Virtual synchronous machine control method and system for switching rotating speed function based on power difference

Abstract

The invention provides a virtual synchronous machine control method and system for switching the rotating speed function based on power difference, and the method comprises the steps: obtaining the power grid information in a steady state of a power grid, including the output voltage of a converter, the voltage of the power grid, and the output current and power angle at a power balance point of the converter; monitoring the output current of the converter in real time; calculating a parameter k based on the converter output voltage, the power grid voltage and the power angle; judging the product of the output current of the converter and the output current under the parameter k and the power balance point, if the output current of the converter is smaller than the product of the parameter k and the output current under the power balance point, not switching the effect of the power difference on the rotating speed, and if the output current of the converter is larger than the product of the parameter k and the output current under the power balance point, not switching the effect of the power difference on the rotating speed. Switching the effect of the power difference on the rotating speed; and generating a control instruction and transmitting the control instruction to the controller to execute strategy switching.

Description

Technical Field

[0001] The present invention belongs to the technical field of virtual synchronous machine control, and in particular to a virtual synchronous machine control method and system based on switching of the effect of power difference on rotation speed. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Grid-building control technology is aimed at the needs of new power system grid building, and it gives new energy grid building capabilities. It can effectively support the inertia, frequency and voltage of the power grid and improve the stability of the new power system. Among the existing grid-building control strategy schemes, virtual synchronous generator (VSG) control is a mainstream strategy, which simulates the operating mechanism of the synchronous generator to a certain extent. The virtual synchronous generator simulates the rotor motion equation of the synchronous machine and gives the converter similar inertia and damping characteristics as the synchronous machine. When a power grid fails, it usually causes fluctuations in voltage and frequency, and the large phase angle jumps that may be accompanied by the fault cannot be ignored. Referring to the requirements of the British GC0137 standard, the grid-building converter should tolerate large phase jumps and have instantaneous support capabilities under extreme fault conditions.

[0004] When the grid phase angle changes greatly, for the virtual synchronous machine control, due to its grid-type voltage source external characteristics, the inverter output voltage phase can be regarded as constant at this time. Therefore, the system power angle will also change greatly, and transient instability similar to that of the synchronous machine will occur, which will seriously endanger the safe and stable operation of the power system.

[0005] The power angle stability of a synchronous machine refers to the ability of a synchronous generator to maintain its power angle within a stable range after being disturbed. Once the disturbance is too large, the power angle will become unstable, which will lead to non-periodic instability or oscillation instability of the synchronous generator. The power angle curve of the synchronous machine is as follows: Figure 1 The virtual synchronous machine control enables the grid-side converter to have the external characteristics of the synchronous machine, but at the same time it will also face the same power angle stability problem under the large-amplitude phase angle jump disturbance of the power grid as the synchronous machine.

[0006] The grid fault in the prior art is a voltage drop. The phase angle does not change at the moment of the fault. The subsequent change in the power angle is caused by the unbalanced power caused by the voltage drop. Its strategy will not change the position of the stable operation balance point and the unstable operation balance point.

[0007] However, when a large jump in the phase angle of the power grid occurs and the voltage amplitude does not change during the fault, how to ensure the safe and stable operation of the power system is a technical problem to be solved by this application. Summary of the invention

[0008] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a virtual synchronous machine control method based on switching the effect of power difference on speed, which can adaptively adjust the power angle stable operating point. After the strategy takes effect, the power angle of the operating balance point changes from the original δ to (180°-δ), which can improve its power angle stability.

[0009] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0010] In a first aspect, a virtual synchronous machine control method based on switching of the effect of power difference on speed is disclosed, comprising:

[0011] Obtain grid information under steady state, including: converter output voltage, grid voltage, converter output current and power angle at power balance point;

[0012] Real-time monitoring of converter output current;

[0013] Calculate parameter k based on converter output voltage, grid voltage and power angle;

[0014] Determine the size of the product of the converter output current and the parameter k and the output current at the power balance point. If the converter output current is less than the product of the parameter k and the output current at the power balance point, there is no need to switch the effect of the power difference on the speed, and generate a control instruction f(I)=1. If the converter output current is greater than the product of the parameter k and the output current at the power balance point, generate a control instruction f(I)=-1, and switch the effect of the power difference on the speed.

