Network construction converter fault ride-through method and system suitable for symmetric fault

Abstract

The invention discloses a network construction converter fault ride-through method and system suitable for symmetrical faults, and belongs to the technical field of network construction converter fault ride-through. According to the method, reactive synchronization is used for replacing active synchronization to control the power angle of the converter during the fault period, and a reactive power demand derived according to a power grid operation criterion is used as a reactive power target of the network construction converter during the fault ride-through period, so that stable tracking of a reactive power actual value and a reference value during the fault period is realized; according to the method, the calculated amount is small, and the network construction converter has sufficient and appropriate reactive voltage supporting capacity while maintaining good synchronization stability. Besides, the invention also provides a strategy for recovering power angle compensation aiming at the transient overvoltage problem occurring in the fault clearing period of the designed reactive synchronous control strategy for the grid construction converter in the fault period, so that the transient overvoltage phenomenon in the recovery period is inhibited, and meanwhile, the grid construction converter can be smoothly transited back to a normal operation state.

Description

Technical Field

[0001] This invention belongs to the field of grid converter fault ride-through technology, and more specifically, relates to a grid converter fault ride-through method and system applicable to symmetrical faults. Background Technology

[0002] With the profound transformation of the global energy structure, the installed capacity of new energy power generation, represented by wind power and photovoltaics, is increasingly accounting for a significant portion of the power system. However, new energy power sources generally use power electronic converters to connect to the grid, resulting in modern power systems exhibiting the prominent characteristics of "high proportion of new energy and high proportion of power electronic equipment." Against this backdrop, the inertia level of the power system decreases, and its disturbance immunity weakens. Once a short-circuit fault occurs, it can easily trigger a chain reaction of grid disconnection accidents or even system collapse.

[0003] To address this significant challenge, grid-forming converter technology has emerged. Unlike traditional grid-following converters, grid-forming converters actively simulate the external characteristics of synchronous generators by introducing control algorithms such as Virtual Synchronous Generators (VSGs), providing necessary frequency and voltage support for weak grids. When a symmetrical fault occurs in the grid (such as a three-phase symmetrical short circuit), the grid-forming converter can maintain the stability of its output internal potential, effectively preventing power oscillations and grid disconnection risks caused by sudden voltage drops in the grid.

[0004] However, despite the excellent performance of grid-based control in improving system robustness, it still faces significant control challenges in practical engineering applications. Especially during symmetrical grid faults, the dramatic changes in both grid voltage amplitude and phase can easily lead to excessive output current or power angle instability if the converter continues to perform conventional constant frequency or constant power control. Therefore, designing a fault ride-through method for grid-based converters suitable for symmetrical faults is a key research topic in the current field of grid-based converter research.

[0005] Currently, academia and industry have proposed various fault ride-through methods for grid-connected converters applicable to symmetrical faults. For example, some literature proposes an adaptive fault ride-through method that balances the state of charge of the energy storage system with the grid support requirements by dynamically adjusting the control center of gravity; other literature utilizes dynamic internal potential technology combined with voltage-reactive power droop curves for fine-tuning to enhance system voltage stability. Furthermore, some literature addresses transient power angle instability by proposing a joint control method combining second-order sliding mode control and adaptive voltage regulation, aiming to strictly limit power angle fluctuations during faults and provide stable reactive power support. Although these methods can theoretically provide sufficient reactive power support, in practical engineering applications, the reactive power support they provide does not conform to grid operation criteria. At the same time, most of these methods require accurate fault parameter identification or complex nonlinear controller design, and the calculation of reactive power reference values ​​is often complex, increasing the computational burden and implementation difficulty of the system. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a fault ride-through method and system for grid converters with symmetrical faults, which solves the technical problems of the existing technology that cannot provide sufficient reactive power that meets the grid operation criteria and has a large amount of calculation.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a fault ride-through method for grid converters with symmetrical faults, comprising: When a symmetrical fault occurs in the external power grid, the following fault-period control operations are performed: Obtain the reactive power reference value of the grid-connected converter in accordance with the grid operation criteria at the current moment. ;in, This represents the actual capacity of the grid-connected converter at the current moment. This represents the per-unit value of the grid converter port voltage at the current moment. Switch the grid converter to reactive power synchronization mode, thereby using the reactive power reference value. To achieve the control objective, reactive power synchronization control is implemented on the grid converter.

