CN202305673U - Alternating current (AC) impedance testing device suitable for fuel cells - Google Patents

Abstract

The utility model relates to an AC impedance testing device suitable for fuel cells, comprising a program-controlled AC source, a DC blocking capacitor, a preamplifier, an I/V conversion circuit, a low-pass filter, a dual program-controlled filter, and a phase difference detection circuit , amplitude detection circuit, keyboard and liquid crystal display unit, and MCU microprocessor; where the program-controlled AC source is connected in series with a DC blocking capacitor and then connected in parallel with the load and the output of the fuel cell stack, and the MCU microcontroller controls the output of the program-controlled AC source through the CAN bus. frequency current excitation signal; a single AC impedance test device can test the AC impedance of up to 16 fuel cells at the same time, and multiple AC impedance test devices are connected through the CAN network; it can simultaneously test the AC impedance of any fuel cell. The test device has simple and clear circuits, high reliability, moderate cost, high measurement accuracy, fast speed, rich interfaces and easy expansion, meeting the needs of real-time high-precision testing of fuel cell AC impedance.

Description

An AC Impedance Test Apparatus for Fuel Cells

technical field

The utility model belongs to an AC impedance testing device for series power supply units, in particular to an AC impedance testing device suitable for fuel cells.

Background technique

A fuel cell is a device that converts chemical energy stored in fuel and oxidant into electrical energy through an electrochemical reaction. According to the fuel cell power requirements in practical applications, the fuel cell stack is usually composed of several to hundreds of single cells in series. During the operation of the fuel cell, the abnormality of a single cell will affect the performance and safety of the entire stack. Therefore, In order to ensure the efficient operation of fuel cells, real-time monitoring of each individual fuel cell is necessary. Undoubtedly, the AC impedance of the fuel cell is the key data of the power generation performance of the fuel cell, which must be monitored in real time, and the data should be displayed and stored to facilitate analysis and research by researchers.

The current impedance test equipment for fuel cells has some shortcomings, such as: the equipment can only be measured in the laboratory environment of the experiment, and cannot be tested online in real time; it can only test the impedance of a single fuel cell, and cannot meet the simultaneous measurement of multiple fuel cells at the same time; Only the impedance value of the fuel cell at a certain frequency point can be tested. Moreover, these devices generally include high-end complex instruments such as fuel cell test benches, electronic loads, and frequency analyzers, which require technicians to correctly configure their hardware connections, software programs, and interface communication protocols, which makes this type of test operation complex and costly. high.

Contents of the invention

The purpose of the utility model is to provide a simple and reliable AC impedance testing device suitable for fuel cells, so as to overcome the shortcomings of the existing testing devices.

In order to achieve the above object, the utility model includes a program-controlled AC source, a DC blocking capacitor, a preamplifier, an I/V conversion circuit, a low-pass filter, a dual-program filter, a phase difference detection circuit, an amplitude detection circuit, a keyboard and Liquid crystal display unit and MCU microprocessor; where the program-controlled AC source is connected in series with a DC blocking capacitor and connected in parallel with the load and the output of the fuel cell stack, and the MCU microcontroller controls the program-controlled AC source to output current excitation signals of different frequencies through the CAN bus; the front The input terminal of the amplifier is connected with each single cell in the fuel cell stack to collect the AC and DC voltage signals of each single cell, and the I/V conversion circuit is connected with the output terminal of the current sensor to collect the AC and DC current signals of the fuel cell, and the collected signal V _i The AC signals V(v) and V(i) obtained after being filtered by dual program-controlled filters are connected to the phase difference detection circuit and the amplitude detection circuit at the same time; the MCU microcontroller is connected to the phase difference through the SPI1 _and SPI2 interfaces The FPGA in the detection circuit is connected to the A/D converter in the amplitude detection circuit, and the MCU microcontroller can obtain the AC impedance amplitude and phase difference data at different frequencies of the fuel cell through calculation, and transmit them to the keyboard and liquid crystal display through the I/O bus unit, and finally the AC impedance spectrum of the fuel cell can be obtained. A single AC impedance test unit can test up to 16 fuel cells at the same time, and multiple AC impedance test units can be connected through the CAN network to test the AC impedance of any fuel cell.

