Error power low-pass feedforward type virtual synchronous generator transient oscillation suppression method

Abstract

The present application relates to the technical field of power electronic converter, especially to a method for suppressing transient oscillation of error power low-pass feedforward type virtual synchronous generator, the method comprising: obtaining active and reactive power flow power of inverter output of virtual synchronous machine; performing small signal linearization processing on the active and reactive power flow power to obtain accurate small signal relationship of the virtual synchronous machine; establishing small signal model of the virtual synchronous machine by using the accurate small signal relationship; adding parallel low-pass path to error channel of power instruction and power feedback of the virtual synchronous machine according to the small signal model; and suppressing transient oscillation of the virtual synchronous machine by using the parallel low-pass path. The present application enhances the damping of low-frequency power of virtual synchronous machine system by using parallel low-pass path, reduces the oscillation of output active power and output frequency of virtual synchronous machine system, and realizes the suppression of transient oscillation of the virtual synchronous machine. The method is simple, easy to implement and practical.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and in particular to a method for suppressing transient oscillations in a low-pass feedforward virtual synchronous generator with error power. Background Technology

[0002] With the rapid development of distributed power sources, their proportion in the power grid has also increased rapidly. However, this has also brought many challenges, especially the reduction in the inertia of the power system, which leads to excessive maximum frequency deviation during power system transient processes and disrupts the frequency stability of the power grid. In order to enable distributed energy systems to have the same inertia as traditional generators, virtual synchronous machine technology has emerged.

[0003] Virtual synchronous machine (VSM) technology provides voltage source inverter control schemes with inertial support for power grids or isolated microgrids. However, the complex electromagnetic characteristics of VSM technology can lead to significant output active power oscillations and output frequency oscillations when power command steps are triggered or external disturbances occur.

[0004] Currently, there are four main methods for suppressing transient oscillations in the power response of virtual synchronous machines in grid-connected mode: parameter configuration, using varying moments of inertia, increasing virtual impedance, and changing the control structure of the virtual synchronous machine. Patent document CN114552675A provides a transient stability control method and device for grid-connected inverters based on virtual synchronous machines, which uses reactive power feedback to suppress active power oscillations. However, it is prone to coupling between active and reactive power, and the proportional coefficient in the proposed transient compensation power branch is difficult to determine. Patent document CN108418256B provides an adaptive control method for virtual synchronous machines based on output differential feedback. However, this method uses dynamic virtual inertia to weaken the inertia support characteristics of the virtual synchronous machine itself, resulting in higher nonlinearity. The differential feedback loop amplifies the noise in the sampling process, reducing system stability. Patent document CN104734598B provides a virtual synchronous motor control method based on bandpass damped voltage-type converters. The bandpass filter introduced in this method changes the damping characteristics of the virtual synchronous machine, increases the order of the system, easily leads to stability problems, and the parameters are difficult to design. Patent document CN111478365B provides an optimization method and system for the control parameters of a virtual synchronous machine in a direct-drive wind turbine. Increasing the damping coefficient will reduce the dynamic characteristics of the system. Under various constraints in power grids or isolated microgrids, it is difficult to reduce the power and frequency oscillations of traditional virtual synchronous machines when power commands jump or external disturbances occur through core parameter configuration. Patent document CN111917133B provides a control method based on the damping effect of a virtual synchronous machine with dynamic virtual impedance. However, this method has a complex design process, where changing virtual inertia alters the frequency support characteristics of the system. Furthermore, the nonlinearity of dynamically adjusting the virtual impedance is too complex and difficult to implement in practice. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for suppressing transient oscillations in a low-pass feedforward virtual synchronous generator with error power.

[0006] The embodiments of the present invention are implemented as follows: The present invention provides a method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator (VSR). The method includes: obtaining the active and reactive power flow outputs of the inverter of the VSR; performing small-signal linearization on the active and reactive power flow to obtain the precise small-signal relationship of the VSR; establishing a small-signal model of the VSR using the precise small-signal relationship; adding a parallel low-pass path to the error channel between the power command and power feedback of the VSR based on the small-signal model; and using the parallel low-pass path to suppress the transient oscillations of the VSR. The present invention utilizes the parallel low-pass path to enhance the damping of low-frequency power in the VSR system, reducing the oscillations of the output active power and output frequency when the power command or output power changes abruptly, thereby suppressing the transient oscillations of the VSR. This method is simple, easy to implement, and highly practical.

