PEMFC maximum power tracking control method, system and equipment

Abstract

The invention discloses a PEMFC maximum power tracking control method, system and device, and relates to the technical field of fuel cells, and the method comprises the following steps: obtaining a system state space equation of a PEMFC power system; defining a sliding mode surface based on the power of the PEMFC and the derivative of the galvanic pile current, deriving the system state through the sliding mode surface, and inputting a system state space equation into a derivation result to obtain an equivalent control quantity; defining a switching control quantity by adopting an over-torsion sliding mode; adding the equivalent control quantity and the switching control quantity to obtain a control law; and adjusting the duty ratio through the control law at the current moment, and carrying out tracking control on the system state through the adjusted duty ratio until the sliding mode surface is 0, and at the moment, the PEMFC power system reaches the maximum power point. Maximum power point tracking is carried out by adopting a sliding mode control method, the convergence speed is higher, the steady-state oscillation is smaller, and the tracking precision is higher.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a PEMFC maximum power point tracking control method, system and device. Background Technology

[0002] With the energy crisis becoming increasingly severe, the development of clean energy is in full swing. Among them, proton exchange membrane fuel cells (PEMFCs) are considered the most promising clean energy devices due to their advantages such as high energy conversion efficiency, cleanliness, and low operating temperature.

[0003] The output performance of PEMFCs is affected by various factors, such as operating conditions like temperature, pressure, and moisture content. Therefore, achieving the maximum power output of a PEMFC is a crucial research topic. Maximum Power Point Tracking (MPPT) technology, as a control strategy capable of adjusting the operating parameters of a PEMFC system in real time to keep it operating near its maximum power point, is of great significance for improving the energy conversion efficiency of PEMFCs, extending battery life, and enhancing the performance of the entire energy system.

[0004] The perturbation-observation method is a type of MPPT control method. Its main advantages are its simple principle and ease of implementation. However, due to the complexity and nonlinearity of PEMFC systems, existing perturbation-observation methods are prone to tracking errors in complex environments, failing to balance convergence speed and steady-state oscillations, and resulting in significant tracking power errors. Summary of the Invention

[0005] Based on the shortcomings of the existing technology, the present invention provides a PEMFC maximum power point tracking control method, system and device, which solves the problem that the existing disturbance observation method is prone to erroneous tracking in complex environments, cannot take into account convergence speed and steady-state oscillation, and produces large tracking power errors.

[0006] The present invention adopts the following technical solution: In a first aspect, the present invention provides a PEMFC maximum power point tracking control method, comprising the following steps: A dynamic model of the PEMFC power system is built in the simulation platform, and the corresponding system state-space equations are obtained based on the dynamic model; where the system state of the PEMFC power system is the inductor current and the output voltage. The sliding mode surface is defined based on the derivative of the power and stack current of the PEMFC. When the sliding mode surface is 0, the PEMFC is at its maximum power point. The system state is differentiated through the sliding mode surface, and the system state-space equation is input into the differentiation result to obtain the equivalent control quantity. The switching control quantity is defined using the super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added together to obtain the control law. The equivalent control quantity is the control quantity that enables the system state to reach the sliding mode surface in a finite time, and the switching control quantity is the control quantity that drives the system state to the sliding mode surface under system uncertainties and external disturbances. The duty cycle is adjusted by the control law at the current moment, and the system state is tracked and controlled by the adjusted duty cycle until the sliding mode surface is 0. At this time, the PEMFC power system reaches the maximum power point.

[0007] Preferably, the system state-space equations are as follows: ; in, ; In the formula, The derivative of the system state. For about x The first function, For about x The second function, D Duty cycle, For inductor current, For output voltage, This is the fuel cell stack voltage. For inductance C For capacitors, It is a resistor.

[0008] Preferably, the sliding modal surface is as follows: ; In the formula, s For sliding modal surfaces, I This represents the fuel cell current.

[0009] Preferably, the control law is as follows: ; in, ; ; ; In the formula, For control laws, For equivalent control quantity, To switch control quantities, As the first control variable, This is the second control variable. The derivative of the first control variable. and It is a positive coefficient. for s The symbolic function.

