Adaptive transient synchronous stability control method for new energy grid-connected inverter under asymmetric fault of power grid

Abstract

The invention discloses an adaptive transient synchronous stability control method for a new energy grid-connected inverter under an asymmetric fault of a power grid, and the method comprises the steps: enabling a system to adaptively adjust a proportionality coefficient and an integral coefficient of a positive-sequence or negative-sequence phase-locked loop during the asymmetric fault of the power grid; the positive and negative sequence phase-locked loop output angular frequency when the additional controller is adopted during the fault duration is changed, so that the deviation of the positive and negative sequence phase-locked loop output angular frequency during the fault duration is zero, and the transient synchronous stable control of the new energy grid-connected inverter under the asymmetric fault of the power grid is realized. On the basis of not adding an additional control device, according to the fault information of the system, by improving the control structure of the positive and negative sequence phase-locked loops of the new energy grid-connected inverter, the transient synchronization stability of the new energy grid-connected inverter during the asymmetric short-circuit fault period of the power grid can be remarkably improved, and the fault tolerance of the new energy grid-connected inverter is improved. And the risk of transient synchronous instability of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the field of renewable energy power generation technology, and in particular to a method for adaptive transient synchronization stability control of a renewable energy grid-connected inverter under asymmetric grid faults. The method can significantly improve the transient synchronization stability of the renewable energy grid-connected inverter under asymmetric grid faults. Background Art

[0002] With the large-scale access of new energy inverters with power electronic converters as interfaces to the power grid, the dominant characteristics of traditional synchronous generators are continuously weakening, and the dynamic interaction between new energy grid-connected inverters and the power grid is becoming more and more intense. Especially under the condition of asymmetric short-circuit faults in the power grid, due to the weak ability of power electronic converters to resist voltage disturbances, new energy grid-connected inverters are very prone to transient synchronization stability problems such as transient loss of step, cascading failures, and even grid disconnection during the fault. Therefore, in order to improve the transient synchronization stability of new energy grid-connected inverters during asymmetric short-circuit faults in the power grid and reduce the risk of system instability, it is urgent to further study the transient synchronization stability control method of new energy grid-connected inverters under 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]HE XQ,GENG H,XI JB,et al.Resynchronization analysis and improvement of grid-connected VSCs during grid faults[J].IEEE Journal ofEmerging and Selected Topics in Power Electronics,2021,9(1):438-450.

[0004] [2]WU C,XIONG

[0005] Reference [1] proposed an improved phase-locked loop with voltage normalization control, which maintains the amplitude of the detection voltage by multiplying the input voltage with an additional gain. Therefore, even in the case of a sudden drop in the grid voltage, the damping ratio of the phase-locked loop can be maintained. However, this method still cannot effectively solve the transient instability problem caused by the lack of a balance point.

[0006] Reference [2] proposed a phase-locked loop freezing method. By shielding the proportional-integral link and continuously outputting the reference phase angle during the fault period according to the frequency and angle at the freezing moment, the system can be protected from the influence of grid voltage drop, thereby improving the transient stability of the system. However, this method has a static error problem and cannot track the phase jump caused by grid faults. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to propose an adaptive transient synchronization stability control method for a new energy grid-connected inverter under asymmetric grid faults. Without adding additional control devices, the present invention improves the control structure of the positive and negative sequence phase-locked loop of the new energy grid-connected inverter according to the fault information of the system, thereby significantly improving the transient synchronization stability of the new energy grid-connected inverter during an asymmetric short-circuit fault in the grid, thereby reducing the risk of transient synchronization instability in the system.

[0008] The technical solution of the present invention is achieved as follows:

[0009] A method for adaptive transient synchronous stability control of a new energy grid-connected inverter under asymmetric grid fault conditions, comprising the following steps:

[0010] A1) The new energy grid-connected inverter adopts the generator convention to detect the three-phase AC voltage U at the grid connection point. t , respectively, through the positive sequence and negative sequence phase locked loops using the grid voltage d axis orientation method to U t Convert from the three-phase stationary coordinate system to the two-phase rotating coordinate system, and use a low-pass filter to filter out the double frequency components respectively to obtain the positive and negative sequence terminal voltage q-axis components and

[0011] A2) Calculate the output angular frequency deviation of the positive and negative sequence phase-locked loop at the initial moment of the fault according to the following formula and

[0012]

[0013] in, is the positive sequence phase locked loop output angular frequency at the initial moment of fault, is the negative sequence phase locked loop output angular frequency at the initial moment of fault, ω g is the rated angular frequency of the grid;

[0014] if and If it is not 0, go to step A3);

[0015] A3) The positive and negative sequence phase locked loop output angular frequency deviation at the initial moment of the fault obtained in step A2) is and Substituting the following equation, we can obtain the positive and negative sequence phase-locked loop output angular frequency when the additional controller is used during the fault period: and

[0016]

