Power angle change trend prediction and power grid intensity self-adaption-based transient stability control method and system for network-constructing converter

Abstract

The invention discloses a power angle change trend prediction and power grid intensity self-adaption-based transient stability control method and system for a network-forming converter, and the method comprises the steps: judging whether a power grid fault exists or not based on a power grid voltage obtained in real time, and obtaining a fault severity level based on the voltage transient characteristics of the power grid voltage if the power grid fault exists; selecting a control strategy combination based on the fault severity level to perform stable control; and when the power grid fault does not exist, the intensity of the control strategy combination is regulated and controlled based on the voltage recovery speed and the power angle stability until normal and stable operation is realized. According to the method, the transient stability and the fault ride-through capability of the grid-forming converter are remarkably improved, and the method has the advantages of high control precision, high response speed, high adaptability and the like, does not depend on complex external fault detection equipment, and can reliably operate under the conditions of a weak power grid and a strong power grid.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronics and grid control, and particularly relates to a grid-forming converter transient stability control method and system based on power angle change trend prediction and grid strength self-adaptation. BACKGROUND

[0002] With the increasing penetration of renewable energy in the grid, grid-forming energy storage systems based on virtual synchronous generator (VSG) technology have become a key technology to solve the problem of grid stability, because they can simulate the inertia and damping characteristics of synchronous generators and provide active support for the grid. The active-frequency control link of the grid-forming converter simulates the rotor motion equation of the synchronous generator, which is:

[0003]

[0004] where J is the virtual moment of inertia, D is the virtual damping coefficient, P0 and P are the active power command value and actual output value, and ω and ω0 are the actual value and rated value of the grid angular frequency, respectively.

[0005] However, the grid-forming converter also exposes its inherent vulnerability when it faces serious grid faults (such as voltage sag). On the one hand, a sudden drop in grid voltage causes the active power P output by the grid-forming converter to drop sharply, while the active power command value P0 input by the grid-forming converter cannot change instantaneously. This huge power imbalance (P0-P) will cause the power angle (the phase angle difference between the virtual internal voltage and the grid voltage) to increase rapidly through the above rotor motion equation, and if not controlled, it will easily cause transient power angle instability, causing the grid-forming converter and the grid to lose synchronization.

[0006] On the other hand, in order to respond to voltage sag and provide voltage support, the reactive-voltage control loop of the grid-forming converter will quickly adjust the virtual internal voltage, which interacts with the power angle instability and may cause a huge fault current at the converter outlet. The d-q axis components of the fault current can be expressed as:

[0007] i d =(Ecosδ-u g ) / X eq ;

[0008] i q =(Esinδ) / X eq ;

[0009] As can be seen from the above formula, the increase in power angle δ will directly cause the active current component i d to increase, while the adjustment of internal voltage E and voltage sag will affect the reactive current component i q , together causing the total current to exceed the limit.

[0010] Existing technologies typically treat transient power angle instability and fault overcurrent as two separate problems. For example, some methods improve power angle stability by adjusting the inertia J and damping D of the grid-connected converter, while others focus on designing various current limiting strategies. However, these methods neglect the profound intrinsic coupling between power angle instability and fault overcurrent. Therefore, existing technologies struggle to simultaneously address these two interrelated challenges during faults.

[0011] In recent years, some studies have proposed precise calculation methods based on system models, acquiring fault information through traveling wave ranging and designing active power reference values ​​and reactive power droop coefficients in stages. However, these methods have significant limitations: First, they heavily rely on accurate fault information, requiring complex traveling wave ranging technology, which increases system cost and complexity; second, the calculation of control parameters involves complex mathematical operations, placing high demands on controller performance; third, they only divide the process into two stages, "during the fault" and "after the fault tangent," and switching control strategies may lead to system oscillations; finally, they do not consider the impact of grid strength on control effectiveness, and may not be able to effectively balance reactive power support and power angle stability under weak grid conditions. Therefore, existing technical solutions struggle to simultaneously and efficiently address the interrelated challenges of power angle instability and fault overcurrent under various grid conditions. Summary of the Invention

[0012] To address the aforementioned technical problems, this invention proposes a transient stability control method and system for grid-connected converters based on power angle change trend prediction and grid strength adaptation, thereby resolving the issues existing in the prior art.

