AC power grid simulation source and control method thereof

Abstract

The invention discloses an alternating current power grid simulation source and a control method thereof. The control method comprises the following steps: acquiring an output voltage of a converter; enabling the output voltage of the converter to pass through a first impedance ratio link to obtain a feedback voltage; a target control voltage is obtained after the virtual electromotive force passes through a second impedance ratio link; and obtaining a modulation voltage according to the feedback voltage and the target control voltage, so as to generate a control signal, control a switching tube of the converter and simulate the broadband impedance characteristic of a power grid. According to the invention, the impedance ratio component is respectively introduced into the acquisition voltage and the virtual electromotive force, and a current loop in a traditional control method is canceled in a mode of obtaining the modulation voltage through the target control voltage and the feedback voltage, so that the tracking error of the current loop on the broadband component is reduced, and the virtual impedance characteristic of a non-working frequency band is ensured.

Description

Technical Field

[0001] This application relates to the field of grid connection technology, and in particular to an AC power grid simulation source and its control method. Background Technology

[0002] With the ever-increasing demand for energy and the intensifying consumption of traditional fossil fuels, the energy crisis is an unavoidable problem facing humanity. To address this crisis, countries worldwide have begun to vigorously develop new energy sources, such as wind power and solar power. my country also attaches great importance to the development of new energy sources. However, wind power and solar power are often connected to the power grid via converters. To avoid significant damage to the stability, security, and power quality of the power grid after these converters are connected, it is necessary to conduct various grid connection standard tests on the new energy converters connected to the grid. This will prevent substandard new energy converters from being connected to the grid.

[0003] In testing renewable energy converters, an AC grid simulation source (ACSource) is essential. While traditional AC grid simulation sources can effectively simulate various scenarios at the power grid frequency (50Hz), verifying the broadband characteristics of renewable energy converters requires an ACSource that simulates the broadband impedance characteristics of the power grid. However, traditional ACSources with virtual impedance control can only guarantee the accuracy of virtual impedance in the power frequency band, while the error in virtual impedance in non-power frequency bands is very large. Summary of the Invention

[0004] This application provides an AC power grid simulation source and its control method to ensure virtual impedance characteristics in non-power frequency bands.

[0005] This application provides a control method for an AC power grid simulation source, wherein the AC power grid simulation source includes a converter, and the AC terminal of the converter is connected to the device under test through a filter impedance; the control method includes:

[0006] Obtain the output voltage of the converter;

[0007] The output voltage of the converter is passed through a first impedance ratio circuit to obtain the feedback voltage.

[0008] The target control voltage is obtained by passing the virtual electromotive force through the second impedance ratio stage;

[0009] The modulation voltage is obtained based on the feedback voltage and the target control voltage to generate a control signal and control the switching transistors of the converter and simulate the wideband impedance characteristics of the power grid.

[0010] In another aspect, this application provides an AC power grid simulation source, which includes a converter, the AC terminal of which is connected to the device under test via a filter impedance; the AC power grid simulation source also includes a control unit configured to execute the steps of the control method of the AC power grid simulation source.

[0011] The AC power grid simulation source and its control method provided in this application introduce impedance ratio components into the acquired voltage and virtual electromotive force respectively, and obtain the modulation voltage through the target control voltage and feedback voltage. This eliminates the current loop in the traditional control method, thereby reducing the tracking error of the current loop in the wideband component and ensuring the virtual impedance characteristics in the non-power frequency band. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of an AC power grid simulation source provided in an embodiment of this application;

[0013] Figure 2 This is a schematic diagram of the control method for an AC power grid simulation source provided in an embodiment of this application;

[0014] Figure 3 This is a schematic diagram of the fitting of the broadband phase compensation stage provided in the embodiments of this application;

[0015] Figure 4 This is a schematic diagram of the impedance sweep frequency of the AC power grid simulation source provided in the embodiments of this application.

[0016] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0018] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] Definitions of relevant variables:

[0020] Virtual electromotive force

[0021] Target control voltage

[0022] Feedback voltage

[0023] Converter output voltage

[0024] Filter impedance

[0025] Virtual impedance

[0026] Load impedance

[0027] DC side capacitor

[0028] Current across the filter impedance

[0029] AC side voltage

[0030] DC bus voltage

[0031] Energy storage battery

[0032] like Figure 1 As shown in the figure, an AC power grid simulation source provided in this application includes a converter, wherein the AC terminal of the converter is connected to a filter impedance. With the device under test Connection. Device under test. This can also be referred to as load impedance. Since AC sources are often used for testing grid-connected equipment, load impedance will be used here. As the device being tested.

