Grid construction converter ride-through control method based on power loop coefficient optimization

Abstract

The invention discloses a grid construction converter ride-through control method based on power loop coefficient optimization, and belongs to the technical field of converter control, and the method comprises the steps: obtaining an output voltage, an output current and an inductive current of a grid construction converter in a steady state of a power grid in real time based on a VSG control mode, so as to achieve the ride-through control of the grid construction converter when the fault of the power grid is detected; adjusting an active loop coefficient and a reactive loop coefficient in a VSG control mode based on the voltage amplitude of the network construction converter to obtain a fault VSG control mode; based on the output voltage, the output current and the fault VSG control mode, obtaining a modulation angle and an output internal potential of the network construction converter under a power grid fault, calculating virtual impedance according to the inductive current to obtain a reference internal potential corresponding to the modulation angle and the output internal potential, and further modulating the modulation angle and the output internal potential according to the reference internal potential to obtain a modulation result of the network construction converter. Therefore, by implementing the method and the device, the problem of unstable operation of the power grid and the converter in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and particularly to a grid-forming converter crossing control method based on power loop coefficient optimization. Background Art

[0002] With the increasing proportion of renewable energy in the power system, the voltage support ability of the power grid has been weakened to a certain extent, and the power system has gradually shown a weak grid system situation, which has led to a series of problems such as weak inertia of the power system, poor reactive voltage support ability, accelerated change speed of the power system frequency, voltage collapse, and power system faults. In order to solve the above technical problems without adding additional control strategies, controlling the power grid based on the Virtual Synchronous Generator (VSG) control strategy has become an important control means for the power system.

[0003] The existing VSG control strategy enables the converter to have certain inertia and frequency modulation ability like a synchronous generator by building a swing equation in the converter, thereby improving its efficiency. In addition, VSG control can also assist the converter to damp the grid oscillation and has a synchronization mechanism with the grid. However, it improves the stability of the grid operation.

[0004] However, when the existing technology uses the converter and the VSG control strategy to improve the stability of the grid operation, the overcurrent impact caused by the grid voltage sag formed due to faults such as short circuits and shutdowns in the complex and changeable environment of the grid will pose a threat to the key components inside the grid-forming converter. For example, a serious overcurrent fault will burn out the fragile power devices inside the converter, which not only poses a threat to the safety of the grid-forming converter, but even leads to the converter tripping accident, resulting in a large-area power outage and reducing the stability of the grid operation. Summary of the Invention

[0005] The present invention provides a grid-forming converter crossing control method based on power loop coefficient optimization, which can solve the problem in the existing technology that it cannot cope with the overcurrent impact caused by grid faults, thereby affecting the stable operation of the converter and the grid.

[0006] In order to solve the above technical problems, the present invention discloses a grid-forming converter crossing control method based on power loop coefficient optimization to improve the stability of the converter and the grid operation. The method includes:

[0007] Based on a preset VSG control mode, the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the grid are obtained in real time;

[0008] When a grid fault is detected based on the output voltage, the active loop coefficient and the reactive loop coefficient in the VSG control mode are adjusted based on the voltage amplitude of the grid-forming converter to obtain a fault VSG control mode with the adjusted active loop coefficient and reactive loop coefficient.

[0009] Based on the output voltage, output current, and the fault VSG control mode, the modulation angle and the output internal potential of the grid-forming converter under grid faults are obtained.

[0010] The virtual impedance is calculated according to the inductor current, and the reference internal potential corresponding to the modulation angle and the output internal potential is calculated according to the virtual voltage drop corresponding to the virtual impedance.

[0011] The modulation angle and the output internal potential are modulated according to the reference internal potential to obtain a control signal, and the grid-forming converter is controlled according to the control signal.

[0012] A grid-forming converter crossing control method based on power loop coefficient optimization disclosed by the present invention starts a converter operating based on the VSG control mode when the grid is in a stable state to synchronously detect the fault state of the grid through the output voltage of the converter, improving the efficiency and accuracy of fault detection. Among them, when a grid fault is detected, the active loop coefficient and the reactive loop coefficient in the VSG control mode are adjusted according to the voltage amplitude of the grid-forming converter during the grid fault, so that the impact current caused by the grid fault is reduced according to the adjusted coefficient fault VSG control mode, improving the transient stability of the converter, and enabling the converter and the grid to operate stably. Secondly, when a grid fault occurs, a virtual impedance is introduced to increase the impedance of the converter, thereby resisting the impact current caused by the grid fault and further improving the stability of the grid and the converter operation.

[0013] As a preferred example, the real-time acquisition of the output voltage, output current, and inductor current of the grid-forming converter under grid steady state based on the preset VSG control mode includes:

[0014] When the grid is in a steady state, the grid-forming converter is controlled based on the preset VSG control mode to collect the output voltage, output current, and the inductor current of the inductor connected to the output side of the grid-forming converter in real time; among them, the VSG control mode includes active loop control and reactive loop control; the calculation expression of the active loop control is:

[0015]

[0016] Among them, the P ref represents the expected reference active power of the grid-forming converter; the J represents the virtual inertia introduced by the grid-forming converter; the D prepresents the active damping coefficient introduced by the grid-forming converter; the ω n represents the reference angular frequency of the grid-forming converter; the ω represents the real-time output angular frequency of the grid-forming converter; the P cal represents the real-time output active power of the grid-forming converter;

[0017] The modulation angle input to the grid-forming converter is obtained by integrating the real-time output angular frequency; wherein, the calculation expression of the modulation angle is:

[0018]

[0019] wherein, the θ represents the modulation angle of the grid-forming converter;

[0020] The calculation expression of the reactive power loop control is:

[0021] V m = V ref + D q (Q ref - Q cal )

[0022] wherein, the V m represents the real-time output internal potential of the grid-forming converter; the V ref represents the reference internal potential of the grid-forming converter; the D q represents the reactive power voltage regulation coefficient introduced by the grid-forming converter; the Q ref represents the desired reference reactive power of the grid-forming converter; the Q cal represents the real-time output reactive power of the grid-forming converter.

[0023] In the above solution, when the power grid is in a stable state, that is, there is no fault, the VSG control mode is adopted to control the grid-forming converter connected to the power grid. Through the active power loop control and reactive power loop control in the VSG control mode, the converter is provided with a certain inertia and frequency modulation ability, thereby improving the stability of the power grid operation. At the same time, the active power loop control in the VSG control mode assists the converter to damp the power grid oscillation and has a synchronization mechanism with the power grid, thereby improving the stability of the power grid operation. And the reactive power loop control is set to ensure that the converter stabilizes the amplitude of its output internal potential by adjusting its own output reactive power, improving the stability of the converter operation.

