A control method of a fuel cell power system integrated with impedance spectrum online measurement

Abstract

The application discloses a kind of integrated impedance spectrum online measurement fuel cell power system control method, belong to fuel cell system technical field, including the following steps: constructing the mathematical model of fuel cell power system;Design fuel cell power system closed loop control strategy and electrochemical impedance spectrum measurement strategy;Design improved active anti-disturbance controller based on multiple resonance control;Introduce the disturbance self-cancellation strategy of multi-stack system electrochemical impedance spectrum, realize the design process of fuel cell power system bus voltage control method based on multiple resonance control.The application uses the above-mentioned integrated impedance spectrum online measurement fuel cell power system control method, breaks through the mutual exclusion limit of online monitoring and voltage stability, realizes full-band impedance spectrum continuous collection under the condition that system continues normal operation, significantly improves bus voltage quality, and provides key technical support for real-time health diagnosis and active life management of fuel cell power system.

Description

Technical Field

[0001] This invention relates to the field of fuel cell system technology, and in particular to a control method for a fuel cell power system with integrated online impedance spectrum measurement. Background Technology

[0002] Fuel cells can directly convert hydrogen into electricity, offering advantages such as environmental friendliness and high energy conversion efficiency. However, single fuel cell systems suffer from bottlenecks such as slow dynamic response, difficulty in cold start, and insufficient durability. Adopting a multi-stack architecture combined with lithium-ion battery power has become the mainstream technical approach to improve system reliability. When this integrated power system operates under complex conditions, the coordinated control and health status monitoring of multiple stacks present new technical challenges, particularly in achieving continuous online monitoring of stack aging during continuous system operation.

[0003] Electrochemical impedance spectroscopy (EIS) can analyze the internal dynamic characteristics of fuel cells by applying specific frequency perturbation signals, providing key state parameters for online diagnostics. However, in practical applications, the multi-stack system architecture significantly amplifies the impact of EIS measurement perturbations on system stability: to achieve continuous online monitoring, the broadband perturbation signals (such as triangular waves and rectangular waves) required for measurement need to be continuously applied to the operating stack. These perturbations are coupled to the bus through the DC / DC converter, inducing voltage harmonic distortion and power oscillations, directly affecting the reliability, efficiency, and lifespan of the fuel cell power system.

[0004] Active disturbance rejection (ADRR) is an advanced control strategy based on real-time disturbance observation and dynamic compensation. Its core lies in treating internal system uncertainties (such as model errors and parameter drift) and external disturbances (such as load abrupt changes and power fluctuations) as a unified "total disturbance" through an extended state observer, and generating a reverse compensation signal to offset their impact on the system. In fuel cell power systems, the stability of the bus voltage directly affects the synergistic efficiency and lifespan of power electronic devices, fuel cell stacks, and lithium batteries. ADRR, with its strong robustness and adaptability, has become a key means to cope with complex disturbance scenarios.

[0005] However, the bandwidth limitations and phase lag characteristics of active disturbance rejection control strategies fundamentally conflict with the continuous requirements of online impedance spectroscopy measurements. For periodic disturbances, if the disturbance frequency is close to or exceeds the controller bandwidth, the extended state observer will be unable to accurately track the phase and amplitude of the disturbance signal, leading to compensation lag or distortion. For triangular and rectangular wave signals commonly used in electrochemical impedance spectroscopy detection, the presence of multiple harmonics poses an even greater challenge to active disturbance rejection control strategies. Simultaneously, online impedance spectroscopy detection requires a periodic signal of a certain amplitude to plot and acquire the electrochemical impedance spectrum. This forces existing systems to sacrifice bus voltage control performance or measurement accuracy when implementing online impedance spectroscopy detection, creating a technical dilemma where "monitoring leads to system instability, while maintaining stability leads to monitoring failure." Summary of the Invention

[0006] The purpose of this invention is to provide a control method for a fuel cell power system that integrates online impedance spectrum measurement. Under the condition of continuous normal operation of the system, it can realize continuous acquisition of impedance spectrum across the entire frequency band, improve bus voltage quality, and provide key technical support for real-time health diagnosis and active life management of fuel cell power systems.

