Fault ride-through stable control method for phase-locked new energy grid-connected converter

Abstract

The invention provides a fault ride-through stable control method for a phase-locked new energy grid-connected converter, and the method comprises the steps: stabilizing the voltage of a DC side through an unloading circuit during a fault, transmitting DC electric energy to an AC side through the grid-connected converter, carrying out the filtering of the AC side through a filtering inductor, and transmitting the filtered electric energy to a power grid through an electric energy transmission line, the voltage of the grid-connected point is Ut, and the output current of the grid-connected converter is Ic; after a fault occurs, a K coefficient adjusting module is started, a new K coefficient matched with a fault working condition is generated through calculation or self-adaptive adjustment, the new K coefficient acts on an LVRT control module to generate a dq current reference value, and then the grid-connected converter is controlled through current inner loop, coordinate transformation and PWM control links. According to the method, the K coefficient is adjusted to be matched with the fault working condition, the current dynamic response is improved, and transient synchronous stability is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid connection and power electronic control technology, in particular to a phase-locked new energy grid-connected converter fault ride-through stability control method, a terminal and a medium. BACKGROUND

[0002] In recent years, the rapid development of new energy technologies such as wind power and photovoltaic has continuously increased the proportion of power grid structure. As a key link between new energy and power grid, grid-connected converters are widely used, and the mainstream control strategy is grid-following control. In this control mode, the grid-connected converter accurately captures the grid phase through phase-locked loop (PLL) technology and effectively decouples active and reactive power based on dq-axis current.

[0003] To ensure the safe and stable operation of the power grid, the current grid connection guide clearly requires low voltage ride through (LVRT) for new energy equipment. That is, new energy units should not take the measures of lockout or off-grid when the grid voltage is reduced to a certain profile, and need to inject reactive current proportional to the grid voltage drop during the fault to support the recovery of the grid voltage. This proportional coefficient is called dynamic reactive current injection coefficient, that is, K coefficient. The size of K coefficient has a significant impact on the transient synchronization stability of grid-following new energy equipment, especially when the K coefficient is not matched, which will cause synchronization instability, resulting in the frequency of the phase-locked loop deviating from the base frequency, and further causing serious problems such as overcurrent and voltage waveform oscillation, which poses a threat to the safety of the equipment.

[0004] Although the current grid connection guide suggests a wide range of K coefficient values ([1.5, 3]), in actual operation, a fixed K coefficient is difficult to ensure transient stability under all fault conditions. Therefore, it is particularly important to develop a stability control strategy that can adaptively adjust the K coefficient during the fault to match the transient condition.

[0005] After searching, we found that the Chinese patent with application number CN116722609A discloses a multi-constrained direct-drive wind power grid-connected system variable reactive current proportion coefficient voltage continuous ride-through control method. This method determines the fault ride-through control interval by monitoring the grid voltage size during the fault in real time, and calculates the reactive current proportion coefficient based on real-time information such as grid voltage and impedance to achieve stability control. However, this method still uses a fixed K coefficient, which may cause synchronization instability due to mismatched K coefficient, and does not provide a clear feasible region definition. SUMMARY

[0006] In view of the defects in the prior art, the purpose of the present application is to provide a phase-locked new energy grid-connected converter fault ride-through stability control method, a terminal and a medium.

[0007] According to one aspect of the present application, a fault ride-through stability control method for a phase-locked new energy grid-connected converter is provided, comprising:

[0008] During the fault, the DC side voltage is stabilized by the unloading circuit, the DC power is transmitted to the AC side through the grid-connected converter, is filtered by the filter inductor at the AC side, and is transmitted to the power grid through the power transmission line, the grid voltage is U g , the grid-connected point voltage is U t , the grid-connected converter output current is I c ;

[0009] After the fault, the K coefficient adjustment module is enabled, a new K coefficient matching the fault working condition is generated by calculation or adaptive adjustment, the new K coefficient is applied to the LVRT control module to generate the dq current reference value, and then the grid-connected converter is controlled through the current inner loop, coordinate transformation and PWM control link;

[0010] The dq current reference value is specifically:

[0011] I max is the current amplitude, i cqref is the q-axis current reference value, i cdref is the d-axis current reference value.

