CN113437732B - Pilot protection method and system for photovoltaic power generation grid-connected tie line - Google Patents
Pilot protection method and system for photovoltaic power generation grid-connected tie line Download PDFInfo
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Abstract
The invention discloses a pilot protection method and a pilot protection system for a photovoltaic power generation grid-connected tie line, wherein the method comprises the following steps: judging whether a phase current sudden change in the three phases meets a first condition or whether the zero sequence voltage meets a second condition; if the sudden change of a certain phase current in the three phases meets a first condition or the zero sequence voltage meets a second condition, starting the pilot protection, delaying to select a data window of a preset time period, and respectively calculating the current sum and the voltage sum of the photovoltaic side and the system side of the tie line according to the phases; performing zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each connecting line, then obtaining the derivative of the voltage, and calculating the correlation coefficient of each phase based on the sum of the currents of the photovoltaic side and the system side of each connecting line; and comparing the calculated correlation coefficient of each phase with a setting threshold value, and executing corresponding protection action based on the comparison result. The method and the device realize accurate action under the condition that different fault types occur at different fault positions.
Description
Technical Field
The invention belongs to the technical field of power system relay protection, and particularly relates to a pilot protection method and system for a photovoltaic power generation grid-connected tie line.
Background
The solar energy is clean and pollution-free, is widely distributed and inexhaustible, has unique advantages in development and utilization, and has become a hotspot field of the development of new energy at present. The method is influenced by the self power supply characteristic of the photovoltaic and the inversion control strategy thereof, the fault characteristic of the photovoltaic system is different from that of the traditional synchronous machine system, the protection principle formed on the basis of analyzing the fault characteristic of the traditional synchronous machine can not adapt to the change of the fault characteristic of the system after large-scale centralized photovoltaic access, and the protection performance can be reduced, even refused to operate or wrongly operated, such as longitudinal differential protection.
Therefore, the fault characteristics of the photovoltaic grid-connected system need to be analyzed, and a suitable protection scheme needs to be researched to guarantee safe and stable operation of the power grid, which is also significant for strategic development of the photovoltaic industry.
Disclosure of Invention
The invention aims to provide a method and a system for pilot protection of a photovoltaic power generation grid-connected tie line, which solve the problem that the sensitivity of the existing pilot differential protection in the photovoltaic power generation grid-connected tie line is reduced and even the pilot differential protection is not operated.
In a first aspect, the invention provides a pilot protection method for a photovoltaic power generation grid-connected tie line, which comprises the following steps: responding to three-phase voltage data and three-phase current data acquired by a pilot protection device, and judging whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, wherein the expression of the first condition is as follows:in the formula (I), wherein,for the purpose of the rated current, the current,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first three periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and the system side of the tie line of each sampling point; the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,unbalanced voltage for normal operation; if the sudden change of a certain phase current in the three phases meets a first condition or the zero sequence voltage meets a second condition, controlling a pilot protection device to start pilot protection, selecting a data window of a preset time period based on the pilot protection device in a delayed mode, and respectively calculating the current sum and the voltage sum of the photovoltaic side of the tie line and the system side of the tie line according to the phases; obtaining a derivative of the voltage of the photovoltaic side of each connecting line and the voltage of the system side of each connecting line after zero sequence compensation, and calculating a correlation coefficient of each phase based on the sum of the currents of the photovoltaic side of each connecting line and the system side of each connecting line, wherein the expression of the correlation coefficient of each phase is as follows:in the formula (I), wherein,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,for the start of a sampling point for a window of data,the number of the sampling points is,andthe following were used:in the formula (I), wherein,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side and the system side of each tie line after zero sequence compensation of each sampling point; and comparing the calculated correlation coefficient of each phase with a setting threshold value, and executing corresponding protection action based on the comparison result.
In a second aspect, the present invention provides a pilot protection system for a photovoltaic power generation grid-connected tie line, including: the judging module is configured to respond to three-phase voltage data and three-phase current data acquired by the pilot protection device, and judge whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, wherein an expression of the first condition is as follows:in the formula (I), wherein,for the purpose of the rated current, the current,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first three periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and the system side of the tie line of each sampling point; the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,unbalanced voltage for normal operation; the first calculation module is configured to control the pilot protection device to start pilot protection if a certain phase current mutation in the three phases meets a first condition or zero-sequence voltage meets a second condition, select a data window of a preset time period based on the pilot protection device in a delayed mode, and calculate the sum of the current and the sum of the voltage of the tie line photovoltaic side and the tie line system side respectively according to the phases; the second calculation module is configured to perform zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each tie line, obtain a derivative of the voltage, and calculate each phase correlation coefficient based on the sum of the currents of the photovoltaic side and the system side of each tie line, wherein the expression of each phase correlation coefficient is as follows:in the formula (I), wherein,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,for the start of a sampling point for a window of data,the number of the sampling points is,andthe following were used:in the formula (I), wherein,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side and the system side of each tie line after zero sequence compensation of each sampling point; and the execution module is configured to compare the calculated correlation coefficient of each phase with a setting threshold value and execute corresponding protection actions based on the comparison result.
