CN116314963B - Fuel cell stack single body impedance on-line diagnosis method and inspection controller - Google Patents

Abstract

This application provides an online diagnosis method of fuel cell stack cell impedance and a patrol inspection controller, which are applied to the patrol inspection controller. The fuel cell stack cell impedance online diagnosis method includes: obtaining the corresponding measurement cells in the fuel cell stack. The collected initial voltage signal and initial current signal are converted into a steady-state voltage signal and a stable current signal respectively. The steady-state voltage signal and the stable current signal are Fourier transformed to obtain the voltage and current signals. The single impedance is calculated based on the amplitude and phase angle contained in the voltage and current signals, so that the fault of the overall stack can be diagnosed online. The embodiments of this specification can not only accurately measure the impedance of each cell in the fuel cell stack, but also evaluate the entire stack based on the precise cell impedance, and quickly and accurately determine the location of the fault when the stack fails.

Description

Fuel cell stack cell impedance online diagnosis method and inspection controller

Technical field

The present application relates to the technical field of fuel cell detection, and specifically relates to an online diagnosis method of single impedance of a fuel cell stack and an inspection controller.

Background technique

A fuel cell stack is composed of multiple single cells assembled in series. Especially high-power fuel cell stacks are composed of hundreds of single cells. Therefore, the operating status of each cell in the stack will inevitably affect the overall operation of the stack.

The existing technology mainly detects the overall operating status of the fuel cell stack, but cannot detect the individual operating status. At present, most inspection controllers CVM can only measure the voltage and impedance of the entire fuel cell stack, but cannot detect the impedance of each individual cell. In some cases, the impedance of some monomers in the overall fuel cell stack is abnormally high, and the impedance of other monomers is abnormally low. Ultimately, the impedance balance of the overall stack makes it impossible to detect the fault location of the stack.

Therefore, a new online diagnosis scheme for fuel cell stack cell impedance is needed.

Contents of the invention

In view of this, embodiments of this specification provide a fuel cell stack cell impedance online diagnosis method and inspection controller, which are applied to the cell detection and fault online diagnosis process during the operation of the fuel cell stack.

The embodiments of this specification provide the following technical solutions:

The embodiments of this specification provide an online diagnosis method of fuel cell stack cell impedance and a patrol inspection controller, which are applied to the patrol inspection controller. The fuel cell stack cell impedance online diagnosis method includes:

Obtain the initial voltage signal and initial current signal corresponding to the measurement unit in the fuel cell stack;

The trend function is used to fit the deviation components in the initial voltage signal and initial current signal;

Subtract the deviation component from the initial voltage signal and initial current signal respectively to obtain the steady-state voltage signal and steady current signal;

The amplitude and phase angle contained in the voltage signal and current signal are obtained by Fourier transforming the steady-state voltage signal and the stable current signal;

The impedance of the monomer is calculated based on the amplitude and phase angle contained in the voltage and current signals, so that the fault of the entire stack can be diagnosed online;

The method of fitting the deviation component trend function includes at least one of the following: polynomial fitting method, Hodrick-Prsecott filtering method, and moving average method.

In some examples, the initial voltage signal and initial current signal corresponding to the measurement unit in the fuel cell stack are obtained, including:

When in the selection mode, determine the cell to be measured among all cells according to the measurement channel and/or cell number in the fuel cell stack that meets the selection conditions, and obtain the initial voltage signal corresponding to the required measurement cell and Initial current signal;

When in the unselected mode, all cells in the fuel cell stack are inspected according to their cell numbers, and the initial voltage signal and initial current signal corresponding to each cell are obtained.

In some options, the monomer to be measured is determined among all the monomers based on the measurement channels and/or monomer numbers in the fuel cell stack that meet the selection conditions, including:

Obtain the voltage values corresponding to all monomers in the fuel cell stack and the variance of all voltage values. When the variance is greater than the evaluation standard, select the measurement channel and/or monomer number corresponding to the lowest voltage value to determine the monomer to be tested;

When the variance is less than or equal to the evaluation standard, select the measurement channel and/or the cell number at the end plate position in the fuel cell stack to determine the cell to be tested;

Each cell corresponds to a measurement channel and/or cell number.

