Virtual synchronous generator grid-connected system distance protection method and device based on least square method, and terminal equipment

Abstract

The invention discloses a virtual synchronous generator grid-connected system distance protection method and device based on a least square method and terminal equipment. The method comprises the following steps: constructing a grid-connected system model according to acquired virtual synchronous generator parameters, power equipment parameters and transmission line parameters; under the condition that the synchronous motor parameter in the power equipment parameters is empty, constructing a fitting objective function of a grid-connected system model and an equation set containing impedance from a fault point to protection; solving an equation set containing impedance from the fault point to the protection room by taking the minimum fitting objective function as an objective, and calculating to obtain first impedance from the fault point to the protection room; determining the position of the fault point according to the first impedance from the fault point to the protection room and the parameters of the virtual synchronous generator; and distance protection is carried out on the virtual synchronous generator grid-connected system according to the position of the fault point. By implementing the method, the position of the fault point of the virtual synchronous generator accessed to the grid-connected system of the power grid can be accurately obtained.

Description

Technical Field

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

[0002] With the transformation of the global energy structure, new energy power generation technology has been rapidly developed and widely used. Among them, new energy motors are connected to the power grid on a large scale through inverters, which brings new challenges to the power system. The power output characteristics of new energy motors and inverters are significantly different from those of traditional synchronous generators. After they are connected to the power grid, the inertia level of the system is greatly reduced, threatening the stability of the power system.

[0003] The traditional grid-connected system distance protection method mainly targets the synchronous motor grid-connected system to ensure the safe operation of the power system and infer the distance of the fault point, but does not consider the control process of the virtual synchronous generator (VSG) grid-connected system. Therefore, the line protection on the virtual synchronous generator side cannot accurately calculate the location of the three-phase fault of the line, resulting in low accuracy of the distance protection of the virtual synchronous generator grid-connected system. Summary of the invention

[0004] The embodiments of the present invention provide a method, apparatus, terminal device and storage medium for distance protection of a virtual synchronous generator grid-connected system based on the least squares method, which can effectively solve the problem that the prior art cannot accurately calculate the location of a three-phase fault in a transmission line of a virtual synchronous generator connected to a power grid system, resulting in low accuracy of distance protection of 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 a least squares method, comprising:

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

[0007] Constructing a grid-connected system model according to 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, constructing a fitting objective function of the grid-connected system model and a set of equations containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0009] According to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, the equation group containing the impedance from the fault point to the protection is solved with the goal of minimizing the fitting objective function, and the first impedance from the fault point to the protection is calculated;

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

[0011] Among them, 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 output power, the converter reactive output power and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

[0012] Further, the location of the fault point is determined according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including:

[0013] According to the first impedance between the fault point and the protection and the virtual synchronous generator parameters, a first transition resistance is calculated to indicate that the synchronous generator parameters are empty;

[0014] The position of the fault point is determined according to the first impedance between the fault point and the protection and the first transition resistance.

[0015] Furthermore, it also includes:

[0016] When the synchronous motor parameters in the power equipment parameters are not empty, constructing a set of equations containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0017] Separating the imaginary part and the real part of the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, and obtaining a nonlinear equation group containing the impedance from the fault point to the protection;

[0018] Solving a nonlinear equation group containing the impedance between the fault point and the protection according to the virtual synchronous generator parameters and the transmission line parameters, and calculating a second impedance between the fault point and the protection;

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

[0020] Further, the location of the fault point is determined according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including:

[0021] According to the second impedance between the fault point and the protection and the virtual synchronous generator parameters, a second transition resistance is calculated to indicate that the synchronous generator parameters are not empty;

[0022] The position of the fault point is determined according to the second impedance between the fault point and the protection and the second transition resistance.

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

[0024] According to the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, a plurality of groups of first sampling values ​​and second sampling values ​​are determined through the grid-connected system model;

[0025] Using several groups of first sample values ​​as function dependent variables and several groups of second sample values ​​as function independent variables;

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

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

[0028] System data acquisition module, used to obtain virtual synchronous generator parameters, power equipment parameters and transmission line parameters;

[0029] A system model building module, used to build a grid-connected system model according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0030] A function and first equation group construction module, used for constructing a fitting objective function of the grid-connected system model and an equation group containing the impedance between the fault point and the protection according to 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;

[0031] A first impedance calculation module is used to solve the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, with the goal of minimizing the fitting objective function, to calculate the first impedance from the fault point to the protection;

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

[0033] Among them, 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 output power, the converter reactive output power 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 according to the first impedance between the fault point and the protection and the virtual synchronous generator parameters; and to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point;

[0035] The location of the fault point is determined based on the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including:

[0036] According to the first impedance between the fault point and the protection and the virtual synchronous generator parameters, a first transition resistance is calculated to indicate that the synchronous generator parameters are empty;

[0037] The position of the fault point is determined according to the first impedance between the fault point and the protection and the first transition resistance.

