected in parallel with a main relay connected to a battery, when the precharge relay is welded, the charge rate for the discharged capacitor is slow. For this reason, in such a system, there is a risk of erroneous determination that the precharge relay is not welded even though the precharge relay is welded.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a fuel cell system that suppresses erroneous determination in welding detection.

  A fuel cell system according to the present invention includes a secondary battery, a first booster circuit that boosts the voltage of the secondary battery, and a capacitor that accumulates electric charge according to the voltage boosted by the first booster circuit. A first main relay that connects or disconnects the high potential terminal of the secondary battery and the high potential terminal of the output control unit, and the low potential terminal of the secondary battery and the output control unit. A battery relay unit comprising: a second main relay that connects or disconnects the low-potential terminal; and a battery precharge relay that is connected in parallel to the second main relay and has a resistance; a fuel cell; and the output control The FC boost unit having a second booster circuit that boosts the voltage of the fuel cell and the voltage of the capacitor are measured to detect that the battery relay unit is welded. And when the fuel cell is not generating power, the control device connects any one of the relays provided in the battery relay unit and shuts off the other relays. Further, when the capacitor is discharged at a predetermined speed and the voltage of the capacitor becomes substantially equal to the voltage of the secondary battery, it is determined that any one of the interrupted relays is welded. When the voltage of the capacitor drops to a predetermined voltage, it is determined that none of the interrupted relays are welded, and the predetermined discharge rate is determined when the battery precharge relay is connected. It is slower than the charging speed at which the capacitor is charged by the secondary battery.

  In this way, by setting the discharge speed of the capacitor to a predetermined speed, when the battery precharge relay to which the limiting resistor is connected is welded, the voltage of the capacitor is lower than the voltage of the secondary battery. Can be suppressed. Therefore, welding detection can be performed similarly to the case where the main relay is welded.

  According to the present invention, it is possible to provide a fuel cell system that suppresses erroneous determination in welding detection.

1 is a circuit diagram of a fuel cell system 100 according to an embodiment. It is a flowchart of the welding detection in the fuel cell system 100 which concerns on embodiment. It is a time chart of welding detection in fuel cell system 100 concerning an embodiment. It is a time chart of welding detection in fuel cell system 100 concerning an embodiment.

<Embodiment>
First, an embodiment according to the present invention will be described. FIG. 1 is a circuit diagram of a fuel cell system according to an embodiment. The fuel cell system 100 includes a control unit 101, an FC stack 102, an FC boost converter 103, an FC relay 104, an output control unit 105, a drive motor 106, a compressor motor 107, a system main relay 108, and a secondary battery 109. The voltage generated by the FC stack 102 is boosted by the FC boost converter 103 and transmitted to the output control unit 105 via the FC relay 104. The voltage of the secondary battery 109 is transmitted to the output control unit 105 via the system main relay 108. The output control unit 105 drives the drive motor 106 and the compressor motor 107.

  Next, the detail of each part is demonstrated. The control unit 101 is connected to each unit and performs operation control. The control unit 101 is connected to voltmeters 200 to 204 and monitors the voltages V0 to V4. Similarly, the control unit 101 is connected to the ammeters 301 and 302 and monitors the currents A1 and A2. Further, the control unit 101 detects welding of the relay terminal.

  The FC stack 102 is a fuel cell that generates electric power by mixing fuel gas and oxidizing gas. The fuel gas is, for example, hydrogen. The oxidizing gas is, for example, air. The FC stack 102 generates power when supplied with fuel gas and oxidizing gas, and stops generating power when the supply of fuel gas and oxidizing gas is stopped. A voltmeter 200 is connected to both terminals of the FC stack, and the voltage V0 of the FC stack 102 is monitored.

  The FC boost converter 103 boosts the voltage of the power generated by the FC stack 102. The FC boost converter 103 includes a booster circuit including a capacitor 103a. The capacitor 103a accumulates electric charge according to the voltage boosted by the booster circuit. The FC boost converter 103 includes an ammeter 301 and a voltmeter 201. The ammeter 301 monitors the current A1 flowing through the switching transistor of the booster circuit. The voltmeter 201 is connected between both terminals of the capacitor 103a and monitors the voltage V1 of the capacitor 103a.

