A transient synchronous stability control method for a droop control type grid-connected inverter

Abstract

The application discloses a kind of transient synchronous stability control methods for droop control type grid-connected inverter, since grid short-circuit fault can cause the active power output of droop control type grid-connected inverter to drop, the imbalance degree between power reference value and output active power intensifies, causing the output angular frequency of droop control type grid-connected inverter to gradually deviate from the rated angular frequency of grid, so the deviation between output angular frequency and rated angular frequency of grid is utilized to construct feedback compensation term, which can be added to the input of active power control loop of droop control type grid-connected inverter.In the period of grid short-circuit fault, the application can automatically adjust the unbalanced active power of droop control type grid-connected inverter, so that the droop control type grid-connected inverter can independently find the balance point and realize smooth transition to the stable balance point, thereby realizing the synchronous stable operation of droop control type grid-connected inverter and grid during short-circuit fault, and enhancing the transient operating capability.

Description

Technical Field

[0001] The present invention relates to the field of renewable energy power generation technology, and in particular to a transient synchronous stability control method for a droop-controlled grid-connected inverter. The method can significantly improve the transient stability of the droop-controlled grid-connected inverter during a power grid short-circuit fault. Background Art

[0002] With the continuous development of new energy power generation technology and the continuous increase in the penetration rate of new energy, the support capacity of traditional power sources such as synchronous generators for the power system continues to weaken, resulting in a decrease in the system inertia level and the gradual emergence of insufficient disturbance suppression capabilities. Especially in the case of severe large disturbances such as grid short-circuit faults, new energy grid-connected inverters are very prone to transient synchronization instability problems, threatening the safe and reliable operation of the power system. Therefore, in order to improve the transient stability operation capability of new energy grid-connected inverters under grid short-circuit faults and ensure the friendly interactive operation of new energy grid-connected inverters and the power grid, it is urgent to conduct in-depth research on the transient synchronization stability control strategy of new energy grid-connected inverters under grid short-circuit faults. At present, some scholars at home and abroad have conducted relevant research, such as the following published literature:

[0003] [1] Zhang Yu, Zhang Chen, Cai Xu, et al. Transient synchronization stability analysis of grid-connected converters: stability region estimation and stabilization control [J]. Proceedings of the CSEE, 2022, 42(21): 7871-7884.

[0004] [2] Remus Teodorescu, Claus Leth Bak, et al. Instability of wind turbine converters during current injection to low voltage grid faults and PLL frequency-based stability solution [J]. IEEE Transactions on PowerSystems, 2014, 29(4): 1683-1961.

[0005] Reference [1] firstly constructs a Lyapunov function suitable for studying the transient synchronization stability problem of the renewable energy grid-connected inverter by using the direct method, and then analytically derives the stability domain expression and the quantitative index of the stability margin; based on this analytical method, it reveals the influence of key parameters on the transient synchronization stability of the system, and thus proposes a transient stability control method from two perspectives: compensating for the negative damping effect of the active current and guiding the state trajectory of the phase-locked loop into the stability domain through the integral limiter. Reference [2] proposes an improved control method for the active current reference value based on the feedback of the phase-locked loop output frequency deviation, which can help the renewable energy grid-connected inverter to autonomously find a stable operating point during a grid short-circuit fault and achieve a smooth transition to the operating point. The above stability strategies are all for phase-locked synchronous control type renewable energy grid-connected inverters, and do not involve the study of transient synchronization stability control methods for droop control type renewable energy grid-connected inverters. Related research work needs to be further carried out. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to propose a transient synchronization stability control method for a droop-controlled grid-connected inverter. This method can significantly improve the transient synchronization stability of the droop-controlled grid-connected inverter during a grid short-circuit fault by simply changing the control strategy of the power control loop of the droop-controlled grid-connected inverter without adding any hardware equipment.

[0007] The technical solution of the present invention is achieved as follows:

[0008] A transient synchronous stability control method for a droop-controlled grid-connected inverter is provided, which is used to improve the transient stability of the droop-controlled grid-connected inverter during a grid short-circuit fault. The method is performed as follows:

[0009] A1) During a grid short-circuit fault, the feedback compensation term ΔP is calculated according to the following formula: o :

[0010]

[0011] Among them, K o is the feedback compensation term ΔP o The proportionality coefficient, ω b is the angular frequency reference, Δω is the difference between the output angular frequency ω of the droop control grid-connected inverter and the rated angular frequency ω of the grid g The deviation between them; 1 / s is the integral symbol;

[0012] Among them, the feedback compensation term ΔP o The proportionality coefficient K o Calculate according to the following formula:

[0013] K o =U n / U g

[0014] Among them, U n is the rated value of the grid voltage, U g is the grid voltage amplitude during the grid short-circuit fault period;

[0015] A2) The feedback compensation term ΔP obtained in step A1) is converted to o The input is added to the active power control loop of the droop-controlled grid-connected inverter, so that the droop-controlled grid-connected inverter can adaptively improve the unbalanced active power during a grid short-circuit fault, thereby enhancing the transient synchronization stability of the droop-controlled grid-connected inverter.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] By designing corresponding feedback compensation items, the present invention enables the droop-controlled grid-connected inverter to automatically adjust the unbalanced active power during a grid short-circuit fault, so that the droop-controlled grid-connected inverter can autonomously find a balance point and achieve a smooth transition to the stable balance point, thereby achieving synchronous and stable operation of the droop-controlled grid-connected inverter and the grid during a short-circuit fault and enhancing transient operation capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of a droop-controlled grid-connected inverter connected to the grid.

