Low voltage ride-through overcurrent suppression method and system for grid-type voltage management device

Abstract

The present invention belongs to the technical field of converter control, and discloses a method and system for suppressing low voltage ride-through overcurrent of a grid-type voltage management device. A phase-locked loop phase-locks the grid voltage, outputs a transformation angle θ, and the d-axis coincides with the grid voltage vector; the q-axis is perpendicular to the voltage vector direction, and the output of the q-axis voltage is adjusted by a PI regulator by giving iq_ref to change the reactive current magnitude, and control the reactive power injected into the grid; the d-axis coincides with the grid voltage vector, and the active component is controlled in the direction of the voltage magnitude in the d-axis direction; the rotation angle of dq / abc is composed of an active droop module, a basic frequency module, and a phase-locked loop module; and a grid amplitude calculation module is used to calculate the grid voltage. The present invention enables the inverter to have both voltage source and current source characteristics, thereby having good grid-building and grid-connected functions. Due to the control of the voltage loop of the d-axis, a stable voltage output can also be maintained when unplanned off-grid occurs.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and in particular relates to a method and system for suppressing low voltage ride-through overcurrent in a grid-type voltage management device. Background Art

[0002] With the increasing proportion of photovoltaic power generation in the power system, the continuous progress and development of photovoltaic industry technology, especially the rapid growth of distributed photovoltaic power generation, the control technology innovation of solar photovoltaic power generation system has attracted great attention. Due to the characteristics of the photovoltaic array itself, the photovoltaic power generation system presents highly nonlinear characteristics, which brings great difficulties to the stability analysis and controller design of the power system; on the other hand, the highly random and intermittent characteristics of solar radiation resources also bring huge challenges to the stable control of the power grid in the substation area, such as frequent voltage fluctuations leading to the burning of power equipment, the scrapping of production products, and even serious power grid accidents. With the further increase in photovoltaic penetration, the continuous access of high-density photovoltaic power sources, the local consumption balance of photovoltaic power, and the stable support of the power grid have put forward many new requirements for photovoltaic control systems.

[0003] In order to fully absorb the massive distributed sources and maximize their utilization, some scholars have proposed a solution to improve the power supply of distribution substations by using grid-type static reactive power generators. Based on a thorough study of voltage over-limit faults in distribution substations, grid-type static reactive power generators with reasonable capacity are configured at key nodes, and the grid-type inverter's active support and networking capabilities for voltage and frequency are utilized, combined with the impedance characteristics of the middle and end of the distribution network, to improve the power supply quality of grid-type distribution substations.

[0004] The grid-type control strategy originates from the simulation of the dynamic characteristics of the synchronous machine, which makes the grid-type converter and the grid-following converter have different operating characteristics. The grid-following converter can be roughly regarded as a controlled current source with high parallel impedance, which indirectly controls the output power or realizes voltage regulation by controlling the output current; while the grid-type converter can be regarded as a controlled voltage source with low series impedance, which controls the output power by controlling the port voltage. In terms of the response to grid disturbances, the grid-following converter exhibits current source characteristics. When the grid-connected point voltage is disturbed, before the phase-locked loop can correctly lock the phase, the grid-following converter tends to keep the output current amplitude and phase angle unchanged, but it also inevitably leads to a sudden change in the output voltage, which is not conducive to maintaining voltage stability; the grid-type converter exhibits voltage source characteristics. When the grid-connected point voltage is disturbed, it tends to keep the internal potential unchanged, which is conducive to maintaining voltage stability. The grid-type converter can achieve self-synchronization by imitating the power balance synchronization mechanism of the synchronous machine and abandoning the detection link. Correspondingly, the grid-type converter also avoids the strong interaction between the converter and the weak grid caused by the phase-locked loop to a certain extent, and is easier to maintain stability under a weak grid. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method and system for suppressing overcurrent in a low voltage ride-through of a grid-type voltage management device.

