Method for determining small signal stability working condition interval and stability margin of grid-connected new energy system

Abstract

The application discloses a method for determining a small signal stability working condition interval and a stability margin of a new energy grid-connected system, and the method comprises the following steps: S1, obtaining a multivariable equivalent binary open-loop transfer function of the new energy grid-connected system with respect to different operating condition variables; S2, calculating phase characteristics and amplitude characteristics of the multivariable open-loop transfer function; S3, setting the phase characteristics as φ k and the amplitude characteristics as 0 dB; drawing a multi-phase contour map containing a plurality of phase contours and amplitude contours; wherein, φ k is a phase value related to critical stability of the new energy grid-connected system; S4, calculating a phase margin of the new energy grid-connected system at the intersection of the phase contours and the amplitude contours, and determining a stable working condition interval of the new energy grid-connected system according to operating condition variables corresponding to the intersection of the phase contours and the amplitude contours. The method can not only obtain a stable running interval of the grid-connected system in the whole operating condition range, but also evaluate the distribution law of the stability margin under different working condition conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of stability analysis of new energy grid-connected system, and particularly relates to a method for determining small signal stability operating condition interval and stability margin of new energy grid-connected system. BACKGROUND

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

[0003] At present, the small signal stability of new energy system is usually analyzed by impedance analysis method or eigenvalue method. However, such stability research is mostly based on several specific operating conditions, and cannot effectively test the stability of new energy system in different operating condition ranges. The paper "Small signal stability analysis of grid-connected converter under different operating conditions based on frequency-coupled impedance model" discloses that the grid-connected point port voltage and current are defined as operating points, and different operating points are brought into the model to analyze the stability under different operating conditions. However, the stability analysis results obtained by this method do not provide the change of stability margin of the system with the change of operating conditions, and it is difficult to guide the stability design of the system.

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

[0005] The purpose of the present application is to provide a method for determining the small signal stability operating condition interval and stability margin of 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 change of stability margin of the system with the change of operating conditions.

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

[0007] S1: obtaining a multivariable equivalent binary open-loop transfer function of new energy grid-connected system about different operating condition variables O pt ;

[0008] S2: calculating the phase characteristic and the amplitude characteristic M(s, O pt ) of the multivariable open-loop transfer function;

[0009] S3: setting the phase characteristic amplitude characteristic M(s, O pt=0dB; Draw a multi-phase contour map containing multiple phase contour lines and amplitude contour lines; where, The phase value is 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 lines and the amplitude contour lines, and calculate the operating condition variable O corresponding to the intersection of the phase contour lines and the amplitude contour lines. pt Determine the stable operating range of the new energy grid-connected system.

[0011] Further, step S1 includes:

[0012] S11: Based on the small-signal equivalent circuit of the new energy grid-connected system, obtain the grid-connected port variable O with respect to the operating conditions. pt Current response I p (s,O pt ):

[0013]

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

[0015] S12: If the new energy subsystem and the power grid in the new energy grid-connected system are made to be independently stable, 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:

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

[0017] Furthermore, in step S2, the phase characteristics and amplitude characteristics M(s,O) pt The formula for calculating ) is:

[0018]

[0019] Further, the phase value related to the critical stability of the new energy grid-connected system in step S3 is -180°; therefore, the phase values related to the critical stability of the new energy grid-connected system are -170°, -180° and -190°. The phase values of -180° and deviating from -180°.

[0020] Further, the calculation formula of the phase margin is:

[0021]

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

[0023] wherein, represents the phase contour The phase margin of the new energy grid-connected system when the phase contour intersects with the amplitude contour M(s, O pt ) = 0dB at the operating variable O pt point.