[0024] As a preferred example, the method for real-time obtaining the output voltage, output current and inductor current of the grid-forming converter under the steady state of the power grid based on the preset VSG control mode further includes:

[0025] Obtain the three-phase output voltage, three-phase output current of the grid-forming converter, and the three-phase inductor current of the inductor, and perform a rotating coordinate transformation on the three-phase output voltage, three-phase output current, and three-phase inductor current according to the modulation angle to obtain two-phase output voltage, two-phase output current, and two-phase inductor current; wherein, the calculation expressions of the two-phase output voltage, two-phase output current, and two-phase inductor current are:

[0026]

[0027] wherein, the U oabc represents the three-phase output voltage of the grid-forming converter; the i oabc represents the three-phase output current of the grid-forming converter; the i abc represents the three-phase inductor current of the inductor; the U odq represents the two-phase output voltage of the grid-forming converter; the i odq represents the two-phase output current of the grid-forming converter; the i dq represents the two-phase inductor current of the inductor; the i0 represents the zero-sequence current.

[0028] In the above solution, in order to simplify the control process and improve the control efficiency, the collected three-phase voltage, current, etc. are subjected to a rotating coordinate system transformation to obtain direct current quantities and then corresponding control and analysis are carried out, which not only improves the control efficiency but also improves the control accuracy.

[0029] As a preferred example, the real-time acquisition of the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid based on the preset VSG control mode further includes:

[0030] Calculate the real-time output active power and real-time output reactive power of the grid-forming converter according to the two-phase output voltage and the two-phase output current; wherein, the calculation expressions of the real-time output active power and real-time output reactive power are:

[0031]

[0032] wherein, the U od , U oq are respectively the voltage components corresponding to the two-phase output voltage U odq in the two-phase coordinate system; the i od , i oq are respectively the current components corresponding to the two-phase output current i odq in the two-phase coordinate system.

[0033] In the above solution, the real-time output active power and the real-time output reactive power calculation accuracy of the grid-forming converter are improved according to the simplified two-phase output voltage and two-phase output current, ensuring the accuracy of the VSG control, and further improving the stability of the power grid and converter operation.

[0034] As a preferred example, the detecting that a grid fault occurs based on the output voltage includes:

[0035] Obtaining in real time the voltage of the capacitor connected to the output side of the grid-forming converter according to the two-phase output voltage, and judging whether the grid has a fault according to the voltage of the capacitor; wherein, the judgment condition for the fault is:

[0036]

[0037] wherein, the u cap represents the voltage of the capacitor; the V ref represents the reference internal electromotive force of the grid-forming converter.

[0038] In the above solution, considering that in a grid-connected system, the output voltage of the converter is equivalent to the voltage level of the grid. At this time, in order to detect faults in the grid in a timely and accurate manner, the output voltage of the converter is used to detect grid faults, improving the detection accuracy and efficiency, and further improving the timeliness of control to ensure the stability of the power grid and converter operation.

[0039] As a preferred example, the adjusting the active loop coefficient and the reactive loop coefficient in the VSG control mode based on the voltage amplitude of the grid-forming converter includes:

[0040] When it is determined that a grid fault occurs, switching the virtual inertia in the active loop control to a first virtual inertia value and switching the active damping coefficient in the active loop control to a first active damping coefficient value; wherein, the virtual inertia includes a first virtual inertia value under grid fault and a second virtual inertia value under grid steady state; the active damping coefficient includes a first active damping coefficient value under grid fault and a second active damping coefficient value under grid steady state; the first virtual inertia value is less than the second virtual inertia value; the first active damping coefficient value is greater than the second active damping coefficient value;

[0041] The switching expressions for the virtual inertia and the active damping coefficient are:

[0042]

[0043] wherein, the J0 represents the second virtual inertia value under grid steady state; the J fault represents the first virtual inertia value under grid fault; the D p0represents the second active damping coefficient value under the steady state of the power grid; the D pfault represents the first active damping coefficient value under the power grid fault.

[0044] In the above solution, when a fault occurs in the power grid to perform fault control on the network-forming converter, reducing the virtual inertia in the active loop control and increasing the damping coefficient in the active loop control within a certain range can improve the operation stability of the power grid and the converter.

[0045] As a preferred example, the active loop coefficient and the reactive loop coefficient in the VSG control mode are adjusted based on the voltage amplitude of the network-forming converter, including:

[0046] When it is determined that a fault occurs in the power grid, determine the first reactive voltage regulation coefficient value of the reactive voltage regulation coefficient in the reactive loop control according to the voltage amplitude of the network-forming converter; wherein, the calculation expression of the first reactive voltage regulation coefficient value is:

[0047]

[0048] wherein, the D q0 represents the second reactive voltage regulation coefficient value of the network-forming converter under the steady state of the power grid; the D qfault represents the first reactive voltage regulation coefficient value of the network-forming converter under the power grid fault; the V g ′ represents the voltage amplitude of the network-forming converter under the power grid fault; the I thresh represents the maximum allowable overcurrent value of the network-forming converter; the X represents the line reactance of the line where the network-forming converter is located.

[0049] In the above solution, based on the reactive voltage regulation coefficient, the output internal potential of the converter can be actively adjusted, and when the voltage regulation coefficient is constant, the bias of the reactive power is proportional to the bias of the output internal potential of the converter. Therefore, by adjusting the reactive power output to adjust its own output internal potential, it is possible to ensure that the output current of the converter is maintained at the maximum output current level as much as possible, and fully improve the voltage support ability of the converter during the transient voltage fault, thereby improving the operation stability of the power grid and the converter.

[0050] As a preferred example, the virtual impedance is calculated according to the inductor current, and the modulation angle and the reference internal potential corresponding to the output internal potential are calculated according to the virtual voltage drop corresponding to the virtual impedance, including:

[0051] When it is determined that the power grid is in a fault, start the preset virtual impedance control mode, and input the modulation angle and the output internal potential into the virtual impedance control mode to obtain the virtual impedance and the reference internal potential based on the virtual impedance control mode; wherein, the calculation expression of the virtual impedance control mode is:

[0052]

[0053] Among them, the k VR and k VX represent preset virtual impedance coefficients; the R vir and X vir represent the virtual impedance; the V dir and V qir are the virtual voltage drops corresponding to the virtual impedance; the Edref and Eqref represent the reference internal electromotive force.

[0054] In the above solution, when a grid fault causes a grid-side transient voltage dip fault, since the equivalent output internal electromotive force of the converter does not change suddenly, the small line impedance of the grid-connected line will easily cause a large overcurrent impact. At this time, in order to prevent the key components inside the converter from being burned out due to the large overcurrent impact, the virtual impedance control strategy is set to achieve low-voltage ride-through control during grid-side faults, avoid the converter from being affected by the overcurrent impact, and improve the stability of the converter and the grid operation.

[0055] As a preferred example, modulating the modulation angle and the output internal electromotive force according to the reference internal electromotive force to obtain a control signal and controlling the grid-forming converter according to the control signal includes:

[0056] Performing sinusoidal pulse width modulation on the modulation angle and the output internal electromotive force according to the reference internal electromotive force to obtain a control signal for controlling the grid-forming converter;

[0057] Controlling the grid-forming converter according to the control signal.

