CN116314963B - Fuel cell stack single body impedance on-line diagnosis method and inspection controller - Google Patents
Fuel cell stack single body impedance on-line diagnosis method and inspection controller Download PDFInfo
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- CN116314963B CN116314963B CN202310552353.1A CN202310552353A CN116314963B CN 116314963 B CN116314963 B CN 116314963B CN 202310552353 A CN202310552353 A CN 202310552353A CN 116314963 B CN116314963 B CN 116314963B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04634—Other electric variables, e.g. resistance or impedance
- H01M8/04641—Other electric variables, e.g. resistance or impedance of the individual fuel cell
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04664—Failure or abnormal function
- H01M8/04679—Failure or abnormal function of fuel cell stacks
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
The application provides a fuel cell stack single impedance on-line diagnosis method and a patrol controller, which are applied to the patrol controller, wherein the fuel cell stack single impedance on-line diagnosis method comprises the following steps: the method comprises the steps of obtaining initial voltage signals and initial current signals which are correspondingly collected by measurement monomers in a fuel cell stack, respectively converting the initial voltage signals and the initial current signals into steady-state voltage signals and steady-state current signals, carrying out Fourier transformation on the steady-state voltage signals and the steady-state current signals to obtain amplitude values and phase angles contained in the voltage signals and the current signals, and calculating to obtain impedance of the monomers according to the amplitude values and the phase angles contained in the voltage signals and the current signals so as to carry out online diagnosis on faults of the whole fuel cell stack. According to the embodiment of the specification, the impedance of each single unit in the fuel cell stack can be accurately measured, the whole stack can be evaluated based on the accurate single unit impedance, and the fault position can be rapidly and accurately obtained when the stack fails.
Description
Technical Field
The application relates to the technical field of fuel cell detection, in particular to an on-line diagnosis method for single impedance of a fuel cell stack and a patrol controller.
Background
Fuel cell stacks are assembled from a plurality of single cells in series, and in particular, high-power fuel cell stacks are composed of hundreds of single cells. Therefore, the operation condition of each single body in the electric pile can influence the overall operation condition of the electric pile.
The prior art mainly detects the overall operation condition of the fuel cell stack, but cannot detect the single operation condition. Most of the current patrol controllers CVM can only measure the voltage and the impedance of the whole fuel cell stack, but cannot detect the impedance of each single cell. In some cases, the impedance of some single cells in the whole fuel cell stack is abnormally high, and the impedance of other single cells is abnormally low, so that the whole cell stack impedance balance is finally caused, and the fault of the cell stack cannot be found.
Therefore, a new fuel cell stack cell impedance online diagnostic scheme is needed.
Disclosure of Invention
In view of this, the embodiments of the present disclosure provide an on-line diagnosis method and an inspection controller for impedance of a fuel cell stack, which are applied to the on-line diagnosis process of single detection and fault during the operation of the fuel cell stack.
The embodiment of the specification provides the following technical scheme:
the embodiment of the specification provides a fuel cell stack single impedance on-line diagnosis method and a patrol controller, which are applied to the patrol controller, wherein the fuel cell stack single impedance on-line diagnosis method comprises the following steps:
acquiring an initial voltage signal and an initial current signal which are correspondingly acquired by a measurement monomer in a fuel cell stack;
fitting deviation components in the initial voltage signal and the initial current signal by adopting a trend function;
subtracting the deviation component from the initial voltage signal and the initial current signal respectively to obtain a steady-state voltage signal and a steady current signal;
performing Fourier transformation on the steady-state voltage signal and the steady-state current signal to obtain amplitude and phase angle contained in the voltage signal and the current signal;
calculating to obtain the impedance of the single body according to the amplitude and the phase angle contained in the voltage and current signals so as to diagnose the faults of the whole electric pile on line;
wherein the method of fitting the bias component trend function comprises at least one of: polynomial fitting, hodrick-Prsecott filtering, moving average.
In some examples, acquiring an initial voltage signal and an initial current signal corresponding to the measurement cell in the fuel cell stack includes:
when in a selection mode, determining the monomer to be measured in all the monomers according to the measurement channels and/or the monomer numbers meeting the selection conditions in the fuel cell stack, and obtaining an initial voltage signal and an initial current signal corresponding to the monomer to be measured;
and when the fuel cell stack is in the unselected mode, all the monomers are inspected according to the monomer numbers of all the monomers in the fuel cell stack, and an initial voltage signal and an initial current signal corresponding to each monomer are obtained.
In some examples, determining the cell to be measured from all the cells according to the measurement channel and/or cell number satisfying the selection condition in the fuel cell stack includes:
acquiring voltage values corresponding to all the monomers in the fuel cell stack and variances of all the voltage values, and when the variances are larger than the evaluation standard, selecting a measuring channel and/or a monomer number corresponding to the lowest voltage value to determine the monomer to be measured;
when the variance is smaller than or equal to the evaluation standard, selecting a measuring channel and/or a monomer number at the end plate position in the fuel cell stack to determine a monomer to be measured;
wherein each monomer corresponds to a measurement channel and/or a monomer number.
