JP6465307B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell system and a control method thereof.

  2. Description of the Related Art Conventionally, a fuel cell system including a fuel cell that generates power by receiving a supply of reaction gas (fuel gas and oxidizing gas) has been proposed and put into practical use. A fuel cell is a power generation system that directly converts energy released by an oxidation reaction into electrical energy by oxidizing fuel by an electrochemical process.

  Such a fuel cell system is provided with an air compressor that supplies air as an oxidizing gas to the fuel cell. As an air compressor, a centrifugal type compressor in which a rotary impeller called an impeller rotates inside the housing and compresses air has been put into practical use. It has been clarified that a phenomenon called a surge occurs in which the air compressor does not function normally due to the reverse flow of the air sent out depending on the state. Surge is likely to occur when the number of revolutions is rapidly reduced in the operating region near the surge. This is because in the operation region near the surge, the pressure on the outlet side is higher than the pressure on the inlet side of the air compressor, so that a reverse flow of air occurs, the impeller runs idle, and self-excited vibration occurs.

  In recent years, various techniques for avoiding such surges have been proposed. For example, a pressure sensor is provided in the air supply flow path that supplies air to the fuel cell, and a discharge valve is provided in the bypass flow path that communicates with the air supply flow path to detect surges based on pressure fluctuations detected by the pressure sensor. However, a technique has been proposed that eliminates the surge by opening the discharge valve and reducing the pressure in the air supply flow path when a surge is detected (see Patent Document 1).

JP 2009-076243 A

  However, in the conventional technique described in Patent Document 1, since the pressure of the air supply flow path is reduced after detecting the surge, the occurrence of the surge cannot be avoided in advance, and the surge is generated. Various problems caused by the above (generation of noise and vibration, decrease in durability of the impeller, decrease in durability of the fuel cell stack due to generation of differential pressure between electrodes, etc.) have not been solved yet. For this reason, a technique for avoiding the occurrence of a surge has been awaited.

  The present invention has been made in view of such circumstances, and an object of the present invention is to avoid occurrence of a surge in a fuel cell system including an air compressor.

  To achieve the above object, a fuel cell system according to the present invention is supplied from a fuel cell, an air compressor that supplies air to the fuel cell via an air supply channel, and an air compressor that is supplied via an air supply channel. A fuel cell system comprising: a bypass flow path that circulates air without passing through the fuel cell; a bypass valve that adjusts a flow rate of air in the bypass flow path; and a control unit that controls the air compressor and the bypass valve. The control unit determines whether or not the current operating point of the air compressor is within the operation region near the surge when reducing the rotation speed of the air compressor, and determines the current operating point. When the valve is in the surge operation area, control is performed to open the bypass valve to reduce the pressure of the air supply flow path, and then the rotation speed of the air compressor is reduced. Is shall.

  The control method according to the present invention includes a fuel cell, an air compressor that supplies air to the fuel cell via the air supply channel, and air supplied from the air compressor via the air supply channel. A control method for a fuel cell system, comprising: a bypass flow path that circulates without passing through; and a bypass valve that adjusts the flow rate of air in the bypass flow path, wherein the air compressor An operating point determination step for determining whether or not the current operating point of the compressor is in the surge vicinity operating region based on a predetermined map, and the current operating point in the surge vicinity operating region in the operating point determination step If it is judged, the pressure reduction process to reduce the pressure of the air supply flow path by controlling to open the bypass valve, and the rotation speed of the air compressor is reduced after the pressure reduction process. A rotational speed control process, is intended to include.

  When such a configuration and method are employed, when the current operating point of the air compressor is within the operation region near the surge, the control is performed to open the bypass valve to reduce the pressure of the air supply flow path. The number of rotations can be reduced. Accordingly, it is possible to prevent the operating point from entering the surge operation region in the process of shifting from the current operating point to the next operating point, and thus it is possible to suppress the load on the air compressor.