[0006] The present invention is implemented as follows: a method for suppressing overcurrent of low voltage ride-through of a grid-type voltage management device, comprising:

[0007] S1: The phase-locked loop phase-locks the grid voltage, outputs a transformation angle θ, and the d-axis coincides with the grid voltage vector;

[0008] S2: The q-axis is perpendicular to the voltage vector direction. The PI regulator adjusts the output of the q-axis voltage by giving iq_ref to change the reactive current and control the reactive power injected into the grid.

[0009] S3: The d-axis coincides with the grid voltage vector, and the active component is controlled in the direction of the voltage magnitude in the d-axis direction;

[0010] S4: The rotation angle of dq / abc is composed of the active droop module, the basic frequency module and the phase-locked loop module;

[0011] S5: When the converter is connected to the grid, the phase-locked loop module is in working state, and the electrical angle output by the active droop module is clamped;

[0012] S6: When the converter is off-grid, the phase-locked loop is cut off, the droop module works normally, and the converter has normal droop characteristics;

[0013] S7: The grid amplitude calculation module is used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible.

[0014] Furthermore, the angle θ of the grid in S1 is given by the phase-locked loop and input to the coordinate transformation module as the transformation angle. When the system is off-grid, the phase-locked loop stops working, and the transformation angle is determined by the integral of the sum of the basic frequency and the frequency increment of the active droop output.

[0015] Furthermore, when setting the reactive current in S2, the restrictions of the maximum current of the converter and the current output active current should be met, as shown in Formula 1:

[0016]

[0017] Furthermore, the S3 outputs a d-axis voltage, so that the system has voltage source characteristics, and its control can be open-loop or closed-loop control.

[0018] Further, v q To control the reactive current i q The relationship between the generated components is shown in Equation 2:

[0019] v q =i q ·ω·L (Formula 2)

[0020] In formula 2, ω is the grid angular velocity, L is the inductance between the inverter and the grid. From formula 2, we can see that even when the reactive current is large, v q It is still much smaller than the grid voltage, so the addition of the q-axis current loop will not affect the voltage source characteristics of the system.

[0021] Furthermore, the active droop module and the basic frequency in S4 can work in real time. When the power grid phase-locked loop works normally, e is the grid angular velocity; when the phase-locked loop is disconnected, the output angular frequency is the basic frequency ω basic With active droop module ω drop The sum of the fundamental frequency ω basic is a constant 2π·f, where f is the reference frequency.

[0022] The present invention also provides a low voltage ride-through overcurrent suppression system for a grid-type voltage management device, comprising:

[0023] Phase-locked loop module: used to phase-lock the grid voltage and output the transformation angle so that the d-axis coincides with the grid voltage vector;

[0024] Reactive current control module: Based on the q-axis direction, the PI regulator adjusts the output of the q-axis voltage to change the reactive current, thereby controlling the reactive power injected into the grid;

[0025] Active current control module: controls the voltage in the d-axis direction, thereby controlling the active component;

[0026] dq / abc coordinate transformation module: its rotation angle is determined by the active power droop module, basic frequency module and phase-locked loop module;

[0027] Grid amplitude calculation module: used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible.

[0028] Furthermore, the phase-locked loop module is in working state when the system is connected to the grid, and outputs an electrical angle to clamp the output of the active power droop module; when the system is off the grid, the phase-locked loop module stops working, and the conversion angle is determined by the integral of the sum of the basic frequency and the frequency increment output by the active power droop module.

[0029] Furthermore, when setting the reactive current, the reactive current control module needs to meet the limitations of the maximum current of the converter and the current output active current.

[0030] Furthermore, the active power droop module and the basic frequency module can operate in real time when the system is connected to the grid or off-grid, wherein the basic frequency is a constant reference frequency; when the grid is operating normally, the phase-locked loop module outputs the grid angular velocity, and when the phase-locked loop module is disconnected, the output angular frequency is the sum of the basic frequency and the active power droop module.