In some examples, the method includes the steps of inspecting all the cells according to the cell numbers of all the cells in the fuel cell stack, and obtaining an initial voltage signal and an initial current signal corresponding to each cell, including:
and sequentially acquiring an initial voltage signal and an initial current signal of each monomer corresponding to each number, wherein each monomer in the fuel cell stack is sequentially connected in series after the number is set, and the number of the middle monomer is set between the first section number and the tail section number.
In some alternatives, the fuel cell stack cell impedance online diagnosis method further includes:
and obtaining the impedance of N channels corresponding to the monomers in all the monomers at the same time, wherein the value range of N is 2-5.
In some alternatives, the fuel cell stack cell impedance online diagnosis method further includes:
obtaining a measurement result corresponding to each measurement monomer;
determining a verification result of each measurement monomer according to the measurement result and the invalid verification judging condition;
uploading the measurement result and the verification result to a fuel cell control system so that the fuel cell control system determines a failure mode of the fuel cell stack;
wherein, the measurement result comprises the impedance value corresponding to the monomer; the verification result includes valid or invalid.
In some examples, determining the verification result of each measurement cell according to the measurement result and the invalid verification judgment condition includes:
detecting whether the monomer impedance is in a preset range, and if the monomer impedance is in the preset range, judging that the monomer impedance measurement is effective;
if the cell impedance is not within the predetermined range, the cell impedance measurement is invalid.
In some examples, determining the verification result of each measurement cell according to the measurement result and the invalid verification judgment condition includes:
detecting whether current errors before and after the single impedance measurement meet detection conditions, and if so, enabling the single impedance measurement to be effective;
if not, the monomer impedance measurement is invalid.
The embodiment of the specification also provides a patrol controller for on-line diagnosis of the single impedance of the fuel cell stack, and the single impedance is obtained and the result is checked by adopting the on-line diagnosis method for the single impedance of the fuel cell stack according to any one of the technical schemes.
Compared with the prior art, the beneficial effects that above-mentioned at least one technical scheme that this description embodiment adopted can reach include at least:
the method comprises the steps of processing an initial voltage signal and an initial current signal acquired by a single body to obtain a steady-state voltage signal and a steady current signal, converting time domain data into frequency domain data through Fourier transformation, and accurately calculating to obtain impedance of the single body, so that the problem that measurement errors caused by a system, detection factors and the like in a vehicle-mounted application scene lead to inaccurate measurement of the impedance of the single body, and further the integral galvanic pile cannot be evaluated according to the impedance of the single body is solved. The embodiment of the specification not only can accurately measure the impedance of each single unit in the fuel cell stack, but also can evaluate the whole stack based on the accurate single unit impedance, and can quickly and accurately obtain the fault position when the stack fails.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a fuel cell stack cell impedance on-line diagnostic system in accordance with the present application;
FIG. 2 is a flow chart of a fuel cell stack cell impedance on-line diagnostic method in accordance with the present application;
FIG. 3 is a schematic diagram of initial signals collected by the corresponding monomers in the present application;
FIG. 4 is a schematic diagram of the signals after detrending the initial signals according to the present application;
FIG. 5 is a schematic diagram of an on-line diagnosis of the impedance of a fuel cell stack cell in accordance with the present application;
FIG. 6 is a schematic diagram of an on-line diagnosis of cell impedance of a fuel cell stack according to yet another embodiment of the present application;
fig. 7 is a schematic diagram of an on-line diagnosis of the impedance of another fuel cell stack cell according to the present application.
Detailed Description
Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
Other advantages and effects of the present application will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present application with reference to specific examples. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. The application may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present application. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It is noted that various aspects of the embodiments are described below within the scope of the following claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the present disclosure, one skilled in the art will appreciate that one aspect described herein may be implemented independently of any other aspect, and that two or more of these aspects may be combined in various ways. For example, apparatus may be implemented and/or methods practiced using any number and aspects set forth herein. In addition, such apparatus may be implemented and/or such methods practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.
It should also be noted that the illustrations provided in the following embodiments merely illustrate the basic concept of the present application by way of illustration, and only the components related to the present application are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.
In addition, in the following description, specific details are provided in order to provide a thorough understanding of the examples. However, it will be understood by those skilled in the art that the present application may be practiced without these specific details.
The fuel cell stack is formed by connecting a plurality of single bodies in series, and the prior art is mainly aimed at detecting the whole operation of the fuel cell stack. The current routing inspection controller can only measure the voltage and the impedance of the whole fuel cell stack, and can not realize the detection of single impedance in the stack, so that when some single impedance is abnormally high and other single impedance is abnormally low in the fuel cell stack, the whole impedance balance of the stack can be finally caused, and the fault can not be found when the whole stack breaks down. Even though the system for detecting the single impedance in the fuel cell stack exists in the prior art, the result of measuring the single impedance is not satisfactory, and the fault position still cannot be accurately determined when the whole stack fails.