  In the fuel cell system according to the present invention, when the current operating point is in the operation region near the surge, at least one difference in the pressure ratio, supply flow rate, and rotation speed of the air compressor at the current operating point and the next operating point. When the difference is equal to or smaller than a predetermined threshold value, a control unit that shifts the current operating point to the next operating point without controlling to open the bypass valve can be employed.

  In the control method according to the present invention, when the current operating point is in the surge vicinity operating region in the operating point determination step, the pressure ratio, supply flow rate, and rotation speed of the air compressor at the current operating point and the next operating point are determined. When the difference calculation step for calculating at least one difference and the difference calculated in the change calculation step are equal to or less than a predetermined threshold, the current operation point is set as the next operation point without controlling to open the bypass valve. And a normal control process to be transferred.

  When such a configuration and method are applied, when the current operating point of the air compressor is within the operation region near the surge, at least one of the pressure ratio, the supply flow rate, and the rotation speed of the air compressor at the current operating point and the next operating point. If the difference between the two is less than or equal to a predetermined threshold (that is, when the next operating point is unlikely to enter the surge region), the current operating point is set to the next operating point without controlling to open the bypass valve. Can be migrated to. Therefore, the response speed of the air compressor can be increased by the amount that the surge region rush avoidance control (control to open the bypass valve in advance) is not performed.

  In the fuel cell system according to the present invention, when the current operating point is within the operation region near the surge and control is performed so that the bypass valve is opened, after the rotational speed of the air compressor is reduced or the rotational speed is reduced, At the same time, it is possible to employ a control unit that controls to close the bypass valve and shifts the current operating point to the next operating point.

  In the control method according to the present invention, after the rotational speed of the air compressor is reduced in the rotational speed control step or at the same time as the rotational speed is reduced, the bypass valve is closed and the current operating point is set to the next operating point. A pressure recovery step of transferring to

  When such a configuration and method are employed, when the current operating point of the air compressor is within the operation region near the surge and the bypass valve is controlled to open, the rotational speed of the air compressor is reduced or reduced. At the same time, the current operating point can be shifted to the next operating point by controlling the bypass valve to close. Therefore, after performing surge region entry avoidance control (control to open the bypass valve in advance), it is possible to promptly shift to the next operating point while recovering the pressure in the air supply flow path.

  According to the present invention, it is possible to avoid occurrence of a surge in a fuel cell system including an air compressor.

It is explanatory drawing which shows the outline of a structure of the fuel cell system which concerns on embodiment of this invention. It is an example of the flow volume / pressure ratio map used with the fuel cell system concerning the embodiment of the present invention. 3 is a flowchart for explaining a control method of the fuel cell system according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the positional relationship such as up, down, left, and right in the drawing is based on the positional relationship shown in the drawing unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, the following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to this embodiment alone. Furthermore, the present invention can be variously modified without departing from the gist thereof.

  First, the configuration of the fuel cell system 10 according to the present embodiment will be described with reference to FIG. The fuel cell system 10 functions as an in-vehicle power supply system mounted on, for example, a fuel cell vehicle as a moving body, and includes a fuel cell 20 that generates power upon receiving a supply of reaction gas (fuel gas and oxidizing gas), An oxidizing gas supply system 30 for supplying air as gas to the fuel cell 20, a fuel gas supply system 40 for supplying hydrogen gas as fuel gas to the fuel cell 20, and charging / discharging power control Power system 50 and a controller 60 that performs overall control of the entire system.

The fuel cell 20 is a solid polymer electrolyte cell stack in which a large number of cells are stacked in series. In the fuel cell 20, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the formula (2) occurs at the cathode electrode. In the fuel cell 20 as a whole, an electromotive reaction of the formula (3) occurs.
H ₂ → 2H ++ 2e− (1)
(1/2) O ₂ + 2H ++ 2e− → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The cell constituting the fuel cell 20 is composed of a polymer electrolyte membrane, an anode electrode, a cathode electrode, and a separator. The anode electrode and the cathode electrode form a sandwich structure with the polymer electrolyte membrane sandwiched from both sides. The separator is composed of a gas-impermeable conductive member, and fuel gas and oxidizing gas flow paths are formed between the anode electrode and the cathode electrode, respectively, with the anode electrode and the cathode electrode sandwiched from both sides.