[0007] To achieve the above objectives, the present invention provides a control method for a fuel cell power system integrating online impedance spectrum measurement, comprising the following steps:

[0008] S1. Construct a mathematical model of the fuel cell power system;

[0009] S2. Based on the established mathematical model, design the equivalent control transfer function of the system, and then design the closed-loop control strategy of the fuel cell power system.

[0010] S3. Design an electrochemical impedance spectroscopy measurement strategy for a fuel cell power system, and introduce the electrochemical impedance spectroscopy signal into the current loop controller to achieve online measurement based on the converter;

[0011] S4. Design a voltage outer loop controller based on active disturbance rejection control, and design an extended state observer to track and estimate the error between the reference voltage and the actual voltage using the system output voltage as the control quantity.

[0012] S5. Design a system state error feedback controller and add a multi-stage resonant control unit to it to obtain an improved active anti-disturbance control strategy for bus voltage. At the same time, introduce a self-cancellation strategy for electrochemical impedance spectral disturbances in multi-stacking systems.

[0013] Preferably, in S1, the mathematical model of the fuel cell power system is:

[0014]

[0015] Among them, Lk i is the inductance value of the Kth fuel cell converter; Lk It is the output current of the Kth fuel cell stack; v fck r is the output voltage of the Kth fuel cell stack; k d is the equivalent parasitic resistance of the inductance of the Kth fuel cell converter; k L0 is the duty cycle of the Kth fuel cell converter; L0 is the inductance value of the lithium battery converter; i b This is the output current of the lithium battery; v b d0 is the output voltage of the lithium battery; r0 is the equivalent parasitic resistance of the lithium battery converter's inductance; d0 is the duty cycle of the lithium battery converter; v o It is the output voltage of the fuel cell power system; i o C is the load current; C is the output capacitance.

[0016] Preferably, in S2, the equivalent control transfer function of the fuel cell power system is:

[0017]

[0018] Where b, c, and a are the coefficients of the equivalent transfer function, L is the inductance value, I Lref is the reference value for the inductor current, and s is the complex frequency variable.

[0019] Preferably, in S4, the equivalent controlled object of the voltage outer loop controller is:

[0020]

[0021] Where b0 is the nominal value of b, f is the total system disturbance, and I Lref This is a reference value for the inductor current. It represents the derivative with respect to time.

[0022] Preferably, in S4, designing the extended state observer includes the following steps:

[0023] Define the state variable γ = [γ1 γ2] T That is, the designed extended state observer tracks the output voltage v. o And the total system disturbance f; at this time, the equivalent controlled object of the voltage outer loop controller is represented by the state equation as:

[0024]

[0025] Where A1, B1, and C1 are all coefficient matrices of the state equations. β1 and β2 are both gains of the extended state observer. By properly configuring the observer gains, the characteristic polynomial of the extended state observer is configured with a specific bandwidth ω. o The pole placement problem, namely:

[0026]

[0027] By selecting the observer bandwidth ω o The gain parameter is directly determined to balance dynamic response speed and noise immunity; therefore, the observer gain matrix is ​​configured as follows:

[0028]

[0029] Define the reference value of the system output voltage as V ref The difference between the output voltage and the reference voltage is the output voltage tracking error e. v Therefore:

[0030]

[0031] In the formula, The output voltage tracking error e is represented by v The derivative; Indicates the output voltage reference value V ref The derivative; Indicates the output voltage v o The derivative;

[0032] The convergence of the reference voltage tracking error is expressed as:

[0033]

[0034] Where, k p It is proportional gain;

[0035]

[0036] in, It is a disturbance estimate.

[0037] Preferably, in S5, the system state error feedback controller is:

[0038]

[0039] Among them, v ref This is the reference value for the system output voltage, k. p It is the proportional gain, v o It is the output voltage of the fuel cell power system, and N is the number of resonant control units;

[0040] G qrNLet be the transfer function of the Nth stage resonant control unit, and its specific expression is as follows:

[0041]

[0042] Where s is the complex frequency variable, k rN ω is the resonance coefficient corresponding to the Nth level resonant control unit. cN ω is the cutoff frequency corresponding to the Nth stage resonant control unit. rN It is the resonant frequency corresponding to the Nth level resonant control unit.