[0007] Optionally, the active and reactive power flows include active power and reactive power, and the active power and reactive power respectively satisfy the following relationships:

[0008] ,

[0009] ,

[0010] Wherein, P represents the active power, and Q represents the reactive power. For active current, It is reactive current. This represents the small-signal change in the d-axis component of the output voltage at the grid connection point. This represents the small-signal change in the q-axis component of the output voltage at the grid connection point.

[0011] Optionally, the following steps may also be included:

[0012] Based on the reactive power, the virtual synchronous machine is subjected to droop integral control, and the control equation satisfies the following relationship:

[0013]

[0014] in, This is the output voltage command. Let be the reactive power droop control coefficient, K be the gain of the integral controller, and s be the Laplace transform operator. This is the rated output voltage. This is the output voltage sample value. This is the reactive power command value. This represents the actual output reactive power.

[0015] Optionally, the precise small-signal relationship includes a coupling term between the active power and the reactive power.

[0016] Optionally, the precise small-signal relation satisfies the following relationship:

[0017] ,

[0018] ,

[0019] ,

[0020] ,

[0021] ,

[0022] ,

[0023] ,

[0024] ,

[0025] ,

[0026] in, This represents the small-signal change in active power. This represents the small-signal change in reactive power. To simplify the algebra, s is the Laplace transform operator, and δ is the power angle difference between the virtual synchronous machine and the power grid. To linearize the power angle difference, E is the output voltage of the virtual synchronizer. This represents the small signal change in the output voltage. This is the grid voltage. This represents a small-signal change in the grid voltage. For the fundamental impedance of the power grid, The line impedance between the grid connection point and the power grid. The line inductance from the virtual synchronizing machine to the power grid is... Let the transfer function be the power angle difference between the virtual synchronous machine and the power grid, which is then used to determine the output active power. Let be the transfer function from the output voltage to the output active power. Let be the transfer function from the grid voltage to the output active power. Let be the transfer function from the power angle difference between the virtual synchronous machine and the power grid to the output reactive power. Let be the transfer function from the output voltage to the output reactive power. Let be the transfer function from the grid voltage to the output reactive power.

[0027] Optionally, the small-signal model includes an active power control loop, a reactive power control loop, a voltage and current dual loop, and an inverter physical model.

[0028] Furthermore, the small-signal model takes into account the coupling between active and reactive power in the virtual synchronous machine power control loop, thus achieving extremely high accuracy.

[0029] Optionally, the transfer function of the parallel low-pass path satisfies the following relationship:

[0030]

[0031] Where G is the transfer function of the parallel low-pass path, and s is the Laplace transform operator. This is the bandwidth adjustment factor for the parallel low-pass path. is the amplitude gain coefficient of the parallel low-pass path.

[0032] Furthermore, the parameters in the transfer function of the parallel low-pass path are simple to set and easy to adjust, and will not introduce nonlinearity or uncertainty issues.

[0033] Optionally, suppressing transient oscillations of the virtual synchronizer using the parallel low-pass path includes the following steps:

[0034] The parallel low-pass path is used to change the suppression effect of different harmonics and interharmonics in the virtual synchronizer, and to increase the active power and frequency response speed of the virtual synchronizer.

[0035] The transient oscillations of the virtual synchronous machine are suppressed by changing the suppression effect of different harmonic and interharmonic powers, and by increasing the response speed of the active power and frequency.

[0036] Optionally, the step of using the parallel low-pass path to change the suppression effect of different harmonic and interharmonic powers in the virtual synchronizer, and to increase the active power and frequency response speed of the virtual synchronizer, includes the following steps:

[0037] The bandwidth adjustment coefficient is used to adjust the power error feedforward filter bandwidth of the virtual synchronizer, thereby improving the suppression effect of different harmonics and interharmonics in the virtual synchronizer.

