Transient synchronous stability control method for droop control type grid-connected inverter

Abstract

The invention discloses a transient synchronous stability control method for a droop control type grid-connected inverter, which is characterized in that the output active power of the droop control type grid-connected inverter is reduced due to a short-circuit fault of a power grid, and the unbalance degree between a power reference value and the output active power is aggravated. As a result, the output angular frequency of the droop control type grid-connected inverter gradually deviates from the rated angular frequency of the power grid, a feedback compensation item is constructed by using the deviation between the output angular frequency and the rated angular frequency of the power grid, and the obtained feedback compensation item is added to the input of an active power control loop of the droop control type grid-connected inverter. During the short-circuit fault period of the power grid, the droop control type grid-connected inverter can automatically adjust the unbalanced active power, so that the droop control type grid-connected inverter can autonomously find a balance point and realize smooth transition to the stable balance point, thereby realizing synchronous and stable operation of the droop control type grid-connected inverter and the power grid during the short-circuit fault period. And the transient operation capability is enhanced.

Description

Technical Field

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

[0002] With the continuous development of renewable energy power generation technology and the continuous increase in the penetration rate of renewable energy, the support capacity of traditional power sources such as synchronous generators for power systems continues to weaken, resulting in a decrease in the system inertia level and the gradual emergence of insufficient disturbance suppression capabilities. Especially under severe disturbances such as power grid short-circuit faults, renewable energy grid-connected inverters are prone to transient synchronous instability problems, threatening the safe and reliable operation of the power system. Therefore, in order to improve the transient stable operation capability of renewable energy grid-connected inverters under power grid short-circuit faults and ensure the friendly interactive operation between renewable energy grid-connected inverters and power grids, it is urgent to conduct in-depth research on the transient synchronous stability control strategy of renewable energy grid-connected inverters under power grid short-circuit faults. At present, some scholars at home and abroad have conducted relevant research, such as the following publicly available 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, the influence of key parameters on the transient synchronization stability of the system is revealed, and thus a transient stability control method is proposed 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 working point during a grid short-circuit fault and achieve a smooth transition to the working point. The above stability strategies are all for phase-locked synchronous control type renewable energy grid-connected inverters, and do not involve the research on 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 control type grid-connected inverter. This method can significantly improve the transient synchronization stability of the droop control type grid-connected inverter during a grid short-circuit fault by only changing the control strategy of the power control loop of the droop control type grid-connected inverter without adding any hardware equipment.

[0007] The technical solution of the present invention is achieved in this way:

[0008] A transient synchronous stability control method for a droop control type grid-connected inverter is used to improve the transient stability of the droop control type grid-connected inverter during a power grid short circuit fault. The method is performed in the following steps:

[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 factor K o Calculate according to the following formula:

[0013] K o =U n / U g

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

[0015] A2) The feedback compensation term ΔP obtained in step A1) is o Adding the input to the active power control loop of the droop control type grid-connected inverter enables the droop control type 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 control type grid-connected inverter.

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

[0017] The present invention designs corresponding feedback compensation items. During a short-circuit fault in the power grid, the droop-controlled grid-connected inverter can automatically adjust the unbalanced active power, 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 power grid during the short-circuit fault and enhancing the transient operation capability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 It is a schematic diagram of the control structure of the transient synchronous stability control method proposed in the present invention.

[0020] Figure 3 It is the simulation waveform diagram of the droop control type grid-connected inverter when using the traditional control strategy under the grid short circuit fault.

[0021] Figure 4 It is a simulation waveform diagram of a droop control type grid-connected inverter after adopting the transient synchronous stability control method proposed by 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 a droop control type grid-connected inverter under a severe grid short-circuit fault. The idea of ​​the present invention to solve the problem is: due to a grid short-circuit fault, the droop control type grid-connected inverter will output active power P e The power reference value P ref And the output active power P eThe imbalance between them increases, 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 rated angular frequency ω of the power grid 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 control type grid-connected inverter connected to the power grid. Figure 2 The control structure diagram of the transient synchronization stability control method proposed in the present invention is as follows. During a short circuit fault in the power grid, the droop control type grid-connected inverter can adaptively adjust the unbalanced active power by adopting the feedback compensation term, thereby improving the transient synchronization stability of the droop control type 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 factor 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;

[0032] A2) The feedback compensation term ΔP obtained in step A1) is converted into o By adding it to the input of the active power control loop of the droop control type grid-connected inverter, the droop control type grid-connected inverter can adaptively improve the unbalanced active power during the grid short circuit fault, thereby enhancing the transient synchronization stability of the droop control type 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 by the present 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 the present invention, Figure 4 It can be seen that under the action of the feedback compensation term, the droop control type grid-connected inverter can quickly recover to the synchronous stable operation state during the fault period, which significantly improves the transient synchronization stability of the droop control type 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, and effectively improve 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 examples for illustrating 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 the preferred embodiments, for those of ordinary skill in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A transient synchronous stability control method for a droop control type grid-connected inverter, used to improve the transient stability of the droop control type grid-connected inverter during a grid short-circuit fault, characterized in that: 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 o Adding the input to the active power control loop of the droop control type grid-connected inverter enables the droop control type 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 control type grid-connected inverter.

2. The transient synchronous stability control method for a droop control type grid-connected inverter according to claim 1, characterized in that: The feedback compensation term ΔP o The proportionality factor K o Calculate according to the following formula: K o =U n / IN g Among them, U n is the rated voltage of the power grid, U g is the grid voltage amplitude during the grid short circuit fault.

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