Aluminum-air fuel cell maximum power point tracking method based on perturbation and observation method

Abstract

The invention provides an aluminum-air fuel cell maximum power point tracking method based on a perturbation and observation method, and the method comprises the steps: calculating the duty ratio of a maximum power point through employing an MPTT control method, and taking the duty ratio as a reference duty ratio; taking the reference duty ratio as a benchmark and setting a self-adaptive disturbance step length, and circularly adjusting the duty ratio of the output power of the aluminum-air fuel cell for multiple times by utilizing the self-adaptive disturbance step length until the reference duty ratio is reached; and determining the optimal working point of the aluminum-air fuel cell in the ohmic polarization region when the reference duty ratio is reached, and determining the optimal working point as the maximum power point. According to the method, the disturbance step length adopts the self-adaptive step length, and the step length is different according to different working point positions, so that the tracking speed is increased, and the tracking precision is also improved; and when near the maximum power point, disturbance can be automatically judged and stopped, relatively stable power output is kept, and the stability of the system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a maximum power point tracking method of an aluminum-air fuel cell based on a perturbation observation method. Background Art

[0002] When external conditions such as load, electrolyte concentration, etc. change, the maximum power point of the fuel cell may shift. In this case, it is necessary to track the shifted maximum power point again (maximum power point tracking, MPPT).

[0003] The perturbation observation method is the most common method in MPPT. Its basic principle is: by collecting the output voltage and current of the battery in real time, the output power of the battery in the current state is obtained, and then a disturbance is introduced into the voltage or current signal, and its power change is measured and compared with the power value of the previous state. Since there is only one maximum power point for the fuel cell, if the power value increases, the disturbance is made in the same direction; if the power decreases, the disturbance is made in the opposite direction. In this way, the aluminum-air battery system can be always disturbed in the direction of the maximum power point. After continuous disturbance, observation and comparison, the battery can be operated near the maximum power point. For example, technical document 1 (Wang Xianan. Research on independent photovoltaic power generation system and its MPPT [D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2008.) and technical document 2 (Zheng Yingnan, Wang Junping, Zhang Xia. Photovoltaic power generation maximum power point tracking control based on dynamic equivalent impedance matching [J]. Proceedings of the CSEE, 2011, 31(2):111-118).

[0004] The perturbation and observation method has a simple principle, requires fewer parameters to be measured, and is easy to implement in hardware, so it has a wide range of applications.

[0005] In the traditional perturbation observation method, the perturbation step size is fixed. When the step size is large, a faster tracking speed can be obtained, but the fluctuation is large near the maximum power point, and the tracking accuracy is low; when the step size is small, the oscillation amplitude at the maximum power point is small, the accuracy is high, but the tracking speed is slow. Therefore, it is difficult to meet the requirements of tracking accuracy and tracking speed at the same time using the traditional perturbation observation method. In addition, when the external environment changes rapidly, the perturbation observation method may cause misjudgment, causing its working point to deviate from the maximum power point. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a maximum power point tracking method for an aluminum-air fuel cell based on a perturbation observation method. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] A maximum power point tracking method for an aluminum-air fuel cell based on a perturbation-observation method includes:

[0008] S1, using the MPTT control method to calculate the duty cycle of the maximum power point and use it as a reference duty cycle;

[0009] S2, taking the reference duty cycle as a reference and setting an adaptive perturbation step length, and using the adaptive perturbation step length to adjust the duty cycle of the output power of the aluminum-air fuel cell in multiple cycles until the reference duty cycle is reached;

[0010] S3, determining the optimal operating point of the aluminum-air fuel cell in the ohmic polarization region when the reference duty cycle is reached, and determining it as the maximum power point.

[0011] Optionally, before S1, the aluminum-air fuel cell maximum power point tracking method based on the perturbation observation method further includes:

[0012] Obtain an equivalent model of an aluminum-air fuel cell;

[0013] The equivalent model is simplified, and the simplified equivalent model is used to construct a simplified model of the aluminum-air fuel cell power generation unit.

