Transient stability recovery method and device for multi-converter grid-connected system, terminal equipment and storage medium

Abstract

The invention discloses a transient stability recovery method and device of a multi-converter grid-connected system, terminal equipment and a storage medium, and relates to the field of control of power electronic equipment grid-connected systems. The method comprises the following steps: acquiring power data of a grid-connected system, and calculating to obtain a first power angle of a grid-forming converter at a stable working point and a second power angle of a grid-following converter; after the fault occurs, obtaining the power grid fault voltage during the fault period and the grid following fault output current of the grid following type converter, and calculating the active power reference value of the grid constructing type converter and the output phase value of the grid following type converter; and according to the active power reference value and the output phase value, adjusting the active power output of the grid-forming converter and the output phase of the grid-following converter. By implementing the method and the device, the problem that in the prior art, transient stability cannot be realized after a series-parallel grid-connected system comprising a network constructing type converter and a network following type converter breaks down can be solved.

Description

Technical Field

[0001] The present invention relates to the field of control of power electronic equipment grid-connected systems, and particularly to a transient stability recovery method, device, terminal device and storage medium for a multi-converter grid-connected system. Background Technique

[0002] New energy sources such as wind power and photovoltaic power will become the main forms of future newly added power sources. With the continuous increase in the installed capacity of new energy, the grid form dominated by traditional synchronous machines is changing. As the direct interface between new energy power generation equipment and the grid and load, the converter greatly affects the safe, stable and efficient operation of the entire new energy power generation system.

[0003] In actual grid-connected systems, there are a large number of scenarios where grid-forming converters and grid-following converters operate in parallel to meet different system requirements at the same time. However, due to the complex interaction between grid-forming converters and grid-following converters in the prior art, the transient stability analysis of the hybrid system is more difficult. Therefore, there is a problem that it is difficult for the hybrid system to recover transient stability after a fault occurs. Summary of the Invention

[0004] The present invention provides a transient stability recovery method, device, terminal device and storage medium for a multi-converter grid-connected system, which can solve the problem in the prior art that it is impossible to make a hybrid system including a grid-forming converter and a grid-following converter recover transient stability after a fault occurs.

[0005] An embodiment of the present invention provides a transient stability recovery method for a multi-converter grid-connected system, including:

[0006] Obtain the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the grid-forming converter, the damping coefficient of the grid-forming converter, the grid angular frequency, the grid-forming output angular frequency of the grid-forming converter, the grid-forming equivalent output voltage of the grid-forming converter, the grid voltage, the grid-forming output inductor of the grid-forming converter, the grid line inductor, the grid-following output angular frequency of the grid-following converter, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the grid-following output current of the grid-following converter, and the phase angle of the grid-following output current;

[0007] According to the power data, calculate the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point;

[0008] After a fault occurs, obtain the grid fault voltage during the fault and the grid-following fault output current of the grid-following converter;

[0009] Calculate the reference value of the active power of the grid-forming converter based on the first power angle, the second power angle, the grid fault voltage, the grid-connected fault output current, the grid angular frequency, the grid-forming equivalent output voltage, the grid-forming output inductor, and the grid line inductor;

[0010] Calculate the output phase value of the grid-connected converter based on the first power angle, the second power angle, the grid-forming equivalent output voltage, the grid-forming output inductor, the grid line inductor, and the grid fault voltage;

[0011] Adjust the active power output of the grid-forming converter and the output phase of the grid-connected converter according to the reference value of the active power and the output phase value to restore the transient stability of the grid-connected system.

[0012] Further, the calculation of the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-connected converter at the stable operating point according to the power data includes:

[0013] Construct the transient analysis equations of the grid-forming converter and the grid-connected converter according to the power data;

[0014] Solve the transient analysis equations to obtain the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-connected converter at the stable operating point.

[0015] Further, the construction of the transient analysis equations of the grid-forming converter and the grid-connected converter according to the power data includes:

[0016] Construct the swing equation of the grid-forming converter according to the grid angular frequency, the grid-forming output angular frequency, the virtual inertia coefficient, the damping coefficient, the grid-forming equivalent output voltage, the grid voltage, the grid-forming output inductor, the grid line inductor, the grid-connected output current, and the grid-connected output current phase angle;

[0017] Construct the swing equation of the grid-connected converter according to the grid-connected output angular frequency, the grid angular frequency, the PLL proportional coefficient, the PLL integral coefficient, the grid line inductor, the grid-forming output inductor, the grid-forming equivalent output voltage, the grid voltage, the grid-connected output current, and the grid-connected output current phase angle;

[0018] Obtain the transient analysis equations according to the swing equation of the grid-forming converter and the swing equation of the grid-connected converter.

[0019] Further, the calculation of the output phase value of the grid-connected converter based on the first power angle, the second power angle, the grid-forming equivalent output voltage, the grid-forming output inductor, the grid line inductor, and the grid fault voltage includes:

[0020] Based on the first power angle, the second power angle, the grid fault voltage, the equivalent grid-connected output voltage, the grid line inductance, and the grid-connected output inductance, an expression for the d-axis component of the grid-following fault output current during a fault is constructed.

[0021] Set the d-axis component of the grid-following fault output current to 0, solve the expression, and obtain the output phase value.

[0022] Based on the above method embodiments, the present invention correspondingly provides apparatus embodiments.

