Differential power feedback and low-pass inertia method for solving transient problem of virtual synchronous machine

Abstract

The present application relates to the technical field of power electronic converter, and especially relates to a differential power feedback and low-pass inertia method for solving transient problem of virtual synchronous machine, and the method comprises the following steps: obtaining active and reactive power flow of inverter output of virtual synchronous machine; performing small signal linearization processing on the active and reactive power flow to obtain accurate small signal relationship of the virtual synchronous machine; establishing a small signal model of the virtual synchronous machine by using the accurate small signal relationship; and according to the small signal model, adopting differential power feedback and low-pass inertia strategy to suppress transient oscillation of the virtual synchronous machine. The present application can perceive fluctuation and change of active power output of virtual synchronous machine in advance, reduce the bad influence of power error between power instruction and feedback power on inverter output frequency, suppress frequency fluctuation, and improve transient characteristics of virtual synchronous machine.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and in particular to a differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines. 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, and the changing virtual inertia will change the frequency support characteristics of the system. Patent document CN111917133B provides a control method based on the damping effect of a virtual synchronous machine with dynamic virtual impedance, but it requires specific system parameters, and the nonlinearity of dynamically adjusting the virtual impedance is too complex and difficult to implement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronizers.

[0006] The embodiments of the present invention are implemented as follows: The present invention provides a differential power feedback and low-pass inertia method for solving the transient problems of virtual synchronous machines. The method includes: obtaining the active and reactive power flow outputs of the inverter of the virtual synchronous machine; performing small-signal linearization processing on the active and reactive power flow outputs to obtain the precise small-signal relationship of the virtual synchronous machine; establishing a small-signal model of the virtual synchronous machine using the precise small-signal relationship; and suppressing the transient oscillations of the virtual synchronous machine using differential power feedback and low-pass inertia strategies based on the small-signal model. The present invention can detect fluctuations and changes in the active power output of the virtual synchronous machine in advance, reduce the adverse effects of power errors between power commands and feedback power on the inverter output frequency, suppress frequency fluctuations, and improve the transient characteristics of the virtual synchronous machine.

[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. 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 method further includes the following step: performing droop integral control on the virtual synchronous machine based on the reactive power.

[0012] Optionally, the control equation for droop integral control of the virtual synchronous machine based on the output reactive power 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 relation satisfies the following relationship:

[0016] ,

[0017] ,

[0018] ,

[0019] ,

[0020] ,

[0021] ,

[0022] ,

[0023] ,

[0024] ,

[0025] in, This represents the small-signal change in active power. Let be the small-signal change in reactive power, s be the Laplace transform operator, and δ be 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 be the transfer function from the power angle difference between the virtual synchronous machine and the power grid to 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.

[0026] Optionally, the precise small-signal relationship includes a coupling term between the active power and the 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 step of suppressing transient oscillations of the virtual synchronizer using differential power feedback and a low-pass inertia strategy based on the small-signal model includes the following steps:

[0030] Based on the small-signal model, an acceleration feedback path is added between the power command signal and the power output signal of the small-signal model;

[0031] Based on the small-signal model, a low-pass filter is added to the inertial control part of the small-signal model;

[0032] The transient oscillations of the virtual synchronizer are suppressed by using the acceleration feedback path and the low-pass filter.

[0033] Furthermore, the acceleration feedback path can detect fluctuations and changes in output active power in advance, and the low-pass filter can reduce the high-frequency noise brought by the acceleration feedback path, effectively increasing the output damping of the virtual synchronous machine system, ensuring the overall stability and steady-state error-free characteristics of the system, which is beneficial to improving the transient performance of the virtual synchronous machine.

[0034] Optionally, the transfer functions of the acceleration feedback path and the low-pass filter stage respectively satisfy the following relationships:

[0035] ,

[0036] ,

[0037] in, Let be the transfer function of the acceleration feedback path, and s be the Laplace transform operator. The scaling factor for the acceleration feedback path; Let be the transfer function of the low-pass filter stage. This is the bandwidth adjustment coefficient for the low-pass filter stage.

[0038] Furthermore, the adjustable parameters in the transfer functions of the acceleration feedback path and the low-pass filter stage are simple to set and easy to adjust, without introducing uncertainties or nonlinear factors, which helps to improve the stability of the virtual synchronizer.