[0013] To achieve the above objectives, this invention provides a transient stability control method for grid-connected converters based on power angle change trend prediction and grid strength adaptation, comprising:

[0014] The presence of a grid fault is determined based on the real-time acquired grid voltage. If a grid fault exists, the severity level of the fault is obtained based on the voltage transient characteristics of the grid voltage.

[0015] Based on the severity level of the fault, a combination of control strategies is selected for stable control.

[0016] When there is no grid fault, the strength of the combined control strategy based on voltage recovery speed and power angle stability control is maintained until normal and stable operation is achieved.

[0017] Optionally, the voltage transient characteristics include voltage drop depth, voltage change rate, and fault duration.

[0018] Optionally, the severity levels of the fault include mild fault, moderate fault, severe fault, and extreme fault; the control strategies include reactive power coordinated control, active power adaptive adjustment, and fault current limiting.

[0019] Optionally, the process of selecting a combination of control strategies for stable control based on the severity level of the fault includes:

[0020] If it is a minor fault, then reactive power coordination control should be selected;

[0021] If it is a moderate fault, then reactive power coordinated control and active power adaptive adjustment are selected.

[0022] For severe or extreme faults, reactive power coordination control, active power adaptive adjustment, and fault current limiting are selected.

[0023] Optionally, the reactive power coordination control process includes:

[0024] The reactive power-voltage droop coefficient K is dynamically adjusted based on the real-time assessment of the grid short-circuit ratio. q The calculation formula is:

[0025] K q =K q_base ×[1-α(1-SCR / SCR min )];

[0026] Among them, K q_base The reactive power-voltage droop factor is the reactive power-voltage droop factor under normal operating conditions, and SCR is the grid short-circuit ratio. min α is the critical short-circuit ratio, and α is the adjustment coefficient.

[0027] Optionally, the active power adaptive adjustment process includes:

[0028] The active power command value P0 in the rotor motion equation of the grid converter is corrected to P 0_new P 0_new The calculation formula is:

[0029]

[0030] Where, k p k is the feedback coefficient for the power angle deviation. d k is the feedback coefficient for the rate of change of work angle. a Here, δ0 is the acceleration feedback coefficient for power angle change, v is the real-time power angle of the grid-type converter, and δ0 is the steady-state power angle before rated operation or fault. and These are the rate of change of the work angle and the acceleration thereof, respectively.

[0031] Optionally, the fault current limiting process includes:

[0032] The magnitude of the current command vector is calculated in the dq coordinate system. The maximum allowable current is determined based on the grid short-circuit ratio and power angle deviation. If the magnitude of the current command is greater than the maximum allowable current, the current is limited based on the magnitude of the current command and the maximum allowable current.

[0033] Optionally, the d-axis current command in the dq coordinate system can be based on the current command amplitude and the maximum allowable current. and q-axis current command The amplitude is limited proportionally, and the calculation formula is as follows:

[0034]

[0035] Among them, I max For the maximum allowable current, I * The magnitude of the current command vector; and These are the d-axis current command and q-axis current command after limiting, respectively.

[0036] Optionally, when there is no grid fault, the process until normal and stable operation is achieved, based on the strength of the combination of voltage recovery speed and power angle stability control strategies, includes:

[0037] When the voltage recovers to 80% of the rated value, fault current limiting is not performed; when the voltage recovers to 90%, active power adaptive regulation is not performed; reactive power coordination control is retained until the voltage is fully restored.

[0038] This invention also provides a transient stability control system for a grid-connected converter based on power angle change trend prediction and grid strength adaptation, comprising:

[0039] The voltage monitoring module is used to acquire the grid voltage in real time and determine whether there is a grid fault.