[0023] The present invention provides a transient stability recovery device for a multi-converter grid-connected system, including:

[0024] A power data acquisition module, a power angle calculation module, a fault data acquisition module, an active power reference value calculation module, an output phase value calculation module, and a parameter adjustment module;

[0025] The power data acquisition module is configured to acquire the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the grid-forming converter, the damping coefficient of the grid-forming converter, the grid angular frequency, the grid-connected output angular frequency of the grid-forming converter, the equivalent grid-connected output voltage of the grid-forming converter, the grid voltage, the grid-connected output inductance of the grid-forming converter, the grid line inductance, the grid-connected output angular frequency of the grid-following converter, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the grid-following output current of the grid-following converter, and the phase angle of the grid-following output current.

[0026] The power angle calculation module is configured to calculate, according to the power data, the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

[0027] The fault data acquisition module is configured to acquire, after a fault occurs, the grid fault voltage during the fault and the grid-following fault output current of the grid-following converter.

[0028] The active power reference value calculation module is configured to calculate, according to the first power angle, the second power angle, the grid fault voltage, the grid-following fault output current, the grid angular frequency, the equivalent grid-connected output voltage, the grid-connected output inductance, and the grid line inductance, the active power reference value of the grid-forming converter.

[0029] The output phase value calculation module is configured to calculate, according to the first power angle, the second power angle, the equivalent grid-connected output voltage, the grid-connected output inductance, the grid line inductance, and the grid fault voltage, the output phase value of the grid-following converter.

[0030] The parameter adjustment module is used to adjust the active power output of the grid-forming converter and the output phase of the grid-following converter according to the active power reference value and the output phase value, so as to restore the transient stability of the grid-connected system.

[0031] Further, the power angle calculation module includes:

[0032] A transient analysis equation construction unit and a power angle calculation unit;

[0033] The transient analysis equation construction unit is used to construct transient analysis equations for the grid-forming converter and the grid-following converter according to the power data.

[0034] The power angle calculation unit is used to solve the transient analysis equations to obtain the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

[0035] Further, the transient analysis equation construction unit includes:

[0036] A grid-forming converter swing equation construction subunit, a grid-following converter swing equation construction subunit, and a transient equation generation subunit;

[0037] The grid-forming converter swing equation construction subunit is used to construct the swing equation of the grid-forming converter according to the grid angular frequency, the grid-forming output angular frequency, the virtual inertia coefficient, the damping coefficient, the grid-forming equivalent output voltage, the grid voltage, the grid-forming output inductor, the grid line inductor, the grid-following output current, and the grid-following output current phase angle.

[0038] The grid-following converter swing equation construction subunit is used to construct the swing equation of the grid-following converter according to the grid-following output angular frequency, the grid angular frequency, the PLL proportional coefficient, the PLL integral coefficient, the grid line inductor, the grid-forming output inductor, the grid-forming equivalent output voltage, the grid voltage, the grid-following output current, and the grid-following output current phase angle.

[0039] The transient equation generation subunit is used to obtain the transient analysis equation according to the swing equation of the grid-forming converter and the swing equation of the grid-following converter.

[0040] Further, the output phase value calculation module includes:

[0041] A component current expression construction unit and an expression solving unit;

[0042] The component current expression construction unit is configured to construct an expression for the d-axis component of the grid-following fault output current during a fault based on the first power angle, the second power angle, the grid fault voltage, the grid-forming equivalent output voltage, the grid line inductance, and the grid-forming output inductance;

[0043] The expression solving unit is configured to set the d-axis component of the grid-following fault output current to 0, solve the expression, and obtain the output phase value.

[0044] Based on the above method item embodiments, the present invention correspondingly provides a terminal device item embodiment;

[0045] The present invention provides a terminal device, including a processor, a memory, and a computer program stored in the above memory and configured to be executed by the above processor. When the above processor executes the above computer program, it implements a transient stability recovery method for a multi-converter grid-connected system according to any embodiment of the present invention.

[0046] Based on the above method item embodiments, the present invention correspondingly provides a storage medium item embodiment;

[0047] The present invention provides a storage medium, including a processor, a memory, and a computer program stored in the above memory and configured to be executed by the above processor. When the above processor executes the above computer program, it implements a transient stability recovery method for a multi-converter grid-connected system according to any embodiment of the present invention.

[0048] The embodiments of the present invention have the following beneficial effects:

[0049] The present invention provides a transient stability recovery method, device, terminal device and storage medium for a multi-converter grid-connected system. The above method includes: First, obtain the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the network-forming converter, the damping coefficient of the network-forming converter, the grid angular frequency, the network-forming output angular frequency of the network-forming converter, the network-forming equivalent output voltage of the network-forming converter, the grid voltage, the network-forming output inductor of the network-forming converter, the grid line inductor, the following-network output angular frequency of the following-network converter, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the following-network output current of the following-network converter, and the phase angle of the following-network output current; Subsequently, according to the power data, calculate the first power angle of the network-forming converter at the stable operating point and the second power angle of the following-network converter at the stable operating point; Then, after a fault occurs, obtain the grid fault voltage during the fault and the following-network fault output current of the following-network converter; Then, according to the first power angle, the second power angle, the grid fault voltage, the following-network fault output current, the grid angular frequency, the network-forming equivalent output voltage, the network-forming output inductor, and the grid line inductor, calculate the reference value of the active power of the network-forming converter; Subsequently, according to the first power angle, the second power angle, the network-forming equivalent output voltage, the network-forming output inductor, the grid line inductor, and the grid fault voltage, calculate the output phase value of the following-network converter; Finally, according to the reference value of the active power and the output phase value, adjust the active power output of the network-forming converter and the output phase of the following-network converter to restore the transient stability of the grid-connected system. Since in a grid-connected system, it is usually to reduce the accelerating area during a fault or increase the decelerating area after the fault recovery to make the system stable, and the essence of reducing the accelerating area during a fault is to reduce the power deviation during the fault. Therefore, the present invention compensates for the power deviation of the network-forming converter by adjusting and correcting the reference value of the active power of the network-forming converter, and at the same time sets the output phase of the following-network converter to eliminate the influence of the coupling term in the system to achieve the transient stability of the system. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions of the present application, the drawings required for the embodiments 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, without creative efforts, other drawings can be obtained based on these drawings.