[0010] Secondly, the present invention provides a PEMFC maximum power point tracking control system, comprising: The acquisition module is used to build a dynamic model of the PEMFC power system in the simulation platform and obtain the corresponding system state-space equations based on the dynamic model; wherein, the system state of the PEMFC power system is the inductor current and the output voltage. The definition module is used to define the sliding mode surface based on the derivative of the power and stack current of the PEMFC. When the sliding mode surface is 0, the PEMFC is at the maximum power point. The system state is differentiated through the sliding mode surface, and the system state space equation is input into the differentiation result to obtain the equivalent control quantity. The switching control quantity is defined using the super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added to obtain the control law. The equivalent control quantity is the control quantity that enables the system state to reach the sliding mode surface in a finite time, and the switching control quantity is the control quantity that drives the system state to the sliding mode surface under the uncertainty of the system and external disturbances. The control module is used to adjust the duty cycle according to the control law at the current moment, and to track and control the system state through the adjusted duty cycle until the sliding mode surface is 0, at which point the PEMFC power system reaches the maximum power point.

[0011] Thirdly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described PEMFC maximum power point tracking control method.

[0012] Compared with the prior art, the above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects: This invention first constructs a dynamic model of the PEMFC power system in a simulation platform and obtains the corresponding system state-space equations based on this model. A sliding mode surface is defined based on the derivatives of the PEMFC power and the stack current. The system state is differentiated using the sliding mode surface, and the system state-space equations are input into the differentiation results to obtain the equivalent control quantity. A switching control quantity is defined using a super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added together to obtain the control law. The sliding mode surface ensures that the PEMFC system can track the maximum power point, and the control law ensures that the PEMFC system can move near this sliding mode surface. This invention uses a sliding mode control method for maximum power point tracking. Compared with the traditional MPPT control method, this invention has a faster convergence speed and smaller steady-state oscillations, improving the MPPT control effect. Furthermore, the use of a super-torsional sliding mode to smooth the control quantity suppresses chattering and achieves higher tracking accuracy. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a structural diagram of the PEMFC power system of the present invention; Figure 2 This is a flowchart of the P&O process of the present invention; Figure 3 This is the INC flowchart of the present invention; Figure 4 This is a schematic diagram of the SMC of the present invention; Figure 5 The PEMFC power characteristic curve of this invention; Figure 6 This is a comparison diagram of the four MPPT control methods of the present invention; Figure 7 For the present invention Figure 5 A magnified view of a portion of the image; Figure 8 This is a flowchart of a PEMFC maximum power point tracking control method according to the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 To address the aforementioned technical problems, this invention discloses a PEMFC maximum power point tracking control method, specifically a PEMFC maximum power point tracking control method based on supertorsion sliding mode, referring to... Figure 8 This includes the following steps: S1: Based on the physical characteristics of the PEMFC stack and the Boost converter circuit, a dynamic model of the PEMFC power system is built in the Matlab / Simulink simulation platform.

[0017] Reference Figure 1 The dynamic model of a PEMFC power system mainly consists of two parts: the PEMFC stack and the boost converter circuit. The PEMFC stack is often constructed using semi-empirical equations.

[0018] (1); (2); (3); (4); (5); (6); (7); In the formula, Represents the fuel cell stack voltage. Represents the voltage of a single cell. Represents Nernst voltage. Represents activation loss, Represents ohmic loss, This represents concentration loss. There are 7 unknown coefficients, which can be calibrated using experimental data. The activation loss coefficient, For external circuit resistance, This refers to the water content of the exchange membrane. For the number of batteries in the fuel cell stack, For the activated area of ​​the exchange membrane, For limiting current density, For the fuel cell stack temperature, For the reaction entropy, The number of electrons transferred in the reaction. It is Faraday's constant. Standard temperature The gas constant is For battery temperature, For hydrogen partial pressure, The partial pressure of oxygen. For water vapor partial pressure, Oxygen concentration; I Represents the battery stack current and the battery stack voltage. correspond.

[0019] Because the PEMFC stack voltage is low and unstable, it cannot be used directly as a DC power supply. Therefore, an external boost converter circuit is required to meet the voltage requirements of the load. The dynamic equation of the boost converter circuit is as follows:

[0020] (8); In the formula, This represents the derivative of the inductor current with respect to time. Represents inductor current. Represents the output voltage. Represents inductance. Represents capacitor, Represents resistance. Represents duty cycle, This represents the derivative of the output voltage with respect to time. Battery stack current. I Numerically with I L equal.