[0038] Furthermore, it also includes:

[0039] A second equation group building module is used to build an equation group containing the impedance from the fault point to the protection according to 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 not empty;

[0040] A third equation group building module is used to separate the imaginary part and the real part according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, so as to obtain a nonlinear equation group containing the impedance from the fault point to the protection;

[0041] A second impedance calculation module is used to solve a nonlinear equation group containing an impedance from a fault point to a protection interval according to the virtual synchronous generator parameters and the transmission line parameters, and calculate a second impedance from the fault point to the protection interval;

[0042] The second distance protection module is used to determine the location of the fault point according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system according to 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, and when the processor executes the computer program, a virtual synchronous generator grid-connected system distance protection method based on least squares method as described in the above embodiment is implemented.

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

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

[0046] The present invention provides a method, device and terminal equipment for distance protection of a virtual synchronous generator grid-connected system based on the least squares method. The method can obtain virtual synchronous generator parameters, power equipment parameters and transmission line parameters; construct a grid-connected system model according to 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, construct a fitting objective function of the grid-connected system model and an equation group containing the impedance between the fault point and the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; construct a fitting objective function of the grid-connected system model and an equation group containing the impedance between the fault point and the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the transmission line parameters. The impedance equation group is solved with the goal of minimizing the fitting objective function, and the first impedance between the fault point and the protection is calculated; the location of the fault point is determined according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and the distance protection of the virtual synchronous generator grid-connected system is performed according to the location of the fault point; wherein the parameters of the virtual synchronous generator 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 output angular frequency of the converter, the grid side angular frequency, the active output power of the converter, the reactive output power of the converter and the parameters of the synchronous motor; the transmission line parameters include: the transmission line inductance and the transmission line resistance. When a fault occurs in the grid-connected system, the parameters of the synchronous motor in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle in the control process of the virtual synchronous generator grid-connected system can be quickly considered, and then a group of equations containing the impedance from the fault point to the protection is constructed. The first impedance from the fault point to the protection is obtained by solving the minimum fitting objective function, so as to accurately calculate the location of the transmission line fault of the virtual synchronous generator connected to the power grid, so as to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point. The control process of the virtual synchronous generator (VSG) grid-connected system is taken into consideration, and the accuracy of the distance protection of the virtual synchronous generator grid-connected system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flow chart of a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method provided by one embodiment of the present invention;

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

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

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

[0051] Figure 5 It is a structural schematic diagram of a distance protection device for a virtual synchronous generator grid-connected system based on the least squares method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] See also Figure 1 , is a flow chart of a distance protection method for a virtual synchronous generator grid-connected system based on the least squares method provided by an embodiment of the present invention, comprising:

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

[0055] S2. constructing a grid-connected system model according to 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 the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0057] S4, according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, with the goal of minimizing the fitting objective function, solving the equation group containing the impedance from the fault point to the protection, and calculating the first impedance from the fault point to the protection;

[0058] S5. Determine the location of the fault point according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and perform distance protection on the virtual synchronous generator grid-connected system according to 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 output power, the converter reactive output power and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance. If the synchronous motor parameters in the power equipment parameters are empty, it means that the synchronous motor parameters in the power equipment parameters are 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 opposite synchronous motor at the first time. At this time, the parameters of the opposite synchronous motor are empty (unknown); the first impedance refers to the impedance from the fault point to the protection room when the parameters of the synchronous motor in the power equipment parameters are empty; the protection room refers to a specific area or facility used to achieve equipment and personnel safety protection in the power system. It usually includes a series of electrical safety measures and equipment to ensure that when a fault or abnormal situation occurs, the power supply can be quickly cut off to prevent the accident from expanding and protect equipment and personnel from harm.

[0060] In a preferred embodiment of the present invention, firstly obtain the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; construct the grid-connected system model according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; then, when the synchronous motor parameters in the power equipment parameters are empty, construct the fitting objective function of the grid-connected system model and the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; then, according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, solve the equation group containing the impedance from the fault point to the protection with the goal of minimizing the fitting objective function, and calculate the first impedance from the fault point to the protection; then, determine the location of the fault point according to the first impedance from the fault point to the protection and the virtual synchronous generator parameters; finally, perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point.

