Control method of fuel cell stack monomer current self-compensation structure

Abstract

The invention discloses a control method of a fuel cell stack single cell current self-compensation structure, the self-compensation structure comprises a fuel cell stack formed by serially connecting N membrane electrode single cells (FC1-FCN), each single cell is provided with a current compensation control loop, the compensation loop is realized through a multi-winding transformer, when the management control system monitors that the maximum voltage difference of the working voltages of the N single batteries is greater than a certain threshold value, the switching tube is controlled to start the primary side coil of the multi-winding transformer, so that the current compensation loop generates compensation current to compensate the membrane electrode with low voltage; by compensating the fuel cell stack membrane electrode with low voltage, the consistency and efficiency of the cell stack can be improved, and the service life of the fuel cell can be prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cell control, and more specifically, relates to a control method for a fuel cell stack monomer current self-compensation structure. Background Art

[0002] Fuel cell technology has always been a research hotspot in the field of new energy storage. Fuel cell power generation is not limited by the Carnot cycle. Compared with direct fuel combustion, the theoretical power generation efficiency of fuel cells can reach 85%-90%. The energy conversion efficiency of existing fuel cell power generation technology can reach 45%-60%. Fuel cell-based backup power supplies have the advantages of being environmentally friendly, highly reliable, highly efficient, and highly adaptable, and are widely used in communication base stations, household electricity, and substations.

[0003] A fuel cell is a chemical device that converts the chemical energy stored in fuel directly into electrical energy. As the place where chemical reactions occur, the fuel cell stack is the core component of the fuel cell system. The fuel cell stack is a power generation device made by assembling a large number of membrane electrode cells in series according to a specific process. Each cell consists of a bipolar plate, a membrane electrode and related kits. The redox reaction inside the cell generates electron movement by injecting hydrogen and oxygen, thereby generating current.

[0004] Since the battery stack is composed of multiple membrane electrode cells connected in series, the performance of each single cell will affect the performance of the entire battery stack. Poor consistency will affect the output voltage of each single cell and thus the output voltage of the entire battery stack. In severe cases, it will also cause excessive local current, easily generate hot spots, and even reverse polarity, leading to battery stack failure.

[0005] In practical applications, the main reasons for the difference in output of single cells in the battery stack are as follows:

[0006] 1. The production and manufacturing of single cells in the battery stack, mainly the membrane electrode, and the differences in assembly levels lead to inconsistencies in the initial performance of the battery.

[0007] 2. The positions of the single cells in the battery stack are different, resulting in different levels of heat dissipation. The heat dissipation level of the batteries at the two ends is higher than that of the batteries in the middle. The temperature distribution of the battery stack is uneven, which affects the performance and life attenuation of each battery cell.

[0008] 3. The air intake method of the battery stack causes each single cell to obtain uneven reactants, resulting in inconsistent output.

[0009] Most existing fuel cell control technologies are to connect supercapacitors or lithium batteries in parallel to the output end of the entire battery stack to compensate the voltage of the entire battery stack to meet the repeated start-stop conditions of the system, but cannot quickly compensate the voltage of each single cell. In addition, related technologies have proposed a solution: monitor the voltage of each single cell in the battery stack. When the voltage deviates, the output performance of the battery stack decreases. Increasing the supply of hydrogen and oxygen reactants can alleviate the problem of insufficient output of the battery stack to a certain extent. This method is to increase the system output by supplementing additional resources, but it does not fundamentally solve the problem of inconsistency in the voltage of the single cells in the battery stack, and there is a problem of waste of reactants.

[0010] Therefore, there is an urgent need to design a control method for the self-compensation structure of the single cell current of a fuel cell stack, which can perform differential compensation control on each single cell in a short time at a low cost to improve the consistency and overall working performance of the stack. Summary of the invention

[0011] 1. Technical issues to be resolved

[0012] Based on the defects mentioned in the above background technology, the present invention discloses a fuel cell stack single cell current self-compensation structure and a control method thereof, which utilizes the polarization curve characteristics of the fuel cell and the non-rechargeable nature of its single cells, and designs a simple current compensation loop at low cost to quickly perform differential current compensation on each single cell, so that the operating voltage of each single cell connected in series remains consistent, thereby improving the consistency and overall working performance of the stack, extending the life of the fuel cell, and reducing hardware costs.