[0017] in, and are the proportional coefficient and integral coefficient of the positive sequence phase locked loop, and is the negative sequence phase locked loop proportional coefficient and integral coefficient, and are the proportional coefficient and integral coefficient of the positive sequence additional controller, and are the negative sequence additional controller proportional coefficient and integral coefficient, and for and The absolute value of

[0018] During an asymmetric fault in the power grid, the system adaptively adjusts the proportional coefficient and integral coefficient of the positive or negative sequence phase-locked loop to change the output angular frequency of the positive or negative sequence phase-locked loop when the additional controller is used during the fault period. and The output angular frequency deviation of the positive and negative sequence phase-locked loop is made zero during the fault period, thereby realizing transient synchronous stability control of the new energy grid-connected inverter under asymmetric grid fault.

[0019] Furthermore, during the asymmetric fault period of the power grid, the positive and negative sequence active and reactive power optimal control strategy is adopted at the same time, so that the positive and negative sequence equivalent power angle δ + , δ - It is controlled to 0, thereby increasing the transient stability margin of the system and better improving the transient synchronization stability of the new energy grid-connected inverter.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] Without adding any additional control devices, the present invention can significantly improve the transient synchronization stability performance of the positive and negative sequence phase-locked loop by improving the control structure of the positive and negative sequence phase-locked loop of the new energy grid-connected inverter according to the fault information of the system, thereby improving the transient synchronization stability of the new energy grid-connected inverter during an asymmetric short-circuit fault in the power grid, reducing the risk of transient synchronization instability in the system, and thus effectively improving the asymmetric fault ride-through capability of the new energy grid-connected inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural diagram of the new energy grid-connected inverter.

[0023] Figure 2 This is a schematic diagram of the improved control structure of the positive and negative sequence phase-locked loop of the present invention.

[0024] Figure 3 These are simulation waveforms of the new energy grid-connected inverter after adopting the traditional control strategy and the control strategy proposed in the present invention respectively under an asymmetric short-circuit fault in the power grid. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] The present invention is used to enhance the transient stability margin of a new energy grid-connected inverter during an asymmetric short-circuit fault in a power grid. Figure 1 This is a structural diagram of the new energy grid-connected inverter. Figure 2 This is a schematic diagram of the improved control structure of the positive and negative sequence phase-locked loop of the present invention. Figure 3 The simulation waveforms of the new energy grid-connected inverter after adopting the traditional control strategy and the control strategy proposed by the present invention under the asymmetric short-circuit fault of the power grid. During the asymmetric fault period, by adopting the positive and negative sequence active and reactive power optimal control strategy, the positive and negative sequence equivalent power angle (δ + , δ - ) is controlled to 0, thereby increasing the transient stability margin of the system and improving the transient stability of the new energy grid-connected inverter.

[0027] The specific implementation steps of the present invention are as follows:

[0028] A1) The new energy grid-connected inverter adopts the generator convention to detect the three-phase AC voltage U at the grid connection point. t , respectively, through the positive sequence and negative sequence phase locked loops using the grid voltage d axis orientation method to U t Convert from the three-phase stationary coordinate system to the two-phase rotating coordinate system, and use a low-pass filter to filter out the double frequency components respectively to obtain the positive and negative sequence terminal voltage q-axis components and

[0029] A2) Calculate the output angular frequency deviation of the positive and negative sequence phase-locked loop at the initial moment of the fault according to the following formula and

[0030]

[0031] in, is the positive sequence phase locked loop output angular frequency at the initial moment of fault, is the negative sequence phase locked loop output angular frequency at the initial moment of fault, ω g is the rated angular frequency of the grid;

[0032] if and If it is not 0, go to step A3);

[0033] A3) The positive and negative sequence phase locked loop output angular frequency deviation at the initial moment of the fault obtained in step A2) is and Substituting the following equation, we can obtain the positive and negative sequence phase-locked loop output angular frequency when the additional controller is used during the fault period: and

[0034]

[0035] in, and are the proportional coefficient and integral coefficient of the positive sequence phase locked loop, and is the negative sequence phase locked loop proportional coefficient and integral coefficient, and are the proportional coefficient and integral coefficient of the positive sequence additional controller, and are the negative sequence additional controller proportional coefficient and integral coefficient, and for and The absolute value of

[0036] During an asymmetric fault in the power grid, the system adaptively adjusts the proportional coefficient and integral coefficient of the positive or negative sequence phase-locked loop to change the output angular frequency of the positive or negative sequence phase-locked loop when the additional controller is used during the fault period. and The output angular frequency deviation of the positive and negative sequence phase-locked loop is made zero during the fault period, thereby realizing transient synchronous stability control of the new energy grid-connected inverter under asymmetric grid fault.

