JP6597973B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  As a fuel cell system mounted on a fuel cell vehicle, etc., it is estimated from the rate of temperature rise even if the coolant outlet temperature of the fuel cell stack is 0 ° C or higher or 0 ° C or lower during warm-up processing When shifting to a state where it can be determined that there is no risk of water freezing, the output from the fuel cell is permitted, and the output permission state is displayed step by step according to the power that can be generated calculated from the coolant outlet temperature (For example, refer to Patent Document 1).

JP 2010-192380 A

  By the way, if the temperature deviation occurs in the cell plane during the warm-up process of the fuel cell stack, the cooling medium may flow only in a portion where the temperature is relatively high, and the cooling medium outlet temperature may rise faster than usual. Therefore, if the output permission is determined only by the coolant outlet temperature of the fuel cell stack, the output permission determination may be erroneous. In this state, if the gas flow rate is increased according to the output demand, the liquid water remaining in the cell flow path moves from the high temperature area to the low temperature area below freezing point and freezes again. It may occur and start reliability at low temperatures may be reduced.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel cell system with high starting reliability at low temperatures.

In order to achieve the above object, the fuel cell system of the present invention comprises:
A fuel cell stack in which a plurality of cells that generate power by supplying reactive gas are stacked;
A coolant circulation system for circulating a coolant in the fuel cell stack;
A temperature sensor that measures a coolant outlet temperature T1 of the fuel cell stack;
When the cooling medium outlet temperature T1 is below freezing point, the fuel cell stack is warmed up until the cooling medium outlet temperature T1 exceeds a preset warm-up end temperature β, and the cooling medium outlet temperature T1 is set in advance. A low temperature start-up control unit that issues a travel permission when the travel permission determination temperature T3 is exceeded,
The low temperature start-up control unit
Before the end of the warm-up operation,
Calculating a coolant outlet estimated temperature T2 that is an estimated value of the coolant outlet temperature of the fuel cell stack;
When the difference (T1-T2) between the cooling medium outlet temperature T1 and the estimated cooling medium outlet temperature T2 after the travel permission is equal to or greater than a predetermined value α, Limit to below scavenging flow rate.

  According to the fuel cell system of this configuration, the movement of liquid water in the cell is suppressed in order to limit the increase in the flow rate of the reaction gas due to the output request response in the state where the low temperature region below freezing point exists in the plane of the cell. be able to. Thereby, the pressure loss of the reaction gas in the flow path due to the liquid water moving to the low temperature region in the cell and refreezing can be suppressed, and the starting reliability at a low temperature can be improved.

  According to the fuel cell system of the present invention, the starting reliability at a low temperature can be improved.

It is a schematic block diagram of the fuel cell system in one Embodiment of this invention. It is a top view of the cell which shows the cell of the state which temperature distribution produced. It is a graph showing the comparison of the moisture content distribution generation | occurrence | production of a cell at the time of normal time, (a) is a graph which shows a cooling medium exit temperature, (b) is a graph which shows the flow volume of air, (c) is a graph of an air inlet. It is a graph which shows a pressure loss. It is a flowchart explaining the control of the below freezing start by the control part provided with the low temperature starting time control part.

  Next, an embodiment of a fuel cell system according to the present invention will be described. Hereinafter, the case where this fuel cell system is applied to an in-vehicle power generation system of a fuel cell vehicle will be described. However, the present invention is not limited to such an application example, and is applicable to all moving objects such as ships, airplanes, trains, and walking robots. For example, the present invention can be applied to a stationary power generation system in which a fuel cell is used as a power generation facility for a building (house, building, etc.).

  FIG. 1 is a schematic configuration diagram of a fuel cell system according to an embodiment of the present invention. The fuel cell system 100 is mounted on a vehicle (hereinafter referred to as “fuel cell vehicle”) that uses electric power obtained by the fuel cell stack 10 as driving electric power. The fuel cell system 100 includes a fuel cell stack 10, a hydrogen supply / discharge system 50 for supplying hydrogen to the fuel cell stack 10, an oxidizing gas supply / discharge system 60 for supplying air containing oxygen to the fuel cell stack 10, and a cooling medium. A cooling medium circulation system 70 that circulates the fuel cell stack 10 to cool the fuel cell stack 10, a power output system 80 that converts electric power from the fuel cell stack 10 into power, a control unit 90 that controls the entire fuel cell system 100, Is provided.

