Fuel cell system

Abstract

To provide a technique for detecting a fault occurring in a component that constitutes an impedance measurement circuit in a fuel cell system.SOLUTION: A fuel cell system includes an impedance measuring device that measures the impedance of a fuel cell stack. The impedance measuring device determines whether the measured impedance of the fuel cell stack is abnormal by comparing the measured impedance of the fuel cell stack with an estimated impedance estimated from the stack temperature and load current of the fuel cell stack, and, when it determines that the measured impedance is abnormal, determines whether the slope of the measured impedance of the fuel cell stack measured when at least two constant load currents of different magnitudes are flowing is abnormal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a fuel cell system. [Background technology]

[0002] In a fuel cell system, the water content of a fuel cell stack is estimated in order to control the water content of the fuel cell stack. Patent Document 1 discloses a technique for measuring the impedance of a fuel cell stack and estimating the water content of the fuel cell stack from the measured impedance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-158248 Summary of the Invention [Problem to be solved by the invention]

[0004] If a component constituting the impedance measurement circuit fails, the impedance of the fuel cell stack cannot be measured accurately. To address this situation, a technology for detecting a failure in the impedance measurement circuit is needed. For example, in the case of a failure such as a power short or a ground short, the measured impedance shows a significantly abnormal value, making it easy to detect such a failure. On the other hand, in the case of a failure that causes an offset in the measured impedance, it is difficult to detect the presence or absence of a failure. This specification provides a technology for detecting a failure that occurs in a component constituting the impedance measurement circuit in a fuel cell system. [Means for solving the problem]

[0005] The fuel cell system disclosed herein may include an impedance measuring device that measures the impedance of the fuel cell stack. The impedance measuring device may determine whether the measured impedance of the fuel cell stack is abnormal by comparing the measured impedance of the fuel cell stack with an estimated impedance estimated from the stack temperature and load current of the fuel cell stack, and, if it determines that the measured impedance is abnormal, determine whether the slope of the measured impedance of the fuel cell stack measured when at least two constant load currents of different magnitudes are flowing is abnormal.

[0006] In the fuel cell system, it is determined whether the slope of the measured impedance measured when at least two constant load currents of different magnitudes are flowing is abnormal. For example, in the case of a fault that causes an offset in the measured impedance, the slope of the measured impedance also shows an abnormal value. Therefore, the fuel cell system can also detect faults that cause an offset in the measured impedance. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a fuel cell system. [Figure 2] FIG. 4 is a diagram showing a flow of an abnormality determination process for an impedance measurement circuit executed by a control ECU. DETAILED DESCRIPTION OF THE INVENTION

[0008] The fuel cell system of this embodiment will be described below with reference to the drawings. The fuel cell system of this embodiment may be mounted on, for example, a fuel cell vehicle or a stationary fuel cell device, although it is not particularly limited thereto.

[0009] As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 10, a boost converter 12, a load 14, and a control ECU 16.

[0010] The fuel cell 10 has a fuel cell stack, various auxiliary devices, and various sensors. The various auxiliary devices include a fuel gas supply unit and an oxidizing gas supply unit, which supply fuel gas (e.g., hydrogen) and oxidizing gas (e.g., air) to the fuel cell stack. The various sensors include a temperature sensor that measures the temperature of the fuel stack, a current sensor that measures the load current output from the fuel stack, and a voltage sensor that measures the voltage between the electrodes of the fuel stack. The fuel cell 10 is a power generation device that generates electricity by electrochemically reacting fuel gas and oxidizing gas, and is connected to a load 14 via a boost converter 12.

[0011] The boost converter 12 is configured as a chopper-type DC / DC converter. The boost converter 12 boosts the DC voltage output from the fuel cell 10 and supplies it to the load 14. The boost converter 12 can also superimpose a sine wave on the load current output from the fuel cell stack by successively changing the duty ratio of the switching element in the abnormality determination process of the impedance measurement circuit, which will be described later.

[0012] The control ECU 16 is a computer that controls the various elements that make up the fuel cell system 1, and is composed of an I / O interface, a CPU, RAM, and ROM. The ROM stores various control programs, a map for calculating estimated impedance from the stack temperature and load current (described later), and the like. The control ECU 16 receives the stack temperature, load current, and output voltage of the fuel cell stack from sensors of the fuel cell 10.

[0013] The control ECU 16 generates a boost command signal in response to a power generation request and inputs the generated boost command signal to the boost converter 12. While the control ECU 16 is causing the boost converter 12 to perform a boost operation, the control ECU 16 starts an abnormality determination process for the impedance measurement circuit, which will be described below. The control ECU 16 is an example of an impedance measurement device.

[0014] As shown in FIG. 2, the control ECU 16 measures the load current of the fuel cell stack (step S1) and the stack temperature (step S2). Next, the control ECU 16 measures the impedance of the fuel cell stack (step S3). At this time, the control ECU 16 successively changes the duty ratio of the switching elements of the boost converter 12 to superimpose a sine wave on the load current output from the fuel cell stack. A sine wave is also superimposed on the output voltage of the fuel cell stack in accordance with the amplitude of the load current. The control ECU 16 calculates the impedance of the fuel cell stack from the AC components superimposed on the load current and the output voltage.

