DEVICE AND METHOD FOR MEASURING THE VOLTAGE AND AVERAGE POWER OF A FUEL CELL

Abstract

Device for measuring the average power of a fuel cell, characterized in that the device comprises: a voltage measuring unit (400) configured to sequentially measure forward voltages of individual cells (111) forming a fuel cell stack (100) from a lower cell to an upper cell, and to sequentially measure reverse voltages of the individual cells (111) from the upper cell to the lower cell; a current measuring unit (300) configured to measure a current of an output terminal of the fuel cell stack (100);and a control unit (500) configured to control the voltage measuring unit (400) to measure the reverse voltages based on the current measurement time after the voltage measuring unit (400) has fully calculated the forward voltages, and to calculate the average power using the forward voltages, the reverse voltages, and the measured current, wherein the voltage measuring unit (400) comprises: a voltmeter (410) configured to measure the voltages of the respective individual cells (111), wherein the voltmeter (410) comprises: one or more voltage sensors (411) installed to correspond one-to-one with each of the individual cells (111) and configured to detect the voltage of each of the individual cells (111); a switch (413) configured to electrically connect the individual cell (111) to the voltage sensor (411);and a replica unit (412) configured to measure a disturbance voltage according to a switching operation of the switch (413).

Description

TECHNICAL BACKGROUND AREA OF INVENTION Exemplary embodiments of the present disclosure relate to a device and a method for measuring the voltage and average power of a fuel cell. EXPLANATION OF THE TECHNICAL BACKGROUND A fuel cell is a type of power generation device that converts the chemical energy of fuel into electrical energy by causing the fuel to react electrochemically in a stack, without converting the chemical energy into heat through combustion. Fuel cells can be used to provide power not only for industrial applications, residential use, and powering vehicles, but also for small electrical / electronic products or, specifically, portable devices. Currently, much research is being conducted on the PEMFC (polymer electrolyte membrane fuel cell, or proton exchange membrane fuel cell), which has the highest power density among fuel cells, as a power source for driving a vehicle. Thanks to its low operating temperature, the PEMFC has a short start-up time and a short energy conversion response time. The PEMFC comprises a membrane electrode assembly (MEA), a gas diffusion layer (GDL), a sealing and clamping mechanism, and a bipolar plate. The MEA has a catalyst / electrode layer where an electrochemical reaction takes place and is attached to both sides of a rigid polymer electrolyte membrane through which hydrogen ions migrate. The GDL serves to uniformly distribute the reaction gases and to transfer the generated electrical energy. The sealing and clamping mechanism maintains the correct clamping pressure and airtightness against the reaction gases and the cooling water. The bipolar plate circulates the reaction gases and the cooling water. When using such individual cell components to assemble a fuel cell stack, a combination of MEA and GDL, which are the main components, is positioned in the innermost part of the cell. The MEA has catalyst / electrode layers applied to both surfaces of the polymer electrolyte membrane, i.e., an anode and a cathode, and the GDL, seal, and similar components are layered on top of each other on the outside of the MEA, where the anode and cathode are located. The catalyst / electrode layers are coated with a catalyst so that oxygen and hydrogen react with each other. The bipolar plate is positioned outside the GDL and has a flow field through which reaction gases, including hydrogen used as fuel and oxygen or air used as oxidant, are supplied and cooling water is passed through. In such a configuration, which is fixed for a single cell, several individual cells are stacked on top of each other, and then an end plate is coupled to the outermost part of the individual cells to support a current collector, an insulating plate, and the stacked cells. The individual cells are then repeatedly stacked and clamped between the end plates to build the fuel cell stack. To achieve the required potential for a vehicle, the necessary number of individual cells corresponding to the required potential must be stacked to build the stack. A single cell generates a potential of approximately 1.3 V, and several cells are stacked in series to produce the power required to propel a vehicle. Since such a fuel cell is subject to significant voltage fluctuations, the voltage of the fuel cell must be measured precisely to accurately calculate its power output. In the related technique, the voltages of all individual cells in the fuel cell stack are measured sequentially, one after the other, and finally, the current is measured. This means that the timing of the voltage measurements differs from the timing of the current measurement, making precise power calculation impossible. Such discrepancies make accurately diagnosing and measuring the condition of a fuel cell exhibiting large voltage fluctuations difficult. In such cases, the fuel cell can be damaged. In the related technique, the voltages of a ground and a lower cell of a sensor semiconductor are measured together to determine the voltage of the fuel cell. If, under a specific condition, the difference between these