[0037] During a fault, the present invention adaptively adjusts the proportional coefficient and integral coefficient of the positive-sequence or negative-sequence phase-locked loop to increase the damping coefficient of the system, thereby increasing the energy consumed by damping, suppressing the accumulation of unbalanced transient energy in the system, and reducing the risk of transient instability in the system, thereby effectively improving the transient synchronization stability of the new energy grid-connected inverter under asymmetric grid faults.

[0038] Furthermore, during the asymmetric fault period of the power grid, the positive and negative sequence active and reactive power optimal control strategy is adopted at the same time, so that the positive and negative sequence equivalent power angle δ + , δ - It is controlled to 0, thereby increasing the transient stability margin of the system and better improving the transient synchronization stability of the new energy grid-connected inverter.

[0039] Effect description of the present invention:

[0040] Figure 3 The simulation waveforms of the new energy grid-connected inverter using the traditional control strategy and the control strategy proposed by the present invention are given when an asymmetric short circuit fault occurs in the grid. Figure 3 In the fault detection delay, the fault detection delay is 18ms. During the fault, the system first outputs positive and negative sequence reactive current according to the grid guidelines, and the remaining converter current capacity outputs positive sequence active current. Under this working condition, when the system adopts the traditional control strategy, the positive and negative sequence phase-locked loops experience transient synchronization instability. At the same time, due to the continuous accumulation of unbalanced transient energy in the system during the fault duration, the system also experiences transient synchronization instability during the fault recovery stage. When the system adopts the proposed improved control strategy for the positive and negative sequence phase-locked loops, the positive and negative sequence phase-locked loops do not experience transient synchronization instability during the fault duration stage, and the system can also quickly restore transient synchronization stability during the fault recovery stage. It can be seen that the control strategy proposed in the present invention can effectively improve the transient synchronization stability of the VSC single-machine grid-connected system under asymmetric short-circuit faults in the grid, and enhance the system's asymmetric short-circuit fault ride-through capability.

[0041] It can be seen that the adaptive transient synchronization stability control method of the new energy grid-connected inverter under the asymmetric fault of the power grid proposed in the present invention can significantly improve the transient synchronization stability of the system, improve the stable operation capability of the new energy grid-connected inverter during the asymmetric fault, and reduce the risk of transient synchronization instability of the new energy grid-connected inverter.

[0042] Finally, it should be pointed out that the specific examples mentioned above are only used to illustrate the present invention and do not constitute a limitation on the embodiments of the present invention. Although the present invention has selected preferred embodiments and has been described in detail, those skilled in the art can make other adjustments and improvements based on the above explanations. It is impossible to list all possible implementation options here. Any direct or indirect adjustments and improvements that fall within the scope of the technical solution of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A method for adaptive transient synchronous stability control of a new energy grid-connected inverter under asymmetric grid fault, characterized by: Here are the steps: A1) The new energy grid-connected inverter adopts the generator convention to detect the three-phase AC voltage U at the grid connection point. t , respectively, through the positive sequence and negative sequence phase locked loops using the grid voltage d axis orientation method to U t Convert from the three-phase stationary coordinate system to the two-phase rotating coordinate system, and use a low-pass filter to filter out the double frequency components respectively to obtain the positive and negative sequence terminal voltage q-axis components and A2) Calculate the output angular frequency deviation of the positive and negative sequence phase-locked loop at the initial moment of the fault according to the following formula and in, is the positive sequence phase locked loop output angular frequency at the initial moment of fault, is the negative sequence phase locked loop output angular frequency at the initial moment of fault, ω g is the rated angular frequency of the grid; if and If it is not 0, go to step A3); A3) The positive and negative sequence phase locked loop output angular frequency deviation at the initial moment of the fault obtained in step A2) is and Substituting the following equation, we can obtain the positive and negative sequence phase-locked loop output angular frequency when the additional controller is used during the fault period: and in, and are the proportional coefficient and integral coefficient of the positive sequence phase locked loop, and is the negative sequence phase locked loop proportional coefficient and integral coefficient, and are the proportional coefficient and integral coefficient of the positive sequence additional controller, and are the negative sequence additional controller proportional coefficient and integral coefficient, and for and The absolute value of During an asymmetric fault in the power grid, the system adaptively adjusts the proportional coefficient and integral coefficient of the positive or negative sequence phase-locked loop to change the output angular frequency of the positive or negative sequence phase-locked loop when the additional controller is used during the fault period. and The output angular frequency deviation of the positive and negative sequence phase-locked loop is made zero during the fault period, thereby realizing transient synchronous stability control of the new energy grid-connected inverter under asymmetric grid fault.

2. The method for adaptive transient synchronous stability control of a new energy grid-connected inverter under asymmetric grid fault according to claim 1 is characterized in that: During the asymmetric fault period of the power grid, the positive and negative sequence active and reactive power optimal control strategy is adopted at the same time, so that the positive and negative sequence equivalent power angle δ + , δ - It is controlled to 0, thereby increasing the transient stability margin of the system and improving the transient synchronization stability of the new energy grid-connected inverter.

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