[0008] More preferably, the actual capacity of the grid converter for:

[0009] in, This refers to the current limiting value for grid-connected converters. This represents the actual port voltage value of the grid converter.

[0010] More preferably, the control expression for the reactive power synchronization mode is:

[0011] in, The preset reactive power synchronization coefficient; The reactive power of the grid converter; The angular velocity of the virtual synchronous machine in the grid converter relative to the external power grid; t Indicates time.

[0012] More preferably, the above-mentioned grid-connected converter fault ride-through method further includes: after the grid symmetrical fault is cleared, switching the grid-connected converter to active power synchronization mode to perform active power synchronization control on the grid-connected converter: The difference between the current active power reference value and the actual active power value of the grid-connected converter is input into the virtual synchronous machine to obtain the virtual angular velocity of the grid-connected converter at the current moment. Then, the virtual power angle is calculated. ; In virtual power angle Superimposed power angle compensation The phase angle reference value of the grid converter at the current moment is obtained. And adjust the phase angle of the grid converter to the phase angle reference value at the current moment. ;in, This is the power angle compensation coefficient; The power angle of the grid converter under normal operating conditions; The power angle of the grid converter after adjustment by the control operation during the aforementioned fault period when a symmetrical fault occurs in the external power grid.

[0013] More preferably, the control expression for the above-mentioned virtual synchronizer is:

[0014] in, The virtual inertia of the virtual synchronizer; The angular velocity of the virtual synchronous machine in the grid converter relative to the external power grid; t Indicates time; This is a reference value for the active power of the grid-connected converter; The actual active power of the grid converter; The rated angular velocity of the external power grid system; This is the virtual damping for the virtual synchronizer.

[0015] In a second aspect, the present invention provides a grid converter system, comprising: a grid converter and a controller; the controller is used to execute the fault ride-through method provided in the first aspect of the present invention.

[0016] Thirdly, the present invention provides an electronic device, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the fault-traversal method provided in the first aspect of the present invention when executing the computer program.

[0017] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device containing the storage medium to perform the fault-traversal method provided in the first aspect of the present invention.

[0018] Fifthly, the invention also provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the fault-crossing method provided in the first aspect of the invention.

[0019] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a fault ride-through method for grid-connected converters applicable to symmetrical faults. It replaces the role of active power synchronization in controlling the converter's power angle during faults with reactive power synchronization, and uses the reactive power demand derived from grid operation criteria as the reactive power target for the grid-connected converter during fault ride-through, achieving stable tracking of the actual reactive power value and the reference value during faults. This invention has a small computational load and can provide sufficient reactive power that conforms to grid operation criteria.

[0020] 2. Furthermore, the fault ride-through method for grid-connected converters provided by this invention addresses the transient overvoltage problem that occurs during fault clearing in the designed reactive power synchronization control strategy of the grid-connected converter during fault clearing. It proposes a power angle compensation strategy, introducing a power angle compensation loop into the power angle generation circuit during fault clearing. Based on the steady-state power angle of the grid-connected converter and the power angle adjusted by the aforementioned fault-period control operation when a symmetrical fault occurs in the external power grid, the power angle compensation amount is calculated. This allows the phase difference between the converter's internal potential and the grid voltage to recover to its original steady-state value as quickly as possible, accelerating the power angle recovery speed during fault clearing, reducing reactive power generation caused by the converter's failure to exit the current-limiting state in time during fault clearing, suppressing transient overvoltage phenomena during recovery, and simultaneously enabling the grid-connected converter to smoothly transition back to normal operation. Attached Figure Description

[0021] Figure 1 This is the equivalent circuit diagram of a single-mechanism grid-connected system provided in the embodiments of the present invention.

[0022] Figure 2 This is the Thevenin equivalent circuit diagram of a single-mechanism grid-connected system experiencing a three-phase symmetrical fault, as provided in an embodiment of the present invention.

[0023] Figure 3 This is a system vector diagram showing how the internal potential amplitude of a network changes after a fault occurs, as provided in an embodiment of the present invention.

[0024] Figure 4 This is a system vector diagram showing how the phase angle of the internal potential of a network changes after a fault occurs, as provided in an embodiment of the present invention.

[0025] Figure 5 This is a control block diagram based on reactive power synchronization when a symmetrical fault occurs in a grid-connected system provided in an embodiment of the present invention.

[0026] Figure 6 This is a vector diagram of a grid-connected single-machine grid-connected system for fault clearing provided in an embodiment of the present invention.