[0019] Figure 2 Schematic diagram of the control structure of the transient synchronous stability control method proposed in the present invention.

[0020] Figure 3 The simulation waveform of the droop control grid-connected inverter using the traditional control strategy under a grid short-circuit fault.

[0021] Figure 4 The figure is a simulation waveform diagram of a droop control type grid-connected inverter after adopting the transient synchronous stability control method proposed in the present invention under a grid short circuit fault. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0023] The present invention is used to improve the transient synchronization stability of the droop control type grid-connected inverter under severe grid short circuit fault. The idea of ​​the present invention to solve the problem: due to the grid short circuit fault, the droop control type grid-connected inverter will output active power P e Decreases, making the power reference value P ref and output active power P eThe imbalance between them intensifies, causing the output angular frequency ω of the droop control grid-connected inverter to gradually deviate from the rated angular frequency ω of the grid. g , the output angular frequency ω and the grid rated angular frequency ω can be used g The deviation Δω between them constructs the feedback compensation term ΔP o , reducing the impact of unbalanced active power on the output angular frequency ω of the droop control type grid-connected inverter.

[0024] Figure 1 This is a structural diagram of a droop-controlled grid-connected inverter connected to the grid. Figure 2 This is a schematic diagram of the control structure of the transient synchronous stability control method proposed in this invention. During a grid short-circuit fault, the droop-controlled grid-connected inverter can adaptively adjust the unbalanced active power by adopting a feedback compensation term, thereby improving the transient synchronous stability of the droop-controlled grid-connected inverter.

[0025] The specific implementation steps of the present invention are as follows, please also refer to Figure 2 :

[0026] A1) During a grid short-circuit fault, the feedback compensation term ΔP is calculated according to the following formula: o :

[0027]

[0028] Among them, K o is the feedback compensation term ΔP o The proportionality coefficient, ω b is the angular frequency reference, 1 / s is the integral symbol;

[0029] Among them, the feedback compensation term ΔP o The proportionality coefficient K o Calculate according to the following formula:

[0030] K o =U n / U g

[0031] Among them, U n is the rated value of the grid voltage, U g is the grid voltage amplitude during the grid short-circuit fault period;

[0032] A2) The feedback compensation term ΔP obtained in step A1) is converted to o By adding it to the input of the active power control loop of the droop-controlled grid-connected inverter, the droop-controlled grid-connected inverter can adaptively improve the unbalanced active power during a grid short-circuit fault, thereby enhancing the transient synchronization stability of the droop-controlled grid-connected inverter.

[0033] Effect description of the present invention:

[0034] Figure 3 and Figure 4 The simulation waveforms of the droop control type grid-connected inverter using the traditional control strategy and the transient synchronous stability control method proposed in this invention are given when the grid voltage drops to 0.3pu. Figure 3 It can be seen that when the droop control type grid-connected inverter adopts the traditional control strategy, the system cannot converge to the stable equilibrium point during the fault period, and transient synchronization instability occurs. In contrast, when the droop control type grid-connected inverter adopts the transient synchronization stability control method proposed in this invention, Figure 4 It can be seen that under the action of the feedback compensation term, the droop control grid-connected inverter can quickly recover to the synchronous and stable operation state during the fault period, which significantly improves the transient synchronous stability of the droop control grid-connected inverter.

[0035] It can be seen that the transient synchronous stability control method proposed in the present invention can help the droop control type grid-connected inverter to achieve a smooth transition to a stable equilibrium point, effectively improving the transient stable operation capability of the droop control type grid-connected inverter during a grid short-circuit fault.

[0036] Finally, it should be noted that the above examples of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art will appreciate that other variations and modifications can be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications derived from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A transient synchronous stability control method for a droop-controlled grid-connected inverter, for improving the transient stability of the droop-controlled grid-connected inverter during a grid short-circuit fault, characterized by: Follow the steps below, A1) During a grid short-circuit fault, the feedback compensation term ΔP is calculated according to the following formula: o : Among them, K o is the feedback compensation term ΔP o The proportionality coefficient, ω b is the angular frequency reference, Δω is the difference between the output angular frequency ω of the droop control grid-connected inverter and the rated angular frequency ω of the grid g The deviation between them; 1 / s is the integral symbol; A2) The feedback compensation term ΔP obtained in step A1) is converted to o Adding an input to the active power control loop of the droop-controlled grid-connected inverter enables the droop-controlled grid-connected inverter to adaptively improve the unbalanced active power during a grid short-circuit fault, thereby enhancing the transient synchronization stability of the droop-controlled grid-connected inverter; The feedback compensation term ΔP o The proportionality coefficient K o Calculate according to the following formula: K o =U n / IN g Among them, U n is the rated value of the grid voltage, U g is the grid voltage amplitude during the grid short circuit fault.

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