[0021] The above dynamic equations are transformed into system state-space equations: (9); The meanings of each term in the formula are as follows: (10); From the above equation, we can derive the following relationship between the load-side current and voltage and the PEMFC stack current and voltage when the system reaches a steady state: (11); (12); In the formula, As shown by the load current, it can be seen that after adjustment by the Boost circuit, the voltage output by the PEMFC to the load is increased, the current output by the PEMFC to the load is decreased, and the power output by the PEMFC to the load remains unchanged, which conforms to the law of conservation of energy.

[0022] S2: Based on the PEMFC power system built in S1, implement its traditional MPPT control method, and use it as a benchmark for comparing control effects.

[0023] The output power of PEMFC is affected by different operating conditions, and MPPT control is needed to maintain its maximum power output stably. Traditional MPPT control methods are represented by the perturbation and observation (P&O) method and the incremental conductance (INC) method.

[0024] MPPT control essentially controls the ratio of the on-time to the off-time (i.e., duty cycle D) of the Boost circuit by controlling the switching frequency of the power switching devices, so that the internal resistance of the PEMFC matches the load resistance, thereby maximizing the output power of the PEMFC stack. The perturbation and observation method (P&O) is the most widely used method in MPPT control. It finds and determines the direction of the maximum power point (MPP) by continuously perturbing the operating point of the PEMFC power system.

[0025] Reference Figure 2 The specific working principle of P&O is as follows: The output voltage V(k) and output current I(k) of the PEMFC stack are acquired in real time during each sampling period. The product of these two values ​​yields the output power value P(k) at that moment. Then, the output current is perturbed, and the power change ΔP(k) is observed. If ΔP(k) is positive, it means the current perturbation direction is correct, so the perturbation continues in that direction; otherwise, it is perturbed in the opposite direction. This perturbation is repeated until MPP is achieved.

[0026] Although P&O is simple and easy to implement, it is prone to tracking errors in rapidly changing environments, resulting in large power errors. It can also sometimes cause "misjudgment" or oscillations. Therefore, a more refined MPPT control method is needed. Reference Figure 3 The incremental conductance (INC) method compares the conductivity of PEMFC stacks. and This enables maximum power point tracking. The output characteristic curve of a PEMFC stack exhibits a single peak; therefore, at the point of maximum output power, the derivative of power with respect to current is zero. To find the maximum power point, simply keep the current constant while maintaining the current at zero, increasing the current in regions where the derivative is greater than zero, and decreasing the current in regions where the derivative is less than zero.

[0027] The derivative of power with respect to current can be expressed as: (13); like ,but Current current The current is less than that corresponding to MPP. ; like ,but Current current Current greater than MPP ; like ,but Current current Equal to the current corresponding to MPP .

[0028] Therefore, INC can be compared. and Determining the magnitude of the current In terms of adjustment direction, compared to P&O, INC has the advantages of high MPP tracking accuracy and small oscillation amplitude, but its disadvantage is that the algorithm is more complex, which increases the difficulty of microprocessor control.

[0029] S3: Based on the PEMFC power system built in S1, design its MPPT control method based on sliding mode control and use super-torsional sliding mode to suppress chattering.

[0030] Reference Figure 4 x1 and x2 refer to the system state. and To overcome the problems of low tracking accuracy, slow convergence speed and large steady-state oscillation in traditional MPPT control, this invention first achieves PEMFC MPP tracking through first-order sliding mode control (SMC) and uses super-torsional sliding mode (STA) to suppress chattering.

[0031] The core idea of ​​Sliding Mode Control (SMC) is to design a sliding surface that allows the system state to slide on the sliding surface, thereby achieving system stability and desired dynamic performance. A sliding mode is the form of motion in which the system state occurs and is maintained on the sliding surface. SMC design typically involves two steps: designing the sliding mode surface and designing the control law.

[0032] The sliding modal surface ensures that the PEMFC system can track the maximum power point, and the control law ensures that the PEMFC system can move near the sliding modal surface.

[0033] In the PEMFC power control system, when the PEMFC stack is in MPP mode: (14); Therefore, the sliding modal surface can be defined as: (15); When the sliding mode surface is 0 (i.e., s=0), the maximum power output of the PEMFC stack can be guaranteed.

[0034] The purpose of a control law is to enable the system state to reach the sliding mode within a finite time and remain in that sliding mode. A common approach is to use equivalent control combined with switching control.

[0035] (16); In the formula, Represents the total control quantity. Represents the equivalent control quantity. This represents the switching control quantity. Equivalent control is the control quantity required to make the system state move in the sliding mode, while switching control is used to overcome system uncertainties and external disturbances and drive the system state to the sliding mode.