voltages exceeds the reverse voltage limit (generally -10V to -20V) of an internal semiconductor element, the sensor semiconductor may burn out. The related technique of the present disclosure is disclosed in KR 10 1 629 579 B1, which was published on June 13, 2016 and is entitled “Method of Detecting Fuel Stack Voltage and Apparatus Performing the Same”. SUMMARY Various embodiments relate to a device and a method for measuring the average power of a fuel cell, which can synchronize the voltage measurement time(s) and the current measurement time of a fuel cell stack, and can accurately calculate the average power of the fuel cell stack through synchronization. Various embodiments also relate to a device and a method for measuring the average power of a fuel cell, which can change the ground voltage by interposing high-impedance elements between an upper single cell and a ground and between a lower single cell and the ground, and prevent breakdown in an element due to a high reverse voltage generated under a specific condition when a voltage of the fuel cell is measured, and for measuring the voltage of the fuel cell. In one embodiment, a device for measuring the average power of a fuel cell may comprise: a voltage measuring unit configured for sequentially measuring forward voltages of individual cells forming a fuel cell stack, from a lower cell to an upper cell, and for sequentially measuring reverse voltages of the individual cells from the upper cell to the lower cell; a current measuring unit configured for measuring a current at an output terminal of the fuel cell stack; and a control unit configured for controlling the voltage measuring unit to measure the reverse voltages based on the current measurement time, after the voltage measuring unit has fully calculated the forward voltages, and to calculate average power using the forward voltages, the reverse voltages, and the measured current. The voltage measurement unit may include: a voltmeter configured to measure the voltages of the individual cells; a MUX configured to sequentially output the voltages measured by the voltmeter for the individual cells; and an ADC configured to convert the voltages of the individual cells output by the MUX into digital signals. The voltage meter may comprise: one or more voltage sensors installed to correspond one-to-one with each of the individual cells and configured to detect the voltage of each of the individual cells; a switch configured to electrically connect the individual cell to the voltage sensor; and a replica unit configured to measure a disturbance voltage according to a switching operation of the switch. The voltage measurement unit may also include an amplifier designed to subtract the interference voltage measured by the replica unit from the voltage measured by the voltage sensor. The voltage measuring unit may also include a level converter, which is designed to convert the levels of the voltages of the individual cells measured by the voltage meter into an operational voltage withstand range and to apply the voltages thus obtained to the MUX. The voltage measuring unit may also include a scaler designed to reduce the voltages of the individual cells measured by the voltmeter. The control unit can calculate an average voltage of the forward and reverse voltages and calculate the average power by multiplying the calculated average voltage by the measured current. The control unit can compare the average power with the instantaneous power of the respective individual cells and detect abnormal operation of an individual cell if the comparison result for the corresponding individual cell indicates that an error is occurring which is greater than or equal to a preset threshold. The control unit can calculate the instantaneous power outputs of the respective individual cells using the voltages of the individual cells measured by the voltage measuring unit and the current measured by the current measuring unit. In one embodiment, a method for measuring the average power of a fuel cell may comprise: sequentially measuring forward voltages of individual cells forming a fuel cell stack, from a lower cell to an upper cell, by a voltage measuring unit; measuring a current of an output terminal of the fuel cell stack by a current measuring unit; sequentially measuring reverse voltages of the individual cells, from the upper individual cell to the lower individual cell, by the voltage measuring unit; and calculating an average voltage of the forward voltages and the reverse voltages by a control unit and calculating the average power of the fuel cell stack using the calculated average voltage and the measured current. When calculating the average power of the fuel cell stack, the control unit can calculate the average power by multiplying the average voltage by the measured current. The procedure may also include comparing the average power output with the instantaneous power outputs of the respective individual cells by the control unit and detecting abnormal operation of an individual cell if the comparison result for the corresponding individual cell indicates that an error occurs which is as large as a preset threshold or larger, after calculating the average power output of the fuel cell stack. In one embodiment, a device for measuring the voltage of a fuel cell may comprise: a voltage measuring unit configured to measure the voltages of individual cells forming a fuel cell stack; and a protection unit connected to one or more of the individual cells and configured to prevent damage to the voltage measuring