New energy grid-connected system small signal stable working condition interval and stability margin determination method

Abstract

The invention discloses a new energy grid-connected system small signal stable working condition interval and stability margin determination method. The method comprises the steps that S1, a multivariable equivalent binary open-loop transfer function of a new energy grid-connected system about different operation working condition variables is acquired; s2, calculating a phase characteristic and an amplitude characteristic of the multivariable open-loop transfer function; s3, the phase characteristic is set to be phi k, and the amplitude characteristic is set to be 0dB; drawing a multi-phase contour map comprising a plurality of phase contour lines and amplitude contour lines; wherein phi k is a phase value related to the critical stability of the new energy grid-connected system; and S4, calculating the phase margin of the new energy grid-connected system at the intersection point of the phase contour line and the amplitude contour line, and determining the stable working condition interval of the new energy grid-connected system according to the operation working condition variable corresponding to the intersection point of the phase contour line and the amplitude contour line. According to the method, the stable operation interval of the grid-connected system in the whole operation working condition range can be obtained, and the distribution rule of the stability margin of the grid-connected system under different working conditions can be evaluated.

Description

Technical Field

[0001] The present invention relates to the field of stability analysis of new energy grid-connected systems, and particularly to a method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system. Background Art

[0002] Actual engineering operation data shows that the small-signal stability characteristics of a new energy grid-connected system change with the operating conditions. The random fluctuation characteristics of the output of the new energy system cause the power electronic equipment of the new energy to be in an operating condition with a wide range of operating points for a long time, and the accidents of grid-connected oscillation instability under variable conditions occur frequently. Therefore, it is particularly important to determine the stable operating condition area and the variation law of the stability margin with the operating conditions to guide the stable operation of the system.

[0003] Currently, impedance analysis method or eigenvalue method is usually used to analyze the small-signal stability of new energy systems. However, most of this stability research is carried out based on several specific operating conditions, and it is unable to effectively test the stability of new energy systems within different operating condition ranges. The paper "Analysis of Small-Signal Stability of Grid-Connected Converters under Different Conditions Based on Frequency Coupling Impedance Model" discloses that the grid connection point port voltage and current are defined as the operating point, and different operating points are brought into the model to analyze the stability under different conditions. However, the stability analysis results obtained by this method do not provide the variation of the stability margin of the system with the operating conditions, and it is difficult to guide the stability design of the system.

[0004] Therefore, an effective method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system is needed. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system, so as to solve the problem that the small-signal stability results of the existing new energy system cannot reflect the variation of the stability margin of the system with the operating conditions.

[0006] To solve the above technical problems, in the first aspect, the present invention provides a method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system, including the steps of:

[0007] S1: Obtain the multi-variable equivalent binary open-loop transfer function of the new energy grid-connected system with respect to different operating condition variables O pt ;

[0008] S2: Calculate the phase characteristics and the magnitude characteristics M(s, O pt ) of the multi-variable open-loop transfer function;

[0009] S3: Set the phase characteristics and the magnitude characteristics M(s, O pt) = 0 dB; Plot a multi-phase contour map including multiple phase contour lines and amplitude contour lines; where, is the phase value related to the critical stability of the new energy grid-connected system;

[0010] S4: Calculate the phase margin of the new energy grid-connected system at the intersection of the phase contour line and the amplitude contour line, and determine the stable operating condition interval of the new energy grid-connected system according to the operating condition variable O corresponding to the intersection of the phase contour line and the amplitude contour line pt Determine the stable operating condition interval of the new energy grid-connected system.

[0011] Further, step S1 includes:

[0012] S11: According to the small-signal equivalent circuit of the new energy grid-connected system, obtain the current response I of the grid connection port with respect to the operating condition variable O pt of p (s, O pt ):

[0013]

[0014] where, I p represents the current at the grid connection point between the new energy subsystem and the power grid; I w represents the output current of the new energy subsystem; Y w represents the admittance of the new energy subsystem; V g represents the voltage of the power grid; Z g represents the impedance of the power grid; O pt represents the operating condition variable of the new energy grid-connected system, O pt includes at least one of power, voltage, and current;

[0015] S12: Let the new energy subsystem and the power grid in the new energy grid-connected system be independently stable, then Y w (s, O pt )V g (s) is stable, and the multi-variable equivalent binary open-loop transfer function of the new energy grid-connected system is obtained as:

[0016] T op (s, O pt ) = Y w (s, O pt )Z g (s).