[0051] Figure 1 It is a flowchart of a transient stability recovery method for a multi-converter grid-connected system provided by an embodiment of the present invention.

[0052] Figure 2 It is a schematic diagram of the main circuit topology of a multi-converter grid-connected system provided by an embodiment of the present invention.

[0053] Figure 3 It is the schematic diagram of the converter control link provided by an embodiment of the present invention.

[0054] Figure 4 It is the equivalent circuit diagram of the grid-connected system provided by an embodiment of the present invention.

[0055] Figure 5 It is the schematic diagram of the virtual synchronous control provided by an embodiment of the present invention.

[0056] Figure 6 It is the schematic diagram of the equal area method considering damping influence provided by an embodiment of the present invention.

[0057] Figure 7 It is the schematic diagram of the transient control switching module provided by an embodiment of the present invention.

[0058] Figure 8 It is the frequency response curve of the grid-forming converter provided by an embodiment of the present invention.

[0059] Figure 9 It is the frequency response curve of the grid-following converter provided by an embodiment of the present invention.

[0060] Figure 10 It is the structural schematic diagram of a transient stability recovery device for a multi-converter grid-connected system provided by an embodiment of the present invention. Detailed implementation manners

[0061] 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 in conjunction with the accompanying drawings in the embodiments of this application. Apparently, 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 creative efforts shall fall within the protection scope of this application.

[0062] 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 accompanying drawing descriptions are intended to cover non-exclusive inclusion.

[0063] 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 specifying 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.

[0064] Reference to "embodiment" in this document means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The phrase appearing at various positions in the specification 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 explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0065] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally represents an "or" relationship between the associated objects before and after.

[0066] In the description of the embodiments of this application, the term "plurality" 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).

[0067] In the description of the embodiments of this application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. 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 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 this application can be understood according to specific situations.

[0068] See Figure 1 , to solve the problem in the prior art that the hybrid system including a grid-forming converter and a grid-following converter cannot restore transient stability after a fault occurs, a method for restoring transient stability of a multi-converter grid-connected system provided by an embodiment of the present invention includes:

[0069] Step S101: Obtain the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the grid-forming converter, the damping coefficient of the grid-forming converter, the grid angular frequency, the grid-forming output angular frequency of the grid-forming converter, the grid-forming equivalent output voltage of the grid-forming converter, the grid voltage, the grid-forming output inductor of the grid-forming converter, the grid line inductor, the grid-following output angular frequency of the grid-following converter, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the grid-following output current of the grid-following converter, and the phase angle of the grid-following output current.

[0070] Specifically, the above power data are the data under the steady state of the grid-connected system, which can be obtained through actual measurement or preset according to the actual situation.

[0071] Step S102: Calculate the first power angle of the network-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point according to the power data;

[0072] In a preferred embodiment, the calculating the first power angle of the network-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point according to the power data includes:

[0073] Construct transient analysis equations for the network-forming converter and the grid-following converter according to the power data;

[0074] Solve the transient analysis equations to obtain the first power angle of the network-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

[0075] Specifically, the above transient analysis equations are shown as follows:

[0076]

[0077] In the formula, represents the first derivative of the power angle of the network-forming converter with respect to time, that is, ω1 represents the angular frequency deviation of the network-forming converter, ω n represents the grid angular frequency, ω VSG represents the network-forming output angular frequency, represents the second derivative of the power angle of the network-forming converter with respect to time, that is, J p represents the virtual inertia coefficient, T0 represents the mechanical torque of the network-forming converter, and its calculation formula is: T0 = P0 / ω n , P0 represents the power command of the network-forming converter, E represents the equivalent network-forming output voltage, U g represents the grid voltage, X1 represents the output reactance of the network-forming converter, X g represents the equivalent grid reactance, and its calculation formula is: X g ≈j(ω1 + ω n )L g , L g represents the grid line inductance, δ1 represents the phase deviation between the output voltage of the network-forming converter and the grid voltage, δ2 represents the phase deviation between the output voltage of the grid-following converter and the grid voltage, θ PCC represents the phase deviation of the PCC point voltage relative to the grid voltage, and obviously θ PCC = δ2, I d represents the grid-following output current at θPCC The d-axis component in the dq coordinate system with reference, and its calculation formula is: I2 represents the effective value corresponding to the vector of the grid-connected output current, represents the phase angle of the grid-connected output current, I q represents the grid-connected output current in the d-axis component in the dq coordinate system with θ PCC as reference, and its calculation formula is: D p represents the damping coefficient of the grid-forming converter, represents the first derivative of the power angle of the grid-following converter with respect to time, that is ω2 represents the angular frequency deviation of the grid-following converter, ω PLL represents the grid-connected output angular frequency, represents the second derivative of the power angle of the grid-following converter with respect to time, that is K i represents the PLL integral coefficient, K p represents the PLL proportional coefficient, L t represents L1 / / L g .