[0012] Preferably, the new K coefficient matching the fault working condition is generated by calculation, comprising:

[0013] The fault working condition is determined, including the fault voltage U eq , the fault inductance X eq , the fault resistance R eq , and the maximum output current I max is selected;

[0014] It is determined whether U eq is greater than or equal to X eq I max ; if yes, it is determined as fault mode 1; if not, it is determined whether U eq is less than R eq I max ; if not, it is determined as fault mode 2, and if yes, it is determined as fault mode 3;

[0015] The corresponding K coefficient feasible region is calculated according to the determined fault mode;

[0016] Mode 1: K min is 0, and K max is +∞;

[0017] Mode 2: K max is +∞, and K minThe numerical calculation is derived from the formula shown in equation (1), which includes i cq and U t Two variables, first solve for i that satisfies the requirement of equation (1). cq and U t Then substitute them into the equation to obtain the corresponding K coefficients;

[0018] Mode 3: K min and K max All are obtained by numerical calculation from equation (1):

[0019]

[0020] Randomly select a number from the feasible region of the calculated K coefficients as the new K coefficients for matching fault conditions.

[0021] Preferably, the step of calculating and generating the K coefficients for new matching fault conditions includes:

[0022] Obtain source data of the static feasible domain of the K coefficient under various working conditions;

[0023] The source data is used to train a neural network. The inputs to the neural network are the equivalent grid impedance, the equivalent grid voltage, and the maximum output current. The output is K. min and K max ;

[0024] Add the trained neural network to the controller;

[0025] During system operation, the controller generates a range of K coefficients in real time, and randomly selects a number from this range as a new K coefficient to match the fault condition.

[0026] Preferably, the step of generating the new matching fault condition K coefficient by calculation includes: directly calculating the K coefficient using the following formula;

[0027]

[0028] Where K cr Critical Z eq The K coefficient, under the action of this K coefficient, can guarantee U eq The system still has an equilibrium point when X = 0; eq For fault sensing reactance, Z eq This is the equivalent impedance.

[0029] Preferably, the step of adaptively adjusting the K coefficients to generate new matching fault conditions includes:

[0030] After detecting a fault, determine whether to initiate adaptive adjustment;

[0031] After adaptive matching is initiated, the K coefficient is adjusted according to the output frequency of the phase-locked loop.

[0032] Preferably, determining whether to initiate adaptive adjustment after detecting a fault includes:

[0033] When the terminal voltage is the grid connection point voltage U t When the value is lower than the set value, fault ride-through control is activated, and the K coefficient is adaptively adjusted according to the fault condition.

[0034] When the terminal voltage is the grid connection point voltage U t When the value exceeds the set value, the fault pass-through control is disconnected.

[0035] Preferably, after initiating adaptive matching, adjusting the K coefficient according to the phase-locked loop output frequency includes:

[0036] An integral controller is used, whose input is the phase-locked loop frequency. The phase-locked loop frequency interacts with the integral coefficient, and the output is the K-coefficient incremental signal.

[0037] The integral coefficient k ik Size, specifically:

[0038]

[0039] Where K cr K is the critical K coefficient, and K0 is the initial K coefficient.

[0040] Preferably, the initial K coefficient K0 takes a value between 1.5 and 3, k ik The value is greater than 0.32 or greater than 0.8.

[0041] According to a second aspect of the present invention, a terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, can be used to perform any of the methods described above.

[0042] According to a third aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, can be used to perform any of the methods described herein.

[0043] Compared with the prior art, the embodiments of the present invention have the following beneficial effect:

[0044] The fault ride-through stability control method for phase-locked loop (PLL) grid-connected converters of new energy sources in this invention adjusts the K coefficient to match the fault conditions during a fault, thereby improving the dynamic current response and achieving transient synchronous stability.

[0045] The fault ride-through stability control method for phase-locked loop (PLL) grid-connected converters of new energy sources in this invention provides a calculation method for the feasible region of the K coefficient under a given operating condition, thereby enabling the K coefficient value to match its corresponding operating condition and improving transient synchronization stability performance. Attached Figure Description

[0046] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0047] Figure 1 This is a common topology for new energy grid-connected systems;

[0048] Figure 2 This is the Thevenin equivalent circuit for the converter-grid.

