A short-circuit current envelope determination method and apparatus for a photovoltaic power generation system

Abstract

The present application belongs to the technical field of power system, discloses a kind of short-circuit current envelope determination method and device for photovoltaic power generation system.The method includes: obtaining photovoltaic power generation system parameter, power grid fault position and impedance;Accordingly determine the voltage amplitude and phase angle jump variable of the access point of the photovoltaic power generation system corresponding to the power grid fault position;Calculate the phase-locked loop output phase angle and the phase-locked deviation of access point voltage phase angle, and current control reference value;Combine both to calculate three-phase output current;Replace fault position, obtain multiple groups of current to determine short-circuit current envelope.The present application realizes the accurate construction of short-circuit current envelope, and provides an effective tool for fault analysis and protection design of new energy power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and particularly relates to a short-circuit current envelope determination method and device for a photovoltaic power generation system. BACKGROUND

[0002] With the increasing penetration of photovoltaic power generation systems in power systems, the influence of their fault characteristics on the safe and stable operation of power grids is becoming increasingly significant. Photovoltaic power generation systems are connected to the grid through power electronic inverters, and their short-circuit current characteristics differ essentially from those of traditional synchronous generators. Influenced by the coupling of factors such as inverter control strategies and phase-locked loop dynamic responses, the short-circuit current characteristics of photovoltaic power generation systems present complex transient characteristics.

[0003] Existing short-circuit current calculation methods are based on steady-state assumptions, resulting in insufficient calculation accuracy of short-circuit current envelopes. SUMMARY

[0004] Therefore, it is necessary to propose a short-circuit current envelope determination method for a photovoltaic power generation system in view of the above problems.

[0005] A short-circuit current envelope determination method for a photovoltaic power generation system, the method comprising:

[0006] obtaining photovoltaic power generation system parameters, a power grid fault location, and a power grid fault impedance;

[0007] determining a voltage amplitude and a voltage phase angle jump variable of an access point of the photovoltaic power generation system corresponding to the power grid fault location according to the photovoltaic power generation system parameters, the power grid fault location, and the power grid fault impedance;

[0008] calculating a phase-locked loop deviation between an output phase angle of a phase-locked loop of the photovoltaic power generation system corresponding to the power grid fault location and a voltage phase angle of the access point according to the photovoltaic power generation system parameters and the voltage amplitude and the voltage phase angle jump variable of the access point of the photovoltaic power generation system corresponding to the power grid fault location;

[0009] calculating a current control reference value of the photovoltaic power generation system corresponding to the power grid fault location according to the photovoltaic power generation system parameters and the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the power grid fault location;

[0010] calculating a three-phase output current of the photovoltaic power generation system corresponding to the power grid fault location according to the phase-locked loop deviation and the current control reference value;

[0011] replacing the power grid fault location, obtaining a plurality of corresponding three-phase output currents of the photovoltaic power generation system and determining a short-circuit current envelope of the photovoltaic power generation system.

[0012] The photovoltaic power generation system parameters include proportional and integral coefficients of a phase-locked loop, active output current and reactive output current of the photovoltaic power generation system before the power grid fault, and maximum current allowed by the photovoltaic power generation system for a short time.

[0013] The voltage amplitude of the access point of the photovoltaic power generation system corresponding to the power grid fault position is determined according to the photovoltaic power generation system parameters, the power grid fault position, and the power grid fault impedance, and specifically includes:

[0014] An equivalent circuit model of the power grid after the fault is constructed according to the power grid fault position, the line impedance before the power grid fault, and the power grid fault impedance;

[0015] The nodal admittance matrix of the power grid after the fault is calculated by using the equivalent circuit model;

[0016] The voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault is solved according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the nodal admittance matrix of the power grid after the fault.

[0017] The voltage phase angle jump variable of the photovoltaic power generation system corresponding to the power grid fault position is determined according to the photovoltaic power generation system parameters, the power grid fault position, and the power grid fault impedance, and specifically includes:

[0018] An equivalent circuit model of the power grid after the fault is constructed according to the power grid fault position, the line impedance before the power grid fault, and the power grid fault impedance;

[0019] The nodal admittance matrix of the power grid after the fault is calculated by using the equivalent circuit model;

[0020] The voltage phase angle of the access point of the photovoltaic power generation system after the power grid fault is solved according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the nodal admittance matrix of the power grid after the fault.

[0021] The nodal admittance matrix of the power grid before the fault is calculated according to the power grid fault impedance;

[0022] The voltage phase angle of the access point of the photovoltaic power generation system before the power grid fault is solved according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the nodal admittance matrix of the power grid before the fault.

