VSG fault ride-through control method and device under three-phase voltage symmetric drop

Abstract

The invention provides a VSG fault ride-through control method and device under three-phase voltage symmetric drop, and the method comprises the steps: calculating the voltage drop depth in real time, setting a fault ride-through control triggering condition, and updating a reactive power reference value according to a reactive current instruction requirement specified by grid connection; determining an injection active current allowable value and a corresponding maximum active power reference value under the condition that reactive support is satisfied and active current limitation is combined; dynamically updating an active power reference value in the active-frequency control loop based on the voltage drop depth, and taking a smaller value as final output; constructing a VSG reference voltage expression containing virtual impedance, and generating a dynamic virtual impedance value based on the voltage and current of the grid-connected point under the dq rotating coordinate system; inputting the obtained reference voltage value into a voltage and current double-closed-loop controller based on feedforward decoupling, and generating a dq component of the output voltage of the inverter through cooperative control of a voltage outer loop and a current inner loop; the control precision and the response capability are improved.

Description

Technical Field

[0001] This invention belongs to the field of VSG fault ride-through control methods, and particularly relates to VSG fault ride-through control methods and devices under three-phase voltage symmetrical drop. Background Technology

[0002] With the accelerated global energy transition, the installed capacity of renewable energy sources such as photovoltaics and wind power has surged, and the dominant force in power systems is shifting from traditional synchronous generators to power electronic converters. However, the inherent low inertia and weak damping characteristics of power electronic converters significantly weaken system stability. Currently widely used grid-connected control relies on phase-locked loops (PLLs), which struggle to actively provide necessary voltage and frequency support during severe grid faults, exacerbating the risk of system instability. Major incidents such as the UK and Australian blackouts have highlighted the limitations of existing technologies in this regard, necessitating new solutions.

[0003] Against this backdrop, grid-based technologies capable of actively constructing and maintaining grid voltage and frequency have become an effective way to support the stable operation of future high-proportion renewable energy power systems. As a typical grid-based technology, the Virtual Synchronous Generator (VSG) has attracted much attention because it accurately simulates the electromechanical transient processes of a synchronous generator, providing crucial inertial support and autonomous synchronization capabilities for new power systems with converters as the grid connection interface. However, in increasingly complex grid environments, VSGs must possess fault ride-through (FRT) capabilities to ensure stable operation and continuous critical support during grid transient faults.

[0004] However, traditional VSG control strategies have the following significant shortcomings when dealing with complex fault-crossing scenarios:

[0005] The stability and support capability of the power angle are limited. Existing research mainly focuses on small-signal stability, and there is insufficient optimization for the system's rapid response capability during large disturbances. Although some solutions propose to avoid positive feedback loss of synchronization after crossing the unstable equilibrium point by dynamically detecting the power angle and switching the control logic, they still need to switch to current limiting control under severe near-end faults, which limits the scope of application. Existing methods lack a timely and efficient optimization mechanism for the dynamic process of the power angle, making it difficult to quickly and effectively suppress rotor acceleration and actively improve the system's stability margin during faults.

[0006] The fault overcurrent suppression and support functions conflict. When a severe voltage drop fault occurs in the system, the mismatch between the converter terminal voltage and the grid voltage increases sharply, causing the output current to rise rapidly. This can easily trigger the overcurrent protection and cause the grid to disconnect, seriously threatening the transient stability of the system.

[0007] Existing fault current limiting technologies have limitations. Although the current loop reference value adjustment method has a fast response, it is difficult to balance the accuracy of current control with the stability of the system power angle. Although the threshold virtual impedance strategy does not require a current saturation limiter, it has a blind spot under time-varying faults. Suppressing transient inrush current by segmenting virtual resistance and combining it with phasor current limiting to constrain steady-state fault current is still a passive current limiting and cannot actively suppress current.

[0008] Therefore, when a large disturbance occurs in the power grid, it is crucial to coordinate the improvement of power angle stability and the effective suppression of overcurrent, while maintaining its active support capability for the power grid as much as possible, and optimizing the fault ride-through capability of the VSG, to ensure the resilience and safe and stable operation of the new power system. Existing methods still have significant shortcomings in achieving coordinated and efficient suppression of steady-state and transient fault currents, while effectively ensuring the key support functions of the system.

[0009] To address the aforementioned problems and to resolve the issues of VSG power angle instability and overcurrent during symmetrical voltage drop faults, and to provide necessary voltage support, this invention proposes a VSG fault ride-through control method and device under three-phase voltage symmetrical voltage drop. Summary of the Invention

[0010] In order to solve the problems existing in the background art, the purpose of the present invention is to provide a VSG fault ride-through control method and device under three-phase voltage symmetrical drop. The method can take into account both fault current over-limit and power angle instability control during the symmetrical voltage drop fault at the grid connection point, provide a certain voltage support capability, realize safe ride-through and improve the survivability of VSG under harsh grid conditions.