[0031] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0032] First, the control strategy designed by the present invention enables the inverter to have both voltage source and current source characteristics, thereby having good grid construction and grid connection functions. In the case of grid connection, the active power and reactive power fed into the grid are controlled by the d-axis and q-axis respectively. Due to the current loop of the q-axis, the grid current can be stably controlled even if the grid drops significantly. At the same time, due to the control of the voltage loop of the d-axis, a stable voltage output can also be maintained when an unplanned grid disconnection occurs.

[0033] Second, the present invention solves the problem of inaccurate grid voltage phase locking in the prior art by introducing a phase-locked loop module and a dq / abc coordinate transformation module. The phase-locked loop module can accurately phase-lock the grid voltage to ensure that the d-axis coincides with the grid voltage vector, thereby achieving more efficient active and reactive power control. This phase-locking technology not only improves the response speed of the system, but also enhances the adaptability of the voltage management device in a complex grid environment.

[0034] Secondly, the present invention adopts an advanced reactive current control algorithm, which adjusts the output of the q-axis voltage through the PI regulator, changes the size of the reactive current, and realizes precise control of the reactive power injected into the power grid. This algorithm fully considers the maximum current limit of the converter and the current output active current in the design, ensuring that the system can operate stably under various operating conditions, thereby avoiding the problem of unstable reactive power control commonly seen in traditional methods.

[0035] In addition, the active power droop control module and the basic frequency module of the present invention solve the frequency control problem in the off-grid state by dynamically adjusting the output frequency of the converter. When the system is in the grid-connected state, the electrical angle output by the active power droop module is clamped by the phase-locked loop module; when the system is off-grid, the phase-locked loop module exits work, and the conversion angle is determined by the integral of the sum of the basic frequency and the frequency increment of the active power droop output. This design ensures that the system can operate stably in both the grid-connected and off-grid states, and has excellent frequency response characteristics.

[0036] Finally, the present invention has also achieved significant technical progress in grid amplitude calculation and control. Through the precise calculation of the grid amplitude calculation module, the output voltage can be as close to the grid voltage as possible, thereby improving the output voltage quality of the voltage management device. Combined with the d-axis voltage output of open-loop or closed-loop control, the present invention enables the system to have good voltage source characteristics, and even in the case of large reactive current, it can maintain the stability and reliability of the system voltage. This series of technical innovations has enabled the present invention to achieve significant progress in voltage management and low voltage ride-through overcurrent suppression.

[0037] Third, the existing technology has large hysteresis and instability in grid voltage phase locking and control, especially in the switching process when the converter is connected to the grid and off the grid, which easily causes system instability. The present invention adds a grid voltage phase locking function to the phase-locked loop module and overlaps the conversion angle of its output with the d-axis voltage vector to achieve rapid phase locking and stable control of the grid voltage. This technical solution solves the problem of grid voltage phase locking hysteresis in the existing technology and improves the response speed and stability of the system.

[0038] The prior art is susceptible to grid voltage fluctuations and converter output current limitations in controlling reactive current and active power components, resulting in unstable reactive power control. The present invention adjusts the q-axis voltage output through a PI regulator to change the size of the reactive current, thereby controlling the reactive power injected into the grid; at the same time, by coinciding the d-axis with the grid voltage vector, the voltage size is controlled in the d-axis direction to achieve precise control of the active power component. This solution achieves stable control of reactive current and active power components while ensuring the maximum current of the converter and the current output active current limit.

[0039] In the prior art, the converter is prone to unstable electrical angle output during the switching process between the grid-connected and off-grid states, which affects the operation of the system. The present invention clamps the electrical angle output by the active droop module when the converter is grid-connected, and cuts off the phase-locked loop when the converter is off-grid, so that the droop module can work normally, ensuring that the converter has a normal droop characteristic, ensuring the smoothness and stability of the system switching between the grid-connected and off-grid states, and solving the switching instability problem in the prior art.