unit due to a reverse voltage. The protection unit may include: a first impedance element, which is connected at one end to a positive (+) terminal of an upper single cell below the single cells and at the other end to a ground of the voltage measuring unit; and a second impedance element, which is connected at one end to a negative (-) terminal of the lower single cell below the single cells and at the other end to ground. The impedance of the first impedance element and the impedance of the second impedance element can be set according to a reversing potential voltage withstand capability of the voltage measuring unit. According to the embodiments of the present disclosure, the device and method for measuring the average power of a fuel cell can sequentially measure forward voltages from the lower individual cell to the upper individual cell of the fuel cell stack, sequentially measure backward voltages from the upper individual cell to the lower individual cell based on the current measurement time, and calculate the average voltage of the forward voltages and the backward voltages, thereby obtaining the same effect as an effect obtained by measuring the voltages of all individual cells at the current measurement time. Furthermore, the device and method can synchronize the voltage and current measurements of the fuel cell stack, thus accurately calculating the average power output of the fuel cell stack. This makes it possible to precisely diagnose the condition of a fuel cell exhibiting large voltage fluctuations and to take appropriate action. It is therefore possible to prevent damage to the fuel cell. The device for measuring the voltage of a fuel cell according to the embodiment of the present disclosure can modify the ground voltage by means of the high-impedance elements connected between the upper individual cell and ground or between the lower individual cell and ground. Therefore, the device can measure the voltage of the fuel cell while preventing breakdown in any element due to a high reverse voltage generated when measuring the voltage of the fuel cell under a specific condition. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating a device for measuring the average power of a fuel cell according to an embodiment of the present disclosure. Fig. 2 is a block diagram illustrating a voltage measuring unit according to an embodiment of the present disclosure. Fig. 3 is a diagram illustrating another example of a voltmeter according to an embodiment of the present disclosure. Fig. 4 is a flowchart illustrating a method for measuring the average power of a fuel cell according to an embodiment of the present disclosure. Fig. 5 is a diagram describing a voltage measurement time and a current measurement time of the fuel cell according to an embodiment of the present disclosure. Fig. 6 is a diagram describing a voltage of a fuel cell according to an embodiment of the present disclosure.Figure 7 is a block diagram illustrating a device for measuring the voltage of a fuel cell according to an embodiment of the present disclosure. Figure 8 is a diagram illustrating a ground voltage according to the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE ILLUSTRATED EXECUTION FORMS The following describes a device and a method for measuring the voltage and average power of a fuel cell with reference to the accompanying drawings, using various embodiments. It should be noted that the drawings are not to scale and the thickness of conductors or the size of components may be exaggerated for illustrative purposes only. Furthermore, the terms used herein are defined in consideration of the functions of the invention and may be modified according to the custom or intention of users or operators. Therefore, the definitions of terms should be made in accordance with the general disclosures set forth herein. [Version 1] Fig. 1 is a block diagram illustrating a device for measuring the average power of a fuel cell according to an embodiment of the present disclosure. The device for measuring the average power of a fuel cell according to the embodiment of the present disclosure, with reference to Fig. 1, comprises a fuel cell stack 100, a power supply unit 200, a current measuring unit 300, a voltage measuring unit 400, and a control unit 500. The device for measuring the average power of a fuel cell illustrated in Fig. 1 is based on one embodiment. Therefore, the components of the device are not limited to the embodiment illustrated in Fig. 1, and some of the components can be added, modified, or removed if necessary. The fuel cell stack 100 comprises several individual cells 111 arranged sequentially. The fuel cell stack 100 can generate a signal current, and the current measuring unit 300 can measure the current of the fuel cell stack 100 by analyzing the signal current applied by the fuel cell stack 100. The power supply unit 200 provides the power required for the operation of the voltage measuring unit 400. The power supply unit 200 removes the ground connection and supplies the ground-free voltage. The current measuring unit 300 measures a current from an output terminal of the fuel cell stack 100 and transmits the measured current to the control unit 500. The voltage measuring unit 400 sequentially measures the forward voltages of the individual cells 111 forming the fuel cell stack 100, from the lower cell to the upper cell, and sequentially measures the reverse voltages of the individual cells 111, from the upper cell to the lower cell. At this point, the voltage measuring unit 400 can measure a reverse