A high stability control method for power grid simulator
By embedding virtual impedance characteristics and dynamically adjusting the integral gain in the power grid simulator, the problems of self-stability and interactive stability of the power grid simulator are solved, achieving high-stability control, reducing costs, and improving flexibility and applicability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI JIAOTONG UNIV
- Filing Date
- 2026-02-12
- Publication Date
- 2026-08-04
AI Technical Summary
Existing power grid simulators suffer from self-stability and interactive stability issues under virtual admittance control. Changes in virtual impedance characteristics can lead to self-instability, and existing methods are costly, inflexible, or introduce simulation errors.
By embedding virtual impedance characteristics into the integral controller of the voltage controller module, a controller structure of Ki×Zvir_ref(s) / s is formed. The integral gain Ki is dynamically adjusted. Combined with impedance networks A and B, the amplitude of the virtual impedance is ensured to be no higher than the physical impedance. This decouples the internal control dynamics of the power grid simulator from the virtual impedance characteristics. Furthermore, the lower boundary of the physical impedance is provided through impedance network B, thereby improving the interaction stability.
The self-stability and interactive stability with the measured object of the power grid simulator under different impedance conditions are realized, avoiding the high cost and simulation error of traditional methods, and improving the applicability and ease of engineering use of the method.
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Figure CN122052130B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power electronics technology, and more specifically, to a high-stability control method for a power grid simulator. Background Technology
[0002] With the increasing number of power electronic converters connected to modern power grids, the interaction stability between converters and the grid is receiving growing attention. For converters, their grid-connected stability changes with variations in grid impedance conditions, thus requiring verification during actual operation. To meet these stability testing needs, existing research has proposed grid simulators with impedance simulation capabilities.
[0003] Existing power grid simulators typically employ virtual impedance control or virtual admittance control to simulate impedance. Considering the often inductive nature of power grid impedance, virtual impedance control introduces a differentiating element during implementation, which can easily lead to high-frequency noise amplification. In contrast, virtual admittance control can simulate inductive impedance without introducing differential operations, and therefore has gained wider application. However, the paper "Self-Stability Analysis of Dual-Frequency-Band Grid Impedance Emulator" points out that virtual admittance control introduces coupling between the virtual impedance characteristics and the internal control dynamics of the power grid simulator. When the virtual impedance characteristics change, virtual admittance control may cause self-instability in the power grid simulator. The paper "Issues of Impedance Emulation of Converter-Based Grid Emulator for LVRT Test" aims to ensure self-stability by limiting the range of virtual impedance characteristics, but the internal coupling introduced by virtual admittance control still exists, and the self-stability problem is not fundamentally solved.
[0004] On the other hand, the interaction stability between the power grid simulator and the object under test is also a significant concern. Due to delays introduced by digital control, sampling, and modulation, the virtual impedance synthesized by the power grid simulator is often non-passive at high frequencies. During stability testing, the non-passive portion of the virtual impedance interacts with the output impedance of the object under test, potentially causing unexpected system instability and hindering the test.
[0005] To improve interaction stability, existing research has shown that the amplitude of the virtual impedance can be reduced, or the amplitude of the output impedance of the test object can be increased. One commonly used stability enhancement method is to transfer some impedance characteristics from the virtual side to the physical side, the so-called "impedance transfer method," described in detail in the paper "The Limitations of Digital Simulation and the Advantages of PHIL Testing in Studying Distributed Generation Provision of Ancillary Services." Another commonly used method is the "feedback filtering method," which introduces a low-pass filter in the current feedback path to attenuate the amplitude of the virtual impedance in the high-frequency range, reported in the paper "Modeling of Asymmetrical Grid Faults for P-HIL Accuracy and Stability Analysis in LVRT Tests." However, because the characteristics of the grid impedance are variable, the "impedance transfer method" requires a large amount of physical impedance to meet the stability requirements under different test conditions, resulting in high cost and poor flexibility. In contrast, the "feedback filtering method" offers some flexibility, but it inevitably introduces additional simulation errors into the feedback path, and these errors cannot be compensated for by closed-loop control. Furthermore, since the output impedance of the object under test is usually unknown, the selection of the cutoff frequency of the low-pass filter often depends on experience or repeated trials, which increases the complexity of engineering implementation.