[0011] The present invention adopts the following technical solution:

[0012] A method for VSG fault ride-through control under three-phase voltage symmetrical drop, comprising the following steps:

[0013] Real-time calculation of voltage drop depth and setting of fault ride-through control conditions; updating of reactive power reference value according to the reactive current command requirements of grid connection, thereby obtaining reactive power support.

[0014] Under the condition of satisfying reactive power support and combining active current limitation, determine the allowable value of injected active current and the corresponding maximum active power reference value; dynamically update the active power reference value in the active-frequency control loop based on the voltage drop depth, and take the smaller value between it and the maximum active power reference value as the final output to maintain power angle stability and current limitation.

[0015] A VSG reference voltage expression with virtual impedance is constructed, and a dynamic virtual impedance value is generated based on the grid connection point voltage and current in the dq rotating coordinate system to ensure that the fault current is lower than the equipment tolerance limit.

[0016] The acquired reference voltage value is input into a voltage-current dual closed loop based on feedforward decoupling. Through the coordinated control of the outer voltage loop and the inner current loop, the dq component of the inverter output voltage is generated and converted into a modulation signal.

[0017] Furthermore, the method for updating the reactive power reference value according to the reactive current command requirements stipulated in the grid connection regulations is as follows:

[0018] When the voltage amplitude at the grid connection point changes from U oN Falling to U oF At that time, the reactive current demand I injected by the inverter into the grid oq * It must meet the national grid connection standards;

[0019] The requirement for reactive current output from the VSG during grid voltage dips is transformed into a requirement for reactive power. This is achieved by changing the reactive power reference value Q of the VSG. ref Provide reactive power support to the system:

[0020]

[0021] Where d is the voltage drop depth, U odF U represents the d-axis component of the residual voltage at the grid connection point. odN I represents the d-axis component of the rated voltage at the grid connection point. oN Q is the rated current amplitude at the grid connection point. ref_0 This is the initial reactive power reference value;

[0022] Furthermore, the allowable value of injected active current and the corresponding maximum active power reference value are determined; the active power reference value in the active-frequency control loop is dynamically updated based on the voltage sag depth, and the smaller value between the active power reference value and the maximum active power reference value is taken as the final output.

[0023] Allowable value of injected active current I od * Must meet:

[0024]

[0025] Among them, I oN I is the rated current amplitude at the grid connection point. oq * This refers to the reactive current demand value injected into the power grid.

[0026] Accordingly, the maximum active power reference value P is calculated based on the allowable value of the injected active current. ref_max Represented as:

[0027]

[0028] Among them, Pref_0 U is the initial active power reference value. odF U represents the d-axis component of the residual voltage at the grid connection point. odN The d-axis component of the rated voltage at the grid connection point;

[0029] The active power reference value P in the active-frequency control loop is dynamically updated based on the voltage sag depth. ref_1 Adjust as follows:

[0030]

[0031] Where, k = U gF / U gN ;U gN U represents the rated voltage of the remote power grid. gF Represents the fault voltage of the remote power grid;

[0032] Ultimately, when the VSG provides reactive power support to the grid during fault ride-through, its set active power reference value P is... ref It can be represented as:

[0033] P ref =min(P ref_max ,P ref_1 )

[0034] Furthermore, the method for constructing a VSG reference voltage expression containing virtual impedance, generating a dynamic virtual impedance value based on the grid connection point voltage and current in the dq rotating coordinate system, and ensuring that the fault current is lower than the equipment's withstand limit is as follows:

[0035] The VSG reference voltage expression including virtual impedance is as follows:

[0036]

[0037] Among them, R V L V These are the virtual resistance and virtual inductance values, respectively; U od_ref U is the active voltage reference value for the voltage loop. oq_ref This is the reference value for reactive voltage in the voltage loop; E ref The virtual internal potential amplitude; ω is the real-time angular velocity; I od I oq These are the d-axis and q-axis components of the grid-connected current, respectively.

[0038] The virtual impedance value is calculated using the following formula:

[0039]

[0040] In the formula, X V I is the virtual reactance value. oFI represents the fault current amplitude at the grid connection point. th To set the peak current threshold, m is the virtual impedance coefficient, and n is the impedance ratio of the virtual impedance;

[0041] Furthermore, the acquired reference voltage value is input into a voltage-current dual closed-loop controller based on feedforward decoupling. Through the coordinated control of the outer voltage loop and the inner current loop, the dq component of the inverter output voltage is generated and converted into a modulation signal.

