Distance protection method, device and terminal equipment for virtual synchronous generator grid-connected system based on least squares method

Abstract

This invention discloses a distance protection method, device, and terminal equipment for a virtual synchronous generator grid-connected system based on the least squares method. The method includes: constructing a grid-connected system model based on acquired virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; when the synchronous generator parameters in the power equipment parameters are empty, constructing a fitting objective function for the grid-connected system model and a set of equations containing the impedance from the fault point to the protection; solving the set of equations containing the impedance from the fault point to the protection with the objective function as the goal, and calculating the first impedance from the fault point to the protection; determining the location of the fault point based on the first impedance from the fault point to the protection and the virtual synchronous generator parameters; and performing distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point. By implementing this invention, the location of the fault point in the virtual synchronous generator connected to the power grid can be accurately obtained.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a distance protection method, device and terminal equipment for a virtual synchronous generator grid-connected system based on the least squares method. Background Technology

[0002] With the transformation of the global energy structure, new energy power generation technologies have developed rapidly and been widely applied. Among them, the large-scale integration of new energy generators into the power grid through converters has brought new challenges to the power system. The power output characteristics of new energy generators and converters differ significantly from those of traditional synchronous generators. After being connected to the grid, their inertia level is greatly reduced, threatening the stability of the power system.

[0003] Traditional distance protection methods for grid-connected systems are mainly designed for synchronous generator grid-connected systems to ensure the safe operation of the power system and to infer the distance to the fault point. However, they do not consider the control process of virtual synchronous generator (VSG) grid-connected systems. Therefore, the line protection on the virtual synchronous generator side cannot accurately calculate the location of the three-phase fault on the line, resulting in low accuracy of distance protection for virtual synchronous generator grid-connected systems. Summary of the Invention

[0004] This invention provides a method, device, terminal equipment, and storage medium for distance protection of a virtual synchronous generator grid-connected system based on the least squares method. It can effectively solve the problem that the existing technology cannot accurately calculate the location of three-phase faults in the transmission lines of the virtual synchronous generator connected to the power grid system, resulting in low accuracy of distance protection for the virtual synchronous generator grid-connected system.

[0005] An embodiment of the present invention provides a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method, comprising:

[0006] Obtain virtual synchronous generator parameters, power equipment parameters, and transmission line parameters;

[0007] A grid-connected system model is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters.

[0008] When the synchronous motor parameters in the power equipment parameters are empty, the fitting objective function of the grid-connected system model and a set of equations containing the impedance between the fault point and the protection are constructed based on the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters.

[0009] Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the set of equations containing the impedance from the fault point to the protection room, with the objective of minimizing the fitting objective function, the set of equations containing the impedance from the fault point to the protection room is solved to calculate the first impedance from the fault point to the protection room.

[0010] The location of the fault point is determined based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0011] The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the power grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

[0012] Furthermore, based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including:

[0013] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated.

[0014] The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

[0015] Furthermore, it also includes:

[0016] If the synchronous motor parameters in the power equipment parameters are not empty, a set of equations containing the impedance from the fault point to the protection is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters.

[0017] Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equations containing the impedance from the fault point to the protection, the imaginary and real parts are separated to obtain a nonlinear equation set containing the impedance from the fault point to the protection.

[0018] The nonlinear equations containing the impedance from the fault point to the protection are solved based on the virtual synchronous generator parameters and the transmission line parameters to calculate the second impedance from the fault point to the protection.

[0019] The location of the fault point is determined based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0020] Furthermore, based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including:

[0021] Based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the second transition resistance used to represent the synchronous generator parameters when they are not empty is calculated.

[0022] The location of the fault point is determined based on the second impedance from the fault point to the protection room and the second transition resistance.

[0023] Furthermore, the construction of the fitting objective function for the grid-connected system model includes:

[0024] Based on the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, several sets of first and second sampled values ​​are determined through the grid-connected system model.

[0025] Several sets of first sampled values ​​are used as the dependent variable of the function, and several sets of second sampled values ​​are used as the independent variable of the function;

[0026] Based on the virtual synchronous generator parameters, the dependent variable of the function, and the independent variable of the function, the fitting target parameters of the grid-connected system model are constructed.

[0027] As an improvement to the above solution, another embodiment of the present invention provides a distance protection device for a virtual synchronous generator grid-connected system based on the least squares method, comprising:

[0028] The system data acquisition module is used to acquire parameters of the virtual synchronous generator, power equipment, and transmission line.