[0039] Optionally, after adopting the differential power feedback and low-pass inertia strategy, the loop gain of the virtual synchronizer satisfies the following relationship:

[0040]

[0041] in, The loop gain is... The proportionality coefficient is mentioned above. Here, s is the bandwidth adjustment coefficient, 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.

[0042] 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

[0043] 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.

[0044] Figure 1 The flowchart shows the differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to an embodiment of the present invention.

[0045] Figure 2 This is a schematic diagram of a small-signal model according to an embodiment of the present invention;

[0046] Figure 3 This is a Bode diagram of the virtual synchronizer in an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of a differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to an embodiment of the present invention;

[0048] Figure 5 A schematic diagram of the frequency offset curves of a virtual synchronizer according to an embodiment of the present invention and a virtual synchronizer after using the method provided by the present invention;

[0049] Figure 6 This is a schematic diagram of the active power response curve of a virtual synchronizer according to an embodiment of the present invention and using the method provided by the present invention.

[0050] Wherein: 1-Virtual synchronous machine controller, 2-Power transmission model, 3-Acceleration feedback path, 4-Inertial control part. Detailed Implementation

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In an optional embodiment, the present invention performs droop integral control on the virtual synchronous machine with reference to the output reactive power, and the control equation satisfies the following relationship:

[0055]

[0056] 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.

[0057] 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.

[0058] Please see Figure 1 In an optional embodiment, the present invention provides a differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronizers, comprising the following steps:

[0059] S1. Obtain the active and reactive power flow output of the inverter of the virtual synchronous machine.

[0060] 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:

[0061] ,

[0062] ,

[0063] Wherein, P represents the active power, and Q represents the reactive power. 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.

[0064] S2. Perform small-signal linearization on the active and reactive power flows to obtain the precise small-signal relationship of the virtual synchronous machine.

[0065] Specifically, in this embodiment, the precise small-signal relation satisfies the following relationship:

[0066] ,

[0067] ,

[0068] ,

[0069] ,

[0070] ,

[0071] ,

[0072] ,

[0073] ,

[0074] ,

[0075] in, This represents the small-signal change in active power. δ represents the small-signal change in reactive power, 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... The transfer function is defined as the transfer function from the power angle difference between the virtual synchronous machine and the power grid to 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. The transfer function from the power angle difference between the virtual synchronous machine and the power grid to the output reactive power is given. Let be the transfer function from the output voltage to the output reactive power. The transfer function from the grid voltage to the output reactive power is given.

[0076] Furthermore, the precise small-signal relationship includes a coupling term between the active power and the reactive power. Therefore, the precision small-signal relationship is highly accurate and can accurately reflect the real relationship between the various responses of the power control loop of the virtual synchronizer, providing a theoretical basis for subsequent steps.

[0077] S3. Use the precise small-signal relation to establish the small-signal model of the virtual synchronizer.

[0078] Specifically, in this embodiment, please refer to Figure 2The 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.

[0079] 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 not only affected by the set active power command value and the grid frequency, but also by the set reactive power command value and the grid voltage due to active-reactive coupling.

[0080] For further details, please see Figure 3 The traditional virtual synchronous machine, i.e. the virtual synchronous machine that does not use the method provided by the present invention, suffers from a deterioration in phase margin due to the inherent integral element in the active power flow. This causes the amplitude-frequency response curve of the virtual synchronous machine to cross the 0dB line at -40dB / dec, thus worsening the transient performance of the virtual synchronous machine's power control.

[0081] S4. Based on the small-signal model, the transient oscillations of the virtual synchronizer are suppressed by using differential power feedback and low-pass inertia strategies.

[0082] Please see below. Figure 4 S4 specifically includes the following steps:

[0083] S41. Based on the small-signal model, add an acceleration feedback path between the power command signal and the power output signal of the small-signal model.

[0084] Specifically, in this embodiment, the transfer function of the acceleration feedback path 3 satisfies the following relationship:

[0085]

[0086] in, The transfer function of the acceleration feedback path 3 is... It is the scaling factor of the acceleration feedback path 3.

[0087] Furthermore, the proportional coefficient represents the magnitude of the output active power of the virtual synchronizer fed back in the form of acceleration. The larger the proportional coefficient, the greater the magnitude of the output active power of the virtual synchronizer fed back in the form of acceleration, and the stronger the power feedback. Therefore, the power response speed of the virtual synchronizer is faster. Thus, by changing the proportional coefficient, the power response speed of the virtual synchronizer in transient states can be adjusted, thereby improving the stability of the output active power of the virtual synchronizer system in transient states.

