A power system oscillation suppression method and a power system

Abstract

The application discloses a power system oscillation suppression method and a power system, and relates to the technical field of electric power. The method is applied to an oscillation suppression device, the oscillation suppression device is a feedback path of a renewable energy grid-connected power system, and the method comprises the following steps: in the first target conjugate pole pair and the second target conjugate pole pair that satisfy a preset mutual approaching condition on a complex plane, the first target conjugate pole pair and the second target conjugate pole pair are determined in the poles of a first transfer function of the renewable energy grid-connected power system; the first conjugate pole pair is determined on the complex plane, the distance between the first conjugate pole pair and the first target conjugate pole pair and / or the second target conjugate pole pair satisfies the preset mutual approaching condition; a second transfer function is constructed according to the first conjugate pole pair; a state variable of the renewable energy grid-connected power system is sampled, and an oscillation suppression signal is generated according to the state variable and the second transfer function and is input into the renewable energy grid-connected power system in reverse phase. The method can realize oscillation suppression on the renewable energy grid-connected power system.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to a method for suppressing power system oscillations and a power system. Background Technology

[0002] Power system oscillation is a critical issue that has plagued power systems since their inception. Current oscillation suppression methods are based on stability analysis, which essentially involves analyzing and controlling the position of the poles corresponding to the oscillation modes in the complex plane. However, for renewable energy grid-connected power systems, stability analysis-based oscillation suppression methods cannot provide a reasonable and clear explanation, nor have they achieved the desired oscillation suppression effect.

[0003] Existing oscillation suppression methods, when applied to renewable energy grid-connected power systems, overlook an important fact: disturbances in traditional power systems are discrete and instantaneous, such as the occurrence and clearing of faults, the commissioning and decommissioning of equipment, and the switching of system operating modes. In stark contrast, for renewable energy grid-connected power systems, disturbances are continuous due to the inherent random fluctuations in wind and solar intensity.

[0004] Another important fact overlooked by existing oscillation suppression methods is that in renewable energy grid-connected power systems, power electronic devices such as wind turbines and photovoltaic power generation units typically exhibit numerous oscillation modes, distributed across frequency bands from low to high frequencies. Consequently, the linearized models corresponding to these power electronic devices, such as state-space models or transfer function models, have a large number of poles widely distributed in the complex plane. Furthermore, the variable operating modes of renewable energy power systems, including wind turbines, lead to high-amplitude oscillations even under small, continuous disturbances. Therefore, existing oscillation suppression methods are ineffective for renewable energy grid-connected power systems. Summary of the Invention

[0005] This application provides a power system oscillation suppression method and power system to solve or at least partially solve the defects or deficiencies in related technologies.

[0006] In a first aspect, this application provides a power system oscillation suppression method applied to an oscillation suppression device in a power system. The power system includes a renewable energy grid-connected power system and the oscillation suppression device serving as a feedback path. The sampling terminal of the oscillation suppression device is connected to a first location of the renewable energy grid-connected power system, and the feedback terminal of the oscillation suppression device is connected to a second location of the renewable energy grid-connected power system. In the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system, the second location is upstream of the first location. The power system oscillation suppression method includes: Among the poles of the first transfer function of the renewable energy grid-connected power system, a first target conjugate pole pair and a second target conjugate pole pair that satisfy a preset mutual proximity condition on the complex plane are determined; A first conjugate pole pair is determined on the complex plane; wherein the distance between the first conjugate pole pair and the first target conjugate pole pair and / or the second target conjugate pole pair satisfies the preset mutual proximity condition; Construct the second transfer function based on the first conjugate pole pair; The state variables of the renewable energy grid-connected power system are sampled from the first location, and an oscillation suppression signal is generated based on the state variables and the second transfer function; The oscillation suppression signal is inverted and input into the renewable energy grid-connected power system through the second position to suppress oscillations in the renewable energy grid-connected power system.

[0007] Secondly, this application provides a power system comprising a renewable energy grid-connected power system and an oscillation suppression device as a feedback path. The sampling end of the oscillation suppression device is connected to a first position of the renewable energy grid-connected power system, and the feedback end of the oscillation suppression device is connected to a second position of the renewable energy grid-connected power system. In the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system, the second position is located upstream of the first position. The oscillation suppression device is used to implement the steps of the power system oscillation suppression method described in the first aspect.

[0008] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application provides a power system oscillation suppression method and a power system. By adding an oscillation suppression device as a feedback path to a renewable energy grid-connected power system, a closed-loop feedback control system is formed. The oscillation suppression device generates an oscillation suppression signal based on the state variables obtained from the renewable energy grid-connected power system and feeds it back to the renewable energy grid-connected power system in reverse phase, thereby suppressing the oscillations of the renewable energy grid-connected power system. When the renewable energy grid-connected power system oscillates due to the presence of two sets of conjugate pole pairs that are close to each other, a set of conjugate pole pairs (i.e., a set of conjugate zero pairs in the entire power system) of the oscillation suppression device's transfer function is designed to be located near the two sets of conjugate pole pairs in the complex plane (i.e., the distance meets a preset proximity condition). Thus, the entire power system can contain a set of conjugate zero pairs located near the two sets of conjugate pole pairs. Mathematical derivation verifies that this reduces the residue of each pole in the two sets of conjugate pole pairs, thereby offsetting the oscillation problem caused by the two sets of conjugate pole pairs and suppressing the oscillations of the renewable energy grid-connected power system. Attached Figure Description

[0009] Figure 1 A schematic diagram of a power system provided in an embodiment of this application; Figure 2 A schematic diagram of a closed-loop feedback control system consisting of a first type of oscillation suppression device and a renewable energy grid-connected power system provided in this application embodiment; Figure 3 A schematic diagram of a closed-loop feedback control system consisting of a second type of oscillation suppression device and a renewable energy grid-connected power system provided in this application embodiment; Figure 4 A schematic diagram of a closed-loop feedback control system consisting of a third type of oscillation suppression device and a renewable energy grid-connected power system provided in this application embodiment; Figure 5 A schematic diagram of a closed-loop feedback control system consisting of a fourth type of oscillation suppression device and a renewable energy grid-connected power system provided in this application embodiment; Figure 6 A schematic diagram illustrating a specific example of a power system provided in this application embodiment; Figure 7 A schematic diagram illustrating another specific example of a power system provided in this application embodiment. Detailed Implementation

[0010] Before introducing the embodiments of this application, we will first further explain the shortcomings of existing oscillation suppression methods when applied to renewable energy grid-connected power systems.

[0011] Existing oscillation suppression methods, when applied to renewable energy grid-connected power systems, overlook a crucial fact: disturbances in traditional power systems are discrete and instantaneous, such as fault occurrence and clearance, equipment commissioning and decommissioning, and system operation mode switching. Under instantaneous disturbance conditions, free oscillations after the disturbance end dominate the oscillation process, and the stability, i.e., the position of the pole corresponding to the oscillation mode in the complex plane, determines whether the free oscillation decays and the rate of decay. In stark contrast, for renewable energy grid-connected power systems, disturbances are continuous due to the inherent random fluctuations in wind and solar intensity. In implementing this application, the inventors discovered that the oscillation characteristics of a renewable energy grid-connected power system during disturbances are determined by the residue of the pole corresponding to the oscillation mode, rather than the pole's own position in the complex plane. The residue of a pole depends on its positional relationship with all other poles and zeros in the complex plane.

[0012] Another important fact overlooked by existing oscillation suppression methods is that in renewable energy grid-connected power systems, power electronic devices such as wind turbines and photovoltaic power generation units typically exhibit numerous oscillation modes, distributed across frequency bands from low to high frequencies. Consequently, the linearized models corresponding to these power electronic devices, such as state-space models or transfer function models, have a large number of poles widely distributed across the complex plane. Furthermore, the variable operating modes of renewable energy power systems, including wind turbines, significantly increase the likelihood of poles converging in the transfer function models of such systems. The residues corresponding to these converging poles have large moduli, leading to high-amplitude oscillations even under small, continuous disturbances. Therefore, oscillation suppression methods that only focus on the location of the poles themselves are ineffective for renewable energy grid-connected power systems.

[0013] Based on the above findings, embodiments of this application provide a power system oscillation suppression method and a power system to suppress oscillations in renewable energy grid-connected power systems.

[0014] The embodiments of this application are described in detail below.

[0015] The power system oscillation suppression method provided in this application embodiment can be applied to, for example, Figure 1The diagram shows an oscillation suppression device 200 in a power system. In this embodiment, both the oscillation suppression device 200 and the renewable energy grid-connected power system 100 are components of the power system. The renewable energy grid-connected power system 100 is the forward path of the power system, and the oscillation suppression device 200 is the feedback path of the power system. The sampling end of the oscillation suppression device 200 is connected to the first position Q1 of the renewable energy grid-connected power system 100, which is the sampling connection end of the renewable energy grid-connected power system 100. The feedback end of the oscillation suppression device 200 is connected to the second position Q2 of the renewable energy grid-connected power system 100, which is the feedback injection end of the renewable energy grid-connected power system 100. In the forward path direction of the transfer function (referred to as the first transfer function) from disturbance to output of the renewable energy grid-connected power system 100, the second position Q2 is located upstream of the first position Q1.

[0016] The following section introduces the relevant content of renewable energy grid-connected power systems, oscillation suppression devices, and the transfer function, poles, and zeros of the entire power system.

[0017] Among them, the renewable energy grid-connected power system may include one or more of the following power systems: wind power grid-connected power system and photovoltaic power grid-connected power system.