[0061] Preferably, determining the location of the fault point according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator includes:

[0062] According to the first impedance between the fault point and the protection and the virtual synchronous generator parameters, a first transition resistance is calculated to indicate that the synchronous generator parameters are empty;

[0063] The position of the fault point is determined according to the first impedance between the fault point and the protection 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, which reflects 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 virtual synchronous generator parameters, the first transition resistance used to represent the synchronous motor parameters being empty is calculated; 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 also includes:

[0066] When the synchronous motor parameters in the power equipment parameters are not empty, constructing a set of equations containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0067] Separating the imaginary part and the real part of the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, and obtaining a nonlinear equation group containing the impedance from the fault point to the protection;

[0068] Solving a nonlinear equation group containing the impedance between the fault point and the protection according to the virtual synchronous generator parameters and the transmission line parameters, and calculating a second impedance between the fault point and the protection;

[0069] The location of the fault point is determined according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system according to 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 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, that is, the case where the synchronous motor parameters in the power equipment parameters are known, at this time, firstly, a group of equations containing the impedance from the fault point to the protection is constructed according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; then, the imaginary part and the real part are separated according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the group of equations containing the impedance from the fault point to the protection, so as to obtain a nonlinear group of equations containing the impedance from the fault point to the protection; then, the nonlinear group of equations containing the impedance from the fault point to the protection is solved according to the virtual synchronous generator parameters and the transmission line parameters, and the second impedance from the fault point to the protection is calculated; finally, the position of the fault point is determined according to the second impedance from the fault point to the protection and the virtual synchronous generator parameters; and distance protection is performed on the virtual synchronous generator grid-connected system according to the position of the fault point.

[0071] Specifically, the location of the fault point is determined according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including:

[0072] According to the second impedance between the fault point and the protection and the virtual synchronous generator parameters, a second transition resistance is calculated to indicate that the synchronous generator parameters are not empty;

[0073] The position of the fault point is determined according to the second impedance between the fault point and the protection and the second transition resistance.

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

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

[0076] According to the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, a plurality of groups of first sampling values ​​and second sampling values ​​are determined through the grid-connected system model;

[0077] Using several groups of first sample values ​​as function dependent variables and several groups of second sample values ​​as function independent variables;

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

[0079] In a preferred embodiment of the present invention, different parameters are used when calculating the first sampling value and the second sampling value. For example, G is the first sampling value and H is the second sampling value. I cmax is the current limit value, is the angle between the current vector and the d-axis (saturation current angle), θ c is the relative phase angle between the virtual synchronous generator and the power grid. First, according to the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, several groups of first sampling values ​​and second sampling values ​​are determined through the grid-connected system model; then, several groups of first sampling values ​​are used as function dependent variables, and several groups of second sampling values ​​are used as function independent variables; finally, according to the virtual synchronous generator parameters, the function dependent variables and the function independent variables, the fitting target parameters of the grid-connected system model are constructed.

[0080] In a preferred embodiment of the present invention, Figure 2As shown in the figure, the research object is a system in which a VSG is connected to the power grid after AC-DC-AC conversion through a converter. According to the parameters of the virtual synchronous generator, the parameters of the power equipment and the parameters of the transmission line, a grid-connected system model is constructed. In order to illustrate the main electrical quantities of the grid-connected system, the following assumptions are made: 1) Compared with the line reactance, the line resistance can be ignored; 2) The access system is very large and can be regarded as an infinite system, with the system frequency as the standard frequency.

[0081] The dynamic equation of the active power control loop of VSG is as follows:

[0082]

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

[0084] In the transient stability analysis of the grid-connected system, the main focus is on the relative phase angle of the VSG relative 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 Represents the relative phase angle between VSG and the network; θ s Represents the phase angle of the infinite busbar.

[0087] In severe AC faults, the converter current may exceed its limit value. The current saturation algorithm (CSA) can effectively limit the fault current:

[0088]

[0089] In the formula, They are the d-axis and q-axis current reference values ​​after current limiting respectively; They are the d-axis and q-axis current reference values ​​provided by the voltage loop before current limiting; I cmax is the current limit value; is the angle between the saturation current vector and the d-axis, defined as the saturation current angle. According to formula (5), if |i c |<I cmax , the current reference value generated by the outer loop voltage control remains unchanged. In this case, setting Figure 3 m=1, the voltage at the common coupling point U p The d-axis component Controlled to match the reference voltage of 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 , and the angle between the current vector and the d-axis is limited to The control mode switches to current limiting control (CLC).