As shown in fig. 1, FC (Fuel cell stack) is a fuel cell stack; DC/DC means direct current to direct current (to) converting circuit (hereinafter referred to as DC/DC converting circuit) which can supply high frequency excitation signal and low frequency excitation signal to the electric pile; FCU (fuel-cell control) is a fuel cell system controller, and CVM represents a patrol controller. The diagnosis system of the impedance of the fuel cell stack unit comprises an FCU fuel cell system controller, a fuel cell stack, a patrol controller and a DC/DC conversion circuit. Wherein the patrol controller is electrically connected to each cell in the fuel cell stack. The fuel cell stack is electrically connected with the inspection controller and the DC/DC conversion circuit respectively, and the FCU is in signal connection with the inspection controller and the DC/DC conversion circuit respectively. In the prior art, a shunt (not shown), a circuit module (not shown) for acquiring the cell voltage in the cell stack and a circuit module (not shown) for acquiring the cell current in the cell stack can be integrated in the fuel cell stack, and the calculation of the cell impedance in the cell stack is realized by acquiring the measurement voltage and the measurement current corresponding to the measurement cell in the cell stack.
Specifically, in the diagnosis process, the FCU starts a DC/DC conversion circuit and sets the operating frequency and amplitude; the FCU sends a signal to the CVM to trigger measurement of the impedance of the single body in the pile, the CVM samples and acquires initial voltage signals and current signals which are acquired by the measurement single body in the pile correspondingly after the FCU sets the whole system to run for a period of time such as 100-300 ms, and then time domain data are converted into frequency domain data through Fourier transformation to achieve acquisition of the impedance of the single body. Although the integral structure can detect the impedance of the single body, the impedance of the single body obtained by detection is inaccurate, and further the detection of the fault of the electric pile cannot be realized.
Particularly in the application scene of the vehicle-mounted fuel cell, the variable load operation of the fuel cell exists in the running process of the vehicle, and the single impedance in the electric pile can be detected, but the detected single impedance is inaccurate, so that the fault problem can not be accurately obtained when the electric pile breaks down.
Based on this, the embodiment of the present specification proposes an online diagnosis scheme for the impedance of the fuel cell stack cell: and acquiring initial voltage signal initial current signals which are acquired by measuring monomers in the fuel cell stack according to the existing monomer impedance detection system. The initial voltage signal and the initial current signal are converted into a steady-state voltage signal and a steady-state current signal, respectively. And then carrying out Fourier transformation on the steady-state voltage signal and the steady-state current signal to obtain amplitude and phase angle contained in the voltage signal and the current signal, and calculating the impedance of the monomer according to the amplitude and the phase angle of the voltage and the current.
The single impedance obtaining process of the embodiment of the description obtains a steady voltage signal and a steady current signal corresponding to a single in the output process of the fuel cell stack by removing disturbance factors and bias factors in all initial acquisition signals, and further obtains the impedance of the single through Fourier transform calculation so as to accurately determine the fault occurrence position when the integral stack breaks down.
Particularly, the research shows that the excitation current signal in the DC/DC conversion circuit in the single body current measurement process in the electric pile of fig. 1 is much larger than the current signal of each single body in the operation process of the electric pile, and the interference of large DC component factors exists in the process of obtaining the corresponding current of the single body.
Therefore, according to the fuel cell stack single impedance on-line diagnosis method disclosed by the embodiment of the specification, the initial voltage signal and the initial current signal corresponding to the single in the fuel cell stack are processed, the large DC component in the measurement waveform and the direct current voltage fluctuation component under the unsteady state condition of the fuel cell are removed, the steady voltage signal and the steady current signal corresponding to the measurement single can be accurately obtained, and therefore the time domain data are converted into the frequency domain data through Fourier transformation, and the accurate result of the single impedance is obtained. The problem of frequency leakage in the monomer acquisition process can also be solved.
The following describes the technical scheme provided by each embodiment of the present application with reference to the accompanying drawings. As shown in FIG. 2, the fuel cell stack cell impedance on-line diagnosis method comprises steps S210-S250. Step S210, acquiring an initial voltage signal and an initial current signal, which are acquired by a measurement unit in the fuel cell stack. S220, fitting deviation components in the initial voltage signal and the initial current signal by adopting a trend function. S230, subtracting deviation components from the initial voltage signal and the initial current signal respectively to obtain a steady-state voltage signal and a steady current signal. S240, carrying out Fourier transformation on the steady-state voltage signal and the steady-state current signal to obtain amplitude and phase angle contained in the voltage and current signals. S250, calculating the impedance of the single body according to the amplitude and the phase angle contained in the voltage and current signals so as to diagnose the faults of the whole galvanic pile on line. The execution main body of the fuel cell stack single body impedance obtaining process is a patrol controller.