[0018] For a renewable energy grid-connected power system, take any continuous random disturbance such as wind speed or wind turbine power, light intensity or photovoltaic power generation unit power as input variables, and any state variable such as line current, synchronous generator speed, DC bus voltage of voltage source inverter, DC line voltage of DC transmission system as output variables, and establish the first transfer function in zero-pole-gain form (factorization form) as shown in formula (1).

[0019] (1).

[0020] Where s is the Laplace operator (i.e., the complex frequency, whose position can be represented by coordinate values ​​on the complex plane, with the horizontal axis representing the real part and the vertical axis representing the imaginary part); U(s) is the Laplace transform of the input variable; Y(s) is the Laplace transform of the output variable; G(s) is the transfer function of the renewable energy grid-connected power system, called the first transfer function, which is also the forward path transfer function of the entire power system; m G n is the number of zeros in the first transfer function (i.e., the solutions s where the numerator of G(s) is 0); G Let m be the number of poles in the first transfer function (i.e., the solution s where the denominator of G(s) is 0); for a practical power system, m G ≤n G z jG(jG=1, 2, 3, …, m G ) represents the j-th zero in G(s); p iG (iG=1, 2, 3, …, n G) Let K be the i-th pole in G(s); G The gain of G(s) (also known as the root locus gain) is the forward path root locus gain of the entire power system.

[0021] In addition, for grid-connected renewable energy power systems, transfer function forms that indirectly reflect zeros and poles can be established, including polynomial forms as shown in formula (2) and state-space forms as shown in formula (3).

[0022] (2).

[0023] (3).

[0024] In formula (2), b0, b1, ..., b m-1 ,b m These represent the coefficients of the numerator; a1, a2, ..., a n denoted by , respectively; m is the number of zeros in the first transfer function (i.e., the solution s where the numerator of G(s) is 0); n is the number of poles in the first transfer function (i.e., the solution s where the denominator of G(s) is 0).

[0025] In formula (3), x represents the state variable; y represents the output variable; u represents the input variable; matrices A, B, C, and D are the state matrix, input matrix, output matrix, and input-output matrix, respectively; and p is the differential operator (d / dx).

[0026] The relationship between formula (2) and formula (1) is as follows: z in formula (2) jG and p iG and K G Substituting the numerical value into formula (1) yields formula (2); factoring the numerator and denominator of formula (2) with respect to s yields formula (1).

[0027] The relationship between formula (3) and formula (1) is as follows: Applying the Laplace transform to equation (3) yields equations (4) and (5): (4); (5).

[0028] In formulas (4) and (5), U(s) is the Laplace transform of the input variable u; Y(s) is the Laplace transform of the output variable y; and X(s) is the Laplace transform of the state variable x.

[0029] Formula (4) can be transformed into: (6).

[0030] In formula (6), I represents an identity diagonal matrix of the same order as matrix A; the superscript -1 indicates matrix inversion. Substituting formula (6) into formula (5) yields: (7).

[0031] Right now: (8).

[0032] Comparing formula (8) with formula (1), we can see that in the state-space form shown in formula (3), the first transfer function G(s) is: (9).

[0033] In this embodiment, an oscillation suppression device is integrated with the renewable energy grid-connected power system to form a closed-loop feedback control system. This is achieved by increasing the distance between closely spaced pole pairs to move them further apart, and / or by adding new zeros near the closely spaced poles, thus suppressing the oscillations of the renewable energy grid-connected power system. Increasing the distance between closely spaced pole pairs and adding new zeros near the closely spaced poles both reduce the residue of each pole in the two sets of conjugate pole pairs, thereby solving the oscillation problem of the renewable energy grid-connected power system. This embodiment will construct the second transfer function H(s) of the oscillation suppression device based on the first transfer function G(s) of the renewable energy grid-connected power system.

[0034] It should be noted that in the transfer function, poles appear in pairs of complex conjugate poles (or simply conjugate poles), and similarly, zeros appear in pairs of complex conjugate zeros (or simply conjugate zeros). The real parts of the conjugate pairs are the same, and the imaginary parts are opposites of each other. Therefore, the pole pairs that are close to each other in the embodiments of this application refer to one set of conjugate poles being close to another set of conjugate poles, that is, the upper half-plane poles of each set of conjugate poles are close to each other, and the lower half-plane poles of each set are close to each other.

[0035] It should also be noted that, in this embodiment, "two sets of conjugate pole pairs are close to each other" means that the distance between the two sets of conjugate pole pairs (this distance refers to the distance in the complex plane) satisfies a preset condition for closeness. This distance can be equal to the distance between the two poles in the upper half-plane of the complex plane, or the distance between the two poles in the lower half-plane of the complex plane. In this embodiment, "two sets of conjugate pole pairs are far apart" means that the distance between the two sets of conjugate pole pairs does not satisfy the preset condition for closeness.

[0036] In one alternative implementation, the preset proximity condition includes that the distance between two points on the complex plane (e.g., two poles or zeros located in the upper half of the complex plane, or two poles or zeros located in the lower half of the complex plane) is less than or equal to (not greater than) one-tenth of a target value, where the target value is the larger of the magnitudes of the two points. Correspondingly, the preset proximity condition is not met if the distance between two points on the complex plane is greater than one-tenth of the target value.

[0037] The basic principle of forming a closed-loop feedback control system by integrating oscillation suppression devices with renewable energy grid-connected power systems is as follows: Figure 2 As shown.

[0038] exist Figure 2 In this context, G(s), U(s), and Y(s) have the same meanings as described above. H(s) is the transfer function of the oscillation suppression device, referred to as the second transfer function. The second transfer function is also the feedback path transfer function of the entire power system. Figure 2 In the closed-loop feedback control system shown, the transfer function of the renewable energy grid-connected power system is the aforementioned first transfer function G(s), and the transfer function of the oscillation suppression device can be expressed as the second transfer function H(s) shown in formula (10).

[0039] (10).

[0040] In formula (10), z jH (jH=1, 2, 3, …, m H ) represents the jH-th zero in H(s); p iH (iH=1, 2,3, …, n) represents the iH-th pole in H(s); K H The gain of H(s) (i.e., the root locus gain) is also the root locus gain of the feedback path of the entire power system.

[0041] The transfer function Ф(s) of the closed-loop feedback control system consisting of G(s) and H(s) is: (11).

[0042] From the numerator of formula (11), it can be seen that the zeros of Ф(s) (that is, the solutions of s for which the numerator of Ф(s) is 0) are obtained from the zeros of G(s) z. jG And the poles p of H(s) iH constitute.

[0043] The denominator of Ф(s) is the characteristic polynomial of the feedback control system. As can be seen from the denominator of formula (11), the characteristic polynomial is determined by the gain, zeros and poles of G(s) and H(s).

[0044] The zero point z of G(s) jG Extreme point p iG and gain K G These are inherent parameters determined by the power system; therefore, the zeros z of H(s) can be determined by designing them. jH Extreme point p iH and gain K H This ensures that there are no two sets of conjugate poles that are close to each other in the transfer function Ф(s) of the entire power system.

[0045] Since the transfer function G(s) of a renewable energy grid-connected power system is usually a high-order system, it can be seen from equation (11) that this will lead to a more complex design of the zeros of H(s). Therefore, G(s) is simplified to a fourth-order system G´(s) containing only two sets of complex conjugate poles. The simplification process is as follows.

[0046] The partial fractional expansion of formula (1) is as follows: (12).

[0047] In formula (12), for ease of explanation, let iG = k, C k The k-th pole (i.e., the p-th pole) in G(s) k The residues corresponding to the poles are: (13).

[0048] As can be seen from formula (13), the residue C corresponding to the k-th pole is... k The magnitude of the residue depends on the relative positions of the pole with all other poles and zeros in the complex plane. Specifically, when a pole is close to other poles and there are no other zeros nearby, the magnitude of the residue corresponding to that pole is large; when a pole is surrounded by other zeros and there are no other poles nearby, the magnitude of the residue corresponding to that pole is small. This is also the principle behind how adding new zeros near close poles can solve oscillations—that is, reducing the residue corresponding to close poles can solve the oscillation problem.

[0049] In addition, the oscillation problem arises because the transfer function G(s) of the renewable energy grid-connected power system contains two pairs of conjugate poles that are close to each other (and there are no zeros near the two pairs of conjugate poles that are close to each other). The oscillation problem of the renewable energy grid-connected power system can also be solved by increasing the distance between the pairs of poles that are close to each other so that they are far apart. The principle is that this method can reduce the residues corresponding to the poles that are close to each other.

[0050] Suppose that the k-th and (k+1)-th poles of G(s) are a pair of complex conjugate poles (i.e., the real parts of the two poles are the same, and the imaginary parts are opposites of each other), denoted as p. kG, (k+1)G Suppose that the (n-1)th pole and the nth pole are another set of complex conjugate poles, denoted as p. (n-1)G, nG When p kG With p (n-1)G p (k+1)G With p nG When they are very close (i.e., close to each other) in the complex plane, the residue C kG C (k+1)G C (n-1)G C nG The modulus of will be much larger than the modulus of the residues corresponding to other poles, and C kG Approximately equal to -C (n-1)G and C (k+1)G Approximately equal to -C nG And because of C kG With C (k+1)G C (n-1)G With C nG If the poles are complex conjugates, then G(s) expressed by formula (12) can be simplified to a fourth-order system G´(s) containing only two sets of complex conjugate poles: (14).

[0051] The superscript * indicates complex conjugate. K G ´ is the gain of G´(s), K G The value of ´ is determined by formula (15).

[0052] (15).

[0053] Transform formula (15) into formula (16).

[0054] (16).