[0038] The power error response speed of the virtual synchronizer is adjusted by the amplitude gain coefficient, thereby increasing the active power and frequency response speed of the virtual synchronizer.

[0039] Its advantages are that parameter adjustment is simple and easy, and the response characteristics of the high-frequency components of the virtual synchronous machine system are not changed during the adjustment process.

[0040] Optionally, after adding the parallel low-pass path, the loop gain of the virtual synchronizer satisfies the following relationship:

[0041]

[0042] in, The loop gain is... This is the bandwidth adjustment factor for the parallel low-pass path. Here, s is the amplitude gain coefficient of the parallel low-pass path, s is the Laplace transform operator, and J is the virtual moment of inertia. Where ω is the rated angular frequency, and D is the droop factor. Let be the transfer function from the power angle difference between the virtual synchronous machine and the grid to the output active power. This is the transfer function from the output voltage to the output active power of the virtual synchronous machine. Let be the transfer function from the power angle difference between the virtual synchronous machine and the grid to the output reactive power. This is the transfer function from the output voltage to the output reactive power of the virtual synchronous machine. This is the equivalent transfer function of the reactive power controller.

[0043] In summary, the method proposed in this invention connects a low-pass filter in parallel to the error power path of the virtual synchronous machine, and increases the response speed of the virtual synchronous machine's active power and frequency by adjusting the relevant parameters in the low-pass filter. This enhances the system's damping for low-frequency power, reduces the oscillation of the output active power and output frequency when the system faces sudden changes in power command or output power, and thus improves the transient characteristics of the virtual synchronous machine.

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, optional embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of the transient oscillation suppression method for a low-pass feedforward virtual synchronous generator according to an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of a small-signal model according to an embodiment of the present invention;

[0048] Figure 3 This is a Bode diagram of the virtual synchronizer in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the transient oscillation suppression method for a low-pass feedforward virtual synchronous generator according to an embodiment of the present invention;

[0050] Figure 5 This is a virtual synchronizer according to an embodiment of the present invention, and a Bode diagram of the virtual synchronizer after using the method provided by the present invention.

[0051] Wherein: 1-Virtual synchronous machine controller, 2-Power transfer model, 3-Parallel low-pass path. Detailed Implementation

[0052] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, software, or methods have not been specifically described to avoid obscuring the invention.

[0053] Throughout this specification, references to "an embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale.

[0054] It should be noted in advance that, in one alternative embodiment, except for independent descriptions, the same symbols or letters appearing in all formulas have the same meaning and value.

[0055] In an optional embodiment, the present invention performs droop integral control on the virtual synchronous machine based on reactive power, and the control equation satisfies the following relationship:

[0056]

[0057] in, This is the output voltage command. Let be the reactive power droop control coefficient, K be the gain of the integral controller, and s be the Laplace transform operator. This is the rated output voltage. This is the output voltage sample value. This is the reactive power command value. This represents the actual output reactive power.

[0058] Specifically, in this embodiment, droop integral control is performed on the virtual synchronous machine with the output reactive power as a reference. This can stabilize the output voltage of the virtual synchronous machine, facilitate the adjustment of the output reactive power, and help obtain the coupling relationship between the reactive power and active power of the virtual synchronous machine.

[0059] Please see Figure 1 In an optional embodiment, the present invention provides a method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator with error power, comprising the following steps:

[0060] S1. Obtain the active and reactive power flow output of the inverter of the virtual synchronous machine.

[0061] Specifically, in this embodiment, the active and reactive power flows are obtained using the equivalent power transfer model of a traditional virtual synchronous machine and instantaneous power theory. The active and reactive power flows include active power and reactive power, and the active power and reactive power satisfy the following relationships:

[0062] ,

[0063] ,

[0064] Wherein, P represents the active power, and Q represents the reactive power. For active current, It is reactive current. This represents the small-signal change in the d-axis component of the output voltage at the grid connection point. This represents the small-signal change in the q-axis component of the output voltage at the grid connection point.