[0006] In summary, existing stability control methods for power grid simulators have significant limitations, and their flexibility and applicability still need to be improved. Summary of the Invention
[0007] In view of one of the defects in the prior art, the purpose of this application is to provide a high-stability control method for a power grid simulator.
[0008] A first aspect of this application provides a high-stability control method for a power grid simulator, the power grid simulator comprising: a DC power supply port, a switching bridge, an impedance network A, an impedance network B, an AC test port, a virtual admittance control module, a voltage controller module, and a pulse width modulation module; The virtual admittance control module generates a control error signal based on the equivalent port characteristics of the simulated power grid, the output voltage of the impedance network A, and the AC test port current. The voltage controller module generates a modulation signal based on the control error signal and inputs it into the pulse width modulation module to control the switching behavior of the switching bridge. The control method includes: Virtual impedance features are embedded in the integral controller of the voltage controller module. Z vir_ref (s), forming K i × Z vir_ref The controller structure is (s) / s, where K i Let s be the integral gain, and s be the Laplace operator; The integral gain K i Based on the virtual impedance generated by the power grid simulator Z vir (s) and the physical impedance provided by the impedance network B Z phy (s) Dynamically adjust to satisfy the following inequality: in the frequency range where the virtual impedance is non-passive, the amplitude of the virtual impedance is not higher than the amplitude of the physical impedance; .
[0009] Optionally, the switching bridge is used to chop the DC voltage provided by the DC power supply port into a square wave voltage; The impedance network A is used to filter out the high-frequency components in the square wave voltage. The impedance network B is used to form the lower boundary of the amplitude of the physical impedance, and its output is an AC test port for connecting the object under test.
[0010] Optionally, the equivalent port characteristics of the simulated power grid include equivalent voltage characteristics. v ref and equivalent impedance characteristics Z ref (s); The equivalent impedance characteristics Z ref (s) Based on virtual impedance characteristics Z vir_ref (s) and physical impedance characteristics Z phy_ref (s) superimposed; The equivalent impedance characteristics of the simulated power grid under typical power grid conditions. Z ref (s) exhibits resistivity.
[0011] Optionally, the virtual impedance characteristic Z vir_ref (s) is the control reference signal of the power grid simulator; The virtual impedance Z vir(s) is the external impedance characteristic generated by the power grid simulator, and the virtual impedance characteristic. Z vir_ref The relationship between (s) satisfies: ; In the formula, G VCL (s) and Z out (s) represent the closed-loop transfer function and inherent output impedance of the power grid simulator, respectively.
[0012] Optionally, the virtual impedance being non-passive means that the phase of the virtual impedance is not within ±90°.
[0013] Optionally, when the inequality is not satisfied, the integral gain can be reduced. K i To reduce the closed-loop transfer function of the power grid simulator G VCL The magnitude of (s) is reduced, thereby decreasing the magnitude of the virtual impedance. Z vir (s)|, so that the inequality relation is satisfied again.
[0014] Optionally, the physical impedance characteristics of the simulated power grid Z phy_ref (s), used to define the parameters of the impedance network B; The series equivalent impedance of the impedance network B constitutes the physical impedance. Z phy (s), and the physical impedance Z phy (s) should approximate the physical impedance characteristics of the simulated power grid. Z phy_ref (s).
[0015] Optionally, the physical impedance characteristics Z phy_ref The lower limit of (s) is determined by the maximum virtual impedance characteristic to be simulated. Z vir_ref (s) and the minimum allowed integral gain K i To be determined jointly; Wherein, the minimum permissible integral gain K i Closed-loop transfer function of power grid simulator G VCL The minimum allowable bandwidth of (s) is determined.
[0016] Optionally, the physical impedance characteristics Zphy_ref The upper limit of (s) is determined by the equivalent impedance characteristics of the simulated power grid. Z ref (s) is determined, that is Z phy_ref (s) not greater than Z ref (s).