[0015] The generated control instruction f(I) is transmitted to the active power-frequency branch of the controller to execute the action effect switching.

[0016] The VSG output voltage phase angle is obtained by integrating the VSG control output frequency (ie, rotational speed), and the phase angle is output to the converter.

[0017] As a further technical solution, the calculation formula of the parameter k is:

[0018]

[0019] Among them, E is the converter output voltage, U is the grid voltage, and δ1 is the power angle.

[0020] As a further technical solution, if the converter output current is less than the product of parameter k and the output current at the power balance point, the function f(I)=1; if the converter output current is greater than the product of parameter k and the output current at the power balance point, f(I)=-1.

[0021] As a further technical solution, the switching power difference has an effect on the speed, and the mathematical expression for adjusting the active power-frequency branch is:

[0022]

[0023] As a further technical solution, the output current of the converter is greater than the product of the parameter k and the output current at the power balance point, that is, when the power angle jumps to the unstable operating area through the output current detection, the effect of the switching power difference on the speed can adaptively adjust the power angle stable operating point, and the power angle of the stable operating point changes from δ1 to 180°-δ1.

[0024] As a further technical solution, the controller executes the output phase after strategy switching. The phase is obtained by integrating the output frequency of the VSG control and is output to the coordinate transformation unit together with the dq components of the converter output voltage output by the voltage and current dual closed-loop control for conversion from two-dimensional coordinates to three-dimensional coordinates. After that, a PWM control signal is generated and transmitted to the converter.

[0025] The VSG output voltage phase angle is obtained by integrating the VSG control output frequency (speed).

[0026] The output of the voltage and current double closed loop of the grid-type converter is the dq component of the converter output voltage. The overall control goal is to make the voltage value on the filter capacitor equal to its reference value. This goal is achieved through the PI controller and the current and voltage double loop feedback. This part belongs to the prior art and will not be described in detail here.

[0027] As a further technical solution, when obtaining the power angle of the power grid in a steady state, the power angle is calculated through the circuit parameters of the grid-connected converter, and the grid-connected converter circuit parameters involved include: converter output power, reactance, converter output voltage and grid voltage.

[0028] As a further technical solution, when calculating the converter output current at the power balance point:

[0029]

[0030] Among them, E is the converter output voltage, U is the grid voltage, δ1 is the power angle, and X is the reactance.

[0031] In a second aspect, a virtual synchronous machine control system based on switching of the effect of power difference on speed is disclosed, comprising:

[0032] The data acquisition module is configured to: acquire grid information in a steady state, including: converter output voltage, grid voltage, converter output current and power angle at a power balance point;

[0033] The parameter k calculation module is configured to: monitor the output current of the converter in real time;

[0034] Calculate parameter k based on converter output voltage, grid voltage and power angle;

[0035] The judgment module is configured to: judge the size of the product of the converter output current and the parameter k and the output current at the power balance point; if the converter output current is less than the product of the parameter k and the output current at the power balance point, there is no need to switch the effect of the power difference on the speed; if the converter output current is greater than the product of the parameter k and the output current at the power balance point, switch the effect of the power difference on the speed;

[0036] The switching control module is configured to generate a control instruction and transmit it to the controller to execute the strategy switching.

[0037] One or more of the above technical solutions have the following beneficial effects:

[0038] The technical solution of the present invention adopts an improved virtual synchronous machine control strategy based on the switching effect of power difference on speed, and uses the output current as the switching criterion to adaptively adjust the power angle stable operating point according to the corresponding relationship between power angle and current, so that the power angle unstable operating point under the traditional VSG control strategy is stabilized at a new power angle stable operating point, and can be stabilized at the initial stable operating point after the fault is removed. This is of great significance to improving the power angle stability of VSG type converters.