[0040] The existing technology is difficult to achieve accurate calculation and fast voltage matching in terms of grid amplitude calculation and output voltage matching, resulting in large fluctuations in the system output voltage. The present invention accurately calculates the grid voltage through the grid amplitude calculation module to ensure that the output voltage can be as close to the grid voltage as possible; at the same time, through the real-time working active power droop module and the basic frequency module, the stability of the system output angular frequency under different working conditions is guaranteed, solving the problem of inaccurate voltage matching in the existing technology. This solution significantly improves the voltage source characteristics and operation stability of the system.

[0041] Fourth, the present invention uses a phase-locked loop (PLL) to phase-lock the grid voltage and output a transformation angle so that the d-axis coincides with the grid voltage vector. By optimizing the parameters of the phase-locked loop, the system's response speed to grid voltage changes is significantly improved. In the prior art, there is a lag in the grid voltage phase-locking, which causes the system to react slowly and be unstable. The present invention accurately calculates the grid angle and inputs it as a transformation angle to the coordinate transformation module, so that the system can maintain a stable voltage phase-lock when connected to the grid or off-grid, thereby solving the phase-locking lag problem and improving the real-time and stability of the system.

[0042] The reactive current is controlled by adjusting the q-axis voltage output through the PI regulator, and the active component is controlled by the method of coinciding the d-axis with the grid voltage vector. The present invention realizes the precise control of reactive power and active power. In the conventional technology, the reactive and active power control is often unstable due to the grid voltage fluctuation and the output current limitation of the converter. The present invention takes into account the limitation of the maximum current of the converter and the current output active current during design, and realizes the stable control of the reactive current and active component through the calculation of the mathematical model (such as formula 1), and solves the problem of unstable power control in the prior art.

[0043] When the converter is connected to the grid, the present invention clamps the electrical angle output by the active droop module to ensure that the phase-locked loop module is in working condition; when the converter is off-grid, the phase-locked loop is cut off to enable the droop module to work normally. This design combines active droop control with the phase-locked loop algorithm to achieve smooth switching of the converter between the grid-connected and off-grid states, solving the problem of unstable electrical angle output during the switching process in traditional technologies. The real-time switching mechanism of droop control and phase-locked loop ensures the stable operation of the system in different states, significantly improving the reliability of the system.

[0044] Through the power grid amplitude calculation module, the present invention can accurately calculate the power grid voltage and ensure that the output voltage is as close to the power grid voltage as possible. At the same time, combined with the active droop module and the basic frequency module to work in real time, the precise control of the power grid angular velocity is achieved. When the phase-locked loop is working, the power grid angular velocity is output, and when the phase-locked loop is disconnected, the angular frequency of the sum of the basic frequency and the frequency increment of the active droop module is output. Through the design of this mathematical model (such as formula 2), the present invention solves the problem of inaccurate power grid voltage matching in the prior art, improves the voltage source characteristics and stability of the system, thereby achieving significant technological progress. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of a method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device provided by an embodiment of the present invention;

[0046] Figure 2 is a control block diagram of a grid-connected inverter provided by an embodiment of the present invention;

[0047] Figure 3 is the relationship between the rotating coordinate system and the grid voltage provided by the embodiment of the present invention;

[0048] Figure 4 The grid voltage drop provided by the embodiment of the present invention

[0049] Figure 5 It is an unplanned disconnection provided by an embodiment of the present invention;

[0050] Figure 6 This is a reactive current regulation process provided by an embodiment of the present invention;

[0051] Figure 7 This is a simulation model provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] Example 1: Application in a household photovoltaic grid-connected power generation system

[0054] The household photovoltaic grid-connected power generation system needs to achieve stable voltage control and reactive power compensation under different grid conditions to improve power quality and system stability. Existing photovoltaic grid-connected inverters are prone to overcurrent during low voltage ride-through, affecting the safe operation of the system.