[0055] G(s)∣ s=0 For the DC gain of a renewable energy grid-connected power system, G(s)∣ s=0The value of can be determined by a step response test, that is, when the input variable u steps from its steady-state value u0 to u0+Δu, and the steady-state value of the output variable y stabilizes from y0 to y0+Δy after a dynamic process, then G(s)| s=0 =Δy / Δu.

[0056] Therefore, the transfer function Ф´(s) corresponding to the closed-loop feedback control system composed of G´(s) and H(s) is: (17).

[0057] In the form of formula (17), the zeros of the closed-loop feedback control system Ф´(s) are determined solely by the poles p of the feedback path transfer function H(s). iH Decide.

[0058] It is important to emphasize here that, apart from the poles p of H(s), the zeros of the unsimplified Ф(s) are... iH In addition, the zero z of G(s) should also be included. jG However, if we use formula (14) to simplify G(s) to G'(s), and then use formula (17) to simplify Ф(s) to Ф´(s), then the zeros of the simplified Ф´(s) will no longer include the zero z of G(s). jG .

[0059] On the one hand, although the zeros of the simplified Ф´(s) no longer include the zeros z of G(s). jG However, the other zeros included in Ф(s) (i.e., the zeros z of G(s)) jG The role of ) has been reflected in K G The gain required to determine H(s) for subsequent oscillation suppression is shown in equation (15), i.e., K G The value of ´ depends on G(s) | s=0 And G(s)∣ s=0 The value of depends on the zero z of G(s). jG (Refer to formula (1)), that is, the true Ф(s) includes the zero point z of G(s). jG Its effect has already been demonstrated in oscillation suppression.

[0060] On the other hand, the real Ф(s) also includes the zero z of G(s). jG However, the close conjugate pole pairs in G(s) can cause oscillations precisely because the zeros zjG of G(s) are far apart from the close conjugate pole pairs in G(s), meaning there are no zeros near the close conjugate pole pairs. Therefore, the zeros of Ф(s) include the zeros zjG of G(s). jG This has virtually no impact on oscillations, which means that the zeros based on "Ф´(s)" only include the poles p of H(s).iH This condition is used to design the zero and pole parameters of H(s), and the zeros of Ф(s) include the poles p of H(s). iH and the zero z of G(s) jG "Using this condition to design the zero and pole parameters of H(s) can achieve essentially the same oscillation suppression effect."

[0061] Assume complex conjugate poles p kG, (k+1)G =σ 1G ±jω 1G , and p (n-1)G, nG =σ 2G ±jω 2G When p kG With p (n-1)G p (k+1)G With p nG When they are very close (i.e., close to each other) on the complex plane, we have σ 1G ≈σ 2G ω 1G ≈ω 2G If the design H(s) has a set of complex conjugate poles p 1H , 2H =σ 1H ±jω 1H and make it consistent with p kG, (k+1)G and p (n-1)G, nG They move closer to each other, i.e., σ 1H ±jω 1H ≈σ 1G ±jω 1G and / or σ 1H ±jω 1H ≈σ 2G ±jω 2G Then, a set of complex conjugate zeros σ can be achieved in the closed-loop feedback control system Ф´(s). 1H ±jω 1H In two pairs of poles that are close to each other (pole pair p) kG, (k+1)G And the poles of p (n-1)G, nG )nearby.

[0062] p kG, (k+1)G =σ 1G ±jω 1G p (n-1)G, nG =σ 2G ±jω 2G ,as well as Substituting into formula (17), we get: (18).

[0063] The denominator of formula (18) is the characteristic polynomial of the closed-loop feedback control system. The solution s that equals 0 of the characteristic polynomial is the pole of the closed-loop feedback control system. At this point, only the gain K of H(s) remains in the characteristic polynomial. H and zero point z jH To be determined.

[0064] Zero point z jH The determination process is illustrated below: The poles of G(s) are simplified to a fourth-order system G´(s) and H(s) and are a set of complex conjugate poles σ. 1H ±jω 1H ≈σ 1G ±jω 1G Under the given conditions, to ensure that the solution of the characteristic polynomial is completely controllable, the order of the zeros of H(s) must be no less than 6, i.e., m H ≥6.

[0065] Take m H =6, then the characteristic polynomial is a sixth-order polynomial in s, corresponding to three pairs of complex conjugate poles: assuming that in the closed-loop feedback control system, the original two pairs of closely spaced complex conjugate poles σ 1G ±jω 1G and σ 2G ±jω 2G They were moved to σ´ respectively 1G ±jω´ 1G and σ´ 2G ±jω´ 2G The remaining set of complex conjugate poles needs to be configured far from σ. 1G ±jω 1G and σ 2G ±jω 2G The position is assumed to be σ´ 3G ±jω´ 3G The characteristic polynomial of the closed-loop feedback control system can be expressed as: (19).

[0066] Among them, K GH Let K' be the gain coefficient determined by the left side of equation (19). From equation (19), it can be seen that when K' G K H When >>1, the solution of the characteristic polynomial is approximately determined by the zeros of H(s), that is: (20).

[0067] As can be seen from formula (20), when K´ G K H >>1, σ´ 1G ±jω´ 1G 、σ´2G ±jω´ 2G and σ´ 3G ±jω´ 3G That is, the zero point z of H(s) jH .

[0068] The gain K of H(s) in the characteristic polynomial is determined below. H .

[0069] In fact, as can be seen from formula (14), K´ G Since K is a relatively large value, H K' can be satisfied within a wide range of values. G K H >>1. To reduce the risk of high-frequency noise amplification by the feedback path, K H The value range (i.e., the target gain value range) can be determined as follows: K can be determined by taking any value within this range. H .

[0070] At this point, the poles p of the transfer function parameter (i.e., H(s)) corresponding to the oscillation suppression device are determined. iH 0 point z jH and gain K H All confirmed: (twenty one).

[0071] In this embodiment, the input signal of the oscillation suppression device is the oscillation signal of the renewable energy grid-connected power system. Therefore, when the renewable energy grid-connected power system is operating normally, the oscillation suppression device has no input signal and no output signal, and does not affect the operation of the renewable energy grid-connected power system. It only plays a role when oscillation occurs.

[0072] In this embodiment, an oscillation suppression device and a renewable energy grid-connected power system are used to form a closed-loop feedback control system. In an optional implementation, the method for determining the poles, zeros, and gain of the transfer function H(s) of the oscillation suppression device is summarized as follows: (1) Measure the frequency of oscillations in the grid-connected renewable energy power system, that is, determine the imaginary part ω of the complex conjugate poles that are close to each other in G(s). 1G and ω 2G The real part σ of the complex conjugate poles that are close to each other in G(s) 1G and σ 2G It is usually impossible to obtain this information by measuring the oscillation signal. However, since the distance between the poles corresponding to the oscillation mode and other poles or zeros in the complex plane is mainly determined by the imaginary part of the poles, i.e., the oscillation frequency, therefore, σ 1G It is possible to have -1 < σ 1G Valuation within the range of <0, σ 2GIt is possible to have -1 < σ 2G Valuation within the range of <0, σ 1G In -1<σ 1G σ can take any value within the range <0. 2G In -1<σ 2G Any value within the range <0 is acceptable. Thus, the two sets of complex conjugate poles σ in G(s) that are close to each other are now defined. 1G ±jω 1G (i.e., the first target conjugate pole) and σ 2G ±jω 2G (i.e., the second target conjugate pole) can be determined.

[0073] (2) Determine the poles σ of the transfer function H(s) of the oscillation suppression device. 1H ±jω 1H (i.e., the first conjugate pole pair), only needs to satisfy σ 1H ±jω 1H ≈σ 1G ±jω 1G and / or σ 1H ±jω 1H ≈σ 2G ±jω 2G That is, the pole σ 1H ±jω 1H With σ 1G ±jω 1G and / or σ 1G ±jω 1G The distances on the complex plane satisfy a preset condition for mutual proximity. In this way, zeros can be added near mutually close poles.

[0074] (3) Determine the zero point σ' of the transfer function H(s) of the oscillation suppression device. 1G ±jω´ 1G (i.e., the first conjugate zero pair), σ´ 2G ±jω´ 2G (i.e., the second conjugate zero pair) and σ' 3G ±jω´ 3G (i.e., the third conjugate zero pair). First, ensure that the zero lies in the left half of the complex plane, meaning the range of the real part of the zero of H(s) is: -1 < σ'. 1G <0,-1<σ´ 2G <0,-1<σ´ 3G <0, any value within this range will yield the real part of all zeros of H(s). Secondly, to ensure that ω´ is within the range of values ​​that feedback control is employed, 1G With ω´ 2G To keep them far apart (i.e., not close to each other), ω´ should be made 1G With ω´ 2G One of them is not equal to (i.e., greater than or less than) ω1G and / or ω 2G , and σ´ 1G ±jω´ 1G With σ´ 2G ±jω´ 2G They need to be far apart from each other, i.e., σ´ 1G ±jω´ 1G With σ´ 2G ±jω´ 2G The distance between them needs to be such that it does not meet the preset condition for them to get close to each other, ω´ 1G With ω´ 2G The other one remaining with ω 1G and ω 2G The magnitude relationship needs to be considered in relation to the transfer function between the second position Q2 and the first position Q1, which includes σ. 1G ±jω 1G and σ 2G ±jω 2G Depending on the circumstances, which will be explained in detail later. For example, ω´ 1G It can take the value ω´ 1G >(ω 1G ×1.05); ω´ 2G It can take the value ω´ 2G <(ω 1G ×0.95), this value can achieve σ´ 1G ±jω´ 1G With σ´ 2G ±jω´ 2G They move away from each other. For zero point σ´ 3G ±jω´ 3G It needs to satisfy -1 < σ´ 3G <0, and ω´ 3G With ω 1G and ω 2G All satisfy the condition of being far apart, meaning none satisfy the preset condition of being close together. For example, the value ω´ is used. 3G Satisfy∣ω´ 3G -ω 1G |>0.1×|ω 1G | In this way, it is possible to move poles that are close to each other away from each other.