[0014] Optionally, the aluminum-air fuel cell includes three working regions, namely, a concentration polarization region, an activation polarization region, and an ohmic polarization region, and the equivalent model includes a DC voltage source E, an equivalent resistance R of the activation polarization region, and a act , the equivalent resistance R of the concentration polarization region conc 、Equivalent resistance R in ohmic polarization region ohm and equivalent capacitance C e ;

[0015] The positive end of the DC voltage source E is connected to the equivalent resistance R of the activated polarization region. act One end and the equivalent capacitance C e The first end of the activated polarization region has an equivalent resistance R act , the equivalent resistance R of the concentration polarization region conc 、Equivalent resistance R in ohmic polarization region ohm are connected in series, the equivalent capacitance C e The second end is connected to the equivalent resistor R in the concentration polarization region conc The second end.

[0016] Optionally, the simplified model includes a DC voltage source E, a battery internal resistance R in , MPPT controller, Boost controller, inductor L, switch tube M, diode D, load capacitor C and load R L ;

[0017] The positive terminal of the DC voltage source E is connected to the battery internal resistance R in The first end of the battery internal resistance R in The second end of the inductor L is connected to the first end of the inductor L, the second end of the inductor L is connected to the input end of the diode D and the drain of the switch tube M, and the output end of the diode D is connected to the load capacitor C and the load R L The first end; the load capacitor C, the load R L The second end is connected to the source of the switch tube M and the negative end of the DC voltage source E, the MPPT controller is connected to the DC voltage source E, the input of the Boost controller is connected to the output of the MPPT controller, and the output of the Boost controller is connected to the gate of the switch tube M.

[0018] Optionally, S1 includes:

[0019] S1-1, controlling the switch tube M through a Boost controller to place the aluminum-air fuel cell in an ohmic polarization region, and determining two operating points in the ohmic polarization region;

[0020] S1-2, sampling the output currents I1 and I2 of the aluminum-air fuel cell at the two working points;

[0021] S1-2, sampling the output voltages U1 and U2 corresponding to the output currents I1 and I2;

[0022] S1-3, judge U1>U min And U2>U max Is it established? If so, execute S1-4; if not, return to S1-1 to adjust the two working points of the aluminum-air fuel cell in the ohmic polarization region;

[0023] S1-4, using the DC voltage source E and the battery internal resistance R of the aluminum-air fuel cell in , I1, I2, U1 and U2 calculate the reference duty cycle of the maximum power point.

[0024] Among them, the reference duty cycle of the maximum power point is expressed as:

[0025]

[0026] In the formula, R L Represents the load resistance.

[0027] Optionally, S2 includes:

[0028] S2-1, set i as the cycle number;

[0029] S2-2, set the duty cycle D(k+i)=D at the current time k in the i-th cycleref ; Among them, D ref represents the reference duty cycle;

[0030] S2-3, controlling the switch tube M through the Boost controller so that the aluminum-air fuel cell is in the ohmic polarization region at the current time k;

[0031] S2-4, sampling the output voltage U(k+i) and output current I(k+i) of the aluminum-air fuel cell at the current time k, and calculating the output power P(k+i)=U(k+i)×I(k+i);

[0032] S2-5, let the gradient dP = P(k+i)-P(k+i-1);

[0033] S2-6, determine whether dP| is less than the threshold e, if so, execute S2-7; if not, execute S2-8;

[0034] S2-7, let D(k+i+1)=D(k+i), and determine whether the maximum number of loops has been reached. If not, return to S2-3. If yes, execute S2-12.

[0035] S2-8, determine whether dP is greater than 0, if so, execute S2-9, if not, execute S2-10;

[0036] S2-9, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)+step. If not, set D(k+i+1)=D(k+i)-step; step represents the perturbation step of the duty cycle.

[0037] S2-10, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)-step. If not, set D(k+i+1)=D(k+i)+step.

[0038] S2-10, let i=i+1;

[0039] S2-11, determine whether the maximum number of cycles has been reached, if so, execute S2-12; if not, execute S2-3;

[0040] S2-12, ending the cycle so that the duty cycle of the output power of the aluminum-air fuel cell reaches the reference duty cycle.

[0041] Among them, the perturbation step of the duty cycle is expressed as:

[0042]

[0043] Where M is the tracking factor;

[0044] The duty cycle at the current time k is expressed as:

[0045] D(k)=D(k-1)+step.