[0017] Optionally, the impedance network A has a low-pass voltage characteristic; the equivalent series impedance amplitude of the impedance network B increases with increasing frequency.
[0018] This application provides a high-stability control method for a power grid simulator. Addressing the self-oscillation problem that may be introduced by virtual admittance control, it decouples the internal control dynamics of the power grid simulator from the virtual impedance characteristics by embedding virtual impedance features in the integral controller of the voltage controller module, thereby ensuring the self-stability of the power grid simulator under different impedance simulation conditions. To address the potential interactive oscillation problem between the power grid simulator and the measured object, an impedance network B is introduced to provide physical impedance. Furthermore, by dynamically adjusting the integral gain of the voltage controller, it ensures that the virtual impedance synthesized by the power grid simulator and the physical impedance satisfy the Nyquist stability criterion, thereby improving the interactive stability between the power grid simulator and the measured object.
[0019] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description
[0020] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a high stability control method for a power grid simulator according to an embodiment of this application.
[0021] Figure 2 This is a block diagram of virtual admittance control in one embodiment of this application; wherein, (a) is a common form of virtual admittance control, and (b) is an equivalent form of virtual admittance control.
[0022] Figure 3 This is the amplitude-frequency characteristic diagram of the closed-loop transfer function of the power grid simulator in one embodiment of this application.
[0023] Figure 4 shows the power topology of the power grid simulator-tested object in one embodiment of this application.
[0024] Figure 5 The following is a simulation waveform diagram of the power grid simulator under no-load operation in one embodiment of this application; wherein, (a) is the virtual impedance characteristic waveform, (b) is the output voltage waveform of the power grid simulator using a common PI controller, and (c) is the output voltage waveform of the power grid simulator using the proposed method.
[0025] Figure 6 The above is an interactive simulation waveform diagram of the power grid simulator and the object under test in one embodiment of this application; wherein, (a) is the waveform without the proposed method, that is, without impedance network B and without dynamic adjustment of integral gain, and (b) is the simulation waveform with the proposed method.
[0026] In the diagram, 1 is the DC power supply port; 2 is the switch bridge; 3 is the impedance network A; 4 is the impedance network B; 5 is the AC test port; 6 is the virtual admittance control module; 7 is the voltage controller module; and 8 is the pulse width modulation module. Detailed Implementation
[0027] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.
[0028] In existing technologies, the self-oscillation problem introduced by virtual admittance control is mainly addressed by limiting the range of virtual impedance characteristics to ensure self-stability. However, the internal coupling introduced by virtual admittance control still exists, and the self-oscillation problem is not fundamentally solved. For the interactive oscillation problem between the power grid simulator and the object under test, existing technologies mainly employ the "impedance transfer method" and "feedback filter." However, since the power grid impedance characteristics are variable, the "impedance transfer method" requires a large number of physical impedances to meet stability requirements under different test conditions, resulting in high cost and poor flexibility. In contrast, the "feedback filtering method" offers some flexibility, but it inevitably introduces additional simulation errors into the feedback path, and these errors cannot be compensated for by closed-loop control. Furthermore, since the output impedance of the object under test is usually unknown, the selection of the low-pass filter cutoff frequency often relies on experience or repeated experiments, increasing the complexity of engineering implementation. Based on the above problems, this application provides a high-stability control method for a power grid simulator to solve the aforementioned issues.
[0029] Reference Figure 1 As shown in one embodiment of this application, a high stability control method for a power grid simulator is provided. The power grid simulator includes: a DC power supply port 1, a switching bridge 2, an impedance network A 3, an impedance network B 4, an AC test port 5, a virtual admittance control module 6, a voltage controller module 7, and a pulse width modulation module 8.
[0030] The virtual admittance control module 6 generates a control error signal based on the equivalent port characteristics of the simulated power grid, the output voltage of the impedance network A3, and the current of the AC test port 5; the voltage controller module 7 generates a modulation signal based on the control error signal and inputs it into the pulse width modulation module 8 to control the switching behavior of the switch bridge 2.