[0015] Next, the control ECU 16 estimates an estimated impedance from the load current measured in step S1 and the stack temperature measured in step S2, and compares the estimated impedance with the measured impedance calculated in step S3 to determine whether the measured impedance is abnormal (step S4). The estimated impedance is an impedance that is preset as an appropriate value based on the stack temperature and the load current. A map that associates stack temperature, load current, and estimated impedance is stored in the ROM of the control ECU 16, and the control ECU 16 can estimate the estimated impedance based on the stack temperature and the load current by referring to the map. The control ECU 16 determines that the measured impedance is abnormal when the measured impedance does not satisfy an upper limit, a lower limit, or both, determined based on the estimated impedance. If the control ECU 16 determines that the measured impedance is abnormal, it sets an abnormality flag (step S5). If the measured impedance is normal, the abnormality determination process for the impedance measurement circuit ends.

[0016] Next, the control ECU 16 determines whether the fuel cell system 1 is undergoing shutdown processing (step S6). If the fuel cell system 1 has not started shutdown processing, the control ECU 16 waits until the shutdown processing starts. When the control ECU 16 confirms that the fuel cell system 1 has started shutdown processing, it executes the processing described below. Note that if the fuel cell system 1 is mounted on a fuel cell vehicle, the shutdown processing of the fuel cell system 1 may start when the ignition is turned off.

[0017] Next, the control ECU 16 commands the load 14 to sweep a constant load current at a low load (e.g., 10 A) (step S7). The load 14 is not particularly limited, but may be, for example, an air compressor provided in an oxygen supply unit that supplies oxygen gas (e.g., air) to the fuel cell 10. The control ECU 16 further measures the impedance of the fuel stack when a constant load current at a low load (e.g., 10 A) is output from the fuel stack (step S8). The method for measuring the impedance is the same as in step S3 above.

[0018] Next, the control ECU 16 commands the load 14 to sweep a constant load current at a high load (for example, 20 A) (step S9). The load 14 is not particularly limited, but may be, for example, an air compressor provided in an oxygen supply unit that supplies oxygen gas (for example, air) to the fuel cell 10. The control ECU 16 further measures the impedance of the fuel stack when a constant load current at a high load (for example, 20 A) is output from the fuel stack (step S10). The impedance is measured in the same manner as in step S3 above. Note that, if the fuel cell system 1 is mounted on a fuel cell vehicle, the processes from step S7 to step S10 may be performed after the ignition is turned off and before the fuel cell system 1 is stopped (when the high-voltage path starts to be cut off).

[0019] Next, the control ECU 16 calculates the slope of the measured impedance measured in step S9 and the measured impedance measured in step S10 (i.e., the slope of the load current versus the measured impedance) (step S11). The control ECU 16 determines whether the magnitude of the calculated slope is abnormal (step S12). If the magnitude of the calculated slope is not within a normal range, the control ECU 16 determines that the magnitude of the calculated slope is abnormal. If the control ECU 16 determines that the magnitude of the calculated slope is abnormal, it notifies the user (step S13). If the magnitude of the calculated slope is normal, the abnormality determination process for the impedance measurement circuit ends.

[0020] In the abnormality determination process of the impedance measurement circuit described above, two abnormality determinations are performed. The first abnormality determination is performed when the boost converter 14 is performing a boost operation. If the measured impedance significantly deviates from the estimated impedance, a fault that causes an offset in the measured impedance is suspected. The measured impedance measured when the boost converter 14 is performing a boost operation constantly changes due to constantly changing load current, etc., so it is difficult to determine from the first abnormality determination alone that a fault that causes an offset in the measured impedance has occurred. For this reason, in the first abnormality determination, an abnormality flag is set in such a case. The second abnormality determination is performed after the fuel cell system 1 starts the shutdown process. Because the fuel cell system 1 is performing the shutdown process, the control ECU 16 can output two constant load currents with different magnitudes, a low load (e.g., 10 A) and a high load (e.g., 20 A), from the fuel stack. In the second abnormality determination, the impedance is measured when a constant load current is flowing and the slope of the measured current is determined to be abnormal, thereby detecting a fault that causes an offset in the measured impedance. In this abnormality determination process, a second abnormality determination is performed only when the abnormality flag is set, making it possible to detect a fault that causes an offset in the measured impedance while suppressing power consumption. [Explanation of symbols]

[0021] 1: fuel cell system, 10: fuel cell, 12: boost converter, 14: load, 16: control ECU

Claims

[Claim 1] 1. A fuel cell system, comprising: an impedance measuring device for measuring the impedance of the fuel cell stack; The impedance measuring device is determining whether the measured impedance is abnormal by comparing the measured impedance of the fuel cell stack with an estimated impedance estimated from the stack temperature and load current of the fuel cell stack; When it is determined that the measured impedance is abnormal, the fuel cell system determines whether the slope of the measured impedance of the fuel cell stack measured when at least two constant load currents of different magnitudes are flowing is abnormal.

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