[0075] (4) Determine the gain K of the transfer function H(s) of the oscillation suppression device. H Because of K´ G Typically, K is a large value, and to reduce the risk of the transfer function H(s) amplifying potential high-frequency signals, H The range of values ​​is The gain K of H(s) can be obtained by taking any value within this range. H .

[0076] Actual power systems often span large geographical areas, making implementation difficult. Figure 2 The closed-loop feedback control system shown requires long-distance signal transmission, which poses a challenge for practical engineering applications. Therefore, in an optional implementation, a partial closed-loop feedback control structure can be adopted, such as... Figure 3 As shown.

[0077] exist Figure 3 In the above, the transfer function of the renewable energy grid-connected power system (i.e., the forward path transfer function of the entire power system) is composed of the first sub-transfer function G1(s), the second sub-transfer function G2(s), and the third sub-transfer function G3(s) connected in series. Obviously, G1(s)G2(s)G3(s)=G(s). After G(s) is simplified to a fourth-order system G´(s), according to formula (14), we have: (twenty two).

[0078] Among them, K´ G1 K´ G2 and K´ G3 The gains are G1(s), G2(s), and G3(s), respectively, and K' is given. G1 K´ G2 K´ G3 =K´ G The order of the denominator of G1(s) is n. G1 The order of the denominator of G2(s) is n. G2 The order of the denominator of G3(s) is n. G3 From formula (22), we know that n G1 n G2 and n G3 The sum is 4, that is, n G1 ≤4 and n G2 ≤4 and n G3 ≤4 and n G1 + n G2+ n G3 =4.

[0079] for Figure 3 The closed-loop feedback control system shown has the following transfer function: (twenty three).

[0080] Where, p iG2 Let i be the iG2th pole of G2(s) (iG2=1, …, n) G2 As can be seen from the numerator of formula (23), the zeros of Ф´(s) are still derived from the poles p of H(s). iHThe decision is made. Therefore, the method for determining the poles of H(s) is the same as the second method in the previous section on "Determining the Pole, Zero, and Gain of H(s)," and n... H =2 (because the oscillation suppression device is designed with a pair of poles), then the order n of the first term of the characteristic polynomial of Ф´(s) is 2. G2 +n H ≤6 (because n) G2 ≤4 and n H =2). And because m H =6. Then when K' G2 K H When >>1, similar to formula (20), the solution of the characteristic polynomial of Ф´(s) is still determined by the zeros of H(s).

[0081] The method for determining the zeros and gain of H(s) is based on G2(s) and two sets of complex conjugate poles (p... kG, (k+1)G and p (n-1)G, nG There are three different cases regarding the inclusion relationship of ) : Case 1: p kG, (k+1)G and p (n-1)G, nG All of them are contained in G2(s), that is, G1(s), G2(s) and G3(s) can be expressed as: (twenty four).

[0082] K´ G1 K´ G2 and K´ G3 The method for determining K can be found in formula (15). G The method described above can be used to determine K' by conducting step response tests on G1(s), G2(s), and G3(s) respectively. G1 K´ G2 and K´ G3 The value of .

[0083] Referring to point four of the previous section on "Methods for Determining the Poles, Zeros, and Gain of H(s)," K H The value is .

[0084] Under the conditions of formula (24), n is in formula (23). G2 +n H =6, where n G2 =4,n H =2,n G2 +n H=6 indicates that the zeros of H(s) (i.e., all six poles of the transfer function Ф´(s) of the entire power system) can be designed. The method for determining the zeros of H(s) can be found in point 3 of the previous section, "Methods for Determining the Poles, Zeros, and Gain of H(s)". At this point, the poles, zeros, and gain parameters of H(s) in Case 1 are completely determined.

[0085] In this case, feedback control can both move the two sets of poles that are close to each other away from each other, and at the same time add a pair of zeros near the two sets of poles that are close to each other (i.e., a pair of complex conjugate zeros of Ф´(s), which is also the first conjugate pole pair of H(s)).

[0086] Case 2: p kG, (k+1)G and p (n-1)G, nG Only one pair of poles is contained in G2(s). Assume G2(s) contains only pole p. kG, (k+1)G Then G1(s), G2(s), and G3(s) can be expressed as the following formula (25) or formula (26): (25); (26).

[0087] For case 2, K´ can be determined by performing a step response test on G2(s). G2 The value of K. Referring to point four in the previous section "Methods for Determining the Poles, Zeros, and Gain of H(s)," K... H The value is .

[0088] Under the conditions of formula (25) or formula (26), n is in formula (23). G2 +n H =4, where n G2 =2,n H =2,n G2 +n H =4 indicates that only 4 of the 6 zeros of H(s) (i.e., all the poles of the transfer function Ф´(s) of the entire power system) can be designed, and the other 2 are poles p that are not included in G2(s). (n-1)G, nG At this point, we still use the third method from the previous section on "Determining the Poles, Zeros, and Gain of H(s)" to determine the zeros of H(s). Thus, the poles, zeros, and gain parameters of H(s) in Case 2 are completely determined.

[0089] In this case, feedback control can only move one pair of poles away from the other pair of poles whose positions remain unchanged, while at the same time it can add a pair of zeros near the poles whose positions remain unchanged (i.e., a pair of complex conjugate zeros of Ф´(s), which is also the first conjugate pole pair of H(s)).

[0090] Case 3: p kG, (k+1)G and p (n-1)G, nG Since there are no poles contained in G2(s), G1(s), G2(s), and G3(s) are represented as follows: (27); or: (28); or: (29); or: (30).

[0091] K´ G2 The value of K can be determined by performing a step response test on G2(s). Therefore, referring to point four of the previous section on "Methods for Determining the Poles, Zeros, and Gain of H(s)", K... H The value is .

[0092] In this case, n is in formula (23) G2 +n H =2, where n G2 =0, n H =2,n G2 +n H =2 indicates that only 2 of the 6 zeros of H(s) (i.e., all the poles of the transfer function Ф´(s) of the entire power system) can be designed, and the other 4 are poles p that are not included in G2(s). kG, (k+1)G and p (n-1)G, nG At this point, the third method for determining the poles, zeros, and gain of H(s) mentioned earlier is still used to determine the zeros of H(s). Thus, the poles, zeros, and gain parameters of H(s) in case 3 are completely determined.

[0093] In this case, feedback control cannot move any pair of poles; it can only add a pair of zeros near the poles that are close to each other (i.e., a pair of complex conjugate zeros of Ф´(s), which is also the first conjugate pole pair of H(s)).

[0094] All three scenarios can add zeros near the poles that are close to each other, thus suppressing oscillations. Increasing the distance between the poles that are close to each other, making them farther apart, is more effective in suppressing oscillations. Therefore, scenario 1 is more effective than scenario 2, and scenario 2 is more effective than scenario 3.

[0095] Figure 3 The closed-loop feedback control system shown is Figure 2One special case of the closed-loop feedback control system shown is when Figure 3 When G1(s) = G3(s) = 1, we can obtain Figure 2 The closed-loop feedback control system shown.

[0096] Figure 3 The closed-loop feedback control system shown may also include Figure 4 and Figure 5 The closed-loop feedback control system shown, when Figure 3 When G1(s) = 1, we can obtain Figure 4 The closed-loop feedback control system shown, when Figure 3 When G3(s) = 1, we can obtain Figure 5 The closed-loop feedback control system shown.

[0097] To enable the oscillation suppression device to form a feedback control system with the renewable energy grid-connected power system, the oscillation suppression device can be functionally divided into three modules: a signal sampling module, a calculation module, and an output module. The signal sampling module samples the state variables of the renewable energy grid-connected power system from the first position Q1, such as transmission line current, AC bus voltage, DC voltage of the DC transmission system, or synchronous generator rotor speed, and determines the oscillation signal based on the state variables and their corresponding steady-state or rated values. The calculation module constructs a second transfer function H(s) using the method described above, determines the oscillation signal based on the state variables, and then multiplies the oscillation signal in the frequency domain (which can be converted from the time domain to the frequency domain using Laplace transform) with the second transfer function H(s). Finally, the result is converted back to the time domain to obtain a second intermediate signal (which can be converted from the frequency domain to the time domain using inverse Laplace transform). The output module converts the second intermediate signal into an oscillation suppression signal that can be received by the second position Q2 of the renewable energy grid-connected power system for output. Depending on the actual needs of the power system, the output module may include digital-to-analog conversion and power amplification functions. It can control the output quantities of power system components, such as synchronous generator excitation controller command values ​​and converter current command values, and can also output voltage and current directly connected to the power system.

[0098] The Laplace transform is the same as the Laplace transform, and the inverse Laplace transform is the same as the inverse Laplace transform.

[0099] The following provides specific examples of two power system oscillation suppression devices forming a closed-loop feedback control system (i.e., a complete power system capable of oscillation suppression) with a renewable energy grid-connected power system.

