Adaptive control method for fuel cell grid-connected converter based on virtual impedance compensation

Abstract

The application provides a fuel cell grid-connected converter adaptive control method based on virtual impedance compensation. The fuel cell grid-connected converter comprises a fuel cell, a Boost converter and a DC-AC inverter. The output end of the fuel cell is connected to the input end of the Boost converter. The output end of the Boost converter is connected to the DC-AC inverter. The Boost converter is controlled by a compensation control module. The adaptive control method comprises the following steps: injecting disturbance signals with different frequency points to the output side of the fuel cell, and obtaining voltage response and current response; determining impedance values under different frequency points based on the voltage response and the current response; finding the frequency point corresponding to the maximum impedance value in the impedance values under different frequency points as a dominant frequency; determining a virtual impedance and a virtual inductance based on the impedance value of the fuel cell corresponding to the dominant frequency, and determining the duty cycle of the PWM control signal output by the compensation control module based on the virtual impedance and the virtual inductance.

Description

Technical Field

[0001] This invention relates to a power grid system control method, and more particularly to an adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have shown broad application prospects in distributed generation, backup power, and new energy vehicles due to their advantages such as low operating temperature, fast start-up speed, and high energy conversion efficiency. However, practical operating experience shows that PEMFCs, as power sources, have significant low inertia and weak damping characteristics, and their output impedance exhibits complex frequency-dependent characteristics. When connected to the grid via a power electronic converter, especially under conditions of weak grids or drastic load changes, PEMFC grid-connected systems are prone to oscillations and instability.

[0003] In the existing technology, the control of grid-connected systems based on proton exchange membrane fuel cells often uses fixed control parameters. In this process, the dynamic change of the impedance of the proton exchange membrane fuel cell with the operating conditions is ignored. As a result, the grid-connected system based on proton exchange membrane fuel cells has poor dynamic performance and stability under grid disturbances and load changes, and cannot meet the dynamic response requirements of the grid system.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation. By injecting a disturbance signal into the output side of the fuel cell, the virtual impedance of the response is determined, and the duty cycle of the control signal of the fuel cell grid-connected system is determined by the virtual impedance. This achieves active compensation for the low-frequency impedance and negative impedance effects of the proton exchange membrane fuel cell, which can improve the voltage and current dynamic response characteristics of the system under grid disturbances and load changes, enhance the active adaptability of the fuel cell grid-connected system to grid disturbances, and the whole process has high control accuracy, stability and reliability, does not require complex calculation process, and has a wide range of applications.

[0006] This invention provides an adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation. The fuel cell grid-connected converter includes a fuel cell, a Boost converter, and a DC-AC inverter. The output terminal of the fuel cell is connected to the input terminal of the Boost converter, and the output terminal of the Boost converter is connected to the DC-AC inverter. The Boost converter is controlled by a compensation control module.

[0007] The adaptive control method includes the following steps:

[0008] Perturbation signals at different frequencies are injected into the output side of the fuel cell, and the voltage and current responses are obtained.

[0009] The impedance values ​​at different frequencies are determined based on the voltage and current responses.

[0010] Find the frequency point corresponding to the maximum impedance value at different frequency points as the dominant frequency;

[0011] The virtual impedance and virtual inductance are determined based on the impedance value of the fuel cell corresponding to the dominant frequency, and the duty cycle of the PWM control signal output by the compensation control module is determined by the virtual impedance and virtual inductance.

[0012] Furthermore, the duty cycle of the PWM control signal output by the compensation control module is determined specifically by the virtual impedance and virtual inductance, including:

[0013] The voltage compensation amount is determined by virtual resistance and virtual inductance. :

[0014] ;

[0015] in: This represents the virtual impedance of the fuel cell. This represents the virtual inductance of the fuel cell. This indicates the output current of the fuel cell. express The change in;

[0016] Determine the duty cycle compensation amount :

[0017] ;

[0018] in: This represents the theoretical duty cycle of a fuel cell at its steady-state operating point. This represents the actual output voltage of the fuel cell in steady state;

[0019] Determine the duty cycle of the compensation control module output. :

[0020] ;

[0021] in: This indicates the real-time duty cycle of the PI controller output of the Boost converter.

[0022] Furthermore, it is determined by the following method. :

[0023] ;

[0024] in: This represents the virtual resistance at the (k+1)th iteration. This represents the virtual resistance adjustment coefficient. This represents the virtual resistance at step k. This represents the virtual resistance of the fuel cell determined under a disturbance signal.

[0025] Furthermore, it is determined by the following method. :

[0026] ;

[0027] in: This represents the virtual inductance at the (k+1)th iteration. This represents the virtual inductance adjustment coefficient. This represents the virtual inductance at step k. This represents the virtual inductance of the fuel cell determined under a disturbance signal.

[0028] Furthermore, the virtual resistance of the fuel cell is determined under the perturbation signal. for:

[0029] ;

[0030] in: This represents the desired damping ratio. This indicates the DC bus capacitance of the fuel cell output. Let represent the equivalent resistance of the fuel cell, and be the real part of the fuel cell impedance value at the dominant frequency. ; This indicates the desired inherent frequency.