[0058] In the above solution, the reference internal electromotive force formed in the virtual impedance control strategy is used to perform sinusoidal pulse width modulation on the internal electromotive force and the modulation angle output by the fault VSG control mode, which not only ensures the generation of a control signal that can be used to control the converter, completes the control of the converter, but also enables the converter to resist the overcurrent impact caused by the fault according to the control signal, and improves the stability of the converter operation.

[0059] As a preferred example, modulating the modulation angle and the output internal electromotive force according to the reference internal electromotive force to obtain a control signal and controlling the grid-forming converter according to the control signal further includes:

[0060] When it is detected according to the output voltage that there is no fault in the grid, obtaining the modulation angle and the output internal electromotive force of the grid-forming converter under the grid steady state based on the VSG control mode;

[0061] Perform sinusoidal pulse width modulation on the modulation angle and the output internal electromotive force to obtain a control signal for controlling the grid-forming converter, and control the grid-forming converter according to the control signal.

[0062] In the above solution, when there is no fault in the power grid, the control mode of the converter is timely switched to the VSG control mode to ensure the stable operation of the converter and the power grid. Brief Description of the Drawings

[0063] In order to more clearly illustrate the technical solutions of the present application, the drawings required for implementation will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0064] Figure 1 It is a schematic flowchart of a grid-forming converter crossing control method based on power loop coefficient optimization provided by an embodiment of the present invention;

[0065] Figure 2 It is a schematic structural diagram of a grid-forming converter crossing control system based on power loop coefficient optimization provided by an embodiment of the present invention;

[0066] Figure 3 It is a schematic flowchart of a grid-forming converter crossing control method based on power loop coefficient optimization provided by another embodiment of the present invention;

[0067] Figure 4 It is a structural topology diagram when a converter is controlled based on the VSG control strategy provided by another embodiment of the present invention;

[0068] Figure 5 It is a structural diagram of a virtual impedance control strategy provided by another embodiment of the present invention;

[0069] Figure 6 It is a voltage-current phase diagram of a converter before and after a power grid fault provided by another embodiment of the present invention;

[0070] Figure 7 It is a structural topology diagram when a converter is controlled based on the VSG control strategy with optimized power loop coefficients provided by another embodiment of the present invention;

[0071] Figure 8 It is a schematic diagram of the output power of a converter when it is controlled by a traditional control method provided by another embodiment of the present invention;

[0072] Figure 9 It is a schematic diagram of the output current of a converter when it is controlled by a traditional control method provided by another embodiment of the present invention;

[0073] Figure 10 It is a schematic diagram of the output internal potential of a converter when controlled by a traditional control method provided by another embodiment of the present invention;

[0074] Figure 11 It is a schematic diagram of the output power of a converter when controlled by a control strategy based on power loop coefficient optimization provided by another embodiment of the present invention;

[0075] Figure 12 It is a schematic diagram of the output current of a converter when controlled by a control strategy based on power loop coefficient optimization provided by another embodiment of the present invention;

[0076] Figure 13 It is a schematic diagram of the output internal potential of a converter when controlled by a control strategy based on power loop coefficient optimization provided by another embodiment of the present invention. Detailed implementation manners

[0077] To make the objectives, technical solutions and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without making creative efforts shall fall within the scope of protection of this application.

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0079] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more unless otherwise specifically defined.

[0080] Referring to "embodiment" herein means that a specific feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0081] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0082] In the description of the embodiments of the present application, the term "multiple" refers to two or more (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0083] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", and "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0084] See Figure 1 , to solve the problem that in the prior art, the power grid and the converter cannot operate stably due to the inability to resist the overcurrent impact caused by the power grid fault, this embodiment provides a grid-forming converter crossing control method based on power loop coefficient optimization, including:

[0085] Step 101: Based on a preset VSG control mode, obtain the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid in real time.

[0086] In this embodiment, this step includes: when the power grid is in a steady state, controlling the grid-forming converter based on a preset VSG control mode to collect the output voltage, output current, and inductor current of the inductor connected to the output side of the grid-forming converter in real time; where the VSG control mode includes active loop control and reactive loop control; the calculation expression of the active loop control is:

[0087]

[0088] where the P ref represents the expected reference active power of the grid-forming converter; the J represents the virtual inertia introduced by the grid-forming converter; the D p represents the active damping coefficient introduced by the grid-forming converter; the ω n represents the reference angular frequency of the grid-forming converter; the ω represents the real-time output angular frequency of the grid-forming converter; the Pcal representing the real-time active power output of the grid-forming converter; obtaining the modulation angle input to the grid-forming converter by integrating the real-time output angular frequency; wherein, the calculation expression of the modulation angle is:

[0089] θ = ∫ωdt

[0090] wherein, the θ represents the modulation angle of the grid-forming converter;

[0091] The calculation expression of the reactive power loop control is:

[0092] V m = V ref + D q (Q ref - Q cal )

[0093] wherein, the V m represents the real-time output internal potential of the grid-forming converter; the V ref represents the reference internal potential of the grid-forming converter; the D q represents the reactive power voltage regulation coefficient introduced by the grid-forming converter; the Q ref represents the expected reference reactive power of the grid-forming converter; the Q cal represents the real-time output reactive power of the grid-forming converter.

[0094] Wherein, obtaining the three-phase output voltage, three-phase output current of the grid-forming converter and the three-phase inductor current of the inductor, and performing a rotating coordinate transformation on the three-phase output voltage, three-phase output current and three-phase inductor current according to the modulation angle to obtain two-phase output voltage, two-phase output current and two-phase inductor current; wherein, the calculation expressions of the two-phase output voltage, two-phase output current and two-phase inductor current are:

[0095]

[0096] wherein, the U oabc represents the three-phase output voltage of the grid-forming converter; the i oabc represents the three-phase output current of the grid-forming converter; the i abc represents the three-phase inductor current of the inductor; the U odq represents the two-phase output voltage of the grid-forming converter; the i odq represents the two-phase output current of the grid-forming converter; the i dqThe two-phase inductor current representing the inductor; the i0 represents the zero-sequence current; calculate the real-time output active power and real-time output reactive power of the grid-forming converter according to the two-phase output voltage and the two-phase output current; wherein, the calculation expressions of the real-time output active power and real-time output reactive power are:

[0097]

[0098] Wherein, the U od , U oq are respectively the voltage components corresponding to the two-phase output voltage U odq in the two-phase coordinate system; the i od , i oq are respectively the current components corresponding to the two-phase output current i odq in the two-phase coordinate system.

