Wind power system synchronous stability control method based on additional voltage controller under asymmetric fault

Abstract

The invention provides a wind power system synchronous stability control method based on an additional voltage controller under an asymmetric fault. The method comprises the following steps: collecting a three-phase AC voltage signal of a grid-connected point; obtaining a d-axis positive sequence voltage signal, a d-axis negative sequence voltage signal, a q-axis positive sequence voltage signal and a q-axis negative sequence voltage signal; taking the q-axis positive sequence voltage signal and the q-axis negative sequence voltage signal as input signals of a positive sequence phase-locked loop and a negative sequence phase-locked loop respectively; during an asymmetric fault period, respectively calculating an additional positive sequence voltage q-axis component delta U + q + and an additional negative sequence voltage q-axis component delta U-q-; during the asymmetric fault period, if positive sequence instability occurs in the wind power grid-connected system, delta U + q + is added to the input of the positive sequence phase-locked loop; and if negative sequence instability occurs in the wind power grid-connected system, delta U-q-is added to the input of the negative sequence phase-locked loop. According to the method, the synchronization stability of the wind power system during the asymmetric fault period is enhanced on the basis of not increasing hardware equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a synchronous stability control method for a wind power system based on an additional voltage controller under asymmetric faults, which can significantly improve the synchronous stability of a wind power grid-connected system under asymmetric short-circuit faults in a power grid. Background Art

[0002] With the rapid development of wind energy utilization technology, traditional synchronous power generation equipment will be continuously replaced, and the weakening of the power grid will become more and more serious. In the case of weak grid, wind power systems are prone to synchronous instability during grid faults. Compared with symmetrical short-circuit faults in the power grid, asymmetrical short-circuit faults in the power grid are more likely to occur in actual systems, and it is necessary to consider the synchronous stability under the double sequence domain (positive sequence and negative sequence). Therefore, in order to ensure that the wind power system can maintain grid-connected operation under asymmetrical faults, it is necessary to further study the synchronous stability control method of the wind power system under asymmetrical faults. At present, scholars at home and abroad have carried out relevant research, such as the following published documents:

[0003] [1]S.Ma,H.Geng,L.Liu,et al.Grid-Synchronization Stability Improvement of Large Scale Wind Farm During Severe Grid Fault[J].IEEE Transactions onPower Systems,2018,33(1):216-226;[2]X.He,H.Geng,J.Xi,et al.ResynchronizationAnalysis and Improvement of Grid-Connected VSCs During Grid Faults[J].IEEE Journal of Emerging and Selected Topics in Power Electronics.2021,9(1):438-450.

[0004] Reference [1] obtained the differential equations describing the dynamic process of system synchronization and proposed an adaptive current injection method to ensure that the system can maintain synchronization when the power grid is seriously faulty. However, this method relies on the accurate estimation of the power grid impedance and is not adaptive. Reference [2] pointed out that the key factor affecting synchronization is the integral regulator of the phase-locked loop, and then proposed a control method for locking the integral regulator of the phase-locked loop during the fault. However, this method cannot make the system run back to the equilibrium point and is not suitable for systems without equilibrium points. In addition, the above methods are all proposed for symmetrical short-circuit faults in the power grid, and do not consider the double-sequence instability that may occur during asymmetrical short-circuit faults. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a synchronous stability control method for a wind power system based on an additional voltage controller under asymmetric faults. This method can enhance the synchronous stability of the wind power system during asymmetric faults by only changing the control mode of the positive and negative sequence phase-locked loops of the wind power system without adding hardware equipment.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a synchronous stability control method for a wind power system based on an additional voltage controller under an asymmetric fault, and the steps are as follows:

[0008] A1. Collect three-phase AC voltage signals at the grid connection point;

[0009] A2. Obtain a d-axis positive-sequence voltage signal, a d-axis negative-sequence voltage signal, a q-axis positive-sequence voltage signal, and a q-axis negative-sequence voltage signal through a rotating coordinate transformation according to the three-phase AC voltage signal of the grid connection point;