[0031] Furthermore, the virtual inductance of the fuel cell is determined under the perturbation signal. for:

[0032] ;

[0033] in: This indicates the desired inherent frequency. This indicates the DC bus capacitance of the fuel cell output. This represents the equivalent inductance of the fuel cell, and is the imaginary part of the fuel cell impedance value corresponding to the dominant frequency.

[0034] Furthermore, the fuel cell is a proton exchange membrane fuel cell.

[0035] The beneficial effects of this invention are as follows: By injecting a disturbance signal into the output side of the fuel cell, the virtual impedance of the response is determined, and the duty cycle of the control signal of the fuel cell grid-connected system is determined by the virtual impedance. This enables active compensation for the low-frequency impedance and negative impedance effects of the proton exchange membrane fuel cell, which can improve the voltage and current dynamic response characteristics of the system under grid disturbances and load changes, enhance the active adaptability of the fuel cell grid-connected system to grid disturbances, and achieve high control precision, stability and reliability throughout the process. It does not require complex calculations and has a wide range of applications. Attached Figure Description

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0037] Figure 1 This is a schematic diagram of the topology of the present invention.

[0038] Figure 2 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0039] The present invention will be further described in detail below:

[0040] This invention provides an adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation. The fuel cell grid-connected converter includes a fuel cell, a Boost converter, and a DC-AC inverter. The output terminal of the fuel cell is connected to the input terminal of the Boost converter, and the output terminal of the Boost converter is connected to the DC-AC inverter. The Boost converter is controlled by a compensation control module. The compensation control module is an existing PI controller for the Boost converter; that is, the PI controller in the original system can be used.

[0041] The adaptive control method includes the following steps:

[0042] Disturbance signals at different frequencies are injected into the output side of the fuel cell, and the voltage and current responses are obtained. The disturbance signals are injected according to a set period, that is, the corresponding disturbance signals are injected at set intervals, and then subsequent steps are performed to monitor the impedance changes of the fuel cell in real time. The voltage and current responses are realized by existing sensors or instruments, which will not be described in detail here.

[0043] The impedance values ​​at different frequencies are determined based on the voltage and current responses.

[0044] Find the frequency point corresponding to the maximum impedance value at different frequency points as the dominant frequency;

[0045] Based on the impedance value of the fuel cell corresponding to the dominant frequency, virtual impedance and virtual inductance are determined, and the duty cycle of the PWM control signal output by the compensation control module is determined from the virtual impedance and virtual inductance. Using this method, by injecting a disturbance signal into the output side of the fuel cell, the corresponding virtual impedance is determined, and the duty cycle of the control signal for the fuel cell grid-connected system is determined from the virtual impedance. This achieves active compensation for the low-frequency impedance and negative impedance effects of the proton exchange membrane fuel cell, improving the system's voltage and current dynamic response characteristics under grid disturbances and load changes, enhancing the active adaptability of the fuel cell grid-connected system to grid disturbances. Furthermore, the entire process boasts high control precision, stability, and reliability, requires no complex calculations, and has a wide range of applications.

[0046] In this embodiment, the duty cycle of the PWM control signal output by the compensation control module is determined by virtual impedance and virtual inductance, specifically including:

[0047] The voltage compensation amount is determined by virtual resistance and virtual inductance. :

[0048] ;

[0049] in: This represents the virtual impedance of the fuel cell. This represents the virtual inductance of the fuel cell. This indicates the output current of the fuel cell. express The change in current, generally speaking, is due to the fact that the output current of a fuel cell is direct current, thus its change... The value is 0 because, under steady state, when there is a disturbance in the power grid or other factors, the output current of the fuel cell will also change, so the change in its output current will not be 0.

[0050] Determine the duty cycle compensation amount :

[0051] ;

[0052] in: This represents the theoretical duty cycle of the fuel cell at its steady-state operating point. This duty cycle is determined by existing methods based on the output voltage and current of the fuel cell under ideal steady-state conditions. Ideally, the Boost converter, controlled by this duty cycle, can meet the requirements of actual operating conditions. This represents the actual output voltage of the fuel cell in steady state;

[0053] Determine the duty cycle of the compensation control module output. :

[0054] ;

[0055] in: This represents the real-time duty cycle output by the PI controller of the Boost converter. This base duty cycle is the real-time duty cycle determined by the controller of the Boost converter at the current moment based on the actual output voltage and reference voltage of the Boost converter. In the above process, the duty cycle is actively compensated based on the virtual impedance corresponding to the impedance value determined by the disturbance signal, which can significantly improve the voltage and current dynamic response characteristics of the system under grid disturbances and load changes.

[0056] In this embodiment, it is determined by the following method. :

[0057] ;

[0058] in: This represents the virtual resistance at the (k+1)th iteration. This represents the virtual resistance adjustment coefficient. This represents the virtual resistance at step k. This represents the target virtual resistance of the fuel cell determined under the disturbance signal.

[0059] Determined by the following method :

[0060] ;

[0061] in: This represents the virtual inductance at the (k+1)th iteration. This represents the virtual inductance adjustment coefficient. This represents the virtual inductance at step k. This represents the target virtual inductance of the fuel cell determined under the disturbance signal.