[0042] In voltage-current dual closed-loop control, the deviation between the actual component of the grid-connected point voltage in the dq rotating coordinate system and the reference value of the voltage in the dq coordinate system generated by the virtual impedance loop is first calculated. The reference value of the inductor current component in the dq coordinate system is derived through the circuit transfer function and used as the input reference for the inner current loop. Subsequently, the deviation between the actual inductor current component in the dq coordinate system and the reference value is calculated. Based on this difference, and through analysis using the circuit mathematical model, the component parameters of the inverter port voltage in the dq coordinate system are obtained. Finally, this is converted into a modulation signal via Park inverse transform.

[0043] Furthermore, when the grid connection point current exceeds the set current threshold I... th When the current changes, the dynamic virtual impedance is activated and its value changes dynamically with the current; otherwise, the virtual impedance value is set to zero. The set current threshold I... th It is greater than the limit value of the steady-state current component amplitude during the fault period, ensuring that the virtual impedance will not be activated under normal operation and after the instantaneous current component decays to zero during the fault period.

[0044] Furthermore, the virtual impedance coefficient m is determined by the virtual impedance equivalent circuit equation and the virtual impedance voltage drop equation, and the virtual impedance coefficient m is as follows:

[0045]

[0046] A VSG fault ride-through control device under three-phase voltage symmetrical drop includes:

[0047] The reactive power support acquisition module is used to calculate the voltage drop depth in real time and set the fault ride-through control conditions, and update the reactive power reference value according to the reactive current command requirements specified by the grid connection, thereby acquiring reactive power support.

[0048] The power angle stabilization and current limiting module is used to determine the allowable value of injected active current and the corresponding maximum active power reference value under the condition of satisfying reactive power support and combining active current limitation; it dynamically updates the active power reference value in the active-frequency control loop based on the voltage drop depth, and takes the smaller value between it and the maximum active power reference value as the final output to maintain power angle stabilization and current limitation.

[0049] The virtual impedance dynamic adjustment module is used to construct a VSG reference voltage expression containing virtual impedance and dynamically adjust the virtual impedance value based on the voltage drop depth to ensure that the fault current is lower than the equipment's tolerance limit.

[0050] The voltage and current dual closed-loop module is used to input the acquired reference voltage value into the voltage and current dual closed-loop controller based on feedforward decoupling. Through the coordinated control of the voltage outer loop and the current inner loop, the dq component of the inverter output voltage is generated and converted into a modulation signal.

[0051] A non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the VSG fault ride-through control method under three-phase voltage symmetrical drop as described above.

[0052] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the VSG fault ride-through control method under three-phase voltage symmetrical drop as described above.

[0053] The beneficial technical effects of this invention are as follows:

[0054] During voltage dips at the grid connection point, this invention transforms the reactive current requirement into a reactive power target by adjusting the reactive power reference value of the VSG, supporting continuous system operation without grid disconnection and providing effective voltage support. It also ensures power angle stability and active current limitation during faults by adjusting the active power reference value. Furthermore, it introduces a virtual impedance control strategy and combines it with output current feedback information to dynamically adjust the virtual impedance parameters, effectively suppressing instantaneous inrush currents generated under fault conditions and generating reference commands for the voltage outer loop. Through a dual closed-loop voltage and current system, it achieves feedforward decoupling and generates a voltage modulation signal, improving control accuracy and response capability. Attached Figure Description

[0055] Figure 1 This is a flowchart illustrating the VSG fault ride-through control method under three-phase voltage symmetrical drop in an embodiment of the present invention.

[0056] Figure 2 A schematic diagram of the system control for the VSG fault ride-through control method under three-phase voltage symmetrical drop provided in an embodiment of the present invention;

[0057] Figure 3 A schematic diagram of the power reference value adjustment process of the VSG fault ride-through control method under three-phase voltage symmetrical drop provided in an embodiment of the present invention;

[0058] Figure 4 A schematic diagram of virtual impedance current limiting measures for the VSG fault ride-through control method under three-phase voltage symmetrical drop provided in an embodiment of the present invention;

[0059] Figure 5 This is a schematic diagram of the voltage and current dual closed-loop decoupling measures of the VSG fault ride-through control method under three-phase voltage symmetrical drop provided in an embodiment of the present invention. Detailed Implementation

[0060] The VSG fault ride-through control method and apparatus under three-phase voltage symmetrical drop provided by the present invention will be further described clearly and completely below with reference to the accompanying drawings:

[0061] Example 1

[0062] like Figure 1 As shown, this embodiment provides a VSG fault ride-through control method under three-phase voltage symmetrical dips, applicable to three-phase grid-connected inverter systems. This method can simultaneously address fault current over-limit and power angle instability control during faults, and provides a certain voltage support capability. When a symmetrical voltage dip occurs at the grid connection point, it achieves safe ride-through and improves the survivability of the VSG under harsh grid conditions. The invention will be further described in detail below with reference to the accompanying drawings:

[0063] In this embodiment, the inductor current, the voltage and current at the grid connection point are collected by a sensor, and the collected signals are subjected to Park transform to obtain the d-axis and q-axis components of the inductor current in the dq rotating coordinate system, respectively. Ld I Lq The d-axis and q-axis components of the grid connection point voltage are U... od U oq And the d-axis and q-axis components of the grid connection point current are respectively I od I oq This allows for the processing and control of direct current in the dq rotating coordinate system; for example... Figure 2 As shown, the detailed steps of the method in this embodiment are as follows:

[0064] S1. Based on the d-axis and q-axis components of the voltage and current at the grid connection point in the dq rotating coordinate system, calculate the voltage and current amplitudes at the grid connection point. Define a voltage drop depth d greater than 0.1 pu as a fault occurrence. Specifically:

[0065] Based on the d-axis and q-axis components of the voltage and current at the grid connection point in the dq rotating coordinate system, the voltage and current amplitudes are calculated in real time.

[0066] Calculate the voltage drop depth based on the voltage amplitude at the grid connection point before and after the fault:

[0067]

[0068] Among them, U oF U represents the residual voltage amplitude at the grid connection point. oN The rated voltage amplitude at the grid connection point;

[0069] When a voltage drop below 90% of the rated voltage (i.e., d>0.1pu) is detected for more than one power frequency cycle, a voltage drop fault is determined to have occurred, triggering the fault ride-through control mode; otherwise, the system operates in normal VSG control mode.

[0070] S2. Determine the reactive current demand value injected into the power grid according to the grid connection standard requirements, and then calculate and update the reactive power reference value accordingly; Figure 3 As shown, the detailed method for adjusting the reactive power reference value in this embodiment is as follows:

[0071] Based on the voltage and current vectors at the grid connection point in the dq rotating coordinate system, the instantaneous power calculation formula is as follows:

[0072]

[0073] Among them, P e Q represents the instantaneous active power value. e This represents the instantaneous reactive power value.

[0074] In inverter control, the voltage vector direction is often fully aligned with the d-axis, and the q-axis component is zero, to simplify analysis or control. Therefore, this method is used to calculate the power reference value.

[0075] According to grid connection standards, when the voltage amplitude at the grid connection point changes from U... oN Falling to U oF At that time, the reactive current demand I injected by the inverter into the grid oq * Must meet:

[0076]

[0077] Among them, I oN This refers to the rated current amplitude at the grid connection point.

[0078] During voltage dip faults, the demand for reactive current is translated into a demand for reactive power, which can then be addressed by adjusting the reactive power reference value of the VSG to provide reactive power support to the system. When no voltage dip fault occurs, the initial reactive power reference value Q... ref_0 Set to zero. To prevent reactive current injection failure due to excessive voltage sag, in cases of severe voltage sag (i.e., d > 0.8pu), 20% of the d-axis component of the grid-connected point rated voltage is selected for calculation. The specific adjustment strategy is as follows:

[0079]

[0080] Among them, Q ref To set the reactive power reference value, U odFU represents the d-axis component of the residual voltage at the grid connection point. odN The d-axis component of the rated voltage at the grid connection point;

[0081] This step ensures that when the grid connection point voltage drops following the grid voltage, the reactive power output of the VSG will increase, and when the grid connection point voltage recovers, the reactive power output will decrease. This reactive power regulation characteristic helps the VSG to quickly provide reactive power support to the grid.

[0082] S3. Limit the fault overcurrent to within 1.2 pu. While ensuring reactive current requirements, determine the allowable value of injected active current, calculate the maximum active power reference value as the threshold, and simultaneously adjust the active power reference value based on the voltage sag depth. Determine the relative magnitudes of the two values ​​and output the smaller active power value. Figure 3 As shown, the detailed method for adjusting the active power reference value in this embodiment is as follows:

[0083] When a voltage dip occurs, the reactive power reference value is adjusted to provide voltage support. However, this can lead to excessive current, potentially damaging equipment. Therefore, active current must be limited while providing reactive power support. To avoid active current overcurrent in the VSG during fault ride-through and ensure the safe operation of power electronic equipment, the fault overcurrent is limited to within 1.2 pu. Considering the reactive current injection requirement of the VSG into the grid during fault ride-through, the allowable value of the injected active current, I, is determined. od * Must meet:

[0084]

[0085] When no voltage dip fault occurs, the initial active power reference value is P. ref_0 The maximum active power reference value P calculated based on the allowable active current value for different voltage drop depths. ref_max It can be represented as:

[0086]

[0087] According to the equal area method criterion, without any control strategy, when the system experiences a voltage dip disturbance, it will sequentially undergo acceleration and deceleration phases due to the active power deviation. The system can only return to synchronous operation when the actual fault clearing angle is less than the limiting clearing angle. To improve the system's power angle stability, the active power reference value can be adjusted during the fault occurrence period to reduce the deviation between it and the actual active power value, thereby effectively reducing the acceleration area and increasing the deceleration area, thus enhancing the system's power angle stability.

[0088] Specifically, during voltage dip faults, by monitoring the grid connection point voltage and the grid voltage in real time, the active power reference value can be actively and dynamically reduced, which can quickly eliminate the active power imbalance during the fault, maintain the relative stability of the power angle, and thus improve the power angle stability of the system.

[0089] When the power grid is operating in steady state, let the initial instantaneous active power value P e_0 and the initial active power reference value P ref_0 equal:

[0090]

[0091] Among them, U gN Represents the rated voltage of the remote power grid, δ0 represents the initial power angle, and R g X represents the equivalent resistance of the circuit. g Represents the equivalent reactance of the line;

[0092] When a fault causes a voltage drop, the instantaneous active power value P after the fault occurs. eF as follows:

[0093]

[0094] Where, δ F Represents the fault angle; U gF Represents the fault voltage of the remote power grid;

[0095] The requirement is to maintain power balance after a fault (i.e., P). ref_1＝ P eF If the active power reference value is not found, then the following adjustment is required:

[0096]

[0097] Assume the angle of attack remains stable after rapid adjustment (which can be considered as δ). F =δ0), considering that the actual system is purely inductive (i.e.

[0098] X g >>R g To achieve rapid response to control commands, the above formula can be modified and approximated as follows:

[0099]

[0100] Where k = U gF / U gN ;

[0101] Considering the difficulty in obtaining the actual voltage of the remote power grid, a method for estimating the grid voltage is adopted. The specific estimation method is as follows:

[0102]

[0103] Among them, U gdF U represents the d-axis component of the fault voltage in the remote power grid. gqF Represents the q-axis component of the fault voltage in the remote power grid;

[0104] The active power reference value of VSG is corrected according to the voltage drop depth, and the active power reference value is adjusted as follows:

[0105]

[0106] Ultimately, while the VSG provides reactive power support to the grid during fault ride-through, its set active power reference value P... ref It can be represented as:

[0107] P ref =min(P ref_max ,P ref_1 S4. Construct a VSG reference voltage expression containing virtual impedance. Introducing virtual impedance allows for readjustment of the VSG's equivalent output impedance. The virtual impedance value is generated based on the grid connection point voltage and current in the dq rotating coordinate system. By dynamically adjusting its gain coefficient, the instantaneous short-circuit current is constrained to be below the equipment's tolerance limit. Figure 4 As shown, the detailed method for dynamic virtual impedance current limiting in this embodiment is as follows:

[0108] This strategy generates a reference command for the outer voltage loop by establishing a virtual internal potential amplitude model and combining it with grid connection point current feedback information. The virtual impedance used is equivalent to connecting an impedance element in series in the grid-connected line. When a voltage dip fault occurs, adjusting the parameters of the virtual impedance can effectively suppress the overcurrent generated under fault conditions. The circuit relationship corresponding to this control strategy is as follows:

[0109]

[0110] Among them, R V L V These are the virtual resistance and virtual inductance values, respectively; e d * e q * These are the d-axis and q-axis components of the equivalent output command voltage, respectively, and ω is the real-time angular velocity;

[0111] Due to the voltage source characteristics of the VSG, its equivalent output command voltage satisfies e d * =E ref And e q * Given the constraint that = 0, the mathematical model is as follows:

[0112]

[0113] Among them, U od_ref U is the active voltage reference value for the voltage loop. oq_ref E is the reference value for reactive voltage in the voltage loop. ref This represents the amplitude of the virtual internal potential.

[0114] Since the derivative term easily introduces high-frequency noise and affects control performance, it is simplified in engineering terms:

[0115]

[0116] The dynamic virtual impedance is activated based on the fault current to limit the peak value of the VSG transient inrush current and accelerate the decay of the aperiodic component of the fault current. The virtual impedance is generated based on the grid connection point voltage and current in the dq rotating coordinate system, and its value is dynamically adjusted. The virtual impedance value is calculated using the following formula:

[0117]

[0118] In the formula, X V I is the virtual reactance value. oF I represents the fault current amplitude at the grid connection point. th To set the peak current threshold, m is the virtual impedance coefficient, and n is the virtual impedance ratio, which is determined by the system impedance ratio.

