CN113791309A - Link single-end fault location method based on output characteristics of photovoltaic inverter power supply - Google Patents
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- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
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Abstract
A tie line single-end fault location method based on photovoltaic inverter power supply output characteristics is characterized in that output current in inverter distributed power supply faults has nonlinearity and current-limiting characteristics, and influences are generated on tie line fault location, so that selection of photovoltaic inverter power supply control strategies in asymmetric earth faults, expression of positive sequence and negative sequence components of photovoltaic inverter power supply output current and a new fault location scheme containing photovoltaic inverter power supply tie lines are achieved, a fault location method containing the photovoltaic inverter power supply tie lines is simplified, and the precision of fault location containing the photovoltaic inverter power supply tie lines is improved.
Description
Technical Field
The invention relates to a technology in the field of power grid fault detection, in particular to a tie line single-end fault location method based on the output characteristic of a photovoltaic inverter power supply.
Background
In recent years, in order to solve a series of problems of environmental pollution, resource shortage and the like caused by thermal power generation, more and more people aim at utilizing novel energy such as solar energy, wind energy and the like, and distributed power sources are paid more and more attention and are applied. The photovoltaic power supply is generally connected to the existing power distribution system through power electronic elements such as a three-phase inverter, and photovoltaic power generation is also a photovoltaic inverter power supply. For a power grid with high permeability of distributed energy, when a system has a short-circuit fault and the voltage of the system drops temporarily, if a corresponding control means is not adopted for the photovoltaic inverter power supply during the voltage drop, the photovoltaic inverter power supply can be caused to quit operation on a large scale, and the stability of the power grid is reduced.
With the development and wide application of new energy and power electronic components, distributed power sources gradually permeate into the existing power grid. Most distributed power supplies need to be connected to a power distribution network tie line after passing through an inverter, namely the inverter power supply. Different control strategies of the inverter power supply influence the output characteristic and the fault characteristic of the inverter power supply, so that the fault current output characteristic and the fault distance measuring method in the power distribution network connecting line are influenced. Firstly, a control strategy of an inverter power supply under the condition of asymmetric power grid voltage drop needs to be analyzed to obtain the output characteristic of the inverter power supply, then the fault characteristic of the inverter power supply is analyzed in detail, and the difficulty brought by the fault location of a tie line due to the photovoltaic inverter power supply access and a new method for the fault location of the tie line of the power distribution network including the photovoltaic inverter power supply access are researched by combining the existing fault location basic principle of the tie line of the power distribution network.
Disclosure of Invention
The invention provides a tie line single-end fault location method based on the output characteristics of a photovoltaic inverter power supply, which aims at the defects of the prior art, considers the characteristics that the output current has nonlinearity and current-limiting characteristics when an inverter type distributed power supply fails, influences the tie line fault location, realizes the selection of a photovoltaic inverter power supply control strategy, the expression of positive sequence and negative sequence components of the output current of the photovoltaic inverter power supply and a new fault location scheme containing the tie line of the photovoltaic inverter power supply, simplifies the fault location method containing the tie line of the photovoltaic inverter power supply, and improves the precision of the fault location containing the tie line of the photovoltaic inverter power supply.
The invention is realized by the following technical scheme:
the invention relates to a tie line single-end fault location method based on output characteristics of a photovoltaic inverter, which comprises the following steps of:
step 1) when an asymmetric fault occurs in a power distribution network connecting line accessed by a photovoltaic inverter power supply, positive sequence, negative sequence and zero sequence components occur in the voltage of a power grid, and expressions of instantaneous active power p and reactive power q in an alpha beta coordinate system are obtained according to the sum of the three components of positive and negative zero sequences of output voltage and current, so that three-phase active power is deduced, wherein the expressions specifically comprise the following steps:
wherein:
and
is the average of the active and reactive power, Pc2、Ps2、Qc2、Qs2Respectively harmonic components of the oscillation, vα、vβ、iα、iβRespectively, the values of the voltage and the current in the α β coordinate system. According to the relation between the positive sequence negative sequence component and the current and voltage in the d-q coordinate system, the following results are obtained:
step 2) inverting the power supply under asymmetric faultsThe control targets are as follows: outputting symmetrical three-phase current, i.e. eliminating asymmetrical components in three-phase current, so that
And then, the output unbalanced three-phase voltage is required to be converted from an a, b and c coordinate system to an alpha beta coordinate system, the values of the positive and negative sequence components in the alpha beta coordinate system are obtained through a delay cancellation technology, and then the values are respectively converted into corresponding positive and negative sequence synchronous rotating coordinate systems to be independently controlled.
The delay cancellation technology is as follows: in order to eliminate the negative sequence component of the inverter, the positive and negative sequence voltages are firstly changed from a three-phase static coordinate system to a two-phase static coordinate system, and then the three-phase static coordinate system is inversely transformed to obtain:
and
wherein: [ V ]αβ]、
The matrix of the voltage quantity in an alpha beta coordinate system and the matrix of the voltage quantity in a positive sequence alpha beta coordinate system and a negative sequence alpha beta coordinate system,
to transform the matrix, j is a twiddle factor representing a phase angle rotation of 90 °, i.e., a time-delay effect, to achieve positive and negative order separation from α β.