[0029] The system model construction module is used to construct a grid-connected system model based on the parameters of the virtual synchronous generator, the parameters of the power equipment, and the parameters of the transmission line;

[0030] The function and first equation system construction module is used to construct, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters, the fitting objective function of the grid-connected system model and the equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are empty;

[0031] The first impedance calculation module is used to solve the set of equations containing the impedance from the fault point to the protection room based on the parameters of the virtual synchronous generator, the parameters of the power equipment, the parameters of the transmission line, and the set of equations containing the impedance from the fault point to the protection room, with the goal of minimizing the fitting objective function, and to calculate the first impedance from the fault point to the protection room.

[0032] The first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0033] The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the power grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

[0034] Furthermore, the first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0035] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including:

[0036] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated.

[0037] The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

[0038] Furthermore, it also includes:

[0039] The second equation system construction module is used to construct an equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are not empty, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters.

[0040] The third equation system construction module is used to separate the imaginary and real parts of the equation system containing the impedance from the fault point to the protection based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equation system containing the impedance from the fault point to the protection.

[0041] The second impedance calculation module is used to solve the nonlinear equation system containing the impedance from the fault point to the protection room based on the virtual synchronous generator parameters and the transmission line parameters, and calculate the second impedance from the fault point to the protection room.

[0042] The second distance protection module is used to determine the location of the fault point based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0043] Another embodiment of the present invention provides a terminal device, including 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 distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in the above embodiments.

[0044] Another embodiment of the present invention provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the distance protection method for a virtual synchronous generator grid-connected system based on the least squares method described in the above embodiment.

[0045] By implementing this invention, at least the following beneficial effects are achieved:

[0046] This invention provides a distance protection method, apparatus, and terminal equipment for a virtual synchronous generator grid-connected system based on the least squares method. The method acquires virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; constructs a grid-connected system model based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; when the synchronous generator parameters in the power equipment parameters are empty, constructs a fitting objective function for the grid-connected system model and a set of equations containing the impedance from the fault point to the protection device based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; and constructs a set of equations containing the impedance from the fault point to the protection device based on the virtual synchronous generator parameters, power equipment parameters, transmission line parameters, and transmission line parameters. The system of impedance equations, with the objective function of minimizing the fitting objective function, is solved to obtain the first impedance from the fault point to the protection zone. Based on this first impedance and the virtual synchronous generator parameters, the location of the fault point is determined. Distance protection is then applied to the virtual synchronous generator grid-connected system based on the fault point's location. The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the grid, the current limit value, and the saturation current angle. The power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous generator parameters. The transmission line parameters include: the transmission line inductance and the transmission line resistance. When a fault occurs in the grid-connected system, the synchronous motor parameters in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle during the control process of the virtual synchronous generator grid-connected system can be quickly considered. Then, a set of equations containing the impedance between the fault point and the protection is constructed. The first impedance between the fault point and the protection is obtained by minimizing the fitting objective function. This allows for accurate calculation of the location of the transmission line fault connected to the grid by the virtual synchronous generator. Based on the location of the fault point, distance protection is performed on the virtual synchronous generator grid-connected system. This approach considers the control process of the virtual synchronous generator (VSG) grid-connected system and improves the accuracy of distance protection for the virtual synchronous generator grid-connected system. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method, according to an embodiment of the present invention.

[0048] Figure 2 This is a primary wiring diagram of a virtual synchronous generator grid-connected system provided in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the control principle of a virtual synchronous generator provided in an embodiment of the present invention;

[0050] Figure 4This is a schematic diagram of a three-phase fault model of a virtual synchronous generator grid-connected system transmission line provided in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the structure of a distance protection device for a virtual synchronous generator grid-connected system based on the least squares method, provided in an embodiment of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] See Figure 1 This is a flowchart illustrating a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method, according to an embodiment of the present invention, comprising:

[0054] S1. Obtain virtual synchronous generator parameters, power equipment parameters, and transmission line parameters;

[0055] S2. Construct a grid-connected system model based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters;

[0056] S3. When the synchronous motor parameters in the power equipment parameters are empty, construct the fitting objective function of the grid-connected system model and a set of equations containing the impedance between the fault point and the protection based on the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters.

[0057] S4. Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the set of equations containing the impedance from the fault point to the protection room, with the objective of minimizing the fitting objective function, solve the set of equations containing the impedance from the fault point to the protection room to calculate the first impedance from the fault point to the protection room.