[0088] Furthermore, since the acceleration feedback path 3 is located between the power command signal and the power output signal of the small signal model, the proportional coefficient is equivalent to the rate of change of the output active power. By adjusting the proportional coefficient, the rate of change of the output active power of the virtual synchronous machine can be changed. Therefore, the fluctuation and change of the output active power can be detected in advance through the proportional coefficient, and the proportional coefficient can be adjusted according to the actual situation of the output active power waveform of the virtual synchronous machine. This solves the problem that the output active power of the virtual synchronous machine will oscillate greatly when faced with power command or sudden changes in output power during transients.

[0089] S42. Based on the small signal model, a low-pass filter is added to the inertial control part of the small signal model.

[0090] Specifically, in this embodiment, the transfer function of the low-pass filter stage satisfies the following relationship:

[0091]

[0092] in, Let be the transfer function of the low-pass filter stage. This is the bandwidth adjustment coefficient for the low-pass filter stage.

[0093] Furthermore, the bandwidth adjustment coefficient represents a smoothing process performed on the signal passing through the inertial control section 4. By adjusting the bandwidth adjustment coefficient, the bandwidth of the low-pass filter can be adjusted, and the signal frequency in the virtual synchronizer can be selectively filtered out, which is beneficial to improving the stability of the output frequency of the virtual synchronizer system during transients.

[0094] Furthermore, while using the acceleration feedback path 3 to improve the output power stability of the virtual synchronizer system, it also amplifies high-frequency noise in the virtual synchronizer system, thereby affecting the stability of the virtual synchronizer's output frequency. Therefore, the bandwidth adjustment coefficient can be adjusted according to the proportional coefficient, so that without increasing the order of the virtual synchronizer system, the low-pass filter can completely suppress high-frequency noise in the signal passing through the inertial control section 4, maintaining the frequency support characteristics of the virtual synchronizer system and improving the stability of the virtual synchronizer system's output frequency during transients. At the same time, the low-pass filter also effectively increases the output damping of the virtual synchronizer system, ensuring the overall stability and steady-state error-free characteristics of the virtual synchronizer system. Therefore, the low-pass filter can adjust the frequency response characteristics of the virtual synchronizer system, solving the problem of large oscillations in the output frequency caused by power commands or sudden changes in output power during transients.

[0095] S43. The transient oscillation of the virtual synchronizer is suppressed by using the acceleration feedback path and the low-pass filter.

[0096] Specifically, in this embodiment, the acceleration feedback path 3 is used to address the problem of large oscillations in the output active power of the virtual synchronizer caused by sudden changes in power commands or output power during transient states. The low-pass filter is used to address the problem of large oscillations in the output frequency caused by sudden changes in power commands or output power during transient states. Therefore, the acceleration feedback path 3 and the low-pass filter can improve the transient performance of the virtual synchronizer and suppress its transient oscillations.

[0097] Furthermore, after adopting the differential power feedback and low-pass inertia strategy, the loop gain of the virtual synchronizer satisfies the following relationship:

[0098]

[0099] in, The loop gain is... Where ω is the rated angular frequency, and D is the droop factor. This is the equivalent transfer function of the reactive power controller. Since the proportional gain and the bandwidth adjustment factor are adjustable, after adopting the differential power feedback and low-pass inertia strategy, the loop gain of the virtual synchronous machine can be controlled by adjusting the proportional gain and the bandwidth adjustment factor, ensuring that the loop gain of the virtual synchronous machine will not decrease. This is beneficial to improving the overall performance of the virtual synchronous machine and suppressing its transient oscillations.

[0100] Furthermore, the parameters of the acceleration feedback path 3 and the low-pass filter are simple to set and easy to adjust. The controllable adjustment parameters will not increase the uncertainty and nonlinearity factors in the virtual synchronizer system, nor will they weaken the inertia support characteristics of the virtual synchronizer itself.

[0101] The feasibility and superiority of the method provided by this invention will be demonstrated through specific experimental results below.