[0055] 1. System configuration:

[0056] The grid-connected voltage management device of the present invention is connected to a household photovoltaic grid-connected inverter to form a photovoltaic grid-connected power generation system.

[0057] The photovoltaic array is connected to the DC side of the inverter through a DC / DC converter, and the AC side of the inverter is connected to the grid.

[0058] 2. Low voltage ride through and over current suppression:

[0059] In the grid-connected state, the system phase-locks the grid voltage through a phase-locked loop (PLL) and outputs a transformation angle so that the d-axis coincides with the grid voltage vector (step S1).

[0060] During low voltage ride-through, the system adjusts the q-axis voltage output through the PI regulator, changes the reactive current, controls the reactive power injected into the grid (step S2), and controls the voltage in the d-axis direction to control the active component (step S3).

[0061] The rotation angle of dq / abc is composed of an active power droop module, a basic frequency module and a phase-locked loop module (step S4).

[0062] When the converter is connected to the grid, the phase-locked loop module is in operation, and the electrical angle output by the active droop module is clamped (step S5). When the converter is off the grid, the phase-locked loop is cut off, and the droop module works normally (step S6).

[0063] The grid amplitude calculation module is used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible (step S7).

[0064] Effect:

[0065] Through the low voltage ride-through overcurrent suppression method of the present invention, the photovoltaic grid-connected inverter can effectively suppress overcurrent during low voltage ride-through, thereby ensuring the safe operation of the system.

[0066] It improves the stability of grid voltage and power quality, and provides a reliable photovoltaic power generation solution for household users.

[0067] Example 2: Application in industrial wind power generation system

[0068] In industrial wind power generation systems, wind turbines need to achieve stable voltage control and reactive power compensation under different grid conditions to ensure the quality of power output and system stability. Wind turbines are prone to voltage instability when switching between grid-connected and off-grid states.

[0069] 1. System configuration:

[0070] The grid-type voltage management device of the present invention is connected with an industrial wind power generator set to form a wind power generation system.

[0071] The wind turbine generator is connected to the power grid via a converter, and the voltage management device of the present invention is integrated into the control system of the converter.

[0072] 2. Grid voltage control and reactive power compensation:

[0073] In the grid-connected state, the system phase-locks the grid voltage through a phase-locked loop and outputs a transformation angle so that the d-axis coincides with the grid voltage vector (step S1).

[0074] During operation, the system adjusts the q-axis voltage output through the PI regulator, changes the reactive current, controls the reactive power injected into the grid (step S2), and controls the voltage in the d-axis direction to control the active component (step S3).

[0075] The rotation angle of dq / abc is composed of an active power droop module, a basic frequency module and a phase-locked loop module (step S4).

[0076] When the converter is connected to the grid, the phase-locked loop module is in operation, and the electrical angle output by the active droop module is clamped (step S5). When the converter is off the grid, the phase-locked loop is cut off, and the droop module works normally (step S6).

[0077] The grid amplitude calculation module is used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible (step S7).

[0078] Effect:

[0079] By means of the voltage management device of the present invention, the wind turbine generator set can realize stable voltage control and reactive power compensation when switching between grid-connected and off-grid states.

[0080] It improves the stability of grid voltage and power quality, ensures the reliable operation of wind power generation system under different working conditions, and provides industrial users with efficient and stable wind power generation solutions.

[0081] An embodiment of the present invention provides a method for suppressing overcurrent of a low voltage ride-through of a grid-type voltage management device, comprising:

[0082] S1: The phase-locked loop phase-locks the grid voltage, outputs a transformation angle θ, and the d-axis coincides with the grid voltage vector. The relationship is as follows: Figure 3 As shown;

[0083] S2: The q-axis is perpendicular to the voltage vector direction. The PI regulator adjusts the output of the q-axis voltage by giving iq_ref to change the reactive current and control the reactive power injected into the grid.