[0100] In the first example, such as Figure 6As shown, the renewable energy grid-connected power system specifically refers to a photovoltaic (PV) power generation grid-connected power system, including: a PV power plant, a flexible DC transmission system, and an AC transmission channel. This PV power generation grid-connected power system may also include other power equipment or systems, which are not specifically limited in this application embodiment. The PV power plant consists of multiple PV power generation units, each of which consists of PV modules, a grid-connected inverter, a filter inductor, a transformer, etc. The PV power plant transmits power through a hybrid AC / DC transmission channel. The hybrid AC / DC transmission channel consists of a flexible DC transmission system and an AC transmission channel. When the dominant oscillation frequency ω of the PV power plant... wind The oscillation frequency ω dominated by the flexible DC transmission system HVDC When the voltage is very close to the grid, even slight power disturbances in the photovoltaic power plant caused by changes in sunlight will cause high-amplitude oscillations in the DC voltage of the flexible DC transmission system. Therefore, the forward path of the transfer function from disturbance to output in this photovoltaic grid-connected power system is from the photovoltaic modules in the photovoltaic power plant to the inverter station of the flexible DC transmission system. When the DC voltage of the flexible DC transmission system oscillates, the DC voltage... u dc The steady-state value of DC voltage in a DC transmission line u dc0 Based on the superposition of oscillation signal Δ u dc The superposition result, Δ u dc Will include ω wind With ω HVDC Two frequency components.

[0101] The first position Q1 of the photovoltaic power generation grid-connected power system is located on the DC transmission line of the flexible DC transmission system, and the second position Q2 of the photovoltaic power generation grid-connected power system is located on the power output path of the photovoltaic modules in the photovoltaic power station. That is, the sampling terminal of the oscillation suppression device is connected to the DC transmission line of the flexible DC transmission system to obtain the DC voltage u of the flexible DC transmission system from the photovoltaic power generation grid-connected power system. dc The oscillation suppression device samples the state variables and connects its feedback terminal to the power output path of the photovoltaic modules in the photovoltaic power station so as to inject the oscillation suppression signal generated by the oscillation suppression device into the photovoltaic power grid-connected power system from the power output path of the photovoltaic modules.

[0102] In this example, the closed-loop feedback control system consisting of the photovoltaic power generation grid-connected power system and the oscillation suppression device is as follows: Figure 3 As shown.

[0103] In this example, the signal sampling module of the oscillation suppression device can specifically be a voltage transformer.

[0104] In this example, the state variable is the DC voltage of the DC transmission line.u dc The steady-state value corresponding to the state variable is the steady-state value of the DC voltage of the DC transmission line. u dc0 The second intermediate signal is the current signal Δ i battery * The oscillation suppression device's computational module can obtain the steady-state value of the DC voltage of the DC transmission line. u dc0 and determine u dc and u dc0 The deviation signal Δ u dc Since H(s) is dimensionless (the reason why H(s) is dimensionless will be explained below), it is necessary to convert Δ... u dc Standardize by dividing by the rated DC voltage. u dcB The per-unit value Δ is obtained. u dc * Δ u dc * It can be identified as an oscillation signal of a flexible DC transmission system.

[0105] In this example, the arithmetic module first determines Δ u dc Includes two oscillation frequencies ω wind With ω HVDC Thus, the ω mentioned above can be obtained. 1G and ω 2G And estimate σ in the interval (-1,0). 1G and σ 2G That is, σ can be obtained by taking any value within the interval (-1,0). 1G and σ 2G This allows us to determine the two sets of complex conjugate poles (i.e., the first target conjugate pole pair) that are close to each other in the transfer function G(s) of the photovoltaic grid-connected power system. 1G ±jω 1G and σ 2G ±jω 2G (i.e., the second target conjugate pole pair). For the first conjugate pole pair σ of the transfer function H(s) of the oscillation suppression device. 1H ±jω 1H Take σ 1H ±jω 1H ≈σ 1G ±jω 1G(That is, the distance between the first conjugate pole pair and the first target conjugate pole pair satisfies the preset condition of mutual proximity). For the first conjugate zero pair σ´ of H(s) 1G ±jω´ 1G The second conjugate zero pair σ´ 2G ±jω´ 2G and the third conjugate zero pair σ´ 3G ±jω´ 3G Estimate σ´ in the interval (-1,0) 1G 、σ´ 2G and σ´ 3G That is, σ´ can be obtained by taking any value within the interval (-1,0). 1G 、σ´ 2G and σ´ 3G For example, when ω 1G ≈ω 2G When = 10 × 2π, ω´ 1G It can take the value ω´ 1G =ω 1G ×1.05=10.5×2π, and ω´ 2G It can take the value ω´ 2G =ω 1G ×0.95 = 9.5 × 2π, so that the two sets of complex conjugate poles that were originally close to each other in the photovoltaic power grid-connected power system will have a frequency difference of 1 Hz in the complex plane after feedback control. ω´ 3G The value is ω´ 3G =ω 1G +10×2π=20×2π. K H The value is set to 0.1. Therefore, all parameters of H(s) are determined, and H(s) is constructed.

[0106] Then, the arithmetic module processes the oscillation signal Δu dc * Multiplying the Laplace transform of H(s) by H(s) yields the first intermediate signal H(s)Δu. dc * Then, for the first intermediate signal H(s)Δu dc * Performing the inverse Laplace transform yields the second intermediate signal Δi. battery * Among them, the first intermediate signal H(s)Δu dc * The second intermediate signal Δi battery * The Laplace transform form, the second intermediate signal Δi battery * The first intermediate signal H(s)Δu dc *The inverse Laplace transform form. The arithmetic module can convert the second intermediate signal Δi... battery * Output to the output module of the oscillation suppression device.

[0107] In this example, the output module of the oscillation suppression device may include a current controller and an energy storage device. The current controller may include a proportional-integral (PI) controller, a PWM (Pulse Width Modulation) generator, and an inverter. The energy storage device may include a Buck-Boost circuit and an energy storage battery, with the Buck-Boost circuit containing a filter capacitor, a filter inductor, and two sets of anti-parallel IGBTs (Insulated Gate Bipolar Transistors) and diodes.

[0108] i batteryref * The current command value of the energy storage battery i batteryref The per-unit value is used to control the charging and discharging of energy storage batteries. i battery * The actual charge and discharge current value of the energy storage battery i battery The per-unit value will cause the current controller to invert. i battery * and i batteryref * Superimpose (i.e.) i batteryref * +(- i battery * The first current signal is obtained. i batteryref * - i battery * Then, the inverted second intermediate signal Δ i battery * With the first current signal i batteryref * - i battery * Superimpose (i.e.) i batteryref * +(- ibattery * )+(-Δ i battery * ), to obtain the second current signal i batteryref * - i battery * -Δ i battery * Then, the second current signal is subjected to PI control calculation by a proportional-integral controller to generate the per-unit value M of the control current signal. battery * The transfer function of the proportional-integral controller is: C(s) = K pi + K ii / s, in C(s), K pi and K ii are the proportional coefficient and integral coefficient of the current control loop, respectively, and s is a Laplace complex variable.

[0109] The per-unit value M of the control current signal generated by the proportional-integral controller battery * The modulation wave signal used by the PWM generator is compared with the carrier signal to generate a trigger signal P used to control the on / off state of the IGBTs in the energy storage device. battery1 and P battery2 P battery1 and P battery2 All are digital signals with values ​​of 0 or 1. The NOT gate of the inverter is used to logically invert the signals, i.e., P... battery1 When P is 0 battery2 Take 1, P battery1 When P is 1 battery2 Take 0.

[0110] In energy storage devices, the Buck-Boost circuit is based on a trigger signal P. battery1 and P battery2 By regulating the voltage of the energy storage battery, the battery can output an oscillation suppression current signal Δ. i d0 The inverted oscillation suppresses the current signal Δ. i d0 With photovoltaic module output current i d0 Superposition (i.e.) i d0 +(-Δ i d0 After that, it is injected into the grid-connected inverter to suppress the oscillation of the photovoltaic power generation grid-connected power system.

[0111] In the second example, such as Figure 7 As shown, the renewable energy grid-connected power system specifically refers to a wind power grid-connected power system, including: a wind farm, synchronous generator sets, and an AC transmission channel. This wind power grid-connected power system may also include other power equipment or systems, which are not specifically limited in this embodiment. The wind farm and synchronous generator sets form a combined wind-thermal power generation base, which transmits power through a common AC transmission channel. The synchronous generator set shaft system consists of a generator, a low-pressure cylinder, one or more intermediate-pressure cylinders, and a high-pressure cylinder. According to the steam flow direction and work sequence, the high-pressure cylinder is the first-stage cylinder, the intermediate-pressure cylinder is the second-stage cylinder, and the low-pressure cylinder is the third-stage cylinder. The high-pressure cylinder is the cylinder with the highest inlet pressure among the multiple stages of cylinders in the synchronous generator set, followed by the intermediate-pressure cylinder, and then the low-pressure cylinder. The natural angular frequency of the torsional oscillation of the mechanical parts of the shaft system is... ω T Wind farms, through transmission lines, transformers, and generators, form electrical coupling, resulting in electrical oscillations at angular frequencies. ω E .when ω T and ω E When the wind farm is very close to the synchronous generator set, even a small power fluctuation can cause high-amplitude shaft torsional oscillations. Therefore, the forward path of the transfer function from disturbance to output in this wind-powered grid-connected power system is from the wind farm to the high-voltage cylinder of the synchronous generator set. When shaft torsional oscillations occur in the synchronous generator set, the high-voltage cylinder rotational speed angular frequency ω... Gen The steady-state speed ω of the first-stage cylinder B Based on the superposition of oscillation signal Δω Gen ,Δω Gen Will include ω T and ω E Two frequency components.

[0112] The first position Q1 of the wind power grid-connected power system is located in the first stage cylinder of the synchronous generator set, and the second position Q2 of the wind power grid-connected power system is located in the excitation controller of the synchronous generator set. That is, the sampling terminal of the oscillation suppression device is connected to the high-voltage cylinder of the synchronous generator set to obtain the high-voltage cylinder rotational speed angular frequency ω from the wind power grid-connected power system. Gen The oscillation suppression device (i.e., state variables) is sampled, and its feedback terminal is connected to the excitation controller in the synchronous generator set so that the oscillation suppression signal generated by the oscillation suppression device is injected from the excitation controller into the wind power grid-connected power system.