[0031] The control method includes: embedding virtual impedance characteristics in the integral controller of the voltage controller module 7. Z vir_ref (s), forming K i × Z vir_ref The controller structure is (s) / s, where K i Let s be the integral gain, and s be the Laplace operator.
[0032] Integral gain K i Based on the virtual impedance generated by the power grid simulator Z vir (s) and the physical impedance provided by impedance network B4 Z phy (s) Dynamically adjust to satisfy the following inequality: In the frequency range where the virtual impedance is non-passive, the amplitude of the virtual impedance is not higher than the amplitude of the physical impedance. .
[0033] Specifically, firstly, the virtual admittance control module 6 is used to control the voltage characteristics of the simulated power grid. v ref (s) Virtual impedance characteristics Z vir_ref (s), combined with the real-time acquired impedance network A3 output side voltage v out AC test port 5 current i PCC The control error signal reflecting the deviation between the target power grid characteristics and the actual output is calculated; subsequently, the voltage controller module 7 employs a unique... K i × Z vir_ref The controller structure (s) / s, which embeds a virtual impedance feature in the integral controller, uses this structure to process the error signal and generate a modulation signal. This decouples the internal control dynamics of the power grid simulator from the virtual impedance feature, thus ensuring the self-stability of the power grid simulator under different impedance simulation conditions. The modulation signal is converted into a switch drive signal by the pulse width modulation module 8, which ultimately controls the switching behavior of the switch bridge 2 to achieve DC-to-AC power conversion. The integral gain...K i It will be based on the virtual impedance synthesized by the power grid simulator. Z vir (s) and the physical impedance provided by impedance network B4 Z phy (s) Dynamically adjust to ensure that the amplitude of the virtual impedance is not higher than the amplitude of the physical impedance in the frequency range where the virtual impedance is non-passive, thereby improving the interaction stability between the power grid simulator and the object under test.
[0034] The embodiments described above in this application, by embedding the virtual impedance characteristics into the integral controller, actively cancel the coupling effect introduced by the virtual admittance control within the control loop, thereby decoupling the internal control dynamics of the power grid simulator from the external impedance simulation target. This fundamentally ensures the self-stability of the power grid simulator under different virtual impedance conditions; unlike existing technologies, it does not require limiting the value range of the virtual impedance characteristics, thus expanding the range of simulating impedances. Simultaneously, by dynamically adjusting the integral gain... K i Furthermore, relying on impedance network B4, the virtual impedance is made to be non-passive within a frequency range, and the amplitude of the virtual impedance is no higher than the amplitude of the physical impedance, which improves the interaction stability between the power grid simulator and the object under test. It avoids the high cost of traditional impedance transfer methods and the error problems introduced by feedback filtering methods. It does not require accurate identification of the impedance of the object under test, thus improving the applicability and ease of use of the method.
[0035] In this application, the self-stability problem of virtual admittance control is addressed when it is introduced. (Refer to...) Figure 2 As shown in (a), a typical control block diagram for virtual admittance control is presented; refer to Figure 2 As shown in (b), the equivalent control block diagram after its equivalent transformation into a single-loop structure is given. Figure 2 In (b), virtual admittance control introduces 1 / in the forward path. Z vir_ref (s). This means that when the virtual impedance characteristic Z vir_ref When (s) changes, the control loop gain of the power grid simulator also changes. This coupling between the virtual impedance characteristic and the internal control dynamics of the power grid simulator may cause self-stability issues. For example... Z vir_ref When (s) approaches zero, the control loop gain approaches infinity, and the power grid simulator cannot operate stably.
[0036] This application embeds virtual impedance characteristics into the integral controller to form... K i × Z vir_refThe controller structure of (s) / s, such as Figure 1 As shown. Under this control structure, the 1 / introduced by virtual admittance control Z vir_ref (s) can be used with the voltage controller Z vir_ref The terms (s) cancel each other out. At this point, the coupling relationship introduced by the virtual admittance control is eliminated, thereby avoiding the self-instability of the power grid simulator that may be caused by changes in virtual impedance characteristics, and realizing the self-stable operation of the power grid simulator under different impedance simulation conditions.