And 3) after the output characteristic of the photovoltaic inverter power supply is well controlled, enabling the negative sequence component output by the photovoltaic inverter power supply to be zero. And further, when the connecting line has an asymmetric fault, utilizing the negative sequence component provided for the connecting line by the existing power supply side to carry out fault distance measurement. Because the negative sequence component is utilized, the photovoltaic inversion power supply side in the tie line does not output current, and the magnitude and the phase of the current flowing through the existing power supply side and the fault point are in phaseAnd the like. Because of the occurrence of the ground fault, the voltage of the fault point is zero, and the relation of the voltage quantity measured by the power supply terminal is utilized:
wherein:
for the negative sequence component of the voltage measured at the existing power side outlet of the tie line,
a negative sequence component of the current measured for the existing power supply side outlet of the tie line;
and
respectively a real part and an imaginary part of a negative sequence component of the voltage measured by the existing power supply side outlet of the connecting line; in a similar manner to that described above,
and
respectively a real part and an imaginary part of a negative sequence component of the current measured by the existing power supply side outlet of the connecting line; l is the distance from the existing power supply to the fault point, RgA ground transition resistance as a fault point; r is2+j*x2Is the unit impedance value of the line.
In the relation of voltage measured by the power supply end, unknown quantity is the grounding transition resistance R of a fault pointgAnd the distance L from the existing power supply to the fault point, known quantities are real parts and imaginary parts of a voltage quantity negative sequence and a current quantity negative sequence measured at the protection installation position of the existing power supply outlet, and the binary linear equation set is solved
The distance L from the existing power source to the fault point can be found.
Technical effects
Compared with the prior art, the method disclosed by the invention fully utilizes the control strategy of positive and negative double-sequence decoupling independent control and negative sequence component elimination of the photovoltaic inverter power supply, simplifies the complex tie line distance measurement needing to consider the electric quantity at two ends into a single-end electric quantity distance measurement method utilizing the negative sequence component, and enables the tie line fault distance measurement result containing the photovoltaic inverter power supply to be more accurate.
Drawings
FIG. 1 is a schematic diagram of an IGBT control unit;
FIG. 2 is a schematic diagram of a photovoltaic inverter control unit;
FIG. 3 is a schematic diagram of a tie line unit including a photovoltaic inverter power supply;
fig. 4 is a comparison graph of the prior art power supply and the fault point output current of the tie line.
Detailed Description
This embodiment relates to a tie line single-ended fault location system based on photovoltaic inverter output characteristic, includes: IGBT the control unit, photovoltaic invertion power supply the control unit, contain photovoltaic invertion power supply's tie line unit and fault location unit, wherein: the IGBT control unit is connected with the photovoltaic inverter power supply and is used for switching on and switching off the IGBT according to the requirements of the power grid and outputting photovoltaic inverter current; the photovoltaic inverter power supply control unit is used for controlling a built-in PQ controller and an LVRT controller according to the fault type of a connecting line, and adopting a delay cancellation technology during the period of the asymmetric ground fault to obtain the results of positive sequence output current and negative sequence non-output current of the photovoltaic inverter power supply; the tie line unit obtains the current quantity and the voltage quantity of the protection position according to the current and the voltage mutual inductor output of the protection element; and the fault distance measuring unit calculates the fault distance and the size of the transition resistor according to the voltage quantity and the current quantity transmitted by the mutual inductor.
As shown in fig. 1, the IGBT control unit includes a three-phase bridge IGBT circuit composed of six IGBTs.
As shown in fig. 2, the photovoltaic inverter control unit employs a d-q decoupling method to independently control the output of the photovoltaic inverter by positive and negative dual-sequence decoupling, and employs a delay cancellation technique to eliminate negative sequence component output, and the unit includes: the device comprises a delay cancellation module, a PWM module and a d-q decoupling module.
According to the actual topology and parameters of a certain domestic new energy station, a new energy station sending-out connection line model shown in fig. 3 is built on a PSCAD, the station capacity is 100MW, the voltage level of a sending-out line is 220kV, and the length of the sending-out line is 40 km. The impedance of the positive sequence and the zero sequence of the unit length of the sent line is 0.076+ j0.338 omega/km and 0.284+ j0.824 omega/km respectively, and the capacitance of the positive sequence and the zero sequence of the unit length is 0.0086F/km and 0.0061F/km respectively.
In this embodiment, based on the above system, the method for single-ended fault location of the tie line based on the output characteristics of the photovoltaic inverter power supply selects a control strategy for decoupling and eliminating a negative sequence component by positive and negative double-sequence independent control, and solves the problem by using the negative sequence component, and the method specifically includes the following steps:
step 1: and controlling the photovoltaic inverter power supply to only output positive-sequence current and zero negative-sequence output current by using a special control strategy and output characteristics of the photovoltaic inverter power supply, so as to obtain zero negative-sequence output current quantity on the photovoltaic inverter power supply side of the tie line.