[0027] Figure 7 This is a control block diagram of the fault clearing network structure using power angle compensation provided in an embodiment of the present invention.

[0028] Figure 8(a) is a system voltage and current waveform obtained when the control strategy proposed in the embodiment of the present invention is adopted.

[0029] Figure 8(b) is a waveform diagram of the reactive power of the grid structure obtained when the control strategy proposed in the embodiment of the present invention is adopted.

[0030] Figure 9(a) is a diagram showing the virtual power angle variation without power angle compensation.

[0031] Figure 9(b) shows the power response waveform of the grid configuration without power angle compensation.

[0032] Figure 9(c) is a diagram showing the virtual power angle change when power angle compensation is used.

[0033] Figure 9(d) is a power response waveform diagram of the grid configuration when power angle compensation is used.

[0034] Figure 10 This is a diagram showing the control effect of the fault ride-through control strategy proposed in this invention under different short-circuit ratio conditions.

[0035] Figure 11 This is a diagram showing the control effect of the fault-crossing control strategy proposed in this embodiment of the invention under different fault locations (degrees). Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] To achieve the above objectives, in a first aspect, the present invention provides a fault ride-through method for grid converters with symmetrical faults, comprising: When a symmetrical fault occurs in the external power grid, the following fault-period control operations are performed: Obtain the reactive power reference value of the grid-connected converter in accordance with the grid operation criteria at the current moment. ;in, This represents the actual capacity of the grid-connected converter at the current moment. This represents the per-unit value of the grid converter port voltage at the current moment. Switch the grid converter to reactive power synchronization mode, thereby using the reactive power reference value. To achieve the control objective, reactive power synchronization control is implemented on the grid converter.

[0038] It should be noted that the actual capacity of the grid-connected converter at the current moment can be calculated in advance using the following formula; specifically, the actual capacity of the grid-connected converter... for:

[0039] in, This refers to the current limiting value for grid-connected converters. This represents the actual port voltage value of the grid converter.

[0040] In one optional implementation, the control expression for the above reactive power synchronization mode is:

[0041] in, The preset reactive power synchronization coefficient; The reactive power of the grid converter; The angular velocity of the virtual synchronous machine in the grid converter relative to the external power grid; t Indicates time.

[0042] Preferably, in an optional implementation, the above-mentioned grid-connected converter fault ride-through method further includes: after the grid symmetrical fault is cleared, switching the grid-connected converter to active power synchronization mode to perform active power synchronization control on the grid-connected converter. The difference between the current active power reference value and the actual active power value of the grid-connected converter is input into the virtual synchronous machine to obtain the virtual angular velocity of the grid-connected converter at the current moment. For virtual angular velocity Integrating, we obtain the virtual work angle. ; In virtual power angle Superimposed power angle compensation The phase angle reference value of the grid converter at the current moment is obtained. And adjust the phase angle of the grid converter to the phase angle reference value at the current moment. ;in, This is the power angle compensation coefficient; The power angle of the grid converter under normal operating conditions; The power angle of the grid converter after adjustment by the control operation during the aforementioned fault period when a symmetrical fault occurs in the external power grid.

[0043] In one alternative implementation, the control expression for the virtual synchronizer is:

[0044] in, The virtual inertia of the virtual synchronizer; The angular velocity of the virtual synchronous machine in the grid converter relative to the external power grid; t Indicates time; This is a reference value for the active power of the grid-connected converter; The actual active power of the grid converter; The rated angular velocity of the external power grid system; This is the virtual damping for the virtual synchronizer.

[0045] To further illustrate the fault ride-through method for grid converters with symmetrical faults provided by this invention, a detailed description is given below with reference to a specific embodiment: This embodiment proposes a symmetrical fault ride-through strategy for grid-connected converters based on reactive power synchronization control. Reactive power synchronization replaces the active power synchronization control of the converter's power angle during faults. Based on the reactive power demand for converter fault ride-through derived from grid operation criteria, sufficient reactive voltage support is provided. Furthermore, to address the transient overvoltage problem during fault clearing, a power angle recovery compensation strategy is proposed, achieving full coverage of the grid-connected converter fault process by the control strategy. Further, simulation results comparing different control effects with fault conditions verify the effectiveness of the proposed fault ride-through control strategy.