[0065] S2. Perform small-signal linearization on the active and reactive power flows to obtain the precise small-signal relationship of the virtual synchronous machine.

[0066] Specifically, in this embodiment, the precise small-signal relation satisfies the following relationship:

[0067] ,

[0068] ,

[0069] ,

[0070] ,

[0071] ,

[0072] ,

[0073] ,

[0074] ,

[0075] ,

[0076] in, This represents the small-signal change in active power. This represents the small-signal change in reactive power. To simplify the algebra, δ represents the power angle difference between the virtual synchronous machine and the power grid. To linearize the power angle difference, E is the output voltage of the virtual synchronizer. This represents the small signal change in the output voltage. This is the grid voltage. This represents a small-signal change in the grid voltage. For the fundamental impedance of the power grid, The line impedance between the grid connection point and the power grid. The line inductance from the virtual synchronizing machine to the power grid is... Let the transfer function be the power angle difference between the virtual synchronous machine and the power grid, which is then used to determine the output active power. Let be the transfer function from the output voltage to the output active power. Let be the transfer function from the grid voltage to the output active power. Let be the transfer function from the power angle difference between the virtual synchronous machine and the power grid to the output reactive power. Let be the transfer function from the output voltage to the output reactive power. Let be the transfer function from the grid voltage to the output reactive power.

[0077] Furthermore, the simplified algebra has no specific meaning and is only for ease of writing; the precise small-signal relation includes the coupling term between the active power and the reactive power, therefore the precise small-signal relation is extremely accurate and can accurately reflect the real relationship between the various responses of the power control link of the virtual synchronous machine, providing a theoretical basis for subsequent steps.

[0078] S3. Use the precise small-signal relation to establish the small-signal model of the virtual synchronizer.

[0079] Specifically, in this embodiment, please refer to Figure 2 The small-signal model includes an active power control loop, a reactive power control loop, a voltage-current dual loop, and an inverter physical model. Compared to the simplified models of existing virtual synchronous machines, the small-signal model considers all factors that can affect the active and reactive power, including capacitor voltage, grid voltage, and power angle. Furthermore, unlike previous models that neglected the coupling between active and reactive power, the small-signal model also includes coupling terms. Therefore, the small-signal model is more accurate than the simplified models of existing virtual synchronous machines and can provide a sound theoretical basis for suppressing transient oscillations in the virtual synchronous machine.

[0080] Furthermore, Figure 2 The virtual synchronous machine controller 1 in the text represents the power control stage of the virtual synchronous machine, including the active power control stage and the reactive power control stage. Figure 2 Power transfer model 2 in the text is an expression of the voltage-current dual-loop of the virtual synchronous machine and the physical model of the inverter. It is easy to see that, for the virtual synchronous machine, its active power flow is affected not only by the set active power command value and the grid frequency. In addition to the influence of active and reactive power coupling, it is also affected by the set reactive power command value and the grid voltage.

[0081] For further details, please see Figure 3 , Figure 3 The virtual synchronizer used does not use the method provided by this invention, that is, a traditional virtual synchronizer. Due to the phase lag caused by the inherent integral element in the active power flow, the phase margin of the virtual synchronizer is deteriorated, causing the amplitude-frequency characteristic curve of the virtual synchronizer to cross the 0dB line at -40dB / dec, which worsens the transient performance of the power control of the virtual synchronizer.

[0082] S4. Based on the small-signal model, add a parallel low-pass path to the error channel of the power command and power feedback of the virtual synchronizer.

[0083] Specifically, in this embodiment, please refer to Figure 4 To address the response lag issue in the power control stage of the virtual synchronizer, a parallel low-pass path 3 was added to the error channel between the power command and power feedback of the virtual synchronizer. The transfer function of the parallel low-pass path 3 satisfies the following relationship:

[0084]

[0085] Wherein, G is the transfer function of the parallel low-pass path 3. This is the bandwidth adjustment factor for the parallel low-pass path 3. is the amplitude gain coefficient of the parallel low-pass path 3.