[0058] S5. Determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0059] Specifically, the virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance. An empty synchronous motor parameter in the power equipment parameters indicates that the synchronous motor parameter is unknown, such as the synchronous reactance X of the synchronous motor. d and terminal voltage U b When a fault occurs, the grid-connected system protection device may not obtain the specific parameters of the synchronous motor on the opposite side immediately; at this time, the parameters of the synchronous motor on the opposite side are empty (unknown). The first impedance represents the impedance from the fault point to the protection room when the synchronous motor parameters in the power equipment parameters are empty. The protection room refers to a specific area or facility in the power system used to achieve the safety protection of equipment and personnel. It typically includes a series of electrical safety measures and equipment to ensure that the power supply can be quickly cut off in the event of a fault or abnormal situation, preventing the accident from escalating and protecting equipment and personnel from harm.

[0060] In a preferred embodiment of the present invention, firstly, virtual synchronous generator parameters, power equipment parameters, and transmission line parameters are obtained; based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters, a grid-connected system model is constructed; then, when the synchronous generator parameters in the power equipment parameters are empty, based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters, a fitting objective function and a set of equations containing the impedance from the fault point to the protection are constructed for the grid-connected system model; next, based on the virtual synchronous generator parameters, power equipment parameters, transmission line parameters, and the set of equations containing the impedance from the fault point to the protection, with the goal of minimizing the fitting objective function, the set of equations containing the impedance from the fault point to the protection is solved to calculate the first impedance from the fault point to the protection; then, based on the first impedance from the fault point to the protection and the virtual synchronous generator parameters, the location of the fault point is determined; finally, distance protection is performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0061] Preferably, the location of the fault point is determined based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, including:

[0062] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated.

[0063] The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

[0064] In a preferred embodiment of the present invention, the first impedance refers to the electrical impedance from the fault point to the protection room, reflecting the electrical distance between the fault point and the protection device, and is an important basis for locating the fault point. First, based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, a first transition resistance is calculated to represent the situation when the synchronous generator parameters are empty; then, based on the first impedance from the fault point to the protection room and the first transition resistance, the location of the fault point is determined.

[0065] Preferably, it further includes:

[0066] If the synchronous motor parameters in the power equipment parameters are not empty, a set of equations containing the impedance from the fault point to the protection is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters.

[0067] Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equations containing the impedance from the fault point to the protection, the imaginary and real parts are separated to obtain a nonlinear equation set containing the impedance from the fault point to the protection.

[0068] The nonlinear equations containing the impedance from the fault point to the protection are solved based on the virtual synchronous generator parameters and the transmission line parameters to calculate the second impedance from the fault point to the protection.

[0069] The location of the fault point is determined based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0070] In a preferred embodiment of the present invention, the second impedance represents the impedance from the fault point to the protection room when the synchronous motor parameters in the power equipment parameters are not empty. The case where the synchronous motor parameters in the power equipment parameters are not empty is the case where the synchronous motor parameters in the power equipment parameters are known. In this case, firstly, a set of equations containing the impedance from the fault point to the protection room is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters. Then, the imaginary and real parts of the equations containing the impedance from the fault point to the protection room are separated based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equations containing the impedance from the fault point to the protection room, resulting in a nonlinear set of equations containing the impedance from the fault point to the protection room. Then, the nonlinear set of equations containing the impedance from the fault point to the protection room is solved based on the virtual synchronous generator parameters and the transmission line parameters to calculate the second impedance from the fault point to the protection room. Finally, the location of the fault point is determined based on the second impedance from the fault point to the protection room and the virtual synchronous generator parameters. Distance protection is then performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0071] Specifically, the location of the fault point is determined based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, including:

[0072] Based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the second transition resistance used to represent the synchronous generator parameters when they are not empty is calculated.

[0073] The location of the fault point is determined based on the second impedance from the fault point to the protection room and the second transition resistance.

[0074] In a preferred embodiment of the present invention, a second transition resistance is first calculated based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator to indicate that the synchronous generator parameters are not empty; then, the location of the fault point is determined based on the second impedance from the fault point to the protection room and the second transition resistance.

[0075] Schematic, the construction of the fitting objective function for the grid-connected system model includes:

[0076] Based on the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, several sets of first and second sampled values ​​are determined through the grid-connected system model.