[0039] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] Figure 1 It is a schematic diagram of the power angle curve;

[0042] Figure 2 This is a simplified diagram of the grid-connected circuit of a VSG type converter;

[0043] Figure 3 It is the active power-frequency control diagram;

[0044] Figure 4 It is the power angle operation status analysis diagram;

[0045] Figure 5 Active power-frequency control diagram of VSG control strategy to change the effect of power difference on speed;

[0046] Figure 6 is the circuit equation vector diagram;

[0047] Figure 7 (a) is a schematic diagram showing the switching of the effect of the improved strategy;

[0048] Figure 7(b) is an overall schematic diagram of the switching effect of the improved strategy;

[0049] Figure 8 It is a schematic diagram of the simulation results of the traditional VSG control strategy under the phase jump of -140°;

[0050] Fig. 9 Schematic diagram of simulation results of improved virtual synchronous machine control strategy under phase jump of -140°;

[0051] Fig.10 Schematic diagram of simulation results of improved virtual synchronous machine control strategy under phase jump of -60°;

[0052] Fig.11 Flow chart of a sub-method of an embodiment of the present invention;

[0053] Fig.12 A block diagram of a subsystem of an embodiment of the present invention. DETAILED DESCRIPTION

[0054] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0055] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0056] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0057] The new energy grid-connected inverter based on power electronic equipment has high controllability with synchronous dynamic and flexible adjustment. By real-time monitoring of whether the converter output current related to the power angle reaches the current range corresponding to the unstable operation area, the control strategy is improved. When the output current detects that the power angle jumps to the unstable operation area, the effect of switching the power difference on the speed is switched. The power angle stable operation point can be adaptively adjusted. The power angle of the stable operation point changes from δ1 to 180°-δ1, so that the fault state in the original unstable operation area is stabilized at the new stable operation point, thereby improving the power angle stability of the system.

[0058] After switching the effect of the power difference on the speed based on the amplitude of the output current as the judgment condition, the new effect of the power difference on the speed will cause the power angle of the stable operating point to change from δ1 to 180°-δ1.

[0059] In order to better express the technical solution of the embodiment of the present application, the stability of the VSG power angle under phase angle jump is first analyzed:

[0060] The power angle stability of VSG grid-type converter is analyzed. To simplify the analysis, the converter is simplified to a controlled voltage source, and the resistance part of the line and filter inductor is ignored. The simplified circuit diagram can be obtained as shown in the figure below: Figure 2 As shown in the figure. is the converter output voltage, U∠θ is the grid voltage, X represents the total reactance, and I is the converter output current.

[0061] The VSG active power-frequency branch realizes self-synchronization by simulating the synchronous generator rotor motion equation. The mathematical expression of the active power-frequency branch is:

[0062]

[0063] In the formula, ω0, P ref are the set values ​​of frequency and active power respectively, J is the moment of inertia, D is the damping coefficient, P is the VSG control output power, and ω is the VSG control output frequency.

[0064] Active power-frequency control diagram Figure 3 shown.

[0065] The power angle δ is defined as the voltage at the output of the converter Phase difference of grid voltage U∠θ Converter output active power P:

[0066]

[0067] Figure 4 It is the power angle operation state analysis diagram. Assume that the fault is a phase jump on the grid side, the voltage amplitude remains unchanged, the voltage amplitude, phase and total line impedance of the converter output remain unchanged, and the phase jump does not trigger the current limiting protection strategy. Figure 4 From equation (2), we can see that there are two power balance points a and a' on the power angle characteristic curve. When a power angle disturbance occurs in the operating state at point a, the operating state jumps to point b. At this time, P>P ref , according to formula (1), dω / dt<0, the power angle will decrease. Combined with the equal area rule, the inverter will eventually stabilize and operate at point a again. When a power angle disturbance occurs in the operating state at point a', the operating state jumps to point b'. At this time, P <P ref , dω / dt>0, the power angle increases and loses synchronization. According to the analysis, under the traditional VSG strategy, point a is a stable operating point, point a' is an unstable operating point, and when the phase angle jumps to the operating point after point a', the power angle of the converter will be unstable.

[0068] Embodiment 1

[0069] The characteristics of the converter are determined by its control strategy. To address the problem of large phase angle jumps, the present invention proposes an improved VSG control strategy and adaptively adjusts the power angle stable operating point by real-time switching of the power difference effect on the speed, thereby solving the problem of power angle instability of the converter under large phase angle jump faults.

[0070] The present application uses the amplitude of the output current as a judgment condition to switch the effect of the power difference on the speed, thereby establishing a new power angle stable operating point after a large phase angle jump fault, rather than enhancing the system's ability to recover to the initial stable operating point.