[0010] A3. The q-axis positive-sequence voltage signal and the q-axis negative-sequence voltage signal are used as input signals of the positive-sequence phase-locked loop and the negative-sequence phase-locked loop respectively;

[0011] A4. During an asymmetric fault, the additional positive sequence voltage q-axis component ΔU+q+ and the additional negative sequence voltage q-axis component ΔU﹣q﹣ are calculated respectively;

[0012] A5. During an asymmetric fault, if the wind power grid-connected system suffers from positive-sequence instability, the ΔU+q+ obtained in step A4 is added to the input of the positive-sequence phase-locked loop, so that the wind power grid-connected system regains the positive-sequence balance point; if the wind power grid-connected system suffers from negative-sequence instability, the ΔU﹣q﹣ obtained in step A4 is added to the input of the negative-sequence phase-locked loop, so that the wind power grid-connected system regains the negative-sequence balance point.

[0013] Furthermore, in the step A1, the three-phase AC voltage signal of the grid connection point is collected according to the generator convention of the wind power grid connection system.abc .

[0014] Furthermore, the step A2 is specifically as follows: using the grid voltage d-axis orientation method to transform the three-phase AC voltage signal U abc Through the stationary three-phase abc coordinate system to the forward synchronous angular velocity and reverse synchronous angular velocity rotating coordinate axis system, and then through the notch filter, the d-axis positive-sequence voltage signal U+d+, d-axis negative-sequence voltage signal U﹣d﹣, q-axis positive-sequence voltage signal U+q+, and q-axis negative-sequence voltage signal U﹣q﹣ are obtained.

[0015] Furthermore, the positive-sequence phase-locked loop is a phase-locked loop control structure based on an additional positive-sequence voltage controller.

[0016] Furthermore, the negative-sequence phase-locked loop is a phase-locked loop control structure based on an additional negative-sequence voltage controller.

[0017] Furthermore, in step A4, the additional positive sequence voltage q-axis component ΔU+q+ is calculated as follows:

[0018] The additional positive sequence voltage q-axis component ΔU+q+ is calculated according to the following formula:

[0019]

[0020] Among them, k+pt and k+it are the proportional coefficient and integral coefficient used to calculate the additional positive-sequence voltage q-axis component ΔU+q+, ω+PLL is the positive-sequence phase-locked loop output angular frequency, and ω0 is the rated angular frequency of the power grid.

[0021] Furthermore, in step A4, the additional negative sequence voltage q-axis component ΔU﹣q﹣ is calculated as follows:

[0022] The additional negative sequence voltage q-axis component ΔU﹣q﹣ is calculated according to the following formula:

[0023]

[0024] Among them, k-pt and k-it are the proportional coefficient and integral coefficient used to calculate the additional negative sequence voltage q-axis component ΔU﹣q﹣, ω-PLL is the negative sequence phase-locked loop output angular frequency, and ω0 is the rated angular frequency of the power grid.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] Without adding any hardware equipment, the present invention can enable the wind power system to adaptively find the positive and negative sequence balance points by designing corresponding additional positive and negative sequence voltage controllers, thereby ensuring that the wind power system can maintain synchronization with the power grid during an asymmetric fault in the power grid, thereby improving the synchronization stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 This is a structural diagram of the wind power system connected to the power system.

[0029] Figure 2 This is a schematic diagram of the phase-locked loop control structure based on the additional voltage controller proposed in the present invention.

[0030] Figure 3 The simulation waveform diagrams are of the wind power grid-connected system after adopting the traditional control strategy and the control strategy proposed by the present invention respectively under the two-phase short-circuit grounding fault of the power grid.

[0031] Figure 4 The following are simulation waveform diagrams of the wind power grid-connected system after adopting the traditional control strategy and the control strategy proposed by the present invention respectively under the condition of single-phase short circuit grounding fault in the power grid. DETAILED DESCRIPTION

[0032] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0033] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0034] The embodiment of the present invention is used to enhance the synchronization stability of a wind power system under an asymmetric short circuit fault in a power grid. Figure 1 This is a structural diagram of the wind power system connected to the power system. Figure 2 The schematic diagram of the phase-locked loop control structure based on the additional voltage controller proposed in the present invention is shown in Figure 1. During an asymmetric short circuit fault in the power grid, by using additional positive and negative sequence voltage controllers, the wind power system can adaptively find the positive and negative sequence balance points, thereby enhancing the synchronous stability of the wind power system.

