Method for Determining Small-Signal Stable Operating Region of Converter Grid-Connected System

Abstract

The present invention discloses a method for determining the small-signal stable operation region of a converter grid-connected system, including: S1. Construct a loop gain G loop (ω pc , P, Q); S2. Discretize the reactive power variable Q into several points and solve the relationship between ω pc and P; S3. Based on the relationship between ω pc and P, calculate the critical points of the active power variable P value; S4. Judge the left and right stability margins of each value of P1, P2... P n to obtain the left critical parameters P n , P 1l ... P 2l ... P nl corresponding to P1, P2... P 1r and the right critical parameters P 2r ... P nr ; S5. Determine the small-signal stable operation region according to the left critical parameters and the right critical parameters. The analysis of the present invention is simple and there is no blind area in the stable operation region.

Description

Technical Field

[0001] The present invention relates to the field of converter grid connection, and specifically relates to a method for determining the small-signal stable operation region of a converter grid connection system. Background Art

[0002] Due to climate issues such as global warming, countries have paid increasing attention to the development of new energy.

[0003] However, at present, stability problems often occur in photovoltaic and wind power new energy power stations. Field operation shows that the occurrence of its stability problems is related to power changes. Therefore, it is relatively important to analyze its stable operation region, which can avoid the system operating in the unstable operation region and thus avoid the occurrence of stability problems.

[0004] The change in power can be divided into active power change and reactive power change. Many studies take the plane composed of the active power and reactive power operation ranges of the converter as the operation region. To analyze the small-signal stable operation region within its operation region, by substituting the points in the plane composed of active power and reactive power into the traditional stability analysis method respectively, the points in the operation plane are analyzed one by one to obtain the small-signal stable operation region. This method for determining the small-signal stable operation region is essentially a traditional stability analysis method, which is realized through multiple analyses. The analysis method is complex and cumbersome, and there are certain analysis blind spots.

[0005] Therefore, to solve the above problems, a new method for determining the small-signal stable operation region is needed. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to overcome the defects in the prior art, and provide a method for determining the small-signal stable operation region of a converter grid connection system, which has simple analysis and no blind spots in the stable operation region.

[0007] The method for determining the small-signal stable operation region of the converter grid connection system of the present invention includes the following steps:

[0008] S1. Construct a loop gain G loop (ω pc , P, Q); where ω pc is the crossing angular frequency, P is the active power variable, and Q is the reactive power variable;

[0009] S2. Discretize the reactive power variable Q into several points, and solve the relationship between ω pc and P;

[0010] S3. Based on the relationship between ω pc and P, calculate the critical points of the active power variable P value, that is, P1, P2... P n ;

[0011] S4. Determine the left and right stability margins of P1, P2... P n to obtain the left critical parameters P n corresponding to P1, P2... P 1l , P 2l ... P nl and the right critical parameters P 1r , P 2r ... P nr ;

[0012] S5. If the plane critical points are (P 1l , Q q,1 ), (P 2l , Q q,2 )... (P nl , Q q,n ), then the small-signal stable operating region composed of P and Q is the left half of the curve formed by these critical points;

[0013] Conversely, if the plane critical points are (P 1r , Q q,1 ), (P 2r , Q q,2 )... (P nr , Q q,n ), then the small-signal stable operating region composed of P and Q is the right half of the curve formed by these critical points.

[0014] Furthermore, the step S2 specifically includes:

[0015] Discretize the reactive power variable Q into points Q q,1 , Q q,2 ... Q q,n ; G loop At points Q q,1 , Q q,2 ... Q q,n when the amplitude-frequency response is 0 dB, solve the relationship between ω pc and P, that is

[0016] Furthermore, the step S3 specifically includes:

[0017] Combining the relationship between ω pc and P, using the equation:

[0018]

[0019]

[0020] Calculate the critical points of the active power variable P value, that is, P1, P2... P n; where Im[] represents the function to obtain the imaginary part of the transfer function, and Re[] represents the function to obtain the real part of the transfer function.