voltage based on a current measurement point, and the current measurement point can indicate a time at which the current measuring unit 300 measures a current. The voltage measuring unit 400 transmits the forward and backward voltages to the control unit 500. As described above, the voltage measuring unit 400 may measure the voltages of all the individual cells 111 forming the fuel cell stack 100 not just once, but again in reverse order of the voltages of the individual cells 111 that have already been measured, based on the current measurement time. By measuring the voltages again in reverse order, after the voltages have been measured starting from the bottom individual cell, the voltage measurement times can be synchronized. That is, although the voltages of the individual cells 111 are measured at different times, the voltages of all the individual cells 111 can be measured twice to calculate an average voltage, thus making it possible to obtain the same effect as by measuring all the cell voltages at a specific time (for example, the current measurement time). The voltage measuring unit 400 is described in detail with reference to Fig. 2. When the voltage measuring unit 400 has fully measured the forward voltages, the control unit 500 instructs the voltage measuring unit 400 to measure the reverse voltages based on the current measurement time and calculates the average power using the forward voltages, the reverse voltages, and the current measured by the current measuring unit 300. Then, the control unit 500 can calculate the average voltage of the forward and reverse voltages and calculate the average power by multiplying the calculated average voltage by the measured current. That is, the control unit 500 can calculate the average power of the fuel cell stack 100 using equation 1 below. In equation 1, the measurement time can have the same meaning as the current measurement time and indicate a time at which the current measuring unit 300 measures a current, and the measurement time current can indicate a current measured by the current measuring unit 300 at the measurement time. The control unit 500 compares the average power with the instantaneous power of the respective individual cells and detects abnormal operation of an individual cell if the comparison result for that cell indicates an error greater than or equal to a preset threshold. At this point, the control unit 500 can calculate the instantaneous power of each individual cell using the voltage of the individual cell measured by the voltage measuring unit 400 and the current measured by the current measuring unit 300. Average power can ensure power measurement accuracy even during significant voltage fluctuations. In contrast, instantaneous power can reduce power measurement accuracy due to timing errors when voltage fluctuations occur. Therefore, the 500 control unit can compare average and instantaneous power values ​​in real time. If an error occurs within a specific interval that is equal to or greater than the threshold value, the 500 control unit can detect momentary abnormal operation of the fuel cell. The control unit 500 can be implemented as an MCU (micro control unit) and calculates the average power of the fuel cell stack 100 using the forward and reverse voltages provided by the voltage measurement unit 400 and the current provided by the current measurement unit 300. The device for measuring the average power of a fuel cell according to the embodiment of the present disclosure measures the voltages of the individual cells 111 at different times. However, the device can calculate the average voltage by measuring the voltages of all the individual cells 111 twice, thereby achieving the same effect as measuring the cell voltages at a specific time (for example, the current measurement time). Therefore, the device can improve the accuracy of the average power by synchronizing the voltage measurement time of the fuel cell. Fig. 2 is a block diagram illustrating the voltage measuring unit according to the embodiment of the present disclosure. The voltage measuring unit 400 according to the embodiment of the present disclosure, with reference to Fig. 2, includes a voltage meter 410, a level converter 420, a scaler 430, a multiplexer (MUX) 440, an amplifier 450 and an ADC (analog-to-digital converter) 460. The voltage meter 410 measures the voltage of each individual cell 111. The voltage meter 410 includes several voltage sensors 411, several replica units 412 and several switches 413. The switches 413 are connected at one end via connecting pins C0 to Cn between the respective individual cells 111 and at the other end of the switch 413 to the voltage sensors 411, which are described below, and electrically connect the individual cells 111, which are measurement targets, to the voltage sensors 411 for measuring the voltages of the corresponding individual cells 111. Two switches 413 are connected to a voltage sensor 411, so that each of the voltage sensors 411 is electrically connected. In this case, the switches 413 are connected together with the voltage sensor 411 adjacent to them. For example, the switches 413 connected to the connecting pin C1 can be connected together with the voltage sensor 411 for measuring the voltage of the lower single cell 111 and the voltage sensor 411 for measuring the voltage of an upper single cell of the lower single cell 111, and all can be switched on when the voltage of the upper single cell of the lower single cell 111 as well as the voltage of the lower single cell are being measured. This means