[0046] Specifically, this embodiment first draws a phasor diagram based on the fault ride-through equivalent circuit when a single grid-connected converter is connected to the grid, and further analyzes the impact of different fault ride-through strategies on the fault ride-through capability of the converter. The drawing of the phasor diagram based on the fault ride-through equivalent circuit model when a single grid-connected converter is connected to the grid specifically includes: Phasor diagrams of physical quantities of the grid converter under steady state and under three-phase symmetrical ground fault are drawn respectively. The analysis of the three-phase symmetrical ground fault condition is based on theoretical derivation. It shows that if the influence of the fault grounding resistance is considered, under the three-phase symmetrical ground fault condition, the equivalent grid voltage not only decreases in amplitude, but also the phase angle will shift. Moreover, the more severe the fault, the greater the phase angle shift.

[0047] Based on the phasor diagram of physical quantities, the fault ride-through strategy of grid-connected converters during fault ride-through can be summarized as follows: By appropriately increasing the amplitude of the internal potential and reducing the phase difference between the internal potential and the external equivalent voltage, the reactive power voltage support capability of grid-connected converters can be improved.

[0048] Based on the phasor diagram of physical quantities, the transient overvoltage phenomenon of grid converter during fault clearing is analyzed: When the converter is still in the current limiting state during the fault clearing period, if the phase difference between the internal potential of the converter and the external grid voltage is too small, a relatively serious transient overvoltage phenomenon will occur.

[0049] Based on this, this embodiment designs a symmetrical fault ride-through strategy for grid-connected converters based on reactive power synchronization control, including: a fault-period control strategy for grid-connected converters that switches to reactive power synchronization for power angle adjustment during faults according to grid operation specifications, and a control strategy for rapid power angle compensation during fault clearing (so that the transient overvoltage phenomenon of grid-connected converters during fault clearing can be significantly improved).

[0050] The following section, with reference to the accompanying diagram, provides a detailed description of the aforementioned symmetrical fault ride-through strategy for grid-connected converters based on reactive power synchronization control: 1) Control strategies for grid-connected converters during fault periods, based on grid operation specifications and switching to reactive power synchronization for power angle adjustment in the event of a fault, specifically include: Based on power grid operation guidelines, the reactive power support requirements of grid-connected converters during fault ride are derived. Based on the derived reactive power support requirements, a fault ride-through strategy based on reactive power synchronization is designed to enable the converter to provide reactive power support that meets the grid criteria during fault ride-through.

[0051] Specifically, Figure 1This is the equivalent circuit diagram of a single-unit grid-connected system. In this embodiment, virtual admittance control is used in the voltage loop to achieve better current limiting, while PI control is used in the current loop, with a circular current limiter limiting the current reference value. In the equivalent current model of a single-unit grid-connected system, the response rate of the inner loop control is usually much faster than that of the outer power loop, so the dynamic response of the inner current loop is ignored in the analysis. Furthermore, since the dynamic impact of virtual admittance on the converter is generally greater than the impact of the converter's filter inductance and capacitance, the filter circuit is also omitted here. The converter using virtual admittance for current limiting can be equivalently represented as a voltage source model in series with a virtual impedance during external characteristic analysis. Simultaneously, according to Kirchhoff's voltage law, to maintain a constant voltage drop, the equivalent virtual impedance in the equivalent circuit analysis should be appropriately amplified based on the current limiting ratio between the actual current reference value and the current limit value.

[0052] Under normal operating conditions, the reactive power expression of the grid converter is:

[0053] in, For the reactive power of the converter, This is the reference value for the internal potential of the converter. This is the grid voltage. This is the phase angle difference between the converter's internal potential and the grid voltage. The sum of system impedances, where system impedances may include:

[0054] in, For grid impedance, This represents the virtual impedance within the converter. Since the filter reactance of the converter is generally small, it is omitted here.

[0055] When a symmetrical fault occurs in the external power grid, the excessive difference between the converter port voltage and internal potential leads to an increase in current. The current limiter inside the converter activates, limiting the fault current to a set current limit value. Although a converter using virtual impedance current limiting can be considered as a voltage source with series virtual impedance during fault analysis, its external port characteristics can still be equivalent to a current source with a constant output current limit value. In this case, the reactive power expression of the converter can be rewritten as:

[0056] in, This refers to the reactive power after the converter current limiting during fault ride-through. This is the current limiting value for the converter; The external equivalent reactance of the external power grid at the converter port after a fault occurs; This is the equivalent voltage of the external power grid to the converter after the fault occurs; This is the phase difference between the current phasor inside the converter and the equivalent voltage phasor of the external power grid.