[0035] The specific implementation steps of the present invention are as follows:

[0036] A synchronous stability control method for a wind power system based on an additional voltage controller under an asymmetric fault, the steps are as follows:

[0037] A1) According to the wind power grid-connected system, the generator convention is used to collect the three-phase AC voltage signal U at the grid-connected point abc , using the grid voltage d-axis orientation method to abc Through the stationary three-phase abc coordinate system to the forward synchronous angular velocity and reverse synchronous angular velocity rotating coordinate axis system, and then through the notch filter, the d-axis positive-sequence voltage signal U+d+, d-axis negative-sequence voltage signal U﹣d﹣, q-axis positive-sequence voltage signal U+q+, and q-axis negative-sequence voltage signal U﹣q﹣ are obtained.

[0038] A2) U+q+ and U﹣q﹣ are used as the input signals of the positive sequence phase locked loop and the negative sequence phase locked loop respectively for subsequent control; Figure 2 As shown, the positive-sequence phase-locked loop is a phase-locked loop control structure based on an additional positive-sequence voltage controller, and the negative-sequence phase-locked loop is a phase-locked loop control structure based on an additional negative-sequence voltage controller.

[0039] A3) During an asymmetric fault, the additional positive sequence voltage q-axis component ΔU+q+ and the additional negative sequence voltage q-axis component ΔU﹣q﹣ are calculated according to the following formulas:

[0040]

[0041] Among them, k+pt and k+it are the proportional coefficient and integral coefficient used to calculate the additional positive-sequence voltage q-axis component ΔU+q+, k-pt and k-it are the proportional coefficient and integral coefficient used to calculate the additional negative-sequence voltage q-axis component ΔU﹣q﹣, ω+PLL is the positive-sequence phase-locked loop output angular frequency, ω-PLL is the negative-sequence phase-locked loop output angular frequency, and ω0 is the rated angular frequency of the power grid.

[0042] A4) During an asymmetric fault, if the wind power grid-connected system has positive sequence instability, the ΔU+q+ obtained in step A3) is added to the input U+q+ of the positive sequence phase-locked loop; if the wind power grid-connected system has negative sequence instability, the ΔU﹣q﹣ obtained in step A3) is added to the input U﹣q﹣ of the negative sequence phase-locked loop, so that the wind power grid-connected system can regain the positive and negative sequence balance points, thereby improving the synchronization stability of the wind power grid-connected system during an asymmetric fault.

[0043] Effect description of the present invention:

[0044] Figure 3The simulation waveforms of the wind power system using the traditional control strategy and the phase-locked loop control strategy based on the additional voltage controller proposed in the present invention are given when a two-phase short-circuit grounding fault occurs in the power grid. The fault occurs at 0.5s, and the positive and negative sequence voltages at the fault point are both 0.5pu. Figure 3 (1) It can be seen that when the traditional control strategy is adopted, the wind power system will experience positive sequence instability. Figure 3 (2) It can be seen that when the wind power system adopts the phase-locked loop control strategy based on the additional voltage controller proposed in the present invention, under the action of the additional positive-sequence voltage controller, the wind power system adaptively finds a positive-sequence balance point, so that the system can quickly keep in sync with the power grid, effectively enhancing the synchronization stability of the wind power system under asymmetric faults.

[0045] Figure 4 The simulation waveforms of the wind power system using the traditional control strategy and the phase-locked loop control strategy based on the additional voltage controller proposed in the present invention are given when a single-phase short-circuit grounding fault occurs in the power grid. The fault occurs at 0.5s, and the positive sequence voltage at the fault point is 0.86pu and the negative sequence voltage is 0.17pu. Figure 4 (1) It can be seen that when the traditional control strategy is adopted, the wind power system will experience negative sequence instability. Figure 4 (2) It can be seen that when the wind power system adopts the phase-locked loop control strategy based on the additional voltage controller proposed in the present invention, under the action of the additional negative-sequence voltage controller, the wind power system adaptively finds a negative-sequence balance point, so that the system can quickly keep in sync with the power grid, effectively enhancing the synchronization stability of the wind power system under asymmetric faults.