[0062] Wherein: the target virtual resistance of the fuel cell determined under the disturbance signal. for:

[0063] ;

[0064] in: This represents the desired damping ratio. This indicates the DC bus capacitance of the fuel cell output. Let represent the equivalent resistance of the fuel cell, and be the real part of the fuel cell impedance value at the dominant frequency. ; This indicates the desired inherent frequency.

[0065] The target virtual inductance of the fuel cell determined under disturbance signals. for:

[0066] ;

[0067] in: This indicates the desired inherent frequency. This indicates the DC bus capacitance of the fuel cell output. This represents the equivalent inductance of the fuel cell, and is the imaginary part of the fuel cell impedance value corresponding to the dominant frequency.

[0068] In fact, and The virtual impedance of the fuel cell, determined based on the disturbance signal, can be directly substituted into the voltage compensation amount. The duty cycle of the response is determined directly through calculations performed in the model. In this situation, excessive duty cycle fluctuations can lead to control instability, resulting in grid oscillations. Therefore, the above process does not directly... and Substitute into voltage compensation amount In the model, it is achieved through the above adaptive smoothing formula, that is: when k=0, the initial state is... and Given the virtual resistance and virtual inductance corresponding to the current dominant frequency, substitute these two values ​​into... and In the calculation model, the corresponding and Then substitute it into the voltage compensation amount. In the model, the duty cycle at this time is obtained. Then and Substitute into and In the model, the corresponding and Iterate in the above manner until... and The value gradually with and To converge, thereby reducing the duty cycle from the current Smooth transition to and The corresponding duty cycle effectively prevents excessive fluctuations in the duty cycle.

[0069] The fuel cell is a proton exchange membrane fuel cell.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. 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 be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation, characterized in that: The fuel cell grid-connected converter includes a fuel cell, a Boost converter, and a DC-AC inverter. The output of the fuel cell is connected to the input of the Boost converter, and the output of the Boost converter is connected to the DC-AC inverter. The Boost converter is controlled by a compensation control module. The adaptive control method includes the following steps: Perturbation signals at different frequencies are injected into the output side of the fuel cell, and the voltage and current responses are obtained. The impedance values ​​at different frequencies are determined based on the voltage and current responses. Find the frequency point corresponding to the maximum impedance value at different frequency points as the dominant frequency; The virtual impedance and virtual inductance are determined based on the impedance value of the fuel cell corresponding to the dominant frequency, and the duty cycle of the PWM control signal output by the compensation control module is determined by the virtual impedance and virtual inductance.

2. The adaptive control method for fuel cell grid-connected converters based on virtual impedance compensation according to claim 1, characterized in that: The duty cycle of the PWM control signal output by the compensation control module, determined by virtual impedance and virtual inductance, specifically includes: The voltage compensation amount is determined by virtual resistance and virtual inductance. : ； in: This represents the virtual impedance of the fuel cell. This represents the virtual inductance of the fuel cell. This indicates the output current of the fuel cell. express The change in; Determine the duty cycle compensation amount : ； in: This represents the theoretical duty cycle of a fuel cell at its steady-state operating point. This represents the actual output voltage of the fuel cell in steady state; Determine the duty cycle of the compensation control module output. : ； in: This indicates the real-time duty cycle of the PI controller output of the Boost converter.

3. The adaptive control method for fuel cell grid-connected converters based on virtual impedance compensation according to claim 2, characterized in that: Determined by the following method : ； in: This represents the virtual resistance at the (k+1)th iteration. This represents the virtual resistance adjustment coefficient. This represents the virtual resistance at step k. This represents the virtual resistance of the fuel cell determined under a disturbance signal.

4. The adaptive control method for fuel cell grid-connected converters based on virtual impedance compensation according to claim 2, characterized in that: Determined by the following method : ； in: This represents the virtual inductance at the (k+1)th iteration. This represents the virtual inductance adjustment coefficient. This represents the virtual inductance at step k. This represents the virtual inductance of the fuel cell determined under a disturbance signal.

5. The adaptive control method for fuel cell grid-connected converters based on virtual impedance compensation according to claim 3, characterized in that: Virtual resistance of the fuel cell determined under disturbance signal for: ； in: This represents the desired damping ratio. This indicates the DC bus capacitance of the fuel cell output. Let represent the equivalent resistance of the fuel cell, and be the real part of the fuel cell impedance value at the dominant frequency. ; This indicates the desired inherent frequency.

6. The adaptive control method for fuel cell grid-connected converters based on virtual impedance compensation according to claim 4, characterized in that: Virtual inductance of a fuel cell determined under disturbance signals for: ； in: This indicates the desired inherent frequency. This indicates the DC bus capacitance of the fuel cell output. This represents the equivalent inductance of the fuel cell, and is the imaginary part of the fuel cell impedance value corresponding to the dominant frequency.

7. The adaptive control method for a fuel cell grid-connected converter based on virtual impedance compensation according to any one of claims 1-6, characterized in that: The fuel cell is a proton exchange membrane fuel cell.

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