[0043] Preferably, in S5, a self-cancelling strategy for perturbation of the electrochemical impedance spectral spectrum of a multi-stall system is introduced, introducing a different phase shift angle into the electrochemical impedance spectral signal corresponding to each stack, as shown in the following formula:

[0044] f k (t)=M k f(t+θ k ), k = 1, 2, ... N;

[0045] Among them, f k (t) represents the electrochemical impedance spectral signal introduced by the k-th stack, M k θ k These represent the signal amplitude and phase angle, respectively, where f represents the fundamental frequency signal and t represents the time variable.

[0046] Therefore, the present invention adopts the above-mentioned control method for fuel cell power systems with integrated online impedance spectrum measurement, which breaks through the mutual exclusion limitation between online monitoring and voltage stability in traditional methods. Under the condition of continuous normal operation of the system, it realizes continuous acquisition of impedance spectrum across the entire frequency band, significantly improves the bus voltage quality, and provides key technical support for real-time health diagnosis and active life management of fuel cell power systems.

[0047] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0048] Figure 1 This is a flowchart of an embodiment of a control method for a fuel cell power system integrating online impedance spectrum measurement according to the present invention;

[0049] Figure 2 This is a typical structural diagram of the fuel cell power system in an embodiment of the present invention;

[0050] Figure 3 This is a block diagram of the control scheme for the fuel cell power system in an embodiment of the present invention;

[0051] Figure 4 This is a block diagram of the online electrochemical impedance spectroscopy detection structure in an embodiment of the present invention;

[0052] Figure 5 This is a block diagram of the improved active disturbance rejection control strategy in an embodiment of the present invention;

[0053] Figure 6 The output voltage of a typical control strategy when faced with triangular wave electrochemical impedance spectral perturbation;

[0054] Figure 7 This refers to the output voltage of the improved active anti-disturbance control strategy in this embodiment of the invention when faced with triangular wave electrochemical impedance spectral disturbances.

[0055] Figure 8 The output voltage of a typical control strategy when faced with rectangular wave electrochemical impedance spectral perturbation;

[0056] Figure 9 The output voltage of the improved active disturbance rejection control strategy in this embodiment of the invention when faced with rectangular wave electrochemical impedance spectral disturbances. Detailed Implementation

[0057] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0058] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0059] Example 1

[0060] This embodiment uses the example of online measurement of triangular or rectangular wave electrochemical impedance spectroscopy signals in a fuel cell power system as an example.

[0061] like Figure 2 As shown, a typical fuel cell power system consists of one lithium battery and two fuel cell stacks. The lithium battery and fuel cells are connected to the DC bus and load respectively via DC-DC converters, and their main circuit parameters are shown in Table 1.

[0062] Table 1. Key Parameters of a Typical Fuel Cell Power System Circuit

[0063]

[0064] This embodiment provides a control method for a fuel cell power system with integrated online impedance spectrum measurement, including the following steps:

[0065] S1. Construct a mathematical model of the fuel cell power system.

[0066] Based on Kirchhoff's voltage and current laws and the working principle of DC-DC converters, Figure 2 The fuel cell power system model in the image is as follows:

[0067]

[0068] Among them, L k i is the inductance value of the Kth fuel cell converter; Lk It is the output current of the Kth fuel cell stack; v fck r is the output voltage of the Kth fuel cell stack; k d is the equivalent parasitic resistance of the inductance of the Kth fuel cell converter; k L0 is the duty cycle of the Kth fuel cell converter; L0 is the inductance value of the lithium battery converter; i b This is the output current of the lithium battery; v b d0 is the output voltage of the lithium battery; r0 is the equivalent parasitic resistance of the lithium battery converter's inductance; d0 is the duty cycle of the lithium battery converter; v o It is the output voltage of the fuel cell power system; i o C is the load current; C is the output capacitance.