[0046] Beneficial effects:

[0047] The present invention provides a maximum power point tracking method for an aluminum-air fuel cell based on a perturbation observation method, wherein the method uses an MPTT control method to calculate the duty cycle of the maximum power point, and uses it as a reference duty cycle; taking the reference duty cycle as a reference and setting an adaptive perturbation step length, the duty cycle of the output power of the aluminum-air fuel cell is adjusted by using the adaptive perturbation step length for multiple cycles until the reference duty cycle is reached; determining the optimal working point of the aluminum-air fuel cell in the ohmic polarization region when the reference duty cycle is reached, and determining it as the maximum power point. The perturbation step length of the present invention adopts an adaptive step length, which is different according to the position of the working point, which not only improves the tracking speed, but also improves the tracking accuracy; when near the maximum power point, it can automatically judge and stop the perturbation, maintain a relatively stable power output, and improve the stability of the system.

[0048] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of a maximum power point tracking method of an aluminum-air fuel cell based on a perturbation observation method provided by the present invention;

[0050] Figure 2 It is a process schematic diagram of the S1 and S2 links provided by the present invention;

[0051] Figure 3 is a schematic diagram of an equivalent model of a fuel cell provided by the present invention;

[0052] Figure 4 It is a simplified model schematic diagram of the aluminum-air battery power generation unit provided by the present invention;

[0053] Figure 5 is a process flow chart of S1 provided by the present invention;

[0054] Figure 6 It is a schematic diagram of the voltage and power characteristic curve of the aluminum-air battery provided by the present invention;

[0055] Figure 7 This is a diagram showing the maximum power tracking effect under stable conditions provided by the present invention;

[0056] Figure 8 This is a maximum power tracking effect diagram when the load changes provided by the present invention;

[0057] Fig. 9 This is a maximum power tracking effect diagram when the internal resistance changes provided by the present invention. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0059] Combination Figures 1 to 3 The present invention provides a maximum power point tracking method for an aluminum-air fuel cell based on a perturbation observation method, comprising:

[0060] S1, using the MPTT control method to calculate the duty cycle of the maximum power point and use it as a reference duty cycle;

[0061] S2, taking the reference duty cycle as a reference and setting an adaptive perturbation step length, and using the adaptive perturbation step length to adjust the duty cycle of the output power of the aluminum-air fuel cell in multiple cycles until the reference duty cycle is reached;

[0062] S3, determining the optimal operating point of the aluminum-air fuel cell in the ohmic polarization region when the reference duty cycle is reached, and determining it as the maximum power point.

[0063] In an optional implementation manner of the present invention, before S1, the aluminum-air fuel cell maximum power point tracking method based on the perturbation observation method further includes:

[0064] a, obtain the equivalent model of aluminum-air fuel cell;

[0065] The aluminum-air fuel cell includes three working regions, namely, a concentration polarization region, an activation polarization region, and an ohmic polarization region. Figure 4 The equivalent model includes a DC voltage source E, an equivalent resistance R of the activation polarization region act , the equivalent resistance R of the concentration polarization region conc 、Equivalent resistance R in ohmic polarization region ohm and equivalent capacitance C e The positive end of the DC voltage source E is connected to the equivalent resistance R of the activated polarization region. act One end and the equivalent capacitance C e The first end of the activated polarization region has an equivalent resistance R act , the equivalent resistance R of the concentration polarization region conc 、Equivalent resistance R in ohmic polarization region ohm are connected in series, the equivalent capacitance C e The second end is connected to the equivalent resistor R in the concentration polarization region conc The second end.

[0066] b. Simplify the equivalent model and use the simplified equivalent model to construct a simplified model of the aluminum-air fuel cell power generation unit.

[0067] refer to Figure 5 The simplified model includes a DC voltage source E, a battery internal resistance R in , MPPT controller, Boost controller, inductor L, switch tube M, diode D, load capacitor C and load R L ;

[0068] The positive terminal of the DC voltage source E is connected to the battery internal resistance R in The first end of the battery internal resistance R in The second end of the inductor L is connected to the first end of the inductor L, the second end of the inductor L is connected to the input end of the diode D and the drain of the switch tube M, and the output end of the diode D is connected to the load capacitor C and the load R L The first end; the load capacitor C, the load R L The second end is connected to the source of the switch tube M and the negative end of the DC voltage source E, the MPPT controller is connected to the DC voltage source E, the input of the Boost controller is connected to the output of the MPPT controller, and the output of the Boost controller is connected to the gate of the switch tube M.

