Aluminum-air fuel cell maximum power point tracking method and system based on two-stage control

Abstract

The invention discloses an aluminum-air fuel cell maximum power point tracking method and system based on two-stage control, and the method comprises the steps: S1, sequentially controlling a switching tube to be switched on for a first preset time Ton within a period; controlling the switching tube Qs to be switched off for a second preset time Toff; s2, adjusting the turn-on or turn-off time of the first preset time Ton and the second preset time Toff, so that the load meets the maximum power point threshold first power under the reference duty ratio; s3, in a period, setting a preset disturbance step length, and iteratively adjusting the current of the output end to obtain the battery output power before and after adjustment so as to enable the load to meet the maximum power point threshold second power; and S4, adjusting the second power of the maximum power point threshold according to a fuzzy control method, so that the load meets the optimal power of the maximum power point threshold. Based on the maximum power transmission theory and the fuzzy control theory of resistance matching, the maximum power point is approached, and stable control is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of new energy batteries, and in particular relates to a maximum power point tracking method and system for an aluminum-air fuel cell based on two-stage control. Background Art

[0002] Aluminum-air fuel cells are a new type of battery in recent years. Compared with hydrogen fuel cells and other metal fuel cells, they have larger capacity, lower reaction temperature, no explosion, higher safety and reliability, and long-term storage capacity. When emergency power generation is needed, they can be "plug and play". In theory, as long as there are enough aluminum plates, uninterrupted power generation can be achieved. Aluminum-air fuel cells have a large ohmic polarization area, a fast battery reaction time, and high energy utilization.

[0003] However, the output voltage of aluminum-air fuel cell monomers is small and difficult to control when the capacity is small; there is a relatively obvious segmented internal resistance characteristic, and the power output is easily affected by external environment such as temperature and load. Therefore, it is difficult for aluminum-air fuel cells to maintain a high energy utilization rate in different application scenarios or environments. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a maximum power point tracking method and system for an aluminum-air fuel cell based on two-stage control. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] A maximum power point tracking method for an aluminum-air fuel cell based on two-stage control, comprising:

[0006] S1. In one cycle, the switch tubes are controlled to conduct for the first preset time T. on , so that the Boost converter stores energy; controlling the switch tube Q s Turn off the second preset time T off , so that the Boost converter can discharge;

[0007] S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the duty cycle of the switch tube so that the load meets the maximum power point threshold first power under the reference duty cycle;

[0008] S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point;

[0009] S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

[0010] In a specific implementation, the reference duty cycle adjustment formula is:

[0011] Among them, V w1 To adjust the output voltage of the boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

[0012] In a specific implementation, the S3 step specifically includes:

[0013] S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage;

[0014] S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage.

[0015] S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power;

[0016] S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35;

[0017] S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current;

[0018] S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

[0019] In a specific embodiment, the objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

[0020] In a specific implementation, the fuzzy domain △P(n)∈[-5,5], and the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large;

[0021] The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

[0022] The present invention also provides an aluminum-air fuel cell maximum power point tracking system based on two-stage control, including a Boost boost converter, wherein the Boost boost converter includes: a voltage source V AAFC 、Inductance L in , switch tube Q s 、Diode D p , capacitor C o 、Load R w , where the voltage source V AAFC 、Inductance L in 、Diode D p , capacitor C o Form a charging circuit; capacitor C o 、Load R w A discharge circuit is formed between

[0023] The Boost converter specifically includes the following steps when realizing the maximum power point tracking of the aluminum-air fuel cell:

[0024] S1, in one cycle, controls the switch tube Q in turn s The first preset time T on so that the voltage source V AAFC To inductor L in Charging; controlling the switch tube Q s Turn off the second preset time T off , so that the inductance L in To load R w Discharge;

[0025] S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the switch Q sA duty cycle such that, under a reference duty cycle, the load satisfies a maximum power point threshold first power;

[0026] S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point;

[0027] S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

[0028] In a specific implementation, the reference duty cycle adjustment formula is:

[0029] Among them, V w1 To adjust the output voltage of the front Boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the front Boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

[0030] In a specific implementation, the S3 step specifically includes:

[0031] S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage;

[0032] S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage.

[0033] S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power;

[0034] S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35;

[0035] S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current;

[0036] S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

[0037] In a specific embodiment, the objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

[0038] In a specific implementation, the fuzzy domain △P(n)∈[-5,5], and the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large;

[0039] The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

[0040] Beneficial effects of the present invention:

[0041] The aluminum-air fuel cell maximum power point tracking method based on two-stage control of the present invention is based on the maximum power transmission theory of resistance matching in the first stage. By real-time detection of the fuel cell output port current, incremental disturbance is applied to it to seek optimization, and the maximum power point threshold is approached with a larger step size. In the second stage, based on fuzzy control theory, according to the relationship between the previous moment and the current moment of the corresponding variable, the membership function of the power change and the duty cycle step change is set to further approach the maximum power point and achieve stable control.