In some examples, all cells in the fuel cell stack are inspected based on their cell numbers, and the initial voltage signal and initial current signal corresponding to each cell are obtained, including:

The initial voltage signal and initial current signal of the monomer corresponding to each number are obtained in turn. Each monomer in the fuel cell stack is connected in series by setting the number, and the number of the intermediate monomer is set at the first section number and the last section number. between.

In some examples, the fuel cell stack cell impedance online diagnosis method also includes:

At the same time, the impedances of N channels corresponding to the monomers in all monomers are obtained, where the value range of N is 2-5.

In some examples, the fuel cell stack cell impedance online diagnosis method also includes:

Obtain the measurement results corresponding to each measurement unit;

Determine the calibration results of each measurement unit based on the measurement results and invalid calibration judgment conditions;

Upload the measurement results and calibration results to the fuel cell control system so that the fuel cell control system can determine the failure mode of the fuel cell stack;

Among them, the measurement results include the impedance value corresponding to the monomer; the verification results include valid or invalid.

In some examples, the calibration results of each measurement unit are determined based on the measurement results and invalid calibration conditions, including:

Detect whether the monomer impedance is within the preset range. If the monomer impedance is within the preset range, the monomer impedance measurement is judged to be valid;

If the cell impedance is not within the preset range, the cell impedance measurement is invalid.

In some examples, the calibration results of each measurement unit are determined based on the measurement results and invalid calibration conditions, including:

Detect whether the current error before and after the single impedance measurement meets the detection conditions. If so, the single impedance measurement is valid;

Otherwise, the single impedance measurement is invalid.

The embodiments of this specification also provide an inspection controller for online diagnosis of fuel cell stack cell impedance, which adopts the fuel cell stack cell impedance online diagnosis method according to any of the above technical solutions to achieve the acquisition and results of the cell impedance. check.

Compared with the existing technology, the beneficial effects achieved by at least one of the above technical solutions adopted in the embodiments of this specification at least include:

By processing the initial voltage signal and initial current signal collected by the monomer, a steady-state voltage signal and a stable current signal are obtained, and then the time domain data is converted into frequency domain data through Fourier transform to accurately calculate the impedance of the monomer, thereby It solves the problem in vehicle application scenarios that measurement errors caused by system and detection factors lead to inaccurate measurement of single impedance, making it impossible to evaluate the overall stack based on single impedance. The embodiments of this specification can not only accurately measure the impedance of each cell in the fuel cell stack, but also evaluate the entire stack based on the precise cell impedance, and quickly and accurately determine the location of the fault when the stack fails.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. Those skilled in the art can also obtain other drawings based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram of the fuel cell stack cell impedance online diagnosis system in this application;

Figure 2 is a flow chart of a fuel cell stack cell impedance online diagnosis method in this application;

Figure 3 is a schematic diagram of the initial signal collected corresponding to the monomer in this application;

Figure 4 is a schematic diagram of the signal after detrending the initial signal in this application;

Figure 5 is a schematic diagram of online diagnosis of fuel cell stack cell impedance in this application;

Figure 6 is another schematic diagram of online diagnosis of fuel cell stack cell impedance in this application;

Figure 7 is a schematic diagram of another fuel cell stack cell impedance online diagnosis in this application.

Detailed ways

The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

The following describes the implementation of the present application through specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. This application can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, as long as there is no conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

To illustrate, the following describes various aspects of embodiments that are within the scope of the appended 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 illustrative only. Based on this application, those skilled in the art will appreciate that one aspect described herein can be implemented independently of any other aspect, and that two or more of these aspects can be combined in various ways. For example, apparatuses may be implemented and/or methods practiced using any of the numbers and aspects set forth herein. Additionally, such apparatus may be implemented and/or methods practiced using other structures and/or functionality in addition to one or more of the aspects set forth herein.

It should also be noted that the diagrams provided in the following embodiments are only schematically illustrating the basic concept of the present application. The drawings only show the components related to the present application and are not based on the number, shape and number of components during actual implementation. Dimension drawing, in actual implementation, the type, quantity and proportion of each component can be arbitrarily changed, and the component layout type may also be more complex.

Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, one skilled in the art will understand that practices may be practiced without these specific details.

The fuel cell stack is composed of multiple monomers connected in series. The existing technology is mainly aimed at detecting the overall operation of the fuel cell stack. At present, the inspection controller can only measure the voltage and impedance of the entire fuel cell stack, and cannot detect the impedance of individual cells in the stack. In this way, when the impedance of some cells in the fuel cell stack is abnormally high, the impedance of other cells in the stack is abnormally high. The monomer impedance is abnormally low, which will eventually lead to the balance of the overall impedance of the stack, causing the failure to be found when the overall stack fails. Even though there is a system for detecting the cell impedance in the fuel cell stack in the prior art, the results of measuring the cell impedance are not satisfactory, and it is still impossible to accurately determine the fault location when the overall stack fails.

As shown in Figure 1, FC (Fuel cell stack) is a fuel cell stack; DC/DC represents a DC to DC conversion circuit (hereinafter referred to as DC/DC conversion circuit). The DC/DC conversion circuit can provide High-frequency excitation signal and low-frequency excitation signal; FCU (fuel-cell control) is the fuel cell system controller, and CVM means inspection controller. The diagnostic system for the fuel cell stack monomer impedance includes the FCU fuel cell system controller, fuel cell stack, inspection controller and DC/DC conversion circuit. The inspection controller is electrically connected to each cell in the fuel cell stack. The fuel cell stack is electrically connected to the inspection controller and the DC/DC conversion circuit respectively, and the FCU is signally connected to the inspection controller and the DC/DC conversion circuit respectively. The existing technology can integrate a shunt (not shown) in the fuel cell stack, a circuit module (not shown) for obtaining the voltage of the cells in the stack, and a circuit for obtaining the current of the cells in the stack. The module (not shown) realizes the calculation of the impedance of the cells in the stack by obtaining the measured voltage and measured current corresponding to the measuring cells in the stack.

Specifically, during the diagnosis process, FCU turns on the DC/DC conversion circuit and sets the operating frequency and amplitude; FCU sends a signal to CVM to trigger the measurement of the individual impedance in the stack, and FCU sets the overall system to run for a period of time, such as 100ms~300ms. CVM sampling acquires the initial voltage signal and current signal corresponding to the measurement cell in the stack, and then converts the time domain data into frequency domain data through Fourier transform to obtain the cell impedance. Although the overall structure can detect the impedance of the individual cells, the impedance obtained by the detection is inaccurate, and thus the detection of stack faults cannot be achieved.

Especially in vehicle-mounted fuel cell application scenarios, there is variable load operation of the fuel cell during vehicle driving. Although the monomer impedance in the stack can be detected, the detected monomer impedance is inaccurate, so when the stack fails, the fault cannot be accurately obtained. problem lies in.

Based on this, embodiments of this specification propose a fuel cell stack cell impedance online diagnosis solution: obtain the initial voltage signal and initial current signal corresponding to the measurement cell in the fuel cell stack according to the existing cell impedance detection system. The initial voltage signal and initial current signal are converted into a steady-state voltage signal and a steady current signal respectively. Then, the steady-state voltage signal and the stable current signal are Fourier transformed to obtain the amplitude and phase angle contained in the voltage and current signals, and the impedance of the cell is calculated based on the amplitude and phase angle of the voltage and current.

The monomer impedance acquisition process in this illustrated embodiment obtains the steady-state voltage signal and stable current signal corresponding to the monomer during the output process of the fuel cell stack by removing the disturbance factors and bias factors in each initial acquisition signal, and then uses Fourier transform The impedance of the single unit is obtained by transformation calculation, so that when the overall stack fails, the fault location can be accurately determined.

Specifically, through research, it is found that the excitation current signal in the DC/DC conversion circuit during the measurement of the cell current in the stack is much larger than the current signal of each cell during the operation of the stack. In the process of obtaining the current corresponding to the cell, There is interference from large DC (direct current) component factors.