  Each of the anode electrode and the cathode electrode has a catalyst layer and a gas diffusion layer. The catalyst layer has, for example, catalyst-carrying carbon carrying platinum-based noble metal particles that function as a catalyst, and a polymer electrolyte. As a platinum-based material for the noble metal particles, for example, a metal catalyst (Pt, Pt—Fe, Pt—Cr, Pt—Ni, Pt—Ru, etc.) can be used. For example, carbon black can be used as the catalyst-supporting carbon. As the polymer electrolyte, a proton conductive ion exchange resin or the like can be used. The gas diffusion layer is formed of carbon cloth, carbon paper, or carbon felt formed on the surface of the catalyst layer, having both air permeability and electronic conductivity, and woven with yarns made of carbon fibers.

  The polymer electrolyte membrane is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electrical conductivity in a wet state. A membrane-electrode assembly is formed by the polymer electrolyte membrane, the anode electrode, and the cathode electrode.

  As shown in FIG. 1, the fuel cell 20 includes a voltage sensor 71 for detecting an output voltage (FC voltage) of the fuel cell 20 and a current sensor 72 for detecting an output current (FC current). It is attached.

  The oxidant gas supply system 30 includes an oxidant gas channel 33 that circulates an oxidant gas (air) supplied to the cathode electrode of the fuel cell 20, and an oxidant offgas channel 34 that circulates the oxidant offgas discharged from the fuel cell 20. And a bypass channel 35 for allowing the oxidizing gas supplied through the oxidizing gas channel 33 to flow to the oxidizing off-gas channel 34 without passing through the fuel cell 20. The oxidizing gas flow path 33 corresponds to the air supply flow path in the present invention.

  The oxidant gas flow path 33 is provided with an air compressor 32 that takes in the oxidant gas from the atmosphere via the filter 31 and a shutoff valve A1 for shutting off the oxidant gas supply to the fuel cell 20. The oxidation off gas passage 34 is provided with a shutoff valve A2 for shutting off discharge of the oxidation off gas from the fuel cell 20. The bypass flow path 35 is provided with a bypass valve A3 for adjusting the flow rate of the oxidizing gas in the bypass flow path 35.

  The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 43 through which fuel gas supplied from the fuel gas supply source 41 to the anode electrode of the fuel cell 20 flows, and a fuel off-gas discharged from the fuel cell 20. A circulation flow path 44 for returning the fuel gas flow path 43 to the fuel gas flow path 43, a circulation pump 45 for pumping the fuel off-gas in the circulation flow path 44 to the fuel gas flow path 43, and an exhaust drain connected to the circulation flow path 44. And a flow path 46.

  The fuel gas supply source 41 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 70 MPa) hydrogen gas. When the shut-off valve H1 is opened, the fuel gas flows out from the fuel gas supply source 41 into the fuel gas passage 43. The fuel gas is decompressed to about 200 kPa, for example, by the regulator H2 and the injector 42 and supplied to the fuel cell 20.

  The circulation passage 44 is connected to a shutoff valve H4 for shutting off the fuel off-gas discharge from the fuel cell 20 and an exhaust / drain passage 46 branched from the circulation passage 44. An exhaust / drain valve H5 is disposed in the exhaust / drain passage 46. The exhaust / drain valve H <b> 5 is operated according to a command from the controller 60, thereby discharging the fuel off gas containing impurities in the circulation passage 44 and moisture to the outside.

