Photovoltaic grid-connected inverter system transient stability control method based on double-sequence active current regulation

Abstract

The invention discloses a photovoltaic grid-connected inverter system transient stability control method based on double-sequence active current regulation, which comprises the following steps of: firstly, calculating to obtain positive and negative sequence components of additional d-axis active current, and then, during an asymmetric fault period of a power grid, according to a positive and negative sequence synchronous instability condition of a photovoltaic grid-connected inverter system, calculating the positive and negative sequence components of the additional d-axis active current; and negative feedback is carried out on the obtained d-axis active current positive and negative sequence components to corresponding input of the current loop. On the basis of not switching a control strategy, the reference values of the d-axis positive and negative sequence current are adaptively corrected by responding to the change of the positive and negative sequence q-axis components of the voltage of the grid-connected point, so that the deviation of the positive and negative sequence q-axis components of the voltage of the grid-connected point is reduced, a photovoltaic grid-connected inverter system can automatically return to a double-sequence stable balance point, and the stability of the grid-connected inverter system is improved. Finally, the double-sequence synchronous stable operation capability of the photovoltaic grid-connected inverter system during the asymmetric fault period of the power grid is ensured, and the positive and negative sequence synchronous instability risk of the photovoltaic grid-connected inverter system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a method for transient stability control of a photovoltaic grid-connected inverter system based on double-sequence active current regulation, which can significantly improve the double-sequence synchronization stability of the photovoltaic grid-connected inverter system during an asymmetric short-circuit fault of a power grid. Background Art

[0002] In the context of large-scale access of photovoltaic power generation to the power grid, the dominant characteristics of traditional synchronous generators in the power grid are gradually weakening, and the dynamic interaction between the photovoltaic grid-connected inverter system and the power grid and the transient stability of the photovoltaic grid-connected inverter system are becoming more complex and serious. Therefore, in order to improve the safe and stable operation capability of the photovoltaic grid-connected inverter system during asymmetric short-circuit faults in the power grid and reduce the risk of double-sequence synchronous instability of the system, it is urgent to further study the double-sequence synchronous stability control method of the photovoltaic grid-connected inverter system during asymmetric short-circuit faults in the power grid. At present, scholars at home and abroad have carried out relevant research, such as the following published literature:

[0003] [1] M.Graungaard Taul,

[0004] [2]S.Hasan and V.Agarwal.Avoltage support scheme for distributedgeneration with minimal phase current under asymmetrical grid faults[J].IEEETransactions on Industrial Electronics, 2023,70(10):10261-10270.

[0005] Reference [1] analyzes the grid code requirements for positive and negative sequence current injection during asymmetric faults, and proposes an asymmetric fault current reference control strategy that meets the grid code requirements. However, this method is difficult to implement because it involves parameter settings of multiple controllers. In real scenarios, the diversity of asymmetric grid fault conditions may cause this strategy to be inapplicable in some cases. Reference [2] found that the traditional dual-sequence synchronous stability control strategy requires different current injections to restore the system's grid connection point voltage. Once the phase current reaches the rated value of the system, the system's voltage support capability will be affected. A dual-sequence synchronous stability control strategy that reduces the highest phase current and provides additional voltage support for the grid is proposed. However, on the one hand, since this strategy requires the use of a three-dimensional lookup table to find the optimal phase angle, it affects the rapidity of system stability control. On the other hand, this strategy is only applicable to remote fault situations and is difficult to apply to more proximal fault situations. 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 stability control method for a photovoltaic grid-connected inverter system based on double-sequence active current regulation. The present invention, without adding an additional control device, only needs to adjust the d-axis positive and negative sequence active current reference values ​​of the photovoltaic grid-connected inverter system during an asymmetric grid fault, thereby significantly improving the double-sequence synchronization stability of the photovoltaic grid-connected inverter system during an asymmetric grid short-circuit fault.