[0021] Further, step S4 specifically includes:

[0022] By the phase angle judge the left and right stability margins of the values of P1, P2... P n When Q = Q q,1 and P = P1, when the P value is on the left side of P1, the stability margin is positive, and at this time P1 is the left critical parameter P 1l , otherwise it is the right critical parameter P 1r ; Similarly, the left critical parameters P n corresponding to P2, …, P 2l , …, P nl and the right critical parameters P 2r , …, P nr can be obtained.

[0023] The beneficial effect of the present invention is: A method for determining the small-signal stable operation region of a converter grid-connected system disclosed by the present invention determines the small-signal stable operation region by using the active variable P and the reactive variable Q. Compared with the existing methods for determining the small-signal stable operation region, the present invention avoids the complexity of the existing determination methods, improves the calculation speed, and there is no analysis blind area. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the drawings and embodiments:

[0025] Figure 1 (a) is a schematic diagram of the relationship between the crossing angular frequency and the active variable of the present invention;

[0026] Figure 1 (b) is a schematic diagram of the relationship between the crossing angular frequency and the phase angle of the present invention;

[0027] Figure 2 is a schematic diagram of the stable region determination result of the present invention;

[0028] Figure 3 is a schematic diagram of the result of the region where the example points are located obtained according to the determination method of the present invention;

[0029] Figure 4 is a schematic diagram of the simulation result of the example points of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be further described below with reference to the accompanying drawings of the specification, as shown in the figure:

[0031] Method for determining small-signal stable operation region of converter grid-connection system of the present invention, comprising the following steps:

[0032] S1. Construct loop gain G including active variable and reactive variable loop (ω pc , P, Q); where ω pc is the crossover angular frequency, P is the active variable, and Q is the reactive variable;

[0033] S2. Discretize reactive variable Q into several points, and solve the relationship between ω pc and P;

[0034] S3. Based on the relationship between ω pc and P, calculate the critical points of the active variable P value, i.e., P1, P2... P n ;

[0035] S4. Judge the left and right stability margins of each value of P1, P2... P n to obtain the left critical parameters P n , P 1l , P 2l ... P nl corresponding to P1, P2... P 1r , P 2r ... P nr and the right critical parameters P

[0036] S5. If the plane critical points are (P 1l , Q q,1 ), (P 2l , Q q,2 )... (P nl , Q q,n ), then the small-signal stable operation region composed of P and Q is the left half of the curve formed by these critical points;

[0037] Conversely, if the plane critical points are (P 1r , Q q,1 ), (P 2r , Q q,2 )... (P nr , Q q,n ), then the small-signal stable operation region composed of P and Q is the right half of the curve formed by these critical points. Wherein, the plane is the system operation plane composed of two variables, namely the active power variable P and the reactive power variable Q of the grid-connection system.

[0038] In this embodiment, first, construct loop gain containing active variable and reactive variable, expressed as G loop (ω pc , P, Q), where ω pc is the crossover angular frequency, P is the active variable, and Q is the reactive variable.

[0039] Next, the reactive variable Q is discretized into points: Q q,1 , Q q,2 …Q q,n .

[0040] As Figure 1 (a) shows, when the amplitude-frequency response at points Q loop , Q q,1 , …Q q,2 … is 0 dB, the relationship between ω q,n and P is solved, that is pc where the function F can be obtained by mathematical fitting or solving a mathematical equation;

[0041] As Figure 1 (b) shows, combining the relationship between ω pc and P, using the equation:

[0042]

[0043]

[0044]

[0045] the critical points of the active variable P value are calculated, that is, P1, P2…P n . Among them, Im[] represents the function of obtaining the imaginary part of the transfer function, and Re[] represents the function of obtaining the real part of the transfer function; the function inside [] in Im[] is the transfer function corresponding to Im[]; the function inside [] in Re[] is the transfer function corresponding to Re[].