[0013] (II) Technical solution

[0014] The present invention discloses a control method for a fuel cell stack single current self-compensation structure, wherein the fuel cell stack single current self-compensation structure comprises N membrane electrode single cells FC1 to FC N A proton exchange membrane fuel cell stack, a fuel cell management system and a current compensation circuit of N single cells are stacked in series in sequence. The proton exchange membrane fuel cell stack is connected in series with a primary coil of a multi-winding transformer and a switch tube Q to form a closed main control circuit; each single cell FC i Connected in parallel with an independent current compensation loop, i takes a value of 1 to N, each current compensation loop includes a multi-winding transformer secondary coil, a diode D i and resistor R i The primary coil of the multi-winding transformer has the same transformation ratio as the secondary coils of the N multi-winding transformers, and the diode D i Cathode and single cell FC i The positive terminal of the diode D is connected i The anode of thei Connected to the secondary coil of a multi-winding transformer;

[0015] The control method comprises the following steps:

[0016] Step 1: When the proton exchange membrane fuel cell stack is running, the fuel cell management system detects N single cells FC1~FC in real time. N The working voltage V1~V N ;

[0017] Step 2: When the working voltage V1~V N When the maximum pressure difference exceeds the threshold, the fuel cell management system issues a command to start N current compensation loops, generates a control PWM pulse for the main control loop, and drives the switch tube Q to work;

[0018] Step 3: The current compensation circuit of the multi-winding transformer secondary coil generates the FC of the single battery i The voltage opposite to the electromotive force V ib , and form a compensation current in each current compensation loop to perform differentiated compensation on each single cell, so that the voltage of each single cell is stabilized within a certain range.

[0019] Preferably, the same-name end of the primary coil of the multi-winding transformer is connected to the positive electrode of the proton exchange membrane fuel cell stack, and the same-name end of the secondary coil of the multi-winding transformer is connected to the resistor R i One end of the resistor R i The other end of the diode D i The anode of the multi-winding transformer secondary coil is connected to the corresponding single battery FC i negative connection.

[0020] Preferably, the switch tube Q is an NMOS tube, the drain of the NMOS tube is connected to the primary coil of the multi-winding transformer, the source of the NMOS tube is connected to the negative electrode of the proton exchange membrane fuel cell stack, and the gate of the NMOS tube is connected to the output end of the fuel cell management system.

[0021] Preferably, the voltage V of the secondary coil of the multi-winding transformer ib It needs to be greater than or equal to the working voltage of N single cells V1~V N The average value of .

[0022] Preferably, the compensation current in step 3 is automatically formed by a current compensation loop, and no additional current compensation control loop is required. The specific formation principle is as follows:

[0023] Assuming that the windings of the secondary coils of each multi-winding transformer are consistent, that is, the primary and secondary transformation ratios of the transformer are the same, then under the operation of the current compensation circuit, the electromotive force V of each secondary coil is 1b ~V Nb are consistent, as shown in formula (1):

[0024] V 1b =V 2b =···=V Nb (1)

[0025] According to Kirchhoff's law, the compensation current formed in each current compensation loop has the following relationship, as shown in formula (2):

[0026]

[0027] Where, V1~V N is the operating voltage of each single cell, that is, the terminal voltage of the single cell, L m1 ~L mN , R1~R N and V D1 ~V DN are the equivalent excitation inductance, resistance and diode conduction voltage drop of the secondary coil of the multi-winding transformer in each current compensation loop; thus, the compensation current i1(t)~i N (t), as shown in formula (3):

[0028]

[0029] Where t0 is the initial time when the switch is turned on; assuming that the parameters of each current compensation loop are the same, that is, satisfying L m1 =L m2 =…=L mN , R1=R2=…=R N and V D1 =V D2 =…=V DN It can be seen from formula (3) that when the working voltage of the single cell is smaller, the corresponding current compensation circuit will form a larger compensation current to compensate the single cell, and the larger the voltage of the single cell is, the smaller the corresponding compensation current is.

[0030] Preferably, in each switching cycle T, assuming that the on-time is DT, that is, the PWM pulse duty cycle of the driving switch tube is D, the average compensation current I in each cycle is obtained. compensatei , as shown in formula (4):

[0031]

[0032] When the terminal voltage of the single cell is smaller, a larger compensation current will be formed in the corresponding current compensation loop to compensate the single cell, and the larger the voltage of the single cell is, the smaller the corresponding compensation current is.