[0119] The coefficient of the virtual impedance is determined based on a peak current threshold of 1.25 pu. The coefficient m is determined by the equivalent circuit equation of the virtual impedance and the voltage drop equation of the virtual impedance. That is, the voltage drop across the virtual impedance needs to compensate for the voltage sag to reduce the short-circuit current.

[0120]

[0121] In the formula, ΔU d and ΔU q The d-axis and q-axis components of the virtual impedance voltage drop in the dq coordinate system;

[0122] Therefore, the expression containing known quantities is as follows:

[0123]

[0124] The virtual impedance coefficient m can be calculated as follows:

[0125]

[0126] When the grid connection point current exceeds the set threshold, the dynamic virtual impedance is activated and dynamically changes with the current; otherwise, it is set to zero. The set threshold is set to be greater than the amplitude limit of the steady-state current component during a fault, ensuring that the virtual impedance will not be activated under normal operating conditions or after the instantaneous current component decays to zero during a fault.

[0127] S5. The calculated active and reactive voltage reference values ​​are input into a dual closed-loop voltage and current system based on feedforward decoupling. The inner current loop achieves closed-loop control through an inductor current feedback mechanism, while the outer voltage loop uses a grid connection point voltage (equivalent to capacitor voltage) feedback strategy for dynamic adjustment. Figure 5 As shown, the detailed method of voltage and current dual closed loop based on feedforward decoupling in this embodiment is as follows:

[0128] The active voltage reference value U obtained in step S4 od_ref and reactive voltage reference value U oq_ref Input voltage and current dual closed loop.

[0129] Based on the inverter topology modeling, the circuit expression in the three-phase stationary coordinate system is obtained. Then, the Park transformation is used to obtain the circuit expression in the dq coordinate system, which is calculated using the following formula:

[0130]

[0131] Among them, E d E q These are the d-axis and q-axis components of the inverter bridge arm voltages, respectively; I Ld I Lq These are the d-axis and q-axis components of the inductor current, respectively; L f C f These are the values ​​of the filter inductor and the filter capacitor, respectively, R f This is the value of the filter resistor;

[0132] In the dual closed-loop voltage and current control, the inner current loop achieves closed-loop regulation through an inductor current feedback mechanism, while the outer voltage loop uses a grid-connected point voltage (equivalent to capacitor voltage) feedback strategy for dynamic adjustment. Specifically, firstly, the deviation between the actual component of the grid-connected point voltage in the dq rotating coordinate system and the reference value of the voltage in the dq coordinate system generated by the virtual impedance loop is calculated. The reference value of the inductor current component in the dq coordinate system is derived through the circuit transfer function and used as the input reference for the inner current loop. Subsequently, the deviation between the actual inductor current component in the dq coordinate system and the reference value is calculated. Based on this difference, and through analysis using the circuit mathematical model, the component parameters of the inverter port voltage in the dq coordinate system are obtained, and finally converted into a modulation signal via Park inverse transform.

[0133] Deviation adjustment is characterized by a PI circuit to achieve zero steady-state error control, and is calculated using the following formula:

[0134]

[0135] Where s represents the Laplace operator, K pu K iu These are the proportional and integral coefficients of the voltage loop, respectively; K pi K ii These are the current loop proportional and integral coefficients, respectively.

[0136] Its output dynamic characteristics can be mathematically characterized by the following expression:

[0137]

[0138] In the formula, E d_ref E q_ref These are the d-axis and q-axis components of the modulated wave reference voltage, respectively; I Ld_ref I Lq_ref These are the reference values ​​for the d-axis and q-axis of the current loop, respectively.

[0139] S6: Continuously monitor the grid connection point voltage. When the grid connection point voltage recovers to above the fault threshold and remains above it for a certain period of time, the fault is determined to be cleared. Specifically,

[0140] The control system continuously monitors the grid voltage. When it detects that the grid connection point voltage has recovered to above the fault threshold (i.e., d < 0.1pu) and has remained there for a certain period of time, it determines that the fault has been cleared.

[0141] In summary, the method of the present invention can solve the ride-through problem of VSG under three-phase voltage symmetrical faults, not only ensuring the safety of VSG itself, but also providing reactive power support and improving the stability of the power system.

[0142] Example 2

[0143] This embodiment provides a VSG fault ride-through control device under three-phase voltage symmetrical drop, including:

[0144] The reactive power support acquisition module is used to calculate the voltage drop depth in real time and set the fault ride-through control conditions, and update the reactive power reference value according to the reactive current command requirements specified by the grid connection, thereby acquiring reactive power support.