[0090] Under normal operation, the current amplitude is normal and the converter operates in CVC mode. After a three-phase fault occurs in 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, the fault current is limited to

[0091] Ohm's law can be expressed as follows:

[0092]

[0093]

[0094] Where j is the imaginary unit, j 2 =-1. They are the AC voltage on the VSG side and the electromotive force of the synchronous motor on the opposite side, is the short-circuit voltage, X a is the reactance from the short-circuit point to the protection installation, X b is the reactance from the short-circuit point to the synchronous machine end, X d is the synchronous electro-mechanical reactance, is the VSG current, is the synchronous machine current, R g is the transition resistor.

[0095] Formula (7) and formula (8) are combined to eliminate 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 of , and:

[0102]

[0103] is the saturation current angle (the angle between the saturation current vector and the d-axis is defined as the saturation current angle).

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

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

[0106]

[0107] in:

[0108]

[0109] X d , U b is a known constant. Combining equations (12) and (14) with the VSG control principle, we can get that A, B, C, D, E, and F are all known constants. At this time, there are two unknown quantities: X a and R g , there are also two equations, so the equation has an analytical solution.

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

[0111]

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

[0113]

[0114] Therefore, the second impedance X between the fault point and the protection is calculated. a .

[0115] If the synchronous motor parameters in the power equipment parameters are empty (the parameter information of the synchronous motor on the opposite side is unknown), the synchronous reactance X of the synchronous motor d and terminal voltage U bIt is known that by substituting equations (11) and (12) into equation (10), we can obtain the following set of equations:

[0116]

[0117] in:

[0118]

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

[0120]

[0121] in:

[0122]

[0123] At this time, the equation has no analytical solution. The least square method can be used to calculate the numerical solution of the impedance from the fault point to the protection. The numerical solution here is obtained by fitting:

[0124] 1) Since X d <<X l , omitting X d , let X d = 0, combine the two equations in (17) and eliminate R g , simplified to:

[0125]

[0126] in:

[0127]

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

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

[0130] 3) Will U b , Assume that G is the dependent variable and H is the independent variable. Using the least squares fitting, assume The residual error of the least squares fitting is minimized, that is, the degree of fitting is the highest, and k is closest to the slope of the fitting objective function g(H), so the problem is transformed into obtaining:

[0131]

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

[0133] 4) Through the constants B, C, E, F and the obtained The first impedance X between the fault point and the protection is calculated by a To calculate the transition resistance R g , X a The value of can be substituted back into formula (17).

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

[0135] By implementing this embodiment, the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters are obtained; according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters, the grid-connected system model is constructed; when the synchronous motor parameters in the power equipment parameters are empty, according to 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 group containing the impedance from the fault point to the protection are constructed; according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, the fitting objective function is minimized. , solve the equation group containing the impedance from the fault point to the protection room, and calculate the first impedance from the fault point to the protection room; determine the location of the fault point according to the first impedance from the fault point to the protection room and the virtual synchronous generator parameters; and perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point; wherein 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 output power, the converter reactive output power and the synchronous motor 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 parameters of the synchronous motor in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle in the control process of the virtual synchronous generator grid-connected system can be quickly considered, and then a group of equations containing the impedance from the fault point to the protection is constructed. Then, the first impedance from the fault point to the protection is obtained by solving the minimum fitting objective function, so as to accurately calculate the location of the fault of the virtual synchronous generator connected to the power grid transmission line, so as to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point. The control process of the virtual synchronous generator (VSG) grid-connected system is taken into consideration, and the accuracy of the distance protection of the virtual synchronous generator grid-connected system is improved.