[0077] Several sets of first sampled values ​​are used as the dependent variable of the function, and several sets of second sampled values ​​are used as the independent variable of the function;

[0078] Based on the virtual synchronous generator parameters, the dependent variable of the function, and the independent variable of the function, the fitting target parameters of the grid-connected system model are constructed.

[0079] In a preferred embodiment of the present invention, the parameters used in calculating the first sample value and the second sample value are different; for example, G is the first sample value and H is the second sample value. I cmax This is the current limit value. θ is the angle between the current vector and the d-axis (saturation current angle). c The relative phase angle between the virtual synchronous generator and the power grid is defined as follows: First, based on the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, several sets of first and second sampled values ​​are determined using the grid-connected system model. Then, the several sets of first sampled values ​​are used as the dependent variable of the function, and the several sets of second sampled values ​​are used as the independent variable of the function. Finally, based on the virtual synchronous generator parameters, the dependent variable of the function, and the independent variable of the function, the fitting target parameters of the grid-connected system model are constructed.

[0080] In a preferred embodiment of the present invention, such as Figure 2As shown, the research object is a system where a VSG is connected to the power grid after AC-DC-AC conversion via a converter. A grid-connected system model is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters. To clarify the main electrical quantities of the grid-connected system, the following assumptions are made: 1) Line resistance is negligible compared to line reactance; 2) The connected system is very large and can be considered an infinitely large system, with the system frequency as the standard frequency.

[0081] The dynamic equations of the active power control loop of the VSG are as follows:

[0082]

[0083] In the formula, D is the virtual inertia of the VSG; P (0) The set power for the VSG; θ c,real Phase angle provided for VSG; T J P is the virtual time constant of the VSG. c The active power output of the converter; ω c ω is the angular frequency of the converter output; t is the VSG control time.

[0084] In the transient stability analysis of grid-connected systems, the main focus is on the relative phase angle of the VSG with respect to the grid (the relative phase angle between the virtual synchronous generator and the grid). Therefore, the dynamic equation of the VSG can be expressed as:

[0085]

[0086] In the formula, θ c θ represents the relative phase angle between the VSG and the network. s This represents the phase angle of the infinite busbar.

[0087] In severe AC faults, the converter current may exceed its limit. The Current Saturation Algorithm (CSA) can effectively limit the fault current.

[0088]

[0089] In the formula, These are the d-axis and q-axis current reference values ​​after current limiting; These are the d-axis and q-axis current reference values ​​provided by the voltage loop before current limiting; I cmax This is the current limit value; Let be the angle between the saturation current vector and the d-axis, defined as the saturation current angle. According to equation (5), if |i c |<I cmax The reference value of the current generated by the outer loop voltage control remains unchanged. In this case, set... Figure 3 In the case of m=1, the voltage at the common coupling point U p d-axis components Controlled to a reference voltage consistent with the d-axis This control mode is called Constant Voltage Control (CVC). Once the converter current exceeds its limit value |i... c |≥I cmax Current The current vector is controlled to a constant amplitude. At this time, the fault current amplitude is limited to I. cmax Furthermore, the angle between the current vector and the d-axis is restricted to . The control mode is switched to Current Limiting Control (CLC).

[0090] Under normal operating conditions, the current amplitude is normal, and the converter operates in CVC mode. After a three-phase fault occurs on the transmission line, the current flowing through the transmission line increases sharply. At this time, the converter control mode switches from CVC to CLC, with the xy coordinate system as a reference, and the fault current is limited.

[0091] According to Ohm's law, the following equation can be written:

[0092]

[0093]

[0094] Where j is the imaginary unit, j 2 =-1. These are the AC voltage on the VSG side and the electromotive force of the synchronous motor on the opposite side, respectively. X is the short-circuit voltage. a X is the reactance from the short circuit point to the protection installation location. b X is the reactance from the short-circuit point to the synchronous machine terminal. d For synchronous electromechanical reactors, For VSG current, For synchronous machine current, R g This is the transition resistance.

[0095] Equations (7) and (8) are combined and eliminated. have to:

[0096]

[0097] Substituting equation (6) into equation (9), we can eliminate... have to:

[0098]

[0099] make:

[0100]

[0101] in, For voltage The phase angle, and:

[0102]

[0103] The saturation current angle is the angle between the saturation current vector and the d-axis.