The above-mentioned preamplifier is composed of 16 dual-way relays, a 4-16 decoder and a differential amplifier circuit. Fuel cell output voltage signals V ₀ , V ₁ are connected to the input terminal of the dual relay L 1 , _{V 1 ,} V ₂ are connected to the input terminal of the dual relay L ₂ , and so on, V ₁₅ , V ₁₆ are connected to the dual relay L ₁₆ . The output signals of the 4-16 decoder are respectively connected to 16 relay control terminals. The MCU microcontroller controls the 4-16 decoders through the I/O port to sequentially select the relays L ₁ ~ L ₁₆ , and only one relay is in the open state at each moment, so that the single-chip fuel cell output signals V _n , V _n-1 (n=1, 2, . . . 16) are selected and connected to the input terminal of the differential amplifier circuit. The differential amplification circuit can differentially amplify the input signals V _n , V _n-1 (n=1, 2, ... 16), and the amplification factor is 100 times, so that the preamplifier can collect the weak AC voltage signal.

The above-mentioned dual-program filter is composed of four second-order bandpass filters A, B, C, and D, among which the second-order bandpass filters A and B, C and D can respectively form two fourth-order Butterworth bandpass filters filter. The input terminals of the second-order band-pass filters A and C are respectively connected to the output signal Vv of the preamplifier and the output signal Vi of the I/V conversion circuit, and the output signals Vv' and Vi' are respectively connected to the second-order band-pass filters B and D . The output signal V(v) of the second-order band-pass filter B is connected with the zero-crossing comparison circuit 1 and the effective value detection circuit 1 at the same time, and the output signal V(i) of the second-order band-pass filter D is simultaneously connected with the zero-crossing comparison circuit 2 and the effective value detection circuit 1. Value detection circuit 2 is connected. The MCU microcontroller sends the Fclk signal through the PWM port to connect with the external clock input port of the dual programmable filter. The output signal Vi of the I/V conversion circuit is connected to the input end of the low-pass filter at the same time, and the output signal Vi(R) of the low-pass filter is connected to the port _C3 of the A/D converter in the amplitude detection circuit.

The above-mentioned phase difference detection circuit is composed of zero-crossing comparison circuits 1 and 2 and FPGA, wherein FPGA can be simplified as a combination logic circuit composed of XOR gate, D flip-flop, register, counter module, SPI module and clock module. The input terminals of the zero-crossing comparison circuit 1 and 2 are respectively connected with the AC signals V(v) and V(i), and the output signal Vv(p) of the zero-crossing comparison circuit 1 is simultaneously connected with the input terminal _I2 of the exclusive OR gate and the input terminal of the D flip-flop Clk is connected, and the output signal Vi(p) of the zero-crossing comparison circuit 2 is connected to the input terminal _I1 of the exclusive OR gate and the input terminal D of the D flip-flop at the same time. The XOR gate output signal V(P) is connected to the input terminal of the counter module, and the clock module provides a clock signal Fclk' for the counter module. The output signal V(A) of the D flip-flop is connected to the input end of the register. During the test, the AC signals V(v) and V(i) are transformed into square wave signals Vv(p) and Vi(p) after passing through the zero-crossing comparison circuit. When the levels of the signals Vv(p) and Vi(p) are different At the same time, the signal V(P) output by the XOR gate is at a high level, so the time T of the high level in one cycle of the signal V(P) is the phase difference time of the input signals V(v) and V(i). When V(P) is high level, start the counter module to start timing, and when V(P) becomes low level, the counter module stops timing. Among them, when the D flip-flop output signal V(A) is low level, it means that the signal V(i) is ahead of V(v), and the signal V(A) is high level, which means that the signal V(i) lags behind V(v) ). After the measurement, the counter module and the register respectively transmit the count value and signal V(A) level information to the SPI module through the bus, and then the SPI module transmits the data to the MCU microcontroller through the SPI1 interface.