  The FC relay 104 includes a relay circuit that connects or disconnects the FC boost converter 103 and the output control unit 105. The FC relay 104 includes a relay FCRB on the plus side wiring. Further, the FC relay 104 includes a relay FCRP on the minus side wiring and a relay FCRG connected in parallel to the relay FCRP. The relay FCRP is a precharge relay, and a limiting resistor 104a is connected in series.

  The output control unit 105 converts the direct current of the FC relay 104 or the system main relay 108 into alternating current and drives the drive motor 106 and the compressor motor 107. The output control unit 105 includes a capacitor 105a, a booster circuit 105b, a capacitor 105c, an inverter 105d, a voltmeter 202, and a voltmeter 203. Capacitor 105 a stores a voltage supplied from secondary battery 109 via system main relay 108. The voltmeter 203 monitors the voltage V3 of the capacitor 105a. The booster circuit 105b boosts the voltage of the capacitor 105c. The capacitor 105c accumulates the voltage supplied via the FC relay 104 or the booster circuit 105b, and supplies the voltage to the inverter 105d. The voltmeter 202 monitors the voltage V2 of the capacitor 105c. The inverter 105d converts the direct current supplied from the capacitor 105c into alternating current. The inverter 105d is connected to the drive motor 106 and the compressor motor 107.

  The drive motor 106 and the compressor motor 107 are AC three-phase motors. The drive motor 106 is a motor for driving the fuel cell system 100. The compressor motor 107 is a motor for an air compressor for supplying gas to the fuel cell. By driving the drive motor 106 and the compressor motor 107, the voltage accumulated in the capacitor 105c is discharged. In the present embodiment, the control unit 101 can control the discharge speed of the capacitor 105 c by controlling the drive motor 106. At this time, the voltage value V <b> 2 of the capacitor 105 c is sequentially monitored by the voltmeter 202.

  The system main relay 108 includes a relay circuit that connects or disconnects the secondary battery 109 and the output control unit 105. The system main relay 108 includes a relay SMRB and an ammeter 302 on the plus side wiring. The system main relay 108 includes a relay SMRP on the minus side wiring and a relay SMRG connected in parallel to the relay SMRP. The relay SMRP is a battery precharge relay for precharging, and a limiting resistor 108a is connected in series. The ammeter 302 monitors the current A2.

  The secondary battery 109 is a chargeable / dischargeable secondary battery. The secondary battery is, for example, a nickel metal hydride battery or a lithium ion battery. The secondary battery 109 is connected to the system main relay 108. A voltmeter 204 is connected between both terminals of the secondary battery 109. The voltmeter 204 monitors the voltage V4 of the secondary battery.

  The circuit diagram of the fuel cell system 100 according to the present embodiment has been described so far. In the fuel cell system 100, the FC relay 104 and the system main relay 108 connect or cut off a high voltage of, for example, about 600 volts. Therefore, for example, when a circuit interrupted by each relay included in the system main relay 108 is connected, arc discharge occurs between the terminals of the relay, which may cause the terminals to become hot and the relay terminals to be welded. If the relay terminal is welded, the welded relay terminal cannot be cut off, causing a problem in the system. Therefore, the fuel cell system 100 performs a process of detecting that the relay terminal is not welded. Alternatively, when the relay terminal is welded, the fuel cell system 100 performs processing for detecting which terminal is welded.

  Next, welding detection processing in the fuel cell system 100 according to the present embodiment will be described. The following description is welding detection performed for each relay terminal included in the system main relay 108. Although welding detection is also performed for each relay terminal included in the FC relay 104, it is omitted here.

  FIG. 2 is a flowchart of welding detection in fuel cell system 100 according to the present embodiment. In fuel cell system 100 according to the present embodiment, welding detection is performed when the system is stopped.