that if the voltage of the lower individual cell is to be measured, the switches 413 connected to the two connecting pins C0 and C1 are switched on. At this time, the voltage sensor 411 connected to the corresponding switches 413 measures the voltage of the corresponding lower individual cell. Furthermore, if the voltage of the upper cell 111 of the lower cell is to be measured, the switches 413 connected to the connecting pins C1 and C2 are switched on. At this time, the voltage sensor 411 connected to the corresponding switches 413 measures the voltage of the upper cell 111 of the corresponding lower cell. The voltage sensors 411 are installed so that they correspond one-to-one to each of the individual cells 111 and detect the voltages of the individual cells 111. The voltage sensor 411 can include a capacitor (not illustrated) and measure the voltage of the energy or current stored in the corresponding capacitor when the corresponding switch 413 is turned on. The method by which the voltage sensor 411 detects the voltage of the single cell 111 is not specifically limited and can include any method as long as the respective method can detect the voltage of the single cell 111. The replica unit 412 measures a disturbance voltage following a switching operation of the switch 413. The replica unit 412 can have the same construction as the voltage sensor 411 described above. For example, a disturbance voltage corresponding to the switching operation of the switch 413 can be generated. As a result, the replica unit 412 can detect a disturbance voltage of 0.1 V, even though the voltage sensor 411 detects a voltage of 5 V. The amplifier 450 subtracts the interference voltage measured by the replicator unit 412 from the voltage measured by the voltage sensor 411 and outputs the resulting voltage as the actual voltage of the individual cell 111, thereby minimizing voltage errors. The amplifier 450 can be installed in the voltmeter 410. Alternatively, the amplifier 450 can also be installed after the scaler 430 or the MUX 440, which are described below. That is, the amplifier 450 can be installed behind the MUX 440, as shown in Fig. 2, or behind the voltage sensor 411 and the replica unit 412 in the voltage meter 410, as illustrated in Fig. 3. In the present embodiment, the scaler 430 or the MUX 440 can be omitted. In this case, the amplifier 450 can be installed behind the voltage sensor 411 and the replica unit 412 in the voltmeter 410. In contrast, if the scaler 430 and the MUX 440 are installed, the amplifier 450 can be installed behind the MUX 440 or the scaler 430. The amplifier 450 can be installed in different positions, depending on whether the scaler 430 and the MUX 440 are installed or not. The level shifter 420 reduces the voltages of the individual cells 111 to an operational voltage range. Typically, the voltages of the individual cells 111 are greater than or equal to 100 V. Since the voltages of the individual cells 111 are not suitable for operating the amplifier 450 or the ADC 460, which are described below, the level shifter 420 converts the voltage level of the individual cell 111 to a level at which the amplifier 450 or the ADC 460 can normally operate. Furthermore, the level shifter 420 inputs the voltage measured by the voltage sensor 411 into the scaler 430, so that the scaler 430 or the MUX 440 can operate normally. The scaler 430 increases the voltage detected by the voltage sensor 411 to a voltage that can be received by the MUX 440, the amplifier 450 or the ADC 460 installed behind it. The MUX 440, amplifier 450, or ADC 460 is typically a low-voltage component capable of receiving or absorbing a relatively low voltage. Therefore, the scaler 430, as described above, can scale the voltage detected by the voltage sensor 411 to a voltage that can be detected by the MUX 440, amplifier 450, or ADC 460 installed downstream of it, allowing the MUX 440, amplifier 450, or ADC 460 to operate normally. The MUX 440 sequentially outputs the voltages of the respective individual cells 111, which are applied by the scaler 430. In the present embodiment, it is described that the MUX 440 is installed downstream of the scaler 430. However, the scope of this disclosure is not limited to this, and the MUX 440 can also be installed downstream of the level converter 420. In this case, the scaler 430 does not need to be provided separately. As described above, the amplifier 450 can be installed in the voltage measurement unit 400. However, the amplifier 450 can also be installed behind the MUX 440. The ADC 460 is installed behind the amplifier 450 and converts the voltage output by the amplifier 450 of each individual cell 111 into a digital signal. Fig. 4 is a flowchart illustrating a method for measuring the average power of a fuel cell according to an embodiment of the present disclosure, Fig. 5 is a diagram describing a voltage measurement time and a current measurement time of the fuel cell according to the embodiment of the present disclosure, and Fig. 6 is a diagram describing a voltage of the fuel cell according to the embodiment of the present disclosure. In step S310, with reference to Fig. 4, the voltage measuring unit 400 sequentially measures the forward voltages of the individual cells 111 that form the fuel cell stack 100, from the bottom individual cell to the top individual cell. For example, the voltage measuring unit 400 can sequentially measure the voltages of the individual cells from cell1 to cellN, labeled A in Fig. 5. Once step S310 has been performed, the current measuring unit 300 measures