Specifically, in step S210, voltage and current signals are collected by the system as shown in fig. 1 in the on-line diagnosis process of the impedance of the fuel cell stack, so as to obtain an initial voltage signal and an initial current signal, which are collected by the measurement unit in the fuel cell stack. However, the waveforms of the initial voltage signal and the initial current signal appear as small perturbations in combination with a large DC bias, which can cause a large deviation in the calculated impedance results. Therefore, the initial voltage signal and the current signal need to be processed and then calculated to obtain the single impedance.
Step S220 and step S230 combine the above embodiments, and process the collected initial voltage signal and initial current signal respectively, and convert them into steady-state voltage signal and steady-state current signal.
The steady-state voltage signal is used for ensuring that the fuel cells are in a relative steady state before and after diagnosis, and avoiding phenomena such as voltage rising or falling and even drifting. The stable current signal is used for guaranteeing stable output current of the electric fuel cell before and after diagnosis, and larger current signal deviation caused under the condition of current change is avoided. The steady-state voltage signal and the steady-state current signal also include signal waveforms obtained under high-frequency excitation and under low-frequency excitation, respectively.
In the application scene of the vehicle-mounted fuel cell, because the collected initial voltage signal and the collected initial current signal have smaller disturbance and larger DC (direct current) bias, the impedance module value of the monomer obtained by directly adopting the collected initial voltage signal and the collected initial current signal through Fourier transform calculation in the prior art has larger deviation. As shown in fig. 3, in the voltage frequency domain data obtained by adopting the prior art, a larger deviation exists, and the voltage is in an ascending trend, so that the calculation error of the single impedance is larger. In addition, the voltage of the fuel cell can continuously rise or fall especially after load change, and the instability condition can cause large impedance calculation errors.
In addition, since sampling frequencies of the inspection controllers of different batches are different, frequency leakage is easy to occur when non-integer periodic signals are input, and the deviation of impedance calculation results is also large. Therefore, the deviation component in the acquired signal is removed to obtain a steady-state voltage signal and a steady-state current signal, and then the impedance of the single body is calculated.
Specifically, step S220 and step S230: fitting a deviation component in the initial voltage signal and the initial current signal by adopting a trend function; the deviation component is subtracted from the initial voltage signal and the initial current signal, respectively, to obtain a steady-state voltage signal and a steady current signal. Wherein the deviation component includes a DC voltage fluctuation component due to an unsteady state of the fuel cell and a large DC bias signal.
The waveforms of the single voltage and the single current signals directly obtained from the fuel cell stack are generally slightly disturbed, and a large direct current bias signal exists in the detection process, so that the collected initial voltage signals and initial current signals cannot be directly utilized. Particularly in the application scene of the vehicle-mounted fuel cell, because of unsteady conditions such as continuous rising or falling of voltage and the like after the fuel cell is loaded, direct-current voltage fluctuation components exist, and a large direct-current bias signal exists in the detection process.
Therefore, in the embodiment of the present specification, by fitting the deviation components in the initial voltage signal and the initial current signal and then removing these deviation components from the initial voltage signal and the initial current signal, the steady-state voltage signal and the steady-state current signal are obtained. And obtaining frequency domain data by adopting a steady voltage signal and a steady current signal through Fourier transformation, and calculating to obtain the impedance of the monomer.
In the prior art, the obtained amplitude and phase angle information of the initial voltage signal and the initial current signal are directly obtained through fourier transformation, as in the example of fig. 3, the data of the voltage and the current in the time domain under low-frequency excitation are converted into frequency domain data, and the data of the voltage and the current in the time domain under high-frequency excitation are converted into frequency domain data, but bias signals with larger DC (direct current) exist, and as direct current voltage fluctuation components exist in the unsteady state of the fuel cell, rising trend exists, so that the impedance value obtained by finally calculating the waveforms of the initial voltage and the initial current through fourier transformation has great deviation.
While the present embodiment obtains the steady-state voltage signal and the steady-state current signal by fitting the deviation component in the initial voltage signal and the initial current signal using the trend function and subtracting the deviation component from the initial voltage signal and the initial current signal, respectively (see fig. 4). And further, fourier transformation is adopted on the steady-state voltage signal and the steady-state current signal to obtain the amplitude and phase angle information of the voltage signal and the current signal, and finally, the accurate impedance value of the single body can be obtained. Wherein the abscissa in fig. 3 and 4 represents frequency and the ordinate represents amplitude, respectively.
As illustrated in table 1 below, when v_grad=100, i.e., the initial voltage signal has a large slope trend corresponding to the same frequency value (e.g., high frequency corresponding to 1000, low frequency corresponding to 25), the amplitude is obtained as 4.9 or 1.1 compared to the undeveloped trend, and the amplitude is obtained as true 5.0 or 2.0 after the undeveloped trend is adopted. Therefore, the deviation component in the initial voltage signal and the initial current signal is fitted by adopting a trend function, and the signal waveforms corresponding to the single bodies can be accurately reflected by subtracting the deviation component from the initial voltage signal and the initial current signal to obtain a steady-state voltage signal and a steady current signal. V_grad=100 in this embodiment is expressed as an output voltage of 100V.