[0023] The voltage phase angle jump variable is obtained by subtracting the voltage phase angle of the access point of the photovoltaic power generation system before the power grid fault from the voltage phase angle of the access point of the photovoltaic power generation system after the power grid fault.

[0024] In the scheme, the phase-locked deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the fault position of the power grid and the voltage phase angle of the access point of the photovoltaic power generation system is calculated according to the voltage amplitude and the voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the fault position of the power grid and the parameters of the photovoltaic power generation system, and specifically includes:

[0025] The proportional coefficient and the integral coefficient of the phase-locked loop of the photovoltaic power generation system are obtained.

[0026] If the voltage amplitude is less than 4 times the ratio of the proportional coefficient to the integral coefficient squared, the phase-locked deviation is determined according to the phase-locked deviation decay cosine oscillation formula.

[0027] If the voltage amplitude is greater than or equal to 4 times the ratio of the proportional coefficient to the integral coefficient squared, the phase-locked deviation is determined according to the phase-locked deviation decay hyperbolic sine oscillation formula.

[0028] In the scheme, the phase-locked deviation is determined according to the phase-locked deviation decay cosine oscillation formula, and specifically includes:

[0029]

[0030] wherein, represents the phase-locked deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system and the voltage phase angle of the access point after the power grid fault; t represents the fault duration; represents the voltage phase angle jump of the access point after the power grid fault; represents a first constant; b represents a second constant; represents a first initial phase angle; represents a cosine function phase angle; represents a function with the natural constant e as the base and -bt as the exponent.

[0031] In the scheme, the phase-locked deviation is determined according to the phase-locked deviation decay hyperbolic sine oscillation formula, and specifically includes:

[0032]

[0033] wherein, represents the phase-locked deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system and the voltage phase angle of the access point after the power grid fault; t represents the fault duration; represents the voltage phase angle jump of the access point after the power grid fault; represents a first constant; b represents a second constant; σ represents a second initial phase angle; represents a sine function phase angle; represents a function with the natural constant e as the base and -bt as the exponent.

[0034] In the above scheme, the current control reference value includes the active current reference value. and reactive current reference value The active current reference value is determined according to the following formula. and reactive current reference value :

[0035]

[0036] in, This indicates the voltage amplitude at the connection point of the photovoltaic power generation system after a grid fault; and This indicates that active current and reactive current are related to The expression; This indicates the maximum allowable current for a photovoltaic power generation system during a short period of time. This indicates the reference value for active current; This indicates the reference value for reactive current.

[0037] In the above scheme, calculating the three-phase output current of the photovoltaic power generation system corresponding to the grid fault location based on the phase-locked loop deviation and the current control reference value specifically includes:

[0038]

[0039]

[0040]

[0041] in, Indicates photovoltaic power generation system Phase output current; This represents the output current of phase b of the photovoltaic power generation system; This represents the c-phase output current of the photovoltaic power generation system; This indicates the magnitude of the current control reference value before the fault. This indicates the magnitude of the current control reference value after a fault. The phase angle represents the current reference value before the fault. The phase angle represents the current reference value after a fault. This represents the angle between the d-axis and the q-axis; This represents the phase-locked deviation between the output phase angle of the phase-locked loop and the voltage phase angle at the connection point at time t.

[0042] This application also proposes a short-circuit current envelope determination device for a photovoltaic power generation system, the device comprising: a parameter acquisition module, a voltage calculation module, a phase-locked loop deviation calculation module, a current reference value calculation module, an output current calculation module, and an envelope determination module;

[0043] The parameter acquisition module is configured to acquire photovoltaic power generation system parameters, a power grid fault position, and a power grid fault impedance;

[0044] The voltage calculation module is configured to determine a voltage amplitude and a voltage phase angle jump variable of an access point of a photovoltaic power generation system corresponding to the power grid fault position according to the photovoltaic power generation system parameters, the power grid fault position, and the power grid fault impedance.

[0045] The phase-locked loop deviation calculation module is configured to calculate a phase-locked loop deviation between an output phase angle of a phase-locked loop of the photovoltaic power generation system corresponding to the power grid fault position and a voltage phase angle of the access point according to the photovoltaic power generation system parameters and the voltage amplitude and the voltage phase angle jump variable of the access point of the photovoltaic power generation system corresponding to the power grid fault position.

[0046] The current reference value calculation module is configured to calculate a current control reference value of the photovoltaic power generation system corresponding to the power grid fault position according to the photovoltaic power generation system parameters and the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the power grid fault position.

[0047] The output current calculation module is configured to calculate a three-phase output current of the photovoltaic power generation system corresponding to the power grid fault position according to the phase-locked loop deviation and the current control reference value.