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic flow chart of a maximum power point tracking method of an aluminum-air fuel cell based on two-stage control provided by an embodiment of the present invention;

[0044] Figure 2 The embodiment of the present invention provides a Boost conversion circuit topology structure of an aluminum-air fuel cell maximum power point tracking system based on two-stage control;

[0045] Figure 3a is the membership function of power change provided by the embodiment of the present invention;

[0046] Figure 3b A membership function for a duty cycle step change provided by an embodiment of the present invention;

[0047] Figure 4 Comparison of the maximum power point tracking under stable conditions between the two-stage control method of the present invention and the ripple adaptive method;

[0048] Figure 5 Comparison of the maximum power point tracking when the load increases between the two-stage control method of the present invention and the ripple adaptive method;

[0049] Figure 6 The figure is a comparison of the maximum power point tracking when the internal resistance is reduced by the two-stage control method of the present invention and the ripple adaptive method. DETAILED DESCRIPTION

[0050] 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.

[0051] Embodiment 1

[0052] See also Figure 1 , Figure 1 The present invention provides a schematic flow chart of a maximum power point tracking method for an aluminum-air fuel cell based on two-stage control, including:

[0053] S1. In one cycle, the switch tubes are controlled to conduct for the first preset time T. on , so that the Boost converter stores energy; controlling the switch tube Q s Turn off the second preset time T off , so that the Boost converter can discharge;

[0054] S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the duty cycle of the switch tube so that the load meets the maximum power point threshold first power under the reference duty cycle;

[0055] S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point;

[0056] S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

[0057] In a specific implementation, the reference duty cycle adjustment formula is:

[0058] Among them, V w1 To adjust the output voltage of the boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

[0059] In a specific implementation, the S3 step specifically includes:

[0060] S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage;

[0061] S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage.

[0062] S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power;

[0063] S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35;

[0064] S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current;

[0065] S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

[0066] In a specific embodiment, the objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

[0067] In a specific implementation, the fuzzy domain △P(n)∈[-5,5], and the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large;

[0068] The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

[0069] See also Figure 2 The present invention also provides an aluminum-air fuel cell maximum power point tracking system based on two-stage control, including a Boost boost converter, wherein the Boost boost converter includes: a voltage source V AAFC 、Inductance L in , switch tube Q s 、Diode D p , capacitor C o 、Load R w , where the voltage source V AAFC 、Inductance L in 、Diode D p , capacitor C o Form a charging circuit; capacitor C o 、Load R w A discharge circuit is formed between

[0070] The Boost converter specifically includes the following steps when realizing the maximum power point tracking of the aluminum-air fuel cell:

[0071] S1, in one cycle, controls the switch tube Q in turn s The first preset time T on so that the voltage source V AAFC To inductor L in Charging; controlling the switch tube Q s Turn off the second preset time T off , so that the inductance L in To load R w Discharge;

[0072] S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the switch Q s A duty cycle such that, under a reference duty cycle, the load satisfies a maximum power point threshold first power;

[0073] S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point;

[0074] S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

[0075] Specifically, this implementation performs the following derivation.

[0076] In the Boost circuit, when the switch is turned on, V AAFC Give inductor L in Charging energy storage, by capacitor C o Discharging to load R w Power supply, assuming the switch conduction time is T on , then the inductance L in this stage in The accumulated energy can be expressed as V AAFC i in T on ; When the switch is turned off, V AAFC With inductance L in Common load R w Power supply and charge capacitor at the same time. Assume the switch off time is T off , in this stage the inductor L in The energy released can be expressed as (V w -V AAFC )i in T off When the circuit is in a stable working state, ignoring the loss, a cycle t, where t = T on +T off , internal inductance L in The energy stored is equal to the energy released, that is: V AAFC i in T on =(V w -V AAFC )i in T off , simplify to get: V w =V AAFC (T on +T off ) / T off =tV AAFC / T off . Where t>T off , so the output voltage is higher than the power supply voltage, t / T offis the step-up ratio, which can be adjusted by adjusting the duty cycle of the switch tube to change the output voltage V w The size of the switch tube is assumed to be D = T on / t, (D<1), then there is the following relationship: T on =(1-D p )t=t T off Ignoring the possible losses in the circuit, according to the law of conservation of energy, the power supply V AAFC Output power is equal to load power V AAFC i in =V w i w , so the Boost converter output current i w With the inductor current i in The relationship is i w =V AAFC i in / V w =i in (1-D p ), the load power is P w =i w 2 R w =[V w / (R w +R in )] 2 R w , where R in represents the internal resistance of the fuel cell, and the above formula is converted to R w Taking the derivative, we can get (dP w ) / (dR w )=V w 2 (R in -R w ) / (R in +R w ) 3 By controlling the Boost converter to work at different output currents, the corresponding output voltage can be detected and the expression is obtained: R ohm ×i w1 =V AAFC -V w1 and R ohm ×i w2 =V AAFC -V w2 , where R ohm represents the internal resistance of the ohmic reaction polarization region. Solving for R in ≈R ohm , R ohm =|(V w1 -V w2 ) / (iw1 -i w2 )|=|△V / △i|, when the internal resistance of the battery is equal to the equivalent external resistance, we can get: |(V w1 -V w2 ) / (i w1 -i w2 )|=R w (1-D p ) 2 , then the reference duty cycle of the maximum power point is