TABLE 1
In some embodiments, the method of fitting the bias component trend function includes, but is not limited to, polynomial fitting, hodrick-Prsecott filtering, moving average.
In some embodiments, since sampling frequencies of different batches of inspection controllers are slightly different, frequency leakage is easily caused when voltage and current signals with non-integer periods are collected, and further deviation of impedance calculation results is large.
As illustrated in table 2 below, when the sampling period is not an integer, n=1500, and the period k=n×f/fs, where fs is the sampling frequency, N is the number of sampling points (i.e., the number of samples), and f is the frequency. If the high-frequency sampling period is 131.3, the amplitude obtained when the trend is not removed is 7.3 when the high-frequency is 1000, but the amplitude obtained after the trend is removed is truly 5.0. If the low frequency sampling period is 3.3, the amplitude is 92.3 when the trend is not removed when the low frequency is 25, but the amplitude obtained after the trend is removed is 2.0. From this, it is clear that the impedance model obtained by the prior art untrimmed calculation is completely inaccurate, and thus has no reference value for fault diagnosis. The application can accurately obtain the impedance of the single body.
TABLE 2
Compared with the prior art, the method and the device have the advantages that before the time domain voltage signals and the current signals are converted into the amplitude values and the phase differences of the frequency domain analysis through Fourier transformation, deviation components in the initial voltage signals and the initial current signals are obtained through fitting a trend function, interference of large DC components is eliminated by subtracting the deviation components from the initial voltage signals and the initial current signals, and increasing and decreasing trends in waveforms are removed, so that stable currents and voltages in a short measurement time are ensured to have no increasing or decreasing trend, and accuracy of single impedance calculation is improved. The problem of frequency leakage is also solved.
Step S240 performs fourier transform on the steady voltage signal and the steady current signal to obtain the amplitude and the phase angle included in the voltage and current signals.
The waveforms of the steady voltage signal and the steady current signal change along with time, and the voltage signal and the current signal need to be converted into frequency domain analysis in order to obtain the impedance of the single body. And carrying out Fourier transformation according to the steady voltage signal and the steady current signal to obtain amplitude and phase angle information contained in the voltage and current signals, and further calculating to obtain an impedance mode of the single body.
In step S250, the impedance of the single body is calculated according to the amplitude and the phase angle included in the voltage and current signals, so as to diagnose the fault of the whole pile on line.
And combining the embodiment, carrying out Fourier transformation on the steady-state voltage signal and the steady-state current signal to obtain corresponding amplitude values and phase differences, and then calculating to obtain the impedance value. Specifically, data of voltage and current in a time domain under high-frequency excitation are converted into data in a frequency domain, and data of voltage and current in a time domain under low-frequency excitation are converted into data in a frequency domain, so that signal amplitude and phase angle under high-frequency excitation and signal amplitude and phase angle under low-frequency excitation are obtained according to a data conversion result.
A high-frequency impedance mode is obtained according to the ratio of the amplitude of the voltage signal and the amplitude of the current signal under high-frequency excitation, and the phase angle of impedance is obtained according to the difference between the phase angle of the voltage signal and the phase angle of the current signal. The low frequency impedance mode is obtained according to the ratio of the amplitude of the voltage signal and the current signal under low frequency excitation, and the phase angle of impedance is obtained according to the difference between the phase angle of the voltage signal and the phase angle of the current signal.
In some embodiments, acquiring initial voltage signals and initial current signals corresponding to the measurements of the cells in the fuel cell stack includes: and acquiring voltage signals and current signals of the required measurement monomers in all the monomers. In some embodiments, the required measurement units are specified by the inspection controller, or may be randomly generated. When the initial voltage signal and the current signal which are correspondingly acquired by the monomer to be detected in the fuel cell stack are acquired, the patrol controller can respectively measure the required monomer under the condition of being in an unselected mode or in a selected mode.
Specifically, when in a selection mode, determining a monomer to be measured in all monomers according to a measurement channel and/or a monomer number meeting a selection condition in the fuel cell stack, and obtaining an initial voltage signal and an initial current signal corresponding to the monomer to be measured; and when the fuel cell stack is in the unselected mode, all the monomers are inspected according to the monomer numbers of all the monomers in the fuel cell stack, and an initial voltage signal and an initial current signal corresponding to each monomer are obtained. Wherein, when in the selection mode, the inspection controller can be used for designating the monomer to be measured according to the automatic measurement, or can randomly determine or select to designate a certain monomer to be measured (see fig. 6). And when the fuel cell stack is in the unselected mode, performing impedance measurement inspection on all the single cells in the fuel cell stack. In some embodiments, voltage signals and current signals are obtained for the corresponding cells, and the cell to be measured is determined from all cells according to the measurement channels and/or cell numbers in the fuel cell stack that meet the selection criteria.