  The fuel cell stack 10 has a stack structure in which a plurality of fuel cell cells (hereinafter simply referred to as “cells”) 12 that are power generation unit modules are stacked. Various types of fuel cells can be used as the type of fuel cell. In the present embodiment, a polymer electrolyte fuel cell is used. Each cell 12 includes a membrane electrode assembly (also referred to as MEA) in which anode and cathode electrodes are formed on each surface of an electrolyte membrane. Each cell 12 further includes a gas diffusion layer that is disposed so as to sandwich the MEA and supplies hydrogen and air as reaction gases to the MEA while diffusing them. Each cell 12 of the fuel cell stack 10 generates power by an electrochemical reaction between hydrogen and oxygen contained in air. In the present embodiment, the configuration and specifications of each cell 12 are the same.

  The hydrogen supply / discharge system 50 includes a hydrogen tank 51, a pressure reducing valve 52, a hydrogen supply path 53, a pressure adjustment valve 54, an anode exhaust gas path 55, a hydrogen pump 56, an exhaust gas exhaust path 57, and an on-off valve 58. , Including. The hydrogen supply / discharge system 50 discharges hydrogen as fuel gas stored in the hydrogen tank 51 to the hydrogen supply path 53 after the pressure is reduced by the pressure reducing valve 52. Further, the hydrogen supply / discharge system 50 adjusts the hydrogen released to the hydrogen supply path 53 to a predetermined pressure by the pressure adjustment valve 54 provided in the hydrogen supply path 53 and supplies the adjusted pressure to the anode of the fuel cell stack 10. On the other hand, the hydrogen supply / discharge system 50 supplies the anode exhaust gas discharged to the anode exhaust gas channel 55 to the hydrogen supply channel 53 again by the hydrogen pump 56. Further, the hydrogen supply / discharge system 50 can discharge part of the anode exhaust gas to the outside by opening the on-off valve 58 provided in the exhaust gas discharge passage 57 branched from the anode exhaust gas passage 55.

  The oxidizing gas supply / discharge system 60 includes an air compressor 61, an oxidizing gas supply path 62, and a cathode exhaust gas path 63. The oxidizing gas supply / exhaust system 60 pressurizes air as oxidizing gas taken from outside by an air compressor 61 and supplies the compressed air to the cathode of the fuel cell stack 10 via the oxidizing gas supply path 62. Further, the oxidizing gas supply / discharge system 60 discharges the cathode exhaust gas discharged to the cathode exhaust gas path 63 from the cathode exhaust gas path 63 to the outside of the fuel cell stack 10.

  The cooling medium circulation system 70 includes a radiator 71, a circulation pump 72, a cooling medium supply flow path 73, a cooling medium discharge flow path 74, a bypass flow path 75, a rotary valve 76, a supply side temperature sensor 77, A discharge-side temperature sensor 78. The cooling medium supply channel 73 has an upstream end connected to the radiator 71 and a downstream end connected to the cooling medium supply port 14 of the fuel cell stack 10. In the cooling medium supply flow path 73, a rotary valve 76, a circulation pump 72, and a supply side temperature sensor 77 are arranged in this order from the upstream side toward the downstream side. On the other hand, the cooling medium discharge channel 74 has an upstream end connected to the cooling medium discharge port 16 of the fuel cell stack 10 and a downstream end connected to the radiator 71. A discharge side temperature sensor 78 is arranged in the cooling medium discharge flow path 74. The bypass channel 75 has an upstream end connected to the cooling medium discharge channel 74 and a downstream end connected to the rotary valve 76.