[0077]

[0078] Among them, V w1 To adjust the output voltage of the front Boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the front Boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

[0079] In a specific implementation, the S3 step specifically includes:

[0080] S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage;

[0081] S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage.

[0082] S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power;

[0083] S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35;

[0084] S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current;

[0085] S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

[0086] In a specific embodiment, the objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

[0087] In a specific implementation, the fuzzy domain △P(n)∈[-5,5], and the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large;

[0088] The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

[0089] Specifically, the fuzzy subset selects the triangular membership function, that is, Figure 3a and Figure 3b As shown in Table 1, the fuzzy rules are shown in Table 1.

[0090] Table 1 Fuzzy rules table

[0091]

[0092] This embodiment further simulates the working conditions of the aluminum-air fuel cell under stable conditions, increased load and reduced internal resistance through simulation experiments, and compares it with the ripple adaptive method. In this embodiment, the Boost converter parameters are set to L = 4mH, C = 0.002F, the switching frequency is 10kHz, and the internal resistance of the fuel cell R in is 4Ω, R L is 5Ω.

[0093] The corresponding simulation waveforms obtained in the embodiment are described below.

[0094] Figure 4 The maximum power point tracking under stable conditions of the two-stage control method and the ripple adaptive method of the present invention is compared. It can be seen that the initial tracking time of the two-stage control method proposed in the present invention is about 0.01s, and then it runs smoothly at the maximum power level; the initial tracking time of the ripple adaptive method is about 0.05s. Obviously, the rapidity of the method proposed in the present invention has significant advantages. In addition, it can be seen from the steady-state amplified waveform that the power ripple is smaller under the method proposed in the present invention.

[0095] Figure 5The maximum power point tracking situation when the load increases is compared between the two-stage control method of the present invention and the ripple adaptive method. During the simulation, the load resistance is increased to 8Ω at t=0.3s. When the external resistance changes and the internal resistance remains unchanged, the Boost converter changes the equivalent external resistance by adjusting the duty cycle, thereby achieving impedance matching and outputting maximum power. Since the internal resistance remains unchanged, the output power stabilizes at the original maximum power output power after a short-term fluctuation. It can be seen that the fluctuation time of the two-stage control method proposed by the present invention is only about 0.001s, and then it runs smoothly at the maximum power level; while the fluctuation time of the ripple adaptive method is about 0.05s.

[0096] Figure 6 The maximum power point tracking when the internal resistance decreases is compared between the two-stage control method of the present invention and the ripple adaptive method. To verify the effect of internal resistance on the maximum power point tracking of the aluminum-air fuel cell, the internal resistance is reduced to 3Ω at t=0.3s, and the maximum power point is offset. To achieve maximum power point tracking, the duty cycle changes rapidly and then stabilizes. At this time, the maximum output power of the battery increases as the internal resistance decreases. It can be seen that the two-stage control method proposed in the present invention stabilizes after 0.005s adjustment, and then operates steadily at the maximum power level; while the adjustment time of the ripple adaptive method is about 0.015s.