Therefore, the online diagnosis method of fuel cell stack cell impedance in the embodiment of this specification processes the initial voltage signal and initial current signal corresponding to the cells in the fuel cell stack to eliminate large DC components and fuel cell instability in the measurement waveform. By measuring the DC voltage fluctuation component under normal conditions, the steady-state voltage signal and stable current signal corresponding to the measurement unit can be accurately obtained, thereby converting the time domain data into frequency domain data through Fourier transform to obtain accurate results of the unit impedance. It can also solve the problem of frequency leakage in the monomer acquisition process.

The following describes the technical solutions provided by each embodiment of the present application with reference to the accompanying drawings. As shown in Figure 2, the fuel cell stack cell impedance online diagnosis method includes steps S210 to S250. Step S210 is to obtain the initial voltage signal and the initial current signal corresponding to the measurement unit in the fuel cell stack. S220. Use the trend function to fit the deviation components in the initial voltage signal and the initial current signal. S230. Subtract 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. S240. Perform Fourier transform on the steady-state voltage signal and the steady current signal to obtain the amplitude and phase angle contained in the voltage and current signals. S250: Calculate the impedance of the monomer according to the amplitude and phase angle contained in the voltage and current signals, so as to conduct online diagnosis of the fault of the entire stack. The execution subject of the above fuel cell stack cell impedance obtaining process is the inspection controller.

Specifically, in step S210, during the online diagnosis process of the fuel cell stack cell impedance, the system as shown in Figure 1 is used to collect voltage and current signals to obtain the initial voltage signal and initial current signal corresponding to the measurement cell in the fuel cell stack. However, the waveforms of the initial voltage signal and the initial current signal appear as small disturbances combined with a large DC (direct current) bias, which will cause large deviations in the calculated impedance results. Therefore, it is necessary to process the initial voltage signal and current signal and then calculate the single impedance.

Steps S220 and S230 are combined with the above embodiment to process the collected initial voltage signal and initial current signal respectively and convert them into a steady-state voltage signal and a stable current signal.

Among them, the steady-state voltage signal is used to ensure that the fuel cell is in a relatively stable state before and after diagnosis, to avoid phenomena such as voltage rise or fall, or even drift. The stable current signal is used to ensure the stable output current of the electric fuel cell before and after diagnosis, avoiding large current signal deviations caused by current changes. The steady-state voltage signal and stable current signal also include signal waveforms obtained under high-frequency excitation and low-frequency excitation respectively.

In vehicle fuel cell application scenarios, due to the small disturbance and large DC (direct current) bias in the collected initial voltage signal and initial current signal, the existing technology directly uses the collected initial voltage signal and initial current signal. There is a large deviation in the impedance mode value of the monomer obtained through Fourier transform calculation. As shown in the example in Figure 3, there is a large deviation in the voltage-frequency domain data obtained using the existing technology, and the voltage shows an upward trend, resulting in a large error in the calculation of the single impedance. In addition, the voltage of the fuel cell will continue to rise or fall, especially after a load change. This instability will also cause large impedance calculation errors.

In addition, since different batches of inspection controllers have different sampling frequencies, it is easy to cause frequency leakage when inputting non-integer periodic signals, which will also cause large deviations in the impedance calculation results. Therefore, it is necessary to remove the deviation component in the collected signal to obtain the steady-state voltage signal and stable current signal, and then calculate the impedance of the cell.

Specifically, step S220 and step S230: use the trend function to fit the deviation component in the initial voltage signal and the initial current signal; subtract the deviation component from the initial voltage signal and the initial current signal respectively to obtain a steady-state voltage signal and a stable current signal. . The deviation components include DC voltage fluctuation components and large DC bias signals due to the unsteady state of the fuel cell.

The cell voltage and current signal waveforms directly obtained from the fuel cell stack usually have small disturbances, and there are also large DC bias signals during the detection process, resulting in the collected initial voltage signal and initial current signal not being directly utilized. Especially in vehicle-mounted fuel cell application scenarios, due to unsteady conditions such as the voltage of the fuel cell continuing to rise or fall after a load change, there is a DC voltage fluctuation component, and there is also a large DC bias signal during the detection process.