[0017] Further, in step S2, the calculation formulas for the phase characteristic and the amplitude characteristic M(s, O pt ) are:

[0018]

[0019] Furthermore, in step S3, the phase value at which the new energy grid-connected system is critically stable is -180°; therefore, the phase values related to the critical stability of the new energy grid-connected system take the values of -180° and phase values deviating from -180°.

[0020] Furthermore, the calculation formula for the phase margin is:

[0021]

[0022] M(s,O pt ) = 20Log[|T op (s,O pt )|] = 0dB

[0023] where represents the phase contour intersecting with the magnitude contour M(s,O pt ) = 0dB at the operating variable O pt point, which is the phase margin of the new energy grid-connected system.

[0024] Furthermore, the method for determining the stable operating condition range of the new energy grid-connected system is as follows:

[0025] When the phase margin is greater than 0°, the new energy grid-connected system is in a stable state;

[0026] When the phase margin is equal to 0°, the new energy grid-connected system is in a critically stable state;

[0027] When the phase margin is less than 0°, the new energy grid-connected system is in an unstable state.

[0028] Furthermore, the phase values related to the critical stability of the new energy grid-connected system take the values of: -170°, -180°, and -190° respectively.

[0029] Furthermore, the calculation formula for the phase margin is:

[0030]

[0031] According to the method for determining the stable operating condition range of the new energy grid-connected system, the small-signal stable operating condition range of the new energy grid-connected system is [O ptmin ,O pt2 ).

[0032] In a second aspect, the present invention provides a device for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system, the device comprising: a processor and a memory; wherein, the memory is used to store computer execution instructions, and when the device runs, the processor executes the computer execution instructions stored in the memory so that the device executes the method provided in the first aspect above.

[0033] In a third aspect, the present invention provides a computer-readable storage medium, the computer-readable storage medium comprising instructions that, when executed, cause a computer to execute the method provided in the first aspect above.

[0034] The beneficial effects of the present invention are as follows: By analyzing the response-excitation relationship of the port impedance network, the multi-variable open-loop transfer function of the system is derived; Multiple phase equal-value planes and 0dB amplitude equal-value planes are used to visually reduce the dimensionality of the multi-dimensional Bode plot of the equivalent open-loop transfer function, and the stability boundary is clearly shown using the phase-amplitude equal-value line diagram, which is convenient for quickly locating the critical operating condition points. This method can not only obtain the stable operating range of the new energy grid-connected system within the entire operating condition range, but also evaluate the distribution law of the stability margin of the new energy grid-connected system under different operating conditions, and can provide important references for the oscillation risk screening, operation scheduling and preliminary planning of the new energy grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The same reference numerals are used to represent the same or similar parts in these drawings. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0036] Figure 1 is the equivalent circuit diagram of the new energy grid-connected system;

[0037] Figure 2 is the schematic diagram of the equivalent feedback control system of the new energy grid-connected system;

[0038] Figure 3 is the multi-phase equal-value line diagram. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In a first aspect, the present invention discloses a method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system, comprising the steps of:

[0040] S1: Obtain the multi-variable equivalent binary open-loop transfer function of the new energy grid-connected system with respect to different operating condition variables O pt ; wherein, the operating condition variable O pt can be power, voltage, current, etc.;

[0041] S2: Calculate the phase characteristics of the multi-variable open-loop transfer function and the magnitude characteristic M(s, θ) pt );

[0042] S3: Set the phase characteristic the magnitude characteristic M(s, θ) pt ) = 0 dB; Plot a multi-phase contour plot including multiple phase contour lines and magnitude contour lines; where, is the phase value related to the critical stability of the new energy grid-connected system;

[0043] S4: Calculate the phase margin of the new energy grid-connected system at the intersection of the phase contour line and the magnitude contour line, and determine the stable operating condition interval of the new energy grid-connected system according to the operating condition variable θ pt corresponding to the intersection of the phase contour line and the magnitude contour line.

[0044] The present invention derives the system multi-variable open-loop transfer function by analyzing the response-excitation relationship of the port impedance network; uses multiple phase equal-value planes and the 0 dB magnitude equal-value plane to perform visual dimensionality reduction on the multi-dimensional Bode plot of the equivalent open-loop transfer function, and clearly displays the stability boundary using the phase-magnitude contour plot, facilitating the rapid positioning of the critical operating point. This method can not only obtain the stable operating interval of the new energy grid-connected system within the entire operating condition range, but also evaluate the distribution law of the stability margin of the new energy grid-connected system under different operating conditions, providing an important reference for the oscillation risk screening, operation scheduling, and preliminary planning of the new energy grid-connected system. Moreover, this method is compatible with different new energy types (such as wind power, photovoltaic) and grid structures, and is applicable to complex grid connection scenarios.