[0086] Furthermore, adding the parallel low-pass path 3 to the error channel between the power command and power feedback of the virtual synchronizer enhances the damping of the virtual synchronizer for low-frequency power. This does not alter the frequency support characteristics of the virtual synchronizer system, nor does it introduce coupling between active and reactive power or reduce the system's dynamic characteristics, thus improving the transient characteristics of the virtual synchronizer. In addition, the parameters of the parallel low-pass path 3 are simple to design, do not introduce uncertainties, are easy to implement, and are highly practical.

[0087] Furthermore, since the parallel low-pass path 3 has the characteristics of low-pass filtering, it can suppress noise in the virtual synchronous system, which is beneficial to improving the transient characteristics of the virtual synchronous machine.

[0088] After adding the parallel low-pass path 3, the output of the parallel low-pass path 3 and the loop gain of the virtual synchronizer satisfy the following relationships:

[0089]

[0090] Where S is the output of the parallel low-pass path 3. This is the power command signal for the virtual synchronizer. This is the power feedback signal of the virtual synchronizer. It is a difference signal;

[0091]

[0092] in, The loop gain is... Where ω is the rated angular frequency, and D is the droop factor. This is the transfer function from the grid voltage to the output reactive power. Since the bandwidth adjustment coefficient and the amplitude gain coefficient are adjustable, after using the parallel low-pass path 3, the loop gain of the virtual synchronizer can be controlled by adjusting these coefficients, ensuring that the loop gain of the virtual synchronizer does not decrease. This is beneficial for improving the overall performance of the virtual synchronizer and suppressing its transient oscillations.

[0093] S5. The transient oscillation of the virtual synchronizer is suppressed by using the parallel low-pass path.

[0094] Specifically, S5 includes the following steps:

[0095] S51. The parallel low-pass path is used to change the suppression effect of different harmonics and interharmonics in the virtual synchronizer, and to increase the active power and frequency response speed of the virtual synchronizer.

[0096] Specifically, S51 includes the following steps:

[0097] S511. The power error feedforward filter bandwidth of the virtual synchronizer is adjusted by the bandwidth adjustment coefficient to improve the suppression effect of different harmonics and interharmonics in the virtual synchronizer.

[0098] Specifically, in this embodiment, the bandwidth adjustment coefficient is the denominator of the transfer function of the parallel low-pass path 3. After the difference signal passes through the parallel low-pass path 3, the difference signal will change in phase due to the change of the bandwidth adjustment coefficient. Since the parallel low-pass path 3 is in the active power control link of the virtual synchronizer, the phase frequency characteristics of the virtual synchronizer will also be affected and thus change.

[0099] Furthermore, according to the Laplace transform principle, the signal in the virtual synchronizer will be shifted to the right in the time domain after passing through the parallel low-pass path 3. If the signal undergoes a phase change in the frequency domain, the phase frequency characteristics of the virtual synchronizer can be adjusted by the bandwidth adjustment coefficient, thereby adjusting the power error feedforward filter bandwidth of the virtual synchronizer. This improves the suppression effect of different harmonics and interharmonics in the virtual synchronizer, enhances the transient performance of the virtual synchronizer, and does not change the response characteristics of the high-frequency components of the virtual synchronizer system during the adjustment process.

[0100] S512. Adjust the power error response speed of the virtual synchronizer by using the amplitude gain coefficient, thereby increasing the active power and frequency response speed of the virtual synchronizer.

[0101] Specifically, in this embodiment, the amplitude gain coefficient is the numerator of the transfer function of the parallel low-pass path 3. After being multiplied by the difference signal, it will affect the amplitude-frequency characteristics of the difference signal. Moreover, since the parallel low-pass path 3 is located in the active power control link of the virtual synchronizer, the amplitude-frequency characteristics of the virtual synchronizer will also be affected and thus change. Therefore, the amplitude-frequency characteristics of the virtual synchronizer can be adjusted by changing the value of the amplitude gain coefficient, thereby adjusting the power error response speed of the virtual synchronizer, increasing the active power and frequency response speed of the virtual synchronizer, which is beneficial to improving the transient performance of the virtual synchronizer, and does not change the response characteristics of the high-frequency components of the virtual synchronizer system during the adjustment process.