[0040] The fault assessment module is used to determine the severity level of a fault based on the voltage transient characteristics of the grid voltage.

[0041] The control strategy execution module is used to select and execute a corresponding combination of control strategies according to the severity level of the fault. The combination of control strategies includes at least one of reactive power coordination control, active power adaptive adjustment, and fault current limiting.

[0042] The recovery management module is used to adjust the strength of the control strategy based on the voltage recovery speed and power angle stability when the grid voltage recovers, until the system returns to normal operation.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] (1) Synergistic solution to dual problems: This invention achieves transient power angle stability and full fault current limiting of grid-type converters under severe faults through coordinated control of active power, reactive power and current.

[0045] (2) Stabilize the power angle from the root cause: By adaptively adjusting the active power command, it directly acts on the root cause of power angle instability - power imbalance, and the control effect is direct and efficient.

[0046] (3) Adaptive power grid strength: The control parameters are dynamically adjusted according to the short-circuit ratio (SCR) of the power grid, and the optimal control effect can be achieved under both weak and strong power grid conditions.

[0047] (4) Fault graded response: Select different combinations of control strategies according to the severity of the fault to avoid abrupt changes in control strategies and improve system stability.

[0048] (5) Predictive control mechanism: Introduce the prediction of power angle change trend, adjust control parameters in advance, reduce control delay, and improve control foresight.

[0049] (6) Robust and easy to implement: The method has clear logic, is based on the basic control framework of the grid converter, and is easy to implement in existing digital controllers. Attached Figure Description

[0050] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0051] Figure 1 This is a schematic diagram of the main circuit topology of a grid-connected converter system according to an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram illustrating the structure of the current limiting unit and its position in the control loop according to an embodiment of the present invention;

[0053] Figure 3 This is a structural block diagram of the active power-frequency loop control strategy based on power angle change trend prediction according to an embodiment of the present invention.

[0054] Figure 4 This is a structural block diagram of the reactive power-voltage loop control strategy based on grid strength identification according to an embodiment of the present invention;

[0055] Figure 5 The above is a simulation curve comparing the power angle of the grid-type converter under the grid voltage drop condition of the traditional control method and the control method of the present invention in an embodiment of the present invention.

[0056] Figure 6The above is a simulation curve of the output current of the grid-type converter when the joint control strategy of the present invention is adopted in an embodiment of the present invention. Detailed Implementation

[0057] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0058] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0059] Example 1

[0060] like Figure 1 As shown, this embodiment provides a transient stability control method for grid-connected converters based on power angle change trend prediction and grid strength adaptation, including:

[0061] Step 1: Monitor the grid voltage in real time and assess the grid faults according to the preset voltage drop depth to determine the severity level of the fault;

[0062] Step Two: When a power grid fault is detected, select the corresponding control strategy combination based on the severity level of the fault. The control strategy combination includes:

[0063] For minor faults, only adjust the reactive-voltage control loop parameters of the grid-type converter;

[0064] For moderate faults, while adjusting the parameters of the reactive power-voltage control loop, adaptive adjustment of active power based on the prediction of power angle change trend is initiated.

[0065] For severe faults, active power adaptive adjustment based on power angle change trend prediction, reactive power coordinated control based on grid strength identification, and fault current limiting are activated simultaneously.

[0066] The active power adaptive adjustment based on the prediction of the power angle change trend introduces the prediction feedback of power angle deviation, power angle change rate and power angle change acceleration, and dynamically reduces the active power command value according to the deviation between the current power angle and the rated power angle and the power angle change trend.

[0067] Step 3: When the grid voltage begins to recover, the intensity of the fault control strategy is gradually reduced based on the voltage recovery speed and power angle stability, so as to achieve a smooth transition from the fault control mode to the normal operation mode.