[0078] Specifically, let and in the above transient analysis equation be 0, take the obtained δ1 as the above first power angle, and take the obtained δ2 as the above second power angle. It can be seen from the above transient analysis equation that the parallel connection of two machines will generate interactive power and voltage drop coupling terms, thereby affecting the power balance characteristics of the two machines respectively.

[0079] Schematically, the schematic diagram of the main circuit topology of the multi-converter grid-connected system is as Figure 2 shown, Figure 2 The L in f represents the filter inductor, i GMF represents the output current of the grid-forming converter, U GMF represents the terminal voltage of the grid-forming converter, i GFL represents the output current of the grid-following converter, U GFL represents the terminal voltage of the grid-following converter.

[0080] Schematically, the schematic diagram of the converter control link is as Figure 3 shown, Figure 3 The a part in Figure 3 represents the active loop and reactive loop control schematic diagram of a typical grid-forming converter, and the b part represents the PLL schematic diagram adopted by a typical grid-following converter. ref The θ in represents the power angle, ω represents the angular frequency, P represents the input active power, P ref represents the active power reference value, represents the capacitor voltage reference value, V cnRepresents the rated capacitance voltage, Q ref Represents the reactive power reference, Q represents the input reactive power, θ PLL Represents the phase of the output voltage of the grid-connected converter (i.e., the voltage at the coupling point of the grid), u PCCd Represents the d-axis component of the voltage at the coupling point of the grid, u PCCq Represents the q-axis component of the voltage at the coupling point of the grid. The active power loop of the grid-forming converter adopts the most common virtual synchronous control, simulating the swing equation of the synchronous machine to spontaneously provide inertia support; the reactive power loop adopts the basic droop control for easy analysis. The grid-connected converter uses a phase-locked loop to obtain the phase angle signal of the grid voltage at the connection point, and then controls the output phase of the grid-connected converter to track the phase of the grid voltage at the connection point. When a deep voltage dip fault occurs in the power grid, the grid-connected converter will immediately enter the low-voltage ride-through stage and adopt a single current loop control mode to meet the requirement of rapid reactive current injection in the grid connection guidelines. However, changing the injected current only improves the transient stability to a certain extent and cannot maintain the safe and stable operation of the system under severe fault conditions. Therefore, in order to improve the transient stability ability of the hybrid system, it is necessary to propose corresponding optimization strategies according to its transient stability mechanism.

[0081] In this preferred embodiment, a transient analysis equation is constructed through various power data, and then solved to obtain the first power angle and the second power angle.

[0082] In another preferred embodiment, constructing the transient analysis equations of the grid-forming converter and the grid-connected converter according to the power data includes:

[0083] Constructing the swing equation of the grid-forming converter according to the grid angular frequency, grid-forming output angular frequency, virtual inertia coefficient, damping coefficient, grid-forming equivalent output voltage, grid voltage, grid-forming output inductance, grid line inductance, grid-connected output current, and grid-connected output current phase angle;

[0084] Schematically, the equivalent circuit diagram of the grid-connected system is as Figure 4 shown. According to Figure 4 the equivalent circuit diagram shown, the nodal current equation is obtained:

[0085]

[0086] In the formula, and respectively represent the injection currents of "node 1", "node 2", and "node 3", Y1 represents Figure 4 the line admittance between "node 1" and "node 2" in Figure 4 and Y2 represents the line admittance between "node 2" and "node 3" in Denote the phase voltage corresponding to the grid-forming converter equivalent to a voltage source. Denote the grid voltage.

[0087] Specifically, according to the above node current equation, the output current expression of the grid-forming converter can be obtained:

[0088]

[0089] In the formula, Denote the grid-connected voltage.

[0090] Specifically, furthermore, the output power of the grid-forming converter can be obtained:

[0091]

[0092] In the formula, P e Denote the active output power of the grid-forming converter, Q e Denote the reactive output power of the grid-forming converter, Denote the conjugate of the current injected into "Node 1".

[0093] Schematically, the schematic diagram of virtual synchronous control is as shown in Figure 5 According to Figure 5 , the swing equation of the grid-forming converter analogous to a synchronous machine can be obtained:

[0094]

[0095] According to the grid-following output angular frequency, grid angular frequency, PLL proportional coefficient, PLL integral coefficient, grid line inductance, grid-forming output inductance, grid-forming equivalent output voltage, grid voltage, grid-following output current, and grid-following output current phase angle, the swing equation of the grid-following converter is constructed;

[0096] Schematically, according to Figure 4 Write out the grid-connected voltage expression at the point of common coupling:

[0097]

[0098] In the formula, X t Denote the equivalent impedance formed by the parallel connection of the output impedance of the grid-forming converter and the grid line impedance, and its calculation formula is: X t = j(ω2 + ω n )L t , L t Denote the inductance of the above equivalent impedance, and its calculation formula is: L t = L1 / / L g , L1 denotes the grid-forming output inductance.

[0099] Specifically, at θpcc For the abc / dq coordinate transformation with the reference d-axis, the q-axis component of the grid-connected voltage can be further obtained as follows:

[0100]

[0101] In the formula, U PCCq represents the q-axis component of the grid-connected voltage.