[0102] S52. By changing the suppression effect of different harmonic and interharmonic powers, and increasing the response speed of the active power and frequency, the transient oscillation of the virtual synchronous machine is suppressed.

[0103] Specifically, in this embodiment, as can be seen from steps S511 and S512, by adjusting the bandwidth adjustment coefficient and the amplitude gain coefficient in the parallel low-pass path 3, the amplitude-frequency characteristics and phase-frequency characteristics of the virtual synchronizer can be effectively controlled. This not only adjusts the power error feedforward filter bandwidth of the virtual synchronizer, thereby improving the suppression effect on different harmonics and interharmonics, but also adjusts the power error response speed of the virtual synchronizer, increasing the active power and frequency response speed of the virtual synchronizer.

[0104] Furthermore, the bandwidth adjustment coefficient and the amplitude gain coefficient are simple to set and easy to adjust, without introducing nonlinearity or uncertainty issues. This not only solves the response lag problem in the power control stage of the virtual synchronizer, but also does not change the response characteristics of the high-frequency components in the virtual synchronizer, thereby maximizing the improvement of the transient characteristics of the virtual synchronizer and suppressing transient oscillations.

[0105] The feasibility and superiority of the method provided by this invention will be demonstrated through specific experimental results below.

[0106] Specifically, in this embodiment, please refer to Figure 5 Traditional virtual synchronous machines, i.e., those not using the method provided by this invention, have an amplitude-frequency response curve that crosses the 0dB line at -40dB / dec. However, based on the power low-pass feedforward amplitude-frequency response curve, i.e., after adding the parallel low-pass path 3 to the error channel between the power command and power feedback of the virtual synchronous machine, the amplitude-frequency response curve of the virtual synchronous machine crosses the 0dB line at -20dB / dec, significantly improving the phase margin. Moreover, according to automatic control theory, for the open-loop function of a control system, the larger the phase margin reflected in its Bode plot, the lower the overshoot oscillation in its corresponding time-domain response. Therefore, the method provided by this invention can solve the defects of the virtual synchronous machine in power control and suppress the oscillation of output active power and output frequency. Figure 3 and Figure 5 The x-axis and y-axis are labeled the same.

[0107] It should be noted that in some cases, the actions described in the specification can be performed in different orders and still achieve the desired results. In this embodiment, the order of steps is given only to make the embodiment clearer and easier to explain, and is not intended to limit it. Furthermore, the principles not described in detail in this embodiment are common knowledge in the art.

[0108] In summary, the method proposed in this invention, by connecting a low-pass filter in parallel to the error power path of the virtual synchronizer, can effectively enhance the damping of low-frequency power oscillations without altering the system's high-frequency component response characteristics. By enhancing the damping of low-frequency power, it reduces output frequency oscillations during power command or output power abrupt changes, thereby suppressing transient oscillations in the virtual synchronizer and improving its transient characteristics. Furthermore, this invention features simple parameter settings, is easy to adjust, and avoids nonlinear and uncertain issues, making it highly practical.