[0069] S2. Based on the established mathematical model, design the equivalent control transfer function of the system, and then design the closed-loop control strategy of the fuel cell power system.

[0070] In this embodiment, the fuel cell power system consists of a lithium battery and its converter, and two fuel cell stacks and their converters. The control strategy for the lithium battery and its converter adopts a voltage and current dual closed-loop control strategy, while the control strategy for the fuel cells and their converter adopts a single current loop control, such as... Figure 3 As shown. To achieve online measurement of electrochemical impedance spectroscopy (EIS) signals, triangular or rectangular wave EIS signals can be introduced into the reference current of the fuel cell current loop, such as... Figure 4 As shown.

[0071] Based on the mathematical model of the fuel cell power system, its equivalent control transfer function is:

[0072]

[0073] Where b, c, and a are the coefficients of the equivalent transfer function. L is the inductance value, I Lref is the reference value for the inductor current, and s is the complex frequency variable.

[0074] S3. Design an electrochemical impedance spectroscopy measurement strategy for fuel cell power systems, and introduce the electrochemical impedance spectroscopy signal into the current loop controller to achieve online measurement based on the converter.

[0075] S4. Design a voltage outer loop controller based on active disturbance rejection control, and design an extended state observer to track and estimate the error between the reference voltage and the actual voltage using the system output voltage as the control quantity.

[0076] From formula (2), the equivalent controlled object of the voltage outer loop controller can be obtained as follows:

[0077]

[0078] Where b0 is the nominal value of b, f is the total system disturbance, and I Lref This is a reference value for the inductor current. It represents the derivative with respect to time.

[0079] Typically, an extended state observer needs to be designed to estimate the total disturbance. Designing an extended state observer includes the following steps:

[0080] Define the state variable γ = [γ1 γ2] T That is, the designed extended state observer tracks the output voltage v. o And the total system disturbance f. At this time, formula (3) can be expressed by the state equation as:

[0081]

[0082] Where A1, B1, and C1 are all coefficient matrices of the state equations. β1 and β2 are both gains of the extended state observer. By properly configuring the observer gains, the characteristic polynomial of the extended state observer is configured with a specific bandwidth ω. o The pole placement problem, namely:

[0083]

[0084] By selecting the observer bandwidth ω o This directly determines the gain parameter, thereby balancing dynamic response speed and noise immunity. Therefore, the observer gain matrix is ​​configured as follows:

[0085]

[0086] Define the reference value of the system output voltage as V ref The difference between the output voltage and the reference voltage is the output voltage tracking error e. v Therefore:

[0087]

[0088] In the formula, The output voltage tracking error e is represented by v The derivative; Indicates the output voltage reference value V ref The derivative; Indicates the output voltage v o The derivative of .

[0089] Assuming the designed extended state observer can estimate the system disturbances well, the convergence of the reference voltage tracking error can be expressed as:

[0090]

[0091] Where, k p It is proportional gain.

[0092]

[0093] in, It is a disturbance estimate.

[0094] S5. Design a system state error feedback controller and add a multi-stage resonant control unit to it to obtain an improved active anti-disturbance control strategy for bus voltage. At the same time, introduce a self-cancellation strategy for electrochemical impedance spectral disturbances in multi-stacking systems.

[0095] Since the reference value of the output voltage is a constant, substituting (5) into (4) yields the system state error feedback controller designed without the introduction of a resonant control unit:

[0096] u0 = k p (v ref -v o (10)

[0097] However, due to the bandwidth ω of the extended state observer o Due to various limitations, the disturbance compensation capability of the observer is restricted by the observer bandwidth. When the system faces time-varying periodic disturbances, if the disturbance frequency is close to or exceeds the controller bandwidth, the extended state observer will be unable to accurately track the phase and amplitude of the disturbance signal, resulting in compensation lag or distortion. In this embodiment, the triangular wave and rectangular wave disturbances not only include the fundamental frequency but also multiple harmonic components such as the 3rd, 5th, and 7th harmonics, further challenging the controller's disturbance suppression capability.