  The cooling medium circulation system 70 pumps the cooling medium cooled by the radiator 71 by the circulation pump 72 and supplies the cooling medium to the fuel cell stack 10 through the cooling medium supply flow path 73. The cooling medium supplied to the fuel cell stack 10 is guided from the cooling medium supply port 14 to each cell 12 via the cooling medium supply manifold Ms, and cools each cell 12. The cooling medium after cooling each cell 12 is collected through the cooling medium discharge manifold Me and discharged from the cooling medium discharge port 16 to the cooling medium discharge flow path 74.

  The cooling medium circulation system 70 circulates the cooling medium discharged from the fuel cell stack 10 to the cooling medium discharge flow path 74 to the radiator 71. The coolant circulation system 70 supplies the coolant circulated to the radiator 71 to the fuel cell stack 10 again. The cooling medium circulation system 70 causes the radiator 71 to pass through when the cooling medium discharged from the fuel cell stack 10 to the cooling medium discharge passage 74 is supplied again to the fuel cell stack 10 by switching the rotary valve 76. Alternatively, the fuel cell stack 10 may be supplied from the cooling medium supply flow path 73. Further, the circulation amount of the cooling medium in the cooling medium circulation system 70 can be varied by adjusting the driving force for circulating the cooling medium of the circulation pump 72, that is, the discharge force.

  The supply side temperature sensor 77 is disposed in the vicinity of the cooling medium supply port 14 of the fuel cell stack 10 in the cooling medium supply flow path 73 and detects a cooling medium inlet temperature that is the temperature of the cooling medium supplied to the fuel cell stack 10. . The discharge side temperature sensor 78 is disposed in the vicinity of the coolant discharge port 16 of the fuel cell stack 10 in the coolant discharge passage 74 and detects the coolant exit temperature, which is the temperature of the coolant discharged from the fuel cell stack 10. . In addition, as a cooling medium used by this embodiment, the liquid mixture of water and ethylene glycol other than water can be used.

  The power output system 80 includes a motor 81, a motor control unit 82, and an electrical wiring 83 for supplying electric power from the fuel cell stack 10 to the motor control unit 82. The motor 81 constitutes a main power source of the fuel cell vehicle. The motor control unit 82 controls the output (discharge) of electric power from the fuel cell stack 10. As a result, the power output system 80 converts the electric power generated in the fuel cell stack 10 into motive power for traveling the fuel cell vehicle. The power output system 80 includes a voltage sensor 85 that detects the output voltage of the fuel cell stack 10 and a current sensor 86 that detects the output current of the fuel cell stack 10.

  The control unit 90 is a computer that includes a CPU, a memory, and the like (not shown). In addition to the voltage sensor 85, current sensor 86, supply side temperature sensor 77, and discharge side temperature sensor 78, the control unit 90 receives signals from temperature sensors, pressure sensors, switches, and the like disposed in each part of the fuel cell system 100. Then, the entire fuel cell system 100 is controlled based on the received signal. As switches, a start switch 99 for starting the fuel cell vehicle is provided.

  The control unit 90 in the present embodiment includes a low-temperature start-up control unit 92 that controls the fuel cell system 100 when the fuel cell stack 10 is started at a low temperature, as a functional element corresponding to a part of the overall control of the fuel cell system 100. .

  The control unit 90 including the low-temperature start-up control unit 92 starts by performing rapid warm-up that is a warm-up operation below freezing point. In the rapid warm-up, for example, the circulation of the cooling medium is set to a low circulation, the flow rate of air supplied to the fuel cell stack 10 is reduced, and the voltage of the cells 12 of the fuel cell stack 10 is lowered to about 0 V, thereby The calorific value at 10 is increased.

  By the way, when the moisture content distribution is generated in the plane of the cell 12 at the start below the freezing point, in the cell 12, power generation is biased in the plane. Then, a power generation distribution is generated due to this bias in power generation, and a temperature distribution is generated in the plane of the cell 12 according to this power generation distribution.