[0084] S3: The d-axis coincides with the grid voltage vector, and the active component is controlled in the direction of the voltage magnitude in the d-axis direction;

[0085] S4: The rotation angle of dq / abc is composed of the active droop module, the basic frequency module and the phase-locked loop module;

[0086] S5: When the converter is connected to the grid, the phase-locked loop module is in working state, and the electrical angle output by the active droop module is clamped;

[0087] S6: When the converter is off-grid, the phase-locked loop is cut off, the droop module works normally, and the converter has normal droop characteristics;

[0088] S7: The grid amplitude calculation module is used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible.

[0089] Figure 3The control strategy is expressed in a two-phase rotating coordinate system, where the d-axis coincides with the grid voltage, corresponding to the active component, and the q-axis to the reactive component. The overall idea of ​​the control strategy is to orient the grid voltage vector in the grid-connected state, independently control the q-axis (reactive) current and the d-axis voltage, and control the active and reactive power of the system respectively through the d-axis voltage setting and the q-axis current setting. The system has two working modes: grid-connected and off-grid, in which active and reactive power control can be achieved in the grid-connected mode.

[0090] Furthermore, the angle θ of the grid in S1 is given by the phase-locked loop and input to the coordinate transformation module as the transformation angle. When the system is off-grid, the phase-locked loop stops working, and the transformation angle is determined by the integral of the sum of the basic frequency and the frequency increment of the active droop output.

[0091] Furthermore, when setting the reactive current in S2, the maximum current of the converter and the current output active current limit should be met, as shown in Formula 1:

[0092]

[0093] Furthermore, the S3 outputs a d-axis voltage, so that the system has voltage source characteristics, and its control can be open-loop or closed-loop control.

[0094] Further, v q To control the reactive current i q The relationship between the generated components is shown in Equation 2:

[0095] v q =i q ·ω·L (Formula 2)

[0096] In formula 2, ω is the grid angular velocity, L is the inductance between the inverter and the grid. From formula 2, we can see that even when the reactive current is large, v q It is still much smaller than the grid voltage, so the addition of the q-axis current loop will not affect the voltage source characteristics of the system.

[0097] Furthermore, the active droop module and the basic frequency in S4 can work in real time. When the power grid phase-locked loop works normally, e is the grid angular velocity; when the phase-locked loop is disconnected, the output angular frequency is the basic frequency ω basic With active droop module ω drop The sum of the fundamental frequency ω basic is a constant 2π·f, where f is the reference frequency.

[0098] Taking the three-phase grid-connected system as an example, the main circuit is as follows Figure 7 The present invention will be described in detail with reference to the accompanying drawings.

[0099] Figure 4 The inverter is shown in the grid-connected state. Figure 4 The waveforms in the figure are the inverter filter output voltage and grid-connected current. The initial grid voltage is set to 1P.U., and the grid voltage drops from 1P.U. to 0.5PU between 0.60.7s. Figure 4 It can be seen that the grid-connected current remains stable when the grid voltage drops sharply, which reflects the characteristics of a current source grid-connected inverter. Figure 5 The inverter is in the grid-connected state and is disconnected from the grid at 0.50.6s. It can be seen from the figure that the output voltage of the inverter remains stable after disconnection, indicating that the inverter has good voltage source characteristics. Figure 6 This is the power regulation process when the inverter is connected to the grid, which shows that the system has good power regulation capability.

