Fuel cell system

Abstract

To provide a fuel cell system that can control the temperature of the smoothing capacitor of a boost converter while suppressing output reduction.SOLUTION: A fuel cell system includes a fuel cell 10, an ECU 40 which controls the supply pressure of cathode gas supplied to the fuel cell 10, a boost converter 20 which boosts the voltage of the fuel cell 10, and temperature detection means which detects the temperature Tc of a smoothing capacitor 25 provided in the boost converter 20, and when the temperature Tc of the smoothing capacitor 25 detected by the temperature detection means exceeds a preset threshold value Tcm, the ECU 40 controls the supply pressure of the cathode gas such that the voltage of the fuel cell 10 becomes smaller on the output equal power line W1 of the boost converter 20.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] Patent Document 1 discloses a power generation system for a vehicle mainly composed of a fuel cell system, an electric motor as a load, a DC / DC converter, a secondary battery, and a controller. In this power generation system, the temperature of the DC / DC converter is detected by a PM temperature sensor, and when the temperature of the DC / DC converter is higher than a judgment value for judging a high temperature state, the controller performs suppression control so as to reduce the difference between the stack side voltage and the secondary battery side voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-115011 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above power generation system, when the temperature of the DC / DC converter is in a high temperature state, control is performed taking into consideration the voltage on the secondary battery side, making it difficult to supply the required power to the vehicle side system.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a fuel cell system that can control the temperature of a smoothing capacitor of a boost converter while suppressing a decrease in output. [Means for solving the problem]

[0006] In order to achieve the above object, the fuel cell system of the present invention comprises: A fuel cell; a cathode gas control means for controlling a supply pressure of a cathode gas supplied to the fuel cell; a boost converter that boosts the voltage of the fuel cell; a temperature detection means for detecting a temperature of a smoothing capacitor provided in the boost converter; Equipped with The cathode gas control means includes: When the temperature of the smoothing capacitor detected by the temperature detection means exceeds a preset threshold value, the supply pressure of the cathode gas is controlled so that the voltage of the fuel cell becomes smaller on the output equal power line of the boost converter.

[0007] According to a fuel cell system having this configuration, it is possible to control the temperature of the smoothing capacitor of the boost converter while suppressing a decrease in output. Effect of the Invention

[0008] According to the present invention, it is possible to provide a fuel cell system that can control the temperature of the smoothing capacitor of a boost converter while suppressing a decrease in output. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system according to this embodiment. [Diagram 2] FIG. 2 is a thermal circuit diagram illustrating the flow of heat in the smoothing capacitor. [Diagram 3] FIG. 3 is a flowchart illustrating the control by the ECU. [Figure 4] FIG. 4 is a graph showing the relationship between the boost ratio and the ripple current of the smoothing capacitor in a four-phase interleaved boost chopper circuit. [Diagram 5] FIG. 5 is a graph showing an example of IV characteristics, which are the relationship between the current and voltage of a fuel cell. [Figure 6] FIG. 6 is a graph illustrating the correlation between the air supply pressure and the IV characteristics. [Figure 7] FIG. 7 is a graph showing an example of IV characteristics that are the relationship between the current and voltage of the fuel cell, which is used to explain the temperature control of the smoothing capacitor. [Figure 8] FIG. 8 is a graph showing the relationship between the boost ratio and the ripple current of the smoothing capacitor in a four-phase interleaved boost chopper circuit, which explains the temperature control of the smoothing capacitor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a fuel cell system 100 according to this embodiment.

[0011] 1, a fuel cell system 100 according to this embodiment mainly comprises a fuel cell 10 and a boost converter 20, and the fuel cell 10 supplies power to a vehicle system 30 via the boost converter 20. The fuel cell system 100 also comprises an ECU (cathode control means) 40, which controls the fuel cell 10 and the boost converter 20.