  In such a situation, even if the coolant outlet temperature T1 detected by the discharge-side temperature sensor 78 of the fuel cell stack 10 breaks through the freezing point, as shown in FIG. The low temperature region LA having a low temperature and the high temperature region HA having a higher temperature than the low temperature region LA exist. And since a viscosity changes with temperature, a cooling medium will mainly flow through the high temperature area | region HA side. In such a situation, when the supply amount of air and hydrogen is increased according to the output demand, the liquid water moves from the high temperature area HA to the low temperature area LA, and this liquid water is re-frozen in the low temperature area LA. Blockage of the air and hydrogen flow paths at 12 occurs and the pressure loss increases.

  For example, as shown in FIG. 3 (a), when the moisture content distribution is generated in the plane of the cell 12 in this sub-freezing start, the normal time when there is no moisture content distribution (see the middle wavy line in FIG. 3 (a)). Compared to the case, a part of the cooling medium flowing in the cell 12 is heated and the temperature rises quickly (see the solid line in FIG. 3A). Then, based on the cooling medium outlet temperature T1 detected by the discharge side temperature sensor 78, the travel permission timing commanded when the freezing point (for example, 0 ° C.) is exceeded becomes the timing t2 earlier than the normal timing t1. . Then, as shown in FIG. 3 (b), the air supply timing is also earlier when the water content distribution is generated than when normal (see the middle wavy line in FIG. 3 (b)) (solid line in FIG. 3 (b)). reference). In addition, as shown in FIG. 3 (c), compared to the air pressure loss in the normal state (see the middle wavy line in FIG. 3 (c)), when the moisture content distribution occurs, In this case, the liquid water is re-frozen and the flow path is blocked, so that the pressure loss in the flow path of the cell 12 increases (see the solid line in FIG. 3C), and there is a possibility that start below freezing cannot be performed smoothly.

  For this reason, in the fuel cell system 100 according to this embodiment, the sub-freezing start is performed in consideration of the temperature distribution in the plane of the cell 12.

Next, control of starting below freezing by the control unit 90 including the low temperature start-up control unit 92 will be described.
FIG. 4 is a flowchart for explaining the control for starting below the freezing point by the control unit having the low temperature start-up control unit.

  First, it is determined whether or not the start switch 99 is on (step S01). Here, when it is determined that the start switch 99 is not in the on state, that is, in the off state, the control unit 90 repeatedly executes the process of step S01, and the start switch 99 is operated by the operator to be in the on state. Wait for

  If it is determined in step S01 that the start switch 99 is on, the fuel cell stack 10 is activated (step S02). Specifically, the hydrogen supply / discharge system 50 and the oxidizing gas supply / discharge system 60 are controlled to supply air and hydrogen to the fuel cell stack 10, thereby starting the power generation of the fuel cell stack 10.

  Next, it is determined whether or not the coolant outlet temperature T1 detected by the discharge side temperature sensor 78 is lower than 0 ° C. (step S03). This determination is performed based on the temperature of the cooling medium remaining in the cooling medium supply channel 73 as to whether or not the temperature around the fuel cell system 100 is below the freezing point.

  If it is determined in step S03 that the cooling medium outlet temperature T1 is 0 ° C. or higher (step S03: No), “Ready ON” is displayed on the display unit (not shown) as an output permission state display, Start is started (step S04). In normal starting, the rotary valve 76 provided in the cooling medium circulation system 70 is switched to the flow path side including the radiator 71, and the cooling medium is circulated through the radiator 71.

  On the other hand, when it is determined in step S03 that the cooling medium outlet temperature T1 is lower than 0 ° C. (step S03: Yes), start control at a low temperature after step S05 is performed. The temperature for determining whether the ambient temperature of the fuel cell system 100 is below the freezing point need not be limited to 0 ° C., and may be other temperatures of 0 ° C. or lower, such as −2 ° C. or −4 ° C.

  In the start control at a low temperature, first, a sub-freezing start is performed in order to perform a rapid warm-up that is a warm-up operation (step S05). In this sub-freezing start, the circulation of the cooling medium is set to a low circulation, the flow rate of air supplied to the fuel cell stack 10 is reduced, and the voltage of the cells 12 of the fuel cell stack 10 is lowered to around 0 V, thereby Increase calorific value.