The above-mentioned amplitude detection circuit is composed of RMS detection circuits 1, 2, low-pass filter circuits 1, 2 and A/D converter. The input terminals of the effective value detection circuits 1 and 2 are respectively connected with the signals V(v) and Vv(i). The output signals Vv(M) and Vi(M) of the effective value detection circuits 1 and 2 are respectively connected to the input terminals of the low-pass filter circuits 1 and 2 . The ports of A/D converters C ₁ , C ₂ and C ₃ are respectively connected to the output signals Vv(M)', Vi(M)' of the low-pass filter circuits 1 and 2 and the output signal Vi(R) of the low-pass filter. During measurement, AC signals V(i) and V(v) are transformed into DC signals Vv(M)' and Vi(M)' equal in size to their RMS values after being filtered by RMS detection circuits 1 and 2. The A/D converter performs analog-to-digital conversion on the signals Vv(M)' and Vi(M)', and then transmits the V(i) and V(v) amplitude data to the MCU microcontroller through the SPI2 interface, and the MCU microcontroller The fuel cell AC impedance amplitude ratio can be obtained by calculating the ratio of the two amplitude data; the A/D converter can obtain the DC current output by the fuel cell stack by sampling the DC signal Vi(R) output by the low-pass filter .

The above-mentioned MCU microcontroller is respectively connected to the phase difference detection circuit, amplitude detection circuit, keyboard and liquid crystal display unit through SPI1, SPI2, and I/O bus interfaces, and controls the frequency and current value of the output current signal of the program-controlled AC source through the CAN bus . The MCU microcontrollers of multiple AC impedance test units are connected through the CAN bus to form a CAN network, which can measure any number of fuel cell stacks.

The utility model has simple and clear circuit, high reliability, moderate cost, high measurement accuracy, fast speed, abundant interfaces and easy expansion, and meets the needs of real-time and high-precision testing of fuel cell AC impedance.

Description of drawings

Fig. 1 is a structural principle block diagram of the utility model.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is described in further detail.

The utility model consists of a program-controlled AC source, a DC blocking capacitor, a preamplifier, an I/V conversion circuit, a low-pass filter, a dual-program filter, a phase difference detection circuit, an amplitude detection circuit, a keyboard, a liquid crystal display unit and an MCU. Microprocessor composition (Figure 1), in which the program-controlled AC source is connected in series with the DC blocking capacitor and then connected in parallel with the output end of the fuel cell stack, and the MCU microcontroller controls the AC current source to output current signals of different frequencies through the CAN bus; the input end of the preamplifier It is connected to each single cell in the fuel cell stack to collect the AC and DC voltage signals of each single cell, and the I/V conversion circuit is connected to the output terminal of the current sensor to collect the AC and DC current signals of the fuel cell. The collected AC signals V _i , V _v The AC signals V(v) and V(i) obtained after being filtered by dual-programmable filters are connected to the phase difference detection circuit and the amplitude detection circuit at the same time; the MCU microcontroller is respectively connected to the FPGA in the phase detection circuit through the SPI1 and SPI2 interfaces Communicating with the A/D converter in the amplitude detection circuit, the MCU microcontroller can obtain the AC impedance amplitude and phase difference at different frequencies of the fuel cell through calculation, and transmit them to the keyboard and liquid crystal display unit through the I/O bus, and finally can Acquire the AC impedance spectrum of the fuel cell. A single AC impedance test unit can test 16 pieces of fuel cells 1kHz ~ 100kHz AC impedance data at most at the same time. Multiple AC impedance test units are connected through the CAN network to achieve high-precision testing of the AC impedance of any piece of fuel cell. The entire detection device has a simple and clear circuit, high reliability, low cost, and strong scalability.

In the preamplifier of the utility model, the fuel cell output signals V ₀ , V ₁ are connected to the input terminal of the dual-circuit relay L 1 , _{V 1 ,} V ₂ are connected to the input terminal of the dual-channel relay L ₂ , and so on V ₁₅ , V ₁₆ It is connected with the double-way relay L ₁₆ , and the 16-way level signals at the output end of the decoder are respectively connected to 16 relay control ends. The MCU microcontroller outputs 0000 to 1111 level signals through the 4-way I/O port to control the 4-16 decoder 74HC154 to select the relays L ₁ -L ₁₆ in turn, and only one relay is in the on state at each moment, so that the single chip The fuel cell output signals V _n , V _n-1 (n=1, 2, . . . 16) are gated and connected to the input end of the differential amplifier circuit. The differential amplifier circuit composed of differential amplifier INA106 and compact operational amplifier AD826 performs differential amplification on input signals V _n , V _n-1 (n=1, 2, ... 16), in which the AC signal amplification factor is 100 times, The minimum detectable AC voltage value is 0.1mv (RMS), and the maximum frequency is 100kHz, and the conduction voltage of the dual relay control is 5V.