[0113] In this example, the closed-loop feedback control system consisting of the wind power grid-connected power system and the oscillation suppression device is as follows: Figure 5 As shown.

[0114] In this example, the signal sampling module of the oscillation suppression device can specifically be a speed sensor.

[0115] In this example, the state variable is the angular frequency ω of the high-pressure cylinder. Gen The rated value corresponding to the state variable is the rated value of the high-pressure cylinder's rotational speed and angular frequency ω. B (For example, for a 50Hz renewable energy grid-connected power system, ω) B =100*π), the second intermediate signal is the first voltage signal Δ u f The oscillation suppression device's computational module can obtain the rated value ω of the high-pressure cylinder's rotational angular frequency. B and determine ω Gen With ω B The deviation signal Δω Gen Since H(s) is dimensionless (the reason why H(s) is dimensionless will be explained below), it is necessary to convert Δω... Gen Divide by ω B The per-unit value Δω is obtained. Gen * ,Δω Gen * It can be identified as the oscillation signal of a synchronous generator set.

[0116] In this example, the arithmetic module first determines Δω Gen Includes two oscillation frequencies ω T and ω E Thus, the ω mentioned above can be obtained. 1G and ω 2G And estimate σ in the interval (-1,0). 1G and σ 2G That is, σ can be obtained by taking any value within the interval (-1,0). 1G and σ 2G This allows us to determine the two sets of complex conjugate poles (i.e., the first target conjugate pole pair) that are close to each other in the transfer function G(s) of the wind power grid-connected power system. 1G ±jω 1G and σ 2G ±jω 2G (i.e., the second target conjugate pole pair). For the first conjugate pole pair σ of the transfer function H(s) of the oscillation suppression device. 1H ±jω 1H Take σ 1H ±jω 1H ≈σ1G ±jω 1G (That is, the distance between the first conjugate pole pair and the first target conjugate pole pair satisfies the preset condition of mutual proximity). For the first conjugate zero pair σ´ of H(s) 1G ±jω´ 1G The second conjugate zero pair σ´ 2G ±jω´ 2G and the third conjugate zero pair σ´ 3G ±jω´ 3G Estimate σ´ in the interval (-1,0) 1G 、σ´ 2G and σ´ 3G That is, σ´ can be obtained by taking any value within the interval (-1,0). 1G 、σ´ 2G and σ´ 3G For example, when ω 1G ≈ω 2G When = 10 × 2π, ω´ 1G It can take the value ω´ 1G =ω 1G ×1.05=10.5×2π, and ω´ 2G It can take the value ω´ 2G =ω 1G ×0.95 = 9.5 × 2π, so that the two sets of complex conjugate poles that were originally close to each other in the wind power grid-connected power system will have a frequency difference of 1 Hz in the complex plane after feedback control. ω´ 3G The value is ω´ 3G =ω 1G +10×2π=20×2π. K H The value is set to 0.1. Therefore, all parameters of H(s) are determined, and H(s) is constructed.

[0117] Then, the arithmetic module processes the oscillation signal Δω Gen * Multiplying the Laplace transform of H(s) by H(s) yields the first intermediate signal H(s)Δω. Gen * Then, for the first intermediate signal H(s)Δω Gen * Performing the inverse Laplace transform yields the second intermediate signal Δω. * Among them, the first intermediate signal H(s)Δω Gen * The second intermediate signal Δω * The Laplace transform form, the second intermediate signal Δω * The first intermediate signal H(s)Δω Gen * The inverse Laplace transform form. The arithmetic module can process the second intermediate signal Δω.* Output to the output module of the oscillation suppression device.

[0118] The output module of the oscillation suppression device first converts the second intermediate signal Δω * Multiplying by the target rated value yields the oscillation suppression excitation control signal Δ that the excitation controller can receive. u f Wherein, the target rated value is equal to the generator rated excitation voltage u of the synchronous generator set. fB Therefore, Δ u f = Δω * ×u fB .

[0119] Then, the output module will output the oscillation suppression excitation control signal Δ u f With the inverting input excitation controller, the inverting oscillation suppression excitation control signal Δ is achieved. u f With the original excitation control signal u f0 Superposition (i.e.) u f0 +(-Δ u f The final excitation control signal of the excitation controller is obtained. u f Among them, the original excitation control signal u f0 This is the normal excitation control signal for a wind power grid-connected power system. The final excitation control signal. u f An excitation controller is injected to suppress oscillations in the wind power grid-connected power system.

[0120] The following explains why H(s) is dimensionless. G(s) is also dimensionless, and the reason for both is the same.

[0121] If only a single-component system model is being established, both nominal value models and per-unit models can be used, because a single-component model only contains one type of variable, such as voltage, current, power, and flux linkage. However, if a complex system model containing multiple components is being established, typically only a per-unit model is used, as per-unit values ​​are dimensionless. This is because complex systems (in this embodiment, renewable energy grid-connected power systems and oscillation suppression devices) include various components, each containing different types of state variables. For example, a generator includes electrical quantities such as voltage, current, flux linkage, and power; a steam turbine includes shaft mechanical stiffness and friction coefficient; and a boiler includes thermal quantities such as temperature and pressure. In such cases, it is impossible to establish the transfer function of this system using nominal value equations.

[0122] At this point, it's necessary to measure all state variables using a unified benchmark system, i.e., a benchmark value. Dividing the nominal value (with units and dimensions) of a state variable by its corresponding benchmark value yields its per-unit value. Different types of benchmark values ​​have strict quantitative relationships that follow fundamental physical principles; for example, mechanical torque T... m The baseline value T mB Multiplied by the mechanical speed W m The baseline value ω mB Equal to mechanical power P m The benchmark value P m That is, T mB ×ω mB =P mB For example, for the same power system, the reference value P of mechanical power... mB Equal to electrical power P e The benchmark value P eB The reference value of three-phase power is equal to the reference value of voltage U. B of Multiplied by the reference value I of the current I B That is, P eB = U B ×I B Therefore, T mB ×ω mB =P mB =P eB = U B ×I B This establishes a strict mathematical relationship between the baseline values ​​of different types of variables, forming a baseline value system where all types of variables have corresponding baseline values. This is the basic principle of per-unit model standardization in power systems. Therefore, since both transfer functions H(s) and G(s) are dimensionless, when a variable is used in a calculation with the transfer function, the variable's nominal value must first be converted to a per-unit value based on its corresponding baseline value before being used in the calculation with the transfer function.

[0123] The following describes the selection strategy for the first position Q1 and the second position Q2 when building the entire power system in the embodiments of this application.

[0124] 1) The selection of the first position Q1 must first satisfy the requirement that the signal can be acquired. In the renewable energy grid-connected power system 100, some signals are easy to acquire, while others are not. For example, line current, bus voltage, and high-voltage cylinder speed of synchronous generator sets are easy to measure technically. Therefore, these signals can be used as state variables of the input feedback path, and the corresponding positions can be used as candidate points for the first position Q1. Conversely, the internal state variables of the grid-connected converter controller, the stator flux linkage or rotor flux linkage of the synchronous generator, and the intermediate-pressure cylinder speed and low-pressure cylinder speed of the synchronous generator shaft system are difficult to measure directly. Therefore, these signals cannot be used as state variables of the input feedback path, and the corresponding positions cannot be used as candidate points for the first position Q1.

[0125] Secondly, for the first position Q1, it must also meet the requirement of outstanding oscillation performance.

[0126] Oscillations are prominent, also known as observability. In a given oscillation mode, the oscillation amplitudes of each state variable are different; therefore, the state variable with the relatively larger oscillation amplitude should be selected. For a given oscillation mode (corresponding to a pair of conjugate poles), the right eigenvector measures the relative magnitude of the oscillation amplitudes of each state variable within that mode. The transfer function of a renewable energy grid-connected power system, expressed in state-space form, is as follows: As previously introduced, matrix A is an N-dimensional state matrix, and its eigenvalues ​​are the poles of the transfer function of the renewable energy grid-connected power system. The state variable x is a column vector x=[x1,x2, …, x… N ] T T represents the matrix transpose. If we define the eigenvalue diagonal matrix Λ = diag(λ1, λ2, ..., λ...), then... N The right eigenvector matrix R = [r1, r2, …, r N ], where r i Let r be a column vector. i =[r 1i ,r 2i , …,r Ni ] T T represents the matrix transpose, then r i For the first i eigenvalues ​​λ i (representing the i-th oscillation mode λ) i The corresponding right eigenvector. Oscillation mode λ i The j-th state variable x j and the k-th state variable x k The ratio r of the oscillation amplitudes reflected on (j≠k) i,jkFor |r ji / r ki |

[0127] If r i,jk >1 indicates that in the oscillation mode λ i Below, x j The oscillation at x is more pronounced than x k The oscillations at that location are more pronounced.

[0128] If r i,jk ≈0 indicates that in x j At that point, the oscillation mode λ i The amplitude is almost zero, i.e., the oscillation mode λ i In x j The oscillations are almost unobservable (i.e., the oscillations are not prominent).

[0129] Using the above method, the ratio of the oscillation amplitudes of every two state variables in the state variable set for each oscillation mode is calculated. This state variable set includes all measurable state variables in the renewable energy grid-connected power system 100. This ratio of oscillation amplitudes is then quantified as the basis for selecting the first location Q1. The problem of selecting the first location Q1 is transformed into a constrained location optimization problem. That is, under the constraint that all oscillation modes can be effectively observed, the location with the highest overall benefit (i.e., relatively prominent oscillation performance) corresponding to each state variable in the state variable set within the renewable energy grid-connected power system 100 is selected as a candidate point for the first location Q1. The solution method for the constrained location optimization problem can refer to existing related technologies.