  First, the control unit 101 receives a system stop command (step S10). When receiving a system stop command, the control unit 101 starts welding detection. In addition, before stopping the fuel cell system 100 at this time, among the relays provided in the FC relay 104, the relays FCRB and FCRG are connected. In addition, among the relays included in the system main relay, relay SMRB and relay SMRG are connected.

  The control unit 101 sets the V2 voltage command to the check voltage Vch (step S11). That is, the voltage V2 of the capacitor 105c is set to the check voltage Vch necessary for detecting welding. Here, the voltage of the secondary battery 109 is assumed to be a voltage VB. At this time, the check voltage Vch necessary to detect welding is set to be higher than the voltage VB.

  Next, the booster circuit 105b included in the output control unit 105 boosts the voltage V2 of the capacitor 105c. Then, the control unit 101 determines whether or not the voltage V2 of the voltmeter 202 is substantially equal to the check voltage Vch (step S12). When the voltage V2 of the voltmeter 202 is not equal to Vch (step S12: No), the control unit 101 maintains the operation of the booster circuit 105b. When the voltage V2 of the voltmeter 202 becomes substantially equal to the check voltage Vch (step S12: Yes), the control unit 101 stops the operation of the booster circuit 105b (step S13).

  Next, control unit 101 disconnects relay SMRG (step S14). As a result, the negative relay between the capacitor 105c and the secondary battery 109 is cut off.

  Next, the control unit 101 performs discharge for detection of welding (step S15). Specifically, the control unit 101 drives the drive motor 106 and consumes the electric power stored in the capacitor 105c. When power is consumed by the drive motor 106, the voltage of the capacitor 105c decreases. The discharge for welding detection performed here satisfies the following two conditions in order to perform welding detection described later.

  That is, as the condition 1, the voltage V2 of the capacitor 105c is set to be lower than the voltage VB of the secondary battery 109. In the fuel cell system according to the present embodiment, the voltage V2 after discharge is set to be approximately 0V. However, the voltage V2 after the discharge only needs to satisfy the condition 1, and need not be 0V.

  Further, as condition 2, the discharge speed is set as follows. That is, when the battery precharge relay SMRP is connected, the speed at which the secondary battery 109 increases the voltage of the capacitor 105c is set as the boost speed Vup. Further, the speed at which the voltage is lowered when the drive motor 106 discharges the capacitor 105c is defined as a step-down speed Vdn. At this time, the step-up speed Vup> the step-down speed Vdn.

  By setting in this way, when the battery precharge relay SMRP is welded, it is possible to suppress the voltage drop of the capacitor 105c excessively.

  Next, the control unit 101 determines whether or not the voltage V2 of the voltmeter 202 is substantially equal to 0V (step S16). When the voltage V2 is substantially equal to 0V (step S16: Yes), the voltage V2 of the capacitor 105c is not affected by other blocks. That is, it is determined that the relay SMRP and relay SMRG that are shut off among the relays included in the system main relay 108 are not welded.

  On the other hand, when it is not determined that the voltage V2 is substantially equal to 0 V (step S16: No), the voltage V2 of the capacitor 105c is affected and changed by another block.

  Therefore, next, the control unit 101 determines whether or not the voltage V2 is substantially equal to the voltage VB of the secondary battery 109 (step S21).

  When voltage V2 is substantially equal to voltage VB of secondary battery 109 (step S21: Yes), control unit 101 determines that relay SMRP or relay SMRG is welded (step S22). That is, among the relays included in the system main relay 108, when the interrupted relay SMRP or relay SMRG is welded, the capacitor 105c and the secondary battery 109 are connected. Therefore, the voltage VB of the secondary battery 109 flows to the capacitor 105c. As a result, the voltage V2 becomes substantially equal to the voltage VB.