[0071] Figure 4 The inability of point b' to operate stably is caused by the VSG active power-frequency control strategy. From formula (1), we can know that P <P ref When dω / dt>0, the power angle further increases. If the VSG control strategy is switched when the power angle jumps to the unstable operating point, Figure 2 When the unstable point is reached, the rotor motion equation is changed, the effect of the switching power difference on the speed is adjusted, and the mathematical expression of the active power-frequency branch is adjusted as follows:

[0072]

[0073] The adjustment effect of this formula is the effect of the switching power difference on the speed. Figure 5 Its function has been introduced in the subsequent content, and text description has been supplemented.

[0074] Figure 5 This is the active-frequency control diagram of the VSG control strategy after changing the effect of the power difference on the speed. This strategy changes the effect of the power difference on the VSG speed, and the operating state jumps to Figure 4 At point b', P <P ref , dω / dt<0, the power angle will decrease, and finally it will run stably at point a'. Under this strategy, point a' is transformed from an unstable operating point to a stable operating point, which improves the power angle stability of the VSG converter.

[0075] Effect switching conditions

[0076] Real-time detection of the instantaneous phase of the converter and the power grid to obtain the real-time changing power angle information is directly used as the basis for judging the switching effect of the power difference on the speed. However, it is difficult to monitor the phase information in real time when the power grid is in operation. The present invention starts with other electrical quantities that change in real time with the power angle, and uses the converter output current as the criterion for switching the effect of the power difference on the speed.

[0077] Depend on Figure 2 , according to Ohm's law, the circuit satisfies the equation:

[0078]

[0079] In formula (4), Converter output voltage is the grid voltage U∠θ, represents the total reactance, is the output current of the converter. The vector diagram of formula (4) is as follows Figure 6 shown.

[0080] According to formula (4), Figure 6 and the cosine theorem,

[0081]

[0082] It can be seen from formula (1) that, assuming that the fault is a phase jump on the grid side, the voltage amplitude remains unchanged, the voltage amplitude, phase and total line impedance of the converter output remain unchanged, E, U and X are considered unchanged, and when δ∈[0,π], I increases monotonically with the increase of δ. When δ increases to the unstable operation area after point a', I will also be greater than the critical current I2 corresponding to point a'. Therefore, I>I2 can be used as the criterion for switching the action effect.

[0083] When δ>δ2, the controller issues a switching instruction on the effect of the power difference on the speed, and the corresponding current criterion is I>I2.

[0084] At point a, in the stable operating state, the output current is:

[0085]

[0086] When the operating state is at point a', the output current is:

[0087]

[0088] From formula (6) and formula (7), we can get:

[0089]

[0090] When I>I2,

[0091]

[0092] At this time, δ>δ2, the controller issues a switching instruction for the effect of power difference on speed. The schematic diagram of the effect switching is shown in Figure 7. After the effect is switched, the operating state jumps to Figure 4 When the system reaches point b', the power angle will decrease and eventually it will run stably at point a'. After the fault is cleared, δ<δ2, the controller will issue an instruction to switch to the original strategy, and the system can run stably at point a again.

[0093] By adopting an improved virtual synchronous generator (VSG) control strategy that switches the effect of power difference on speed, according to the corresponding relationship between power angle and current, the output current is used as the switching criterion to adaptively adjust the stable operation point of the power angle, so that the unstable operation point of the power angle under the traditional VSG control strategy is stabilized at the new stable operation point of the power angle, and it can stably operate at the initial stable operation point again after the fault is removed. This is of great significance for improving the power angle stability of VSG converters.

[0094] See the appendix Fig.11 、 12 As shown, specifically, this embodiment discloses a virtual synchronous machine control method based on the switching of the effect of power difference on speed, including:

[0095] Obtain the grid information under grid steady state, including: the output voltage E of the converter, the grid voltage U, the output current I1 at the power balance point of the converter, and the power angle δ1;

[0096] Real-time monitor the output current I of the converter;

[0097] Based on the output voltage E of the converter, the grid voltage U, and the power angle δ1, according to the formula Obtain k;

[0098] Judge the magnitude relationship between the output current of the converter and the product of k and the output current I1 at the power balance point. If I < kI1, there is no need to switch the effect of power difference on speed. If I > kI1, switch the effect of power difference on speed;

[0099] Generate an instruction and transmit it to the controller to execute the strategy switch.