[0037] In existing research, to ensure the interaction stability between the power grid simulator and the object under test, the following criterion is typically used: the magnitude of the virtual impedance | Z vir (s)| less than the amplitude of the output impedance of the measured object| Z CUT (s)| can be written as the following formula.
[0038] ; However, the above criterion only considers the amplitude relationship and not the phase factor, thus it is somewhat conservative. In reality, when the virtual impedance... Z vir (s) When it is passive, it usually helps to improve the interactive stability of the system. Therefore, it is only necessary to make the amplitude of the non-passive part of the virtual impedance smaller than the amplitude of the output impedance of the object being measured, as shown in the following formula, which is easier to satisfy in practical applications.
[0039] .
[0040] On the other hand, the output impedance of the object being measured Z CUT (s) is often difficult to obtain accurately. Although it can be measured using impedance identification methods, this process typically requires additional perturbation injection, signal measurement, and data processing, making it complex and time-consuming. Furthermore, in some cases, the output impedance amplitude of the measured object is | Z CUT (s) may be small, making it difficult to directly satisfy the above criteria.
[0041] To overcome the above problems, this embodiment introduces an impedance network B4 between the power grid simulator and the object under test, such as... Figure 1 As shown. From the perspective of power grid impedance simulation, the series equivalent impedance of impedance network B4 is... Z phy (s) can be considered as part of the simulated grid impedance; and from the perspective of interactive stability, the series equivalent impedance of impedance network B4 is... Z phy(s) can be considered as part of the output impedance of the measured object, thus representing the amplitude of the unknown output impedance of the measured object. Z CUT (s)| provides a clear lower impedance boundary. Based on this, the original interactive stability criterion can be equivalently rewritten as follows.
[0042]
[0043] This application reduces dependence on physical impedance by dynamically adjusting the integral gain to suppress the amplitude of the non-passive portion of the virtual impedance. Simultaneously, it eliminates the need for a low-pass filter in the feedback path, avoiding simulation errors caused by feedback filtering. Furthermore, by setting up an impedance network B in the power grid simulator to determine the lower boundary of the physical impedance amplitude, the selection of the integral gain can be directly determined based on inequality relationships, avoiding repeated trial-and-error processes. Compared with existing "impedance transfer methods" and "feedback filtering methods," this invention has greater applicability.
[0044] In some specific embodiments of this application, the switch bridge 2 is used to chop the DC voltage provided by the DC power supply port 1 into a square wave voltage; the impedance network A 3 is used to filter out the high-frequency components in the square wave voltage; the impedance network B 4 is used to form the lower boundary of the amplitude of the physical impedance, and its output end is the AC test port 5, which is used to connect the object under test.
[0045] The voltage and current at AC test port 5 are respectively expressed as: v PCC and i PCC .
[0046] In the embodiments described above, the DC voltage is chopped into a square wave voltage by the switching bridge 2, thus converting the energy form. Then, the high-frequency harmonic components in the square wave are filtered out using impedance network A3, forming a sinusoidal voltage. Finally, a clear physical impedance lower limit is set for the entire output through impedance network B4, facilitating adaptive adjustment of the integral gain to limit the amplitude of the non-passive portion of the virtual impedance from exceeding this physical impedance lower limit. The output terminal of impedance network B4 is the AC test port 5.
[0047] In some specific embodiments of this application, the equivalent port characteristics of the simulated power grid include equivalent voltage characteristics. v ref and equivalent impedance characteristics Z ref (s); Equivalent impedance characteristics Z ref (s) Based on virtual impedance characteristics Z vir_ref (s) and physical impedance characteristics Z phy_ref(s) Superposition; under typical power grid conditions, the equivalent impedance characteristics of the simulated power grid. Z ref (s) exhibits resistivity.
[0048] Among them, the equivalent voltage characteristics of the simulated power grid v ref and equivalent impedance characteristics Z ref (s) can be obtained through analytical modeling or numerical frequency sweeping of the simulated power grid.