[0099] In the above steps, when the power grid is in a stable state, that is, there is no fault, the VSG control mode is used to control the grid-forming converter connected to the power grid. Through the active loop control and reactive loop control in the VSG control mode, the converter has a certain inertia and frequency modulation ability, thereby improving the stability of the power grid operation. At the same time, the active loop control in the VSG control mode assists the converter to damp the power grid oscillation and has a synchronization mechanism with the power grid, thereby improving the stability of the power grid operation. And the reactive loop control is set to ensure that the converter stabilizes the amplitude of its internal potential by adjusting its own output reactive power, improving the stability of the converter operation. Among them, in order to simplify the control process and improve the control efficiency, the collected three-phase voltage, current, etc. are subjected to a rotating coordinate system transformation, and the direct current is obtained and then corresponding control and analysis are carried out, which not only improves the control efficiency but also improves the control accuracy.

[0100] Step 102: When a fault is detected in the power grid based on the output voltage, adjust the active loop coefficient and reactive loop coefficient in the VSG control mode based on the voltage amplitude of the grid-forming converter to obtain a fault VSG control mode after adjusting the active loop coefficient and reactive loop coefficient.

[0101] In this embodiment, this step includes: obtaining the voltage of the capacitor connected to the output side of the grid-forming converter in real time according to the two-phase output voltage, and judging whether the power grid has a fault according to the voltage of the capacitor; wherein, the judgment condition for the fault is:

[0102]

[0103] Wherein, the u cap represents the voltage of the capacitor; the V ref represents the reference internal potential of the grid-forming converter.

[0104] When it is determined that a power grid fault occurs, switch the virtual inertia in the active power loop control to a first virtual inertia value and switch the active power damping coefficient in the active power loop control to a first active power damping coefficient value; wherein, the virtual inertia includes a first virtual inertia value under power grid faults and a second virtual inertia value under power grid steady state; the active power damping coefficient includes a first active power damping coefficient value under power grid faults and a second active power damping coefficient value under power grid steady state; the first virtual inertia value is less than the second virtual inertia value; the first active power damping coefficient value is greater than the second active power damping coefficient value;

[0105] The switching expressions for the virtual inertia and the active power damping coefficient are:

[0106]

[0107] wherein, the J0 represents the second virtual inertia value under power grid steady state; the J fault represents the first virtual inertia value under power grid faults; the D p0 represents the second active power damping coefficient value under power grid steady state; the D pfault represents the first active power damping coefficient value under power grid faults.

[0108] When it is determined that a power grid fault occurs, determine a first reactive power regulation coefficient value of the reactive power loop control according to the voltage amplitude of the network-forming converter; wherein, the calculation expression for the first reactive power regulation coefficient value is:

[0109]

[0110] wherein, the D q0 represents the second reactive power regulation coefficient value of the network-forming converter under power grid steady state; the D qfault represents the first reactive power regulation coefficient value of the network-forming converter under power grid faults; the V g ′ represents the voltage amplitude of the network-forming converter under power grid faults; the I thresh represents the maximum allowable overcurrent value of the network-forming converter; the X represents the line reactance of the line where the network-forming converter is located.

[0111] In this embodiment, the above steps consider that in a grid-connected system, the output voltage of the converter is equivalent to the voltage level of the grid. At this time, in order to detect faults in the grid in a timely and accurate manner, the output voltage of the converter is used to detect grid faults, improving the detection accuracy and efficiency, and further enhancing the timeliness of control to ensure the stability of the grid and converter operation. When a fault occurs in the grid for fault control of the grid-forming converter, reducing the virtual inertia in the active power loop control and increasing the damping coefficient in the active power loop control within a certain range can improve the stability of the grid and converter operation. Based on the reactive power regulation coefficient, the output internal potential of the converter can be actively adjusted. When the regulation coefficient is constant, the offset of the reactive power is proportional to the offset of the output internal potential of the converter. Therefore, by adjusting the reactive power output to regulate its own output internal potential, it is possible to ensure that the output current of the converter is maintained at the maximum output current level as much as possible, fully improving the voltage support ability of the converter during transient voltage faults, and further enhancing the stability of the grid and converter operation.

[0112] Step 103: Obtain the modulation angle and output internal potential of the grid-forming converter under grid faults based on the output voltage, output current, and the fault VSG control mode.

[0113] Step 104: Calculate the virtual impedance based on the inductor current, and calculate the reference internal potential corresponding to the modulation angle and output internal potential based on the virtual voltage drop corresponding to the virtual impedance.

[0114] In this embodiment, this step mainly includes: when it is determined that the grid is in a fault, start the preset virtual impedance control mode, and input the modulation angle and output internal potential into the virtual impedance control mode to obtain the virtual impedance and the reference internal potential based on the virtual impedance control mode; where the calculation expression of the virtual impedance control mode is:

[0115]

[0116] Among them, the k VR , k VX represent the preset virtual impedance coefficients; the R vir and X vir represent the virtual impedance; the V dir and V qir are the virtual voltage drops corresponding to the virtual impedance; the Edref and Eqref represent the reference internal potential.

[0117] In this embodiment, when a grid fault causes a grid-side transient voltage sag during the above steps, the potential within the converter's equivalent output does not suddenly change, and the small impedance of the grid-connected line can easily lead to a significant overcurrent surge. To prevent critical converter components from burning out due to the significant overcurrent surge, the virtual impedance control strategy is implemented to implement low-voltage ride-through control during a grid-side fault, thereby protecting the converter from overcurrent surges and improving the stability of converter and grid operations.

[0118] Step 105: modulate the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal and control the grid converter according to the control signal.

[0119] In this embodiment, this step mainly includes: performing sinusoidal pulse width modulation on the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal for controlling the grid-forming converter; and controlling the grid-forming converter according to the control signal.

[0120] At the same time, when it is detected that there is no fault in the grid based on the output voltage, the modulation angle and output internal potential of the grid converter in the steady state of the grid are obtained based on the VSG control mode; the modulation angle and the output internal potential are sinusoidally pulse-width modulated to obtain a control signal for controlling the grid converter, and the grid converter is controlled according to the control signal.

[0121] In this embodiment, the above steps utilize the reference internal potential generated by the virtual impedance control strategy to perform sinusoidal pulse width modulation on the internal potential and modulation angle output by the fault VSG control mode. This not only ensures the generation of a control signal that can be used to control the converter, thus completing converter control, but also enables the converter to resist overcurrent shocks caused by the fault according to the control signal, thereby improving converter operational stability. When the grid is fault-free, the converter control mode is promptly switched to the VSG control mode, ensuring stable converter and grid operation.

[0122] like Figure 2 As shown, based on the above method embodiment, a corresponding device embodiment is provided; this embodiment provides a grid-connected converter ride-through control system based on power loop coefficient optimization, including a steady-state control module 201, a coefficient optimization module 202, a control adjustment module 203, a virtual impedance module 204 and a control modulation module 205.

[0123] The steady-state control module 201 is used to obtain the output voltage, output current and inductor current of the grid-connected converter in real time under the steady state of the power grid based on a preset VSG control mode.

