Power angle compensation-based method for quickly recovering active power after fault of network construction type converter

Abstract

The invention belongs to the technical field of stable control of a power system, and particularly discloses a power angle compensation-based method for quickly recovering active power after a fault of a network-forming converter, which comprises the following steps of: monitoring a voltage amplitude and a power difference value at a grid-connected point of the network-forming converter in real time; according to the voltage amplitude and the power difference value, identifying whether the network-forming converter is in an unstable state of active power oscillation after the fault is cleared; if the state is identified as an unstable state, calculating a power angle compensation amount used for counteracting power angle deviation caused by a fault based on detected voltage drop information and system impedance parameters; and superposing the power angle compensation value to a power angle generated by a power control ring of the network-forming type converter, and generating a compensated power angle instruction for controlling pulse modulation of the converter so as to realize active power recovery after the fault is cleared. The method can adapt to different power grid impedance conditions, quickly suppress power oscillation and realize quick recovery of active power, so as to improve the transient stability and reliability of a novel power system.

Description

Technical Field

[0001] This application belongs to the field of power system stability control technology, and more specifically, relates to a method for rapid active power recovery after a grid-type converter fault based on power angle compensation. Background Technology

[0002] With the acceleration of the global energy transition, the proportion of renewable energy sources, such as photovoltaics and wind power, connected to the power system through grid-connected transformers (GFM) has increased significantly. By simulating the characteristics of synchronous generators, GFM converters possess the ability to autonomously establish grid voltage and frequency, becoming key equipment supporting the stable operation of new power systems. However, existing technologies have the following shortcomings in active power recovery after GFM converter failures: Insufficient research on the post-fault phase: Existing studies mostly focus on the voltage drop process during grid faults, with insufficient attention paid to the dynamic process of active power recovery after fault clearance. In actual operation, GFM converters often experience power oscillations or even loss of synchronization after a fault. During prolonged faults or extremely low voltage ride-throughs (LVRTs), post-fault power fluctuations may exceed those during the fault period, leading to deterioration in system stability. Neglecting the influence of grid impedance: Traditional transient stability analyses are mostly based on the assumption of a purely inductive grid, neglecting the influence of the grid impedance R / X ratio. Studies have shown that the presence of grid resistance significantly alters the power output characteristics of GFM converters. When the R / X ratio is large, the power angle offset during the fault is aggravated, easily triggering power oscillations during voltage recovery after the fault. Poor adaptability of control strategies: Existing control strategies, such as power reference adjustment and virtual impedance regulation, struggle to simultaneously address the transient instability caused by power angle offset and the problem of rapid recovery. For example, while the virtual resistance strategy can suppress oscillations, it reduces power output capability and has a long recovery time. Slow transient response: In traditional methods, the time for the active power of a GFM converter to recover to 90% of its rated value after a fault usually exceeds 500ms, which cannot meet the standard requirement of recovery within 0.5 seconds.

[0003] In summary, existing technologies for active power recovery after GFM converter faults suffer from several drawbacks, including insufficient research on the dynamic process in the post-fault stage, failure to consider the influence of grid impedance R / X ratio, poor adaptability of control strategies, and slow transient response speed. There is an urgent need to propose a method and system that can adapt to different grid impedance conditions, quickly suppress power oscillations, and achieve rapid active power recovery in order to improve the transient stability and reliability of new power systems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for rapid active power recovery after a grid-type converter fault based on power angle compensation. This method can adapt to different grid impedance conditions, quickly suppress power oscillations, and achieve rapid active power recovery, thereby improving the transient stability and reliability of new power systems.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for rapid active power recovery after a grid-type converter fault based on power angle compensation, applicable to a power system including the grid-type converter and the power grid, comprising the following steps: S10 monitors the voltage amplitude at the grid connection point of the grid-connected converter in real time, as well as the power difference calculated based on the active power reference value and the actual output value. S20, Based on the voltage amplitude and power difference, identify whether the grid-type converter is in an unstable state with active power oscillation after the fault is cleared; S30, if an unstable state is identified, calculate the power angle compensation amount to offset the power angle offset caused by the fault based on the detected voltage drop information and system impedance parameters. S40, the power angle compensation value is superimposed on the power angle generated by the power control loop of the grid-type converter to generate a compensated power angle command, which is used to control the pulse modulation of the converter to realize the restoration of active power after the fault is cleared.

[0006] As a further preferred embodiment, step S20, the identification step specifically includes: Based on preset voltage and power difference thresholds, the working process of the grid-type converter is divided into multiple stages through state machine logic; The determination condition for the unstable state is as follows: the voltage amplitude recovers from below the voltage threshold to above the voltage threshold, and the power difference is greater than the first power difference threshold, and this continues for a preset delay time.