a current at the output terminal of the fuel cell stack 100 in step S320. For example, as illustrated in Fig. 5, the current measuring unit 300 can measure the current of the fuel cell stack 100 at a current measurement time B. Once step S320 has been performed, the voltage measuring unit 400 sequentially measures reverse voltages from the uppermost cell to the lowermost cell in step S330. For example, the voltage measuring unit 400 can sequentially measure the voltages of the individual cells from cell1 to cellN, labeled C in Fig. 5. Once step S330 has been performed, the control unit 500 calculates the average voltage of the forward and reverse voltages in step S340. For example, the control unit 500 can calculate the average voltage of the forward voltages of individual cells from cell1 to cellN and the average voltage of individual cells from cell1 to cellN. After the average voltage of the forward and reverse voltages has been calculated, the time at which the average voltage is calculated is synchronized with the time at which the current is measured, as illustrated in Fig. 6. It is therefore possible to obtain the same effect as if the result had been obtained by measuring all cell voltages at the measurement time (for example, the current measurement time). Once step S340 has been performed, the control unit 500 calculates the average power of the fuel cell stack 100 in step S350 using the calculated average voltage and the measured current. At this point, the control unit 500 can calculate the average power by multiplying the calculated average voltage by the measured current. Therefore, it is possible to calculate the average power by synchronizing the voltage measurement times, thereby improving the accuracy of the average power. After step S350, the control unit 500 can compare the average power with the instantaneous power of the respective individual cells and detect abnormal operation of an individual cell if the comparison result indicates that an error greater than or equal to a preset threshold is occurring. At this point, the control unit 500 can calculate the instantaneous power of each individual cell using the voltage of the individual cell measured by the voltage measuring unit 400 and the current measured by the current measuring unit 300. In the preceding section, only one method for calculating average power P1 was described with reference to Fig. 5. However, during the execution of step S330, the voltage measuring unit 400 can sequentially measure the reverse voltages of the individual cells from cell N to cell 1, as illustrated by D in Fig. 5. Then, the voltage measuring unit 400 can measure a current of the fuel cell stack 100 at a current measurement time E and measure the forward voltages of the individual cells from cell 1 to cell N, as indicated by F in Fig. 5. Finally, the control unit 500 can measure the average power P2 using the reverse voltages of the individual cells from cell N to cell 1 and the forward voltages of the individual cells from cell 1 to cell N. The device for measuring the average power of a fuel cell can calculate the average power P1 by sequentially measuring the forward and reverse voltages of the individual cells 111 and calculate the average power P2 by sequentially measuring the reverse and forward voltages of the individual cells 111. Therefore, the device can calculate the average power by measuring the voltages of the individual cells 111 in each half of a period. The device and method for measuring the average power of a fuel cell according to the embodiment of the present disclosure can sequentially measure the forward voltages of the individual cells of the fuel cell stack 100 from the lower individual cell to the upper individual cell, sequentially measure the reverse voltages of the individual cells from the upper individual cell to the lower individual cell based on the current measurement time, and then calculate the average voltage of the forward voltages and the reverse voltages, thereby obtaining the same effect as an effect obtained by measuring all cell voltages at the current measurement time. Furthermore, the device and method can synchronize the voltage and current measurement times of the fuel cell stack 100, thus accurately calculating the average power output of the fuel cell stack 100. This makes it possible to accurately diagnose the condition of the fuel cell, which exhibits large voltage fluctuations, and to take appropriate measures for the fuel cell. Therefore, it is possible to prevent damage to the fuel cell. [Version 2] Fig. 7 is a block diagram illustrating a device for measuring a voltage of a fuel cell according to an embodiment of the present disclosure, and Fig. 8 is a diagram illustrating a ground voltage according to the embodiment of the present disclosure. The device for measuring the voltage of a fuel cell according to the embodiment of the present disclosure, with reference to Fig. 7, comprises a fuel cell stack 100, a power supply unit 200, a voltage measuring unit 400, and a protection unit 600. The fuel cell stack 100, the power supply unit 200, and the voltage measuring unit 400 according to the second embodiment correspond to the same components in the first embodiment, and the following descriptions focus on the function and operation of the protection unit 600. The protection unit 600 includes a first impedance element 610 and a second impedance element 620. The protection unit 600 is connected to one or more individual cells 111 of the fuel cell stack 100. The protection unit 600 prevents damage to