[0024] Further, the method for determining the stable operating condition interval of the new energy grid-connected system is:

[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 critical stable state;

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

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

[0029] Further, the calculation formula of the phase margin is:

[0030]

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

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

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

[0034] The present application has the following beneficial effects: the response-excitation relationship of the port impedance network is analyzed to derive the multivariable open-loop transfer function of the system; the multidimensional Bode diagram of the equivalent open-loop transfer function is visualized and reduced in dimension by using multiple phase equivalent planes and 0dB amplitude equivalent planes, and the phase-amplitude contour map is used to clearly show the stability boundary, so that the critical operating condition point can be quickly located. This method not only can obtain the stable operating condition interval of the new energy grid-connected system in the entire operating condition range, but also can evaluate the distribution law of the stability margin of the new energy grid-connected system under different operating condition conditions, which can provide important reference for the oscillation risk screening, operation scheduling and early planning of the new energy grid-connected system. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are included to provide a further understanding of the present application and constitute a part of this application, illustrate certain illustrative embodiments of the present application and together with the description serve to explain the present application. In the drawings, the same reference numbers are used to represent the same or similar parts throughout the drawings. In the drawings:

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

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

[0038] Figure 3 A multi-phase contour map. DETAILED DESCRIPTION

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

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

[0041] S2: calculating the phase characteristics of the multivariable open-loop transfer function and the amplitude characteristic M(s, O pt );

[0042] S3: setting the phase characteristic and the amplitude characteristic M(s, O pt ) = 0 dB; drawing a multi-phase contour map containing a plurality of phase contours and amplitude contours; wherein, is a phase value related to the critical stability of the new energy grid-connected system;

[0043] S4: calculating the phase margin of the new energy grid-connected system at the intersection of the phase contour and the amplitude contour, and determining the stable operating condition interval of the new energy grid-connected system according to the operating condition variable O pt corresponding to the intersection of the phase contour and the amplitude contour.

[0044] The present application derives the multi-variable open-loop transfer function of the system by analyzing the response-excitation relationship of the port impedance network; the multi-dimensional Bode diagram of the equivalent open-loop transfer function is visualized and reduced in dimension by using a plurality of phase contour planes and a 0 dB amplitude contour plane, and the stability boundary is clearly displayed by using the phase-amplitude contour map, so that the critical operating condition point can be quickly located. This method not only can obtain the stable operating condition interval of the new energy grid-connected system in the entire operating condition range, but also can evaluate the distribution law of the stability margin of the new energy grid-connected system under different operating condition conditions, which can provide important reference for the oscillation risk screening, operation scheduling and early planning of the new energy grid-connected system. Moreover, this method is compatible with different new energy types (such as wind power and photovoltaic) and power grid structures, and is suitable for complex grid-connected scenarios.

[0045] According to one embodiment of the present application, step S1 comprises:

[0046] S11: obtaining the current response I pt (s, O p ) of the grid-connected port with respect to the operating condition variable O pt according to the small-signal equivalent circuit of the new energy grid-connected system, as shown in FIG. Figure 1

[0047]

[0048] wherein I p represents the current of the new energy subsystem and the grid-connected point; 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; O pt represents the operating condition variable of the new energy grid-connected system, O pt including at least one of power, voltage and current.​

[0049] S12: make the new energy subsystem and the power grid in the new energy grid-connected system respectively independent stability, then Y w (s, O pt ) V g (s) stable, the new energy grid-connected system can be regarded as a forward path gain of 1 and a feedback gain of Y w (s) Z g (s) closed loop system, as shown in Figure 2 , then the multivariable equivalent binary open-loop transfer function of the new energy grid-connected system can be obtained as:

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

[0051] The embodiment is constructed by constructing an equivalent open-loop transfer function including operating condition variables O pt , overcoming the dependence of the traditional method on the fixed condition assumption, and realizing stability analysis under dynamic conditions

[0052] According to one embodiment of the present application, in step S2, the calculation formula of the phase characteristic and the amplitude characteristic M(s, O pt ) is:

[0053]

[0054] The embodiment calculates the phase characteristic and the amplitude characteristic M(s, O pt ), and provides a quantitative index for frequency domain stability analysis.

[0055] According to one embodiment of the present application, 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° and the phase value deviating from-180°.