[0049] Figure 3 This is the static feasible region calculation process for the K coefficients in a preferred embodiment of the present invention;

[0050] Figure 4 This is an adaptive K-coefficient stabilization control process in a preferred embodiment of the present invention;

[0051] Figure 5 This is a simulation waveform of the reset K coefficient stabilization control in a specific embodiment of the present invention;

[0052] Figure 6 These are simulation waveforms at different fault locations in a preferred embodiment of the present invention;

[0053] Figure 7 This is a simulation waveform under the same power grid parameters in a preferred embodiment of the present invention. Detailed Implementation

[0054] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0055] like Figure 1 and Figure 2 The diagram shows a common grid-connected topology for new energy systems, where front-end modules such as wind turbines, photovoltaics, and energy storage can be simplified as power sources. Based on this topology, this invention provides a fault ride-through stability control method for a phase-locked loop (PLL) grid-connected converter for new energy systems, comprising:

[0056] During a fault, the DC-side voltage is stabilized through an unloading circuit. DC power is then transmitted to the AC side via a grid-connected converter, filtered by a filter inductor, and finally fed into the power grid via transmission lines. The grid voltage is U.g The grid connection point voltage is U t The grid-connected converter output current is I c ;

[0057] After a fault occurs, the K-coefficient adjustment module is activated. A new K-coefficient matching the fault condition is generated by calculation or adaptive adjustment. The new K-coefficient is then applied to the LVRT (Low Voltage Ride Through) control module to generate a dq current reference value. Subsequently, the grid-connected converter is controlled through the current inner loop, coordinate transformation, and PWM (Pulse Width Modulation) control loop.

[0058] Under the LVRT control strategy specified in the existing grid connection guidelines, assuming the current amplitude is I... max The q-axis current reference value is obtained by multiplying a fixed coefficient K0 by the voltage drop at the grid connection point. The d-axis current reference value is generally the residual current capacity, expressed as follows:

[0059]

[0060] Existing research methods do not yield complete feasible regions for the K coefficient. Although current national standards specify the range of K coefficient values ​​as [1.5, 3], they do not explicitly define the values ​​themselves, leaving ambiguity in the industry and creating difficulties for practical applications. Therefore, in a preferred embodiment of this invention, a precise calculation process for the feasible region of the K coefficient under specific operating conditions is provided, thereby ensuring that the K coefficient value matches the corresponding operating condition and improving transient synchronization stability.

[0061] Preferably, in one embodiment, a numerical calculation process for the feasible region using K coefficients is provided, such as... Figure 3 As shown, the specific process is as follows:

[0062] S101, determine the fault condition, including the fault voltage U. eq Fault sensing resistance X eq Fault resistor R eq Select the maximum output current I max ;

[0063] S102, determine U eq Is it greater than or equal to X? eq I max If yes, then it is determined to be fault condition mode 1; if not, then U is further determined. eq Is it less than R? eq I max If not, it is determined to be fault condition mode 2; if yes, it is determined to be fault condition mode 3.

[0064] S103, each fault condition mode corresponds to a minimum value K of the K coefficient. minAnd the maximum value of K coefficient K max This yields three feasible regions for the K coefficients, including:

[0065] Pattern 1: K min K is 0 max +∞;

[0066] Pattern 2: K max For +∞, K min The numerical calculation is derived from the formula shown in equation (1), which includes i cq and U t Given two variables, first find i that satisfies the requirements. cq and U t Then substitute them into the equation to obtain the corresponding K coefficients;

[0067] Mode 3: K min and K max All are obtained by numerical calculation from equation (1):

[0068]

[0069] The above embodiments, through a given numerical calculation process, obtain the complete feasible domain of the K coefficient under the determined fault conditions, providing a reference for the selection of the K coefficient value in practical industrial applications.

[0070] In a preferred embodiment, a data-driven online estimation process for the feasible region of the K coefficients is provided, the specific steps of which are as follows:

[0071] S201, obtain a large amount of static feasible domain source data of K coefficients under various operating conditions.

[0072] S202 uses source data to train a neural network. The inputs to this neural network are the equivalent grid impedance, the equivalent grid voltage, and the maximum output current. The output is K. min and K max .

[0073] S203, Add the trained neural network to the controller;

[0074] S204, the controller generates the range of K coefficients in real time during system operation.

[0075] Preferably, in a preferred embodiment, an optimal K coefficient calculation method is provided, which ensures that U eq When = 0, the system still has an equilibrium point, and its calculation formula is:

[0076]

[0077] By obtaining the range of K coefficients through the above embodiments, one number can be randomly selected from it as a new K coefficient, or the calculated K coefficient can be used directly.

[0078] When the K coefficient does not match the actual fault conditions, the phase-locked loop frequency will continuously accelerate / decelerate, and may even fail to return to normal after the fault is cleared, leading to serious damage to electrical equipment such as voltage and current oscillations. Therefore, in a preferred embodiment of the present invention, a method for adaptive adjustment of K is also provided, such as... Figure 4 As shown, specifically:

[0079] S301, after detecting a fault, determines whether to initiate adaptive adjustment;

[0080] S302, after starting adaptive tuning, adjusts the K coefficient according to the output frequency of the phase-locked loop.