[0036] Equivalent control quantity can be get: (17); In the formula, It is the time derivative of the sliding surface s.

[0037] From equations (10) and (17), we can obtain: (18); In first-order SMC, the sign function is often used as the switching control variable to drive the system state to the sliding mode and maintain its motion. (19); In the formula, It is a positive coefficient. for s The sign function; However, first-order sliding diaphragm control is prone to high-frequency chattering, which can affect control performance and cause mechanical damage. Therefore, this invention uses the most classic second-order sliding diaphragm—the super-torsional sliding diaphragm (STA)—to achieve MPPT control in the PEMFC power system. Its switching control variable is:

[0038] (20); (twenty one); In the formula, and It is a positive coefficient; STA through symbolic functions By embedding it into higher-order derivatives and using integral terms to smooth the input, chattering in traditional SMCs is suppressed.

[0039] Example 2 To ensure that the PEMFC power system converges to the sliding surface s=0, its stability needs to be verified. The Lyapunov function is constructed as follows: (twenty two); According to Lyapunov's second method, if If the system is semi-negative definite, then its stability can be proven. The specific proof is as follows:

[0040] (twenty three); in: (twenty four); (25); (26); From the PEMFC semi-empirical equation, we can obtain: (27); (28); (29); (30); To simplify the calculation, let ,in: (31); (32); (33); Then we have: (34); (35); (36); (37); (38); Since equations (27), (29), (30), (34), and (35) are positive, although equation (42) is negative, its value is small and can be ignored relative to the other terms. Therefore, equations (25) and (26) are negative, and thus:

[0041] (39); (40); In conclusion, it can be proven that: (41); According to Lyapunov's second method, the PEMFC power system is stable.

[0042] Example 3 This invention implements the above four MPPT control methods (P&O, INC, SMC, and STA) on a PEMFC power system with a rated power of 1.2kW, and compares and analyzes their control effects. Figure 5 As shown, the power characteristic curve of PEMFC is single-peaked and has a maximum power point. Its maximum power is 1193.4W at 333K and 944.6W at 293K.

[0043] Since the power characteristic curve of PEMFC is closely related to temperature, this invention applies a step disturbance to the operating temperature of the PEMFC power system to compare the effects of different MPPT control methods, making the system operate at 333K within 0-0.5s and at 293K within 0.5-1s. like Figure 6 As shown, all four MPPT control methods successfully tracked the maximum power point of the PEMFC power system, reaching 1193.4W within 0-0.5s and 944.6W within 0.5-1s. It can be seen that P&O has the longest convergence time and the largest fluctuations during the adjustment process, followed by INC, whose fluctuations during adjustment are still significant. In contrast, SMC and STA show almost no fluctuations during the adjustment process, and their convergence speed is significantly faster than the traditional MPPT methods (P&O and INC). Furthermore, STA has a slight advantage in convergence speed over SMC.

[0044] Figure 7 yes Figure 6 The magnified view is mainly used to compare the steady-state control performance of the four MPPT control methods. It can be seen that the steady-state oscillations of P&O and INC are much larger than those of SMC and STA, which will affect system stability and shorten the PEMFC lifetime to some extent. Furthermore, the steady-state oscillation of STA is significantly smaller than that of SMC. This is because STA uses a sign function... It is embedded in higher-order derivatives and the control input is smoothed using integral terms;

[0045] In summary, this invention provides a PEMFC maximum power point tracking control method based on super-torsional sliding mode, which has a faster convergence speed and smaller steady-state oscillations compared to the traditional MPPT control method. Furthermore, the control input is smoothed through STA, which suppresses the chattering phenomenon of the first-order SMC to a certain extent.

[0046] Example 4 Based on the same concept, the present invention also provides a PEMFC maximum power point tracking control system, including an acquisition module, a definition module and a control module.

[0047] The acquisition module is used to build a dynamic model of the PEMFC power system in the simulation platform and obtain the corresponding system state-space equations based on the dynamic model; where the system state of the PEMFC power system is the inductor current and the output voltage.