[0045] According to an embodiment of the present application, step S1 includes:

[0046] S11: According to the small-signal equivalent circuit of the new energy grid-connected system, as Figure 1 shown, obtain the current response I pt of the grid connection port with respect to the operating condition variable θ p (s, θ pt ):

[0047]

[0048] where, I p represents the current at the grid connection point between the new energy subsystem and the grid; I w represents the output current of the new energy subsystem; Y w represents the admittance of the new energy subsystem; V g represents the voltage of the grid; Z g represents the impedance of the grid; θ pt represents the operating condition variable of the new energy grid-connected system, θ pt includes at least one of power, voltage, and current;

[0049] S12: Make the new - energy sub - system and the power grid in the new - energy grid - connection system independent and stable respectively, then Y w (s, O pt )V g (s) is stable. The new - energy grid - connection system can be regarded as a closed - loop system with a forward - path gain of 1 and a feedback gain of Y w (s)Z g (s). As shown in Figure 2 ), the multi - variable equivalent two - variable open - loop transfer function of the new - energy grid - connection system can be obtained as:

[0050] T op (s, O pt ) = Y w (s, O pt )Z g (s).

[0051] In this implementation, by constructing an equivalent open - loop transfer function containing the operating - condition variable O pt , the dependence on the fixed - condition assumption of the traditional method is overcome, and the stability analysis under dynamic conditions is realized

[0052] According to an embodiment of the present application, in step S2, the calculation formulas for the phase characteristic and the magnitude characteristic M(s, O pt ) are:

[0053]

[0054] In this embodiment, through the calculation of the phase characteristic and the magnitude characteristic M(s, O pt ), a quantitative index is provided for the frequency - domain stability analysis.

[0055] According to an embodiment of the present application, in step S3, the phase value of the critical stability of the new - energy grid - connection system is - 180°; therefore, the phase values related to the critical stability of the new - energy grid - connection system

[0056] take values of - 180° and phase values deviating from - 180°.

[0057] In this embodiment, by setting the phase value of - 180° of the critical stability of the new - energy grid - connection system and the offset values near it, it is convenient to directly determine the stability of the operating - condition interval according to the positive or negative of the phase margin in the subsequent process.

[0058]

[0059] M(s, O pt) = 20Log[|T op (s, O pt )|] = 0dB

[0060] wherein, represents the phase contour line intersects with the magnitude contour line M(s, O pt ) = 0dB at the operating variable O pt point, the phase margin of the new energy grid - connection system.

[0061] In this implementation, by binding the phase margin to the operating condition variable O pt , it reflects the real - time impact of the operating condition change on stability, directly quantifies the phase margin of the system from the critical stability through the formula, and provides a clear stability determination index

[0062] According to an embodiment of the present application, the method for determining the stable operating condition range of the new energy grid - connection system is as follows:

[0063] When the phase margin is greater than 0°, the new energy grid - connection system is in a stable state;

[0064] When the phase margin is equal to 0°, the new energy grid - connection system is in a critically stable state;

[0065] When the phase margin is less than 0°, the new energy grid - connection system is in an unstable state.

[0066] According to an embodiment of the present application, the phase values related to the critical stability of the new energy grid - connection system are respectively: - 170°, - 180° and - 190°. The value of can be set according to the actual engineering needs. When it is necessary to determine the distribution law of the stability margin at intervals of 10°, then the value is - 170°, - 180° and - 190° disclosed in this embodiment; when it is necessary to determine the distribution law of the stability margin at intervals of 20°, then the value is - 160°, - 180°, - 200°; no more details are described here.

[0067] According to an embodiment of the present application, the calculation formula of the phase margin is:

[0068]

[0069] Figure 3 As shown, the - 170°, - 180° and - 190° contour lines intersect with the 0dB contour line at points A, point B and point C respectively, corresponding to O pt1 , O pt2 and O pt3 three operating points; according to the calculation of the phase margin, O pt1, O pt2 and O pt3 The phase margins corresponding to the three operating points are 10°, 0°, and -10° respectively, i.e., PM 1 (O pt1 ) > PM 2 (O pt2 ) > PM 3 (O pt3 ), indicating that as the operating condition changes from O ptmin to O ptmax , the phase margin of the system decreases, the oscillation risk of the system is higher, and the stable operating condition interval of the system is [O ptmin , O pt2 ).