  Here, consider the case where it is the relay SMRP that is welded. When the relay SMRP is welded, the current flowing through the capacitor 105c via the relay SMRP is limited due to the influence of the limiting resistor 108a connected to the relay SMRP. For this reason, the voltage V2 of the capacitor 105c is boosted by a time constant corresponding to the limiting resistor 108a. Here, as described above, since the step-down speed Vdn, which is the discharge speed, is slower than the step-up speed Vup, which is the charge speed, a delay occurs compared to the case where the main relay SMRG is welded, but the capacitor 105c Is equal to the voltage VB of the secondary battery 109.

  On the other hand, when the voltage V2 is not equal to the voltage VB of the secondary battery 109 in step S21 (step S21: No), the control unit 101 determines that an error other than welding has occurred (step S25).

  In Step S16, when it is determined that the relay SMRP and the relay SMRG that are cut off are not welded (Step S16: Yes), the control unit 101 cuts off the relay SMRB (Step S17). Subsequently, the control unit 101 connects the relay SMRP (step S18). Then, the control unit 101 detects welding of the plus side relay SMRB.

  The control unit 101 determines whether or not the voltage V2 is substantially equal to 0V (step S19). When the voltage V2 is substantially equal to 0V (step S19: Yes), the voltage V2 of the capacitor 105c is not affected by other blocks. That is, it is determined that relay SMRB is not welded. Although it can be determined here that the relay SMRP is not welded, it has already been confirmed in step S16.

  In step S19, as a result of determining that the relay SMRB is not welded, all the relays included in the system main relay 108 are not welded. In this case (step S19: Yes), the welding detection process is terminated, and the capacitor 105c is finally discharged (step S20). The final discharge is performed until the voltage of the capacitor 105c approaches zero. Then, the fuel cell system 100 stops the system.

  On the other hand, when it is not determined that the voltage V2 is substantially equal to 0 V (step S19: No), the voltage V2 of the capacitor 103a is changed by being influenced by other blocks.

  Therefore, next, the control unit 101 determines whether or not the voltage V2 is substantially equal to the voltage VB of the secondary battery 109 (step S23).

  When voltage V2 is substantially equal to voltage VB of secondary battery 109 (step S23: Yes), control unit 101 determines that relay SMRB is welded (step S24). That is, when relay SMRB is welded, capacitor 105c and secondary battery 109 are connected. Therefore, the voltage VB of the secondary battery 109 flows to the capacitor 105c. As a result, the voltage V2 becomes substantially equal to the voltage VB.

  On the other hand, when the voltage V2 is not equal to the voltage VB of the secondary battery 109 in step S23 (step S23: No), the control unit 101 determines that an error other than welding has occurred (step S25).

  In the foregoing, the flowchart of the welding detection in the fuel cell system according to the present embodiment has been described. Here, the minus side welding is detected and then the plus side welding is detected. However, the plus side welding may be detected first.

  Next, changes in main signals at the time of detection of welding will be described with reference to FIGS. FIG. 3 is a time chart for detection of welding in the fuel cell system according to the present embodiment. FIG. 3 is a specific example in the case where welding detection is performed on the negative relay in the system main relay 108. FIG. 3 shows the state of disconnection or connection of relay SMRB, relay SMRP, and relay SMRG. Here, On shown in FIG. 3 is a connected state, and Off is a cut-off state. FIG. 3 shows the state of the discharge command DC. Here, On is a state in which the discharge command DC is on, and Off is a state in which the discharge command DC is off.

  Further, FIG. 3 shows the change of the voltage V2 of the capacitor 105c in accordance with the state of each relay and the signal of the discharge command. Here, the broken line Vok1 is a change in the voltage V1 when it is determined that the welding is not performed as a result of performing the welding detection on the minus side. A two-dot chain line Vng1 is a change in the voltage V2 when it is determined that welding is performed as a result of performing welding detection on the minus side.

  Below, each signal for every time is demonstrated. As shown in FIG. 2, upon receiving the system stop command (FIG. 2: step S10), the control device 101 activates the boost converter 105b, and sets the voltage V1 of the capacitor 103a and the voltage V2 of the capacitor 105c to the check voltage Vch. Set. In FIG. 3, the boost converter 105b is started from time t0, and the voltage V1 is boosted to the check voltage Vch before time t1.