[0102] Schematically, according to the principle of the phase-locked loop, the expression of the phase-locked loop principle can be obtained as:

[0103]

[0104] In the formula, since the phase at the coupling point is the output power angle of the phase-locked loop of the grid-following converter, then θ PCC = δ2, represents the second derivative of the power angle of the grid-following converter with respect to time, that is

[0105] Specifically, based on the above expression of the q-axis component of the grid-connected voltage, its derivative expression can be derived as:

[0106]

[0107] Specifically, substituting the above derivative expression into the above phase-locked loop equation, the swing equation of the grid-following converter analogous to the synchronous machine is obtained:

[0108]

[0109] According to the swing equation of the network-forming converter and the swing equation of the grid-following converter, the transient analysis equation is obtained.

[0110] In this preferred embodiment, by respectively constructing the swing equations of the grid-following converter and the network-forming converter, the transient analysis equation is obtained.

[0111] Step S103: After the fault occurs, obtain the grid fault voltage during the fault and the grid-following fault output current of the grid-following converter;

[0112] Specifically, when a voltage dip is detected, it indicates that a fault has occurred at this time. Based on the known equivalent swing equation, the common qualitative transient analysis method is the equal area method. The schematic diagram of the equal area method considering the damping effect is as Figure 6 shown, Figure 6 where the abscissa represents the power angle and the ordinate is the power, δ o represents the initial stable power angle, δ c represents the power angle corresponding to the fault recovery moment, δ m represents the maximum power angle that can be reached during the transient process, Pref Represents the active power reference value of the network-forming converter and the equivalent active reference value of the grid-following converter, P el Represents the active power of the network-forming converter, P eq Represents the equivalent active power of the grid-following converter. A common optimization strategy is to reduce the accelerating area during a fault or increase the decelerating area after fault recovery, so that the system can quickly return to the stable operating point.

[0113] Step S104: Calculate the active power reference value of the network-forming converter according to the first power angle, the second power angle, the grid fault voltage, the grid-following fault output current, the grid angular frequency, the network-forming equivalent output voltage, the network-forming output inductor, and the grid line inductor;

[0114] Specifically, since the bandwidth of the voltage-current double inner loop is much larger than that of the outer loop, the inner loop is considered ideal during transient stability analysis, that is, the actual value is equal to the reference value. The calculation formula for the above active power reference value is:

[0115]

[0116] In the formula, P refF Represents the grid fault voltage, I dF Represents the d-axis component of the grid-following fault output current, I qF Represents the q-axis component of the grid-following fault output current, δ 10 Represents the first power angle, δ 20 Represents the second power angle.

[0117] Preferably, the essence of reducing the accelerating area during a fault is to reduce the power deviation during the fault. In terms of the network-forming converter, the power deviation is the fundamental cause of synchronous instability. Therefore, compensating for the power shortage by correcting the active power reference value during the fault can effectively alleviate the oscillation.

[0118] Step S105: Calculate the output phase value of the grid-following converter according to the first power angle, the second power angle, the network-forming equivalent output voltage, the network-forming output inductor, the grid line inductor, and the grid fault voltage;

[0119] In a preferred embodiment, the calculating the output phase value of the grid-following converter according to the first power angle, the second power angle, the network-forming equivalent output voltage, the network-forming output inductor, the grid line inductor, and the grid fault voltage includes:

[0120] Construct an expression for the d-axis component of the grid-following fault output current during the fault according to the first power angle, the second power angle, the grid fault voltage, the network-forming equivalent output voltage, the grid line inductor, and the network-forming output inductor;

[0121] Specifically, during the fault, let UPCCq = 0, which is equivalent to making the equivalent power deficit of the grid-connected converter zero, and then the I during the fault can be changed dF to eliminate U PCCq . The expression for the d-axis component of the grid-connected fault output current is:

[0122]

[0123] Let the d-axis component of the grid-connected fault output current be 0, solve the above expression, and obtain the output phase value.

[0124] Specifically, when the degree of voltage sag increases, in order to meet the current limiting requirement, simply reducing I dF cannot eliminate the power deviation, and when a deep voltage drop occurs, according to the grid connection guidelines, pure reactive current should be injected to provide effective reactive power support. Therefore, during the fault, let I dF = 0, and the influence of the coupling term is eliminated by setting the output phase of the grid-connected converter:

[0125]

[0126] In the formula, γ represents the output phase value.

[0127] Specifically, the output phase of the original grid-connected converter is generated by a phase-locked loop. During the fault, let I dF = 0. Through mathematical transformation of the formula, the final γ value will be obtained as the final output phase value to replace the output of the phase-locked loop as the phase output of the grid-connected converter.

[0128] In this preferred embodiment, the output phase value of the grid-connected converter is calculated through the first power angle, the second power angle, the equivalent output voltage of the network-forming, the network-forming output inductor, the grid line inductor, and the grid fault voltage.

[0129] Step S106: According to the active power reference value and the output phase value, adjust the active power output of the network-forming converter and the output phase of the grid-connected converter to restore the transient stability of the grid-connected system.

[0130] Specifically, by dynamically correcting the active reference value of the network-forming converter, the active power deviation during the fault is compensated; using the calculated γ to replace the output of the phase-locked loop as the phase output of the grid-connected converter eliminates the influence of the coupling term in the system, and at the same time further enables the system to quickly restore transient stability.

[0131] Schematically, taking a system with two network-forming converters and a grid-connected converter in parallel as an example, a simulation study is carried out, and the system parameters are shown in the following table:

[0132]

[0133]

[0134] When the grid voltage drops to 44V at t = 3s and the fault duration is 0.5s, a transient voltage drop disturbance occurs in the simulation system.