[0048] The envelope determination module is configured to obtain a plurality of three-phase output currents of corresponding photovoltaic power generation systems by replacing the power grid fault position, and determine a photovoltaic power generation system short-circuit current envelope.

[0049] The embodiment of the present application has the following beneficial effects: by acquiring photovoltaic power generation system parameters, a power grid fault position, and an impedance, the method can accurately calculate an access point voltage amplitude and a phase angle jump variable, and then quantize a phase-locked loop deviation generated by a phase-locked loop transient response, combine a voltage amplitude to dynamically adjust a current control reference value, and realize accurate modeling of a three-phase output current; by traversing different fault positions, the system obtains a plurality of current data and fits an envelope curve, thereby completely covering the change characteristics of a short-circuit current in time and space dimensions, providing a reliable basis for power system protection configuration, equipment selection, and stability evaluation, and significantly improving the safe operation level of a power grid containing a photovoltaic power generation system. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0051] wherein:

[0052] Figure 1 This is a schematic flowchart of a method for determining the short-circuit current envelope of a photovoltaic power generation system in one embodiment.

[0053] Figure 2 This is an equivalent circuit diagram of the photovoltaic power generation system under short-circuit fault in the embodiments of this application. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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.

[0055] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention; however, it will be apparent to those skilled in the art that the invention may be practiced without one or more of these details; in other instances, certain technical features well-known in the art have not been described in order to avoid confusion with the invention. It should be understood that the invention can be practiced in different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the invention to those skilled in the art.

[0056] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms, unless the context clearly indicates otherwise. The terms “comprising” and / or “including,” when used in this specification, identify the presence of said features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0057] To fully understand the present invention, a detailed structure will be presented in the following description in order to illustrate the technical solution proposed by the present invention; optional embodiments of the present invention are described in detail below, however, in addition to these detailed descriptions, the present invention may have other embodiments.

[0058] like Figure 1 As shown, in one embodiment, a method for determining the short-circuit current envelope of a photovoltaic power generation system is provided. This method includes steps S101 to S106, detailed below:

[0059] S101, acquiring photovoltaic power generation system parameters, power grid fault position and power grid fault impedance;

[0060] Specifically, the photovoltaic power generation system accesses the power grid through a grid-connected point, and needs to first determine that the power grid has failed by using voltage / current mutation monitoring or AC power root mean square value threshold judgment, and then acquire the power grid fault position and the power grid fault impedance.

[0061] In some embodiments, the photovoltaic power generation system parameters include the proportional coefficient and the integral coefficient of the phase-locked loop, the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault, and the maximum current allowed by the photovoltaic power generation system for a short time.

[0062] S102, determining the voltage amplitude and the voltage phase angle jump variable of the access point of the photovoltaic power generation system corresponding to the power grid fault position according to the photovoltaic power generation system parameters, the power grid fault position and the power grid fault impedance;

[0063] In some embodiments, the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the power grid fault position is determined according to the photovoltaic power generation system parameters, the power grid fault position and the power grid fault impedance, and specifically includes:

[0064] constructing an equivalent circuit model of the power grid after the fault according to the power grid fault position, the line impedance before the power grid fault and the power grid fault impedance;

[0065] calculating the node admittance matrix of the power grid after the fault by using the equivalent circuit model;

[0066] solving the voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the node admittance matrix of the power grid after the fault.

[0067] Preferably, the voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault is calculated by the following formula (1):

[0068] Formula (1)

[0069] the voltage phase angle jump variable calculated by the following formula (2):

[0070] Formula (2)

[0071] wherein, represents the voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault; represents the voltage phase angle jump variable of the access point after the power grid fault; represents the first power grid parameter; represents a second grid parameter; b1 represents a third grid parameter; b2 represents a fourth grid parameter; c1 represents a first photovoltaic power generation system parameter; c2 represents a second photovoltaic power generation system parameter; represents an active power control reference value; represents a reactive power control reference value; represents a grid voltage; R represents a line resistance of a line at a fault location; X represents a line reactance of the line at the fault location; is a voltage phase angle of a point of interconnection after a grid fault.

[0072] Specifically, the first grid parameter , the second grid parameter , the third grid parameter b1, the fourth grid parameter b2, the first photovoltaic power generation system parameter c1, and the second photovoltaic power generation system parameter c2 are calculated by the following formulas (3)-(8), respectively.