[0049] In some specific embodiments of this application, virtual impedance characteristics Z vir_ref (s) is the control reference signal of the power grid simulator; virtual impedance Z vir (s) is the external impedance characteristic generated by the power grid simulator, and the virtual impedance characteristic. Z vir_ref The relationship between (s) satisfies: ; In the formula, G VCL (s) and Z out (s) represent the closed-loop transfer function and inherent output impedance of the power grid simulator, respectively.
[0050] Specifically, virtual impedance characteristics are established in the power grid simulator. Z vir_ref (s) (control reference signal) and virtual impedance Z vir The quantification relationship between (s) (the actual synthesized impedance external characteristics) makes the impedance external characteristics actually exhibited by the power grid simulator more accurate. Z vir (s) can control the reference signal Z vir_ref (s) and known internal transit properties G VCL (s) and Z out (s) to perform quantitative description and prediction; combined with adjusting the integral gain K i This approach enhances the stability of virtual impedance amplitude by regulating it, ensuring that the non-passive part of the virtual impedance does not cause interactive oscillations. This enables the control system to synthesize the target impedance based on the internal model and manage its amplitude-frequency characteristics, avoiding the blindness of relying on trial and error in traditional methods.
[0051] Considering the closed-loop transfer function G VCL (s) has low-pass characteristics, such as Figure 3 As shown, the high-frequency attenuation of the amplitude-frequency response becomes more pronounced as the integral gain decreases. Therefore, the low-pass characteristic of the closed-loop transfer function can be adjusted by changing the integral gain, thereby adjusting the virtual impedance. Z vir The high-frequency amplitude of (s) is used to satisfy the interactive stability criterion.
[0052] In some specific embodiments of this application, the virtual impedance is non-passive, meaning that the phase of the virtual impedance is not within ±90°.
[0053] In some specific embodiments of this application, when the inequality is not satisfied, the integral gain is reduced. K i To reduce the closed-loop transfer function of the power grid simulator G VCL The magnitude of (s) is reduced, thereby decreasing the magnitude of the virtual impedance. Z vir (s)|, which makes the inequality relation satisfied again.
[0054] Specifically, within the frequency range where the virtual impedance exhibits non-passivity, when the amplitude of the virtual impedance | Z vir (s)|Amplitude higher than physical impedance| Z phy When (s)|, by reducing the integral gain K i Adjusting the closed-loop transfer function of the power grid simulator reduces the magnitude of the virtual impedance. Z vir (s)|, making the magnitude of the virtual impedance| Z vir (s)| and the magnitude of the physical impedance| Z phy The inequality between (s) is satisfied again.
[0055] In the above embodiments of this application, when the virtual impedance exhibits non-passive characteristics (phase not within ±90°) within a frequency range, the amplitude of the virtual impedance is monitored. Z vir (s)|Amplitude higher than physical impedance| Z phy When (s)|, that is, when the pre-set inequality does not hold, the integral gain K i The dynamic adjustment mechanism is activated by actively reducing the integral gain. K i To weaken the closed-loop transfer function of the power grid simulator G VCL The amplitude of (s) effectively reduces the amplitude of the virtual impedance synthesized by virtual admittance control.Z vir (s)|, ultimately making | Z vir (s)|falls back to no higher than| Z phy The range of (s)| is ensured to ensure that the inequality constraints between the two are satisfied again; unlike existing impedance transfer methods, it does not require the preparation of a large number of physical impedances, which reduces costs and increases flexibility, and also avoids the simulation errors introduced by feedback filtering methods and the problem of relying on experience to select parameters through trial and error.
[0056] It should be noted that the integral gain K i Adjustments are made in a continuous manner to avoid introducing unexpected control dynamics during parameter switching.
[0057] In some specific embodiments of this application, the physical impedance characteristics of the simulated power grid are... Z phy_ref (s), used to define the parameters of impedance network B4.
[0058] The series equivalent impedance of impedance network B4 constitutes the physical impedance. Z phy (s), and physical impedance Z phy (s) should approximate the physical impedance characteristics of the simulated power grid. Z phy_ref (s).
[0059] In some specific embodiments of this application, regarding physical impedance characteristics Z phy_ref The lower limit of (s) is determined by the maximum virtual impedance characteristic to be simulated. Z vir_ref (s) and the minimum allowed integral gain K i To be determined jointly.