[0100] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. A person of ordinary skill in the art will appreciate that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVDROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0101] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for suppressing overcurrent of low voltage ride-through in a grid-type voltage management device, characterized in that: include: S1: The phase-locked loop phase-locks the grid voltage and outputs the conversion angle , the d-axis coincides with the grid voltage vector; S2: The q axis is perpendicular to the voltage vector direction. By giving i q_ref The PI regulator adjusts the output of the q-axis voltage to change the reactive current and control the reactive power injected into the grid; S3: The d-axis coincides with the grid voltage vector, and the active component is controlled in the direction of the voltage magnitude in the d-axis direction; S4: The rotation angle of dq / abc is composed of the active droop module, the basic frequency module and the phase-locked loop module; S5: When the converter is connected to the grid, the phase-locked loop module is in working state, and the electrical angle output by the active droop module is clamped; S6: When the converter is off-grid, the phase-locked loop is cut off, the droop module works normally, and the converter has normal droop characteristics; S7: The grid amplitude calculation module is used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible.

2. According to the method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device according to claim 1, it is characterized in that: The angle of the grid in S1 It is given by the phase-locked loop and input to the coordinate transformation module as the transformation angle; When the system is off-grid, the phase-locked loop stops working, and the conversion angle is determined by the integral of the sum of the basic frequency and the frequency increment of the active droop output.

3. According to the method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device according to claim 1, it is characterized in that: When setting the reactive current in S2, the maximum current of the converter and the current output active current limit should be met, as shown in Formula 1. (Formula 1).

4. According to the method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device according to claim 1, it is characterized in that: The S3 outputs the d-axis voltage, so that the system has voltage source characteristics, and its control can be selected as open-loop or closed-loop control.

5. According to the method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device according to claim 4, it is characterized in that: v q To control the reactive current i q The relationship between the generated components is shown in Equation 2: (Formula 2) In formula 2 is the grid angular velocity, is the inductance between the inverter and the grid. From Equation 2, we can see that even when the reactive current is large, It is still much smaller than the grid voltage, so the addition of the q-axis current loop will not affect the voltage source characteristics of the system.

6. According to the method for suppressing low voltage ride-through overcurrent of a grid-type voltage management device according to claim 1, it is characterized in that: The active power droop module and the basic frequency in S4 can work in real time. When the power grid phase-locked loop works normally, is the grid angular velocity; when the phase-locked loop is disconnected, the output angular frequency is the basic frequency With active power droop module The sum of the fundamental frequency is constant , is the base frequency.

7. A low voltage ride-through overcurrent suppression system for a grid-type voltage management device, characterized in that: include: Phase-locked loop module: used to phase-lock the grid voltage and output the transformation angle so that the d-axis coincides with the grid voltage vector; Reactive current control module: Based on the q-axis direction, the PI regulator adjusts the output of the q-axis voltage to change the reactive current, thereby controlling the reactive power injected into the grid; Active current control module: controls the voltage in the d-axis direction, thereby controlling the active component; dq / abc coordinate transformation module: its rotation angle is determined by the active power droop module, basic frequency module and phase-locked loop module; Grid amplitude calculation module: used to calculate the grid voltage to ensure that the output voltage is as close to the grid voltage as possible.

8. The low voltage ride-through overcurrent suppression system of the grid-type voltage management device according to claim 7 is characterized in that: The phase-locked loop module is in working state when the system is connected to the grid, and outputs an electrical angle to clamp the output of the active power droop module; when the system is off the grid, the phase-locked loop module stops working, and the conversion angle is determined by the integral of the sum of the basic frequency and the frequency increment output by the active power droop module.

9. The low voltage ride-through overcurrent suppression system of a grid-type voltage management device according to claim 7 is characterized in that: When setting the reactive current, the reactive current control module must meet the limitations of the maximum current of the converter and the current output active current.

10. The low voltage ride-through overcurrent suppression system of a grid-type voltage management device according to claim 7, characterized in that: The active power droop module and the basic frequency module can work in real time in both grid-connected and grid-off states, wherein the basic frequency is a constant reference frequency; when the grid operates normally, the phase-locked loop module outputs the grid angular velocity, and when the phase-locked loop module is disconnected, the output angular frequency is the sum of the basic frequency and the active power droop module.

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