[0056] The embodiment sets the phase value-180° of the critical stability of the new energy grid-connected system and the deviation value near-180°, which can facilitate subsequent determination of the stability of the operating condition interval according to the positive and negative of the phase margin.

[0057] According to one embodiment of the present application, the calculation formula of the phase margin is:

[0058]

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

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

[0061] The embodiment binds the phase margin with the operating variable O pt , reflects the real-time influence 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 judgment index

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

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

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

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

[0066] According to one embodiment of the present application, the phase value related to the critical stability of the new energy grid-connected system is -170°, -180° and -190°. The value of the phase margin can be set according to actual engineering needs. When it is needed to determine the distribution rule of the stability margin at intervals of 10°, the value of the phase margin is -170°, -180° and -190° disclosed in the embodiment; when it is needed to determine the distribution rule of the stability margin at intervals of 20°, the value of the phase margin is -160°, -180° and -200°; here, no more details are given.

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

[0068]

[0069] Figure 3 As shown in the figure, the -170°, -180° and -190° contour lines intersect with the 0dB contour line at points A, B and C, respectively, which correspond to three operating points O pt1 , O pt2 and O pt3 , respectively; according to the calculation of the phase margin, O pt1 ​​, O pt2 and O pt3 The phase margin corresponding to the three operating points are 10°, 0° and -10°, i.e. PM1(O pt1 )>PM2(O pt2 )>PM3(O pt3 ), which indicates that as the operating condition changes from O ptmin to O ptmax , the phase margin of the system decreases, the system is at a higher risk of oscillation, and the stable operating condition interval of the system is [O ptmin ,O pt2 ).

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

[0071] In a third aspect, the present application provides a computer readable storage medium, which comprises instructions that, when executed, cause a computer to execute the method provided in the first aspect. By embedding the method provided in the first aspect into the computer readable storage medium, engineering application and promotion are facilitated.

[0072] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system, characterized in that, Including the following steps: S1: Obtain variables O of the new energy grid-connected system under different operating conditions pt The multivariable equivalent binary open-loop transfer function; S2: Calculate the phase characteristics of the multivariable equivalent binary open-loop transfer function. and amplitude characteristics M(s,O) pt ); S3: Set the phase characteristics The amplitude characteristic M(s,O) pt =0dB; Draw a multi-phase contour map containing multiple phase contour lines and amplitude contour lines; where, The phase value is related to the critical stability of the new 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 a new energy grid-connected system according to claim 1, characterized in that, Step S1 includes: S11: Based on the small-signal equivalent circuit of the new energy grid-connected system, obtain the grid-connected port variable O with respect to the operating conditions. pt Current response I p (s,O pt ): Among them, I p I represents the current at the grid connection point of the new energy subsystem; w Y represents the output current of the new energy subsystem; w V represents the admittance of the new energy subsystem; g Z represents the voltage of the power grid. g Indicates the impedance of the power grid; O pt O represents the operating condition variable of the new energy grid-connected system. pt Includes at least one of power, voltage, and current; S12: If the new energy subsystem and the power grid in the new energy grid-connected system are made to be independently stable, 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 a new energy grid-connected system according to claim 2, characterized in that, In step S2, the phase characteristic and amplitude characteristics M(s,O) pt The formula for calculating ) is:

4. The method for determining the small-signal stable operating range and stability margin of a new energy grid-connected system according to claim 1, characterized in that, In step S3, the critical stability phase value 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... The values ​​are -180° and phase values ​​deviating from -180°.

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

6. The method for determining the small-signal stable operating condition range and stability margin of a new energy grid-connected system according to claim 5, characterized in that, The method for determining the stable operating range of a new energy grid-connected system is as follows: 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 condition range and stability margin of a new energy grid-connected system according to claim 6, 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° respectively.

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

9. A device for determining the 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 execution instructions, and when the device is running, the processor executes the computer execution instructions stored in the memory to cause the device to perform the method of any one of claims 1-8.

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

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