[0007] As a further preferred embodiment, the stages of the state machine logic division include a normal state, a fault state, the unstable state, and a post-fault smoothing state. The conditions for determining the normal state are: the voltage amplitude is higher than or equal to the voltage threshold and the power difference is less than or equal to the second power difference threshold; The fault condition is determined when the voltage amplitude is lower than the voltage threshold. The criteria for determining the smooth state after a fault are: the voltage amplitude is higher than or equal to the voltage threshold and the power difference is less than or equal to the first power difference threshold.

[0008] As a further preferred embodiment, in step S30, power angle compensation... The calculation formula is:

[0009] In the formula, V 0 represents the rated voltage amplitude; Δ V fThe detected voltage drop amplitude is the rated voltage amplitude. V 0 and the lowest voltage amplitude recorded during the fault. V min difference; R v The virtual resistance value set in the control of the grid-type converter; R g This is the resistance value of the power grid; Z Δ These are the calculation parameters related to the total impedance of the converter.

[0010] As a further preferred embodiment, in the identification step, if it is identified as not being in the unstable state, the power angle compensation amount is set to zero, and the compensated power angle command is equal to the power angle generated by the power control loop.

[0011] As a further preferred embodiment, the method further includes: Adaptive adjustment steps: Based on the grid impedance R / X The control parameters of the grid-type converter are adjusted in real time, including the damping coefficient and the virtual resistance value.

[0012] As a further preferred embodiment, the method restores active power while maintaining the outer loop droop control characteristics of the grid-type converter, so that the grid-type converter can continue to provide grid frequency and voltage support.

[0013] Secondly, this application provides an active power recovery system based on power angle compensation for grid-connected converters after a fault, applicable to power systems including grid-connected converters and power grids, comprising the steps of implementing the method described in any one of the above statements, including: The monitoring module is used to monitor the voltage amplitude at the grid connection point of the grid-connected converter in real time, as well as the power difference calculated based on the active power reference value and the actual output value. The status identification module is used to identify whether the grid-type converter is in an unstable state with active power oscillation after the fault is cleared, based on the monitored voltage amplitude and power difference. The compensation calculation module is used to calculate the power angle compensation amount to offset the power angle offset caused by the fault, based on the detected voltage drop information and system impedance parameters when the unstable state is identified. The control synthesis module is used to superimpose the power angle compensation amount onto the power angle generated by the power control loop of the grid-type converter, and generate a compensated power angle command to control the pulse modulation of the converter so as to realize the restoration of active power after the fault is cleared.

[0014] Thirdly, this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method as described in any one of the above.

[0015] Fourthly, this application provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps of the method as described in any one of the above statements.

[0016] The beneficial effects of this application are as follows: (1) The power grid impedance was clearly revealed for the first time. R / X The essential impact mechanism of the active power recovery process after a fault in a grid-type converter is compared, namely, by changing the position of the steady-state equilibrium point during the fault, a power angle jump is generated when the fault is cleared.

[0017] (2) The proposed power angle compensation method directly acts on the power loop, which can quickly eliminate the transient power angle difference caused by the resistive component, significantly shorten the recovery time after the fault, and effectively suppress the risk of power oscillation and loss of step.

[0018] (3) This method does not rely on fault state switching or complex virtual impedance dynamic adjustment. It has a simple structure, is easy to implement, and is applicable to different... R / X It exhibits good adaptability and robustness in both grid conditions and weak grid environments.

[0019] (4) While achieving rapid recovery, the grid-type converter does not affect its ability to support the grid frequency and voltage during transient processes. Attached Figure Description

[0020] Figure 1 This is a flowchart of the control strategy provided in the embodiments of this application, which mainly includes four states: ST0 to ST3. Figure 2 This is a schematic diagram of the GFM converter system structure provided in the embodiments of this application, including the main circuit ( V dc , L f , R f , C f , L g , R g ), control loops (active frequency control, reactive voltage control, virtual impedance control, voltage and current inner loop control) and grid connection; Figure 3 This is a block diagram of active frequency control with added power angle compensation provided in an embodiment of this application; Figure 4 This is a state distribution diagram under the power angle compensation control strategy provided in the embodiments of this application, where ST2 is the start time of the power angle compensation control strategy. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] This application aims to provide a solution that can adapt to different power grid impedances. R / X This paper presents a control method for grid-connected converters that effectively suppresses active power oscillations after faults and achieves rapid active power recovery. This method addresses the problems of power oscillations and slow recovery after faults in existing technologies through dynamic power angle compensation and adaptive control strategies. It enables stable and rapid recovery of the GFM converter under different grid impedance conditions, thereby improving the transient stability and reliability of the power system.