[0098] Furthermore, the fuel cell power system designed in this embodiment includes multiple fuel cell stacks. When multiple stacks are simultaneously subjected to electrochemical impedance spectroscopy measurements, it will have a more severe impact on the system's bus voltage.

[0099] The controller designed using the above process, when faced with a 10Hz triangular wave or rectangular wave disturbance, will have the following steady-state output voltages: Figure 6 , Figure 8 As shown in the figure, the system output voltage quality is poor and the output voltage fluctuates violently.

[0100] In addition, from Figure 6 , Figure 8 The FFT analysis of the system bus voltage shows that the output voltage v o This design includes harmonic components at multiple harmonic frequencies such as 10Hz, 30Hz, and 50Hz. To suppress these harmonic components, this embodiment incorporates a multi-stage resonant control unit into the state error feedback controller to mitigate their impact on the bus voltage. The block diagram of the improved active disturbance rejection control strategy based on this design is shown below. Figure 5 As shown, the state error feedback controller after introducing a multi-stage resonant control unit is as follows:

[0101]

[0102] Among them, v ref This is the reference value for the system output voltage, k. p It is the proportional gain, v o It is the output voltage of the fuel cell power system, and N is the number of resonant control units;

[0103] The value of N is related to the form of the electrochemical impedance spectral perturbation. In this embodiment, in order to achieve a good bus voltage control effect, N is 2 when the electrochemical impedance spectral perturbation is a triangular wave, and N is 10 when the electrochemical impedance spectral perturbation is a rectangular wave.

[0104] G qrN Let be the transfer function of the Nth stage resonant control unit, and its specific expression is as follows:

[0105]

[0106] Where s is the complex frequency variable, k rN ω is the resonance coefficient corresponding to the Nth level resonant control unit. cN ω is the cutoff frequency corresponding to the Nth stage resonant control unit. rN It is the resonant frequency corresponding to the Nth level resonant control unit, i.e., 10Hz, 30Hz, 50Hz, etc.

[0107] In this embodiment, a self-cancelling mechanism for multi-stack electrochemical impedance spectral perturbations is introduced. Taking two stacks as an example, a different phase shift angle is introduced into the electrochemical impedance spectral signal corresponding to each stack, thereby reducing the perturbation estimation burden on the observer when performing electrochemical impedance spectral testing on the fuel cell power system. The formula is as follows:

[0108] f1(t)=22f(t+θ1), f2(t)=16f(t+θ2) (13)

[0109] Where f1(t) and f2(t) represent the electrochemical impedance spectral signals introduced by the two fuel cells, respectively, θ=(θ1,θ2)=(0°,180°), and f represents the fundamental frequency signal.

[0110] After introducing a disturbance self-cancellation mechanism and a multi-stage resonant control unit, the steady-state output voltage of the system in the face of triangular or rectangular wave electrochemical impedance spectrum disturbances is as follows: Figure 7 , Figure 9 As shown in the figure, it can be seen that the fluctuation of the system bus voltage is greatly reduced at this time, and the bus voltage can be basically stabilized at the required 270V.

[0111] The method in this embodiment can be extended to systems such as fuel cells and lithium batteries that require electrochemical impedance spectroscopy detection.