Specifically, voltage values corresponding to all the monomers in the fuel cell stack and variances of all the voltage values are obtained, and measurement channels and/or monomer numbers of the required measurement monomers are determined from all the monomers according to the variances being larger than an evaluation standard and the variances being smaller than or equal to the evaluation standard. Wherein each monomer corresponds to a measurement channel and/or a monomer number. The selection conditions include a first selection condition such as a variance greater than the evaluation criterion and a second selection condition such as a variance less than or equal to the evaluation criterion, the selection conditions being given here by way of example only. It should be noted that the selection condition may be set according to the actual operating condition of the pile.
As shown in fig. 5, the FCU sets an automatic measurement mode, and sends a signal to the DC/DC conversion circuit so that the DC/DC conversion circuit superimposes and excites the stack, and the FCU sends a signal to the CVM to trigger impedance measurement.
The fuel cell stack may measure the voltage value of each cell, obtain the consistent expression variance of all cell voltages from all cell voltage values, and determine the required measured cell by determining whether the variance meets an evaluation criterion.
In some embodiments, the evaluation criterion of the variance is x, and the value range of x is 50-200. As shown in fig. 5, if the variance is greater than the evaluation criterion, the monomer to be measured is determined according to the measurement channel and/or the monomer number of the monomer to be measured. If the variance is larger than x, the measurement channel and/or the monomer number of the monomer corresponding to the lowest voltage value is obtained from the voltages corresponding to the monomers, so that the monomer to be measured is determined. And if the variance is smaller than or equal to the evaluation standard, selecting a monomer to be detected corresponding to the end plate position for detection. As shown in fig. 5, the measurement of the lowest voltage impedance represents obtaining the test channel or the cell number corresponding to the lowest cell voltage to determine the cell to be tested, and further obtaining the impedance of the cell to be tested. In fig. 5, the measured impedance of the end plate node indicates that the variance is less than or equal to the evaluation criterion, and then a single body set at the end plate position in the electric pile is selected as a single body to be measured, so as to obtain the impedance of the single body to be measured. Wherein the end plate segments represent the cells disposed at the end plate locations of the stack.
Since each monomer corresponds to a measurement channel and/or a monomer number. In another embodiment, the selection condition in the selection mode includes obtaining a measurement channel and/or a cell number of the specified cell to be measured, thereby obtaining an initial voltage signal and an initial current signal corresponding to the specified cell to be measured.
As shown in fig. 6, the FCU sets a specified test channel and causes the DC/DC conversion circuit to superimpose and energize the stack by setting the specified measurement mode in the selection mode by the FCU, which also sends a signal to the CVM to trigger a specific impedance measurement. And the CVM obtains the impedance corresponding to the specified section monomer in all the monomers of the electric pile according to the specified test channel.
In summary, the automatic measurement and the specified measurement of the cell impedance in the stack may be achieved by satisfying different selection conditions in the fuel cell stack, and further the failure mode of the stack may be determined by the obtained cell impedance, as described in detail below.
In some embodiments, while in the unselected mode, all cells in the fuel cell stack are inspected according to their cell numbers, and an initial voltage signal and an initial current signal corresponding to each cell are obtained. Specifically, an initial voltage signal and an initial current signal of each monomer corresponding to each number are sequentially obtained, wherein each monomer in the fuel cell stack is sequentially connected in series after the number is set, and the number of the middle monomer is set between the first section number and the tail section number.
The fuel cell stack is formed by connecting a plurality of single cells in series, and when an initial voltage signal and an initial current signal acquired by the single cells in the fuel cell stack are acquired, inspection measurement can be carried out on each single cell in the fuel cell stack. Specifically, each monomer in series connection in turn is numbered, two monomers at the end plate are respectively numbered into a first section number and a tail section number, and the number of the middle monomer is arranged between the first section number and the tail section number.
Referring to fig. 7, when inspection tests are performed on all the monomers, the FCU sets an inspection quantity mode, sends signals to the DC/DC conversion circuit, continuously overlaps and excites to end of detection and collection of all the monomer signals in the electric pile, and simultaneously sends signals to the CVM to trigger impedance measurement, and the CVM starts inspection from the monomer with the first section number to end of measurement of the monomer with the tail section number in the electric pile, so that an initial voltage signal and an initial current signal collected by each monomer are sequentially obtained.
In some embodiments, the impedance of N channels in all the monomers is obtained at the same time, wherein the value of N ranges from 2 to 5.
The fuel cell stack is formed by assembling a plurality of single cells, and the impedance of any value number channel corresponding to the single cell within the range of 2-5 can be obtained in the same time by adopting the single cell impedance test mode in the embodiment of the specification.