[0057] Figure 2 This is the Thevenin equivalent circuit diagram for a three-phase symmetrical fault occurring in a single-unit grid-connected system. Based on the Thevenin equivalent principle, if a three-phase symmetrical ground fault occurs, the equivalent voltage of the external power grid is... It can be represented as:

[0058] in, This refers to the grid voltage. The three-phase symmetrical fault grounding resistance; This represents the impedance between the fault location and the power grid line. Similarly, based on Thevenin's equivalence principle, if a three-phase symmetrical ground fault occurs, the external equivalent impedance of the power grid outside the converter port is... It can be represented as:

[0059] in, This represents the impedance between the fault location and the converter port. It should be noted that when calculating the reactive power of the converter under current-limited conditions, the external equivalent impedance of the external power grid at the converter port is used. The reactance component in The influence of the resistance component is temporarily ignored.

[0060] Figure 3 and Figure 4 These are the system vector diagrams showing the changes in internal potential amplitude and phase angle after a fault occurs. The equivalent voltage between the phasor diagram and the external power grid is analyzed. As can be seen from the expression, when a symmetrical short circuit occurs in the external power grid, the new voltage phasor equivalent to the external power grid exhibits a reduced amplitude and a shifted phase angle compared to the voltage phasor under normal operating conditions. If the internal potential remains unchanged, the phase difference between it and the external equivalent voltage increases, resulting in current limiting by the converter and the converter port voltage falling on the current-limiting circle centered on the external equivalent voltage. Therefore, appropriately increasing the amplitude of the converter's internal potential or decreasing the internal potential phase angle will increase the phasor amplitude of the converter port voltage, which is beneficial for improving its reactive power voltage support capability.

[0061] This embodiment designs a control strategy for reactive power synchronization during fault ride-through based on analytical analysis of reactive power and the reactive power demand of the converter during faults according to power grid operation criteria. Specifically, Figure 5 This is a control block diagram based on reactive power synchronization when a symmetrical fault occurs in a grid-connected system. Under normal circumstances, the grid-connected converter achieves synchronization with the grid through active power frequency virtual synchronizing machine control.

[0062]

[0063] in, The angular velocity of the virtual synchronizer. The rated angular velocity of the external power grid system. The phase angle difference between the converter's internal potential and the grid voltage is also known as the power angle of the virtual synchronous machine. and These are the virtual inertia and virtual damping of the virtual synchronizer, respectively. and These are the reference value and actual active power of the grid converter, respectively.

[0064] During fault ride-through, the grid-connected converter needs to provide a certain amount of reactive power to support the voltage. Taking the reactive power demand of the grid-connected converter based on the grid operation criteria derived above as the control target, the active power synchronization control mode of the grid-connected converter is switched to reactive power synchronization:

[0065]

[0066] in, and These are the reference and actual values ​​of reactive power for the grid-connected converter, respectively. This is the reactive power synchronization coefficient. This represents the actual capacity of the converter during the fault. This represents the per-unit value of the converter port voltage. The reactive power demand for converter fault ride-through is then set based on the power grid operation criteria, and the specific derivation is as follows: The reactive current injection requirements during converter fault ride-through under the known power grid criteria are as follows:

[0067] in, The reactive power injection current required by power grid standards; This is a scaling factor, typically set to 1.5~2, and is set to 2 in this embodiment; This is the rated current of the converter; This represents the per-unit value of the converter port voltage. This formula indicates that for every 0.1 pu drop in the converter port voltage, the grid requires the converter to provide [a certain amount of voltage]. Reactive current injection. Since grid-connected converters are considered current sources during operation, this criterion has more specific requirements for the reactive power support capability of grid-connected converters during fault ride-through. Grid-connected converters are considered voltage sources during operation. Although some fault ride-through strategies convert them to current source operating mode (usually due to current limiting saturation), considering that grid-connected transformers with virtual impedance participating in current limiting can still be equivalent to voltage source mode with internal resistance (virtual impedance) during fault ride-through, it is necessary to derive the reactive power support requirements applicable to grid-connected converter fault ride-through based on the grid operation criteria. The rated capacity of the converter is known to be:

[0068] in, The rated capacity of the converter, The rated voltage of the converter. This is the rated current of the converter. When a symmetrical fault occurs in the external power grid, the converter current increases to the limit value, and the voltage amplitude at the converter port drops. At this time, the actual capacity of the converter becomes:

[0069] in, This represents the actual capacity of the converter during the fault. This is the current limiting value for the converter. This represents the actual value of the converter port voltage. Based on the actual capacity of the converter and the reactive current injection requirements during converter faults according to grid operation criteria, the reactive power injection requirements of the grid-connected converter during faults can be derived:

[0070] in, The reactive power reference value for the converter is directly set as the reactive power injection requirement of the grid-connected converter in this embodiment. This formula shows that for every 0.1 pu drop in the converter port voltage, the converter needs to provide 0.2 pu of reactive power.

[0071] 2) Control strategy for rapid power angle compensation during fault clearing: During the fault clearing process, the external grid voltage returns to normal, but the internal current of the converter does not immediately desaturate. As a result, when the converter returns to normal operating conditions, it is still in a current-limiting state and operates as a current source. At this time, the reactive power of the converter can be expressed as:

[0072] in, The reactive power of the converter that is still in current-limited operation after the fault has been cleared; This refers to the phase difference between the current inside the converter and the normal external grid voltage after the fault is cleared.

[0073] At this time, due to the fault ride-through strategy, the converter's internal potential phase is close to the grid voltage phase, leading to... A sudden increase in voltage can lead to a transient overvoltage phenomenon. Specifically, Figure 6 This is a vector diagram of a grid-connected single-unit grid-connected system during fault clearance. Phasor diagram analysis shows that when the external grid voltage returns to normal after fault clearance, if the converter current does not desaturate in time, the current will remain at the maximum current limit. At this time, the converter port voltage rises, resulting in a transient overvoltage. Accelerating the recovery speed of the internal potential phase angle can effectively suppress the rise in port voltage. Based on this, a fault clearance power angle compensation strategy is designed, such as... Figure 7 As shown, during fault clearing, a power angle compensation circuit is introduced into the power angle generation circuit to restore the phase difference between the converter's internal potential and the grid voltage to its original steady-state value as quickly as possible.

[0074] in, This is the amount of work angle compensation; This is the power angle compensation coefficient; the larger the coefficient, the faster the power angle compensation rate. The power angle under normal operating conditions; The power angle of the converter after adjustment by the fault ride-through strategy during the fault period; and All data were obtained through measurement.

[0075] Figures 8(a) and 8(b) show the control effect of the fault ride-through strategy proposed in this embodiment in the simulation system. Figure 8(a) is the system voltage and current waveform obtained when the control strategy proposed in this embodiment is used; Figure 8(b) is the grid-type reactive power waveform obtained when the control strategy proposed in this embodiment is used. Simulation verification was performed in Matlab / Simulink software. A three-phase symmetrical ground fault was set at 3 seconds, and the fault was cleared after 3.5 seconds. As can be seen from Figures 8(a) and 8(b), the proposed fault ride-through strategy has good control performance during both fault occurrence and fault clearing.

[0076] Figures 9(a) to 9(d) are comparison diagrams of the power angle compensation control effect of the control strategy provided in this embodiment. Figure 9(a) shows the virtual power angle change without power angle compensation; Figure 9(b) shows the power response waveform of the network without power angle compensation; Figure 9(c) shows the virtual power angle change with power angle compensation; and Figure 9(d) shows the power response waveform of the network with power angle compensation. In fault ride-through control without the proposed power angle compensation, the reactive power surge during fault clearing is significant, leading to transient overvoltage. The power angle compensation strategy effectively reduces the reactive power surge after fault clearing, thereby suppressing transient overvoltage.

[0077] Figure 10 and Figure 11 These figures illustrate the control effect of the fault ride-through control proposed in this embodiment under different short-circuit ratios and different fault locations (severities). The effectiveness of the proposed fault ride-through control was verified in simulation software under different operating conditions.

[0078] In summary, this embodiment proposes a symmetrical fault ride-through strategy for grid-connected converters based on reactive power synchronization control. Reactive power synchronization replaces the active power synchronization control of the converter's power angle during faults. Based on the reactive power demand for converter fault ride-through derived from grid operation criteria, it provides sufficient reactive voltage support. This strategy has a low computational load and enables the grid-connected converter to achieve sufficient and appropriate reactive voltage support while maintaining good synchronization stability. Furthermore, this embodiment also proposes a power angle recovery compensation strategy to address the transient overvoltage problem that occurs during fault clearing, achieving full coverage of the grid-connected converter fault process by the control strategy.