[0109] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for suppressing transient oscillations in a low-pass feedforward virtual synchronous generator with error power, characterized in that, Includes the following steps: Obtain the active and reactive power flow output of the inverter of the virtual synchronous machine; The active and reactive power flows include active power and reactive power, and the active power and reactive power satisfy the following relationships respectively: ， ， Wherein, P represents the active power, and Q represents the reactive power. For active current, It is reactive current. This represents the small-signal change in the d-axis component of the output voltage at the grid connection point. The small-signal change in the q-axis component of the output voltage at the grid connection point; Based on the reactive power, the virtual synchronous machine is subjected to droop integral control, and the control equation satisfies the following relationship: ， in, This is the output voltage command. Let be the reactive power droop control coefficient, K be the gain of the integral controller, and s be the Laplace transform operator. This is the rated output voltage. This is the output voltage sample value. This is the reactive power command value. Actual output reactive power The active and reactive power flows are subjected to small-signal linearization to obtain the precise small-signal relationship of the virtual synchronous machine. The precise small-signal relation includes a coupling term between the active power and the reactive power, and the precise small-signal relation satisfies the following relationship: ， ， ， ， ， ， ， ， ， in, This represents the small-signal change in active power. This represents the small-signal change in reactive power. To simplify the algebra, s is the Laplace transform operator, and δ is the power angle difference between the virtual synchronous machine and the power grid. To linearize the power angle difference, E is the output voltage of the virtual synchronizer. This represents the small signal change in the output voltage. This is the grid voltage. This represents a small-signal change in the grid voltage. For the fundamental impedance of the power grid, The line impedance between the grid connection point and the power grid. The line inductance from the virtual synchronizing machine to the power grid is... Let the transfer function be the power angle difference between the virtual synchronous machine and the power grid, which is then used to determine the output active power. Let be the transfer function from the output voltage to the output active power. Let be the transfer function from the grid voltage to the output active power. Let be the transfer function from the power angle difference between the virtual synchronous machine and the power grid to the output reactive power. Let be the transfer function from the output voltage to the output reactive power. Let be the transfer function from the grid voltage to the output reactive power; The small-signal model of the virtual synchronizer is established using the precise small-signal relation. According to the small-signal model, a parallel low-pass path is added to the error channel between the power command and power feedback of the virtual synchronizer; The transient oscillations of the virtual synchronizer are suppressed by using the parallel low-pass path.

2. The method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator according to claim 1, characterized in that: The small-signal model includes an active power control loop, a reactive power control loop, a voltage and current dual loop, and an inverter physical model.

3. The method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator according to claim 1, characterized in that, The transfer function of the parallel low-pass path satisfies the following relationship: ， Where G is the transfer function of the parallel low-pass path, and s is the Laplace transform operator. This is the bandwidth adjustment factor for the parallel low-pass path. is the amplitude gain coefficient of the parallel low-pass path.

4. The method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator according to claim 3, characterized in that, Suppressing transient oscillations of the virtual synchronizer using the parallel low-pass path includes the following steps: The parallel low-pass path is used to change the suppression effect of different harmonics and interharmonics in the virtual synchronizer, and to increase the active power and frequency response speed of the virtual synchronizer. The transient oscillations of the virtual synchronous machine are suppressed by changing the suppression effect of different harmonic and interharmonic powers, and by increasing the response speed of the active power and frequency.

5. The method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator according to claim 4, characterized in that, The method of using the parallel low-pass path to modify the suppression effect of different harmonics and interharmonics in the virtual synchronizer, and to increase the active power and frequency response speed of the virtual synchronizer, includes the following steps: The bandwidth adjustment coefficient is used to adjust the power error feedforward filter bandwidth of the virtual synchronizer, thereby improving the suppression effect of different harmonics and interharmonics in the virtual synchronizer. The power error response speed of the virtual synchronizer is adjusted by the amplitude gain coefficient, thereby increasing the active power and frequency response speed of the virtual synchronizer.

6. The method for suppressing transient oscillations of a low-pass feedforward virtual synchronous generator according to claim 3, characterized in that, After adding the parallel low-pass path, the loop gain of the virtual synchronizer satisfies the following relationship: ， in, The loop gain is... This is the bandwidth adjustment factor for the parallel low-pass path. Here, s is the amplitude gain coefficient of the parallel low-pass path, s is the Laplace transform operator, and J is the virtual moment of inertia. Where ω is the rated angular frequency, and D is the droop factor. Let be the transfer function from the power angle difference between the virtual synchronous machine and the grid to the output active power. This is the transfer function from the output voltage to the output active power of the virtual synchronous machine. Let be the transfer function from the power angle difference between the virtual synchronous machine and the grid to the output reactive power. This is the transfer function from the output voltage to the output reactive power of the virtual synchronous machine. This is the equivalent transfer function of the reactive power controller.

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