[0130] Among all candidate points for the first position Q1, the candidate point that simultaneously satisfies both the conditions of signal acquisition and outstanding oscillation performance is determined, and this candidate point can be identified as the first position Q1. If there are multiple candidate points for the first position Q1 that simultaneously satisfy the above two conditions, then any one of them can be selected as the first position Q1.

[0131] 2) The second position Q2 must first satisfy the condition that it is upstream of the first position Q1 in the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system 100. All positions upstream of the first position Q1 in the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system 100 can be used as candidate points for the second position Q2.

[0132] Secondly, the second position Q2 must also satisfy the requirement of controllability, meaning the signal can be controlled. The bus voltage, the excitation controller voltage, and the line current can be controlled in magnitude; therefore, these signals can be used as control variables for feedback injection, and the positions corresponding to these signals can be candidate points for the second position Q2. Conversely, the internal state variables of the grid-connected converter controller, the stator or rotor flux linkage of the synchronous generator set, and the rotational speeds of the cylinders in the synchronous generator set's shaft system cannot be directly controlled; therefore, these signals cannot be used as state variables in the input feedback path, and the positions corresponding to these signals cannot be candidate points for the second position Q2.

[0133] In addition, the second position Q2 also needs to have a significant impact on the oscillation mode, that is, to select a state variable that has a significant impact on the oscillation mode for control.

[0134] The left eigenvector matrix V of matrix A is V=(R -1 ) T -1 represents matrix inversion, T represents matrix transpose, where V = [v1, v2, …, v N ], v i Let v be a column vector. i =[v 1i ,v 2i , …,v Ni ] T If T represents the matrix transpose, then v i For the first i eigenvalues ​​λ i The corresponding left eigenvector. Then the j-th state variable x j and the k-th state variable x k (j≠k) for oscillation mode λ i The ratio of the degree of influence v i,jk For |v ji / v ki |

[0135] If v i,jk >1, indicating x j oscillation mode λ i The degree of influence is greater than x k The location is more prominent.

[0136] If v i,jk ≈0 indicates that in x j oscillation mode λ i The impact is almost zero.

[0137] Using the above method, the ratio of the influence of every two state variables in the state variable set under each oscillation mode is calculated. This state variable set includes all controllable state variables in the renewable energy grid-connected power system 100. This ratio of influence is then quantified as the basis for selecting the second position Q2. The problem of selecting the second position Q2 is transformed into a constrained point selection optimization problem. That is, under the constraint that all oscillation modes can be effectively controlled, the point with the highest overall benefit (i.e., the relatively large influence on the oscillation mode) corresponding to each state variable in the state variable set within the renewable energy grid-connected power system 100 is found and can be used as a candidate point for the second position Q2. The solution method for the constrained point selection optimization problem can refer to existing related technologies.

[0138] Among all candidate points for the second position Q2, the candidate point that simultaneously satisfies the following three conditions—being located upstream of the first position Q1 in the forward path direction of the transfer function from disturbance to output in the renewable energy grid-connected power system 100, being controllable, and having a significant impact on the oscillation mode—can be determined as the second position Q2. If there are multiple candidate points for the second position Q2 that simultaneously satisfy the above three conditions, any one of them can be randomly selected as the second position Q2.

[0139] After selecting the first position Q1 and the second position Q2, a suitable oscillation suppression device can be designed or selected accordingly. This device can output an oscillation suppression signal that is acceptable to the second position Q2 based on the state variables collected from the first position Q1. Then, the sampling terminal of the oscillation suppression device is connected to the first position Q1 of the renewable energy grid-connected power system, and the feedback terminal is connected to the second position Q2, forming a complete power system capable of suppressing oscillations. Once the complete power system is operational, oscillation-free power output can be achieved.

[0140] In an exemplary embodiment of this application, an oscillation suppression device is added to the renewable energy grid-connected power system as a feedback path to form a closed-loop feedback control system. The oscillation suppression device generates an oscillation suppression signal based on the state variables obtained from the renewable energy grid-connected power system and feeds it back to the renewable energy grid-connected power system, thereby suppressing oscillations in the renewable energy grid-connected power system. When oscillations occur in the renewable energy grid-connected power system due to the presence of two closely spaced conjugate pole pairs, by designing a set of conjugate pole pairs (i.e., a set of conjugate zero pairs in the entire power system) of the oscillation suppression device's transfer function to be located near the aforementioned two closely spaced conjugate pole pairs in the complex plane (i.e., the distance satisfies a preset proximity condition), the entire power system can contain a set of conjugate zero pairs located near the two closely spaced conjugate pole pairs. Mathematical derivation verifies that this reduces the residue of each pole in the two closely spaced conjugate pole pairs, thereby offsetting the oscillation problem caused by the two closely spaced conjugate pole pairs and suppressing the oscillations of the renewable energy grid-connected power system.

[0141] In an exemplary embodiment of this application, when a renewable energy grid-connected power system experiences oscillations due to the presence of two sets of conjugate pole pairs that are close to each other, the first and second conjugate zero pairs (i.e., the two sets of conjugate pole pairs of the entire power system) of the oscillation suppression device transfer function can be designed to keep them far apart from each other or one set far apart from the other (i.e., the distance does not meet the preset condition of being close to each other). Furthermore, the absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair (i.e., one of the two sets of conjugate pole pairs that are close to each other). Through mathematical derivation and verification, the residue corresponding to each pole in the two sets of conjugate pole pairs that are close to each other can be reduced, thereby offsetting the oscillation problem caused by the two sets of conjugate pole pairs that are close to each other, and thus suppressing the oscillation of the renewable energy grid-connected power system.

[0142] This application embodiment also provides a power system including a renewable energy grid-connected power system and an oscillation suppression device as a feedback path. The sampling end of the oscillation suppression device is connected to a first position of the renewable energy grid-connected power system, and the feedback end of the oscillation suppression device is connected to a second position of the renewable energy grid-connected power system. In the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system, the second position is located upstream of the first position. The oscillation suppression device is used to implement the steps of a power system oscillation suppression method, which includes: In the poles of the first transfer function of the renewable energy grid-connected power system, determine the first target conjugate pole pair and the second target conjugate pole pair that satisfy the preset mutual proximity condition on the complex plane; A first conjugate pole pair is determined on the complex plane; wherein the distance between the first conjugate pole pair and the first target conjugate pole pair and / or the second target conjugate pole pair satisfies a preset condition of mutual proximity. Construct the second transfer function based on the first conjugate pole pair; The state variables of the renewable energy grid-connected power system are sampled from the first position, and an oscillation suppression signal is generated based on the state variables and the second transfer function. The oscillation suppression signal is input in reverse phase into the renewable energy grid-connected power system through the second position to suppress oscillations in the renewable energy grid-connected power system.

[0143] Optionally, the power system oscillation suppression method further includes: On the left half of the complex plane, determine the first conjugate zero pair and the second conjugate zero pair; wherein the distance between the first conjugate zero pair and the second conjugate zero pair does not satisfy the preset condition of mutual proximity, and the absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair. Based on the first conjugate pole pair, construct the second transfer function, including: Construct the second transfer function based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair.

[0144] Optionally, the power system oscillation suppression method further includes: The DC gain between the second and first positions was determined by step response testing. The gain of the transfer function between the second position and the first position is determined based on the DC gain and the first target conjugate pole pair and the second target conjugate pole pair. The range of the target gain is determined based on the gain of the transfer function between the second position and the first position. The gain of the second transfer function is determined from the range of the target gain values; Based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair, construct the second transfer function, including: The second transfer function is constructed based on the first conjugate pole pair, the first conjugate zero pair, the second conjugate zero pair, and the gain of the second transfer function.

[0145] Optionally, the power system oscillation suppression method further includes: A third pair of conjugate zeros is determined on the left half of the complex plane; wherein the distances between the third pair of conjugate zeros and the first and second target conjugate poles do not satisfy the preset condition of mutual proximity. Based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair, construct the second transfer function, including: Construct the second transfer function based on the first conjugate pole pair, the first conjugate zero pair, the second conjugate zero pair, and the third conjugate zero pair.

[0146] Optionally, the absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair, including any of the following cases: The absolute value of the imaginary part of the first conjugate zero pair is greater than the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is less than the absolute value of the imaginary part of the first target conjugate pole pair. The absolute value of the imaginary part of the first conjugate zero pair is less than the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is greater than the absolute value of the imaginary part of the first target conjugate pole pair; The absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is equal to the absolute value of the imaginary part of the first target conjugate pole pair.

[0147] Optionally, the target gain value range includes: greater than 10 / And less than 1; where, Let be the gain of the transfer function between the second position and the first position.

[0148] Optionally, the preset condition for proximity includes that the distance between two points on the complex plane is less than or equal to one-tenth of the target value, where the target value is the larger of the two moduli.

[0149] Optionally, an oscillation suppression signal is generated based on the state variables and the second transfer function, including: Obtain the steady-state value or rated value corresponding to the state variable, and determine the deviation signal between the state variable and the steady-state value or rated value corresponding to the state variable to obtain the oscillation signal; Multiplying the Laplace transform of the oscillating signal by the second transfer function yields the first intermediate signal; Perform an inverse Laplace transform on the first intermediate signal to obtain the second intermediate signal; The second intermediate signal is converted into an oscillation suppression signal that can be received at the second position.