[0136] See also Figure 5 , is a structural diagram of a distance protection device for a virtual synchronous generator grid-connected system based on a least squares method provided by an embodiment of the present invention, comprising:

[0137] System data acquisition module, used to obtain virtual synchronous generator parameters, power equipment parameters and transmission line parameters;

[0138] A system model building module, used to build a grid-connected system model according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters;

[0139] A function and first equation group construction module, used for constructing a fitting objective function of the grid-connected system model and an equation group containing the impedance between the fault point and the protection according to 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;

[0140] A first impedance calculation module is used to solve the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, with the goal of minimizing the fitting objective function, to calculate the first impedance from the fault point to the protection;

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

[0142] Among them, 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 output power, the converter reactive output power 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 according to the first impedance between the fault point and the protection and the virtual synchronous generator parameters; and to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point;

[0144] The location of the fault point is determined based on the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including:

[0145] According to the first impedance between the fault point and the protection and the virtual synchronous generator parameters, a first transition resistance is calculated to indicate that the synchronous generator parameters are empty;

[0146] The position of the fault point is determined according to the first impedance between the fault point and the protection and the first transition resistance.

[0147] Preferably, it also includes:

[0148] A second equation group building module is used to build an equation group containing the impedance from the fault point to the protection according to 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 not empty;

[0149] A third equation group building module is used to separate the imaginary part and the real part according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, so as to obtain a nonlinear equation group containing the impedance from the fault point to the protection;

[0150] A second impedance calculation module is used to solve a nonlinear equation group containing an impedance from a fault point to a protection interval according to the virtual synchronous generator parameters and the transmission line parameters, and calculate a second impedance from the fault point to the protection interval;

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

[0152] The present invention provides a virtual synchronous generator grid-connected system distance protection device based on the least squares method. According to a system data acquisition module, virtual synchronous generator parameters, power equipment parameters and transmission line parameters are acquired; in a system model construction module, a grid-connected system model is constructed according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; through a function and a first equation group construction module, when the synchronous motor parameters in the power equipment parameters are empty, a fitting objective function of the grid-connected system model and an equation group containing the impedance from the fault point to the protection are constructed according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; in a first impedance calculation module, according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and The equation group containing the impedance from the fault point to the protection is solved with the goal of minimizing the fitting objective function, and the first impedance from the fault point to the protection is calculated; finally, the position of the fault point is determined through the first distance protection module according to the first impedance from the fault point to the protection and the parameters of the virtual synchronous generator; and the distance protection of the virtual synchronous generator grid-connected system is performed according to the position of the fault point; wherein the parameters of the virtual synchronous generator 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 output angular frequency of the converter, the grid side angular frequency, the active output power of the converter, the reactive output power of the converter and the parameters of the synchronous motor; the transmission line parameters include: the transmission line inductance and the transmission line resistance. When a fault occurs in the grid-connected system, the parameters of the synchronous motor in the power equipment parameters are unknown. By constructing a grid-connected system model, the changing current limit value and saturation current angle in the control process of the virtual synchronous generator grid-connected system can be quickly considered, and then a group of equations containing the impedance from the fault point to the protection is constructed. Then, the first impedance from the fault point to the protection is obtained by solving the minimum fitting objective function, so as to accurately calculate the location of the fault of the virtual synchronous generator connected to the power grid transmission line, so as to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point. The control process of the virtual synchronous generator (VSG) grid-connected system is taken into consideration, and the accuracy of the distance protection of the virtual synchronous generator grid-connected system is improved.

[0153] It should be noted that the device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the accompanying drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art may understand and implement it without paying any creative effort.

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

[0155] Another embodiment of the present invention further 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, wherein when the processor executes the computer program, a virtual synchronous generator grid-connected system distance protection method based on the least squares method as described in the above embodiment is implemented. The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, and a cloud server. The terminal device may include, but is not limited to, a processor and a memory.

[0156] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal device, and uses various interfaces and lines to connect various parts of the entire terminal device.

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

[0158] Another embodiment of the present invention provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a virtual synchronous generator grid-connected system distance protection method based on least squares method as 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 the computer program is executed by the processor, the steps of each of the above-mentioned method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium.

[0160] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. 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 least squares method, characterized in that: include: Obtaining virtual synchronous generator parameters, power equipment parameters, and transmission line parameters; Constructing a grid-connected system model according to 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, constructing a fitting objective function of the grid-connected system model and a set of equations containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; According to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, the equation group containing the impedance from the fault point to the protection is solved with the goal of minimizing the fitting objective function, and the first impedance from the fault point to the protection is calculated; Determine the location of the fault point based on the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator; And according to the location of the fault point, distance protection is performed on the virtual synchronous generator grid-connected system; Among them, 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 output power, the converter reactive output power and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

2. A distance protection method for a virtual synchronous generator grid-connected system based on least squares method as claimed in claim 1, characterized in that: It is characterized in that The location of the fault point is determined based on the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including: According to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, a first transition resistance is calculated to indicate that the parameters of the synchronous generator are empty; The position of the fault point is determined according to the first impedance between the fault point and the protection and the first transition resistance.

