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

Abstract

The application discloses a new energy grid-connected inverter adaptive transient synchronous stability control method under power grid asymmetric fault. During the power grid asymmetric fault, the system adaptively adjusts the proportional coefficient and integral coefficient of the positive sequence or negative sequence phase-locked loop to change the positive and negative sequence phase-locked loop output angular frequency when the additional controller is used during the fault duration, so that the positive and negative sequence phase-locked loop output angular frequency deviation is 0 during the fault duration, thereby realizing the transient synchronous stability control of the new energy grid-connected inverter under the power grid asymmetric fault. 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 loop of the new energy grid-connected inverter, the transient synchronous stability of the new energy grid-connected inverter during the power grid asymmetric short-circuit fault can be obviously improved, and the risk of transient synchronous instability of the system is reduced.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, specifically to an adaptive transient synchronization stability control method for new energy grid-connected inverters under grid asymmetric faults. This method can significantly improve the transient synchronization stability of new energy grid-connected inverters under grid asymmetric faults. Background Technology

[0002] With the large-scale grid connection of renewable energy inverters using power electronic converters as interfaces, the dominant characteristics of traditional synchronous generators are continuously weakening, and the dynamic interaction between renewable energy grid-connected inverters and the grid is becoming increasingly intense. Especially under asymmetrical short-circuit fault conditions, due to the weak voltage disturbance immunity of power electronic converters, renewable energy grid-connected inverters are highly susceptible to transient synchronization stability problems such as transient loss of synchronization, cascading faults, and even grid disconnection during fault periods. Therefore, to improve the transient synchronization stability of renewable energy grid-connected inverters during asymmetrical short-circuit faults and reduce the risk of system instability, further research on transient synchronization stability control methods for renewable energy grid-connected inverters during asymmetrical short-circuit faults is urgently needed. Currently, scholars both domestically and internationally have conducted relevant research, as evidenced by 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] proposes an improved phase-locked loop with voltage normalization control, which maintains the amplitude of the detected voltage by multiplying the input voltage by an additional gain. Therefore, the damping ratio of the phase-locked loop can be maintained even in the event of a sudden drop in grid voltage. However, this method still cannot effectively solve the transient instability problem caused by the lack of an equilibrium point.

[0006] Reference [2] proposes a phase-locked loop freezing method, which, by shielding both the proportional and integral circuits, continuously outputs a reference phase angle during the fault period based on the frequency and angle at the freezing time, thus ensuring that the system is not affected by the grid voltage drop and improving the transient stability of the system. However, this method has a static error problem and cannot track the phase jump that accompanies the grid fault. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to propose an adaptive transient synchronization stability control method for renewable energy grid-connected inverters under grid asymmetric faults. Without adding additional control devices, the present invention significantly improves the transient synchronization stability of renewable energy grid-connected inverters during grid asymmetric short-circuit faults by improving the control structure of the positive and negative sequence phase-locked loops of the renewable energy grid-connected inverters based on the system fault information, thereby reducing the risk of transient synchronization instability of the system.

[0008] The technical solution of this invention is implemented as follows:

[0009] An adaptive transient synchronization stability control method for grid-connected inverters of new energy sources under asymmetrical grid faults, comprising the following steps:

[0010] A1) The new energy grid-connected inverter adopts the generator convention, detecting the three-phase AC voltage U at the grid connection point. t U is oriented using the grid voltage d-axis orientation method through positive-sequence and negative-sequence phase-locked loops respectively. t The system is transformed from a three-phase stationary coordinate system to a two-phase rotating coordinate system, and the second harmonic components are filtered out using a low-pass filter to obtain the q-axis components of the positive and negative sequence terminal voltages. and

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

[0012]

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

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

[0015] A3) The positive and negative sequence phase-locked loop output angular frequency deviation obtained in step A2) at the initial fault moment is calculated. and Substituting into the following formula, we obtain the positive and negative sequence phase-locked loop output angular frequencies when an additional controller is used during the fault duration. and

[0016]

[0017] in, and These are the proportional and integral coefficients of the positive-sequence phase-locked loop. and These are the proportional and integral coefficients of the negative-sequence phase-locked loop. and Add proportional and integral coefficients to the controller for positive sequence. and Add proportional and integral coefficients to the negative sequence controller. and for and The absolute value;

[0018] During asymmetrical faults in the power grid, the system adaptively adjusts the proportional and integral coefficients of the positive-sequence or negative-sequence phase-locked loop (PLL) to change the output angular frequency of the positive-sequence or negative-sequence PLL when an additional controller is used during the fault duration. and This ensures that the output angular frequency deviation of the positive and negative sequence phase-locked loop is 0 during the fault duration, thereby achieving transient synchronous and stable control of the new energy grid-connected inverter under grid asymmetric faults.