[0145] The power angle stabilization and current limiting module is used to determine the allowable value of injected active current and the corresponding maximum active power reference value under the condition of satisfying reactive power support and combining active current limitation; it dynamically updates the active power reference value in the active-frequency control loop based on the voltage drop depth, and takes the smaller value between it and the maximum active power reference value as the final output to maintain power angle stabilization and current limitation.

[0146] The virtual impedance dynamic adjustment module is used to construct a VSG reference voltage expression containing virtual impedance and dynamically adjust the virtual impedance value based on the voltage drop depth to ensure that the fault current is lower than the equipment's tolerance limit.

[0147] The voltage and current dual closed-loop module is used to input the acquired reference voltage value into the voltage and current dual closed-loop controller based on feedforward decoupling. Through the coordinated control of the voltage outer loop and the current inner loop, the dq component of the inverter output voltage is generated and converted into a modulation signal.

[0148] Furthermore, the present invention adopts the following technical solution:

[0149] A non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the VSG fault ride-through control method under three-phase voltage symmetrical drop as described above.

[0150] Furthermore, the present invention adopts the following technical solution:

[0151] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the VSG fault ride-through control method under three-phase voltage symmetrical drop as described above.

[0152] From the above description of the embodiments, those skilled in the art will clearly understand that the facilities of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Embodiments of the present invention can be implemented using existing processors, or by dedicated processors used for this or other purposes for suitable systems, or by hardwired systems. Embodiments of the present invention also include non-transitory computer-readable storage media, comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon; such machine-readable media can be any available medium accessible by a general-purpose or special-purpose computer or other machine with a processor. For example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store the required program code in the form of machine-executable instructions or data structures and is accessible by a general-purpose or special-purpose computer or other machine with a processor. When information is transmitted or provided to a machine via a network or other communication connection (hardwired, or wireless, or a combination of hardwired and wireless), that connection is also considered a machine-readable medium.

[0153] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A VSG fault ride-through control method under three-phase voltage symmetrical sag, characterized in that, The method includes the following steps: Real-time calculation of voltage drop depth and setting of fault ride-through control trigger conditions; updating of reactive power reference value according to the reactive current command requirements specified by the grid connection, thereby obtaining reactive power support; Under the condition of satisfying reactive power support and combining active current limitation, determine the allowable value of injected active current and the corresponding maximum active power reference value; dynamically update the active power reference value in the active-frequency control loop based on the voltage drop depth, and take the smaller value between it and the maximum active power reference value as the final output to maintain power angle stability and current limitation. A VSG reference voltage expression with virtual impedance is constructed, and a dynamic virtual impedance value is generated based on the grid connection point voltage and current in the dq rotating coordinate system to ensure that the fault current is lower than the equipment tolerance limit. The acquired reference voltage value is input to a voltage-current dual closed-loop controller based on feedforward decoupling. Through the coordinated control of the outer voltage loop and the inner current loop, the dq component of the inverter output voltage is generated and converted into a modulation signal.

2. The VSG fault ride-through control method under three-phase voltage symmetrical drop as described in claim 1, characterized in that, The method for updating the reactive power reference value according to the reactive current command requirements stipulated in the grid connection regulations is as follows: When the voltage amplitude at the grid connection point changes from U oN Falling to U oF At that time, the reactive current demand I injected by the inverter into the grid oq * It must meet the national grid connection standards; The requirement for reactive current output from the VSG during voltage dips at the grid connection point is transformed into a requirement for reactive power. This is achieved by changing the reactive power reference value Q of the VSG. ref Provide reactive power support to the system: Where d is the voltage drop depth, U odF U represents the d-axis component of the residual voltage at the grid connection point. odN I represents the d-axis component of the rated voltage at the grid connection point. oN Q is the rated current amplitude at the grid connection point. ref_0 This is the initial reactive power reference value.