  The fuel off-gas discharged through the exhaust / drain valve H5 is mixed with the oxidizing off-gas flowing through the oxidizing off-gas flow path 34 and diluted by a diluter (not shown). The circulation pump 45 circulates and supplies the fuel off gas in the circulation system to the fuel cell 20 by driving the motor.

  The power system 50 includes a DC / DC converter 51, a battery 52, a traction inverter 53, a traction motor 54, and auxiliary machinery 55. The DC / DC converter 51 steps up the DC voltage supplied from the battery 52 and outputs it to the traction inverter 53 and the DC power generated by the fuel cell 20 or the regenerative power collected by the traction motor 54 by regenerative braking. And charging the battery 52.

  The battery 52 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle, and the like. As the battery 52, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is suitable. The battery 52 is attached with an SOC sensor 73 for detecting SOC (State of charge) which is the remaining capacity.

  The traction inverter 53 is a PWM inverter driven by, for example, a pulse width modulation method, and converts a DC voltage output from the fuel cell 20 or the battery 52 into a three-phase AC voltage in accordance with a control command from the controller 60, thereby obtaining traction. The rotational torque of the motor 54 is controlled. The traction motor 54 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

  The auxiliary machines 55 are motors arranged in each part of the fuel cell system 10, inverters for driving these motors, and various on-vehicle auxiliary machines (for example, the air compressor 32, the injector 42). , Circulation pump 45, radiator, cooling water circulation pump, etc.).

  The controller 60 is a computer system including a CPU, a ROM, a RAM, and an input / output interface, and controls each part of the fuel cell system 10. For example, when the controller 60 receives the start signal IG output from the ignition switch, the controller 60 starts the operation of the fuel cell system 10, and the accelerator opening signal ACC output from the accelerator sensor or the vehicle speed signal VC output from the vehicle speed sensor. Based on the above, the required power of the entire system is obtained. The required power of the entire system is the total value of the vehicle running power and the auxiliary machine power.

  Auxiliary power includes power consumed by in-vehicle accessories (air compressor 32, circulation pump 45, cooling water circulation pump, etc.), and equipment required for vehicle travel (transmission, wheel control device, steering device, suspension device, etc.) ), Power consumed by devices (such as air conditioners, lighting fixtures, and audio) disposed in the passenger space.

  The controller 60 determines the distribution of output power between the fuel cell 20 and the battery 52, and controls the oxidizing gas supply system 30 and the fuel gas supply system 40 so that the power generation amount of the fuel cell 20 matches the target power. At the same time, the DC / DC converter 51 is controlled to adjust the output voltage of the fuel cell 20, thereby controlling the operating point (output voltage, output current) of the fuel cell 20.

  During operation of the fuel cell system 10, in the fuel cell 20, as shown in the above formula (1), hydrogen ions generated at the anode electrode permeate the electrolyte membrane and move to the cathode electrode, and then move to the cathode electrode. As shown in the above equation (2), the hydrogen ions cause an electrochemical reaction with oxygen in the oxidizing gas supplied to the cathode electrode to cause a reduction reaction of oxygen, thereby generating water.

Further, the controller 60 determines whether or not the current operating point (supply flow rate, pressure ratio) of the air compressor 32 is in the surge vicinity operating region based on a predetermined map. Controller 60 in this embodiment is based on the flow rate / pressure ratio map shown in FIG. 2, the current operating point of the air compressor 32 is determined whether there are any surge vicinity operating in basin A _CS. Here, the surge vicinity operation area A _CS is in contact with the surge line L _S shown in FIG. 2 (the boundary line separating the surge operation area A _S and the non-surge operation area A _NS ) and on the non-surge operation area A _NS side. It is an operating region having a predetermined width. The width of the surge vicinity operation area A _CS can be appropriately set according to the specifications of the air compressor 32, the diameter and capacity of the pipe from the air compressor 32 to the fuel cell 20, and the like.