[0068] The specific method for adaptive adjustment of active power based on the prediction of the power angle change trend is as follows:

[0069] In the rotor motion equation of the grid-type converter, the active power command value P0 is corrected to P 0_new The calculation formula is:

[0070]

[0071] Where, k p k is the feedback coefficient for the power angle deviation. d k is the feedback coefficient for the rate of change of work angle. a Here, δ is the acceleration feedback coefficient for power angle change, δ is the real-time power angle of the grid-type converter, and δ0 is the steady-state power angle before rated operation or fault. and These are the rate of change of the work angle and the acceleration thereof, respectively.

[0072] The specific method of reactive power coordinated control based on grid strength identification is as follows:

[0073] Based on the real-time assessed grid short-circuit ratio (SCR), the reactive power-voltage droop coefficient K is dynamically adjusted. q The calculation formula is:

[0074] K q =K q_base ×[1-α(1-SCR / SCR min )]

[0075] Among them, K q_base SCR is the reactive power-voltage droop factor under normal operating conditions. min The critical short-circuit ratio is α, which is an adjustment coefficient ranging from 0.3 to 0.7.

[0076] The specific method for fault current limiting is as follows:

[0077] 1) Obtain the d-axis current command output by the outer voltage loop in the dq synchronous rotating coordinate system. and q-axis current command

[0078] 2) Calculate the vector magnitude of the current command.

[0079] 3) Dynamically determine the maximum allowable current I based on the grid short-circuit ratio (SCR) and power angle deviation (δ-δ0). max ;

[0080] 4) Determine I * Is it greater than I? max ;

[0081] 5) If I * >Imax Then proportionally and Limit the amplitude.

[0082] proportionally and The specific calculation formula for limiting the amplitude is as follows:

[0083]

[0084] And and As the input reference value for the inner current loop.

[0085] The severity level of the fault is assessed based on the voltage drop depth ΔV, as defined in Table 1:

[0086] Table 1

[0087] Fault level AV range Level 0 (Normal operation) ΔV < 10% Level 1 (Mild fault) 10% < ΔV < 30% Level 2 (Moderate fault) 30% < ΔV < 60% Level 3 (Severe fault) 60% < ΔV < 90% Level 4 (Extreme fault) AV > 90%

[0088] This invention also provides a transient stability control system for a grid-connected converter based on power angle change trend prediction and grid strength adaptation, comprising:

[0089] The voltage monitoring module is used to acquire the grid voltage in real time and determine whether there is a grid fault.

[0090] The fault assessment module is used to determine the severity level of a fault based on the voltage transient characteristics of the grid voltage.

[0091] The control strategy execution module is used to select and execute a corresponding combination of control strategies according to the severity level of the fault. The combination of control strategies includes at least one of reactive power coordination control, active power adaptive adjustment, and fault current limiting.

[0092] The recovery management module is used to adjust the strength of the control strategy based on the voltage recovery speed and power angle stability when the grid voltage recovers, until the system returns to normal operation.

[0093] This invention first involves the system monitoring the grid voltage in real time and then assessing the severity of faults based on the voltage drop depth. Unlike the simple binary judgment in existing technologies, this invention defines multiple fault levels, enabling more refined fault assessment and avoiding abrupt changes in control strategies.

[0094] Secondly, when a voltage dip fault is detected in the power grid, the system selects the corresponding combination of control strategies based on the severity of the fault. For minor faults, only reactive power control parameters are adjusted; for moderate faults, active power adaptive regulation and reactive power coordinated control are activated; for severe faults, active power regulation, reactive power coordination, and current limiting are activated simultaneously. This tiered response mechanism enables precise control for different fault severity levels.

[0095] Regarding adaptive adjustment of active power, this invention innovatively introduces a power angle change trend prediction mechanism. This is achieved by real-time calculation of the power angle deviation (δ-δ0), the power angle change rate (dδ / dt), and the power angle change acceleration (d...). 2 δ / dt 2 A second-order prediction model is constructed to adjust the active power command in advance. This measure can not only respond to the current power angle deviation, but also predict the development trend of the power angle, thus more effectively suppressing power angle instability at its root.