[0124] The coefficient optimization module 202 is configured to, when a grid fault is detected based on the output voltage, adjust the active loop coefficient and the reactive loop coefficient in the VSG control mode based on the voltage amplitude of the grid-forming converter, so as to obtain a fault VSG control mode with the adjusted active loop coefficient and reactive loop coefficient.

[0125] The control adjustment module 203 is configured to obtain the modulation angle and the output internal potential of the grid-forming converter under a grid fault based on the output voltage, the output current, and the fault VSG control mode.

[0126] The virtual impedance module 204 is configured to calculate a virtual impedance based on the inductor current, and calculate a reference internal potential corresponding to the modulation angle and the output internal potential based on the virtual voltage drop corresponding to the virtual impedance.

[0127] The control modulation module 205 is configured to modulate the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal, and control the grid-forming converter according to the control signal.

[0128] It can be understood that the above device item embodiments correspond to the method item embodiments of the present invention, and can implement a grid-forming converter crossing control method based on power loop coefficient optimization provided by any one of the above method item embodiments of the present invention.

[0129] It should be noted that the above-described device embodiments are merely illustrative, and some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the attached drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that they have a communication connection, which can be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement without creative efforts.

[0130] Based on the above embodiment of a grid-forming converter crossing control method based on power loop coefficient optimization, another embodiment of the present invention provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements a grid-forming converter crossing control based on power loop coefficient optimization according to any embodiment of the present invention.

[0131] Exemplarily, in this embodiment, the computer program can be divided into one or more modules, and the one or more modules are stored in the memory and executed by the processor to complete the present invention. The one or more module elements can be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in the terminal device.

[0132] The terminal device may be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The terminal device may include, but is not limited to, a processor and a memory.

[0133] The so-called processor may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The processor is the control center of the terminal device and connects all parts of the entire terminal device through various interfaces and lines.

[0134] Based on the above method item embodiments, another embodiment of the present invention provides a computer-readable storage medium, including a stored computer program, wherein when the computer program runs, it controls the device where the computer-readable storage medium is located to execute a grid-connected converter crossing control based on power loop coefficient optimization described in any one of the above method item embodiments of the present invention.

[0135] Wherein, if the modules / units integrated in the device / terminal device are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes in the above method embodiments of the present invention, it can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0136] A grid-forming converter crossing control method, system, device and medium provided in this embodiment start a converter operating in a VSG control mode when the power grid is in a stable state, so as to synchronously detect the fault state of the power grid through the output voltage of the converter, improving the efficiency and accuracy of fault detection. Among them, when a power grid fault is detected, the active power loop coefficient and the reactive power loop coefficient in the VSG control mode are adjusted according to the voltage amplitude of the grid-forming converter during the power grid fault, so that the fault VSG control mode after adjusting the coefficients reduces the impact current caused by the power grid fault, improves the transient stability of the converter, and enables the converter and the power grid to operate stably. Secondly, when a power grid fault occurs, a virtual impedance is introduced to increase the impedance of the converter, thereby resisting the impact current caused by the power grid fault and further improving the stability of the operation of the power grid and the converter.

[0137] Embodiment 2

[0138] To improve the stability of power grid operation, in the prior art, a virtual synchronous generator (VSG) control strategy is introduced into the converter, so that by embedding a swing equation in the converter, it has certain inertia and frequency modulation ability like a synchronous generator, forming a grid-forming converter. However, facing the complex and changeable environmental impacts, the power grid will inevitably face fault threats such as short circuits and outages. The above fault threats cause voltage sags in the power grid, and the overcurrent impact generated in the line will be an important factor affecting the reliability of key components inside the grid-forming converter and the stability of the grid-connected system.

[0139] To ensure the safe and stable operation of the grid-connected system, the prior art mostly focuses on the dynamic response and small-signal stability analysis of the grid-forming converter under steady state, or the power-frequency fluctuation problem under changing operating conditions. However, the crossing control of the grid-forming converter under the transient voltage drop fault of the power grid is equally important. Some studies achieve the low-voltage crossing control of the grid-forming converter by increasing virtual impedance and other measures, but ignore the influence of important parameters of the power loop in the VSG control on the transient stability performance of the grid-connected system.

[0140] To solve the above technical problems, referring to Figure 3 , this embodiment provides a grid-forming converter crossing control method based on power loop coefficient optimization, which is used to improve the stable operation of the power grid and the converter when a transient fault occurs in the power grid. Specifically, the grid-forming converter control method includes:

[0141] Step 301: Construct a VSG control model of the converter, and when the power grid is in a steady state, control the converter based on the VSG control model to collect the output voltage, output current and inductor current of the converter in real time.

[0142] In this embodiment, to ensure the operating stability of the converter based on VSG control and the operating stability of the power grid where the converter is connected to the grid, a VSG control model with active loop control and reactive loop control is used to control the converter.

[0143] Specifically, in an implementation manner of this embodiment, the circuit structure topology diagram for controlling the converter using the VSG control model is as Figure 4 shown. Referring to Figure 4 , a filter inductor Lf and a filter capacitor Cf are connected in series between the output side of the converter and the power grid. Among them, a grid-side equivalent impedance Zg is connected in series between the filter capacitor Cf and the power grid.

[0144] Secondly, referring to Figure 4 , during the process of controlling the converter based on the VSG control model, the output voltage of the converter, the output current of the converter, and the inductor current of the inductor connected to the output side of the converter will be subjected to a rotating coordinate system conversion in real time. Specifically, the three-phase output voltage U oabc , the three-phase output current i oabc of the grid-forming converter and the three-phase inductor current i abc of the inductor are obtained; then the three-phase output voltage U oabc , the three-phase output current i oabc and the three-phase inductor current i abc are subjected to a dq coordinate system conversion to obtain the two-phase output voltage U odq of the grid-forming converter, the two-phase output current i odq of the grid-forming converter, and the two-phase inductor current i dq of the inductor;

[0145] Then, according to the two-phase output voltage U odq , the two-phase output current i odq , the real-time output active power P cal and the real-time output reactive power Q cal of the converter are calculated; furthermore, the real-time output active power P cal and the real-time output reactive power Q cal are input into the VSG control model with a reactive loop and an active loop to obtain the modulation angle θ of the converter and the equivalent output internal electromotive force V m of the converter, and the V dc represents the input voltage of the DC side of the converter.