[0097] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0098] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0099] 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 viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in a claim. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0100] 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 an aluminum-air fuel cell based on two-stage control, characterized in that: include: S1. In one cycle, the switch tubes are controlled to conduct for the first preset time T. on , so that the Boost converter stores energy; controlling the switch tube Q s Turn off the second preset time T off , so that the Boost converter can discharge; S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the duty cycle of the switch tube so that the load meets the maximum power point threshold first power under the reference duty cycle; S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point; S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

2. The maximum power point tracking method of aluminum-air fuel cell with two-stage load control according to claim 1 is characterized in that: The reference duty cycle adjustment formula is: Among them, V w1 To adjust the output voltage of the boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

3. The maximum power point tracking method of aluminum-air fuel cell with two-stage load control according to claim 1 is characterized in that: The S3 step specifically includes: S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage; S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage. S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power; S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35; S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current; S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

4. The maximum power point tracking method of aluminum-air fuel cell with two-stage load control according to claim 1 is characterized in that: The objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

5. The maximum power point tracking method of aluminum-air fuel cell with two-stage load control according to claim 4 is characterized in that: The fuzzy domain △P(n)∈[-5,5], the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large; The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

6. A maximum power point tracking system for aluminum-air fuel cells based on two-stage control, characterized in that: A Boost converter is included, wherein the Boost converter includes: a voltage source V AAFC 、Inductance L in , switch tube Q s 、Diode D p , capacitor C o 、Load R w , where the voltage source V AAFC 、Inductance L in 、Diode D p , capacitor C o Form a charging circuit; capacitor C o 、Load R w A discharge circuit is formed between The Boost converter specifically includes the following steps when realizing the maximum power point tracking of the aluminum-air fuel cell: S1, in one cycle, controls the switch tube Q in turn s The first preset time T on so that the voltage source V AAFC To inductor L in Charging; controlling the switch tube Q s Turn off the second preset time T off , so that the inductance L in To load R w discharge; S2. Adjust the first preset time T on and the second preset time T off The on or off time is used to adjust the switch Q s A duty cycle such that, under a reference duty cycle, the load satisfies a maximum power point threshold first power; S3. Within one cycle, set a preset disturbance step size, iteratively adjust the output terminal current to obtain the battery output power before and after the adjustment, so that the load meets the maximum power point threshold second power, wherein the absolute value of the difference between the maximum power point threshold second power and the maximum power point is less than the absolute value of the difference between the maximum power point threshold first power and the maximum power point; S4. Adjust the maximum power point threshold second power according to a fuzzy control method so that the load meets the maximum power point threshold optimal power.

7. The maximum power point tracking system of aluminum-air fuel cell with two-stage load control according to claim 6 is characterized in that: The reference duty cycle adjustment formula is: Among them, V w1 To adjust the output voltage of the front Boost converter, V w2 is the output voltage of the Boost converter after adjustment, i w1 To adjust the output current of the front Boost converter, i w2 is the output current of the Boost converter after adjustment, R w For load.

8. The aluminum-air fuel cell maximum power point tracking system with two-stage load control according to claim 6 is characterized in that: The S3 step specifically includes: S31, collecting the current aluminum-air open-circuit voltage to determine the slow-start tracking voltage; S32, slowly start the bus current and determine whether the current aluminum-air voltage is greater than the slow start tracking voltage. If so, increase the bus slow start current until the current aluminum-air voltage is less than the slow start tracking voltage. S33, collecting the current aluminum-air voltage and the current aluminum-air current, and calculating the current aluminum-air power; S34, judging whether the current aluminum-air voltage is less than the preset lower limit voltage value, if not, judging whether the current aluminum-air power is equal to the aluminum-air power at the previous moment, if the current aluminum-air power is equal to the aluminum-air power at the previous moment, it is considered that the load meets the maximum power point threshold second power, if the current aluminum-air power is greater than the aluminum-air power at the previous moment, executing step S35; S35, determining whether the current output terminal current is greater than the output terminal current at the previous moment, if so, increasing the current corresponding to the preset disturbance step length to the current output terminal current, if not, decreasing the current corresponding to the preset disturbance step length to the current output terminal current; S36. After limiting the current at the current output end, the current aluminum-to-air voltage, the current aluminum-to-air current, and the current aluminum-to-air power are all equal to the aluminum-to-air voltage, the aluminum-to-air current, and the aluminum-to-air power at the previous moment, then it is considered that the load meets the second power of the maximum power point threshold.

9. The aluminum-air fuel cell maximum power point tracking system with two-stage load control according to claim 6 is characterized in that: The objective function of the fuzzy control method is the output power P of the aluminum-air fuel cell, the control variable is the duty cycle D, the change in system power △P(n) at the nth moment and the change in duty cycle step △D(n) at the nth moment are the inputs of the fuzzy controller at the nth moment, and the duty cycle step D(n) at the nth moment is the output at the nth moment.

10. The maximum power point tracking system of aluminum-air fuel cell with two-stage load control according to claim 9, characterized in that: The fuzzy domain △P(n)∈[-5,5], the fuzzy subsets of the fuzzy domain △P(n) include: negative large, negative small, zero, positive small, positive large; The fuzzy domain ΔD(n)∈[-4, 4], and the fuzzy subsets of the fuzzy domain ΔD(n) include: negative, zero, and positive.

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