In a third aspect, an electronic device is provided, comprising: the protection method comprises at least one processor and a memory which is in communication connection with the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the steps of the photovoltaic grid-connected pilot protection method according to any embodiment of the invention.
In a fourth aspect, the present invention also provides a computer-readable storage medium having stored thereon a computer program comprising program instructions which, when executed by a computer, cause the computer to perform the steps of the method for pv grid tie pilot protection according to any of the embodiments of the present invention.
According to the method and the system for pilot protection of the photovoltaic power generation grid-connected tie line, the derivative of the sum of the currents on the two sides and the sum of the voltages is calculated according to the phases, the correlation coefficient is obtained, whether the grid-connected tie line fault is located in the region or out of the region is judged according to the magnitude between the obtained correlation coefficient and the setting threshold value, the corresponding fault type is judged, the photovoltaic inversion control strategy and the photovoltaic power generation output magnitude are not influenced, accurate action can be achieved under the condition that different fault types occur at different fault positions, the method and the system have strong anti-transition resistance capacity, and the sensitivity and the reliability are high.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a flowchart of a pilot protection method for a photovoltaic power generation grid-connected tie line according to an embodiment of the present invention;
fig. 2 is an equivalent circuit diagram of the photovoltaic power generation grid-connected tie line provided by an embodiment of the present invention when an external fault occurs;
fig. 3 is an equivalent circuit diagram of a fault in a photovoltaic power generation grid-connected tie line area according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a fault simulation of a centralized photovoltaic power generation grid-connected system according to an embodiment of the present invention;
fig. 5 is a block diagram of a pilot protection system of a photovoltaic power generation grid-connected tie line according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of an electronic device according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a flow chart of a pilot protection method for a photovoltaic power generation grid-connected tie line according to the present application is shown.
As shown in fig. 1, in S101, in response toThe method comprises the steps of acquiring three-phase voltage data and three-phase current data acquired by a pilot protection device, and judging whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, wherein the expression of the first condition is as follows:in the formula (I), wherein,for the purpose of the rated current, the current,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first three periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and the system side of the tie line of each sampling point;
the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,is an unbalanced voltage in normal operation.
In S102, if a phase current sudden change in three phases meets a first condition or a zero sequence voltage meets a second condition, the pilot protection device is controlled to start pilot protection, a data window of a preset time period is selected based on the pilot protection device in a delayed manner, and the sum of the current and the sum of the voltage of the tie line photovoltaic side and the tie line system side are respectively calculated according to the phases.
In this embodiment, after pilot protection is started, a data window of a preset time period is selected in a delayed mode, and the sum of the current and the sum of the voltage of the photovoltaic side of the tie line and the system side of the tie line are calculated according to the phase, so that the data after delay are calculated, and the influence of a control transient on protection is reduced.
In S103, the sum of the voltages on the photovoltaic side and the tie line system side of each tie line is zero-sequence compensated, and then the derivative thereof is obtained, and correlation coefficients of each phase are calculated based on the sum of the currents on the photovoltaic side and the tie line system side of each tie line, wherein the expression of the correlation coefficients of each phase is:
in the formula (I), the compound is shown in the specification,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,for the start of a sampling point for a window of data,the number of the sampling points is,andthe following were used:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentAnd the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation of each sampling point.
In this embodiment, the expression for performing zero sequence compensation on the sum of the voltages on the photovoltaic side and the tie line system side of each tie line is as follows:
in the formula (I), the compound is shown in the specification,the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the sum of the voltages on the photovoltaic side of each tie line and on the system side of the tie line,is a phase A, a phase B or a phase C,for zero sequence voltage on two sides of the grid-connected tie line,is a zero-sequence compensation coefficient, and the zero-sequence compensation coefficient,the zero sequence capacitor is a grid-connected tie line unit length zero sequence capacitor, and the grid-connected tie line unit length positive sequence capacitor.
And after carrying out zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each connecting line, calculating a derivative of the voltage through a differential derivative method, wherein the expression of the derivative is as follows:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentAnd the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation of each sampling point.
Further, the correlation coefficient of each phaseHas a value range of [ -1,1 [)]When is coming into contact withIs shown byAndnegative correlation;is shown byAndnon-correlation;is shown byAndand (4) positively correlating.The closer the value is to 1, the more the representationAndthe stronger the positive correlation;the closer the value is to-1, the stronger the negative correlation. When a fault occurs outside the zone, each phaseAndconforms to the capacitance circuit model and shows strong positive correlation,a value close to 1; when in-zone fault, non-fault phaseAndconforming to a capacitive circuit modelThe positive correlation is strong and the negative correlation is strong,the value is close to 1, while the faulted phase does not fit the capacitive circuit model,the value is less than 1.
In S104, the calculated correlation coefficient of each phase is compared with a setting threshold value, and a corresponding protection operation is executed based on the comparison result.