[0100] Comparison of theoretical calculation results: Compared with the traditional virtual synchronous machine control strategy, the power angle stability of the grid-connected system under the improved virtual synchronous machine control strategy based on the switching of the effect of power difference on speed has been improved. Under the grid-connected converter circuit parameters shown in Table 1, the power angle in the stable operation state when no fault occurs can be obtained from Equation (2).

[0101] Table 1 Grid-connected converter circuit parameters

[0102]

[0103]

[0104] The output current I1 and k at this time can be obtained from Equation (6) and Equation (8).

[0105]

[0106] kI1 = 1.69 (13)

[0107] (1) When a -60° phase jump occurs in the grid fault

[0108] The power angle δ jumps from 23.79° to 83.79° at this time, and the output current can be obtained from Equation (5).

[0109]

[0110] At this time, I < kI1, there is no need to switch the effect of the power difference on the rotational speed, and the system can automatically return to the original power angle stable operating point (δ1 = 23.79°).

[0111] (2) When a -140° phase jump occurs during a power grid fault

[0112] The power angle δ jumps from 23.79° to 163.79° at this time, and the output current can be obtained from Equation (5).

[0113]

[0114] At this time, I > kI1, switch the effect of the power difference on the rotational speed, and the system can be stably adapted to the new power angle stable operating point (δ2 = 180° - 23.79° = 156.21°).

[0115] δ2 = 180° - 23.79° = 156.21° is the calculation process Figure 4 At point a' in is the only stable operating point on the power angle curve after switching the effect of the power difference on the rotational speed, and it is symmetric with point a (δ1 = 23.79°) about δ = 90°. The effect of the power difference on the rotational speed (Equation (3)) will make P > P ref when dω / dt > 0, the power angle increases, P < P ref when dω / dt < 0, the power angle decreases. Thus, the operating state with the power angle jumping to 163.79° finally stabilizes at δ2 = 156.21°. Since P = P at δ2 ref the power difference is zero, and the steady state can only be reached at this point.

[0116] Simulation comparison:

[0117] Taking the traditional VSG control strategy as the comparison object, the improved virtual synchronous generator control strategy proposed in the present invention based on switching the effect of the power difference on the rotational speed can significantly improve the power angle stability of the system. As Figure 8 shown, after a -140° phase jump occurs in the power grid at t = 3s, neither the power angle nor the VSG rotational speed of the system can remain stable under the traditional VSG control strategy, and they cannot return to stability after the fault is removed at t = 10s.

[0118] As Fig. 9As shown in the figure, after the grid fault occurs at t=3s and the phase jump of -140° occurs, the power angle δ jumps from 23.79° to 163.79°, and the control signal changes from 1 to -1. At this time, the effect of the power difference on the speed is switched, and the system stabilizes at the new power angle stable operation point. At t=10s, the fault is removed, the control signal changes from -1 to 1, and the initial control strategy is switched. The system can stabilize at the original power angle stable operation point again, and the VSG speed can remain stable. By comparing the simulation results of the traditional VSG control strategy, the power angle stability of the system under the improved virtual synchronous machine control strategy based on the switching of the power difference effect on the speed is significantly improved.

[0119] like Fig.10 As shown, after a -60° phase jump occurred due to a grid fault at t=3s, the power angle δ jumped from 23.79° to 83.79°, without triggering the switching of the effect of the VSG power difference on the speed. The power angle stability was restored under the original control strategy, verifying the accuracy of the switching criterion.

[0120] Embodiment 2

[0121] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0122] Embodiment 3

[0123] The purpose of this embodiment is to provide a computer-readable storage medium.

[0124] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0125] Embodiment 4

[0126] The purpose of this embodiment is to provide a virtual synchronous machine control system based on switching of the effect of power difference on speed, including:

[0127] The data acquisition module is configured to: acquire grid information in a steady state, including: converter output voltage, grid voltage, converter output current and power angle at a power balance point;

[0128] The parameter k calculation module is configured to: monitor the output current of the converter in real time;

[0129] Calculate parameter k based on converter output voltage, grid voltage and power angle;

[0130] The judgment module is configured to: judge the size of the converter output current and the product of the parameter k and the output current at the power balance point; if the converter output current is less than the product of the parameter k and the output current at the power balance point, there is no need to switch the effect of the power difference on the speed, and generate a control instruction f(I)=1; if the converter output current is greater than the product of the parameter k and the output current at the power balance point, generate a control instruction f(I)=-1, and switch the effect of the power difference on the speed;

[0131] The switching control module is configured to: transmit the generated control instruction f(I) to the active power-frequency branch of the controller to execute the action effect switching.