[0023] like Figure 1 As shown, this application provides a method for rapid active power recovery after a grid-type converter fault based on power angle compensation, including the following steps: (1) System modeling and fault stage determination: Establish a system including grid impedance ( R g , L g ) and virtual impedance ( R v , L v The equivalent circuit model of the GFM converter is obtained by detecting the voltage amplitude at the point of common coupling (PCC). V mg and active power difference Δ P = P ref P e The failure process is divided into four stages: ST0 (Normal State): V mg ≥0.8pu and Δ P ≤0.1pu; ST1 (Fault Status): V mg <0.8pu; ST2 (Unstable state after failure): V mg Rebounded to above 0.8 pu and Δ P >0.2 pu, duration Td =200ms; ST3 (Post-fault smoothing state): V mg ≥0.8pu and Δ P ≤0.2pu.

[0024] (2) Quantitative analysis of power angle offset: Based on the active power expression considering grid resistance:

[0025] in X ∑ = X g + X v , R ∑ = R g + R v Derive the power angle difference at the stable equilibrium point (SEP) before and after the fault:

[0026] In the formula Δ V f = V 0 V mg This represents the voltage drop value. It is quantified using this formula. R / X Compare the effects of power angle offset.

[0027] (3) Dynamic power angle compensation control: When the system is determined to be in ST2 state, frequency feedback power angle compensation is started: Δ d e Superimposed on the power angle reference value d ref Adjust the input of the active power control loop to suppress power angle oscillation.

[0028] (4) Adaptive parameter co-optimization: based on grid impedance R / X Compared to real-time adjustment of control parameters: Damping coefficient D :when R / X When the ratio increases, the ratio increases. D Up to 40 50 p.u., suppressing power angle overshoot; Virtual impedance parameter: dynamically adjust virtual resistance R v Up to 0.03 0.05 pu, balancing power decoupling and system damping; Power reference adjustment factor: based on voltage sag depth Δ V f Dynamic adjustment P ref = P 0 k m ( V 0 V mg In ) k m = P 0 / V 0.

[0029] Based on the same inventive concept, this application also provides a fast active power recovery system for grid-type converters after a fault, based on power angle compensation, comprising: (1) Intelligent status determination module: Voltage / power detection unit: Real-time acquisition of PCC voltage amplitude V mg and active power P The fault stage identification unit, based on threshold comparison and timing logic, outputs ST0-ST3 status signals to trigger corresponding control strategies. The voltage / power detection unit in the intelligent status determination module uses high-precision voltage and power sensors to accurately collect voltage amplitude and active power data at the PCC point in real time. The fault stage identification unit analyzes and processes the collected data based on pre-set voltage amplitude and power difference thresholds, combined with time-series logic, to accurately determine the fault stage of the converter and output corresponding status signals, providing clear trigger commands for subsequent control modules.

[0030] (2) Power angle analysis calculation module: Impedance parameter estimation unit: through the grid impedance ( R g , L g ) and virtual impedance ( R v , L v )calculate R / X Compare; Power angle offset calculation unit: Calculated through the impedance parameter estimation unit. R / X Compared to, combined with the work angle compensation Δ d e The calculation formula quantifies the difference in power angle before and after the fault. The power angle offset calculation unit, based on the previously established compensation calculation formula, substitutes real-time collected data such as voltage drop values ​​and impedance parameters into the formula to calculate the difference in power angle before and after the fault, providing a key calculation basis for the power angle compensation strategy.

[0031] (3) Dynamic compensation control module: The Δ obtained from the power angle offset calculation unit is used to calculate the dynamic compensation control module. d e The input of the power angle control loop is dynamically corrected by superimposing it onto the power angle reference value. By dynamically correcting the input of the power angle control loop in real time, effective compensation of the power angle is achieved, power oscillation is suppressed, and active power is rapidly restored.

[0032] (4) Parameter adaptive module: control parameter adjustment unit: according to R / X Compared to dynamic adjustment k freq , D , R v Parameters such as these are used to optimize transient response, enabling the system to operate under different conditions. R / X It can maintain optimal transient response performance under all conditions, enabling rapid and stable recovery of active power after converter failure.

[0033] The beneficial effects of this application are as follows: (1) The power grid impedance was clearly revealed for the first time. R / X The essential impact mechanism of the active power recovery process after a fault in a grid-type converter is compared, namely, by changing the position of the steady-state equilibrium point during the fault, a power angle jump is generated when the fault is cleared.