[0033] In some examples, the DC terminal of the converter is connected to the energy storage battery B via a positive DC bus and a negative DC bus. A DC bus capacitor is connected between the positive and negative DC buses. .

[0034] In some examples, the specific construction of the converter is not limited here; it can be a two-level construction, a three-level construction, or a cascaded construction.

[0035] like Figure 2 As shown, this application provides a control method for an AC power grid simulation source, which can be referred to in the foregoing section. The control method includes the following steps:

[0036] S11. Obtain the output voltage of the converter;

[0037] like Figure 1 As shown, the sampled output voltage of the converter is .

[0038] S12. The output voltage of the converter is passed through the first impedance ratio circuit to obtain the feedback voltage;

[0039] In some examples, the first impedance ratio element is ;in, For virtual impedance, This is the filter impedance.

[0040] For example, the sampled output voltage of the converter is After impedance ratio stage Then, the feedback voltage is obtained. for .

[0041] S13. The virtual electromotive force is passed through the second impedance ratio stage to obtain the target control voltage;

[0042] In some examples, the second impedance ratio element is ;in, For virtual impedance, This is the filter impedance.

[0043] For example, the virtual electromotive force is The electromotive force E passes through an impedance ratio circuit ( After that, the target control voltage is obtained. for .

[0044] S14. A modulation voltage is obtained based on the feedback voltage and the target control voltage to generate a control signal and control the switching transistors of the converter to simulate the wideband impedance characteristics of the power grid.

[0045] For example, the modulated voltage is modulated by a pulse width modulation (PWM) circuit to obtain the PWM wave of the converter, which is used to control the switching transistors of the converter.

[0046] In this way, by introducing impedance ratio components into the acquired voltage and virtual electromotive force respectively, and obtaining the modulation voltage through the target control voltage and feedback voltage, the current loop in the traditional control method is eliminated, thereby reducing the tracking error of the current loop in the wide frequency range and ensuring the virtual impedance characteristics in the non-power frequency range.

[0047] In some examples, obtaining the feedback voltage by passing the output voltage of the converter through a first impedance ratio circuit includes:

[0048] The output voltage of the converter is sequentially passed through a wideband phase compensation stage and a first impedance ratio stage to obtain the feedback voltage.

[0049] The sampled output voltage of the converter is The output voltage of the converter is then passed sequentially through a wideband phase compensation stage and a first impedance ratio stage to obtain the feedback voltage. for ,in For wideband phase compensation, such as low-pass wideband phase compensation.

[0050] Thus, a wideband phase compensation circuit was further adopted, which improved the accuracy of wideband impedance simulation.

[0051] In some examples, the transfer function of the broadband phase compensation stage includes at least one of the following:

[0052] , , , ;in , , , , , s is the parameter of the transfer function, and s is a complex variable.

[0053] In some examples, the broadband phase compensation stage consists of a filtering stage and a phase compensation stage, that is, the filtering stage and the phase compensation stage are integrated into a unified broadband phase compensation stage, realizing the unification of the two delay stages. The transfer function of the broadband phase compensation stage is used as an example. For example, one part is the low-pass filter stage. The other part is the phase compensation stage: .

[0054] Please refer to Figure 3 To understand this, in some examples, the broadband phase compensation stage is determined in the following way:

[0055] Select the transfer function of the broadband phase compensation stage;

[0056] Select the parameter optimization algorithm that matches the transfer function;

[0057] The amplitude-frequency characteristic curve of the transfer function is fitted to the amplitude-frequency characteristic curve of the lead element using the parameter optimization algorithm to obtain the optimized transfer function.

[0058] The amplitude-frequency characteristics of the optimized transfer function are compared with those of the lead element.

[0059] If the matching degree between the optimized transfer function and the lead element is higher than a preset matching threshold, then the optimized transfer function is used as the transfer function of the broadband phase compensation element; otherwise, a new transfer function for the broadband phase compensation element is selected. It should be noted that "higher than" can mean greater than or equal to, while "lower than" can mean less than; conversely, "lower than" is also possible.

[0060] In some examples, the parameter optimization algorithm for the transfer function matching includes particle swarm optimization (PSO). PSO is an evolutionary computation technique based on swarm intelligence that achieves global optimization by simulating the foraging behavior of bird flocks; specific algorithms can be found in existing technologies.

[0061] In some examples, the degree of matching between the optimized transfer function and the lead element is determined in the following way:

[0062] Calculate the phase difference and amplitude difference between the optimized transfer function and the lead element;

[0063] The phase difference is compared with a preset phase threshold, and the amplitude difference is compared with a preset amplitude threshold to obtain the matching degree between the optimized transfer function and the lead element.