[0150] Optionally, the renewable energy grid-connected power system includes: photovoltaic power plants, flexible DC transmission systems, and AC transmission channels; The first location is in the DC transmission line of the flexible DC transmission system, and the second location is in the power output path of the photovoltaic modules in the photovoltaic power station. The state variable is the DC voltage of the DC transmission line, the steady-state value corresponding to the state variable is the steady-state value of the DC voltage of the DC transmission line, and the second intermediate signal is the current signal. The oscillation suppression device includes a current controller and an energy storage device. It converts a second intermediate signal into an oscillation suppression signal that can be received at a second position. The process includes: superimposing the inverted second intermediate signal with a first current signal through the current controller and then obtaining a trigger signal through current regulation. The first current signal is the deviation signal between the per-unit value of the command current value of the energy storage battery in the energy storage device and the per-unit value of the actual charge and discharge current value of the energy storage battery. The trigger signal is input into the energy storage device, and the oscillation suppression current signal that can be received by the power output path of the photovoltaic module is output through the energy storage device.

[0151] Optionally, the renewable energy grid-connected power system includes: wind farms, synchronous generator units, and AC transmission channels; The synchronous generator set includes a multi-stage cylinder, wherein the first-stage cylinder is the cylinder with the highest steam inlet pressure among the multi-stage cylinders, the first position is located in the first-stage cylinder, and the second position is located in the excitation controller of the synchronous generator set; The state variable is the angular frequency of the first-stage cylinder, the steady-state value corresponding to the state variable is the steady-state value of the angular frequency of the first-stage cylinder, and the second intermediate signal is a voltage signal. Converting the second intermediate signal into an oscillation suppression signal receivable at the second position includes: multiplying the second intermediate signal by a target rated value to obtain an oscillation suppression excitation control signal receivable by the excitation controller, wherein the target rated value is equal to the ratio of the generator rated excitation voltage of the synchronous generator set to the rated power frequency angular velocity of the synchronous generator set.

[0152] Optionally, the real parts of the first conjugate pole pair are all greater than -1 and less than 0.

[0153] Optionally, the real parts of the first conjugate zero pair are all greater than -1 and less than 0, the real parts of the second conjugate zero pair are all greater than -1 and less than 0, and the real parts of the third conjugate zero pair are all greater than -1 and less than 0.

[0154] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0155] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for suppressing power system oscillations, characterized in that, An oscillation suppression device is applied to a power system, the power system including a renewable energy grid-connected power system and the oscillation suppression device as a feedback path. The sampling end of the oscillation suppression device is connected to a first location of the renewable energy grid-connected power system, and the feedback end of the oscillation suppression device is connected to a second location of the renewable energy grid-connected power system. In the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system, the second location is located upstream of the first location. The power system oscillation suppression method includes: Among the poles of the first transfer function of the renewable energy grid-connected power system, a first target conjugate pole pair and a second target conjugate pole pair that satisfy a preset mutual proximity condition on the complex plane are determined; A first conjugate pole pair is determined on the complex plane; wherein the distance between the first conjugate pole pair and the first target conjugate pole pair and / or the second target conjugate pole pair satisfies the preset mutual proximity condition; Construct the second transfer function based on the first conjugate pole pair; The state variables of the renewable energy grid-connected power system are sampled from the first location, and an oscillation suppression signal is generated based on the state variables and the second transfer function; The oscillation suppression signal is inverted and input into the renewable energy grid-connected power system through the second position to suppress oscillations in the renewable energy grid-connected power system.

2. The power system oscillation suppression method according to claim 1, characterized in that, The power system oscillation suppression method also includes: On the left half of the complex plane, a first pair of conjugate zeros and a second pair of conjugate zeros are determined; wherein the distance between the first pair of conjugate zeros and the second pair of conjugate zeros does not satisfy the preset condition of mutual proximity, and the absolute value of the imaginary part of the first pair of conjugate zeros is not equal to the absolute value of the imaginary part of the first target pair of conjugate poles. The step of constructing the second transfer function based on the first conjugate pole pair includes: The second transfer function is constructed based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair.

3. The power system oscillation suppression method according to claim 2, characterized in that, The power system oscillation suppression method also includes: The DC gain between the second position and the first position is determined by step response testing; Based on the DC gain and the first target conjugate pole pair and the second target conjugate pole pair, determine the gain of the transfer function between the second position and the first position; The target gain range is determined based on the gain of the transfer function between the second position and the first position. The gain of the second transfer function is determined from the range of the target gain values; The step of constructing the second transfer function based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair includes: The second transfer function is constructed based on the first conjugate pole pair, the first conjugate zero pair, the second conjugate zero pair, and the gain of the second transfer function.

4. The power system oscillation suppression method according to claim 2, characterized in that, The power system oscillation suppression method also includes: A third pair of conjugate zeros is determined on the left half of the complex plane; wherein the distances between the third pair of conjugate zeros and the first pair of target conjugate poles and the second pair of target conjugate poles do not satisfy the preset condition of mutual proximity. The step of constructing the second transfer function based on the first conjugate pole pair, the first conjugate zero pair, and the second conjugate zero pair includes: The second transfer function is constructed based on the first conjugate pole pair, the first conjugate zero pair, the second conjugate zero pair, and the third conjugate zero pair.

5. The power system oscillation suppression method according to claim 2, characterized in that, The absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair, including any of the following cases: The absolute value of the imaginary part of the first conjugate zero pair is greater than the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is less than the absolute value of the imaginary part of the first target conjugate pole pair; The absolute value of the imaginary part of the first conjugate zero pair is less than the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is greater than the absolute value of the imaginary part of the first target conjugate pole pair; The absolute value of the imaginary part of the first conjugate zero pair is not equal to the absolute value of the imaginary part of the first target conjugate pole pair, and the absolute value of the imaginary part of the second conjugate zero pair is equal to the absolute value of the imaginary part of the first target conjugate pole pair.

6. The power system oscillation suppression method according to claim 3, characterized in that, The target gain range includes: greater than 10 / And less than 1; where, The gain of the transfer function between the second position and the first position.

7. The power system oscillation suppression method according to claim 1, characterized in that, The preset condition for mutual proximity includes that the distance between two points on the complex plane is less than or equal to one-tenth of a target value, where the target value is the larger of the moduli of the two points.

8. The power system oscillation suppression method according to claim 3, characterized in that, The step of generating an oscillation suppression signal based on the state variable and the second transfer function includes: Obtain the steady-state value or rated value corresponding to the state variable, and determine the deviation signal between the state variable and the steady-state value or rated value corresponding to the state variable to obtain the oscillation signal; Multiplying the Laplace transform of the oscillating signal by the second transfer function yields the first intermediate signal; Perform an inverse Laplace transform on the first intermediate signal to obtain the second intermediate signal; The second intermediate signal is converted into an oscillation suppression signal that can be received at the second position.

9. The power system oscillation suppression method according to claim 8, characterized in that, The renewable energy grid-connected power system includes: photovoltaic power plants, flexible DC transmission systems, and AC transmission channels; The first location is located on the DC transmission line in the flexible DC transmission system, and the second location is located on the power output path of the photovoltaic module in the photovoltaic power station; The state variable is the DC voltage of the DC transmission line, the steady-state value corresponding to the state variable is the steady-state value of the DC voltage of the DC transmission line, and the second intermediate signal is a current signal; The oscillation suppression device includes a current controller and an energy storage device. The step of converting the second intermediate signal into an oscillation suppression signal receivable at the second position includes: superimposing the inverted second intermediate signal with a first current signal through the current controller and then obtaining a trigger signal through current regulation, wherein the first current signal is the deviation signal between the per-unit value of the command current value of the energy storage battery in the energy storage device and the per-unit value of the actual charge and discharge current value of the energy storage battery; inputting the trigger signal into the energy storage device, and outputting an oscillation suppression current signal receivable by the power output path of the photovoltaic module through the energy storage device.

10. The power system oscillation suppression method according to claim 8, characterized in that, The renewable energy grid-connected power system includes: wind farms, synchronous generator sets, and AC transmission channels; The synchronous generator set includes a multi-stage cylinder, wherein the first-stage cylinder is the cylinder with the highest steam inlet pressure among the multi-stage cylinders, the first position is located in the first-stage cylinder, and the second position is located in the excitation controller of the synchronous generator set. The state variable is the rotational speed angular frequency of the first stage cylinder, the rated value corresponding to the state variable is the rated value of the rotational speed angular frequency of the first stage cylinder, and the second intermediate signal is a voltage signal; The step of converting the second intermediate signal into an oscillation suppression signal receivable at the second position includes: multiplying the second intermediate signal by a target rated value to obtain an oscillation suppression excitation control signal receivable by the excitation controller, wherein the target rated value is equal to the generator rated excitation voltage of the synchronous generator set.

11. The power system oscillation suppression method according to claim 1, characterized in that, The real parts of the first conjugate pole pair are all greater than -1 and less than 0.

12. The power system oscillation suppression method according to claim 3, characterized in that, The real parts of the first conjugate zero pairs are all greater than -1 and less than 0, the real parts of the second conjugate zero pairs are all greater than -1 and less than 0, and the real parts of the third conjugate zero pairs are all greater than -1 and less than 0.

13. An electric power system, characterized in that, The power system includes a renewable energy grid-connected power system and an oscillation suppression device as a feedback path. The sampling end of the oscillation suppression device is connected to a first position of the renewable energy grid-connected power system, and the feedback end of the oscillation suppression device is connected to a second position of the renewable energy grid-connected power system. In the forward path direction of the transfer function from disturbance to output of the renewable energy grid-connected power system, the second position is located upstream of the first position. The oscillation suppression device is used to implement the steps of the power system oscillation suppression method according to any one of claims 1-12.

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