[0073] Formula (3)

[0074] Formula (4)

[0075] Formula (5)

[0076] Formula (6)

[0077] Formula (7)

[0078] Formula (8)

[0079] wherein, represents a resistance value of a transition resistance after the fault; represents a ratio of a line impedance between the point of interconnection of the photovoltaic power generation system and the fault location to a total line impedance of an entire line at the fault location before the fault; represents a grid voltage; R represents a line resistance of a line at a fault location; a square of a line resistance of a line at a fault location; X represents a line reactance of the line at the fault location; represents an active power control reference value; represents a reactive power control reference value; represents the first grid parameter , the second grid parameter b1, the third grid parameter b2, the first photovoltaic power generation system parameter c1, and the second photovoltaic power generation system parameter c2.

[0080] The power grid short-circuit fault calculation needs to determine the fault location; and construct an equivalent circuit diagram of the post-fault power grid including the photovoltaic power generation system, equivalent system and line, as shown in Figure 2 Each line has its own line impedance, the total line impedance of the line where the fault location is Z, the line impedance of the line between the access point of the photovoltaic power generation system and the fault location is kZ, and the line impedance of the line between the fault location and the power grid side is Z-kZ. Figure 2 represents the voltage of the access point of the photovoltaic power generation system, i.e. represents the voltage of the power grid.

[0081] The voltage phase angle of the access point after the power grid fault The voltage phase angle of the access point after the power grid fault is calculated by the following formula (9):

[0082] Formula (9)

[0083] wherein, is the voltage phase angle of the access point after the power grid fault; represents the first power grid parameter; represents the second power grid parameter; b1 represents the third power grid parameter; b2 represents the fourth power grid parameter; c1 represents the first photovoltaic power generation system parameter; and c2 represents the second photovoltaic power generation system parameter.

[0084] In addition, the phase describes the measure of signal waveform change, usually in angle as a unit, also known as phase angle. The voltage phase angle of the embodiment refers to the phase of the voltage. The voltage phase angle jump value refers to the difference between the voltage phase angles before and after the fault.

[0085] In some embodiments, the voltage phase angle jump value of the photovoltaic power generation system corresponding to the power grid fault location is determined according to the photovoltaic power generation system parameters, the power grid fault location and the power grid fault impedance, specifically comprising:

[0086] According to the power grid fault location, the line impedance before the power grid fault and the power grid fault impedance, an equivalent circuit model of the post-fault power grid is constructed;

[0087] The post-fault power grid node admittance matrix is calculated by using the equivalent circuit model;

[0088] The voltage phase angle of the access point of the photovoltaic power generation system after the power grid fault is solved according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the post-fault power grid node admittance matrix;

[0089] The pre-fault power grid node admittance matrix is calculated according to the power grid fault impedance;

[0090] ​S101, obtaining the voltage phase angle of the access point of the photovoltaic power generation system before the power grid fault according to the active output current and the reactive output current of the photovoltaic power generation system before the power grid fault and the node admittance matrix of the power grid before the power grid fault;

[0091] S102, obtaining the voltage phase angle jump of the access point of the photovoltaic power generation system after the power grid fault by subtracting the voltage phase angle of the access point of the photovoltaic power generation system after the power grid fault from the voltage phase angle of the access point of the photovoltaic power generation system before the power grid fault.

[0092] S103, calculating the phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the power grid fault position and the voltage phase angle of the access point of the photovoltaic power generation system according to the voltage amplitude and the voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the power grid fault position.

[0093] In one embodiment, the phase-locked loop deviation is calculated by the following formula (10):

[0094] Formula (10)

[0095] Specifically, when t is greater than or equal to t0, is equal to ; when t is less than t0, is equal to .

[0096] wherein, represents the phase-locked loop deviation between the output phase angle of the phase-locked loop and the voltage phase angle of the access point at t moment; represents the phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system before the power grid fault and the voltage phase angle of the access point at t moment; represents the phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system after the power grid fault and the voltage phase angle of the access point; t0 represents the initial moment of the fault; t represents the fault duration moment; represents the unit step function.

[0097] Specifically, considering the influence of the photovoltaic power generation system phase-locked loop control parameters and the access point voltage on the phase-locked loop deviation, the phase-locked loop transfer function is established, and the phase-locked loop output phase angle and the voltage phase angle of the access point of the photovoltaic power generation system between the phase-locked loop deviation are solved. The phase-locked loop deviation is a decay component.

[0098] If t is any moment after the fault, t is greater than or equal to t0. t can also be the moment when the fault ends. The phase-locked loop deviation solved in this embodiment is the phase-locked loop deviation between the output phase angle of the phase-locked loop and the voltage phase angle of the access point of the photovoltaic power generation system after the fault occurs, that is, t is greater than or equal to t0.