[0112] Therefore, the present invention adopts the above-mentioned control method for fuel cell power systems with integrated online impedance spectrum measurement, which breaks through the mutual exclusion limitation between online monitoring and voltage stability in traditional methods. Under the condition of continuous normal operation of the system, it realizes continuous acquisition of impedance spectrum across the entire frequency band, significantly improves the bus voltage quality, and provides key technical support for real-time health diagnosis and active life management of fuel cell power systems.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A control method for a fuel cell power system integrating online impedance spectroscopy measurement, characterized in that, Includes the following steps: S1. Construct a mathematical model of the fuel cell power system; S2. Based on the established mathematical model, design the equivalent control transfer function of the system, and then design the closed-loop control strategy of the fuel cell power system. S3. Design an electrochemical impedance spectroscopy measurement strategy for a fuel cell power system, and introduce the electrochemical impedance spectroscopy signal into the current loop controller to achieve online measurement based on the converter; S4. Design a voltage outer loop controller based on active disturbance rejection control, and design an extended state observer to track and estimate the error between the reference voltage and the actual voltage using the system output voltage as the control quantity. S5. Design a system state error feedback controller and add a multi-stage resonant control unit to it to obtain an improved active anti-disturbance control strategy for bus voltage. At the same time, introduce a self-cancellation strategy for electrochemical impedance spectral disturbances in multi-stacking systems. In S5, the system state error feedback controller is: ； in, This is a reference value for the system output voltage. It is the proportional gain, v o It is the output voltage of the fuel cell power system, and N is the number of resonant control units; Let be the transfer function of the Nth stage resonant control unit, and its specific expression is as follows: ； Where s is the complex frequency variable, k rN It is the resonance coefficient corresponding to the Nth level resonant control unit. It is the cutoff frequency corresponding to the Nth stage resonant control unit. It is the resonant frequency corresponding to the Nth level resonant control unit; In S5, a self-cancelling strategy for perturbation of the electrochemical impedance spectral spectrum of a multi-stall system is introduced, which introduces a different phase shift angle into the electrochemical impedance spectral signal corresponding to each stack. The formula is shown below: ； in, This represents the electrochemical impedance spectral signal introduced by the k-th stack. , These represent the signal amplitude and phase angle, respectively, where f represents the fundamental frequency signal and t represents the time variable.

2. The control method for a fuel cell power system with integrated online impedance spectrum measurement according to claim 1, characterized in that: In S1, the mathematical model of the fuel cell power system is: ； Among them, L k i is the inductance value of the k-th fuel cell converter; Lk It is the output current of the k-th fuel cell stack; v fck r is the output voltage of the k-th fuel cell stack; k d is the equivalent parasitic resistance of the inductance of the k-th fuel cell converter; k L0 is the duty cycle of the k-th fuel cell converter; L0 is the inductance value of the lithium battery converter; i b This is the output current of the lithium battery; v b d0 is the output voltage of the lithium battery; r0 is the equivalent parasitic resistance of the lithium battery converter's inductance; d0 is the duty cycle of the lithium battery converter; v o It is the system output voltage; i o C is the load current; C is the output capacitance.

3. The control method for a fuel cell power system with integrated online impedance spectrum measurement according to claim 2, characterized in that: In S2, the equivalent control transfer function of the fuel cell power system is: ； Where b, c, and a are the coefficients of the equivalent transfer function, , , L is the inductance value. is the reference value for the inductor current, and s is the complex frequency variable.

4. The control method for a fuel cell power system with integrated online impedance spectrum measurement according to claim 3, characterized in that: In S4, the equivalent controlled object of the voltage outer loop controller is: ； Where b0 is the nominal value of b, and f is the total system disturbance. This is a reference value for the inductor current. It represents the derivative with respect to time.

5. The control method for a fuel cell power system with integrated online impedance spectrum measurement according to claim 4, characterized in that: In S4, designing the extended state observer includes the following steps: Define state variables That is, the designed extended state observer tracks the system output voltage respectively. and total system disturbance At this point, the equivalent controlled object of the voltage outer loop controller is represented by the state equation as follows: ； in, , , Both are coefficient matrices of the state equations. , , ; and All of these represent the gain of the extended state observer. By appropriately configuring the observer gain, the characteristic polynomial of the extended state observer can be configured to a specific bandwidth. The pole placement problem, namely: ； By selecting the observer bandwidth The gain parameter is directly determined to balance dynamic response speed and noise immunity; therefore, the observer gain matrix is ​​configured as follows: ； Define the reference value for the system output voltage as follows: The difference between the output voltage and the reference voltage is the output voltage tracking error. Therefore: ； In the formula, Indicates output voltage tracking error The derivative; Indicates the output voltage reference value The derivative; Indicates output voltage The derivative; The convergence of the reference voltage tracking error is expressed as: ； in, It is proportional gain; ； in, It is a disturbance estimate.

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