[0060] Physical impedance characteristics Z phy_ref The upper limit of (s) is determined by the equivalent impedance characteristics of the simulated power grid. Z ref (s) is determined, i.e., physical impedance characteristics. Z phy_ref (s) is not greater than the equivalent impedance characteristic Z ref (s); Among them, the minimum allowable integral gain K i Closed-loop transfer function of power grid simulator G VCL The minimum allowable bandwidth of (s) is determined.
[0061] It should be noted that the maximum virtual impedance characteristic Z vir_ref (s) and the closed-loop transfer function G VCL The minimum allowed bandwidth of (s) is set by the user according to the test requirements.
[0062] The above embodiments of this application determine the physical impedance characteristics. Z phy_ref The rules for determining the upper and lower limits of (s) are based on the lower limit of physical impedance and the maximum virtual impedance and the minimum allowable control bandwidth of the system (corresponding to the minimum). K i The correlation ensures that, under any preset test scenario, adjustments can be made to ensure compatibility. K i Suppressing the virtual impedance amplitude within the physical impedance boundary ensures interactive stability. Simultaneously, constraining the upper limit of the physical impedance to not exceed the total equivalent impedance of the simulated power grid avoids simulating negative virtual impedance and reduces the risk of interactive instability. Taking a purely inductive negative virtual impedance as an example, its phase is -90 degrees. Any delay in the control system will cause its phase to drop below -90 degrees, i.e., into the non-passive region. At this point, the risk of interactive instability is extremely high and must be avoided.
[0063] In some specific embodiments of this application, impedance network A3 has a low-pass voltage characteristic; the equivalent series impedance amplitude of impedance network B4 increases with increasing frequency.
[0064] In the above embodiments, the impedance network A3 is typically an LC-type filter network, and the impedance network B4 is typically an L-type filter network.
[0065] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.
[0066] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.
[0067] Application Example 1: The power topology of the application example is as follows Figure 4 As shown, the left side represents the power grid simulator, using a real 1 mH inductor as the impedance network B; the right side represents the device under test, which is actually a current-controlled converter using an LCL filter. In this topology, the power grid simulator is used to simulate preset power grid port characteristics and verify whether the device under test can operate stably under preset power grid conditions. System parameters are shown in Tables 1 and 2.
[0068] Table 1 Power grid simulator parameters
[0069] Table 2 Parameters of the object under test
[0070] First, the power grid simulator was run under no-load to verify its self-stability. For example... Figure 5 As shown in (a), the control reference of the power grid simulator, i.e., the virtual impedance characteristic, changes in 0.1 s. If a conventional PI controller is used, the system may become unstable due to the coupling between the virtual impedance characteristic and the internal control dynamics of the power grid simulator. Figure 5 As shown in (b), the port voltage diverges from a three-phase sinusoidal waveform to an oscillating waveform, i.e., self-instability. If the proposed... K i × Z vir_ref (s) / s control structure, then as Figure 5 As shown in (c), the virtual impedance characteristics are completely decoupled from the internal control dynamics of the power grid simulator, and the port voltage waveform remains stable; Next, the interaction stability between the power grid simulator and the device under test (DUT) is verified. When the virtual impedance characteristic increases, the amplitude of the virtual impedance generated by the power grid simulator may be greater than the output impedance amplitude of the DUT. In this case, the Nyquist stability criterion may be violated, and high-frequency interactive instability may occur between the power grid simulator and the DUT. Figure 6 As shown in (a). By inserting impedance network B4 and dynamically adjusting... K i If the Nyquist stability criterion can be guaranteed to be satisfied at all times, then high-frequency oscillations can be avoided, such as... Figure 6 As shown in (b). It should be noted that, Figure 6 (b) shows low-to-medium frequency oscillations, which are inherent properties of the tested object under weak grid conditions and are the expected waveform of the test.
[0071] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.