[0033] (III) Beneficial effects

[0034] Compared with the prior art, the present invention is an improved solution combining software and hardware. It adopts a multi-winding transformer with multiple secondary sides and the same transformation ratio to construct a current self-compensation structure for the single cell of a fuel cell stack. The polarization curve characteristics and non-rechargeability of the fuel cell are utilized to enable the current compensation loop to accurately control the real-time voltage balance and stability of each membrane electrode unit. At the same time, its control method is simple. As long as the management system monitors that the maximum voltage deviation of N single cells exceeds the preset value, a suitable PWM pulse is given to drive the switch tube Q, so that each current compensation loop will automatically generate a corresponding compensation current. No additional current loop control is required, thereby reducing hardware costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments:

[0036] Figure 1 A schematic diagram of the circuit structure of the current self-compensation structure of a single cell of a fuel cell stack of the present invention;

[0037] Figure 2 A flowchart of the working steps of the control method of the current self-compensation structure of a fuel cell stack single cell of the present invention;

[0038] Figure 3 For the present invention Figure 1 The operating circuit diagram of the system when the middle switch tube is closed;

[0039] Figure 4 For the present invention Figure 1 The operating circuit diagram of the system when the middle switch tube is disconnected;

[0040] Figure 5 For the present invention Figure 1 A schematic diagram showing that the current of the compensation loop in the middle current compensation loop and the current of the single battery together form the current of the main control loop;

[0041] Figure 6 This is the polarization curve of the fuel cell. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] In view of the defects in the prior art, the present invention proposes a fuel cell stack single cell current self-compensation structure and a control method thereof.

[0044] The following will describe in detail the current self-compensation structure of the fuel cell stack of the present invention. Figure 1 As shown, it includes N membrane electrode single cells FC1~FC N The proton exchange membrane fuel cell stack, fuel cell management system and current compensation circuit of N single cells are stacked in series in sequence, wherein the proton exchange membrane fuel cell stack is connected in series with the primary coil of the multi-winding transformer and a switch tube Q to form a closed main control circuit; each single cell FC i Connected in parallel with an independent current compensation loop, each current compensation loop includes a multi-winding transformer secondary coil (equivalent to an ideal coil and an excitation inductor), a diode D i and resistor R i The primary coil of the multi-winding transformer has the same transformation ratio as the secondary coils of the N multi-winding transformers. The diode D i Cathode and single cell FC i The positive terminal of the diode D i The anode of the i Connected to the secondary coil of the multi-winding transformer, each independent current compensation loop can detect the corresponding working voltage V of each single battery in real time. i , i takes values ​​from 1 to N. When the working voltage is V1 to V N When the maximum voltage difference exceeds a certain threshold (i.e., voltage V1~V N When the difference between the maximum voltage and the minimum voltage exceeds the preset threshold, the fuel cell management system controls the switch tube to turn on, and the current compensation loop starts to operate; through the multi-winding transformer, each multi-winding transformer secondary coil generates the same electromotive force. Due to the different battery voltages, the compensation current formed by each compensation loop is different, so differential current compensation is performed for single cells with different voltages. Through the current-voltage polarization curve of the fuel cell, the voltage of each single cell can be stabilized within a certain range.

[0045] Specifically, the same-name end of the primary coil of the multi-winding transformer is connected to the positive electrode of the proton exchange membrane fuel cell stack, and the same-name end of the secondary coil of the multi-winding transformer is connected to the resistor R i One end of the resistor R i The other end of the diode D i The anode connection of the multi-winding transformer secondary coil is connected to the non-same-name end of the single battery FC i negative connection.

[0046] Specifically, the switch tube Q is an NMOS tube, the drain of the NMOS tube is connected to the primary coil of the multi-winding transformer, the source of the NMOS tube is connected to the negative electrode of the proton exchange membrane fuel cell stack, and the gate of the NMOS tube is connected to the output end of the fuel cell management system.

[0047] Figure 2 The present invention is shown Figure 1 The working steps flow chart of the proposed current self-compensation structure includes the following steps:

[0048] Step 1: When the proton exchange membrane fuel cell stack is running, the fuel cell management system detects N single cells FC1~FC in real time. N The working voltage V1~V N ;

[0049] Step 2: When the working voltage V1~V N When the maximum pressure difference in exceeds the threshold, the fuel cell management system issues a command to start N current compensation loops, generates a control PWM pulse for the main control loop, and drives the switch tube Q to work;

[0050] Step 3: The current compensation circuit of the multi-winding transformer secondary coil generates the FC of the single battery i The voltage opposite to the electromotive force V ib , and form a compensation current in each current compensation loop to perform differentiated compensation on each single cell, so that the voltage of each single cell is stabilized within a certain range.