[0069] In a specific embodiment of the present invention, reference Figure 3 , S1 includes:

[0070] S1-1, controlling the switch tube M through a Boost controller to place the aluminum-air fuel cell in an ohmic polarization region, and determining two operating points in the ohmic polarization region;

[0071] The equivalent model of aluminum-air fuel cell is as follows Figure 4 As shown, U fc ,I fc are the output voltage and current of the fuel cell respectively. When the fuel cell works in different areas, the equivalent resistance R in the current working area o h m (or R conc and R act ) will play a leading role. In the activation polarization region and the concentration polarization region, the battery voltage decreases rapidly with the increase of current, so it can be obtained that R conc and R act It changes in real time with the output current and has a large resistance value. When operating in the ohmic polarization region, R ohm plays a leading role and is approximately a constant value. At this time, R conc and R act Quite small, at this time the battery internal resistance Rin =R conc +R act +R ohm Remains approximately unchanged.

[0072] In order to ensure the quality and reliability of power supply, the working point of the fuel cell power generation system is usually required to be in the ohmic polarization region. At this time, it can be equivalent to a DC voltage source E and an internal resistance R in Since the fuel cell power generation system works in the ohmic polarization region, R in ≈R ohm The output voltage of the fuel cell can be simplified to:

[0073] U fc =ER ohm I fc ≈ER in I fc (1)

[0074] S1-2, sampling the output currents I1 and I2 of the aluminum-air fuel cell at the two working points;

[0075] S1-2, sampling the output voltages U1 and U2 corresponding to the output currents I1 and I2;

[0076] According to formula (1), the structure of the aluminum-air battery power generation unit can be simplified as Figure 5 As shown, Figure 5 The aluminum-air battery supplies energy to the load through the Boost converter. Since the ohmic polarization region is the ideal region for the aluminum-air battery to work, the battery operating point can be kept in the ohmic polarization region by controlling its output current.

[0077] The maximum power point of aluminum-air fuel cells is usually located in the ohmic polarization region. Since the voltage characteristic curve in the ohmic polarization region is approximately linear, the two working points in the ohmic polarization region can be detected in real time, and the slope of a straight line can be determined using the two points to obtain the approximate internal resistance. By controlling the Boost converter to work at different output currents I1 and I2, the corresponding output voltages U1 and U2 can be detected, and the following expression can be obtained:

[0078]

[0079] From formula (2), we can get:

[0080]

[0081] When the internal resistance of the battery and the equivalent external resistance R in =R L (1-D) 2 When they are equal, we can get:

[0082]

[0083] S1-3, judge U1>U min And U2>U max Is it established? If so, execute S1-4; if not, return to S1-1 to adjust the two working points of the aluminum-air fuel cell in the ohmic polarization region;

[0084] S1-4, using the DC voltage source E and the battery internal resistance R of the aluminum-air fuel cell in , I1, I2, U1 and U2 calculate the reference duty cycle of the maximum power point, expressed as:

[0085]

[0086] In the formula, R L Represents the load resistance.

[0087] In a specific embodiment of the present invention, reference Figure 6 , S2 includes:

[0088] S2-1, set i as the cycle number;

[0089] S2-2, set the duty cycle D(k+i)=D at the current time k in the i-th cycle ref ; Among them, D ref represents the reference duty cycle;

[0090] S2-3, controlling the switch tube M through the Boost controller so that the aluminum-air fuel cell is in the ohmic polarization region at the current time k;

[0091] S2-4, sampling the output voltage U(k+i) and output current I(k+i) of the aluminum-air fuel cell at the current time k, and calculating the output power P(k+i)=U(k+i)×I(k+i);

[0092] S2-5, let the gradient dP = P(k+i)-P(k+i-1);

[0093] S2-6, determine whether dP| is less than the threshold e, if so, execute S2-7; if not, execute S2-8;

[0094] S2-7, let D(k+i+1)=D(k+i), and determine whether the maximum number of loops has been reached. If not, return to S2-3. If yes, execute S2-12.

[0095] S2-8, determine whether dP is greater than 0, if so, execute S2-9, if not, execute S2-10;

[0096] S2-9, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)+step. If not, set D(k+i+1)=D(k+i)-step. Step represents the step length of the duty cycle.

[0097] S2-10, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)-step. If not, set D(k+i+1)=D(k+i)+step.