Claims
1. A high-stability control method for a power grid simulator, characterized in that, The power grid simulator includes: a DC power supply port, a switch bridge, impedance network A, impedance network B, an AC test port, a virtual admittance control module, a voltage controller module, and a pulse width modulation module. The DC power supply port, the switch bridge, the impedance network A, the impedance network B, and the AC test port are connected in sequence; The virtual admittance control module generates a control error signal based on the equivalent port characteristics of the simulated power grid, the output voltage of the impedance network A, and the AC test port current. The voltage controller module generates a modulation signal based on the control error signal and inputs it into the pulse width modulation module to control the switching behavior of the switching bridge. The control method includes: Virtual impedance features are embedded in the integral controller of the voltage controller module. Z vir_ref (s), forming K i × Z vir_ref The controller structure of (s) / s, where K i Let s be the integral gain, and s be the Laplace operator; The integral gain K i Based on the virtual impedance generated by the power grid simulator Z vir (s) and the physical impedance provided by the impedance network B Z phy (s) Dynamically adjust to satisfy the following inequality: in the frequency range where the virtual impedance is non-passive, the amplitude of the virtual impedance is not higher than the amplitude of the physical impedance; 。 2. The high stability control method for a power grid simulator according to claim 1, characterized in that, The switching bridge is used to chop the DC voltage provided by the DC power supply port into a square wave voltage. The impedance network A is used to filter out the high-frequency components in the square wave voltage. The impedance network B is used to form the lower boundary of the amplitude of the physical impedance, and its output is the AC test port for connecting the object under test.
3. The high stability control method for a power grid simulator according to claim 1, characterized in that, The equivalent port characteristics of the simulated power grid include equivalent voltage characteristics. v ref and equivalent impedance characteristics Z ref (s); The equivalent impedance characteristics Z ref (s) Based on virtual impedance characteristics Z vir_ref (s) and physical impedance characteristics Z phy_ref (s) superimposed; The equivalent impedance characteristics of the simulated power grid under typical power grid conditions. Z ref (s) exhibits resistivity.
4. The high stability control method for a power grid simulator according to claim 1, characterized in that, The virtual impedance feature Z vir_ref (s) is the control reference signal of the power grid simulator; The virtual impedance Z vir (s) is the impedance external characteristic generated by the power grid simulator, and the virtual impedance characteristic. Z vir_ref The relationship between (s) satisfies: ； In the formula, G VCL (s) and Z out (s) represent the closed-loop transfer function and inherent output impedance of the power grid simulator, respectively.
5. The high stability control method for a power grid simulator according to claim 1, characterized in that, The virtual impedance is non-passive if and only if its phase is not within ±90°.
6. The high stability control method for a power grid simulator according to claim 1, characterized in that, When the inequality is not satisfied, the integral gain is reduced. K i To reduce the closed-loop transfer function of the power grid simulator G VCL The magnitude of (s) is reduced, thereby decreasing the magnitude of the virtual impedance. Z vir (s)|, so that the inequality relation is satisfied again.
7. The high stability control method for a power grid simulator according to claim 1, characterized in that, The physical impedance characteristics of the simulated power grid Z phy_ref (s), used to define the parameters of the impedance network B; The series equivalent impedance of the impedance network B constitutes the physical impedance. Z phy (s), and the physical impedance Z phy (s) should approximate the physical impedance characteristics of the simulated power grid. Z phy_ref (s).
8. The high stability control method for a power grid simulator according to claim 7, characterized in that, The physical impedance characteristics Z phy_ref The lower limit of (s) is determined by the maximum virtual impedance characteristic to be simulated. Z vir_ref (s) and the minimum allowed integral gain K i To be determined jointly; Wherein, the minimum permissible integral gain K i Closed-loop transfer function of power grid simulator G VCL The minimum allowable bandwidth of (s) is determined.
9. The high stability control method for a power grid simulator according to claim 7, characterized in that, The physical impedance characteristics Z phy_ref The upper limit of (s) is determined by the equivalent impedance characteristics of the simulated power grid. Z ref (s) is determined, that is Z phy_ref (s) not greater than Z ref (s).
10. The high stability control method for a power grid simulator according to claim 1, characterized in that, The impedance network A has a low-pass voltage characteristic; the equivalent series impedance amplitude of the impedance network B increases with increasing frequency.