[0104] If the synchronous motor parameters in the power equipment parameters are not empty at this time (the synchronous motor parameter information on the other side is known),

[0105] Substituting equations (11) and (12) into equation (10), and separating the imaginary and real parts, we obtain the following set of nonlinear equations:

[0106]

[0107] in:

[0108]

[0109] X d U b Since these are known constants, and combining equations (12) and (14) with the VSG control principle, we can obtain that A, B, C, D, E, and F are all known constants. At this point, there are two unknowns: X a and R g There are two equations, so the equation has an analytical solution.

[0110] According to equation (13), we can directly solve for:

[0111]

[0112] To calculate the transition resistance R g X a Substituting into equation (13) and simplifying, we get:

[0113]

[0114] Therefore, the second impedance X from the fault point to the protection room is calculated. a .

[0115] If the synchronous motor parameters in the power equipment parameters are empty at this time (the synchronous motor parameter information on the other side is unknown), the synchronous reactance X of the synchronous motor... d and terminal voltage U bGiven that substituting equations (11) and (12) into equation (10) yields the following system of equations:

[0116]

[0117] in:

[0118]

[0119] X s U b Unknown, due to X l Given that X is known, we can first solve for X. Σ , and then calculate X d At this point, B, C, E, and F are all known constants, and there are four unknowns (X). a R g X Σ U b ) and two equations:

[0120]

[0121] in:

[0122]

[0123] Since the equation has no analytical solution, the least squares method can be used to calculate the numerical solution of the impedance from the fault point to the protection inter-station. This numerical solution is obtained through fitting.

[0124] 1) Due to the fact that X in the power grid d <<X l X omitted d , let X d =0, combine the two equations in (17) and eliminate R. g Simplifying, we get:

[0125]

[0126] in:

[0127]

[0128] At this point, the only unknown parameter is U. b X a .

[0129] 2) Obtain n sets of G and H values ​​through system sampling, and use the set number i as their number.

[0130] 3) Will U b , Consider G as a parameter, H as the dependent variable of the function, and G as the independent variable of the function. Using least squares fitting, let... To minimize the residuals of the least squares fit, i.e., to achieve the highest degree of fit, k is closest to the slope of the objective function g(H). Therefore, the problem is transformed into finding:

[0131]

[0132] The parameter U can be found using the minimum value function in MATLAB. b , The value of .

[0133] 4) Obtained through constants B, C, E, F, and... The first impedance X from the fault point to the protection room is calculated. a To calculate the transition resistance R g X a The value can be substituted back into equation (17).

[0134] like Figure 4 As shown, the DC-DC converter adopts control strategies such as VSG control and current saturation algorithm. It uses the electrical quantity relationship of the protected line to accurately calculate the distance between the fault point and the protection installation point to realize the protection function. Compared with the existing distance protection strategy, it requires fewer parameters, identifies the fault distance more accurately, improves the reliability and sensitivity of relay protection, and improves the reliability and safety of power grid operation.

[0135] By implementing this embodiment, virtual synchronous generator parameters, power equipment parameters, and transmission line parameters are obtained; a grid-connected system model is constructed based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; when the synchronous generator parameters in the power equipment parameters are empty, a fitting objective function and a set of equations containing the impedance from the fault point to the protection are constructed based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; the goal is to minimize the fitting objective function based on the virtual synchronous generator parameters, power equipment parameters, transmission line parameters, and the set of equations containing the impedance from the fault point to the protection. The system of equations containing the impedance from the fault point to the protection room is solved to calculate the first impedance from the fault point to the protection room. Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined. Distance protection is then applied to the virtual synchronous generator grid-connected system based on the location of the fault point. The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the grid, the current limit value, and the saturation current angle. The power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous generator parameters. The transmission line parameters include: the transmission line inductance and the transmission line resistance. When a fault occurs in the grid-connected system, the synchronous motor parameters in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle during the control process of the virtual synchronous generator grid-connected system can be quickly considered. Then, a set of equations containing the impedance between the fault point and the protection is constructed. The first impedance between the fault point and the protection is obtained by minimizing the fitting objective function. This allows for accurate calculation of the location of the fault in the transmission line connected to the grid by the virtual synchronous generator. Based on the location of the fault point, distance protection is performed on the virtual synchronous generator grid-connected system. This approach considers the control process of the virtual synchronous generator (VSG) grid-connected system and improves the accuracy of distance protection for the virtual synchronous generator grid-connected system.