[0012] The boost converter 20 boosts the voltage of the power from the fuel cell 10 and supplies it to the vehicle system 30. The boost converter 20 has a multi-phase (four-phase in this example) interleaved boost chopper circuit. Specifically, the boost converter 20 has an A-phase circuit 23a for output current ia, a B-phase circuit 23b for output current ib, a C-phase circuit 23c for output current ic, and a D-phase circuit 23d for output current id connected in parallel between an input side 21 on the fuel cell 10 side and an output side 22 on the vehicle system 30 side. The boost converter 20 including the A-phase circuit 23a, the B-phase circuit 23b, the C-phase circuit 23c, and the D-phase circuit 23d outputs a current with a drive phase shift of 90° (360° / 4 phases) in each phase. Then, the boost converter 20 outputs a current iabcd, which is a combination of the output currents of each phase, at the output side 22.

[0013] The boost converter 20 is provided with a smoothing capacitor 25 on the output side 22, and the AC component of the current iabcd is absorbed and stabilized by this smoothing capacitor 25. In other words, a ripple current irip, which is the AC component of the current iabcd, flows through this smoothing capacitor 25, and a stabilized output current iout is output to the vehicle system 30.

[0014] The ECU 40 is connected to the fuel cell 10 , the boost converter 20 , and the vehicle system 30 , and transmits and receives signals to and from these fuel cell 10 , the boost converter 20 , and the vehicle system 30 .

[0015] The ECU 40 detects the input voltage Vfc, which is the voltage of the fuel cell 10 at the input side 21 of the boost converter 20, and the output voltage VH, which is the voltage of the vehicle system 30 at the output side 22 of the boost converter 20. Then, the ECU 40 determines the boost ratio (VH / Vfc) of the boost converter 20 based on the input voltage Vfc and the output voltage VH. The ECU 40 also controls an air compressor (not shown) of the fuel cell 10 to adjust the supply pressure of air, which is the cathode gas, to the fuel cell 10.

[0016] FIG. 2 shows a thermal circuit of the smoothing capacitor 25. As shown in FIG. 2, the smoothing capacitor 25 generates heat (Pc) by the flow of a ripple current irip of an AC component of the current iabcd. In addition to the heat (Pc), heat (Pout) is transferred to the smoothing capacitor 25 from a terminal block (not shown) of the boost converter 20. The smoothing capacitor 25 dissipates heat to the cooling water at a water temperature (Tw) through a thermal resistance (Rw), and dissipates heat to the atmosphere at an ambient temperature (Ta) through a thermal resistance (Ra). In the boost converter 20, it is necessary to prevent the temperature of the smoothing capacitor 25, which is determined by the heat received from nearby components, the heat generated by the smoothing capacitor 25 itself, and the heat dissipated to the cooling water and the atmosphere, from exceeding the heat resistance temperature.

[0017] Here, in order to suppress the temperature rise of the smoothing capacitor 25, it is conceivable to reduce the output of the boost converter 20 and suppress the heat (Pout) from the terminal block. However, if the output of the boost converter 20 is reduced, it becomes difficult to supply the required power to the vehicle system 30.

[0018] For this reason, in this embodiment, in order to suppress the temperature rise of the smoothing capacitor 25 without suppressing the output to the vehicle system 30, the ECU 40 controls the air compressor of the fuel cell 10 and adjusts the amount of air, which is the cathode gas, supplied to the fuel cell 10.

[0019] The control performed by the ECU 40 will now be described. FIG. 3 is a flowchart illustrating the control performed by the ECU 40.

[0020] The amount of heat generated by the smoothing capacitor 25 due to its own heat generation (Pc) is calculated based on the ripple current irip flowing through the smoothing capacitor 25 of the boost converter 20. Then, the temperature Tc of the smoothing capacitor 25, which is determined by the self-heat generation (Pc), heat received from nearby components (Pout), and heat dissipated to the cooling water and the atmosphere, is estimated (step S01). Note that the boost converter 20 may be provided with a temperature sensor for detecting the temperature of the smoothing capacitor 25, and the temperature of the smoothing capacitor 25 may be detected by this temperature sensor.