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

[0008] A method for transient stability control of a photovoltaic grid-connected inverter system based on double-sequence active current regulation is used to enhance the double-sequence synchronization stability of the photovoltaic grid-connected inverter system during an asymmetric fault, characterized in that the steps are as follows:

[0009] A1) The photovoltaic grid-connected inverter system adopts the generator convention to detect the three-phase AC voltage signal U at the grid connection point. s , using the grid voltage d-axis orientation method to achieve U s The three-phase stationary coordinate system is transformed into a two-phase rotating coordinate system, and the two-phase positive and negative sequence components are obtained by using a bandpass filter with a cutoff frequency of twice the power frequency. as well as

[0010] A2) During an asymmetric fault, the additional d-axis active current positive and negative sequence components are calculated according to the following formula and

[0011]

[0012] Among them, k p_c+ and k i_c+The additional d-axis active current positive sequence component is calculated as The proportional and integral coefficients used, k p_c- and k i_c- The additional d-axis active current negative sequence component is calculated as The proportional and integral coefficients used, is the deviation of the positive sequence q-axis component of the grid connection point voltage, is the deviation of the negative sequence q-axis component of the grid connection point voltage, is the actual value of the positive sequence q-axis voltage, is the actual value of the negative sequence q-axis voltage;

[0013] A3) During the asymmetric fault of the power grid, if the photovoltaic grid-connected inverter system has positive sequence synchronization instability, the positive sequence component of the d-axis active current obtained in step A2) is Negative feedback to the input of the current loop If the photovoltaic grid-connected inverter system has negative sequence synchronous instability, the negative sequence component of the d-axis active current obtained in step A2) is converted to Negative feedback to the input of the current loop That is, the photovoltaic grid-connected inverter system is made to return to the positive and negative sequence stable balance point, and the dual-sequence synchronization stability of the photovoltaic grid-connected inverter system is enhanced during asymmetric faults.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] On the basis of not switching the control strategy before and after the power grid fault, the present invention adaptively corrects the d-axis positive and negative sequence current reference values ​​by responding to the changes of the positive and negative sequence q-axis components of the grid-connected point voltage, thereby reducing the deviation of the positive and negative sequence q-axis components of the grid-connected point voltage, so that the photovoltaic grid-connected inverter system can autonomously return to the double-sequence stable equilibrium point, and finally ensure the double-sequence synchronous stable operation capability of the photovoltaic grid-connected inverter system during the asymmetric power grid fault, and reduce the positive and negative sequence synchronous instability risk of the photovoltaic grid-connected inverter system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of a photovoltaic grid-connected inverter system.

[0017] Figure 2 This is a schematic diagram of the control structure of the double-sequence active current regulation strategy proposed in the present invention.

[0018] Figure 3 The following is a comparison diagram of simulation waveforms of a photovoltaic grid-connected inverter system after adopting the traditional control strategy and the double-sequence active current regulation strategy proposed by the present invention under an asymmetric short-circuit fault in the power grid. DETAILED DESCRIPTION

[0019] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] The present invention is used to enhance the dual-sequence synchronization stability of a photovoltaic grid-connected inverter system during an asymmetric short-circuit fault in a power grid. Figure 1 This is a schematic diagram of the structure of a photovoltaic grid-connected inverter system. Figure 2 The figure is a schematic diagram of the control structure of the double-sequence active current regulation strategy proposed in the present invention. During an asymmetric fault, by adopting the double-sequence active current regulation strategy, the deviation of the positive and negative sequence q-axis components of the grid-connected point voltage can be reduced, so that the photovoltaic grid-connected inverter system can return to the double-sequence stable equilibrium point autonomously, thereby improving the double-sequence synchronization stability of the photovoltaic grid-connected inverter system.

[0021] The specific implementation steps of the present invention are as follows, and please refer to Figure 2 :

[0022] A1) The photovoltaic grid-connected inverter system adopts the generator convention to detect the three-phase AC voltage signal U at the grid connection point. s , using the grid voltage d-axis orientation method to achieve U s The three-phase stationary coordinate system is transformed into a two-phase rotating coordinate system, and the two-phase positive and negative sequence components are obtained by using a bandpass filter with a cutoff frequency of twice the power frequency. as well as

[0023] A2) During an asymmetric fault, the additional d-axis active current positive and negative sequence components are calculated according to the following formula and

[0024]

[0025] Among them, k p_c+ and k i_c+ The additional d-axis active current positive sequence component is calculated as The proportional and integral coefficients used, k p_c- and k i_c- The additional d-axis active current negative sequence component is calculated as The proportional and integral coefficients used, is the deviation of the positive sequence q-axis component of the grid connection point voltage, is the deviation of the negative sequence q-axis component of the grid connection point voltage, is the actual value of the positive sequence q-axis voltage, is the actual value of the negative sequence q-axis voltage;