[0135] Specifically, the schematic diagram of the transient control switching module of the grid-forming / grid-following converter during the fault is as Figure 7 shown, Figure 7 In part c of [figure number] is the schematic diagram of the active power reference control switching of the grid-forming converter during the fault. In part d of [figure number] is the schematic diagram of changing the injected current according to the grid connection guidelines of the grid-following converter during the fault. In part e of [figure number] is the schematic diagram of the control switching of the output phase angle of the grid-following converter during the fault. Figure 7 The P in [figure number] ref0 represents the active power reference value of the grid-forming converter during normal operation, v cd represents the d-axis component of the capacitor voltage, represents the d-axis capacitor voltage command value, represents the q-axis capacitor voltage command value, v cq represents the q-axis component of the capacitor voltage, represents the d-axis command value of the output current of the grid-forming converter, i d0 represents the command value of the d-axis output current of the grid-forming converter during normal operation, i q0 represents the command value of the q-axis output current of the grid-forming converter during normal operation, represents the q-axis command value of the output current of the grid-forming converter.

[0136] Schematically, the frequency response curve of the grid-forming converter is as Figure 8 shown, and the frequency response curve of the grid-following converter is as Figure 9 shown. Figure 8 And Figure 9 "Scenario 1" in [figure number] represents the scenario where the grid-connected system does not adopt the transient stability recovery method provided by the present invention. The phase-locked loop structure and parameter settings are as follows: The grid-forming converter does not adopt control switching, and the grid-following converter only adopts the control switching shown in part d of [figure number] and changes the injected current in accordance with the grid connection guidelines; "Scenario 2" represents the scenario where the grid-connected system adopts the transient stability recovery method provided by the present invention. The phase-locked loop structure and parameter settings are as follows: The grid-forming converter adopts the control switching shown in part c of [figure number], and the grid-following converter simultaneously adopts the control switching shown in part d of [figure number] and Figure 7 in [figure number], and Figure 7 in [figure number], and Figure 7 in part d of [figure number] and Figure 7The control switching shown in the e - diagram part in adopts the transient stability improvement method proposed by the present invention. When the voltage drops deeply to 44V (0.2p.u.) at 3 - 3.5s, in "Scenario 1", both the grid - forming converter and the grid - following converter lose transient synchronous stability after the fault recovery and cannot operate stably at the rated frequency of 50Hz; in "Scenario 2", both the grid - forming converter and the grid - following converter can quickly recover stability, achieve fault ride - through, and the transient stability is significantly improved. Therefore, the present invention can effectively improve the transient stability of the grid - connected system of multiple grid - following / grid - forming converters.

[0137] Based on the above - mentioned method - item embodiments, the present invention correspondingly provides device - item embodiments.

[0138] As Figure 10 shown, based on the above - mentioned method - item embodiments, corresponding device - item embodiments are provided;

[0139] An embodiment of the present invention provides a transient stability recovery device for a multi - converter grid - connected system, including:

[0140] a power data acquisition module, a power angle calculation module, a fault data acquisition module, an active power reference value calculation module, an output phase value calculation module, and a parameter adjustment module;

[0141] The power data acquisition module is used to acquire the power data of the grid - connected system; wherein, the power data includes: the virtual inertia coefficient of the grid - forming converter, the damping coefficient of the grid - forming converter, the grid angular frequency, the grid - forming output angular frequency of the grid - forming converter, the grid - forming equivalent output voltage of the grid - forming converter, the grid voltage, the grid - forming output inductor of the grid - forming converter, the grid line inductor, the grid - following output angular frequency of the grid - following converter, the PLL proportional coefficient, the PLL integral coefficient, the grid - following output current of the grid - following converter, and the grid - following output current phase angle;

[0142] The power angle calculation module is used to calculate the first power angle of the grid - forming converter at the stable operating point and the second power angle of the grid - following converter at the stable operating point according to the power data;

[0143] The fault data acquisition module is used to acquire the grid fault voltage during the fault and the grid - following fault output current of the grid - following converter after the fault occurs;

[0144] The active power reference value calculation module is used to calculate the active power reference value of the grid - forming converter according to the first power angle, the second power angle, the grid fault voltage, the grid - following fault output current, the grid angular frequency, the grid - forming equivalent output voltage, the grid - forming output inductor, and the grid line inductor;

[0145] The output phase value calculation module is used to calculate the output phase value of the grid-following converter according to the first power angle, the second power angle, the equivalent output voltage of the grid-forming network, the grid-forming output inductor, the grid line inductor, and the grid fault voltage;

[0146] The parameter adjustment module is used to adjust the active power output of the grid-forming converter and the output phase of the grid-following converter according to the active power reference value and the output phase value, so as to restore the transient stability of the grid-connected system.