The controller 60, if the current operating point of the air compressor 32 is determined to be in the surge near operating region A _CS, control to reduce the pressure of the oxidizing gas channel 33 to open the bypass valve A3 Thereafter, the rotational speed of the air compressor 32 is reduced. That is, the controller 60 corresponds to a control unit in the present invention. After the controller 60 reduces the rotational speed of the air compressor 32 in this way (or at the same time as reducing the rotational speed), the controller 60 controls to close the bypass valve A3 and shifts the current operating point to the next operating point. It can also be made.

For example, in the case of shifting from the initial operation point P _P in the surge vicinity operation region A _{CS of} FIG. 2 to the target operation point P _{T in} the non-surge operation region A _NS , conventional control (simply the air compressor 32 by employing the control for reducing the rotational speed), the operating point is migrated as indicated by a broken line in FIG. 2, there is a possibility that enters the surge operation area a _S in the middle.

On the other hand, in this embodiment, the controller 60 first opens the bypass valve A3 to reduce the pressure in the oxidizing gas flow path 33, so that the initial operating point P _P is an intermediate operating point that moves away from the surge vicinity operating region A _CS. the process proceeds to P _I. Thereafter, the controller 60 by reducing the rotational speed of the air compressor 32, an intermediate operating point P _I moves to a target operating point P _T. Therefore, by employing the present control, the operating point, without rush into the surge operation area A _S, the transition from the initial position (the initial operating point P _P) to the position of the target (target operating point P _T) It will be.

In addition, the controller 60 in the present embodiment, when the current operating point is in the surge vicinity operating region A _CS , the state quantity (for example, pressure ratio and supply flow rate) of the air compressor 32 at the current operating point and the next operating point. The difference of at least one of the above is calculated. Then, the controller 60 reduces the rotational speed of the air compressor 32 without performing control so as to open the bypass valve A3 when the calculated difference in state quantity (state change amount) is equal to or smaller than a predetermined threshold value. The operating point of is shifted to the next operating point. If it does in this way, the response speed of the air compressor 32 can be raised only by the part which does not perform surge area | region rush avoidance control (control which opens bypass valve A3). The threshold employed here can be set as appropriate according to the specifications of the air compressor 32, the diameter and capacity of the pipe from the air compressor 32 to the fuel cell 20, and the like.

  Next, a control method (surge region rush avoidance control) of the fuel cell system 10 according to the present embodiment will be described using the flowchart of FIG.

  During normal operation of the fuel cell system 10, the fuel gas is supplied from the fuel gas supply source 41 to the anode electrode of the fuel cell 20 through the fuel gas passage 43, and the oxidizing gas is passed through the oxidizing gas passage 33. Then, power is generated by being supplied to the cathode electrode of the fuel cell 20. At this time, the power (required power) to be drawn from the fuel cell 20 is calculated by the controller 60, and fuel gas and oxidizing gas in amounts corresponding to the amount of power generation are supplied into the fuel cell 20.

During this normal operation, the controller 60 determines whether or not the current operating point (initial operating point P _P ) of the air compressor 32 is within the surge vicinity operating region A _CS based on the flow rate / pressure ratio map of FIG. Determination (operating point determination step: S1). When the controller 60 determines that the current operating point (initial operating point P _P ) is within the surge vicinity operating area A _CS in the operating point determination step S1, the current operating point (initial operating point P _P ). And the difference of the state quantity (pressure ratio and / or supply flow rate) of the air compressor 32 at the next operating point (target operating point P _T ) is calculated (change amount calculating step: S2).

  The controller 60 determines whether or not the difference calculated in the change amount calculation step S2 exceeds a predetermined threshold value (change amount determination step: S3). When this difference exceeds the threshold value, the bypass valve A3 is opened. To reduce the pressure of the oxidizing gas flow path 33 (pressure reduction step: S4). In the present embodiment, the opening degree of the bypass valve A3 adjusted in the pressure reduction step S4 is determined using a predetermined map based on information on the next operating point.