The dual-program filter of the present invention is composed of the LTC1264 chip of Lingte Company and peripheral circuits, wherein the peripheral circuits are designed by FilterCAD filter design software. In order to ensure the filtering effect, all the resistors of the peripheral circuits are precision resistors with an accuracy of 0.1%. When the dual-programmable filter is working, the MCU microcontroller provides a clock signal Fclk to the LTC1264 through the PWM port, and its frequency is 20 times the filter center frequency. The power supply voltage is ±5v. After filtering, the noise of the output signals V(v) and V(i) is small, which is convenient for the detection of the subsequent stage circuit and improves the measurement accuracy.

What FPGA selected in the phase difference detection circuit of the present invention is EP2C5T144C8N of ALTERA Company, and the clock used is 50M. The zero-crossing comparator circuit is composed of LM3116 of TI Company. During the test, assuming that the count value of the counter module is T and the frequency of the output current signal of the program-controlled AC source is f, the MCU microcontroller can obtain the phase difference data of the AC impedance of the fuel cell through calculation:

Δphase=360*T*f/Fclk', where Fclk' is the frequency of the FPGA crystal oscillator.

When the test frequency is up to 100kHz, the FPGA measurement phase accuracy is

100kHz/50M*360=0.72 degrees.

When the minimum test frequency is 1kHz, the FPGA measurement phase accuracy is

1kHz/50M*360 = 0.0072 degrees.

In the amplitude detection circuit of the utility model, effective value detection circuits 1 and 2 are composed of AD637 of ADI Company and peripheral circuits, which can convert AC signals into DC voltage signals equal to their effective values. Depending on the size of the input signal, the bandwidth of the AD637 input signal can reach 8M, and when the effective value of the input signal is 200mV, the frequency of the input signal can reach up to 600kHz. The low-pass filter circuit is a second-order low-pass filter composed of precision operational amplifier AD826 and peripheral circuits, and its design cut-off frequency is 1kHz. The A/D converter is composed of TI's 16-bit 8-channel ADC chip TLC3548 and peripheral circuits. TCL3548 transmits the collected AC signal V(v), V(i) amplitude data VMG1 and VMG2 to the MCU micro-controller through the SPI1 interface. The MCU microcontroller can obtain the fuel cell AC impedance amplitude ratio data by calculating the ratio of the two amplitude data:

|Z|=VMG1/VMG2.

The MCU microcontroller of the utility model is respectively connected with the phase difference detection circuit, the amplitude detection circuit, the keyboard and the liquid crystal display unit through the SPI1, SPI2 and I/O bus interfaces, and controls the frequency of the output current signal of the program-controlled AC source through the CAN bus and current value. The MCU microcontrollers of multiple AC impedance test units are connected through the CAN bus to form a CAN network, which can measure any number of fuel cell stacks. After the detection, the MCU microcontroller can finally obtain the AC impedance of the fuel cell through calculation:

Z=|VMG1/VMG2|cos(Δphase)+j|VMG1/VMG2|sin(Δphase).

During the test, the AC impedance of the fuel cell at different frequencies can be measured by changing the output frequency of the programmed AC source, and finally the AC impedance spectrum of the single-chip fuel cell can be obtained. Among them, what MCU microcontroller chooses is PIC18F458 of MICROCHIP Company.

Finally, it should be noted that the implementation of the present utility model is only for illustrating the technical solution rather than limiting. All modifications and replacements that do not deviate from the spirit and scope of the technical solutions of the present utility model shall be covered by the claims of the present utility model.

The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims (5)