the internal components of the voltage measuring unit 400 caused by a reverse voltage generated under a specific condition. The first impedance element 610 is connected at one end to a positive (+) terminal of an upper single cell below the single cells 111 and at the other end to a ground GND of the voltage measuring unit 400. The second impedance element 620 is connected at one end to a negative (-) terminal of the lower single cell below the single cells 111 and at the other end to the ground GND of the voltage measuring unit 400. The impedance of the first impedance element 610 and the impedance of the second impedance element 620 can each be variably set according to a reversing potential voltage withstand capability of the voltage measuring unit 400. As described above, the first impedance element 610 is connected at one end to the positive (+) terminal of the upper single cell and at the other end to the ground of the voltage measuring unit 400, and the second impedance element 620 is connected at one end to the negative (-) terminal of the lower single cell and at the other end to the ground of the voltage measuring unit 400. Therefore, the ground voltage is different. Therefore, when the voltage measuring unit 400 measures the voltage of the single cell 111, the grounding voltage can be varied, although a relatively high reverse voltage is generated, thus making it possible to prevent the internal elements of the voltage measuring unit 400 from burning out due to the reverse potential voltage withstand capability. A conventional device for measuring the voltage of a fuel cell, as shown in Fig. 8, has a fixed ground voltage. Therefore, if the voltage difference between the ground voltage and the voltage of the top cell (Top_Cell) of the individual cells becomes greater than or equal to -12 V (corresponding to the voltage level of a general semiconductor element), breakdown of internal cells can occur. In the embodiment of the present disclosure, however, the first and second impedance elements 610 and 620, which each have a relatively high impedance, are connected in order to vary the grounding voltage. Therefore, no voltage difference occurs that would cause breakdown in the internal elements of the voltage measuring unit 400. Therefore, the internal elements of the voltage measuring unit 400 are safely protected. As described above, the first impedance element 610 is connected at one end to the positive (+) terminal of the upper cell and at the other end to the ground of the voltage measuring unit 400. The second impedance element 620 is connected at one end to the negative (-) terminal of the lower cell and at the other end to the ground of the voltage measuring unit 400. The first and second impedance elements 610 and 620 are each designed to have a high impedance, corresponding to a level that prevents breakdown of an internal element of the voltage measuring unit 400. Therefore, no current flows through the first and second impedance elements 610 and 620. Consequently, no voltage can be measured using the existing current measurement method. Therefore, the voltage measuring unit 400 directly measures the voltages of the individual cells 111 that form the fuel cell stack 100 using the voltage measurement method, not the current measurement method. The components of the voltage measuring unit 400 can be configured like those of the first embodiment, and the operation of the voltage measuring unit 400 can be carried out in the same way as in the first embodiment. As described above, the device for measuring the voltage of a fuel cell according to the embodiment of the present disclosure can change the ground voltage by means of the high-impedance elements connected between the upper individual cell and ground or between the lower individual cell and ground. Therefore, the device can measure the voltage of the fuel cell while preventing breakdown of an element by a high reverse voltage generated when measuring the voltage of the fuel cell under a specific condition. Up to now, the first and second embodiments have been described separately. However, the protection unit 600 of the second embodiment can be applied to the circuit arrangement of the first embodiment to perform the function of preventing damage to the voltage measuring unit 400 according to the first embodiment. The embodiments described in this patent description can be implemented, for example, by a method or process, a device, a software program, a data stream, or a signal. Although a feature is discussed only in a single context (for example, only in relation to a method), the discussed feature can be implemented in a different type (for example, a device or a program). A device can be implemented in suitable hardware, software, or firmware. The method can be implemented in a device such as a processor, which generally refers, for example, to a processing device, including a computer, a microprocessor, an integrated circuit, or a programmable logic circuit.The processor includes a communication device, such as a computer, a mobile phone, a PDA (Personal Digital Assistant), and another device that can enable data exchange between end users. For illustrative purposes, exemplary embodiments of the disclosure have been disclosed; however, persons skilled in the art will recognize that various modifications, additions, and substitutions are possible without deviating from the scope and meaning of the disclosure as defined in the appended claims. Therefore, the true technical scope of the disclosure is to be defined by the following claims.