[0147] In a preferred embodiment, the power angle calculation module includes:

[0148] A transient analysis equation construction unit and a power angle calculation unit;

[0149] The transient analysis equation construction unit is used to construct the transient analysis equations of the grid-forming converter and the grid-following converter according to the power data;

[0150] The power angle calculation unit is used to solve the transient analysis equations to obtain the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

[0151] In another preferred embodiment, the transient analysis equation construction unit includes:

[0152] A grid-forming converter swing equation construction subunit, a grid-following converter swing equation construction subunit, and a transient equation generation subunit;

[0153] The grid-forming converter swing equation construction subunit is used to construct the swing equation of the grid-forming converter according to the grid angular frequency, the grid-forming output angular frequency, the virtual inertia coefficient, the damping coefficient, the grid-forming equivalent output voltage, the grid voltage, the grid-forming output inductor, the grid line inductor, the grid-following output current, and the grid-following output current phase angle;

[0154] The grid-following converter swing equation construction subunit is used to construct the swing equation of the grid-following converter according to the grid-following output angular frequency, the grid angular frequency, the PLL proportional coefficient, the PLL integral coefficient, the grid line inductor, the grid-forming output inductor, the grid-forming equivalent output voltage, the grid voltage, the grid-following output current, and the grid-following output current phase angle;

[0155] The transient equation generation subunit is used to obtain the transient analysis equation according to the swing equation of the grid-forming converter and the swing equation of the grid-following converter.

[0156] In another preferred embodiment, the output phase value calculation module includes:

[0157] Component current expression construction unit and expression solving unit;

[0158] The component current expression construction unit is configured to construct an expression for the d-axis component of the grid-following fault output current during a fault according to the first power angle, the second power angle, the grid fault voltage, the grid-forming equivalent output voltage, the grid line inductance, and the grid-forming output inductance;

[0159] The expression solving unit is configured to set the d-axis component of the grid-following fault output current to 0 and solve the expression to obtain the output phase value.

[0160] It can be understood that the above device item embodiments correspond to the method item embodiments of the present invention, and can implement the transient stability recovery method for a multi-converter grid-connected system provided by any one of the above method item embodiments of the present invention.

[0161] It should be noted that the device embodiments described above 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 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 it without creative work.

[0162] Based on the above embodiments of the transient stability recovery method for a multi-converter grid-connected system, 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 the transient stability recovery method for a multi-converter grid-connected system according to any one of the embodiments of the present invention.

[0163] Exemplarily, in this embodiment, the above computer program can be divided into one or more modules. The above one or more modules are stored in the above memory and executed by the above processor to complete the present invention. The above one or more module elements can be a series of computer program instruction segments capable of completing specific functions, and the instruction segments are used to describe the execution process of the above computer program in the above device;

[0164] The above terminal device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The above device may include, but is not limited to, a processor and a memory;

[0165] The so-called processor may be a central processing module (Central Processing Unit, CPU), or may also be other general-purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field-programmable gate arrays (Field-Programmable Gate Array, FPGA), 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 above-mentioned processor is the control center of the above-mentioned device, and connects various parts of the entire device through various interfaces and lines;

[0166] The above-mentioned memory can be used to store the above-mentioned computer programs and / or modules. The above-mentioned processor realizes various functions of the above-mentioned device by running or executing the computer programs and / or modules stored in the above-mentioned memory, and by calling the data stored in the memory. The above-mentioned memory mainly includes a program storage area and a data storage area. Among them, the program storage area can store an operating system, application programs required for at least one function, etc.; In addition, the memory may include high-speed random access memory, and may also include non-volatile memory, such as hard disks, memory, plug-in hard disks, smart media cards (Smart Media Card, SMC), secure digital (Secure Digital, SD) cards, flash memory cards (Flash Card), at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage devices.

[0167] 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 the transient stability recovery method of a multi-converter grid-connected system described in any one of the above method item embodiments of the present invention.

[0168] In this embodiment, the above storage medium is a computer-readable storage medium, the above computer program includes computer program code, and the above computer program code may be in the form of source code, object code, executable file, or some intermediate form, etc. The above computer-readable medium may include: any entity or device capable of carrying the above computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0169] The above are the preferred embodiments 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 transient stability restoration method for a multi-converter grid-connected system, characterized in that, Including: Obtain the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the grid-forming converter, the damping coefficient of the grid-forming converter, the grid angular frequency, the grid-forming output angular frequency of the grid-forming converter, the grid-forming equivalent output voltage of the grid-forming converter, the grid voltage, the grid-forming output inductor of the grid-forming converter, the grid line inductor, the grid-following output angular frequency of the grid-following converter, the PLL proportional coefficient, the PLL integral coefficient, the grid-following output current of the grid-following converter, and the phase angle of the grid-following output current; According to the power data, calculate the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point; After a fault occurs, obtain the grid fault voltage during the fault and the grid-following fault output current of the grid-following converter; According to the first power angle, the second power angle, the grid fault voltage, the grid-following fault output current, the grid angular frequency, the grid-forming equivalent output voltage, the grid-forming output inductor, and the grid line inductor, calculate the reference value of the active power of the grid-forming converter; According to the first power angle, the second power angle, the grid-forming equivalent output voltage, the grid-forming output inductor, the grid line inductor, and the grid fault voltage, calculate the output phase value of the grid-following converter; According to the reference value of the active power and the output phase value, adjust the active power output of the grid-forming converter and the output phase of the grid-following converter to restore the transient stability of the grid-connected system.