[0098] S2-10, let i=i+1;

[0099] S2-11, determine whether the maximum number of cycles has been reached, if so, execute S2-12; if not, execute S2-3;

[0100] S2-12, ending the cycle, so that the duty cycle of the output power of the aluminum-air fuel cell reaches the reference duty cycle;

[0101] Among them, the perturbation step of the duty cycle is expressed as:

[0102]

[0103] Where M is the tracking factor;

[0104] The duty cycle at the current time k is expressed as:

[0105] D(k)=D(k-1)+step.

[0106] M is the tracking factor. The selection of the tracking factor M determines the sensitivity of the adaptive adjustment. Figure 6 It can be seen that when the operating point is far away from the maximum power point Larger, can improve the tracking speed; as the operating point and the maximum power point approach, Gradually decreases, and when it reaches the maximum power point, When the minimum value is reached, the perturbation step also tends to zero, thus satisfying the tracking accuracy. In practice, the appropriate threshold e should be selected according to the accuracy requirements.

[0107] In order to verify the accuracy of the proposed maximum power tracking method based on adaptive duty cycle perturbation observation method under stable conditions and when external conditions change, a simulation model was built in Matlab / Simulink, and a DC voltage source and a resistor were used to simulate the aluminum-air battery. The boost converter parameters are L=4mH, C=0.002F, the switching frequency is 10kHz, the fuel cell internal resistance Rin is 4Ω, and RL is 5Ω.

[0108] Example 1:

[0109] The MPPT strategy proposed under stable conditions is simulated and verified. The simulation results are as follows: Figure 7 As shown. The fuel cell can quickly track the maximum power point, at which the duty cycle is about 0.12. The impedance matching can be verified by calculating 5(1-0.12)2=3.88 according to formula (4). Due to the set threshold e, there is a certain error. The simulation results verify the effectiveness and accuracy of the proposed MPPT strategy under stable conditions.

[0110] Example 2

[0111] In order to verify the correctness of the proposed MPPT strategy when the load changes, the load resistance is increased to 8Ω at t=0.5s during the simulation process. Figure 8 This is the simulation result when the load changes. It can be observed that after the load changes, the duty cycle changes rapidly to track the maximum power point. Since the internal resistance remains unchanged, the output power stabilizes at the original maximum power output power after a short fluctuation. The output current and voltage stabilize rapidly and remain at the original value. They do not change with the change of load and have good stability.

[0112] Example 3

[0113] When the equivalent internal resistance of the battery changes, the simulation results are as follows: Fig. 9 As shown in the figure, when the internal resistance of the battery increases at t=1s, the maximum power point shifts. In order to achieve maximum power point tracking, the duty cycle changes rapidly and then tends to be stable. At this time, the maximum output power of the battery and the corresponding output current both decrease with the increase of internal resistance. The simulation results verify the accuracy of the proposed MPPT control strategy.

[0114] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components or steps.

[0115] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A maximum power point tracking method for aluminum-air fuel cells based on the perturbation-observation method. It is characterized in that include: S1, using the MPTT control method to calculate the duty cycle of the maximum power point and use it as a reference duty cycle; S2, taking the reference duty cycle as a reference and setting an adaptive perturbation step length, and using the adaptive perturbation step length to adjust the duty cycle of the output power of the aluminum-air fuel cell in multiple cycles until the reference duty cycle is reached; S3, determining the optimal operating point of the aluminum-air fuel cell in the ohmic polarization region when the reference duty cycle is reached, and determining it as the maximum power point.

2. The maximum power point tracking method of aluminum-air fuel cell based on perturbation observation method according to claim 1, It is characterized in that Before S1, the maximum power point tracking method of aluminum-air fuel cell based on the perturbation observation method also includes: Obtain an equivalent model of an aluminum-air fuel cell; The equivalent model is simplified, and the simplified equivalent model is used to construct a simplified model of the aluminum-air fuel cell power generation unit.

3. The maximum power point tracking method of aluminum-air fuel cell based on perturbation observation method according to claim 2, It is characterized in that The aluminum-air fuel cell includes three working regions, namely, a concentration polarization region, an activation polarization region, and an ohmic polarization region. The equivalent model includes a DC voltage source E, an equivalent resistance R of the activation polarization region, and a act , the equivalent resistance R of the concentration polarization region conc 、Equivalent resistance R in ohmic polarization region ohm and equivalent capacitance C e ; The positive end of the DC voltage source E is connected to the equivalent resistance R of the activated polarization region. act One end and the equivalent capacitance C e The first end of the activated polarization region has an equivalent resistance R ac t, equivalent resistance R in concentration polarization zone conc 、Equivalent resistance R in ohmic polarization region ohm are connected in series, the equivalent capacitance C e The second end is connected to the equivalent resistor R in the concentration polarization region conc The second end.