[0048] The definition module is used to define the sliding mode surface based on the derivative of the power and stack current of the PEMFC. When the sliding mode surface is 0, the PEMFC is at the maximum power point. The system state is differentiated by the sliding mode surface, and the system state space equation is input into the differentiation result to obtain the equivalent control quantity. The switching control quantity is defined using the super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added to obtain the control law. The equivalent control quantity is the control quantity that enables the system state to reach the sliding mode surface in a finite time, and the switching control quantity is the control quantity that drives the system state to the sliding mode surface under the uncertainty of the system and external disturbances.

[0049] The control module is used to adjust the duty cycle according to the control law at the current moment, and to track and control the system state through the adjusted duty cycle until the sliding mode surface is 0, at which point the PEMFC power system reaches the maximum power point.

[0050] This invention discloses a PEMFC maximum power point tracking (MPPT) control method based on super-torsional sliding mode, mainly including the following steps: Based on the physical characteristics of the PEMFC stack and the Boost converter circuit, a dynamic model of the PEMFC power system is built in the Matlab / Simulink simulation platform; based on the built PEMFC power system, its traditional MPPT control method is implemented, which serves as a benchmark for control performance comparison; based on the built PEMFC power system, a sliding mode control-based MPPT control method is designed, and super-torsional sliding mode is used to suppress chattering. This invention first achieves MPPT control through first-order sliding mode control, overcoming the problems of low tracking accuracy, slow convergence speed, and large steady-state oscillations in traditional MPPT control. Then, super-torsional smoothing control is used to suppress chattering in first-order sliding mode control.

[0051] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0052] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A PEMFC maximum power point tracking control method, characterized in that, Includes the following steps: A dynamic model of the PEMFC power system is built in the simulation platform, and the corresponding system state-space equations are obtained based on the dynamic model; where the system state of the PEMFC power system is the inductor current and the output voltage. The sliding mode surface is defined based on the derivative of the power and stack current of the PEMFC. When the sliding mode surface is 0, the PEMFC is at its maximum power point. The system state is differentiated through the sliding mode surface, and the system state-space equation is input into the differentiation result to obtain the equivalent control quantity. The switching control quantity is defined using the super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added together to obtain the control law. The equivalent control quantity is the control quantity that enables the system state to reach the sliding mode surface in a finite time, and the switching control quantity is the control quantity that drives the system state to the sliding mode surface under system uncertainties and external disturbances. The duty cycle is adjusted by the control law at the current moment, and the system state is tracked and controlled by the adjusted duty cycle until the sliding mode surface is 0. At this time, the PEMFC power system reaches the maximum power point.

2. The PEMFC maximum power point tracking control method as described in claim 1, characterized in that, The system state-space equations are as follows: ； in, ； In the formula, The derivative of the system state. For about x The first function, For about x The second function, D Duty cycle, For inductor current, For output voltage, This is the fuel cell stack voltage. For inductance C For capacitors, It is a resistor.

3. The PEMFC maximum power point tracking control method as described in claim 2, characterized in that, The specific sliding modal surface is shown below: ； In the formula, s For sliding modal surfaces, I This represents the fuel cell current.

4. The PEMFC maximum power point tracking control method as described in claim 3, characterized in that, The control law is as follows: ； in, ； ； ； In the formula, For control laws, For equivalent control quantity, To switch control quantities, As the first control variable, This is the second control variable. The derivative of the first control variable. and It is a positive coefficient. for s The symbolic function.

5. A PEMFC maximum power point tracking control system, characterized in that, include: The acquisition module is used to build a dynamic model of the PEMFC power system in the simulation platform and obtain the corresponding system state-space equations based on the dynamic model; wherein, the system state of the PEMFC power system is the inductor current and the output voltage. The definition module is used to define the sliding mode surface based on the derivative of the power and stack current of the PEMFC. When the sliding mode surface is 0, the PEMFC is at the maximum power point. The system state is differentiated through the sliding mode surface, and the system state space equation is input into the differentiation result to obtain the equivalent control quantity. The switching control quantity is defined using the super-torsional sliding mode. The equivalent control quantity and the switching control quantity are added to obtain the control law. The equivalent control quantity is the control quantity that enables the system state to reach the sliding mode surface in a finite time, and the switching control quantity is the control quantity that drives the system state to the sliding mode surface under the uncertainty of the system and external disturbances. The control module is used to adjust the duty cycle according to the control law at the current moment, and to track and control the system state through the adjusted duty cycle until the sliding mode surface is 0, at which point the PEMFC power system reaches the maximum power point.

6. A computer device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the PEMFC maximum power point tracking control method according to any one of claims 1-4.

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