3. A virtual synchronous generator grid-connected system distance protection method based on least squares method as claimed in claim 1, characterized in that: Also includes: When the synchronous motor parameters in the power equipment parameters are not empty, constructing a set of equations containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; Separating the imaginary part and the real part of the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, and obtaining a nonlinear equation group containing the impedance from the fault point to the protection; Solving a nonlinear equation group containing the impedance between the fault point and the protection according to the virtual synchronous generator parameters and the transmission line parameters, and calculating a second impedance between the fault point and the protection; The location of the fault point is determined according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and distance protection is performed on the virtual synchronous generator grid-connected system according to the location of the fault point.

4. A distance protection method for a virtual synchronous generator grid-connected system based on least squares method as claimed in claim 1, characterized in that: The location of the fault point is determined based on the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including: According to the second impedance between the fault point and the protection and the virtual synchronous generator parameters, a second transition resistance is calculated to indicate that the synchronous generator parameters are not empty; The position of the fault point is determined according to the second impedance between the fault point and the protection and the second transition resistance.

5. A virtual synchronous generator grid-connected system distance protection method based on least squares method as claimed in claim 1, characterized in that: The construction of the fitting objective function of the grid-connected system model includes: According to the transmission line inductance in the transmission line parameters and the synchronous machine parameters in the power equipment parameters, a plurality of groups of first sampling values ​​and second sampling values ​​are determined through the grid-connected system model; Using several groups of first sample values ​​as function dependent variables and several groups of second sample values ​​as function independent variables; According to the virtual synchronous generator parameters, the function dependent variables and the function independent variables, the fitting target parameters of the grid-connected system model are constructed.

6. A virtual synchronous generator grid-connected system distance protection device based on least squares method, characterized in that: include: System data acquisition module, used to obtain virtual synchronous generator parameters, power equipment parameters and transmission line parameters; A system model building module, used to build a grid-connected system model according to the virtual synchronous generator parameters, the power equipment parameters and the transmission line parameters; A function and first equation group construction module, used for constructing a fitting objective function of the grid-connected system model and an equation group containing the impedance between the fault point and the protection according to 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; A first impedance calculation module is used to solve the equation group containing the impedance from the fault point to the protection according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, with the goal of minimizing the fitting objective function, to calculate the first impedance from the fault point to the protection; A first distance protection module, used to determine the location of the fault point according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator; And according to the location of the fault point, distance protection is performed on the virtual synchronous generator grid-connected system; Among them, 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 output power, the converter reactive output power and the synchronous motor parameters; the transmission line parameters include: the transmission line inductance and the transmission line resistance.

7. A virtual synchronous generator grid-connected system distance protection device based on least squares method as claimed in claim 6, characterized in that: The first distance protection module is used to determine the location of the fault point according to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point; The location of the fault point is determined based on the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, including: According to the first impedance between the fault point and the protection and the parameters of the virtual synchronous generator, a first transition resistance is calculated to indicate that the parameters of the synchronous generator are empty; The position of the fault point is determined according to the first impedance between the fault point and the protection and the first transition resistance.

8. A virtual synchronous generator grid-connected system distance protection device based on least square method as claimed in claim 6, characterized in that: Also includes: A second equation group building module is used to build an equation group containing the impedance from the fault point to the protection according to 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 not empty; A third equation group building module is used to separate the imaginary part and the real part according to the virtual synchronous generator parameters, the power equipment parameters, the transmission line parameters and the equation group containing the impedance from the fault point to the protection, so as to obtain a nonlinear equation group containing the impedance from the fault point to the protection; A second impedance calculation module is used to solve a nonlinear equation group containing an impedance from a fault point to a protection interval according to the virtual synchronous generator parameters and the transmission line parameters, and calculate a second impedance from the fault point to the protection interval; The second distance protection module is used to determine the location of the fault point according to the second impedance between the fault point and the protection and the parameters of the virtual synchronous generator; and to perform distance protection on the virtual synchronous generator grid-connected system according to the location of the fault point.

9. A terminal device, characterized in that: It comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and when the processor executes the computer program, it implements a virtual synchronous generator grid-connected system distance protection method based on 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 running, the device where the computer-readable storage medium is located is controlled to execute a virtual synchronous generator grid-connected system distance protection method based on least squares method as described in any one of claims 1 to 5.

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