[0099] S104、According to the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the grid fault position, the current control reference value of the photovoltaic power generation system corresponding to the grid fault position is calculated;

[0100] In some embodiments, according to the voltage amplitude and the voltage phase angle jump variable of the access point of the photovoltaic power generation system corresponding to the grid fault position, the phase-locked deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the grid fault position and the voltage phase angle of the access point is calculated, specifically including:

[0101] The proportional coefficient and the integral coefficient of the phase-locked loop of the photovoltaic power generation system are obtained;

[0102] If the voltage amplitude is less than 4 times the ratio of the proportional coefficient and the square of the integral coefficient, the phase-locked deviation is determined according to the phase-locked deviation decay cosine oscillation formula;

[0103] If the voltage amplitude is greater than or equal to 4 times the ratio of the proportional coefficient and the square of the integral coefficient, the phase-locked deviation is determined according to the phase-locked deviation decay hyperbolic sine oscillation formula.

[0104] In some embodiments, the phase-locked deviation is determined according to the phase-locked deviation decay cosine oscillation formula, specifically including:

[0105] Formula (11)

[0106] Wherein, represents the phase-locked deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system after the grid fault and the voltage phase angle of the access point; t represents the fault duration; represents the voltage phase angle jump variable of the access point after the grid fault; represents the first constant; b represents the second constant; represents the first initial phase angle; represents the phase angle of the cosine function; represents the function with the natural constant e as the base and the exponential as-bt.

[0107] Specifically, and b represent the constants affecting the change rate and the decay degree of the angular displacement, respectively; determines the starting position of the angular displacement.

[0108] In some embodiments, the phase-locked deviation is determined according to the phase-locked deviation decay hyperbolic sine oscillation formula, specifically including:

[0109] Formula (12)

[0110] Wherein, The phase-locked loop (PLL) deviation between the output phase angle of the PLL of the photovoltaic power generation system and the voltage phase angle at the connection point is represented by t; t represents the duration of the fault. This indicates the voltage phase angle jump variable at the connection point after a power grid fault; b represents the first constant; σ represents the second constant; and σ represents the second initial phase angle. This represents the phase angle of a sine function; This represents a function with the natural constant e as the base and the exponent -bt.

[0111] In one embodiment, the parameters of the photovoltaic power generation system include the proportional coefficient and integral coefficient of the phase-locked loop (PLL) of the photovoltaic power generation system; and the phase-locking deviation between the output phase angle of the PLL of the photovoltaic power generation system and the voltage phase angle at the connection point before the grid fault at time t. The phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system and the voltage phase angle at the connection point after a grid fault. It can be calculated using the following formulas (13), (14) or formulas (15), (16):

[0112] like ,but:

[0113] Formula (13)

[0114] Formula (14)

[0115] like ,but:

[0116] Formula (15)

[0117] Formula (16)

[0118] like ,but:

[0119] Formula (13)

[0120] Formula (14)

[0121] or, Formula (15)

[0122] Formula (16)

[0123] in, This indicates the voltage phase angle at the connection point before the power grid fault. This indicates the voltage amplitude at the connection point of the photovoltaic power generation system after a grid fault; This indicates the voltage phase angle jump variable at the connection point after a power grid fault; a proportional coefficient of a phase-locked loop of the photovoltaic power generation system; an integral coefficient of the phase-locked loop of the photovoltaic power generation system; a phase-locked deviation between an output phase angle of the phase-locked loop of the photovoltaic power generation system and a voltage phase angle of the access point at a time t after the power grid fault; a phase-locked deviation between an output phase angle of the phase-locked loop of the photovoltaic power generation system and a voltage phase angle of the access point at a time t before the power grid fault; a first constant; b represents a second constant; a first initial phase angle; σ represents a second initial phase angle; a time at which the fault occurs; t represents a time at which the fault lasts; a function with a natural constant e as a base and an exponent of -bt; a function with a natural constant e as a base and an exponent of .

[0124] Specifically, , b, , are obtained by the following formulas (17)-(20), respectively:

[0125] Formula (17)

[0126] Formula (18)

[0127] Formula (19)

[0128] Formula (20)

[0129] wherein, a first constant; b represents a second constant; a first initial phase angle; σ represents a second initial phase angle; a voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault; a proportional coefficient of a phase-locked loop of the photovoltaic power generation system; an integral coefficient of the phase-locked loop of the photovoltaic power generation system.

[0130] S105, calculating, according to the phase-locked deviation and the current control reference value, a three-phase output current of the photovoltaic power generation system corresponding to the power grid fault position;

[0131] In some embodiments, the current control reference value includes an active current reference value and a reactive current reference value The active current reference value and the reactive current reference value :

[0132]

[0133] wherein, represents the voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault; and represent the expressions of the active current and the reactive current with respect to ; represents the maximum current allowed by the photovoltaic power generation system in a short time; represents the active current reference value; represents the reactive current reference value.