[0051] The compensation current in step 3 of the present invention is automatically formed by the current compensation loop, and no additional current compensation control loop is required. The specific formation principle is as follows:

[0052] Assuming that the windings of the secondary coils of each multi-winding transformer are consistent, that is, the primary and secondary transformation ratios of the transformer are the same, then under the operation of the current compensation circuit, the electromotive force V of each secondary coil is 1b ~V Nb are consistent, as shown in formula (1):

[0053] V1b=V2b=···=VNb (1)

[0054] According to Kirchhoff's law, the compensation current formed in each current compensation loop has the following relationship, as shown in formula (2):

[0055]

[0056] Where, V1~V N is the operating voltage of each single cell, that is, the terminal voltage of the single cell, L m1 ~L mN , R1~R N and V D1 ~V DN are the equivalent excitation inductance, resistance and diode conduction voltage drop of the secondary coil of the multi-winding transformer in each current compensation loop; thus, the compensation current i1(t)~i N (t), that is, i1~i N , as shown in formula (3):

[0057]

[0058] Where t0 is the initial time when the switch is turned on; assuming that the parameters of each current compensation loop are the same, that is, satisfying L m1 =L m2 =…=L mN , R1=R2=…=R N and V D1 =V D2 =…=V DN ; It can be seen from formula (3) that when the working voltage of the single cell is smaller, the corresponding current compensation circuit will form a larger compensation current to compensate the single cell, and the larger the voltage of the single cell is, the smaller the corresponding compensation current is. Under the effect of this differentiated current compensation, the voltage difference between each single cell will become smaller until it stabilizes within a certain range.

[0059] Figure 3 The operating circuit diagram of the system is shown when the switch tube is closed when the management system is running. When the switch tube Q is turned on, the voltage of the primary coil of the multi-winding transformer is the terminal voltage of the entire battery stack, and an electromotive force V opposite to the voltage of the single battery is formed on the secondary side. ib , through the resistor R i and diode D i Generate a compensation current, as shown in formula (3).

[0060] Figure 4 The operating circuit diagram of the system when the fuel cell management system is running and the switch tube Q is disconnected is shown. When the switch tube is closed, the primary coil voltage of the multi-winding transformer is zero, and the compensation circuit will not form a compensation current.

[0061] In each switching cycle T, assuming that the on-time is DT, that is, the PWM pulse duty cycle driving the switch tube is D, the average compensation current I per cycle can be obtained. compensatei , as shown in formula (4):

[0062]

[0063] It can be seen that when the terminal voltage of the single cell is smaller, the corresponding current compensation circuit will form a larger compensation current to compensate the single cell, and the larger the voltage of the single cell, the smaller the corresponding compensation current. Under the effect of this differentiated current compensation, the voltage difference between each single cell will become smaller until it stabilizes within a certain range.

[0064] like Figure 5 As shown in the figure, the compensation current generated by the current compensation loop and the output current of the single battery together form the current of the main control loop. It should be emphasized that since the principle of fuel cells is different from that of batteries in the usual sense, they cannot be charged and their Figure 6 The fuel cell polarization curve describes the relationship between the output voltage and current of the fuel cell, reflecting the performance of the fuel cell under different operating conditions. The polarization curve is usually presented as a downward sloping curve. As the output current increases, the output voltage of the fuel cell gradually decreases. Therefore, the compensation device used in the present invention reduces the output current of the low-voltage battery cell, thereby increasing the output voltage, thereby playing a role in voltage compensation.

[0065] Assume that the load output current of the kth membrane electrode unit cell in series is I k , because the current magnitude of the main control circuit in the single battery series circuit is the same, i1+I1=i2+I2=i k +I k =…=i N +I N Therefore, the compensation structure in the present invention is provided by providing k The same direction compensation current i k To reduce the load output current I of the low voltage battery cell k , thereby increasing the output voltage V of the single battery k The self-compensation structure can perform differential current compensation for the difference in output voltage of each battery cell, so that the voltage of each battery cell can be stabilized within a certain range.

[0066] In addition, in order to perform positive current compensation for the low-voltage battery cells in the series circuit through the current compensation loop, the voltage V ib It needs to be greater than or equal to the working voltage of N single cells V1~V N The average value of the sum, that is, satisfying V ib≥(V1+V2+V3+……+V N ) / N.