[0102] Specifically, in this embodiment, please refer to Figure 5 The traditional solution is the virtual synchronous machine, while the solution of this invention is the virtual synchronous machine after using the method provided by this invention. In terms of frequency change, the solution of this invention has a significant advantage in suppressing output frequency oscillations compared to the traditional solution. After the grid-connected power command changes, the frequency change curve of the solution of this invention is smoother than that of the traditional solution. This means that the method provided by this invention also has a good suppression effect on output frequency oscillations, stronger frequency support capability for grid connection, and better grid friendliness. At the same time, the smoother system output frequency is also conducive to suppressing the oscillation of the output active power.

[0103] Specifically, in this embodiment, please refer to Figure 6 In the figure, the dashed line represents the traditional scheme, i.e., the output active power curve corresponding to the virtual synchronizer, while the solid line represents the scheme of the present invention, i.e., the output active power curve corresponding to the virtual synchronizer after using the method provided by the present invention. Figure 5 In the middle, at 0.1s, the active power command shows a step jump of 10kW.

[0104] Furthermore, under grid-connected operation, when the set output active power suddenly changes by 10kW, the output active power curve of the traditional scheme exhibits significant oscillations, with an overshoot reaching an alarming 70%, before gradually stabilizing at 10kW without steady-state error. Excessive oscillations in output active power pose a significant threat to the safe and stable operation of the virtual synchronous machine, potentially causing it to automatically shut down and disconnect from the grid due to overcurrent, or even damaging the power electronic equipment.

[0105] It should be noted that in some cases, the actions described in the specification can be performed in a different order and still achieve the desired result. In this embodiment, the order of steps is given only to make the embodiment clearer and easier to explain, and not to limit it.

[0106] In summary, the method provided by this invention introduces an acceleration feedback path and a low-pass filter into the virtual synchronous machine, and by adjusting the relevant parameters in the acceleration feedback path and the low-pass filter, it achieves early detection of fluctuations and changes in the active power output of the virtual synchronous machine. This accelerates the power response speed and suppresses high-frequency noise, reduces the adverse effects of the power error between the power command and the feedback power on the inverter output frequency, and thus suppresses the oscillations of the output active power and output frequency of the virtual synchronous machine during transients, improving the transient performance of the virtual synchronous machine. Furthermore, the parameter settings of this invention are simple and easy to adjust, making it highly practical. Moreover, the controllable adjustment parameters do not increase the uncertainties, nonlinearities, or order of the virtual synchronous machine system, nor do they weaken the inertia support characteristics of the virtual synchronous machine itself, which is conducive to the further promotion and application of virtual synchronous machines.

[0107] 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 differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines, 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 are subjected to small-signal linearization to obtain the precise small-signal relationship of the virtual synchronous machine. The small-signal model of the virtual synchronizer is established using the precise small-signal relation. Based on the small-signal model, an acceleration feedback path is added between the power command signal and the power output signal of the small-signal model; Based on the small-signal model, a low-pass filter is added to the inertial control part of the small-signal model; The transfer functions of the acceleration feedback path and the low-pass filter stage satisfy the following relationships: ， ， in, Let be the transfer function of the acceleration feedback path, and s be the Laplace transform operator. The scaling factor for the acceleration feedback path; Let be the transfer function of the low-pass filter stage. This is the bandwidth adjustment coefficient for the low-pass filter stage; The transient oscillations of the virtual synchronizer are suppressed by using the acceleration feedback path and the low-pass filter. After adopting differential power feedback and a low-pass inertial strategy, the loop gain of the virtual synchronous machine satisfies the following relationship: ， in, Let J be the loop gain, and J be 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.

2. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 1, characterized in that, 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. 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.

3. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 2, characterized in that, It also includes the following step: performing droop integral control on the virtual synchronous machine based on the reactive power.

4. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 3, characterized in that, The control equations for droop integral control of the virtual synchronous machine based on the reactive power satisfy 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. This represents the actual output reactive power.

5. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 1, characterized in that, The precise small-signal relation satisfies the following relationship: ， ， ， ， ， ， ， ， ， in, This represents the small-signal change in active power. Let be the small-signal change in reactive power, s be the Laplace transform operator, and δ be 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 be the transfer function from the power angle difference between the virtual synchronous machine and the power grid to 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.

6. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 5, characterized in that: The precise small-signal relationship includes a coupling term between the active power and the reactive power.

7. The differential power feedback and low-pass inertia method for solving the transient problem of virtual synchronous machines according to claim 6, 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.

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