  After the rapid warm-up, it is determined whether or not the coolant outlet temperature T1 is lower than the travel permission determination temperature T3 (step S06). Here, the travel permission determination temperature T3 is a temperature at which a supercooled state such as −10 ° C. is maintained.

  In step S06, after the rapid warm-up, if the coolant outlet temperature T1 is equal to or higher than the travel permission determination temperature T3 (step S06: No), the output from the fuel cell stack 10 while the rapid warm-up is continued. Is allowed to travel, and “Ready ON” is displayed on the display unit (not shown) as an output permission state display (step S09). For example, when the travel permission determination temperature T3 is set to −10 ° C., the process proceeds to step S09 when −10 ° C. ≦ T1 <0 ° C.

  In step S06, when the coolant outlet temperature T1 has not reached the travel permission determination temperature T3 (step S06: Yes), the vehicle is disabled from being output by the output from the fuel cell stack 10, and a display unit (not shown). The rapid warm-up is continued without displaying “Ready ON”, which is an output permission status display (step S07).

  The difference (T1−T2) between the cooling medium outlet temperature T1 and the estimated cooling medium outlet temperature T2 is lower than the predetermined value α in the state where running is not possible (“Ready ON” is not displayed) and the rapid warm-up is continued. It is determined whether or not (step S08).

  Here, the estimated coolant outlet temperature T2 is, for example, an estimated value of temperature estimated from the relationship between the amount of heat generated by the power generation of the fuel cell stack 10 and the heat capacity. Specifically, the coolant outlet estimated temperature T2 that is the estimated temperature of the fuel cell stack 10 is detected by the output sensor and current sensor 86 detected by the voltage sensor 85 based on the following equations (1) and (2). Output current, the relationship between the heat capacity (kJ / K) of the fuel cell stack 10 and the integrated value (kJ) of the calorific value (kW).

Calorific value = output current x (theoretical electromotive voltage-output voltage) (1)
Cooling medium outlet estimated temperature T2 = heat value integrated value / heat capacity (2)

  Further, the predetermined value α is a preset temperature value, and in the cells 12 of the fuel cell stack 10, the temperature at which the in-plane temperature rise becomes uneven and the temperature distribution may occur in the plane of the cells 12. Value.

  When the difference (T1−T2) between the cooling medium outlet temperature T1 and the cooling medium outlet estimated temperature T2 is equal to or larger than the predetermined value α (step S08: No), the in-plane temperature rise of the cell 12 is uneven. It is determined that there is a low-temperature region LA below freezing point in the plane of the cell 12, and a state in which rapid warm-up is continued in a state in which traveling is not possible is maintained.

  When the difference (T1−T2) between the coolant outlet temperature T1 and the coolant outlet estimated temperature T2 is lower than the predetermined value α (step S08: Yes), the fuel cell stack 10 is kept in the state where the rapid warm-up is continued. The vehicle is allowed to travel by the output from the terminal and “Ready ON” is displayed on the display unit (not shown) as an output permission state display (step S09).

  It is determined whether or not the coolant outlet temperature T1 is higher than the rapid warm-up end temperature β in the state where the travel is permitted (“Ready ON” is displayed) and the rapid warm-up is continued (step S10). Here, the rapid warm-up end temperature β is a preset temperature value, for example, a temperature value at which power generation in the fuel cell stack 10 of about 30 ° C. to 50 ° C. is appropriately performed.

  When the cooling medium outlet temperature T1 is higher than the rapid warm-up end temperature β (step S10: Yes), the rapid warm-up is terminated and normal operation is started, and normal vehicle travel is enabled (step S11).

  When the cooling medium outlet temperature T1 is equal to or lower than the rapid warming-up end temperature β (step S10: No), the cooling medium outlet temperature is maintained while maintaining the state where the warming-up is continued (displayed “Ready ON”) and the rapid warming up is continued. It is determined whether or not the difference (T1−T2) between T1 and the estimated coolant outlet temperature T2 is below a predetermined value α (step S12).