[0136] See Figure 5 This is a schematic diagram of the structure of a distance protection device for a virtual synchronous generator grid-connected system based on the least squares method, according to an embodiment of the present invention, comprising:

[0137] The system data acquisition module is used to acquire parameters of the virtual synchronous generator, power equipment, and transmission line.

[0138] The system model construction module is used to construct a grid-connected system model based on the parameters of the virtual synchronous generator, the parameters of the power equipment, and the parameters of the transmission line;

[0139] The function and first equation system construction module is used to construct, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters, the fitting objective function of the grid-connected system model and the equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are empty;

[0140] The first impedance calculation module is used to solve the set of equations containing the impedance from the fault point to the protection room based on the parameters of the virtual synchronous generator, the parameters of the power equipment, the parameters of the transmission line, and the set of equations containing the impedance from the fault point to the protection room, with the goal of minimizing the fitting objective function, and to calculate the first impedance from the fault point to the protection room.

[0141] The first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0142] The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the power grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

[0143] Specifically, the first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0144] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including:

[0145] Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated.

[0146] The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

[0147] Preferably, it further includes:

[0148] The second equation system construction module is used to construct an equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are not empty, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters.

[0149] The third equation system construction module is used to separate the imaginary and real parts of the equation system containing the impedance from the fault point to the protection based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equation system containing the impedance from the fault point to the protection.

[0150] The second impedance calculation module is used to solve the nonlinear equation system containing the impedance from the fault point to the protection room based on the virtual synchronous generator parameters and the transmission line parameters, and calculate the second impedance from the fault point to the protection room.

[0151] The second distance protection module is used to determine the location of the fault point based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

[0152] This invention provides a distance protection device for a virtual synchronous generator grid-connected system based on the least squares method. The device acquires virtual synchronous generator parameters, power equipment parameters, and transmission line parameters via a system data acquisition module. In a system model construction module, a grid-connected system model is constructed based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters. Through a function and first equation system construction module, when the synchronous generator parameters in the power equipment parameters are empty, a fitting objective function for the grid-connected system model and a set of equations containing the impedance between the fault point and the protection are constructed based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters. In a first impedance calculation module, the device calculates the impedance based on the virtual synchronous generator parameters, power equipment parameters, and transmission line parameters. A set of equations containing the impedance from the fault point to the protection zone is solved with the objective function of minimizing the fitting objective function, to calculate the first impedance from the fault point to the protection zone. Finally, the location of the fault point is determined by the first distance protection module based on the first impedance from the fault point to the protection zone and the parameters of the virtual synchronous generator. Distance protection is then performed on the virtual synchronous generator grid-connected system based on the location of the fault point. The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous generator parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance. When a fault occurs in the grid-connected system, the synchronous motor parameters in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle during the control process of the virtual synchronous generator grid-connected system can be quickly considered. Then, a set of equations containing the impedance between the fault point and the protection is constructed. The first impedance between the fault point and the protection is obtained by minimizing the fitting objective function. This allows for accurate calculation of the location of the fault in the transmission line connected to the grid by the virtual synchronous generator. Based on the location of the fault point, distance protection is performed on the virtual synchronous generator grid-connected system. This approach considers the control process of the virtual synchronous generator (VSG) grid-connected system and improves the accuracy of distance protection for the virtual synchronous generator grid-connected system.

[0153] It should be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the device embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0154] Those skilled in the art will understand that, for convenience and brevity, the specific working process of the device described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0155] Another embodiment of the present invention provides a terminal device, including 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 distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in the above embodiments. The terminal device can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. The terminal device may include, but is not limited to, a processor and a memory.

[0156] The processor can be a Central Processing Unit (CPU), or 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 can be a microprocessor or any conventional processor. The processor is the control center of the terminal device, connecting various parts of the terminal device via various interfaces and lines.

[0157] The memory can be used to store the computer program. The processor implements various functions of the terminal device by running or executing the computer program stored in the memory and calling data stored in the memory. The memory may mainly include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function, etc.; the data storage area may store data created based on the use of the mobile phone, etc. In addition, the memory may include high-speed random access memory, and may also include non-volatile memory, such as hard disk, RAM, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0158] Another embodiment of the present invention provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the distance protection method for a virtual synchronous generator grid-connected system based on the least squares method described in the above embodiment.