  Next, at time t1, relay SMRG is cut off (FIG. 2: step S14), and subsequently, at time t2, discharge command DC is turned on (FIG. 2: step S15).

  Here, when the voltage V2 is in the state of the broken line Vok1, neither the negative-side relay SMRP nor the relay SMRG included in the system main relay 108 is welded (FIG. 2: Step S16: Yes). On the other hand, as indicated by the two-dot chain line Vng1, when either the negative relay SMRP or the relay SMRG included in the system main relay 108 is welded (FIG. 2: Step S16: No), the voltage V2 is 0V. It drops to near.

  Next, with reference to FIG. 4, a specific example in the case where welding detection is performed on the plus side relay SMRB in the system main relay 108 will be described. FIG. 4 is a time chart for detection of welding in the fuel cell system according to the present embodiment.

  When welding is not detected in the negative relay in system main relay 108 (FIG. 2: step S16: Yes), relay SMRB is cut off at time t3 as shown in FIG. 4 (FIG. 2: step S17). . Subsequently, at time t4, relay SMRG is connected (FIG. 2: step S18).

  Here, when voltage V2 is in the state of broken line Vok2, relay SMRB is not welded (FIG. 2: Step S19: Yes). On the other hand, as indicated by the two-dot chain line Vng2, when the relay SMRB is welded (FIG. 2: Step S19: No), the voltage V2 is substantially equal to the voltage VB of the secondary battery 109.

  When the welding detection for each relay included in the FC relay 104 is completed, the control unit 101 turns on the discharge command DC and performs the final discharge (FIG. 2: step S20). Specifically, the relay FCRP is cut off at time t5, and then discharge is performed between time t6 and time t7.

  As described above, by setting the step-down speed Vdn of the capacitor 105c slower than the step-down speed Vup charged from the secondary battery 109, the battery precharge relay SMRP to which the limiting resistor 108a is connected is welded. It can be suppressed that the voltage V2 of the capacitor 105c is lower than the voltage VB of the secondary battery 109. Therefore, welding detection can be performed similarly to the case where the main relay is welded. Therefore, the fuel cell system 100 can suppress erroneous determination in welding detection.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the present invention in addition to the contents described here.

DESCRIPTION OF SYMBOLS 100 Fuel cell system 101 Control part 102 FC stack 103 FC boost converter 104 FC relay 105 Output control part 106 Drive motor 107 Compressor motor 108 System main relay 109 Secondary battery 200, 201, 202, 203, 204 Voltmeter 301, 302 Current Total 103a, 105a, 105c Capacitor 104a, 108a Limiting resistor 105d Inverter FCRB, FCRG, FCRP relay SMRB, SMRG, SMRP relay Vch check voltage

Claims (1)

A secondary battery,
An output control unit comprising: a first booster circuit that boosts the voltage of the secondary battery; and a capacitor that accumulates electric charge according to the voltage boosted by the first booster circuit;
A first main relay for connecting or disconnecting the high potential terminal of the secondary battery and the high potential terminal of the output control unit, or connecting the low potential terminal of the secondary battery and the low potential terminal of the output control unit; A battery relay unit comprising: a second main relay to be cut off; and a battery precharge relay connected in parallel to the second main relay and having a resistance;
A fuel cell;
An FC booster connected to the output controller and having a second booster that boosts the voltage of the fuel cell;
A control device for detecting that the battery relay unit is welded by measuring the voltage of the capacitor;
With
The controller is
When the fuel cell is not generating electricity, when any one of the relays provided in the battery relay unit is connected, the other relays are shut off, and the capacitor is discharged at a predetermined speed ,
When the voltage of the capacitor is substantially equal to the voltage of the secondary battery, it is determined that any one of the interrupted relays is welded,
When the voltage of the capacitor drops to a predetermined voltage, it is determined that none of the interrupted relays are welded,
The predetermined discharge rate is slower than a charge rate at which the capacitor is charged by the secondary battery when the battery precharge relay is connected,
Fuel cell system.

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