[0046] It can be seen that the phase-locked loop control strategy of the additional voltage controller proposed in the present invention can enable the wind power system to adaptively find the positive and negative sequence balance points during asymmetric faults, so that the system can quickly maintain synchronization with the power grid, effectively enhancing the synchronization stability of the wind power system under asymmetric faults.

[0047] The above is a detailed introduction to the synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A synchronous stability control method for a wind power system based on an additional voltage controller under asymmetric faults, characterized in that: Here are the steps: A1. Collect three-phase AC voltage signals at the grid connection point; A2. Obtain a d-axis positive-sequence voltage signal, a d-axis negative-sequence voltage signal, a q-axis positive-sequence voltage signal, and a q-axis negative-sequence voltage signal through a rotating coordinate transformation according to the three-phase AC voltage signal of the grid connection point; A3. The q-axis positive-sequence voltage signal and the q-axis negative-sequence voltage signal are used as input signals of the positive-sequence phase-locked loop and the negative-sequence phase-locked loop respectively; A4. During an asymmetric fault, the additional positive sequence voltage q-axis component ΔU+q+ and the additional negative sequence voltage q-axis component ΔU﹣q﹣ are calculated respectively; A5. During an asymmetric fault, if the wind power grid-connected system suffers from positive sequence instability, the ΔU+q+ obtained in step A4 is added to the input of the positive sequence phase-locked loop, so that the wind power grid-connected system regains the positive sequence balance point; If negative sequence instability occurs in the wind power grid-connected system, the ΔU﹣q﹣ obtained in step A4 is added to the input of the negative sequence phase-locked loop, so that the wind power grid-connected system regains the negative sequence balance point.

2. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 1 is characterized in that: In the step A1, the three-phase AC voltage signal of the grid connection point is collected according to the generator convention of the wind power grid connection system. abc .

3. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 2 is characterized in that: The step A2 is specifically as follows: using the grid voltage d-axis orientation method to transform the three-phase AC voltage signal U abc Through the stationary three-phase abc coordinate system to the forward synchronous angular velocity and reverse synchronous angular velocity rotating coordinate axis system, and then through the notch filter, the d-axis positive-sequence voltage signal U+d+, d-axis negative-sequence voltage signal U﹣d﹣, q-axis positive-sequence voltage signal U+q+, and q-axis negative-sequence voltage signal U﹣q﹣ are obtained.

4. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 1, characterized in that: The positive sequence phase locked loop is a phase locked loop control structure based on an additional positive sequence voltage controller.

5. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 1, characterized in that: The negative sequence phase locked loop is a phase locked loop control structure based on an additional negative sequence voltage controller.

6. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 1, characterized in that: In step A4, the additional positive sequence voltage q-axis component ΔU+q+ is calculated as follows: The additional positive sequence voltage q-axis component ΔU+q+ is calculated according to the following formula: Among them, k+pt and k+it are the proportional coefficient and integral coefficient used to calculate the additional positive-sequence voltage q-axis component ΔU+q+, ω+PLL is the positive-sequence phase-locked loop output angular frequency, and ω0 is the rated angular frequency of the power grid.

7. The synchronous stability control method of a wind power system based on an additional voltage controller under an asymmetric fault according to claim 1, characterized in that: In step A4, the additional negative sequence voltage q-axis component ΔU﹣q﹣ is calculated as follows: The additional negative sequence voltage q-axis component ΔU﹣q﹣ is calculated according to the following formula: Among them, k-pt and k-it are the proportional coefficient and integral coefficient used to calculate the additional negative sequence voltage q-axis component ΔU﹣q﹣, ω-PLL is the negative sequence phase-locked loop output angular frequency, and ω0 is the rated angular frequency of the power grid.

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