1. An AC impedance testing device suitable for fuel cells, including a program-controlled AC source, a DC blocking capacitor, a preamplifier, an I/V conversion circuit, a low-pass filter, a dual-programmable filter, a phase difference detection circuit, an amplitude Value detection circuit, keyboard and liquid crystal display unit, and MCU microprocessor, characterized in that: the program-controlled AC source is connected in series with a DC blocking capacitor and then connected in parallel with the load and the output end of the fuel cell stack, and the MCU microcontroller controls the output of the program-controlled AC source through the CAN bus Current signals of different frequencies; the input end of the preamplifier is connected to each single cell in the fuel cell stack to collect the AC and DC voltage signals of each single cell; the I/V conversion circuit is connected to the output end of the current sensor to collect the AC and DC voltage signals of the fuel cell Current signal; the collected signal is filtered by a dual program-controlled filter to obtain an AC signal, and is connected to the phase difference detection circuit and the amplitude detection circuit at the same time; the MCU microcontroller is connected to the FPGA and the phase detection circuit through the SPI1 and SPI2 interfaces respectively. The A/D converter is connected to the amplitude detection circuit, and the MCU microcontroller obtains the AC impedance amplitude and phase difference data of the fuel cell at different frequencies through calculation, and transmits the data to the keyboard and liquid crystal display unit through the I/O bus, and finally obtains the fuel cell AC Impedance Spectroscopy. 2. A kind of AC impedance testing device applicable to fuel cells as claimed in claim 1, characterized in that: the preamplifier is made up of 16 dual-way relays, a 4-16 decoder and a differential amplifier circuit, and the output of the fuel cell Voltage signals V ₀ , V ₁ are connected to the input terminal of the dual-circuit relay L1, V ₁ , V ₂ are connected to the input terminal of the dual-channel relay L ₂ , and so on, V ₁₅ , V ₁₆ are connected to the dual-channel relay L ₁₆ ; 4- The output signals of the 16 decoders are respectively connected to 16 relay control terminals; the MCU microcontroller controls the 4-16 decoders through the I/O port to select the relays L ₁ ~ L ₁₆ sequentially, and only one relay is turned on at each moment state, so that the single-chip fuel cell output signals V _n , V _n-1 are gated, where n=1, 2, ... 16, and are connected to the input terminal of the differential amplifier circuit. 3. A kind of AC impedance testing device suitable for fuel cells as claimed in claim 1, characterized in that: the double-programmable filter is composed of 4 second-order bandpass filters A, B, C, D, wherein the second-order The band-pass filters A and B, C and D can form two fourth-order Butterworth band-pass filters respectively; the input ends of the second-order band-pass filters A and C are respectively converted with the output signal Vv and I/V of the preamplifier The circuit output signal Vi is connected, and its output signals Vv', Vi' are respectively connected with the second-order band-pass filter B, D; the output signal V(v) of the second-order band-pass filter B is simultaneously compared with the zero-crossing circuit 1 and the effective value The detection circuit 1 is connected, and the output signal V(i) of the second-order bandpass filter D is connected with the zero-crossing comparison circuit 2 and the effective value detection circuit 2 at the same time; The clock input port is connected; the output signal Vi of the I/V conversion circuit is connected with the input end of the low-pass filter at the same time, and the output signal Vi(R) of the low-pass filter is connected with the port _C3 of the A/D converter in the amplitude detection circuit. 4. fuel cell AC impedance testing device as claimed in claim 1, is characterized in that: phase difference detection circuit is made up of zero-crossing comparison circuit 1,2 and FPGA, and wherein FPGA is simplified as XOR gate, D flip-flop, register, Combination logic circuit composed of counter module, SPI module and clock module; the input terminals of zero-crossing comparison circuit 1 and 2 are respectively connected with AC signals V(v) and V(i), and the output signal Vv(p) of zero-crossing comparison circuit 1 is simultaneously It is connected with the input terminal I2 of the exclusive OR gate and the input terminal Clk of the D flip-flop, and the output signal Vi(p) of the zero-crossing comparison circuit 2 is connected with the input terminal _I1 of the exclusive OR gate and the input terminal D of the D flip-flop at the same time; the output signal of the exclusive OR gate V(P) is connected to the input terminal of the counter module, and the clock module provides the clock signal Fclk' for the counter module; the output signal V(A) of the D flip-flop is connected to the input terminal of the register, and the register and the counter module are connected to the SPI module through the bus. 5. The fuel cell AC impedance testing device as claimed in claim 1, characterized in that: the amplitude detection circuit consists of an effective value detection circuit 1, an effective value detection circuit 2, a low-pass filter circuit 1, a low-pass filter circuit 2 and a /D converter, the effective value detection circuit 1 and the input terminals of the effective value detection circuit 2 are connected with the signals V(v) and V(i) respectively; the output signal Vv( M) and Vi(M) are respectively connected to the input ends of low-pass filter circuit 1 and low-pass filter circuit 2; the ports of A/D converter C ₁ , A/D converter C ₂ and A/D converter C ₃ are respectively connected to The output signal Vv(M)' of the low-pass filter circuit 1, the output signal Vi(M)' of the low-pass filter circuit 2 and the output signal Vi(R) of the low-pass filter are connected.

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