Claims

Device for measuring the average power of a fuel cell, characterized in that the device comprises: a voltage measuring unit (400) configured to sequentially measure forward voltages of individual cells (111) forming a fuel cell stack (100) from a lower cell to an upper cell, and to sequentially measure reverse voltages of the individual cells (111) from the upper cell to the lower cell; a current measuring unit (300) configured to measure a current of an output terminal of the fuel cell stack (100);and a control unit (500) configured to control the voltage measuring unit (400) to measure the reverse voltages based on the current measurement time after the voltage measuring unit (400) has fully calculated the forward voltages, and to calculate the average power using the forward voltages, the reverse voltages, and the measured current, wherein the voltage measuring unit (400) comprises: a voltmeter (410) configured to measure the voltages of the respective individual cells (111), wherein the voltmeter (410) comprises: one or more voltage sensors (411) installed to correspond one-to-one with each of the individual cells (111) and configured to detect the voltage of each of the individual cells (111); a switch (413) configured to electrically connect the individual cell (111) to the voltage sensor (411);and a replica unit (412) configured to measure a disturbance voltage according to a switching operation of the switch (413). Device according to claim 1, wherein the voltage measuring unit (400) comprises: a multiplexer (MUX) (440) configured for sequentially outputting the voltages measured by the voltage meter for the respective individual cells (111); and an analog-to-digital converter (ADC) (460) configured for converting the voltages of the respective individual cells (111) output by the multiplexer (440) into digital signals. Device according to one of the preceding claims, wherein the voltage measuring unit (400) further comprises an amplifier (450) which is configured to subtract the interference voltage measured by the replica unit (412) from the voltage measured by the voltage sensor (411). Device according to claim 2, wherein the voltage measuring unit (400) further comprises a level converter (420) which is configured to convert the levels of the voltages of the individual cells (111) measured by the voltage meter (410) into an operational voltage withstand range and to apply the voltages thus obtained to the multiplexer (440). Device according to one of claims 2 to 4, wherein the voltage measuring unit (400) further comprises a scaler (430) which is configured to reduce the voltages of the respective individual cells (111) measured by the voltage meter (410). Device according to one of the preceding claims, wherein the control unit (500) calculates an average voltage of the forward voltages and the reverse voltages and calculates the average power by multiplying the calculated average voltage by the measured current. Device according to one of the preceding claims, wherein the control unit (500) compares the average power with instantaneous power of the respective individual cells (111) and detects abnormal operation of an individual cell (111) if the comparison result for the corresponding individual cell (111) indicates that an error is occurring which is greater than or equal to a preset threshold. Device according to claim 7, wherein the control unit (500) calculates the instantaneous powers of the respective individual cells (111) using the voltages of the individual cells (111) measured by the voltage measuring unit (400) and the current measured by the current measuring unit (300). Method for measuring the average power of a fuel cell, characterized in that the method comprises: sequential measurement of forward voltages of individual cells (111) forming a fuel cell stack (100), from a lower cell to an upper cell by a voltage measuring unit (400); measurement of a current of an output terminal of the fuel cell stack (100) by a current measuring unit (300); sequential measurement of reverse voltages of the individual cells (111) from the upper individual cell to the lower individual cell by the voltage measuring unit (400);and calculating an average voltage of the forward and reverse voltages by a control unit (500) and calculating average power of the fuel cell stack (100) using the calculated average voltage and the measured current, wherein the voltage measuring unit (400) comprises: a voltmeter (410) configured to measure voltages of the respective individual cells (111), wherein the voltmeter (410) comprises: one or more voltage sensors (411) installed to correspond one-to-one with each of the individual cells (111) and configured to detect the voltage of each of the individual cells (111); a switch (413) configured to electrically connect the individual cell (111) to the voltage sensor (411); and a replica unit (412) configured to measure a disturbance voltage according to a switching operation of the switch (413). Method according to claim 9, wherein the control unit (500) calculates the average power of the fuel cell stack (100) by multiplying the average voltage by the measured current. The method according to claim 9, which further comprises the control unit (500) comparing the average power with instantaneous power of the respective individual cells (111) and detecting abnormal operation of an individual cell (111) if the comparison result for the corresponding individual cell (111) indicates that an error occurs which is as large as a preset threshold or larger, after calculating the average power of the fuel cell stack (100). Device for measuring the voltage of a fuel cell, characterized in that the device comprises: a voltage measuring unit (400) configured for measuring the voltages of individual cells (111) forming a fuel cell stack (100); and a protection unit (600) connected to one or more of the individual cells (111) and configured to prevent damage to the voltage measuring unit (400) due to a reverse voltage, the protection unit (600) comprising: a first impedance element (610) connected at one end to a positive (+) terminal of an upper individual cell below the individual cells (111) and at the other end to a ground of the voltage measuring unit (400); and a second impedance element (620) connected at one end to a negative (-) terminal of the lower individual cell below the individual cells (111) and at the other end to ground. Device according to claim 12, wherein the impedance of the first impedance element (610) and the impedance of the second impedance element (620) are set according to a reversing potential voltage withstand of the voltage measuring unit (400).

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