[0064] The transfer function of the broadband phase compensation stage For example, using the particle swarm optimization algorithm, the parameters in this transfer function are... , , , , As the object to be optimized, the amplitude-frequency response curve of the transfer function is fitted with a lead element. The amplitude-frequency response curve is used to achieve wideband phase delay compensation, thereby obtaining suitable parameters. , , , , .

[0065] Based on optimized parameters , , , , The optimized transfer function is obtained and compared with the lead function. The amplitude-frequency characteristics are compared. Within a specific frequency band, if the phase and amplitude deviations are within a certain range, the matching degree is considered high; if the deviations exceed a certain range, the matching degree is considered low. Finally, the transfer function and parameters with high matching degree are used as the broadband phase compensation stage.

[0066] In the example above, the target control voltage Add feedback voltage The modulation voltage is obtained, and after passing through a PWM modulation stage, the PWM waveform of the converter is generated. Ignoring the nonlinear part, the AC side voltage of the converter can be obtained: .

[0067] Calculate the current across the filter impedance considering the current in the filter circuit: .

[0068] Combining the above two equations, we can derive the virtual impedance: As can be seen from this formula, the final virtual impedance exhibited by ACSource is... Its wideband characteristics.

[0069] Reference Figure 4 For clarity, the theoretical design value of the ACSource's internal impedance is shown as the blue curve. When the ACSource is controlled using the traditional virtual impedance method, an impedance sweep of the ACSource yields an output impedance represented by the green curve, which deviates significantly from the theoretical value (blue curve) in both amplitude and phase angle. When the ACSource employs the control method proposed in this application, an impedance sweep of the ACSource yields an output impedance represented by the red curve, which deviates less significantly from the theoretical value (blue curve) in both amplitude and phase angle. This fully demonstrates the effectiveness of the impedance simulation method proposed in this application.

[0070] The preferred embodiments of this application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and spirit of this application shall be within the scope of the claims.

Claims

1. A control method for an AC power grid simulation source, wherein the AC power grid simulation source includes a converter, and the AC terminal of the converter is connected to the device under test through a filter impedance; characterized in that, The control method includes: Obtain the output voltage of the converter; The output voltage of the converter is passed through a first impedance ratio circuit to obtain the feedback voltage. The target control voltage is obtained by passing the virtual electromotive force through the second impedance ratio stage; The modulation voltage is obtained based on the feedback voltage and the target control voltage to generate a control signal and control the switching transistors of the converter and simulate the wideband impedance characteristics of the power grid.

2. The control method according to claim 1, characterized in that, The first impedance ratio element is ;in, For virtual impedance, This is the filter impedance.

3. The control method according to claim 1, characterized in that, The second impedance ratio element is ;in, For virtual impedance, This is the filter impedance.

4. The control method according to claim 1, characterized in that, The step of obtaining the feedback voltage by passing the output voltage of the converter through a first impedance ratio circuit includes: The output voltage of the converter is sequentially passed through a wideband phase compensation stage and a first impedance ratio stage to obtain the feedback voltage.

5. The control method according to claim 4, characterized in that, The broadband phase compensation stage consists of a filtering stage and a phase compensation stage.

6. The control method according to claim 4, characterized in that, The transfer function of the broadband phase compensation stage includes at least one of the following: , , , ;in , , , , , s is the parameter of the transfer function, and s is a complex variable.

7. The control method according to claim 4, characterized in that, The broadband phase compensation stage is determined in the following manner: Select the transfer function of the broadband phase compensation stage; Select the parameter optimization algorithm that matches the transfer function; The amplitude-frequency characteristic curve of the transfer function is fitted to the amplitude-frequency characteristic curve of the lead element using the parameter optimization algorithm to obtain the optimized transfer function. The amplitude-frequency characteristics of the optimized transfer function are compared with those of the lead element. If the matching degree between the optimized transfer function and the lead element is higher than the preset matching threshold, then the optimized transfer function is used as the transfer function of the broadband phase compensation element; otherwise, the transfer function of the broadband phase compensation element is reselected.

8. The control method according to claim 7, characterized in that, The parameter optimization algorithm for transfer function matching includes particle swarm optimization.

9. The control method according to claim 7, characterized in that, The degree of matching between the optimized transfer function and the lead element is determined using the following method: Calculate the phase difference and amplitude difference between the optimized transfer function and the lead element; The phase difference is compared with a preset phase threshold, and the amplitude difference is compared with a preset amplitude threshold to obtain the matching degree between the optimized transfer function and the lead element.

10. An AC power grid simulation source, characterized in that, The AC power grid simulation source includes a converter, the AC terminal of which is connected to the device under test through a filter impedance; the AC power grid simulation source also includes a control unit, which is configured to execute the steps of the control method of the AC power grid simulation source according to any one of claims 1-9.

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