Step 2: the amplitude and the phase of the output current quantity and the output voltage quantity of the existing power supply side after the fault occurs are measured through a voltage transformer and a current transformer at the protection position of the existing power supply side, and the amplitude and the phase of the output current quantity and the voltage quantity at each moment are recorded by utilizing Fourier filtering.
As shown in fig. 4, the negative-sequence current output for the conventional power source terminal is compared with the result of the negative-sequence current flowing through the fault point. The real part and the imaginary part of the magnitude of the negative sequence current at the two positions are compared to obtain that the negative sequence current flowing through the fault point is basically consistent with the negative sequence current output by the existing power supply side, the actual negative sequence current output by the photovoltaic inverter under a special control strategy is zero, and calculation can be carried out according to the method.
And step 3: outputting the recorded current and voltage of the existing power supply to a calculation program, using the equations in the inventionProgram calculates to obtain fault distance L and transition resistance Rg。
The simulation result shows that the condition that the current output by the existing power supply end is equal to the current flowing through the fault point is satisfied, and under the method for fault location of the single end of the tie line based on the output characteristic of the photovoltaic inverter power supply, the photovoltaic inverter power supply can be connected to the tie line, and fault location of the tie line containing the photovoltaic inverter power supply can be accurately performed.
Compared with the prior art, the method is suitable for the fault location method of the tie line containing the photovoltaic inverter power supply new energy, simplifies the fault location method of the tie line containing the photovoltaic inverter power supply, and improves the precision of fault location.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (3)
1. A method for locating a fault of a single end of a connecting line based on the output characteristic of a photovoltaic inverter power supply is characterized by comprising the following steps:
step 1) when an asymmetric fault occurs in a power distribution network connecting line accessed by a photovoltaic inverter power supply, positive sequence, negative sequence and zero sequence components occur in the voltage of a power grid, and expressions of instantaneous active power p and reactive power q in an alpha beta coordinate system are obtained according to the sum of the three components of positive and negative zero sequences of output voltage and current, so that three-phase active power is deduced, wherein the expressions specifically comprise the following steps:
wherein:
and
is the average of the active and reactive power, Pc2、Ps2、Qc2、Qs2Respectively harmonic components of the oscillation, vα、vβ、iα、iβThe values of the voltage and the current in an alpha beta coordinate system respectively; according to the relation between the positive sequence negative sequence component and the current and voltage in the d-q coordinate system, the following results are obtained:
step 2) the control target of the inverse power supply under the asymmetric fault is as follows: outputting symmetrical three-phase current, i.e. eliminating asymmetrical components in three-phase current, so that
The output unbalanced three-phase voltage is required to be converted from an a, b and c coordinate system to an alpha beta coordinate system, the values of positive and negative sequence components in the alpha beta coordinate system are obtained through a delay cancellation technology, and then the values are respectively converted into corresponding positive and negative sequence synchronous rotating coordinate systems to be independently controlled;
step 3), after the output characteristics of the photovoltaic inverter power supply are well controlled, enabling the negative sequence component output by the photovoltaic inverter power supply to be zero; further, when the tie line has an asymmetric fault, the negative sequence component provided for the tie line by the existing power supply side is utilized to carry out fault location; because the negative sequence component is utilized, the photovoltaic inversion power supply side in the connecting line does not output current, and the magnitude and the phase of the current output by the existing power supply side and the current flowing through a fault point are equal; because of the occurrence of the ground fault, the voltage of the fault point is zero, and the relation of the voltage quantity measured by the power supply terminal is utilized:
2. The method for single-ended fault location of the tie line based on the output characteristics of the photovoltaic inverter power supply as claimed in claim 1, wherein the delay cancellation technique is as follows: in order to eliminate the negative sequence component of the inverter, the positive and negative sequence voltages are firstly changed from a three-phase static coordinate system to a two-phase static coordinate system, and then the three-phase static coordinate system is inversely transformed to obtain:
and
wherein:
the matrix of the voltage quantity in an alpha beta coordinate system and the matrix of the voltage quantity in a positive sequence alpha beta coordinate system and a negative sequence alpha beta coordinate system,
to transform the matrix, j is a twiddle factor representing a phase angle rotation of 90 °, i.e., a time-delay effect, to achieve positive and negative order separation from α β.
3. The method for single-ended fault location of tie line based on output characteristics of photovoltaic inverter power supply as claimed in claim 1, wherein unknown quantity in the relation of voltage measured by power supply terminals is the grounding transition resistance R of fault pointgAnd the distance L from the existing power supply to the fault point, known quantities are real parts and imaginary parts of a voltage quantity negative sequence and a current quantity negative sequence measured at the protection installation position of the existing power supply outlet, and the binary linear equation set is solved
The distance L from the existing power source to the fault point can be found.
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Application publication date: 20211214 |