Therefore, in the embodiments of this specification, a steady-state voltage signal and a stable current signal are obtained by fitting the deviation components of the initial voltage signal and the initial current signal, and then eliminating these deviation components from the initial voltage signal and the initial current signal. Subsequently, the steady-state voltage signal and the stable current signal are used to obtain the frequency domain data through Fourier transform to calculate the impedance of the cell.

The existing technology directly converts the obtained initial voltage signal and initial current signal through Fourier transformation to obtain the amplitude and phase angle information. As shown in Figure 3, the voltage and current data under low-frequency excitation in the time domain are converted into frequency domain data. , and convert the voltage and current data in the time domain under high-frequency excitation into frequency domain data, but there is a large DC (direct current) bias signal, and there is a DC voltage fluctuation component due to the unsteady state of the fuel cell. , leading to an upward trend, so there is a large deviation in the impedance value obtained by directly calculating the waveforms of the initial voltage and initial current through Fourier transformation.

The embodiment of this specification uses a trend function to fit the deviation components in the initial voltage signal and the initial current signal and subtracts the deviation components from the initial voltage signal and the initial current signal respectively, thereby obtaining a steady-state voltage signal and a stable current signal (see Figure 4). Then, Fourier transform is used on the steady-state voltage signal and stable current signal to obtain the amplitude and phase angle information of the voltage and current signals, and finally the accurate impedance value of the single unit can be obtained. The abscissas in Figures 3 and 4 represent frequencies, and the ordinates represent amplitudes.

As an example in Table 1 below, when V_grad=100, that is, when the initial voltage signal has a large slope trend corresponding to the same frequency value (such as high frequency corresponding to 1000 and low frequency corresponding to 25), the amplitude obtained by comparing the untrend is 4.9 or 1.1, and After detrending, the amplitude obtained is the true 5.0 or 2.0. Therefore, the trend function is used to fit the deviation component in the initial voltage signal and initial current signal, and the deviation component is subtracted from the initial voltage signal and initial current signal to obtain the steady-state voltage signal and stable current signal, which can accurately reflect the signal waveform corresponding to the monomer. In this embodiment, V_grad=100 represents an output voltage of 100V.

Table 1

In some embodiments, methods for fitting the bias component trend function include but are not limited to polynomial fitting method, Hodrick-Prsecott filtering method, and moving average method.

In some embodiments, since the sampling frequencies of the inspection controllers of different batches are slightly different, frequency leakage may easily occur when collecting voltage and current signals with non-integer periods, further causing large deviations in the impedance calculation results.

As an example in Table 2 below, when the sampling period is not an integer, N=1500, the period k=N*f/fs, where fs is the sampling frequency, N is the number of sampling points (that is, the number of samples), and f is the frequency. If the high-frequency sampling period is 131.3, and the high-frequency frequency is 1000, the amplitude obtained without detrending is 7.3, but the amplitude obtained after detrending is the true 5.0. If the low-frequency sampling period is 3.3 and the low-frequency frequency is 25, the amplitude obtained without detrending is 92.3, but the amplitude obtained after detrending is the true 2.0. It can be seen from this that the impedance model obtained by using the existing technology without detrending calculation is completely inaccurate, and therefore has no reference value for fault diagnosis. This application can accurately obtain the impedance of the monomer.

Table 2

Compared with the prior art, the embodiments of this specification obtain the initial voltage signal and the initial current signal by fitting the trend function before converting the time domain voltage signal and current signal into the amplitude and phase difference of frequency domain analysis through Fourier transform. The deviation component is subtracted from the initial voltage signal and the initial current signal to eliminate the interference of the large DC component, and remove the increasing and decreasing trends in the waveform, thereby ensuring that stable current and voltage do not exist within a short measurement time. The increasing or decreasing trend increases the accuracy of single impedance calculation. 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 phase angle contained in the voltage and current signals.

The specific steady-state voltage signal and stable current signal waveforms change with time. In order to obtain the impedance of the cell, the voltage signal and current signal need to be converted into frequency domain analysis. After performing Fourier transform on the steady-state voltage signal and the steady current signal, the amplitude and phase angle information contained in the voltage and current signals are obtained, and then the impedance mode of the single body is calculated.