[0079] Compared to existing fault ride-through strategies, the fault ride-through strategy designed in this embodiment has the advantages of simple control structure and easy control switching. Furthermore, it does not require precise knowledge of the fault degree and location during the fault occurrence. It only needs to measure the voltage and current at the grid connection point and the virtual power angle generated by the virtual synchronous machine to meet the reactive power injection requirements of the power grid operation specifications. At the same time, it effectively suppresses transient overvoltages during fault clearing.

[0080] In a second aspect, the present invention provides a grid converter system, comprising: a grid converter and a controller; the controller is used to execute the fault ride-through method provided in the first aspect of the present invention.

[0081] The related technical solutions are the same as the fault-crossing method provided in the first aspect of this invention, and will not be described in detail here.

[0082] Thirdly, the present invention provides an electronic device, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the fault-traversal method provided in the first aspect of the present invention when executing the computer program.

[0083] The related technical solutions are the same as the fault-crossing method provided in the first aspect of this invention, and will not be described in detail here.

[0084] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device containing the storage medium to perform the fault-traversal method provided in the first aspect of the present invention.

[0085] The related technical solutions are the same as the fault-crossing method provided in the first aspect of this invention, and will not be described in detail here.

[0086] Fifthly, the invention also provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the fault-crossing method provided in the first aspect of the invention.

[0087] The related technical solutions are the same as the fault-crossing method provided in the first aspect of this invention, and will not be described in detail here.

[0088] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fault ride-through method for grid converters with symmetrical faults, characterized in that, include: When a symmetrical fault occurs in the external power grid, the following fault-period control operations are performed: Obtain the reactive power reference value of the grid-connected converter in accordance with the grid operation criteria at the current moment. ;in, This represents the actual capacity of the grid-connected converter at the current moment. This represents the per-unit value of the grid converter port voltage at the current moment. Switch the grid converter to reactive power synchronization mode, thereby using the reactive power reference value. To achieve the control objective, reactive power synchronization control is implemented on the grid converter.

2. The grid converter fault ride-through method according to claim 1, characterized in that, Actual capacity of grid converter for: in, This refers to the current limiting value for grid-connected converters. This represents the actual port voltage value of the grid converter.

3. The grid converter fault ride-through method according to claim 1, characterized in that, The control expression for the reactive power synchronization mode is: in, The preset reactive power synchronization coefficient; The reactive power of the grid converter; The angular velocity of the virtual synchronous machine in the grid converter relative to the external power grid; t Indicates time.

4. The grid converter fault ride-through method according to any one of claims 1-3, characterized in that, Also includes: After the grid symmetrical fault is cleared, the grid converter is switched to active power synchronization mode to perform active power synchronization control on the grid converter: The difference between the current active power reference value and the actual active power value of the grid-connected converter is input into the virtual synchronous machine to obtain the virtual angular velocity of the grid-connected converter at the current moment. Then, the virtual power angle is calculated. ; In the virtual power angle Superimposed power angle compensation The phase angle reference value of the grid converter at the current moment is obtained. And adjust the phase angle of the grid converter at the current moment to the phase angle reference value. ;in, This is the power angle compensation coefficient; The power angle of the grid converter under normal operating conditions; The power angle of the grid converter after the control operation during the fault period when a symmetrical fault occurs in the external power grid.

5. The grid converter fault ride-through method according to claim 4, characterized in that, The control expression for the virtual synchronizer is: in, The virtual inertia of the virtual synchronizer; The angular velocity of the virtual synchronizer relative to the external power grid; t Indicates time; This is a reference value for the active power of the grid-connected converter; The actual active power of the grid converter; The rated angular velocity of the external power grid system; This is the virtual damping for the virtual synchronizer.

6. A grid-connected converter system, characterized in that, include: Grid converters and controllers; The controller is used to execute the fault-crossing method according to any one of claims 1-5.

7. An electronic device, characterized in that, include: A memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the fault-traversal method according to any one of claims 1-5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, it controls the device containing the storage medium to perform the fault-crossing method according to any one of claims 1-5.

9. A computer program product, characterized in that, Includes a computer program / instruction that, when executed by a processor, implements the fault-crossing method according to any one of claims 1-5.

Images