3. The VSG fault ride-through control method under three-phase voltage symmetrical drop as described in claim 1, characterized in that, The method for determining the allowable value of injected active current and the corresponding maximum active power reference value, and dynamically updating the active power reference value in the active-frequency control loop based on the voltage sag depth, and taking the smaller value between the current value and the maximum active power reference value as the final output is as follows: Allowable value of injected active current I od * Must meet: Among them, I oN I is the rated current amplitude at the grid connection point. oq * This refers to the reactive current demand value injected into the power grid. Accordingly, the maximum active power reference value P is calculated based on the allowable value of the injected active current. ref_max Represented as: Among them, P ref_0 U is the initial active power reference value. odF U represents the d-axis component of the residual voltage at the grid connection point. odN The d-axis component of the rated voltage at the grid connection point; The active power reference value P in the active-frequency control loop is dynamically updated based on the voltage sag depth. ref_1 Adjust as follows: Where, k = U gF / U gN ;U gN U represents the rated voltage of the remote power grid. gF Represents the fault voltage of the remote power grid; Ultimately, when the VSG provides reactive power support to the grid during fault ride-through, its set active power reference value P is... ref It can be represented as: P ref =min(P ref_max ,P ref_1 )。 4. The VSG fault ride-through control method under three-phase voltage symmetrical drop as described in claim 1, characterized in that, The method for constructing a VSG reference voltage expression with virtual impedance, generating a dynamic virtual impedance value based on the grid connection point voltage and current in the dq rotating coordinate system, and ensuring that the fault current is lower than the equipment's withstand limit is as follows: The VSG reference voltage expression including virtual impedance is as follows: Among them, R V L V These are the virtual resistance and virtual inductance values, respectively; U od_ref U is the active voltage reference value for the voltage loop. oq_ref This is the reference value for reactive voltage in the voltage loop; E ref The virtual internal potential amplitude; ω is the real-time angular velocity; I od I oq These are the d-axis and q-axis components of the grid-connected current, respectively. The virtual impedance value is calculated using the following formula: In the formula, X V I is the virtual reactance value. oF I represents the fault current amplitude at the grid connection point. th To set the peak current threshold, m is the virtual impedance coefficient, and n is the impedance ratio of the virtual impedance.

5. The VSG fault ride-through control method under three-phase voltage symmetrical drop as described in claim 1, characterized in that, The acquired reference voltage value is input into a voltage-current dual closed-loop controller based on feedforward decoupling. Through the coordinated control of the outer voltage loop and the inner current loop, the dq component of the inverter output voltage is generated and converted into a modulation signal as follows: In voltage and current dual closed-loop control, the deviation between the actual component of the grid connection point voltage in the dq rotating coordinate system and the reference value of the voltage in the dq coordinate system generated by the virtual impedance loop is first calculated. The reference value of the inductor current component in the dq coordinate system is derived through the circuit transfer function and used as the input reference of the inner current loop. Subsequently, the deviation between the actual inductor current component in the dq coordinate system and the reference value is calculated. Based on this difference, the component parameters of the inverter port voltage in the dq coordinate system are obtained through analysis using the circuit mathematical model. Finally, the signal is converted into a modulation signal through Park inverse transform.

6. The VSG fault ride-through control method under three-phase voltage symmetrical drop according to claim 4, characterized in that, When the grid connection point current exceeds the set current threshold I th When the current changes, the dynamic virtual impedance is activated and changes dynamically with the current; otherwise, it is set to zero. The current threshold I is then set. th Set to a value greater than the amplitude limit of the steady-state current component during a fault, ensuring that the virtual impedance will not be activated under normal operating conditions and after the instantaneous current component decays to zero during a fault.

7. The VSG fault ride-through control method under three-phase voltage symmetrical drop according to claim 4, characterized in that, The virtual impedance coefficient m is determined by the virtual impedance equivalent circuit equation and the virtual impedance voltage drop equation. The virtual impedance coefficient m is as follows:

8. A VSG fault ride-through control device under three-phase voltage symmetrical drop, characterized in that, include: The reactive power support acquisition module is used to calculate the voltage drop depth in real time and set the fault ride-through control conditions, and update the reactive power reference value according to the reactive current command requirements specified by the grid connection, thereby acquiring reactive power support. The power angle stabilization and current limiting module is used to determine the allowable value of injected active current and the corresponding maximum active power reference value under the condition of satisfying reactive power support and combining active current limitation; it dynamically updates the active power reference value in the active-frequency control loop based on the voltage drop depth, and takes the smaller value between it and the maximum active power reference value as the final output to maintain power angle stabilization and current limitation. The virtual impedance dynamic adjustment module is used to construct a VSG reference voltage expression containing virtual impedance. It generates a dynamic virtual impedance value based on the grid connection point voltage and current in the dq rotating coordinate system to ensure that the instantaneous fault inrush current is lower than the equipment's tolerance limit. The voltage and current dual closed-loop module is used to input the acquired reference voltage value into the voltage and current dual closed loop based on feedforward decoupling. Through the coordinated control of the voltage outer loop and the current inner loop, the dq component of the inverter output voltage is generated.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the VSG fault ride-through control method under three-phase voltage symmetrical drop as described in any one of claims 1 to 7.

10. 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 VSG fault ride-through control method under three-phase voltage symmetrical drop as described in any one of claims 1 to 7.

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