[0134] In some embodiments, according to the phase-locked deviation and the current control reference value, the three-phase output current of the photovoltaic power generation system corresponding to the power grid fault position is calculated, specifically comprising:

[0135] Formula (22)

[0136] Formula (23)

[0137] Formula (24)

[0138] wherein, represents the phase output current of the photovoltaic power generation system; represents the b-phase output current of the photovoltaic power generation system; represents the c-phase output current of the photovoltaic power generation system; represents the amplitude of the current control reference value before the fault; represents the amplitude of the current control reference value after the fault; represents the phase angle of the current reference value before the fault; represents the phase angle of the current reference value after the fault; represents the angle between the d-axis and the q-axis; represents the phase-locked deviation between the output phase angle of the phase-locked loop and the voltage phase angle of the access point at time t.

[0139] wherein, the d-axis and the q-axis are commonly known and widely used in the field of power electronic converter control. The d-axis, the q-axis and the cross-axis are standard coordinate axes in the synchronous rotating coordinate system.

[0140] Specifically, , , , are calculated by the following formulas (25)-(28), respectively:

[0141] Equation (25)

[0142] Equation (26)

[0143] Equation (27)

[0144] Equation (28)

[0145] wherein, and represent the d-axis and q-axis current control reference values of the photovoltaic power generation system before the power grid fault; and both represent the d-axis and q-axis current control reference values of the photovoltaic power generation system after the power grid fault; represents the amplitude of the current control reference value before the fault; represents the amplitude of the current control reference value after the fault; represents the phase angle of the current reference value before the fault; represents the phase angle of the current reference value after the fault.

[0146] In addition, the d-axis current control reference value of the photovoltaic power generation system before the power grid fault is the active power control reference value and the ratio of the rated voltage amplitude of the photovoltaic power generation system; the q-axis current control reference value of the photovoltaic power generation system before the power grid fault is zero. The included angle between the d-axis and the q-axis is determined by the voltage phase angle of the access point before the power grid fault , the unit step function and the voltage phase angle jump of the access point after the power grid fault .

[0147] The present application is directed to the transmission process of the voltage amplitude and phase angle jump of the access point caused by the power grid fault through the phase-locked loop and the converter control system of the photovoltaic power generation system. The influence of the short-time asynchronization of the phase-locked loop and the power grid phase angle caused by the voltage phase angle jump on the output current of the photovoltaic power generation system is fully considered, and the existing photovoltaic power generation system output current calculation method which ignores the phase-locked transient response is modified. The accuracy of the output current calculation of the photovoltaic power generation system in the whole process of the power grid fault can be improved, which can be used for the transient analysis, fault protection and control research and engineering application of the power system containing the photovoltaic power generation system.

[0148] S106, replacing the power grid fault position, obtaining a plurality of corresponding three-phase output currents of the photovoltaic power generation system and determining the short-circuit current envelope of the photovoltaic power generation system.

[0149] Preferably, peak extraction and interpolation algorithms are used to fit the peak current at multiple fault locations into a short-circuit current envelope curve.

[0150] This application fully considers the impact of short-time asynchronous voltage phase angle changes between the photovoltaic power generation system's phase-locked angle and the grid's phase angle on the short-circuit current of the photovoltaic power generation system, and fully considers the impact of voltage amplitude changes coupled through converter control on the short-circuit current of the photovoltaic power generation system. It can accurately calculate the transient short-circuit current envelope of the photovoltaic power generation system, providing a basis for the design, operation control, and protection of power systems.

[0151] In one specific embodiment, the initial value of the phase-locked error, the error value after 0.02s, and the time taken for the phase-locked error to decay to less than 0.01 are shown in Table 1 below:

[0152] Table 1

[0153]

[0154] Table 1 shows the phase-locked loop (PLL) deviation under different PLL control parameters; the initial value of the PLL deviation is the value at time 1 second, and the deviation value after 0.02 seconds is the value at time 1.02 seconds. The proportional gain of the phase-locked loop in a photovoltaic power generation system, This represents the integral coefficient of the phase-locked loop in the photovoltaic power generation system.

[0155] In one specific embodiment, under different phase-locked loop control parameters Phase-locked transient component of phase output current The initial and peak values ​​are shown in Appendix Table 2:

[0156] Table 2

[0157]

[0158] Table 2 is Phase-locked transient component of phase output current Initial value and peak value; The proportional gain of the phase-locked loop in a photovoltaic power generation system, This represents the integral coefficient of the phase-locked loop in the photovoltaic power generation system.

[0159] This application also proposes a short-circuit current envelope determination device for a photovoltaic power generation system. The device includes: a parameter acquisition module, a voltage calculation module, a phase-locked deviation calculation module, a current reference value calculation module, an output current calculation module, and an envelope determination module.