[0026] A3) During the asymmetric fault of the power grid, if the photovoltaic grid-connected inverter system has positive sequence synchronization instability, the positive sequence component of the d-axis active current obtained in step A2) is Negative feedback to the input of the current loop If the photovoltaic grid-connected inverter system has negative sequence synchronous instability, the negative sequence component of the d-axis active current obtained in step A2) is converted to Negative feedback to the input of the current loop That is, the photovoltaic grid-connected inverter system is made to return to the positive and negative sequence stable balance point, and the dual-sequence synchronization stability of the photovoltaic grid-connected inverter system is enhanced during asymmetric faults.

[0027] Effect description of the present invention:

[0028] Figure 3 The time domain simulation results of the photovoltaic grid-connected inverter system under the traditional control strategy and the double-sequence active current regulation strategy proposed in this invention are given when an asymmetric short-circuit fault occurs in the power grid. Figure 3 (1) It is known that when the traditional control strategy is adopted, the photovoltaic grid-connected inverter system suffers from double-sequence synchronous instability. Figure 3 (2) It can be seen that after adopting the double-sequence active current regulation strategy proposed in the present invention, the deviation of the positive and negative sequence q-axis components of the grid-connected point voltage is improved, so that the photovoltaic grid-connected inverter system can autonomously return to the double-sequence stable equilibrium point, and the transient synchronization process of the photovoltaic grid-connected inverter system during the asymmetric fault of the power grid is greatly improved, which significantly improves the double-sequence synchronous stable operation capability of the photovoltaic grid-connected inverter system during the asymmetric fault.

[0029] It can be seen that the dual-sequence active current regulation strategy proposed in the present invention can significantly improve the transient synchronization process of the photovoltaic grid-connected inverter system, improve the dual-sequence synchronization stable operation capability of the photovoltaic grid-connected inverter system during asymmetric faults, and reduce the risk of dual-sequence synchronization instability of the photovoltaic grid-connected inverter system.

[0030] Finally, it should be pointed out that the specific examples mentioned above are only used to explain the present invention and do not constitute a limitation on the embodiments of the present invention. Although the present invention selects preferred examples and makes relevant descriptions, for those skilled in the art, other forms of adjustments and improvements can be made based on the above explanations. It is impossible to list all possible implementation schemes here. Any direct or indirect adjustments and improvements within the scope of the technical solution of the present invention can be regarded as the protection scope of the present invention.

Claims

1. A transient stability control method for a photovoltaic grid-connected inverter system based on double-sequence active current regulation, used to enhance the double-sequence synchronization stability of a photovoltaic grid-connected inverter system during an asymmetric fault, characterized in that: Here are the steps: A1) The photovoltaic grid-connected inverter system adopts the generator convention to detect the three-phase AC voltage signal U at the grid connection point. s , using the grid voltage d-axis orientation method to achieve U s The three-phase stationary coordinate system is transformed into a two-phase rotating coordinate system, and the two-phase positive and negative sequence components are obtained by using a bandpass filter with a cutoff frequency of twice the power frequency. as well as A2) During an asymmetric fault, the additional d-axis active current positive and negative sequence components are calculated according to the following formula and Among them, k p_c+ and k i_c+ The additional d-axis active current positive sequence component is calculated as The proportional and integral coefficients used, k p_c- and k i_c- The additional d-axis active current negative sequence component is calculated as The proportional and integral coefficients used, is the deviation of the positive sequence q-axis component of the grid connection point voltage, is the deviation of the negative sequence q-axis component of the grid connection point voltage, is the actual value of the positive sequence q-axis voltage, is the actual value of the negative sequence q-axis voltage; A3) During the asymmetric fault of the power grid, if the photovoltaic grid-connected inverter system has positive sequence synchronization instability, the positive sequence component of the d-axis active current obtained in step A2) is Negative feedback to the input of the current loop If the photovoltaic grid-connected inverter system has negative sequence synchronous instability, the negative sequence component of the d-axis active current obtained in step A2) is converted to Negative feedback to the input of the current loop That is, the photovoltaic grid-connected inverter system is made to return to the positive and negative sequence stable balance point, and the dual-sequence synchronization stability of the photovoltaic grid-connected inverter system is enhanced during asymmetric faults.

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