[0019] Furthermore, during asymmetrical faults in the power grid, by simultaneously employing a positive and negative sequence optimal active and reactive power control strategy, the positive and negative sequence equivalent power angle δ is made possible. + δ - By controlling it to 0, the transient stability margin of the system is increased, which can better improve the transient synchronization stability of the grid-connected inverter for new energy.

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

[0021] This invention, without adding any additional control devices, improves the transient synchronization stability of the positive and negative sequence phase-locked loop (PLL) of the new energy grid-connected inverter by modifying the control structure based on the system's fault information. This enhances the transient synchronization stability of the new energy grid-connected inverter during asymmetrical short-circuit faults in the power grid, reduces the risk of transient synchronization instability, and effectively improves the asymmetrical fault ride-through capability of the new energy grid-connected inverter. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a grid-connected inverter for new energy sources.

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

[0024] Figure 3 Simulation waveforms of a new energy grid-connected inverter under asymmetrical short-circuit faults in the power grid, using both traditional control strategies and the control strategy proposed in this invention. Detailed Implementation

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

[0026] This invention is used to enhance the transient stability margin of grid-connected inverters for new energy sources during asymmetrical short-circuit faults in the power grid. Figure 1 This is a schematic diagram of the structure of a grid-connected inverter for new energy sources. Figure 2 This is a schematic diagram of the improved positive and negative sequence phase-locked loop control structure of the present invention. Figure 3 Simulation waveforms of a new energy grid-connected inverter under an asymmetrical short-circuit fault in the power grid, using both traditional and the control strategy proposed in this invention, are shown. During the asymmetrical fault, by employing the optimal control strategy for positive and negative sequence active and reactive power, the equivalent power angle (δ) of the positive and negative sequences can be optimized. + δ - The transient stability margin of the system is controlled to 0, thereby increasing the transient stability of the grid-connected inverter for new energy.

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

[0028] A1) The new energy grid-connected inverter adopts the generator convention, detecting the three-phase AC voltage U at the grid connection point. t U is oriented using the grid voltage d-axis orientation method through positive-sequence and negative-sequence phase-locked loops respectively. t The system is transformed from a three-phase stationary coordinate system to a two-phase rotating coordinate system, and the second harmonic components are filtered out using a low-pass filter to obtain the q-axis components of the positive and negative sequence terminal voltages. and

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

[0030]

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

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

[0033] A3) The positive and negative sequence phase-locked loop output angular frequency deviation obtained in step A2) at the initial fault moment is calculated. and Substituting into the following formula, we obtain the positive and negative sequence phase-locked loop output angular frequencies when an additional controller is used during the fault duration. and

[0034]

[0035] in, and These are the proportional and integral coefficients of the positive-sequence phase-locked loop. and These are the proportional and integral coefficients of the negative-sequence phase-locked loop. and Add proportional and integral coefficients to the controller for positive sequence. and Add proportional and integral coefficients to the negative sequence controller. and for and The absolute value;

[0036] During asymmetrical faults in the power grid, the system adaptively adjusts the proportional and integral coefficients of the positive-sequence or negative-sequence phase-locked loop (PLL) to change the output angular frequency of the positive-sequence or negative-sequence PLL when an additional controller is used during the fault duration. and This ensures that the output angular frequency deviation of the positive and negative sequence phase-locked loop is 0 during the fault duration, thereby achieving transient synchronous and stable control of the new energy grid-connected inverter under grid asymmetric faults.

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

[0038] Furthermore, during asymmetrical faults in the power grid, by simultaneously employing a positive and negative sequence optimal active and reactive power control strategy, the positive and negative sequence equivalent power angle δ is made possible. + δ - The system is controlled to 0, thereby increasing the transient stability margin of the system and improving the transient synchronization stability of the grid-connected inverter for new energy sources.