[0067] Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a fuel cell stack monomer current self-compensation structure, characterized in that: The fuel cell stack single current self-compensation structure comprises N membrane electrode single cells FC1 to FC N A proton exchange membrane fuel cell stack, a fuel cell management system and a current compensation circuit of N single cells are stacked in series in sequence. The proton exchange membrane fuel cell stack is connected in series with a primary coil of a multi-winding transformer and a switch tube Q to form a closed main control circuit; each single cell FC i Connected in parallel with an independent current compensation loop, i takes a value of 1 to N, each current compensation loop includes a multi-winding transformer secondary coil, a diode D i and resistor R i The primary coil of the multi-winding transformer has the same transformation ratio as the secondary coils of the N multi-winding transformers, and the diode D i Cathode and single cell FC i The positive terminal of the diode D is connected i The anode of the i Connected to the secondary coil of a multi-winding transformer; The control method comprises the following steps: Step 1: When the proton exchange membrane fuel cell stack is running, the fuel cell management system detects N single cells FC1~FC in real time. N The working voltage V1~V N ; Step 2: When the working voltage V1~V N When the maximum pressure difference exceeds the threshold, the fuel cell management system issues a command to start N current compensation loops, generates a control PWM pulse for the main control loop, and drives the switch tube Q to work; Step 3: The multi-winding transformer secondary coil of the current compensation circuit generates the FC i The voltage opposite to the electromotive force V ib , and the compensation current formed in each current compensation loop performs differentiated compensation for each single cell, so that the voltage of each single cell is stabilized within a certain range.

2. The control method of the fuel cell stack monomer current self-compensation structure according to claim 1, characterized in that: The same-name end of the primary coil of the multi-winding transformer is connected to the positive electrode of the proton exchange membrane fuel cell stack, and the same-name end of the secondary coil of the multi-winding transformer is connected to the resistor R i One end of the resistor R i The other end of the diode D i The anode of the multi-winding transformer secondary coil is connected to the corresponding single battery FC i negative connection.

3. The control method of the fuel cell stack monomer current self-compensation structure according to claim 2, characterized in that: The switch tube Q is an NMOS tube, the drain of the NMOS tube is connected to the primary coil of the multi-winding transformer, the source of the NMOS tube is connected to the negative electrode of the proton exchange membrane fuel cell stack, and the gate of the NMOS tube is connected to the output end of the fuel cell management system.

4. The control method of the fuel cell stack monomer current self-compensation structure according to any one of claims 1 to 3, characterized in that: The voltage V of the secondary coil of the multi-winding transformer ib It needs to be greater than or equal to the working voltage of N single cells V1~V N The average of the sum.

5. The control method of the fuel cell stack monomer current self-compensation structure according to any one of claims 1 to 3, characterized in that: The compensation current in step 3 is automatically formed by the current compensation loop, and no additional current compensation control loop is required. The specific formation principle is as follows: Assuming that the windings of the secondary coils of each multi-winding transformer are consistent, that is, the primary and secondary transformation ratios of the transformer are the same, then under the operation of the current compensation circuit, the electromotive force V of each secondary coil is 1b ~V Nb are consistent, as shown in formula (1): V 1b =V 2b =···=V Nb (1) According to Kirchhoff's law, the compensation current formed in each current compensation loop has the following relationship, as shown in formula (2): Where, V1~V N is the operating voltage of each single cell, that is, the terminal voltage of the single cell, L m1 ~L mN , R1~R N and V D1 ~V DN are the equivalent excitation inductance, resistance and diode conduction voltage drop of the secondary coil of the multi-winding transformer in each current compensation loop; thus, the compensation current i1(t)~i N (t), as shown in formula (3): Where t0 is the initial time when the switch is turned on; assuming that the parameters of each current compensation loop are the same, that is, satisfying L m1 =L m2 =…=L mN , R1=R2=…=R N and V D1 =V D2 =…=V DN It can be seen from formula (3) that when the working voltage of the single cell is smaller, a larger compensation current will be formed in the corresponding current compensation loop to compensate the single cell, and the larger the voltage of the single cell is, the smaller the corresponding compensation current is.

6. The control method of the fuel cell stack monomer current self-compensation structure according to claim 5, characterized in that: In each switching cycle T, assuming that the on-time is DT, that is, the PWM pulse duty cycle of the driving switch tube is D, the average compensation current I in each cycle can be obtained. compensatei , as shown in formula (4): When the terminal voltage of the single cell is smaller, a larger compensation current will be formed in the corresponding current compensation loop to compensate the single cell, and the larger the voltage of the single cell is, the smaller the corresponding compensation current is.

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