  In step S12, when the difference (T1-T2) between the cooling medium outlet temperature T1 and the cooling medium outlet estimated temperature T2 is lower than the predetermined value α (step S12: Yes), the traveling permission state (“Ready ON” display). ) And in a state where the rapid warm-up is continued (step S09), the process proceeds to a determination of whether or not the coolant outlet temperature T1 exceeds the rapid warm-up end temperature β (step S10).

  If the difference (T1−T2) between the cooling medium outlet temperature T1 and the estimated cooling medium outlet temperature T2 is equal to or greater than the predetermined value α in step S12 (step S12: No), the cell 12 of the fuel cell stack 10 is still cell 12. It is estimated that the in-plane temperature rise is uneven. In this case, the gas flow rate restriction process is performed until the difference (T1-T2) between the cooling medium outlet temperature T1 and the estimated cooling medium outlet temperature T2 is lower than the predetermined value α (step S13). Specifically, the scavenging flow rate for the scavenging process performed at the previous stop is maximized, and the supply amount of air and hydrogen to the fuel cell stack 10 is limited to the scavenging flow rate or less. In this way, the liquid water that has not moved in the scavenging process at the previous stop can be prevented from moving even in a state where it is estimated that the in-plane temperature rise of the cell 12 is uneven. Thereby, refreezing due to the liquid water moving to the low temperature region LA below the freezing point in the plane of the cell 12 is suppressed, and the blockage of the flow path is suppressed.

  As described above, according to the fuel cell system 100 according to the present embodiment, the flow rate of air and hydrogen is increased by the output request response in the state where the low temperature region LA such as the sub-freezing portion exists in the plane of the cell 12. Since the restriction is imposed, the movement of liquid water in the cell 12 can be suppressed. Thereby, the pressure loss of the air and hydrogen in the flow path due to the liquid water moving to the low temperature region LA in the cell 12 and refreezing can be suppressed, and the starting reliability at the low temperature can be improved.

  In addition, this embodiment is suitable when the cell 12 which has the flow path of the straight shape etc. in which two or more were paralleled rather than the flow path of the serpentine shape etc. which are connected continuously while a flow path bends.

DESCRIPTION OF SYMBOLS 10 Fuel cell stack 12 Cell 70 Cooling medium circulation system 78 Temperature sensor 92 Low temperature starting control unit 100 Fuel cell system T1 Cooling medium outlet temperature T2 Cooling medium outlet estimated temperature T3 Travel permission judgment temperature α Predetermined value β Warm-up completion temperature

Claims (1)

A fuel cell stack in which a plurality of cells that generate power by supplying reactive gas are stacked;
A coolant circulation system for circulating a coolant in the fuel cell stack;
A temperature sensor that measures a coolant outlet temperature T1 of the fuel cell stack;
When the cooling medium outlet temperature T1 is below freezing point, the fuel cell stack is warmed up until the cooling medium outlet temperature T1 exceeds a preset warm-up end temperature β, and the cooling medium outlet temperature T1 is set in advance. A low temperature start-up control unit that issues a travel permission when the travel permission determination temperature T3 is exceeded,
The low temperature start-up control unit
Before the end of the warm-up operation,
Calculating a coolant outlet estimated temperature T2 that is an estimated value of the coolant outlet temperature of the fuel cell stack;
The difference (T1-T2) between the cooling medium outlet temperature T1 and the estimated cooling medium outlet temperature T2 before the travel permission is a low temperature region below the freezing point in the plane of the cell and a high temperature higher than the low temperature region. When the temperature value including the region is less than the predetermined value α set to the estimated temperature value , the vehicle is allowed to run while the warm-up operation is continued, and the cooling medium outlet temperature T1 The warm-up operation is continued until the warm-up end temperature β exceeds
When the difference (T1−T2) becomes equal to or greater than the predetermined value α before the coolant outlet temperature T1 after the travel permission exceeds the warm-up end temperature β, the supply amount of the reaction gas Is less than or equal to the scavenging flow rate at the previous stop, and the scavenging flow rate is an amount that suppresses refreezing due to the liquid water remaining in the plane of the cell moving to the low temperature region. /> Fuel cell system.

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