[0039] Description of the effects of this invention:

[0040] Figure 3 Simulation waveforms of a new energy grid-connected inverter under an asymmetrical short-circuit fault are presented, showing the results using both traditional and the proposed control strategy. Figure 3 In this case, 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 condition, when the system adopts the traditional control strategy, the positive and negative sequence phase-locked loop (PLL) experiences transient synchronization instability. Simultaneously, due to the continuous accumulation of unbalanced transient energy during the fault duration, the system also experiences transient synchronization instability during the fault recovery phase. When the system adopts the proposed improved positive and negative sequence PLL control strategy, the PLL does not experience transient synchronization instability during the fault duration, and the system can quickly restore transient synchronization stability during the fault recovery phase. Therefore, the control strategy proposed in this invention can effectively improve the transient synchronization stability of a VSC single-unit grid-connected system under asymmetrical short-circuit faults in the grid, and enhance the system's asymmetrical short-circuit fault ride-through capability.

[0041] Therefore, the adaptive transient synchronization stability control method for new energy grid-connected inverters under asymmetrical grid faults proposed in this invention can significantly improve the transient synchronization stability of the system, enhance the stable operation capability of new energy grid-connected inverters during asymmetrical faults, and reduce the risk of transient synchronization instability of new energy grid-connected inverters.

[0042] Finally, it should be noted that the specific examples mentioned above are only for explaining the present invention and do not constitute a limitation on the embodiments of the present invention. Although the present invention has selected preferred examples and described them accordingly, those skilled in the art can make other forms of adjustments and improvements based on the above explanations. It is impossible to list all possible embodiments here. Any adjustments and improvements that fall directly or indirectly within the scope of the technical solutions of the present invention can be considered within the protection scope of the present invention.

Claims

1. An adaptive transient synchronization stability control method for grid-connected inverters of new energy sources under asymmetrical grid faults, characterized in that: The steps are as follows: A1) The new energy grid-connected inverter adopts the generator convention, detecting the three-phase AC voltage U at the grid connection point. t U is oriented using the grid voltage d-axis orientation method through positive-sequence and negative-sequence phase-locked loops respectively. t The system is transformed from a three-phase stationary coordinate system to a two-phase rotating coordinate system, and the second harmonic components are filtered out using a low-pass filter to obtain the q-axis components of the positive and negative sequence terminal voltages. and A2) Calculate the positive and negative sequence phase-locked loop output angular frequency deviation at the initial moment of the fault using the following formula. and in, The positive-sequence phase-locked loop output angular frequency at the initial moment of the fault. ω is the negative sequence phase-locked loop output angular frequency at the initial moment of the fault. g The rated angular frequency of the power grid; if and If it is not 0, proceed to step A3); A3) The positive and negative sequence phase-locked loop output angular frequency deviation obtained in step A2) at the initial fault moment is calculated. and Substituting into the following formula, we obtain the positive and negative sequence phase-locked loop output angular frequencies when an additional controller is used during the fault duration. and in, and These are the proportional and integral coefficients of the positive-sequence phase-locked loop. and These are the proportional and integral coefficients of the negative-sequence phase-locked loop. and Add proportional and integral coefficients to the controller for positive sequence. and Add proportional and integral coefficients to the negative sequence controller. and for and The absolute value; During asymmetrical faults in the power grid, the system adaptively adjusts the proportional and integral coefficients of the positive-sequence or negative-sequence phase-locked loop (PLL) to change the output angular frequency of the positive-sequence or negative-sequence PLL when an additional controller is used during the fault duration. and This ensures that the output angular frequency deviation of the positive and negative sequence phase-locked loop is 0 during the fault duration, thereby achieving transient synchronous and stable control of the new energy grid-connected inverter under grid asymmetric faults.

2. The adaptive transient synchronization and stability control method for a new energy grid-connected inverter under asymmetrical grid faults as described in claim 1, characterized in that: During the asymmetric fault of power grid, the positive and negative sequence active and reactive optimal control strategy is adopted at the same time, so that 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 synchronous stability of the new energy grid-connected inverter.

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