After passing through the pressure reduction step S4, the controller 60 reduces the rotational speed of the air compressor 32 and shifts the operating point to the next operating point (target operating point P _T ) (rotational speed control step: S5). In addition, after reducing the rotation speed of the air compressor 32 in the rotation speed control step S5 (or simultaneously with reducing the rotation speed), the bypass valve A3 is controlled to be closed to restore the pressure of the oxidizing gas passage 33. However, it may be shifted to the next operating point (target operating point P _T ) (pressure recovery step).

On the other hand, when the controller 60 determines that the difference calculated in the change amount calculation step S2 is equal to or smaller than a predetermined threshold, the controller 60 reduces the rotational speed of the air compressor 32 without performing control to open the bypass valve A3. Then, the current operating point (initial operating point P _P ) is shifted to the next operating point (target operating point P _T ) (normal control process: S6).

Or in the fuel cell system 10 according to the embodiment described, the current when the operating point is in the surge near operating region A _CS, controlled to open the bypass valve A3 with the oxidizing gas channel 33 of the air compressor 32 , And the number of revolutions of the air compressor 32 can be reduced thereafter. Thus, in the process of transition from the current operating point to the next operating point, it is possible to avoid in advance that the operating point enters the surge operation area A _S, suppressing the load on the air compressor 32 Can do.

Further, in the fuel cell system 10 according to the embodiment described above, when the current operating point of the air compressor 32 is within the surge vicinity operating region A _CS , the air compressor 32 at the current operating point and the next operating point. If the difference between the pressure ratio and / or the supply flow rate is below a predetermined threshold (i.e., if the next operating point is less likely to rush into the surge operation area a _S), the control to open the bypass valve A3 The current operating point can be shifted to the next operating point without doing so. Therefore, the response speed of the air compressor 32 can be increased by the amount that the surge region rush avoidance control (control to open the bypass valve A3 in advance) is not performed.

Further, in the fuel cell system 10 according to the embodiment described above, when the current operating point of the air compressor 32 is controlled to open the bypass valve A3 is in the surge near operating region A _CS, the air compressor 32 It is also possible to shift the current operating point to the next operating point by controlling the bypass valve A3 to be closed after the rotational speed is reduced or simultaneously with the reduction of the rotational speed. Therefore, after performing the surge region rush avoidance control (control to open the bypass valve A3 in advance), it is possible to promptly shift to the next operating point while recovering the pressure of the oxidizing gas flow path 33.

  In the present embodiment, the difference (change amount) in the state quantity (pressure ratio and / or supply flow rate) of the air compressor 32 at the current operating point and the next operating point is calculated, and this change amount is a predetermined threshold value. Although an example in which surge region rush avoidance control is performed in the case of exceeding the above is shown, a method different from such a method can also be adopted. For example, the surge region rush avoidance control may be performed when the state quantity (for example, both the pressure ratio and the supply flow path) at the next operating point becomes ½ or less of the state quantity at the current operating point. .

  Further, in the present embodiment, an example is shown in which “pressure ratio” and “supply flow rate” are adopted as state quantities of the air compressor 32 referred to when determining whether or not to perform surge region rush avoidance control. Instead of these state quantities (or together with these state quantities), the “rotation speed” of the air compressor 32 may be employed. For example, at least one difference (change amount) between the “pressure ratio”, “supply flow rate”, and “rotational speed” of the air compressor 32 at the current operation point and the next operation point is calculated, and this change amount is a predetermined threshold value. The surge region rush avoidance control can be performed when exceeding.

  Moreover, in this embodiment, although the example which controlled both the air compressor 32 and the bypass valve A3 by one controller 60 was shown, the air compressor 32 and the bypass valve A3 are controlled separately using a plurality of controllers. You can also. In such a case, the plurality of controllers correspond to the control unit in the present invention.