2. The transient stability restoration method of a multi-converter grid-connected system according to claim 1, characterized in that The step of calculating the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point according to the power data includes: According to the power data, construct the transient analysis equations of the grid-forming converter and the grid-following converter; Solve the transient analysis equations to obtain the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

3. A transient stability restoration method for a multi-converter grid-connected system according to claim 2, characterized in that, The step of constructing the transient analysis equations of the grid-forming converter and the grid-following converter according to the power data includes: According to the grid angular frequency, the grid-forming output angular frequency, the virtual inertia coefficient, the damping coefficient, the grid-forming equivalent output voltage, the grid voltage, the grid-forming output inductor, the grid line inductor, the grid-following output current, and the phase angle of the grid-following output current, construct the swing equation of the grid-forming converter; According to the grid-following output angular frequency, the grid angular frequency, the PLL proportional coefficient, the PLL integral coefficient, the grid line inductor, the grid-forming output inductor, the grid-forming equivalent output voltage, the grid voltage, the grid-following output current, and the phase angle of the grid-following output current, construct the swing equation of the grid-following converter; According to the swing equation of the grid-forming converter and the swing equation of the grid-following converter, obtain the transient analysis equations.

4. A transient stability restoration method for a multi-converter grid-connected system according to claim 3, characterized in that, The step of calculating the output phase value of the grid-following converter according to the first power angle, the second power angle, the grid-forming equivalent output voltage, the grid-forming output inductor, the grid line inductor, and the grid fault voltage includes: According to the first power angle, the second power angle, the grid fault voltage, the equivalent output voltage of the grid-forming converter, the grid line inductance, and the grid-forming output inductance, an expression for the d-axis component of the grid-following fault output current during the fault is constructed; Let the d-axis component of the grid-following fault output current be 0, solve the expression, and obtain the output phase value.

5. A transient stability restoration device for a multi-converter grid-connected system, characterized in that, Including: A power data acquisition module, a power angle calculation module, a fault data acquisition module, an active power reference value calculation module, an output phase value calculation module, and a parameter adjustment module; The power data acquisition module is used to acquire the power data of the grid-connected system; wherein, the power data includes: the virtual inertia coefficient of the grid-forming converter, the damping coefficient of the grid-forming converter, the grid angular frequency, the grid-forming output angular frequency of the grid-forming converter, the equivalent output voltage of the grid-forming converter, the grid voltage, the grid-forming output inductance of the grid-forming converter, the grid line inductance, the grid-following output angular frequency of the grid-following converter, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the grid-following output current of the grid-following converter, and the phase angle of the grid-following output current; The power angle calculation module is used to calculate the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point according to the power data; The fault data acquisition module is used to acquire the grid fault voltage during the fault and the grid-following fault output current of the grid-following converter after the fault occurs; The active power reference value calculation module is used to calculate the active power reference value of the grid-forming converter according to the first power angle, the second power angle, the grid fault voltage, the grid-following fault output current, the grid angular frequency, the equivalent output voltage of the grid-forming converter, the grid-forming output inductance, and the grid line inductance; The output phase value calculation module is used to calculate the output phase value of the grid-following converter according to the first power angle, the second power angle, the equivalent output voltage of the grid-forming converter, the grid-forming output inductance, the grid line inductance, and the grid fault voltage; The parameter adjustment module is used to adjust the active power output of the grid-forming converter and the output phase of the grid-following converter according to the active power reference value and the output phase value to restore the transient stability of the grid-connected system.

6. The transient stability restoration device of a multi-converter grid-connected system according to claim 5, characterized in that, The power angle calculation module includes: A transient analysis equation construction unit and a power angle calculation unit; The transient analysis equation construction unit is used to construct the transient analysis equations of the grid-forming converter and the grid-following converter according to the power data; The power angle calculation unit is used to solve the transient analysis equations to obtain the first power angle of the grid-forming converter at the stable operating point and the second power angle of the grid-following converter at the stable operating point.

7. The transient stability restoration device for a multi-converter grid-connected system according to claim 6, characterized in that, The transient analysis equation construction unit includes: A grid-forming converter swing equation construction subunit, a grid-following converter swing equation construction subunit, and a transient equation generation subunit; The swing equation construction subunit of the network-forming converter is used to construct the swing equation of the network-forming converter according to the grid angular frequency, the network-forming output angular frequency, the virtual inertia coefficient, the damping coefficient, the network-forming equivalent output voltage, the grid voltage, the network-forming output inductor, the grid line inductor, the grid-following output current, and the phase angle of the grid-following output current; The swing equation construction subunit of the grid-following converter is used to construct the swing equation of the grid-following converter according to the grid-following output angular frequency, the grid angular frequency, the proportional coefficient of the phase-locked loop, the integral coefficient of the phase-locked loop, the grid line inductor, the network-forming output inductor, the network-forming equivalent output voltage, the grid voltage, the grid-following output current, and the phase angle of the grid-following output current; The transient equation generation subunit is used to obtain the transient analysis equation according to the swing equation of the network-forming converter and the swing equation of the grid-following converter.

8. The transient stability recovery device for a multi-converter grid-connected system according to claim 7, characterized in that, The output phase value calculation module includes: A component current expression construction unit and an expression solving unit; The component current expression construction unit is used to construct an expression for the d-axis component of the grid-following fault output current during a fault according to the first power angle, the second power angle, the grid fault voltage, the network-forming equivalent output voltage, the grid line inductor, and the network-forming output inductor; The expression solving unit is used to set the d-axis component of the grid-following fault output current to 0 and solve the expression to obtain the output phase value.

9. A terminal device, characterized in that, It 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 transient stability recovery method for a multi-converter grid-connected system according to any one of claims 1 to 4.

10. A storage medium, characterized in that, The storage medium includes a stored computer program. When the computer program runs, it controls the device where the storage medium is located to execute a transient stability recovery method for a multi-converter grid-connected system according to any one of claims 1 to 4.

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