[0081] Furthermore, in a preferred embodiment, an adaptive adjustment mode for K is provided. Specifically, S301 is further implemented to determine whether to enter or exit fault ride-through mode based on the terminal voltage amplitude. Specifically, when the terminal voltage U... t When the voltage U is below the set value, the proposed fault ride-through control strategy is activated, and the K coefficient is adaptively adjusted according to the fault condition. t When the value exceeds the set value, the proposed fault-crossing control strategy is discontinued.

[0082] Furthermore, in a preferred embodiment, a specific control mode for adaptive adjustment of K is provided, further implementing S302, using an integral controller. The input of the integral controller is the phase-locked loop frequency, and the output is the incremental signal of the K coefficient. The incremental signal is superimposed on the initial K coefficient, thereby obtaining a new K coefficient.

[0083] The integral coefficient of the integral controller is expressed as follows:

[0084]

[0085] Where K cr Generally, the value should not exceed 4, while the value of K0 is between 1.5 and 3. Therefore, this patent recommends k. ik The value is greater than 0.32-0.8.

[0086] Based on the same inventive concept, in other embodiments of the present invention, a terminal is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to perform the above-described method or to run the above-described system.

[0087] Optionally, the memory is used to store programs; the memory may include volatile memory, such as random-access memory (RAM), such as static random-access memory (SRAM), double data rate synchronous dynamic random-access memory (DDRSDRAM), etc.; the memory may also include non-volatile memory, such as flash memory. The memory is used to store computer programs (such as application programs, functional modules, etc. that implement the above methods), computer instructions, etc., and the above-mentioned computer programs, computer instructions, etc., may be partitioned and stored in one or more memories.

[0088] A processor is used to execute a computer program stored in memory to implement the various steps of the methods involved in the above embodiments. For details, please refer to the relevant descriptions in the preceding method embodiments.

[0089] The processor and memory can be separate structures or integrated structures. When the processor and memory are separate structures, they can be coupled together via a bus.

[0090] Based on the same inventive concept, in other embodiments of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, can be used to perform the above-described method or to run the above-described system.

[0091] Computer-readable media include computer storage media and communication media, wherein communication media include any medium that facilitates the transfer of computer programs from one place to another. Storage media can be any available medium accessible to a general-purpose or special-purpose computer. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in a user device. Of course, the processor and storage medium can also exist as discrete components in a communication device.

[0092] To verify the feasibility and effectiveness of the fault ride-through stability control method for the phase-locked loop (PLL) renewable energy grid-connected converter in the above embodiments, simulation verification is performed in a specific implementation of this invention.

[0093] Please see Figure 5 The figure shows the verification waveform after determining and resetting the K-coefficient using the above-mentioned optimal K-coefficient calculation method. A pure resistor with a fault grounding impedance of 0.001Ω was set; the fault occurred at 0.5s and was cleared after 500ms. Under the fixed K-coefficient, the system experienced synchronous instability, with both voltage and current oscillating. However, when using the fault ride-through stability control method for the phase-locked loop (PLL) grid-connected converter of this invention, the K-coefficient was reset after the fault occurred to match the fault conditions. Therefore, the system did not experience synchronous instability during the fault, and the system returned to stability after the fault was cleared. This demonstrates the effectiveness of the fault ride-through stability control method for the PLL grid-connected converter of this invention in improving transient synchronous stability performance.

[0094] Please see Figure 6 The figure shows simulation waveforms at different fault locations using a fixed K coefficient and an adaptive K adjustment method according to the embodiment of the present invention. Figure 6 It can be seen that regardless of the distance of the fault, the K adaptive adjustment method can maintain frequency stability during the fault period, and the frequency and voltage can quickly recover to the pre-fault state after the fault is cleared. However, if only a fixed K coefficient K0=2 is used, it can be seen that the PLL frequency continuously drops during mid-range and near-end faults, and takes a long time to recover after the fault is cleared. During far-end faults, due to the large equivalent grid impedance, the reactive current injection is insufficient under the action of K0=2, the PLL frequency rises rapidly, and the current oscillates violently after the fault is cleared. This demonstrates the effectiveness of the K adaptive adjustment method in improving current injection stability and fault recovery performance in the embodiments of the present invention.