[0046] As Figure 1 (a) and 1(b) show, by the phase angle judge the left and right stability margins of each value of P1, P2…P n . When Q = Q q,1 and P = P1, when the P value is on the left side of P1, the stability margin is positive, and at this time P1 is the left critical parameter P 1l , otherwise it is the right critical parameter P 1r ; similarly, the left critical parameters P n corresponding to P2, …, P 2l , …, P nl as well as the right critical parameters P 2r , …, P nr can be obtained.

[0047] Therefore, the plane critical points are (P 1l , Q q,1 ), (P​2l , Q q,2 )…(P nl , Q q,n ), the small-signal stable operating region composed of P and Q is the left half of the curve, and its schematic diagram is as Figure 2 shown.

[0048] Of course, the above method for determining the small-signal stable operating region composed of P and Q can also be applied to the method for determining the small-signal stable operating region composed of other two variables, which will not be elaborated here.

[0049] Based on the above steps, the analysis results of the stability region of a certain converter grid-connected system are as Figure 3 shown: In the figure, Ap(6.64kW, 0.39kvar) and Bp(6.64kW, 0.78kvar) are located within the small-signal stable operating region, and Cp(7.44kW, 0.78kvar) is located within the unstable operating region.

[0050] And Figure 4 gives the simulation structures of Ap, Bp, and Cp. It can be seen that the simulation results are consistent with the results analyzed by using the method of the present invention, which also illustrates the effectiveness of the method of the present invention.

[0051] 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 by the scope of the claims of the present invention.

Claims

1. A method for determining the small-signal stable operation region of a converter grid-connected system, characterized in that: It includes the following steps: S1. Construct a loop gain G including active variables and reactive variables loop (ω pc , P, Q); where ω pc is the crossover angular frequency, P is the active variable, and Q is the reactive variable; S2. Discretize the reactive power variable Q into several points and solve the relationship between ω pc and P; S3. Based on the relationship between ω pc and P, calculate the critical points of the active power variable P value, namely P1, P2... P n ; S4. Determine the left and right stability margins of the values of P1, P2…P n to obtain the left critical parameters P n , P 1l , …, P 2l corresponding to P1, P2…P respectively, and the right critical parameters P nl , P 1r , …, P 2r corresponding to P1, P2…P respectively, specifically including: nr ​ By phase angle judge the left and right stability margins of P1, P2…P n each value. When Q = Q q,1 and P = P1, if the P value is on the left side of P1, the stability margin is positive, and at this time P1 is the left critical parameter P 1l , otherwise it is the right critical parameter P 1r ; Similarly, obtain the left critical parameters P n corresponding to P2, …, P 2l respectively, …, P nl and the right critical parameters P 2r , …, P nr ; S5. If the plane critical points are (P 1l , Q q,1 ), (P 2l , Q q,2 )…(P nl , Q q,n ), then the small-signal stable operation region composed of P and Q is the left half of the curve formed by these critical points; On the contrary, if the plane critical points are (P 1r , Q q,1 ), (P 2r , Q q,2 )…(P nr , Q q,n ), then the small-signal stable operation region composed of P and Q is the right half of the curve formed by these critical points.

2. The method for determining the small-signal stable operation region of the converter grid-connected system according to claim 1, characterized in that: The specific steps of step S2 include: Discretize the reactive variable Q into points Q q,1 , Q q,2 …Q q,n ; G loop At points Q q,1 , Q q,2 …Q q,n When the lower frequency response is 0 dB, solve for the relationship between ω pc and P, that is 3. The method for determining the small-signal stable operation region of the converter grid-connected system according to claim 1, characterized in that: The specific steps of step S3 include: Combined with ω pc and the relationship between P, use the equation: Calculate the critical points of the active power variable P value, namely P1, P2... P n ; where Im[] represents the function to obtain the imaginary part of the transfer function, and Re[] represents the function to obtain the real part of the transfer function.

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