[0034] (2) The proposed power angle compensation method directly acts on the power loop, which can quickly eliminate the transient power angle difference caused by the resistive component, significantly shorten the recovery time after the fault, and effectively suppress the risk of power oscillation and loss of step.

[0035] (3) This method does not rely on fault state switching or complex virtual impedance dynamic adjustment. It has a simple structure, is easy to implement, and is applicable to different... R / X It exhibits good adaptability and robustness in both grid conditions and weak grid environments.

[0036] (4) While achieving rapid recovery, the grid-type converter does not affect its ability to support the grid frequency and voltage during transient processes.

[0037] In one embodiment, the technical solution for achieving the above objective can be specifically as follows: Figure 2 This embodiment illustrates the topology of a grid-type converter fault-based fast active power recovery system. The grid-type converter is connected to the grid via an LCL filter, and the grid impedance includes resistance. R g and inductor L g The control section includes active frequency control for generating synchronization angles. d 0. Reactive voltage control is used to generate virtual internal potential.E ref Virtual impedance control and voltage-current inner loop control generate the modulation voltage. This embodiment adds a power angle compensation module to the active power frequency control loop.

[0038] The core implementation steps of the method in this embodiment are as follows: Electrical quantity acquisition: Acquire the three-phase AC signals of the system, including the three-phase grid connection point voltage. u abc Three-phase grid connection point current i abc First, Clark and Park transformations are performed on the three-phase AC voltage to transform the three-phase stationary coordinate system (abc) into a two-phase stationary coordinate system (dq). The transformation matrix is ​​as follows:

[0039] Similarly, the same transformation is performed on the current to obtain... i d , i q Calculate key intermediate variables Grid connection point voltage amplitude:

[0040] Output active power:

[0041] Power deviation value:

[0042] in P ref This is a reference value for active power.

[0043] Fault stage detection and identification: such as Figure 1 As shown in the control strategy flowchart, the voltage amplitude at the point of common coupling is detected in real time. V mg And the difference between the power reference value and the actual value ( P ref - P e It jumps between four states: ST0 to ST3. ST0 (normal operating state): Voltage is stable, and power difference is close to zero.

[0044] ST1 (Fault Status): Voltage is below the threshold (<0.8pu).

[0045] ST2 (Post-Instantaneous Fault State): After the fault is cleared, the voltage rises rapidly, and the power difference exceeds the threshold (>0.2 pu). This state lasts for a fixed period of time. T d (200ms).

[0046] ST3 (Post-fault smoothing status): The voltage has recovered (≥0.8pu) after the fault is cleared, but the power difference is very small (≤0.2pu).

[0047] The state transition logic is as follows: During initialization, the system is in ST0.

[0048] When the voltage amplitude at the point of common coupling is detected V mg Below the preset voltage drop threshold V th At 0.8 pu, the system enters ST1. During ST1, the lowest voltage drop is continuously recorded. .

[0049] When detected V mg Restored to a voltage recovery level higher than the preset threshold. V th Upon determining that the fault has been cleared, the system transitions to ST2. Simultaneously, a timer is started, with a duration set to [specify duration]. T d (200ms).

[0050] During ST2, the power deviation value Δ was continuously monitored. P If Δ P The absolute value is less than the preset power deviation threshold. P th If the output is 0.2 pu, the system is considered stable and transitions to ST3.

[0051] In ST3, if the system remains stable (Δ P ≤ P th and V mg ≥ V th If a voltage drop is detected again, the system returns to ST0. If another voltage drop is detected, the system jumps directly to ST1.

[0052] The power angle compensation calculation and injection provided in this embodiment are as follows: like Figure 4 As shown, when the system is identified as being in ST2 state, power angle compensation is triggered. The power angle compensation control strategy block diagram is as follows: Figure 3 As shown, the compensation amount Δ d eThe calculation formula is:

[0053] Where, Δ V f For voltage drop depth, Δ V f =1.0- V min , V min The lowest voltage amplitude (per unit) recorded during the fault period; R v , L v The virtual resistance and virtual inductance parameters (known) are set in the control. R g , L g These are the grid resistance and reactance parameters; Z Δ For calculation parameters related to the total impedance of the converter, .

[0054] The power angle synthesis and command generation provided in this embodiment are as follows: Fundamental frequency power angle of grid converter d 0 is obtained by integrating the frequency reference value, which is generated by active-frequency control.

[0055]

[0056] in oh 0 is the rated angular frequency. J Moment of inertia D is the damping coefficient.