The measurement is realized in the measuring switch array through N acquisition chips in the system. In the diagnosis system of the cell impedance of the fuel cell stack of fig. 1, N acquisition chips (not shown) are disposed in a cell measurement switch array (not shown) to obtain the impedance of the corresponding cell. In this way, the impedance of the corresponding single body of 5 channels can be acquired at the same time.
In some embodiments, a measurement result corresponding to each measurement cell is obtained, a verification result of each measurement cell is determined according to the measurement result and an invalid verification judgment condition, and the verification result and the measurement result are uploaded to the fuel cell control system, so that the fuel cell control system determines a failure mode according to the verification result and the measurement result corresponding to the cell. Wherein the failure mode includes poisoning, flooding, undergassing, or film drying. The measurement result is an accurate monomer impedance value. The verification result includes valid or invalid. The invalid check judging condition may include detecting whether the impedance of the single body is within a preset range, or detecting whether the current error before and after the measurement of the impedance of the single body meets the detecting condition, which is described in detail below.
In some embodiments, the single impedance measurement is represented by a valid bit 1 if it is valid and a valid bit 0 if it is not valid.
In some cases, when the operating voltage of the fuel cell stack is low, the stack single body measurement result and the verification result are uploaded to the fuel cell system controller FCU, so that the FCU determines a failure mode according to the measurement result and the verification result, and the specific FCU determines the failure mode of the fuel cell stack according to the measurement result and the verification result of all single body impedance in the stack by setting a failure algorithm and combining high/low frequency impedance and direct current voltage in the measurement process, wherein the failure mode comprises poisoning, flooding, undergassing or film drying. The failure algorithm is set according to mass transfer, reaction process, water balance state and the like in the fuel cell stack. Some embodiments FCU employ a neural network model to determine failure modes of the stack.
In order to eliminate the situation that when the analog-to-digital converter ADC samples a particularly small signal (the voltage is lower than the limit Kv and the current is lower than the limit Ki), the measurement of the single body is inaccurate due to the nonlinear error, therefore, the amplitude of the excitation signal is required to be set higher than a certain limit value to realize that the amplitude of the collected voltage and the current are correspondingly higher than the limit Kv and Ki, and if the excitation amplitude is set unreasonably, the impedance error of the measured single body is unacceptable, so that whether the measurement result is qualified or not should be checked.
In some embodiments, the verification result of each measurement cell is determined according to the measurement result and the invalid verification judgment condition, and the verification result includes whether the cell impedance is valid within a preset range. Detecting whether the single impedance is in a preset range, and if the single impedance is in the preset range, judging that the single impedance measurement is effective. If the impedance of the single body is not in the preset range, judging that the impedance measurement of the single body is invalid. Wherein the preset range is determined according to the electrical property and chemical property of the galvanic pile.
In combination with the above embodiment, the check result of the single body is determined by directly checking the obtained impedance of each measurement single body. If the measured value of the impedance is within the preset range, judging that the single impedance measurement is effective. If the measured value of the impedance is not within the preset range, the single impedance measurement is invalid. The preset range is set in detail according to specific galvanic pile conditions.
In other embodiments, the verification result of each measurement cell is determined by detecting whether the current error before and after the cell impedance measurement satisfies the detection condition, if so, the cell impedance measurement is valid; if not, the monomer impedance measurement is invalid. The detection condition comprises that the value range of the error a is 5-10%, if the current error before and after impedance measurement meets the error range of a, the single impedance meets the detection condition, and the single impedance measurement is effective; if the current errors before and after the impedance measurement do not meet the error range of a, the single impedance does not meet the detection condition, and the single impedance measurement is invalid.
By combining the above embodiments, the verification result is obtained through impedance verification of the single body, and the verification can also be performed according to current errors before and after impedance measurement. In order to ensure that the single impedance measurement in the galvanic pile is in a stable operation process, the error detection is required to be carried out on the current within a certain time range before and after the single impedance measurement.
If the current errors before and after the single impedance measurement belong to the error range of a, the single impedance measurement is effective if the current errors before and after the impedance measurement meet the detection condition; if the current errors before and after the impedance measurement do not belong to the error range of a, the single impedance does not meet the detection condition, and the single impedance measurement is invalid.
According to the embodiment of the specification, the initial voltage signal and the initial current signal acquired by the single body are processed to obtain the steady-state voltage signal and the steady current signal, and then the time domain data are converted into the frequency domain data through Fourier transformation to accurately calculate and obtain the impedance of the single body, so that the problem that the measurement of the impedance of the single body is inaccurate due to measurement errors caused by a system, detection factors and the like in a vehicle-mounted application scene, and the whole galvanic pile cannot be evaluated according to the accurate impedance of the single body is solved. The impedance of each measuring unit in the fuel cell stack can be accurately measured, the whole stack can be evaluated based on the accurate unit impedance, and the fault position can be rapidly and accurately obtained when the stack fails.