[0095] Please see Figure 7 The figure shows the simulated waveforms of the K adaptive adjustment method under different grid parameters in this embodiment of the invention. Regardless of changes in the fault grid voltage, fault impedance, or inductance ratio, the K adaptive adjustment method maintains good stability, demonstrating the strong adaptability of the fault ride-through stability control method of the phase-locked loop type renewable energy grid-connected converter in this embodiment of the invention to fault conditions.

[0096] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter, characterized in that, include: During a fault, the DC-side voltage is stabilized through an unloading circuit. DC power is then transmitted to the AC side via a grid-connected converter, filtered by a filter inductor, and finally fed into the power grid via transmission lines. The grid voltage is U. g The grid connection point voltage is U t The grid-connected converter output current is I c ; After a fault occurs, the K coefficient adjustment module is activated. A new K coefficient matching the fault condition is generated by calculation or adaptive adjustment. The new K coefficient is then applied to the LVRT control module to generate a dq current reference value. Subsequently, the grid-connected converter is controlled through the current inner loop, coordinate transformation, and PWM control loop. Specifically, the reference value for the dq current is: i represents the current amplitude. cqref i is the reference value for the q-axis current. cdref This is the reference value for the d-axis current.

2. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 1, characterized in that, The step of generating new K coefficients for matching fault conditions by calculation includes: Determine the fault conditions, including the fault voltage U. eq Fault sensing resistance X eq Fault resistor R eq Select the maximum output current I max ; Determine U eq Is it greater than or equal to X? eq I max If yes, then it is determined to be fault condition mode 1; if not, then U is further determined. eq Is it less than R? eq I max If not, it is determined to be fault condition mode 2; if yes, it is determined to be fault condition mode 3. Calculate the feasible region of the corresponding K coefficient based on the determined failure mode; Pattern 1: K min K is 0 max +∞; Pattern 2: K max For +∞, K min The numerical calculation is derived from the formula shown in equation (1), which includes i cq and U t Two variables, first solve for i that satisfies the requirement of equation (1). cq and U t Then substitute them into the equation to obtain the corresponding K coefficients; Mode 3: K min and K max All are obtained by numerical calculation from equation (1): Randomly select a number from the feasible region of the calculated K coefficients as the new K coefficients for matching fault conditions.

3. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 1, characterized in that, The step of generating new K coefficients for matching fault conditions by calculation includes: Obtain source data of the static feasible domain of the K coefficient under various working conditions; The source data is used to train a neural network. The inputs to the neural network are the equivalent grid impedance, the equivalent grid voltage, and the maximum output current. The output is K. min and K max ; Add the trained neural network to the controller; During system operation, the controller generates a range of K coefficients in real time, and randomly selects a number from this range as a new K coefficient to match the fault condition.

4. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 1, characterized in that, The step of generating new matching fault conditions by calculation includes: directly calculating the K coefficient using the following formula; Where K cr Critical Z eq The K coefficient, under the action of this K coefficient, can guarantee U eq The system still has an equilibrium point when X = 0; eq For fault sensing reactance, Z eq This is the equivalent impedance.

5. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 1, characterized in that, The process of adaptively adjusting the K coefficients to generate new matching fault conditions includes: After detecting a fault, determine whether to initiate adaptive adjustment; After adaptive matching is initiated, the K coefficient is adjusted according to the output frequency of the phase-locked loop.

6. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 5, characterized in that, The step of determining whether to initiate adaptive adjustment after detecting a fault includes: When the terminal voltage is the grid connection point voltage U t When the value is lower than the set value, fault ride-through control is activated, and the K coefficient is adaptively adjusted according to the fault condition. When the terminal voltage is the grid connection point voltage U t When the value exceeds the set value, the fault pass-through control is disconnected.

7. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 6, characterized in that, After the adaptive tuning is initiated, the K coefficient is adjusted according to the phase-locked loop output frequency, including: An integral controller is used, whose input is the phase-locked loop frequency. The phase-locked loop frequency interacts with the integral coefficient, and the output is the K-coefficient incremental signal. The integral coefficient k ik Size, specifically: Where K cr K is the critical K coefficient, and K0 is the initial K coefficient.

8. The fault ride-through stability control method for a phase-locked loop (PLL) renewable energy grid-connected converter according to claim 7, characterized in that, The initial K coefficient K0 takes a value between 1.5 and 3, k ik The value is greater than 0.32 or greater than 0.

8.

9. A terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it can be used to perform the method of any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, this program can be used to perform the method of any one of claims 1-8.

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