[0096] In terms of reactive power coordinated control, this invention breaks through the limitations of traditional static parameter adjustment, and dynamically adjusts the reactive power-voltage droop coefficient K based on the real-time assessed grid short-circuit ratio (SCR). q Under weak grid conditions, the reactive power support intensity is appropriately reduced to avoid power angle instability caused by excessive reactive power support; under strong grid conditions, the reactive power support capability is enhanced. This adaptive strategy based on grid strength achieves an intelligent balance between reactive power support and power angle stability.

[0097] Regarding fault current limiting, this invention not only considers current amplitude limitations but also dynamically determines the maximum allowable current value based on the grid short-circuit ratio and power angle deviation. This intelligent limiting strategy ensures equipment safety while maximizing system stability.

[0098] When the fault is cleared and the grid voltage begins to recover, the system gradually reduces the intensity of the fault control strategy based on the voltage recovery rate and power angle stability, achieving a smooth transition from fault control mode to normal operation mode and avoiding secondary impacts. Specifically: when the voltage recovers to 80% of its rated value, the current limiting function is first deactivated; when the voltage recovers to 90%, active power adaptive regulation is deactivated; only reactive power coordination control is retained until the voltage is fully restored. This gradual recovery strategy effectively avoids system oscillations caused by abrupt changes in the control strategy.

[0099] Reference Figure 1 The present invention is implemented on a typical grid-connected converter system, and its control system is the core of the invention. The implementation process is divided into three stages: normal operation, fault handling, and fault recovery.

[0100] Phase 1: Normal operation;

[0101] During normal operation, grid-type converters employ methods such as... Figure 1 The traditional control strategy shown. The control system monitors the grid voltage u at the PCC point in real time. g . Figure 1 In the middle, V dc This is the DC side voltage; R f L f and Cf These are the filter resistor, filter inductor, and filter capacitor, respectively; i f ω0 is the filter current; ω0 is the reference frequency; R g and L g These are the line resistance and line inductance, respectively; i g U is the inverter output current; g P is the grid voltage; E is the inverter output voltage; e and Q e These output active power and reactive power, respectively. The active frequency control and reactive voltage control loops generate phase signals θ, respectively. ref and voltage amplitude signal U ref , with i f i g Together with E, they serve as the input to the voltage and current inner loop control to generate the PWM reference signal, driving the inverter to operate normally.

[0102] Phase Two: Troubleshooting;

[0103] Assume that at time t1, a three-phase symmetrical short-circuit fault occurs in the power grid, and the voltage u at point PCC is... g A voltage drop to 50% of the rated value (Level 3, severe fault). The fault severity assessment module within the control system detects the voltage drop and determines the fault severity level to Level 3 based on preset voltage drop depth, voltage change rate, and duration.

[0104] (1) Initiate adaptive adjustment of active power based on prediction of power angle change trend;

[0105] Active-frequency control loop switched to Figure 3 The improved structure is shown. Based on the original rotor motion equations, a predictive feedback branch for the power angle deviation and its changing trend is introduced. The corrected active power command P... 0_new It becomes:

[0106]

[0107] Where, k p k d k a The feedback coefficients for the power angle deviation, rate of change, and acceleration are 0.8, 0.5, and 0.3, respectively. This P... 0_new Substituting into the rotor motion equation:

[0108]

[0109] Because δ tends to increase after the fault, and Make P 0_new This significantly reduces the acceleration term (P), thus directly reducing it. 0_new-P) effectively suppressed the rapid increase of the power angle δ. Simulation results ( Figure 5 The results show that after adopting the method of the present invention (dashed line), the power angle δ quickly stabilizes, while the power angle of the traditional method (solid line) shows a large oscillation trend.