[0159] The storage medium is a computer-readable storage medium, and the computer program is stored in the computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0160] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A distance protection method for a virtual synchronous generator grid-connected system based on the least squares method, characterized in that, include: Obtain virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; A grid-connected system model is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters. When the synchronous motor parameters in the power equipment parameters are empty, the fitting objective function of the grid-connected system model and a set of equations containing the impedance between the fault point and the protection are constructed based on the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters. Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the set of equations containing the impedance from the fault point to the protection room, with the objective of minimizing the fitting objective function, the set of equations containing the impedance from the fault point to the protection room is solved to calculate the first impedance from the fault point to the protection room. The location of the fault point is determined based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator. And distance protection is provided for the virtual synchronous generator grid-connected system based on the location of the fault point; The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the power grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

2. The distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 1, characterized in that, Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including: Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated. The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

3. The distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 1, characterized in that, Also includes: If the synchronous motor parameters in the power equipment parameters are not empty, a set of equations containing the impedance from the fault point to the protection is constructed based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters. Based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equations containing the impedance from the fault point to the protection, the imaginary and real parts are separated to obtain a nonlinear equation set containing the impedance from the fault point to the protection. The nonlinear equations containing the impedance from the fault point to the protection are solved based on the virtual synchronous generator parameters and the transmission line parameters to calculate the second impedance from the fault point to the protection. The location of the fault point is determined based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system based on the location of the fault point.

4. The distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 1, characterized in that, Based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including: Based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the second transition resistance used to represent the synchronous generator parameters when they are not empty is calculated. The location of the fault point is determined based on the second impedance from the fault point to the protection room and the second transition resistance.

5. The distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 1, characterized in that, The construction of the fitting objective function for the grid-connected system model includes: Based on the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, several sets of first and second sampled values ​​are determined through the grid-connected system model. Several sets of first sampled values ​​are used as the dependent variable of the function, and several sets of second sampled values ​​are used as the independent variable of the function; Based on the virtual synchronous generator parameters, the dependent variable of the function, and the independent variable of the function, the fitting target parameters of the grid-connected system model are constructed.

6. A distance protection device for a virtual synchronous generator grid-connected system based on the least squares method, characterized in that, include: The system data acquisition module is used to acquire parameters of the virtual synchronous generator, power equipment, and transmission line. The system model construction module is used to construct a grid-connected system model based on the parameters of the virtual synchronous generator, the parameters of the power equipment, and the parameters of the transmission line; The function and first equation system construction module is used to construct, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters, the fitting objective function of the grid-connected system model and the equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are empty; The first impedance calculation module is used to solve the set of equations containing the impedance from the fault point to the protection room based on the parameters of the virtual synchronous generator, the parameters of the power equipment, the parameters of the transmission line, and the set of equations containing the impedance from the fault point to the protection room, with the goal of minimizing the fitting objective function, and to calculate the first impedance from the fault point to the protection room. The first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator. And distance protection is provided for the virtual synchronous generator grid-connected system based on the location of the fault point; The virtual synchronous generator parameters include: the relative phase angle between the virtual synchronous generator and the power grid, the current limit value, and the saturation current angle; the power equipment parameters include: the converter output angular frequency, the grid-side angular frequency, the converter active power output, the converter reactive power output, and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

7. The distance protection device for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 6, characterized in that, The first distance protection module is used to determine the location of the fault point based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point. Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the location of the fault point is determined, including: Based on the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator, the first transition resistance used to represent the synchronous generator parameters when they are empty is calculated. The location of the fault point is determined based on the first impedance from the fault point to the protection room and the first transition resistance.

8. The distance protection device for a virtual synchronous generator grid-connected system based on the least squares method as described in claim 6, characterized in that, Also includes: The second equation system construction module is used to construct an equation system containing the impedance between the fault point and the protection when the synchronous motor parameters in the power equipment parameters are not empty, based on the virtual synchronous generator parameters, the power equipment parameters, and the transmission line parameters. The third equation system construction module is used to separate the imaginary and real parts of the equation system containing the impedance from the fault point to the protection based on the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters, and the equation system containing the impedance from the fault point to the protection. The second impedance calculation module is used to solve the nonlinear equation system containing the impedance from the fault point to the protection room based on the virtual synchronous generator parameters and the transmission line parameters, and calculate the second impedance from the fault point to the protection room. The second distance protection module is used to determine the location of the fault point based on the second impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system based on the location of the fault point.

9. A terminal device, characterized in that, The system 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 distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in any one of claims 1 to 5.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to perform a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method as described in any one of claims 1 to 5.

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