[0160] The parameter acquisition module is used to acquire photovoltaic power generation system parameters, grid fault location, and grid fault impedance;

[0161] The voltage calculation module is configured to determine a voltage amplitude and a voltage phase angle jump of an access point of the photovoltaic power generation system corresponding to the power grid fault position according to the photovoltaic power generation system parameters, the power grid fault position and the power grid fault impedance.

[0162] The phase-locked deviation calculation module is configured to calculate a phase-locked deviation between an output phase angle of a phase-locked loop of the photovoltaic power generation system corresponding to the power grid fault position and a voltage phase angle of the access point according to the photovoltaic power generation system parameters and the voltage amplitude and the voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the power grid fault position.

[0163] The current reference value calculation module is configured to calculate a current control reference value of the photovoltaic power generation system corresponding to the power grid fault position according to the photovoltaic power generation system parameters and the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the power grid fault position.

[0164] The output current calculation module is configured to calculate a three-phase output current of the photovoltaic power generation system corresponding to the power grid fault position according to the phase-locked deviation and the current control reference value.

[0165] The envelope determination module is configured to obtain a plurality of three-phase output currents of the photovoltaic power generation system corresponding to the power grid fault position by replacing the power grid fault position, and determine a short-circuit current envelope of the photovoltaic power generation system.

[0166] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a non-volatile computer readable storage medium. When the program is executed, the processes of the above-mentioned embodiments can be included. Any reference to a memory, storage, database or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memory.

[0167] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0168] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application. The above disclosure is only the preferred embodiment of the present application, and of course cannot limit the scope of the patent of the present application. Therefore, the equivalent changes made according to the claims of the present application still fall within the scope of the present application.

Claims

1. A method for determining the short-circuit current envelope in a photovoltaic power generation system, characterized in that, The method includes: Acquire photovoltaic power generation system parameters, grid fault location, and grid fault impedance; the photovoltaic power generation system parameters include the proportional coefficient and integral coefficient of the phase-locked loop, the active power output current and reactive power output current of the photovoltaic power generation system before the grid fault, and the maximum allowable current of the photovoltaic power generation system in a short time. Based on the photovoltaic power generation system parameters, the location of the grid fault, and the grid fault impedance, determine the voltage amplitude and voltage phase angle jump at the connection point of the photovoltaic power generation system corresponding to the grid fault location; specifically including: Based on the location of the power grid fault, the line impedance before the power grid fault, and the power grid impedance after the fault, an equivalent circuit model of the power grid after the fault is constructed; the admittance matrix of the power grid nodes after the fault is calculated using the equivalent circuit model; and the voltage amplitude of the access point of the photovoltaic power generation system after the power grid fault is solved based on the active and reactive output currents of the photovoltaic power generation system before the power grid fault and the admittance matrix of the power grid nodes after the fault. The voltage phase angle at the connection point of the photovoltaic power generation system after the grid fault is calculated based on the active and reactive current output of the photovoltaic power generation system before the grid fault and the admittance matrix of the grid nodes after the fault; the admittance matrix of the grid nodes before the fault is calculated based on the grid fault impedance; the voltage phase angle at the connection point of the photovoltaic power generation system before the grid fault is calculated based on the active and reactive current output of the photovoltaic power generation system before the grid fault and the admittance matrix of the grid nodes before the fault; the difference between the voltage phase angle at the connection point of the photovoltaic power generation system after the grid fault and the voltage phase angle at the connection point of the photovoltaic power generation system before the grid fault is obtained; Based on the parameters of the photovoltaic power generation system and the voltage amplitude and voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the location of the grid fault, calculate the phase-locking deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the location of the grid fault and the voltage phase angle of the access point. Based on the parameters of the photovoltaic power generation system and the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the location of the grid fault, calculate the current control reference value of the photovoltaic power generation system corresponding to the location of the grid fault. Based on the phase-locked loop deviation and the current control reference value, calculate the three-phase output current of the photovoltaic power generation system corresponding to the grid fault location; By changing the location of the grid fault, the three-phase output current of several corresponding photovoltaic power generation systems is obtained, and the short-circuit current envelope of the photovoltaic power generation system is determined.