  In the present embodiment, the “fuel cell vehicle” is exemplified as the moving body. However, the fuel cell system according to the present invention may be mounted on various moving bodies (robots, ships, aircrafts, etc.) other than the fuel cell vehicle. it can.

  The present invention is not limited to the above-described embodiment, and those in which those skilled in the art appropriately modify the design are included in the scope of the present invention as long as they have the features of the present invention. . In other words, each element included in the embodiment and its arrangement, material, condition, shape, size, and the like are not limited to those illustrated, and can be appropriately changed. Moreover, each element with which the said embodiment is provided can be combined as much as technically possible, and the combination of these is also included in the scope of the present invention as long as it includes the features of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell 32 ... Air compressor 33 ... Oxidation gas flow path (air supply flow path)
35 ... Bypass channel 60 ... Controller (control part)
A3 ... Bypass valve A _CS ... Surge vicinity operating region P _P ... Initial operating point (current operating point)
P _T ... Target operating point (next operating point)
S1 ... Operating point determination process S2 ... Change amount calculation process S4 ... Pressure reduction process S5 ... Rotational speed control process S6 ... Normal control process

Claims (6)

A fuel cell, an air compressor that supplies air to the fuel cell via an air supply channel, and air that is supplied from the air compressor via the air supply channel is circulated without passing through the fuel cell. A fuel cell system comprising a bypass channel, a bypass valve that adjusts a flow rate of air in the bypass channel, and a control unit that controls the air compressor and the bypass valve,
The controller determines whether or not the current operating point of the air compressor is within a surge vicinity operating region when reducing the rotation speed of the air compressor based on a predetermined map, and the current operation When the point is in the operation region near the surge, the fuel cell system controls the opening of the bypass valve to reduce the pressure of the air supply flow path, and then reduces the rotation speed of the air compressor.   The control unit, when the current operating point is in the operation region near the surge, at least one difference in pressure ratio, supply flow rate, and rotation speed of the air compressor at the current operating point and the next operating point. 2. The fuel cell system according to claim 1, wherein when the difference is equal to or smaller than a predetermined threshold value, the current operating point is shifted to the next operating point without controlling to open the bypass valve. .   When the control unit reduces the rotational speed of the air compressor or when the rotational speed of the air compressor is reduced when the current operating point is in the operation region near the surge and the bypass valve is opened. The fuel cell system according to claim 1 or 2, wherein the current operating point is shifted to the next operating point by controlling the bypass valve to be closed at the same time. A fuel cell, an air compressor that supplies air to the fuel cell via an air supply channel, and air that is supplied from the air compressor via the air supply channel is circulated without passing through the fuel cell. A control method for a fuel cell system, comprising: a bypass channel; and a bypass valve that adjusts a flow rate of air in the bypass channel,
An operation point determination step of determining whether or not the current operation point of the air compressor is within a surge vicinity operation region when reducing the rotation speed of the air compressor, based on a predetermined map;
A pressure reducing step of reducing the pressure of the air supply flow path by controlling to open the bypass valve when it is determined in the operating point determining step that the current operating point is in the operation region near the surge; ,
A rotational speed control step for reducing the rotational speed of the air compressor after the pressure reducing step;
A control method for a fuel cell system, comprising: In the operating point determination step, when the current operating point is in the operation region near the surge, at least one of the pressure ratio, supply flow rate, and rotation speed of the air compressor at the current operating point and the next operating point. A change amount calculating step for calculating a difference;
A normal control step of shifting the current operating point to the next operating point without controlling to open the bypass valve when the difference calculated in the change amount calculating step is less than or equal to a predetermined threshold;
The control method of the fuel cell system of Claim 4 containing these.   The pressure at which the current operating point is shifted to the next operating point by controlling the bypass valve to close after the rotational speed of the air compressor is reduced or simultaneously with the reduction of the rotational speed in the rotational speed control step. The method for controlling a fuel cell system according to claim 4, comprising a recovery step.