It is noted that the terms "first," "second," "third," "fourth," and the like in the description and claims of the application and in the foregoing figures, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the application described herein may be implemented in sequences other than those illustrated or otherwise described herein.
The same and similar parts of the embodiments in this specification are all mutually referred to, and each embodiment focuses on the differences from the other embodiments. In particular, for the product embodiments described later, since they correspond to the methods, the description is relatively simple, and reference is made to the description of parts of the system embodiments.
The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present application should be included in the present application. Therefore, the protection scope of the application is subject to the protection scope of the claims.
Claims (9)
1. The fuel cell stack single impedance on-line diagnosis method is characterized by being applied to a patrol controller and comprising the following steps of:
acquiring an initial voltage signal and an initial current signal which are correspondingly acquired by a measurement monomer in a fuel cell stack;
fitting deviation components in the initial voltage signal and the initial current signal by adopting a trend function;
subtracting the deviation component from the initial voltage signal and the initial current signal respectively to obtain a steady-state voltage signal and a steady current signal;
performing Fourier transformation on the steady-state voltage signal and the steady-state current signal to obtain amplitude and phase angle contained in the voltage and current signals;
calculating to obtain the impedance of the single body according to the amplitude and the phase angle contained in the voltage and current signals so as to diagnose the faults of the whole electric pile on line;
wherein the method of fitting the bias component trend function comprises at least one of: polynomial fitting, hodrick-Prsecott filtering, moving average.
2. The method for on-line diagnosis of cell impedance of a fuel cell stack according to claim 1, wherein obtaining an initial voltage signal and an initial current signal corresponding to the measurement cell in the fuel cell stack comprises:
when in a selection mode, determining the monomer to be measured in all the monomers according to the measurement channels and/or the monomer numbers meeting the selection conditions in the fuel cell stack, and obtaining an initial voltage signal and an initial current signal corresponding to the monomer to be measured;
and when the fuel cell stack is in the unselected mode, all the monomers are inspected according to the monomer numbers of all the monomers in the fuel cell stack, and an initial voltage signal and an initial current signal corresponding to each monomer are obtained.
3. The fuel cell stack cell impedance on-line diagnosis method according to claim 2, wherein determining the cell to be measured from among all cells according to the measurement channel and/or cell number satisfying the selection condition in the fuel cell stack comprises:
acquiring voltage values corresponding to all the monomers in the fuel cell stack and variances of all the voltage values, and when the variances are larger than the evaluation standard, selecting a measuring channel and/or a monomer number corresponding to the lowest voltage value to determine the monomer to be measured;
when the variance is smaller than or equal to the evaluation standard, selecting a measuring channel and/or a monomer number at the end plate position in the fuel cell stack to determine a monomer to be measured;
wherein each monomer corresponds to a measurement channel and/or a monomer number.
4. The method for on-line diagnosis of cell impedance of a fuel cell stack according to claim 2, wherein the step of inspecting all cells according to cell numbers of all cells in the fuel cell stack and obtaining an initial voltage signal and an initial current signal corresponding to each cell comprises:
and sequentially acquiring an initial voltage signal and an initial current signal of each monomer corresponding to each number, wherein each monomer in the fuel cell stack is sequentially connected in series after the number is set, and the number of the middle monomer is set between the first section number and the tail section number.
5. The fuel cell stack cell impedance on-line diagnostic method of claim 4, further comprising:
and obtaining the impedance of N measuring channels in all the monomers corresponding to the monomers at the same time, wherein the value range of N is 2-5.
6. The fuel cell stack cell impedance on-line diagnostic method of claim 1, further comprising:
obtaining a measurement result corresponding to each measurement monomer;
determining a verification result of each measurement monomer according to the measurement result and the invalid verification judging condition;
uploading the measurement result and the verification result to a fuel cell control system so that the fuel cell control system determines a failure mode of the fuel cell stack;
wherein, the measurement result comprises the impedance value corresponding to the monomer; the verification result includes valid or invalid.
7. The fuel cell stack cell impedance on-line diagnosis method according to claim 6, wherein determining the verification result of each measurement cell based on the measurement result and the invalid verification judgment condition comprises:
detecting whether the monomer impedance is in a preset range, and if the monomer impedance is in the preset range, judging that the monomer impedance measurement is effective;
if the cell impedance is not within the predetermined range, the cell impedance measurement is invalid.
8. The fuel cell stack cell impedance on-line diagnosis method according to claim 6, wherein determining the verification result of each measurement cell based on the measurement result and the invalid verification judgment condition comprises:
detecting whether current errors before and after the single impedance measurement meet detection conditions, and if so, enabling the single impedance measurement to be effective;
if not, the monomer impedance measurement is invalid.
9. A patrol controller for on-line diagnosis of cell impedance of a fuel cell stack, characterized in that the on-line diagnosis method of cell impedance of the fuel cell stack according to any one of claims 1-8 is adopted to achieve obtaining of cell impedance and verification of result.
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