[0021] After estimating the temperature Tc of the smoothing capacitor 25, the temperature Tc is compared with a preset threshold value Tcm to determine whether the temperature Tc is higher than the threshold value Tcm (step S02). The threshold value Tcm is a temperature calculated in advance from the heat resistance temperature of the smoothing capacitor 25, and is, for example, the upper limit temperature at which the smoothing capacitor 25 operates normally. If the temperature Tc of the smoothing capacitor 25 does not exceed the threshold value Tcm in this temperature determination (step S02) (step S02: NO), the boost converter 20 is not controlled to adjust the temperature Tc of the smoothing capacitor 25 (step S03), and the temperature determination (step S02) is continued to monitor the temperature Tc of the smoothing capacitor 25.

[0022] When it is determined that the temperature Tc of the smoothing capacitor 25 exceeds the threshold value Tcm (step S02: YES), it is determined whether or not the ripple current irip of the smoothing capacitor 25 is higher than the upper limit value imax (step S04).

[0023] In the process of determining the ripple current irip (step S04), if the ripple current irip does not exceed the upper limit value imax (step S04: NO), it is determined that the temperature rise of the smoothing capacitor 25 is due to something other than self-heating (Pc), and the boost converter 20 is controlled to limit the power output to the vehicle system 30 (step S05). This suppresses the heat received (Pout) other than the self-heating (Pc) of the smoothing capacitor 25, and then the process following the estimation of the temperature Tc of the smoothing capacitor 25 (step S01) is performed.

[0024] In the process of determining the ripple current irip (step S04), if the ripple current irip exceeds the upper limit value imax (step S04: YES), it is determined that the cause of the temperature rise in the smoothing capacitor 25 is self-heating (Pc), and the air compressor of the fuel cell 10 is controlled to adjust the supply pressure of air, which is the cathode gas to the fuel cell 10 (step S06). Specifically, the supply pressure of the air to the fuel cell 10 is reduced. This reduces the ripple current irip flowing through the smoothing capacitor 25, suppressing the temperature rise due to the self-heating (Pc) of the smoothing capacitor 25. Thereafter, the process following the estimation of the temperature Tc of the smoothing capacitor 25 (step S01) is performed.

[0025] Next, the principle of the process (step S06) of reducing the temperature Tc of the smoothing capacitor 25 by adjusting the supply pressure of air, which is the cathode gas, to the fuel cell 10 will be described.

[0026] (ripple current) Fig. 4 shows the relationship between the boost ratio (VH / Vfc) in a four-phase interleaved boost chopper circuit and the ripple current irip of smoothing capacitor 25. As shown in Fig. 4, in boost converter 20, the D ratio, which indicates the proportion of the ON time of the semiconductor element in each phase, varies depending on the boost ratio (VH / Vfc). In the interleaved boost chopper circuit, when the D ratio varies, the ripple current irip flowing through smoothing capacitor 25 also changes.

[0027] (Determining the boost ratio) The output voltage VH of the boost converter 20, which is the voltage of the vehicle system 30, is determined by the vehicle system 30. Therefore, the input voltage Vfc, which is the voltage of the fuel cell 10, is determined by the IV characteristics (current-voltage characteristics) of the fuel cell 10 and the current iout that the boost converter 20 wants to output.

[0028] FIG. 5 shows an example of an IV characteristic, which is the relationship between the current ifc and the voltage vfc of the fuel cell 10. The boost converter 20 receives the current that can be output on this IV characteristic as a command current from the ECU 40 and drives the boost converter 20, thereby determining the operating point on the IV characteristic of the fuel cell 10. For example, when the current ifc is X [A], the voltage vfc is x [V], and when the current ifc is Y [A], the voltage vfc is y [V]. The respective boost ratios (VH / Vfc) are VH / x and VH / y. These boost ratios (VH / Vfc) are different from each other, and VH / x <VH / yとなる。

[0029] (Determination of IV characteristics) One parameter that determines the IV characteristics of the fuel cell 10 is the supply pressure of air, which is the cathode gas. FIG. 6 shows the correlation between the air supply pressure and the IV characteristic. As shown in FIG. 6, when the air supply pressure is increased, the amount of oxygen sent to the fuel cell 10 increases, and the IV characteristic rises to a higher IV characteristic (IV characteristic shown by the two-dot chain line in FIG. 6) than the original IV characteristic (IV characteristic shown by the solid line in FIG. 6) (see arrow A in FIG. 6). Conversely, when the supply pressure is decreased, the amount of oxygen sent to the fuel cell 10 decreases, and the IV characteristic drops to a lower IV characteristic (IV characteristic shown by the one-dot chain line in FIG. 6) than the original IV characteristic (IV characteristic shown by the solid line in FIG. 6) (see arrow B in FIG. 6). In this way, the IV characteristic of the fuel cell 10 can be shifted by adjusting the air supply pressure to the fuel cell 10.