[0110] (2) Initiate reactive power coordination control based on grid strength identification;

[0111] At the same time, the reactive power-voltage control loop also switches to such Figure 4 The fault modes are shown in the figure, where U0 is the desired voltage reference value. This invention innovatively adjusts the reactive power-voltage droop coefficient K dynamically based on the real-time assessed grid short-circuit ratio (SCR). q :

[0112] K q =K q_base ×[1-0.5×(1-SCR / 3)]

[0113] Among them, SCR min Let K be 3. In this embodiment, the system short-circuit ratio is 2.5 (weak grid), and K is calculated. q =0.83×K q_base The reactive power support intensity was appropriately reduced, thus avoiding power angle instability caused by excessive reactive power support under weak grid conditions.

[0114] (3) Start fault current limiting;

[0115] Although power angle stabilization control helps reduce fault current, the risk of overcurrent still exists under severe fault conditions. Therefore, Figure 2 The current limiting unit shown is activated. This unit is located between the outer voltage loop and the inner current loop. It calculates the dq-axis current command output by the voltage loop in real time. and Vector magnitude:

[0116]

[0117] The maximum allowable current I is dynamically determined based on the grid short-circuit ratio and power angle deviation. max :

[0118]

[0119] In this embodiment, I max =0.92×I max_base This ensures both equipment safety and maintains sufficient reactive power support. Assume the converter's maximum allowable current I... max_base It is 250A. When I * >I max When this occurs, the limiting logic is activated, and a proportional limiting method is adopted:

[0120]

[0121] The revised command was used as the final setpoint for the inner current loop. From Figure 6 The simulation results show that, after adding limiting control, the output current of the grid-type converter during the fault period is stably limited to I. max (230A) nearby, effectively protecting the safety of the equipment.

[0122] Figure 2 middle, This is the initial d-axis current reference command. This is the initial q-axis current reference command; For parameters related to current limiting logic, I max These are the current limiting values; both act on the current limiting unit to output the limited value. (d-axis current reference command) and (q-axis current reference command). After entering the inner current loop, This is the actual current feedback value along the d-axis. These are the actual q-axis current feedback values, which are compared with the current reference command after being limited, and adjusted by the PI (proportional-integral) controller, while also taking into account the grid angular frequency ω and the converter branch inductance L. c and d-axis voltage feedforward component q-axis voltage feedforward component Finally, the d-axis voltage reference command for driving the converter is generated. and q-axis voltage reference command The overall control logic consists of "current limiting + current inner loop (PI control + voltage feedforward)".

[0123] Phase 3: Fault Recovery;

[0124] Assuming the grid fault is cleared at time t2, the voltage u at point PCC is... g Recovery begins. The fault severity assessment module detects voltage recovery and, based on the voltage recovery rate and power angle stability, gradually reduces the strength of the fault control strategy to achieve a smooth transition from fault control mode to normal operation mode, avoiding secondary impacts. Specifically: when the voltage recovers to 80% of its rated value, the current limiting function is first deactivated; when the voltage recovers to 90%, active power adaptive regulation is deactivated; only reactive power coordination control is retained until the voltage is fully restored. This gradual recovery strategy effectively avoids system oscillations caused by abrupt changes in control strategy.

[0125] This invention constructs a multi-dimensional stable control system of "prediction-adaptation-gradation" through three major innovations: power angle change trend prediction, grid strength identification, and fault severity graded response. It effectively solves the transient power angle instability and overcurrent problems of grid-type converters under grid faults, and significantly improves the fault ride-through capability and operational reliability of grid-type converters under various grid fault conditions.

[0126] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A transient stability control method for a grid-connected converter based on power angle variation trend prediction and grid strength adaptation, characterized in that, Includes the following steps: The presence of a grid fault is determined based on the real-time acquired grid voltage. If a grid fault exists, the severity level of the fault is obtained based on the voltage transient characteristics of the grid voltage. Based on the severity level of the fault, a combination of control strategies is selected for stable control. When there is no grid fault, the strength of the combined control strategy based on voltage recovery speed and power angle stability control is maintained until normal and stable operation is achieved.

2. The transient stability control method for grid-type converters based on power angle change trend prediction and grid strength adaptation as described in claim 1, characterized in that, The voltage transient characteristics include voltage drop depth, voltage change rate, and fault duration.