[0057] Add the filtered power angle compensation amount to the base power angle to obtain the final compensated power angle command:

[0058] When the compensation enable flag is reset, Δ d e Forced to be set to zero, at this time d = d 0.

[0059] The reactive power-voltage control loop generates voltage amplitude references based on system requirements. E ref The modulation voltage obtained through the virtual impedance loop and voltage-current loop. u d , u q ,use d Three-phase voltage modulation waves are generated through inverse Park transform and inverse Clark transform:

[0060] After being modulated by the PWM module, a PWM signal is generated to drive the inverter switching devices, controlling the inverter to output the required voltage and current. This ultimately shortens the time for the system's active power to recover to 90% of its rated value during fault recovery, and improves the transient stability and reliability of the power system.

[0061] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for rapid active power recovery after a grid-type converter fault based on power angle compensation, applied to a power system including the grid-type converter and the power grid, characterized in that, Includes the following steps: S10 monitors the voltage amplitude at the grid connection point of the grid-connected converter in real time, as well as the power difference calculated based on the active power reference value and the actual output value. S20, Based on the voltage amplitude and power difference, identify whether the grid-type converter is in an unstable state with active power oscillation after the fault is cleared; S30, if an unstable state is identified, calculate the power angle compensation amount to offset the power angle offset caused by the fault based on the detected voltage drop information and system impedance parameters. S40, the power angle compensation value is superimposed on the power angle generated by the power control loop of the grid-type converter to generate a compensated power angle command, which is used to control the pulse modulation of the converter to realize the restoration of active power after the fault is cleared.

2. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 1, characterized in that, In step S20, the identification step specifically includes: Based on preset voltage and power difference thresholds, the working process of the grid-type converter is divided into multiple stages through state machine logic; The determination condition for the unstable state is as follows: the voltage amplitude recovers from below the voltage threshold to above the voltage threshold, and the power difference is greater than the first power difference threshold, and this continues for a preset delay time.

3. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 2, characterized in that, The state machine logic divides the stages into normal state, fault state, unstable state, and post-fault smoothing state. The conditions for determining the normal state are: the voltage amplitude is higher than or equal to the voltage threshold and the power difference is less than or equal to the second power difference threshold; The fault condition is determined when the voltage amplitude is lower than the voltage threshold. The criteria for determining the smooth state after a fault are: the voltage amplitude is higher than or equal to the voltage threshold and the power difference is less than or equal to the first power difference threshold.

4. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 1, characterized in that, In step S30, power angle compensation The calculation formula is: In the formula, V 0 represents the rated voltage amplitude; Δ V f The detected voltage drop amplitude is the rated voltage amplitude. V 0 and the lowest voltage amplitude recorded during the fault. V min difference; R v The virtual resistance value set in the control of the grid-type converter; R g This is the resistance value of the power grid; Z Δ These are the calculation parameters related to the total impedance of the converter.

5. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 1, characterized in that, In the identification step, if it is identified as not being in the unstable state, the power angle compensation amount is set to zero, and the compensated power angle command is equal to the power angle generated by the power control loop.

6. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 1, characterized in that, The method further includes: Adaptive adjustment steps: Based on the grid impedance R / X The control parameters of the grid-type converter are adjusted in real time, including the damping coefficient and the virtual resistance value.

7. The method for rapid active power recovery after a grid-type converter fault based on power angle compensation as described in claim 1, characterized in that, The method achieves active power recovery while maintaining the outer loop droop control characteristics of the grid-type converter, enabling the grid-type converter to continue providing grid frequency and voltage support.

8. A power recovery system for grid-connected converters after a fault, based on power angle compensation, applied to a power system including grid-connected converters and a power grid, for implementing the steps of the method as described in any one of claims 1 to 7, characterized in that, include: The monitoring module is used to monitor the voltage amplitude at the grid connection point of the grid-connected converter in real time, as well as the power difference calculated based on the active power reference value and the actual output value. The status identification module is used to identify whether the grid-type converter is in an unstable state with active power oscillation after the fault is cleared, based on the monitored voltage amplitude and power difference. The compensation calculation module is used to calculate the power angle compensation amount to offset the power angle offset caused by the fault, based on the detected voltage drop information and system impedance parameters when the unstable state is identified. The control synthesis module is used to superimpose the power angle compensation amount onto the power angle generated by the power control loop of the grid-type converter, and generate a compensated power angle command to control the pulse modulation of the converter so as to realize the restoration of active power after the fault is cleared.

9. An electronic device 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 implements the steps of the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by a processor, the computer instructions implement the steps of the method as described in any one of claims 1 to 7.

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