4. The maximum power point tracking method of aluminum-air fuel cell based on perturbation observation method according to claim 3, It is characterized in that The simplified model includes a DC voltage source E, a battery internal resistance R in , MPPT controller, Boost controller, inductor L, switch tube M, diode D, load capacitor C and load R L ; The positive terminal of the DC voltage source E is connected to the battery internal resistance R in The first end of the battery internal resistance R in The second end of the inductor L is connected to the first end of the inductor L, the second end of the inductor L is connected to the input end of the diode D and the drain of the switch tube M, and the output end of the diode D is connected to the load capacitor C and the load R L The first end; the load capacitor C, the load R L The second end is connected to the source of the switch tube M and the negative end of the DC voltage source E, the MPPT controller is connected to the DC voltage source E, the input of the Boost controller is connected to the output of the MPPT controller, and the output of the Boost controller is connected to the gate of the switch tube M.

5. The maximum power point tracking method of aluminum-air fuel cell based on perturbation and observation method according to claim 4, It is characterized in that S1 includes: S1-1, controlling the switch tube M through a Boost controller to place the aluminum-air fuel cell in an ohmic polarization region, and determining two operating points in the ohmic polarization region; S1-2, sampling the output current I of the aluminum-air fuel cell at the two working points 1 and I 2 ; S1-2, sampling and the output current I 1 and I 2 The corresponding output voltage U 1 and U 2 ; S1-3, judge U 1 >U min And U 2 >U max Is it established? If so, execute S1-4; if not, return to S1-1 to adjust the two working points of the aluminum-air fuel cell in the ohmic polarization region; S1-4, using the DC voltage source E and the battery internal resistance R of the aluminum-air fuel cell in ,I 1 ,I 2 , U 1 and U 2 Calculate the reference duty cycle for the maximum power point.

6. The maximum power point tracking method of aluminum-air fuel cell based on perturbation-observation method according to claim 5, It is characterized in that The maximum power point reference duty cycle in S1-4 is expressed as: In the formula, R L Represents the load resistance.

7. The maximum power point tracking method of aluminum-air fuel cell based on perturbation-observation method according to claim 5, It is characterized in that S2 include: S2-1, set i as the cycle number; S2-2, set the duty cycle D(k+i)=D at the current time k in the i-th cycle ref ; Among them, D ref represents the reference duty cycle; S2-3, controlling the switch tube M through the Boost controller so that the aluminum-air fuel cell is in the ohmic polarization region at the current time k; S2-4, sampling the output voltage U(k+i) and output current I(k+i) of the aluminum-air fuel cell at the current time k, and calculating the output power P(k+i)=U(k+i)×I(k+i); S2-5, let the gradient dP = P(k+i)-P(k+i-1); S2-6, determine whether dP| is less than the threshold e, if so, execute S2-7; if not, execute S2-8; S2-7, let D(k+i+1)=D(k+i), and determine whether the maximum number of loops has been reached. If not, return to S2-3. If yes, execute S2-12. S2-8, determine whether dP is greater than 0, if so, execute S2-9, if not, execute S2-10; S2-9, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)+step. If not, set D(k+i+1)=D(k+i)-step; step represents the perturbation step of the duty cycle. S2-10, determine whether D(k+i+1)-D(k+i) is greater than 0. If so, set D(k+i+1)=D(k+i)-step. If not, set D(k+i+1)=D(k+i)+step. S2-10, let i=i+1; S2-11, determine whether the maximum number of cycles has been reached, if so, execute S2-12; if not, execute S2-3; S2-12, ending the cycle so that the duty cycle of the output power of the aluminum-air fuel cell reaches the reference duty cycle.

8. The maximum power point tracking method of aluminum-air fuel cell based on perturbation-observation method according to claim 7, It is characterized in that The perturbation step of the duty cycle is expressed as: Where M is the tracking factor; The duty cycle at the current time k is expressed as: D(k)=D(k-1)+step.

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