[0132] Embodiment 5

[0133] The purpose of this embodiment is to provide a computer program product containing instructions, which, when running on a computer, enables the computer to execute the methods and functions involved in any of the above embodiments.

[0134] The steps involved in the apparatus of the above embodiment correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0135] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0136] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A virtual synchronous machine control method based on switching the effect of power difference on speed, characterized in that: include: Obtain grid information under steady state, including: converter output voltage, grid voltage, converter output current and power angle at power balance point; Real-time monitoring of converter output current; Calculate parameter k based on converter output voltage, grid voltage and power angle; Determine the size of the product of the converter output current and the parameter k and the output current at the power balance point. If the converter output current is less than the product of the parameter k and the output current at the power balance point, there is no need to switch the effect of the power difference on the speed, and generate a control instruction f(I)=1. If the converter output current is greater than the product of the parameter k and the output current at the power balance point, generate a control instruction f(I)=-1, and switch the effect of the power difference on the speed. The generated control instruction f(I) is transmitted to the active power-frequency branch of the controller to execute the action effect switching.

2. The virtual synchronous machine control method based on the switching of the power difference effect on the speed as claimed in claim 1 is characterized in that: The calculation formula of the parameter k is: Among them, E is the converter output voltage, U is the grid voltage, and δ1 is the power angle.

3. The virtual synchronous machine control method based on the switching of the power difference effect on the speed as claimed in claim 1 is characterized in that: The switching power difference has an effect on the speed, and the mathematical expression for adjusting the active power-frequency branch is: In the formula, ω0, P ref are the set values ​​of frequency and active power respectively, J is the moment of inertia, D is the damping coefficient, P is the VSG control output power, and ω is the VSG control output frequency.

4. The virtual synchronous machine control method based on switching of the power difference effect on the speed as claimed in claim 1 is characterized in that: The output current of the converter is greater than the product of the parameter k and the output current at the power balance point, that is, when the power angle jumps to the unstable operating area through the output current detection, the effect of the switching power difference on the speed can adaptively adjust the power angle stable operating point, and the power angle of the stable operating point changes from δ1 to 180°-δ1.

5. The virtual synchronous machine control method based on switching of the power difference effect on the speed as claimed in claim 1 is characterized in that: The controller executes the strategy switching and outputs the phase, which is obtained by integrating the output frequency of the VSG control. It is output together with the dq components of the converter output voltage output by the voltage and current dual closed-loop control to the coordinate transformation unit for conversion from two-dimensional coordinates to three-dimensional coordinates, and then generates a PWM control signal to be transmitted to the converter.

6. The virtual synchronous machine control method based on switching of the power difference effect on the speed as claimed in claim 1 is characterized in that: When obtaining the power angle under the steady state of the power grid, the power angle is calculated by the circuit parameters of the grid-connected converter, and the grid-connected converter circuit parameters involved include: converter output power, reactance, converter output voltage and grid voltage; Preferably, when calculating the converter output current at the power balance point: Among them, E is the converter output voltage, U is the grid voltage, δ1 is the power angle, and X is the reactance.

7. A virtual synchronous machine control system based on switching of the power difference to the speed effect, comprising: The data acquisition module is configured to: acquire grid information in a steady state, including: converter output voltage, grid voltage, converter output current and power angle at a power balance point; The parameter k calculation module is configured to: monitor the output current of the converter in real time; Calculate parameter k based on converter output voltage, grid voltage and power angle; The judgment module is configured to: judge the size of the converter output current and the product of the parameter k and the output current at the power balance point; if the converter output current is less than the product of the parameter k and the output current at the power balance point, there is no need to switch the effect of the power difference on the speed, and generate a control instruction f(I)=1; if the converter output current is greater than the product of the parameter k and the output current at the power balance point, generate a control instruction f(I)=-1, and switch the effect of the power difference on the speed; The switching control module is configured to: transmit the generated control instruction f(I) to the active power-frequency branch of the controller to execute the action effect switching.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method described in any one of claims 1 to 6 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 6 are performed.

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