[0146] It can be seen from Figure 4 that the core part of the VSG control model is mainly composed of two parts: an active loop and a reactive loop. Among them, the active loop is mainly used for active frequency modulation, and its mathematical model expression is as follows:

[0147]

[0148] Among them, the P ref represents the expected reference active power of the network-forming converter; the J represents the virtual inertia introduced by the network-forming converter; the D p represents the active damping coefficient introduced by the network-forming converter; the ω n represents the reference angular frequency of the network-forming converter; the ω represents the real-time output angular frequency of the network-forming converter; the P cal represents the real-time output active power of the network-forming converter;

[0149] The modulation angle θ required for Sinusoidal Pulse Width Modulation (SPWM) is obtained by integrating the real-time output angular frequency; among them, the calculation expression of the modulation angle is:

[0150] θ = ∫ωdt

[0151] Among them, the θ represents the modulation angle of the network-forming converter;

[0152] The reactive power loop is mainly used to realize the reactive power voltage regulation function to ensure that the converter stabilizes the amplitude of the internal electromotive force of its own output by adjusting its own output reactive power. The corresponding expression is as follows:

[0153] V m = V ref + D q (Q ref - Q cal )

[0154] Among them, the V m represents the real-time output internal electromotive force of the network-forming converter; the V ref represents the reference internal electromotive force of the network-forming converter; the D q represents the reactive power voltage regulation coefficient introduced by the network-forming converter; the Q ref represents the expected reference reactive power of the network-forming converter; the Q cal represents the real-time output reactive power of the network-forming converter.

[0155] Furthermore, referring to Figure 4 , in order to simplify the mathematical model of the VSG control model, the collected three-phase voltage and current are usually subjected to dq transformation to obtain two direct currents and then corresponding control and analysis are performed.

[0156] Among them, the abc / dq transformation expressions of the output voltage, output current and inductor current of the converter are as follows:

[0157]

[0158] Among them, the U oabc represents the three-phase output voltage of the grid-forming converter; the i oabc represents the three-phase output current of the grid-forming converter; the i abc represents the three-phase inductor current of the inductor; the U odq represents the two-phase output voltage of the grid-forming converter; the i odq represents the two-phase output current of the grid-forming converter; the i dq represents the two-phase inductor current of the inductor; the i0 represents the zero-sequence current.

[0159] After the dq transformation, the calculation expressions for the real-time output active power and the real-time output reactive power are as follows:

[0160]

[0161] Among them, the U od , U oq are respectively the voltage components corresponding to the two-phase output voltage U odq in the two-phase coordinate system; the i od , i oq are respectively the current components corresponding to the two-phase output current i odq in the two-phase coordinate system.

[0162] Step 302: Construct a virtual impedance control model of the converter when the power grid fails.

[0163] In this embodiment, when a power grid fault causes a grid-side transient voltage drop fault, since the equivalent output internal potential of the converter does not change suddenly, the small line impedance of the grid-connected line will easily lead to a large overcurrent impact. Therefore, in order to prevent the key components inside the converter from being burned out due to a large overcurrent impact, a virtual impedance control strategy is designed to achieve low-voltage ride-through control during grid-side faults.

[0164] Different from the actual line impedance, the virtual impedance only acts during grid faults and does not affect the output voltage and current of the converter during steady-state operation. Specifically, the virtual impedance control strategy is as Figure 5 shown. Referring to Figure 5 , the virtual impedance control strategy obtains the internal potential and modulation angle of the VSG control output to generate the reference internal potential Edref and Eqref required for SPWN modulation.

[0165] Referring to the control strategy shown in Figure 5 , the expression of the virtual impedance control strategy is as follows:

[0166]

[0167] Among them, the I thresh represents the maximum allowable overcurrent value of the network-forming converter, and k VR , k VX represent preset virtual impedance coefficients; the R vir and X vir represent the virtual impedance; the V dir and V qir are the virtual voltage drops corresponding to the virtual impedance; the Edref and Eqref represent the reference internal electromotive forces required for SPWN modulation. A maximum value comparison between the input value and 0 is added to the virtual impedance control strategy to ensure that during non-low-voltage fault periods, the virtual impedance does not act and no additional voltage compensation is generated to reduce the converter output current value.

[0168] Step 303: Detect whether the power grid has a fault according to the output voltage.

[0169] In this embodiment, for the grid-connected system, the filter capacitor voltage is equivalent to the grid voltage and the output voltage level of the converter. When a transient voltage drop fault occurs on the grid side, the filter capacitor voltage will also decrease to a certain extent. When the filter capacitor voltage satisfies: At this time, it can be considered that the power grid has a transient voltage fault, and the network-forming converter needs to perform low-voltage fault ride-through control.

[0170] [[ID=]27]Step 304: When it is determined that the power grid has a fault, adjust the active loop coefficient and the reactive loop coefficient in the VSG control mode based on the voltage amplitude of the network-forming converter to obtain a fault VSG control mode with the adjusted active loop coefficient and reactive loop coefficient.

[0171] In this embodiment, according to Figure 4 the corresponding control topology diagram of the network-forming converter in, when the line is inductive, the output power of the network-forming converter can be approximately expressed by the following formula:

[0172]

[0173] where Z is the equivalent impedance of the grid-connected line.

[0174] Expressing the various variables used in the VSG control mode with rated values and perturbation values, the following formula can be obtained:

[0175]

[0176] In the formula, θ n is the rated modulation angle, represents the perturbation value of the corresponding variable.

[0177] Based on the representation of the rated value and disturbance value, the output power of the grid-forming converter is subjected to canceling the rated value and the disturbance quantities above the second order, and a linearized and Laplace-transformed expression can be obtained:

[0178]

[0179] Where s is the Laplace operator in the complex-domain mathematical model of the control system, which is mainly used to describe the frequency response, stability and other characteristics of the dynamic system.

[0180] Analyzing the above formula, and at this time the active power is nearly decoupled, so the closed-loop transfer function of the active power response of the grid-forming converter can be obtained:

[0181]

[0182] According to the above formula, it can be seen that its closed-loop characteristic equation has a pair of conjugate characteristic roots. When the damping coefficient remains unchanged and the virtual inertia increases, the stability of the system will decrease; when the virtual inertia remains unchanged and the damping coefficient increases, the stability of the system will first increase and then decrease. Therefore, when the grid-forming converter performs low-voltage ride-through control, reducing the virtual inertia and increasing the damping coefficient within a certain range can improve the stability of the grid-connected system. The control method for optimizing the active loop coefficient is as follows:

[0183]

[0184] Where, the J0 represents the second virtual inertia value under the steady state of the power grid; the J fault represents the first virtual inertia value under the power grid fault; the D p0 represents the second active damping coefficient value under the steady state of the power grid; the D pfault represents the first active damping coefficient value under the power grid fault. Obviously, after the grid-side fault is restored, the virtual inertia and damping coefficient will also return to normal to prevent the converter from lacking the ability to resist power grid frequency fluctuations and the decline of dynamic response ability.