[0030] (Suppression of temperature of smoothing capacitor) By lowering the power output of boost converter 20, smoothing capacitor 25 receives less heat Pout from the terminal block, and the temperature rise is suppressed. 7 is a graph showing an example of an IV characteristic that is a relationship between the current ifc and the voltage Vfc of the fuel cell 10, which explains the temperature control of the smoothing capacitor 25. For example, as shown in FIG. 7, the operating point M1 of the boost converter 20 is moved from the output equal-power line W1 on the IV characteristic C1 to an operating point M1a on the output equal-power line W2, which has a lower power than the output equal-power line W1 (see arrow C in FIG. 7). In this way, the power output of the boost converter 20 is reduced, thereby reducing the heat Pout received from the terminal block and suppressing the temperature rise of the smoothing capacitor 25. However, if the power output of the boost converter 20 is reduced in this way, it becomes difficult to supply the required power in the vehicle system 30.

[0031] For this reason, in this embodiment, the temperature Tc of the smoothing capacitor 25 is reduced by adjusting the supply pressure of air, which is the cathode gas to the fuel cell 10. Specifically, as shown in FIG. 7, the IV characteristic C1 (IV characteristic shown by the solid line in FIG. 7) of the fuel cell 10 is shifted to an IV characteristic C2 (IV characteristic shown by the dashed line in FIG. 7) lower than the IV characteristic C1 (see arrow D in FIG. 7). Then, the operating point M1 of the boost converter 20 is shifted from the IV characteristic C1 to an operating point M2 on the IV characteristic C2 on the output equal power line W1 (see arrow E in FIG. 7). In this way, when the operating point M1 of the boost converter 20 is shifted from the IV characteristic C1 to the operating point M2 on the IV characteristic C2, the voltage vfc of the fuel cell 10 is reduced.

[0032] Fig. 8 is a graph showing the relationship between the boost ratio (VH / Vfc) in a four-phase interleaved boost chopper circuit and the ripple current irip of the smoothing capacitor 25, which explains the temperature control of the smoothing capacitor 25. As shown in Fig. 8, when the voltage vfc of the fuel cell 10 decreases, the boost ratio (VH / Vfc) increases, and the ripple current irip1 of the smoothing capacitor 25 becomes a low ripple current irip2 (see arrow F in Fig. 8). Therefore, self-heating (Pc) due to the ripple current irip2 in the smoothing capacitor 25 is suppressed, and the temperature rise is suppressed.

[0033] As described above, the fuel cell system 100 according to this embodiment can control the temperature of the smoothing capacitor 25 of the boost converter 20 while suppressing a decrease in output. This allows an appropriate amount of power to be supplied to the vehicle system 30.

[0034] In the above embodiment, the boost converter 20 equipped with an interleaved boost chopper circuit has been described as an example, but the boost converter 20 is not limited to the interleaved type, and a boost converter having a structure in which the amount of self-heating varies depending on the boost ratio can also be used. [Explanation of symbols]

[0035] 10 fuel cell 20 Boost Converter 25 Smoothing capacitor 40 ECU (cathode gas control means, temperature detection means) 100 Fuel Cell System

Claims

[Claim 1] A fuel cell; a cathode gas control means for controlling a supply pressure of a cathode gas supplied to the fuel cell; a boost converter that boosts the voltage of the fuel cell; a temperature detection means for detecting a temperature of a smoothing capacitor provided in the boost converter; Equipped with The cathode gas control means includes: when the temperature of the smoothing capacitor detected by the temperature detection means exceeds a preset threshold value, the supply pressure of the cathode gas is controlled so that the voltage of the fuel cell becomes smaller on the output equal power line of the boost converter. Fuel cell system.

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