2. The method for determining the short-circuit current envelope of a photovoltaic power generation system according to claim 1, characterized in that, The step of calculating the phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the grid fault location and the voltage amplitude and voltage phase angle jump of the access point of the photovoltaic power generation system at the grid fault location, based on the parameters of the photovoltaic power generation system and the voltage phase angle jump of the access point of the photovoltaic power generation system at the grid fault location, specifically includes: Obtain the proportional coefficient and integral coefficient of the phase-locked loop of the photovoltaic power generation system; If the voltage amplitude is less than 4 times the ratio of the phase-locked loop proportional coefficient to the square of the integral coefficient, the phase-locked deviation is determined according to the phase-locked deviation decay cosine oscillation formula. If the voltage amplitude is greater than or equal to 4 times the ratio of the phase-locked loop proportional coefficient to the square of the integral coefficient, the phase-locked deviation is determined according to the hyperbolic sine oscillation formula for phase-locked deviation decay.

3. The method for determining the short-circuit current envelope of a photovoltaic power generation system according to claim 2, characterized in that, The determination of phase-locked error based on the phase-locked error decay cosine oscillation formula specifically includes: in, The phase-locked loop (PLL) deviation between the output phase angle of the PLL of the photovoltaic power generation system and the voltage phase angle at the connection point is represented by t; t represents the duration of the fault. This indicates the voltage phase angle jump variable at the connection point after a power grid fault; b represents the first constant; b represents the second constant. Indicates the first initial phase angle; Represents the phase angle of the cosine function; This represents a function with the natural constant e as the base and the exponent -bt.

4. The method for determining the short-circuit current envelope of a photovoltaic power generation system according to claim 3, characterized in that, The determination of the phase-locked error based on the hyperbolic sine oscillation formula for phase-locked error attenuation specifically includes: in, The phase-locked loop (PLL) deviation between the output phase angle of the PLL of the photovoltaic power generation system and the voltage phase angle at the connection point is represented by t; t represents the duration of the fault. This indicates the voltage phase angle jump variable at the connection point after a power grid fault; b represents the first constant; σ represents the second constant; and σ represents the second initial phase angle. This represents the phase angle of a sine function; This represents a function with the natural constant e as the base and the exponent -bt.

5. The method for determining the short-circuit current envelope of a photovoltaic power generation system according to claim 1, characterized in that, The current control reference value includes the active current reference value. and reactive current reference value The active current reference value is determined according to the following formula. and reactive current reference value : in, This indicates the voltage amplitude at the connection point of the photovoltaic power generation system after a grid fault; and This indicates that active current and reactive current are related to The expression; This indicates the maximum allowable current for a photovoltaic power generation system during a short period of time. This indicates the reference value for active current; This indicates the reference value for reactive current.

6. The method for determining the short-circuit current envelope of a photovoltaic power generation system according to claim 1, characterized in that, The step of calculating the three-phase output current of the photovoltaic power generation system corresponding to the grid fault location based on the phase-locked loop deviation and the current control reference value specifically includes: in, Indicates photovoltaic power generation system Phase output current; This represents the output current of phase b of the photovoltaic power generation system. This represents the c-phase output current of the photovoltaic power generation system; This indicates the magnitude of the current control reference value before the fault. This indicates the magnitude of the current control reference value after a fault. The phase angle represents the current reference value before the fault. Phase angle representing the current reference value after a fault; This represents the angle between the d-axis and the q-axis; This represents the phase-locked deviation between the output phase angle of the phase-locked loop and the voltage phase angle at the connection point at time t.

7. A device for determining the short-circuit current envelope in a photovoltaic power generation system, characterized in that, The apparatus used in any one of claims 1-6 comprises: a parameter acquisition module, a voltage calculation module, a phase-locked loop deviation calculation module, a current reference value calculation module, an output current calculation module, and an envelope determination module; The parameter acquisition module is used to acquire photovoltaic power generation system parameters, grid fault location, and grid fault impedance; The voltage calculation module is used to determine the voltage amplitude and voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the grid fault location based on the photovoltaic power generation system parameters, grid fault location and grid fault impedance; The phase-locked loop deviation calculation module is used to calculate the phase-locked loop deviation between the output phase angle of the phase-locked loop of the photovoltaic power generation system corresponding to the grid fault location and the voltage amplitude and voltage phase angle jump of the access point of the photovoltaic power generation system corresponding to the grid fault location, based on the parameters of the photovoltaic power generation system and the voltage amplitude and voltage phase angle jump of the access point of the photovoltaic power generation system at the grid fault location. The current reference value calculation module is used to calculate the current control reference value of the photovoltaic power generation system corresponding to the grid fault location based on the parameters of the photovoltaic power generation system and the voltage amplitude of the access point of the photovoltaic power generation system corresponding to the grid fault location. The output current calculation module is used to calculate the three-phase output current of the photovoltaic power generation system corresponding to the grid fault location based on the phase-locked deviation and the current control reference value. The envelope determination module is used to obtain the three-phase output current of several corresponding photovoltaic power generation systems by changing the location of the power grid fault, and to determine the short-circuit current envelope of the photovoltaic power generation system.

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