In step S250, the impedance of the cell is calculated based on the amplitude and phase angle contained in the voltage and current signals, so as to conduct online diagnosis of the overall stack fault.

Combined with the above embodiment, the steady-state voltage signal and the stable current signal are Fourier transformed to obtain the corresponding amplitude and phase difference, and then the impedance value is calculated. Specifically, the data of voltage and current in the time domain under high-frequency excitation are transformed into data in the frequency domain, and at the same time, the data of voltage and current in the time domain under low-frequency excitation are transformed into data in the frequency domain, so as to convert the results according to the data. Obtain the signal amplitude and phase angle under high-frequency excitation, and the signal amplitude and phase angle under low-frequency excitation.

The high-frequency impedance mode is obtained according to the ratio of the amplitude of the voltage signal and the current signal under high-frequency excitation, and the phase angle of the 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 the 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, obtaining the initial voltage signals and initial current signals corresponding to the measurement cells in the fuel cell stack includes: obtaining the voltage signals and current signals of the required measurement cells in all cells. In some embodiments, the required measurement unit is specified by the inspection controller, or may be randomly generated. Therefore, when acquiring the initial voltage signal and current signal corresponding to the unit to be tested in the fuel cell stack, the inspection controller can measure the required unit respectively in the unselected mode or in the selected mode.

Specifically, when in the selection mode, the required measurement monomer is determined among all the cells according to the measurement channel and/or the cell number in the fuel cell stack that meets the selection conditions, and the initial value corresponding to the required measurement cell is obtained. Voltage signal and initial current signal; when in unselected mode, all cells in the fuel cell stack are inspected according to their cell numbers, and the initial voltage signal and initial current signal corresponding to each cell are obtained. . When in the selection mode, the unit to be measured can be specified through the inspection controller based on automatic measurement, or a unit to be measured can be randomly determined or selected (see Figure 6). When in unselected mode, perform impedance measurement inspection on all cells in the fuel cell stack. In some embodiments, the voltage signal and current signal of the corresponding cell are obtained, and the cell to be measured is determined among all cells according to the measurement channels and/or cell numbers in the fuel cell stack that meet the selection conditions.

Specifically, the voltage values corresponding to all monomers in the fuel cell stack and the variances of all voltage values are obtained, and the measurement channels of the required measurement monomers are determined from all monomers based on whether the variance is greater than the evaluation standard and the variance is less than or equal to the evaluation standard. and/or unit number. Among them, each cell corresponds to a measurement channel and/or cell number. The selection conditions include a first selection condition and a second selection condition. The first selection condition is, for example, the variance is greater than the evaluation standard, and the second selection condition is, for example, the variance is less than or equal to the evaluation standard. The selection conditions here are only examples. It should be noted that the selection conditions can also be set according to the actual operation conditions of the stack.

As shown in Figure 5, FCU sets the automatic measurement mode, FCU sends a signal to the DC/DC conversion circuit so that the DC/DC conversion circuit can excite the electrical stack, and FCU sends a signal to the CVM to trigger impedance measurement.

The fuel cell stack can measure the voltage value of each cell, obtain the consistent expression variance of all cell voltages based on the voltage values of all cells, and determine the required measurement cell by judging whether the variance meets the evaluation criteria.

In some embodiments, the evaluation standard for variance is x, and the value range of x is 50 to 200. As shown in Figure 5, if the variance is greater than the evaluation standard, the unit to be tested is determined based on the measurement channel and/or unit number of the unit to be tested. If the variance is greater than x, the measurement channel and/or cell number of the cell corresponding to the lowest voltage value is obtained from the voltage corresponding to each cell, thereby determining the cell to be tested. If the variance is less than or equal to the evaluation standard, select the unit to be tested corresponding to the end plate position for testing. As shown in Figure 5, measuring the impedance of the node with the lowest voltage means obtaining the test channel or cell number corresponding to the lowest cell voltage to determine the cell under test, and then obtain the impedance of the cell under test. The measurement of the end plate section impedance in Figure 5 means that the variance is less than or equal to the evaluation standard, then the monomer set at the end plate position in the stack is selected as the cell to be tested, and the impedance of the cell to be measured is obtained. The end plate section indicates that the monomer is arranged at the position of the stack end plate.