3. The transient stability control method for grid-type converters based on power angle change trend prediction and grid strength adaptation as described in claim 1, characterized in that, The severity levels of the faults include mild faults, moderate faults, severe faults, and extreme faults; the control strategies include reactive power coordinated control, active power adaptive adjustment, and fault current limiting.

4. The transient stability control method for grid-type converters based on power angle change trend prediction and grid strength adaptation according to claim 3, characterized in that, The process of selecting a combination of control strategies for stability control based on the severity level of the fault includes: If it is a minor fault, then reactive power coordination control should be selected; If it is a moderate fault, then reactive power coordinated control and active power adaptive adjustment are selected. For severe or extreme faults, reactive power coordination control, active power adaptive adjustment, and fault current limiting are selected.

5. The transient stability control method for grid-type converters based on power angle change trend prediction and grid intensity adaptation according to claim 4, characterized in that, The reactive power coordination control process includes: The reactive power-voltage droop coefficient K is dynamically adjusted based on the real-time assessment of the grid short-circuit ratio. q The calculation formula is: K q =K q_base ×[1-α(1-SCR / SCR min )]; Among them, K q_base The reactive power-voltage droop factor is the reactive power-voltage droop factor under normal operating conditions, and SCR is the grid short-circuit ratio. min α is the critical short-circuit ratio, and α is the adjustment coefficient.

6. The transient stability control method for grid-type converters based on power angle change trend prediction and grid strength adaptation according to claim 4, characterized in that, The process of adaptive adjustment of active power includes: The active power command value P0 in the rotor motion equation of the grid converter is corrected to P 0_new P 0_new The calculation formula is: Where, k p k is the feedback coefficient for the power angle deviation. d k is the feedback coefficient for the rate of change of work angle. a δ is the acceleration feedback coefficient for power angle change, δ is the real-time power angle of the grid-type converter, and δ0 is the steady-state power angle before the fault. and These are the rate of change of the work angle and the acceleration thereof, respectively.

7. The transient stability control method for grid-type converters based on power angle change trend prediction and grid intensity adaptation according to claim 4, characterized in that, The fault current limiting process includes: The magnitude of the current command vector is calculated in the dq coordinate system. The maximum allowable current is determined based on the grid short-circuit ratio and power angle deviation. If the magnitude of the current command is greater than the maximum allowable current, the current is limited based on the magnitude of the current command and the maximum allowable current.

8. The transient stability control method for grid-type converters based on power angle change trend prediction and grid strength adaptation according to claim 1, characterized in that, Current command based on current command amplitude and maximum allowable current in the d-axis current command of the dq coordinate system and q-axis current command The amplitude is limited proportionally, and the calculation formula is as follows: Among them, I max For the maximum allowable current, I * The magnitude of the current command vector; and These are the d-axis current command and q-axis current command after limiting, respectively.

9. A transient stability control method for a grid-connected converter based on power angle change trend prediction and grid strength adaptation as described in claim 1, characterized in that, When there is no grid fault, the process until normal and stable operation is achieved, based on the strength of the combined control strategy of voltage recovery speed and power angle stability control, includes: When the voltage recovers to 80% of the rated value, fault current limiting is not performed; when the voltage recovers to 90%, active power adaptive regulation is not performed; reactive power coordination control is retained until the voltage is fully restored.

10. A system for implementing a transient stability control method for grid-connected converters based on power angle variation trend prediction and grid intensity adaptation, characterized in that, include: The voltage monitoring module is used to acquire the grid voltage in real time and determine whether there is a grid fault. The fault assessment module is used to determine the severity level of a fault based on the voltage transient characteristics of the grid voltage. The control strategy execution module is used to select and execute a corresponding combination of control strategies according to the severity level of the fault. The combination of control strategies includes at least one of reactive power coordination control, active power adaptive adjustment, and fault current limiting. The recovery management module is used to adjust the intensity of the control strategy based on the voltage recovery speed and power angle stability when the grid voltage is restored, until normal operation is restored.

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