[0185] According to the expression of the reactive power loop control, it can be known that the reactive power voltage regulation coefficient is a system parameter that can actively adjust the internal potential of the converter output. When the voltage regulation coefficient is certain, the reactive power bias is proportional to the internal potential bias of the converter output. Therefore, the converter can adjust its own output internal potential by adjusting the reactive power output at this time. Figure 6 The voltage-current phase diagrams of the converter before and after the grid transient voltage dip fault are given. Among them, I abc and I abc ′, V g and V g′ are the magnitudes of the three-phase output current of the converter and the grid voltage before and after the grid-side fault respectively, and X is the line reactance. In order to fully improve the voltage support ability of the converter during the transient voltage fault while ensuring that the output current is maintained at the maximum output current level as much as possible, the control expression for optimizing the reactive power loop coefficient is as follows:

[0186]

[0187] Among them, the D q0 represents the second reactive power voltage regulation coefficient value of the grid-forming converter under the steady state of the power grid; the D qfault represents the first reactive power voltage regulation coefficient value of the grid-forming converter under the power grid fault; the V g ′ represents the voltage magnitude of the grid-forming converter under the power grid fault; the I thresh represents the maximum allowable overcurrent value of the grid-forming converter; the X represents the line reactance of the line where the grid-forming converter is located. After the grid-side fault is cleared, the reactive power voltage regulation coefficient will recover after a certain delay to ensure the rapid recovery of the reactive power voltage regulation ability.

[0188] Step 305: Obtain the reference internal potential, output internal potential, and modulation angle required for the converter control according to the fault VSG control mode and the virtual impedance control model, and input the reference internal potential, output internal potential, and modulation angle into the SPWN modulation to obtain the control information of the converter.

[0189] In this embodiment, when the converter is controlled with reference to the virtual impedance control model shown in Figure 2 and the fault VSG control mode after optimizing the power coefficient, the structure diagram is as shown in Figure 7 shown.

[0190] With reference to Figure 7 , obtain the three-phase output voltage U oabc of the grid-forming converter, the three-phase output current i oabc and the three-phase inductor current i abc of the inductor; then perform dq coordinate system conversion on the three-phase output voltage U oabc , the three-phase output current i oabc and the three-phase inductor current i abc to obtain the two-phase output voltage U odq of the grid-forming converter, the two-phase output current i odq of the grid-forming converter and the two-phase inductor current i dq of the inductor;

[0191] Then, according to the two-phase output voltage U odq , the two-phase output current i odq , the updated virtual impedance J of the coefficient, and the active damping coefficient Dp and the reactive power regulation coefficient D q Calculate the real-time output active power P of the converter cal and the real-time output reactive power Q cal ; furthermore, input the real-time output active power P cal and the real-time output reactive power Q cal into the fault VSG control model after updating the coefficient, and obtain the modulation angle θ of the converter and the equivalent output internal potential V of the converter m .

[0192] Input the modulation angle θ of the converter and the equivalent output internal potential V of the converter m into the virtual impedance to obtain the reference internal potential required for SPWN modulation, and input the reference internal potential, the modulation angle θ and the equivalent output internal potential V of the converter m into the SPWN modulation to obtain the control information of the converter

[0193] Step 306: When it is detected that there is no fault in the power grid, control the converter based on the VSG control model

[0194] In a certain implementation manner of this embodiment, refer to Figure 3 the grid-forming converter control method shown in

[0195] Variable name Description Value <![CDATA[I thresh > Maximum allowable overcurrent value 100A <![CDATA[k VR > Virtual impedance resistance coefficient 1 <![CDATA[k VX > Virtual impedance reactance coefficient 0.3 <![CDATA[J0]]> Virtual inertia under steady-state operation 5 <![CDATA[J fault > Virtual inertia during grid-side fault 2 <![CDATA[D p0 > Active damping coefficient under steady-state operation 27 <![CDATA[D qfault > Active damping coefficient during grid-side fault 50 <![CDATA[D q0 > Reactive voltage regulation coefficient under steady-state operation 0.002 <![CDATA[P ref > Desired reference active power 29 kW <![CDATA[ω n > Reference angular frequency 314.15926 rad / s <![CDATA[V ref > Reference internal potential 390V

[0196] Refer to the parameter settings shown in the above table, set the grid-forming converter to be connected to the grid at 0s, and enter the stable state at about 1s. Set the power grid to have a transient voltage dip fault at 4s and the fault to be cleared at 5s

[0197] In this embodiment, the power, current and equivalent internal potential output by the converter under the traditional control method are referred to Figures 8 - 10 shown in Figures 8 - 10 . It can be seen from

[0198] that the traditional control method can achieve low-voltage ride-through control during the fault and limit the current level during the fault to 100A. However, after the fault is cleared, there is still a certain oscillation in the output current and power of the converter, and due to the transient voltage fault, the change range of the output power and equivalent output internal potential of the converter is large and the recovery time is long Figures 11 to 13As shown. It can be seen from the figure that the output current of the converter can still remain at the current level of 100 A during the fault. The difference is that, compared with the traditional control method, the method proposed in this embodiment can make the output current of the converter recover as soon as possible after the fault is eliminated without oscillation. At the same time, the oscillation of the output power of the converter is eliminated faster and the change amplitude is relatively smaller. In addition, the change amplitude of the equivalent internal potential of the converter output has also been significantly reduced. Obviously, the control method proposed in this embodiment improves the transient stability of the grid-forming converter system while not affecting the low-voltage ride-through control of the grid-forming converter.

[0199] A grid-forming converter ride-through control method based on power loop coefficient optimization proposed in this embodiment. On the basis of retaining the use of virtual impedance control for fault current limiting, the virtual inertia, active damping coefficient, and reactive voltage regulation coefficient inside the power loop are adjusted during the fault, effectively ensuring the overcurrent suppression of the converter during low-voltage ride-through and accelerating the attenuation of the oscillation that may be brought by the transient voltage drop fault, and improving the transient stability performance of the grid-forming converter to a certain extent.

[0200] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A grid-forming converter crossing control method based on power loop coefficient optimization, characterized in that Including: Based on a preset VSG control mode, the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid are obtained in real time; When a power grid fault is detected based on the output voltage, the active loop coefficient and reactive loop coefficient in the VSG control mode are adjusted based on the voltage amplitude of the grid-forming converter to obtain a fault VSG control mode with the adjusted active loop coefficient and reactive loop coefficient; Based on the output voltage, output current, and the fault VSG control mode, the modulation angle and output internal potential of the grid-forming converter under the power grid fault are obtained; The virtual impedance is calculated according to the inductor current, and the reference internal potential corresponding to the modulation angle and output internal potential is calculated according to the virtual voltage drop corresponding to the virtual impedance; The modulation angle and the output internal potential are modulated according to the reference internal potential to obtain a control signal, and the grid-forming converter is controlled according to the control signal.