Because each cell corresponds to a measurement channel and/or cell number. In another embodiment of the selection mode, the selection condition includes obtaining the measurement channel and/or cell number of the designated cell to be measured, thereby obtaining the initial voltage signal and initial current signal corresponding to the designated cell to be measured.

As shown in Figure 6, by setting the specified measurement mode in the selection mode of the FCU, the FCU sets the specified test channel and causes the DC/DC conversion circuit to excite the electrical stack. The FCU also sends a signal to the CVM to trigger a specific impedance measurement. Among them, CVM obtains the impedance corresponding to the specified section of all cells in the stack based on the specified test channel.

In summary, by meeting different selection conditions in the fuel cell stack, the automatic measurement and specified measurement process of the monomer impedance in the stack can be realized. Furthermore, the failure mode of the stack can be determined by the obtained monomer impedance, as detailed below. details.

In some embodiments, when in the unselected mode, all cells in the fuel cell stack are inspected according to their cell numbers, and the initial voltage signal and initial current signal corresponding to each cell are obtained. Specifically, the initial voltage signal and the initial current signal of the monomer corresponding to each number are obtained in sequence, where each monomer in the fuel cell stack is connected in series by setting the number, and the number of the intermediate monomer is set between the first section number and between the tail section numbers.

The fuel cell stack consists of several single cells connected in series. When the initial voltage signal and initial current signal collected by the single cells in the fuel cell stack are obtained, each cell in the fuel cell stack can be inspected and measured. Specifically, each monomer connected in series is numbered, and the two monomers at the end plate are numbered respectively as the first section number and the last section number, and the number of the middle monomer is set between the first section number and the last section number. between.

Referring to Figure 7, when performing a patrol test on all cells, the FCU sets the patrol measurement mode. The FCU sends a signal to the DC/DC conversion circuit, and continues to superimpose the excitation until the signal detection and collection of all cells in the stack is completed. At the same time, the FCU sends a signal. When the CVM triggers the impedance measurement, the CVM starts the inspection from the first-numbered cell in the stack to the end of the measurement of the last-numbered cell, thereby acquiring the initial voltage signal and initial current signal collected by each cell in turn.

In some embodiments, the impedances of N channels corresponding to monomers in all monomers are obtained at the same time, where the value of N ranges from 2 to 5.

The fuel cell stack is assembled from multiple single cells. Using the single cell impedance testing method in the embodiment of this specification, the impedance corresponding to the single cell can be obtained for any number of channels within the range of 2-5 within the same time.

Specifically, the measurement is realized through the N collection chips in the system and the measurement switch array. As shown in Figure 1, in the fuel cell stack cell impedance diagnosis system, N collection chips (not shown) are set in a cell measurement switch array (not shown) to obtain the impedance of the corresponding cell. If this method is used, the impedance of up to 5 channels corresponding to the monomer can be collected at the same time.

In some embodiments, the measurement results corresponding to each measurement unit are obtained, the calibration results of each measurement unit are determined based on the measurement results and the invalid calibration judgment condition, and the calibration results and measurement results are uploaded to the fuel cell control system, so that the fuel cell control system determines the failure mode based on the corresponding calibration results and measurement results of the unit. Failure modes include poisoning, flooding, lack of air or film drying. The measurement result is the accurate single impedance value. The verification result includes valid or invalid. The invalid verification judgment conditions may include detecting whether the cell impedance is within a preset range, or may include detecting whether the current error before and after the cell impedance measurement meets the detection conditions, as described in detail below.

In some embodiments, if the unit impedance measurement is valid, the effective bit 1 is used to indicate, and if the unit impedance measurement is invalid, the effective bit 0 is used.