[0070] In a third aspect, the present invention provides a device for determining the small-signal stable operating condition interval and stability margin of a new energy grid-connected system. The device includes: a processor and a memory; wherein, the memory is used to store computer execution instructions. When the device runs, the processor executes the computer execution instructions stored in the memory so that the device executes the method provided in the first aspect above. This embodiment realizes the method provided in the first aspect through the device composed of a processor and a memory, which is convenient for engineering application and promotion.

[0071] In a third aspect, the present invention provides a computer-readable storage medium. The computer-readable storage medium includes instructions that, when executed, cause a computer to execute the method provided in the first aspect above. By embedding the method provided in the first aspect into the computer-readable storage medium, it is convenient for engineering application and promotion.

[0072] 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 preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the small signal stable operating range and stability margin of a new energy grid-connected system, characterized in that: Includes steps: S1: Obtain the variables O of the new energy grid-connected system under different operating conditions pt The multivariable equivalent binary open-loop transfer function of ; S2: Calculate the phase characteristic of the multivariable open-loop transfer function and amplitude characteristics M(s,O pt ); S3: Setting the phase characteristics The amplitude characteristic M(s, pt )=0dB; draw a multi-phase contour map containing multiple phase contours and amplitude contours; where, is the phase value related to the critical stability of the renewable energy grid-connected system; S4: Calculate the phase margin of the new energy grid-connected system at the intersection of the phase contour line and the amplitude contour line, and calculate the operating condition variable O corresponding to the intersection of the phase contour line and the amplitude contour line. pt Determine the stable operating range of the new energy grid-connected system.

2. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 1 is characterized in that: The step S1 comprises: S11: According to the small signal equivalent circuit of the new energy grid-connected system, the grid-connected port is obtained with respect to the operating condition variable O pt The current response I p (s,O pt ): Among them, I p Indicates the current at the point where the new energy subsystem is connected to the grid; I w Represents the output current of the new energy subsystem; Y w represents the admittance of the new energy subsystem; V g Indicates the voltage of the power grid; Z g Indicates the impedance of the power grid; pt Represents the operating condition variable of the new energy grid-connected system, O pt Including at least one of power, voltage, and current; S12: Let the new energy subsystem and the power grid in the new energy grid-connected system be stable independently, then Y w (s,O pt )V g (s) is stable, and the multivariable equivalent binary open-loop transfer function of the new energy grid-connected system is expressed as: T op (s,O pt )=Y w (s,O pt )Z g (s)。 3. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 2 is characterized in that: In step S2, the phase characteristic and amplitude characteristics M(s,O pt ) is calculated as:

4. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 1 is characterized in that: In step S3, the phase value of the critical stability of the new energy grid-connected system is -180°; therefore, the phase value related to the critical stability of the new energy grid-connected system is -180°. The phase value is -180° and deviates from -180°.

5. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 4 is characterized in that: The calculation formula of the phase margin is: M(s,O pt )=20Log[|T op (s,O pt )|]=0dB Among them, PM k |M(s,o pt )=0dB represents the phase contour and amplitude contours M(s,O pt )=0dB intersects with the running variable O pt The phase margin of the renewable energy grid-connected system at this point.

6. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 5 is characterized in that: The method for determining the stable operating condition interval of the new energy grid-connected system is: When the phase margin is greater than 0°, the new energy grid-connected system is in a stable state; When the phase margin is equal to 0°, the new energy grid-connected system is in a critical stable state; When the phase margin is less than 0°, the new energy grid-connected system is in an unstable state.

7. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 6 is characterized in that: The phase value related to the critical stability of the new energy grid-connected system The values ​​are: -170°, -180° and -190°.

8. The method for determining the small signal stable operating range and stability margin of the new energy grid-connected system according to claim 7 is characterized in that: The calculation formula of the phase margin is: According to the method for determining the stable operating range of the new energy grid-connected system, the small signal stable operating range of the new energy grid-connected system is [0 ptmin ,O pt2 ).

9. A device for determining small signal stable operating range and stability margin of a new energy grid-connected system, characterized in that: include: A processor and a memory; wherein the memory is used to store computer-executable instructions, and when the device is running, the processor executes the computer-executable instructions stored in the memory so that the device executes the method described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium comprises instructions which, when executed, cause the computer to perform the method of any one of claims 1-8.

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