2. The grid-forming converter crossing control method based on power loop coefficient optimization according to claim 1, characterized in that The step of obtaining the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid based on a preset VSG control mode in real time includes: When the power grid is in a steady state, the grid-forming converter is controlled based on a preset VSG control mode to collect the output voltage, output current, and inductor current of the inductor connected to the output side of the grid-forming converter in real time; wherein, the VSG control mode includes active loop control and reactive loop control; the calculation expression of the active loop control is: Among them, the P ref represents the expected reference active power of the network-forming converter; the J represents the virtual inertia introduced by the network-forming converter; the D p represents the active damping coefficient introduced by the network-forming converter; the ω n represents the reference angular frequency of the network-forming converter; the ω represents the real-time output angular frequency of the network-forming converter; the P cal represents the real-time output active power of the network-forming converter; The modulation angle input to the grid-forming converter is obtained by integrating the real-time output angular frequency; wherein, the calculation expression of the modulation angle is: θ = ∫ωdt wherein, θ represents the modulation angle of the grid-forming converter; The calculation expression of the reactive loop control is: V m = V ref + D q (Q ref - Q cal ) Among them, the V m represents the real-time output internal electromotive force of the network-forming converter; the V ref represents the reference internal electromotive force of the network-forming converter; the D q represents the reactive power regulation coefficient introduced by the network-forming converter; the Q ref represents the expected reference reactive power of the network-forming converter; the Q cal represents the real-time output reactive power of the network-forming converter.

3. The grid-forming converter crossing control method based on power loop coefficient optimization according to claim 2, characterized in that The step of obtaining the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid based on a preset VSG control mode in real time further includes: The three-phase output voltage, three-phase output current, and three-phase inductor current of the grid-forming converter are obtained, and the three-phase output voltage, three-phase output current, and three-phase inductor current are subjected to a rotating coordinate transformation according to the modulation angle to obtain two-phase output voltage, two-phase output current, and two-phase inductor current; wherein, the calculation expressions of the two-phase output voltage, two-phase output current, and two-phase inductor current are: Among them, the U oabc represents the three-phase output voltage of the grid-forming converter; the i oabc represents the three-phase output current of the grid-forming converter; the i abc represents the three-phase inductance current of the inductor; the U odq represents the two-phase output voltage of the grid-forming converter; the i odq represents the two-phase output current of the grid-forming converter; the i dq represents the two-phase inductance current of the inductor; the i0 represents the zero-sequence current.

4. A grid-forming converter crossing control method based on power loop coefficient optimization according to claim 3, characterized in that The step of obtaining the output voltage, output current, and inductor current of the grid-forming converter under the steady state of the power grid based on a preset VSG control mode in real time further includes: The real-time output active power and real-time output reactive power of the grid-forming converter are calculated according to the two-phase output voltage and the two-phase output current; wherein, the calculation expressions of the real-time output active power and real-time output reactive power are: Among them, the U od , U oq are respectively the voltage components corresponding to the two-phase output voltage U odq in the two-phase coordinate system; the i od , i oq are respectively the current components corresponding to the two-phase output current i odq in the two-phase coordinate system.

5. A grid-forming converter crossing control method based on power loop coefficient optimization according to claim 3, characterized in that The step of detecting that a power grid fault occurs based on the output voltage includes: The voltage of the capacitor connected to the output side of the grid-forming converter is obtained in real time according to the two-phase output voltage, and it is judged whether the power grid has a fault according to the voltage of the capacitor; wherein, the judgment condition of the fault is: Among them, the u cap represents the voltage of the capacitor; the V ref represents the reference internal electromotive force of the network-forming converter.

6. The grid-forming converter crossing control method based on power loop coefficient optimization according to claim 2, characterized in that The step of adjusting the active loop coefficient and reactive loop coefficient in the VSG control mode based on the voltage amplitude of the grid-forming converter includes: When it is determined that a power grid fault occurs, switch the virtual inertia in the active power loop control to a first virtual inertia value and switch the active power damping coefficient in the active power loop control to a first active power damping coefficient value; wherein, the virtual inertia includes a first virtual inertia value under power grid faults and a second virtual inertia value under power grid steady state; the active power damping coefficient includes a first active power damping coefficient value under power grid faults and a second active power damping coefficient value under power grid steady state; the first virtual inertia value is less than the second virtual inertia value; the first active power damping coefficient value is greater than the second active power damping coefficient value; The switching expressions of the virtual inertia and the active power damping coefficient are: Among them, the J0 represents the second virtual inertia value under the steady state of the power grid; the J fault represents the first virtual inertia value under the power grid fault; the D p0 represents the second active damping coefficient value under the steady state of the power grid; the D pfault represents the first active damping coefficient value under the power grid fault.

7. A grid-forming converter crossing control method based on power loop coefficient optimization according to claim 2, characterized in that The adjustment of the active power loop coefficient and the reactive power loop coefficient in the VSG control mode based on the voltage amplitude of the network-forming converter includes: When it is determined that a power grid fault occurs, determine a first reactive power voltage regulation coefficient value of the reactive power voltage regulation coefficient in the reactive power loop control according to the voltage amplitude of the network-forming converter; wherein, the calculation expression of the first reactive power voltage regulation coefficient value is: Among them, the D q0 represents the second reactive power voltage regulation coefficient value of the network-forming converter under steady-state grid conditions; the D qfault represents the first reactive power voltage regulation coefficient value of the network-forming converter under grid faults; the V g ' represents the voltage amplitude of the network-forming converter under grid faults; the I thresh represents the maximum allowable overcurrent value of the network-forming converter; the X represents the line reactance of the line where the network-forming converter is located.

8. A grid-forming converter crossing control method based on power loop coefficient optimization according to claim 1, characterized in that The calculation of the virtual impedance based on the inductor current and the calculation of the reference internal potential corresponding to the modulation angle and the output internal potential based on the virtual voltage drop corresponding to the virtual impedance include: When it is determined that the power grid is in a fault state, start a preset virtual impedance control mode, and input the modulation angle and the output internal potential into the virtual impedance control mode to obtain the virtual impedance and the reference internal potential based on the virtual impedance control mode; wherein, the calculation expression of the virtual impedance control mode is: Among them, the k VR and k VX represent preset virtual impedance coefficients; the R vir and X vir represent the virtual impedance; the V dir and V qir are virtual voltage drops corresponding to the virtual impedance; the Edref and Eqref represent the reference internal electromotive potential.

9. The grid-forming converter crossing control method based on power loop coefficient optimization according to claim 8, wherein, The modulation of the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal and the control of the network-forming converter according to the control signal include: Perform sinusoidal pulse width modulation on the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal for controlling the network-forming converter; Control the network-forming converter according to the control signal.

10. A grid-forming converter crossing control method based on power loop coefficient optimization according to any one of claims 1-9, characterized in that, The modulation of the modulation angle and the output internal potential according to the reference internal potential to obtain a control signal and the control of the network-forming converter according to the control signal further include: When it is detected from the output voltage that there is no power grid fault, obtain the modulation angle and the output internal potential of the network-forming converter under power grid steady state based on the VSG control mode; Perform sinusoidal pulse width modulation on the modulation angle and the output internal potential to obtain a control signal for controlling the network-forming converter, and control the network-forming converter according to the control signal.

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