In some cases, when the operating voltage of the fuel cell stack is low, the stack unit measurement results and calibration results are uploaded to the fuel cell system controller FCU so that the FCU can determine the failure mode based on the measurement results and calibration results. The specific FCU can be set by The failure algorithm combines the high/low frequency impedance and DC voltage during the measurement process, and determines the failure mode of the fuel cell stack based on the measurement results and calibration results of all individual impedances in the stack. The failure modes include poisoning, flooding, lack of air or membrane Dry. The failure algorithm is set based on mass transfer, reaction process and water balance state in the fuel cell stack. Some embodiments of the FCU use a neural network model to determine the failure mode of the stack.

In order to eliminate the situation where the nonlinear error occurs when the analog-to-digital converter ADC samples a particularly small signal (the voltage is lower than the limit value Kv and the current is lower than the limit value Ki), resulting in inaccurate single measurement, therefore, the excitation signal needs to be The magnitude of the amplitude is set higher than a certain limit to realize that the magnitude of the collected voltage and current must be correspondingly higher than the limits Kv and Ki. If the excitation size is set unreasonably, the impedance error of the measurement cell will be unacceptable, so it should Check whether the measurement results are qualified.

In some embodiments, the verification result of each measurement cell is determined based on the measurement result and the invalid verification judgment condition. The verification result includes whether the cell impedance is within a preset range and whether it is valid. Detect whether the monomer impedance is within the preset range. If the monomer impedance is within the preset range, the monomer impedance measurement is judged to be valid. If the cell impedance is not within the preset range, the cell impedance measurement is judged to be invalid. The preset range is determined based on the electrical and chemical properties of the stack.

Combined with the above embodiment, the calibration result of the cell is determined by directly performing calibration based on the impedance obtained by each measurement cell. If the measured impedance value is within the preset range, the single impedance measurement is judged to be valid. If the measured impedance value is not within the preset range, the single impedance measurement is invalid. The preset range is set in detail according to the specific stack conditions.

In other embodiments, the calibration result of each measurement unit is determined by detecting whether the current error before and after the unit impedance measurement meets the detection conditions. If so, the unit impedance measurement is valid; otherwise, the unit impedance measurement is invalid. . The detection conditions include that the value range of the error a is 5%-10%. If the current error before and after the impedance measurement meets the error range of a, then the single impedance meets the detection conditions, and the single impedance measurement is valid; if the current error before and after the impedance measurement is If the current error does not meet the error range of a, the single impedance does not meet the detection conditions, and the single impedance measurement is invalid.

Combined with the above embodiment, the calibration result is obtained through the impedance calibration of the monomer, and the calibration can also be performed based on the current error before and after the impedance measurement. In order to ensure the stable operation of the cell impedance measurement in the stack, it is necessary to conduct error detection on the current within a certain time range before and after the cell impedance measurement.

If the current error before and after the single impedance measurement falls within the error range of a, then the current error before and after the impedance measurement meets the detection conditions and the single impedance measurement is valid; if the current error before and after the impedance measurement does not fall within the error range of a, then the single impedance If the detection conditions are not met, the single impedance measurement is invalid.

The embodiment of this specification processes the initial voltage signal and initial current signal collected by the monomer to obtain a steady-state voltage signal and a stable current signal, and then converts the time domain data into frequency domain data through Fourier transform to accurately calculate and obtain the monomer. Impedance, thereby solving the problem in vehicle application scenarios that measurement errors caused by system and detection factors lead to inaccurate single impedance measurement, and thus the overall stack cannot be evaluated based on accurate single impedance. Not only can the impedance of each measurement cell in the fuel cell stack be accurately measured, but the entire stack can also be evaluated based on the precise cell impedance, so that when a stack failure occurs, the fault location can be quickly and accurately determined.

It should be noted that the terms "first", "second", "third", "fourth", etc. (if present) in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects. , and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances so that the embodiments of the invention described herein are capable of being practiced in sequences other than those illustrated or described herein.

The same and similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on its differences from other embodiments. In particular, for the product embodiments described later, since they correspond to the methods, the description is relatively simple. For relevant details, please refer to the partial description of the system embodiments.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application. All are covered by the protection scope of this application. Therefore, the protection scope of this application should be 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.