In this embodiment, comparing the calculated correlation coefficient of each phase with a setting threshold, and executing a corresponding protection action based on the comparison result specifically includes: if the correlation coefficient of one of the three phases is smaller than a setting threshold value, judging that the single-phase fault exists in a photovoltaic power generation grid-connected tie line area, and protecting the action from jumping to the single phase; if the correlation coefficient of a certain two phases is smaller than a setting threshold value or the correlation coefficients of the three phases are smaller than the setting threshold value, judging that two-phase faults and three-phase faults in a grid-connected tie line area exist, and protecting the action from jumping the three phases; if the correlation coefficients of the three phases are all larger than the setting threshold value, the fact that no fault occurs inside the grid-connected tie line is judged, and the protection does not act.
In the method of the embodiment, according to the fact that the derivative of the sum of the currents and the sum of the voltages on the two sides of the photovoltaic power generation grid-connected tie line accords with different circuit models when the photovoltaic power generation grid-connected tie line is in an inside fault and an outside fault, model identification is carried out through correlation analysis so as to judge the fault, when the photovoltaic power generation grid-connected tie line is in the outside fault, the derivative of the sum of the currents on the two sides of each tie line and the derivative of the sum of the voltages on the two sides of each tie line are in strong positive correlation, and the similarity coefficient is close to 1; when the fault occurs in the region, the derivative of the sum of the currents on the two sides of the non-fault phase and the sum of the voltages on the two sides is in strong positive correlation, the similarity coefficient is close to 1, and the similarity coefficient of the derivative of the sum of the currents on the two sides of the fault phase and the sum of the voltages on the two sides is smaller than 1. The invention directly analyzes the correlation by using the derivative of the sum of the voltages at two sides of the connecting line and the sum of the currents, and the algorithm is simple and reliable; the data after the time delay is adopted for calculation, so that the influence of the control transient on the protection is reduced; the photovoltaic inverter control device is not influenced by a photovoltaic inverter control strategy and the output of photovoltaic power generation, can accurately act under the condition that different fault types occur at different fault positions, and has strong anti-transition resistance capability and high reliability and sensitivity.
FIG. 2 is an equivalent circuit diagram of a fault outside a photovoltaic power generation grid-connected line area, wherein a positive direction is defined as a bus flow direction line, a P side is a photovoltaic side,andrespectively photovoltaic side fault voltage and fault current; the S side is the system side,andrespectively a system-side fault voltage and a fault current,is the line impedance of the grid-tie line,in order to be a line-to-ground capacitance,in order to connect the out-of-zone fault point,is the transition resistance of the point of failure,is the current flowing through the transition resistance. The current relation of two sides of the photovoltaic power generation grid-connected tie line is shown as the formula (1):
in the formula (I), the compound is shown in the specification,in order to obtain a photovoltaic side fault current,for each of the associated tie line photovoltaic side fault currents,for each of the associated tie line system side fault currents,in order to be the system-side fault current,、respectively, photovoltaic side and system side capacitance-to-ground current.
In the formula (I), the compound is shown in the specification,in order to obtain a photovoltaic side fault voltage,in order to be a system-side fault voltage,in order to be a line-to-ground capacitance,for the differentiation of the photovoltaic side fault voltage function with respect to time,system for controlling a power supplyDifferential of the side fault voltage function over time.
The sum of the currents on the photovoltaic side and the system side of each tie line isSum of voltages on the photovoltaic side and the system side of each tie,Andthe sizes are equal and the directions are opposite,,
the following can be obtained from formula (1) and formula (2):
as shown in formula (3), the derivative of the sum of the currents on both sides of the tie line and the sum of the voltages on both sides of the tie line conforms to the capacitance circuit model and is in strong positive correlation.
Fig. 3 is a fault equivalent circuit diagram in a photovoltaic power generation grid-connected tie line area. The positive direction is defined as the bus flow to the line. And when the fault occurs in the area, the voltages at two sides of the line meet the following conditions:
in the formula (I), the compound is shown in the specification,in order to obtain a photovoltaic side fault voltage,in order to be a system-side fault voltage,respectively a photovoltaic side resistance value and an inductance value of the connecting line,for each of the associated tie line photovoltaic side fault currents,for each of the associated tie line system side fault currents,is the transition resistance of the point of failure,is the current flowing through the transition resistance and,the resistance value and the inductance value of the tie line system are respectively.
Neglecting the capacitance current to ground, the sum of the currents on both sides of the tie line and the sum of the voltages on both sides are shown as formula (5):
in the formula (I), the compound is shown in the specification,for each of the associated tie line photovoltaic side fault currents,for each of the associated tie line system side fault currents,is the sum of the currents on the photovoltaic side and the tie system side of each tie,is the sum of the voltages on the photovoltaic side of each tie line and on the system side of the tie line.
Current flowing through the transition resistance in the event of an in-zone faultLet the current distribution coefficient be,From formulas (4) and (5), it is possible to obtain:
in the formula (I), the compound is shown in the specification,is the sum of the voltages on the photovoltaic side of each tie line and on the system side of the tie line,in order to obtain the photovoltaic side resistance value of the tie line,in order to obtain a tie line system-side resistance value,for the value of the photovoltaic side inductance of the tie line,for the value of the inductance on the system side of the tie line,for the current distribution coefficient of the photovoltaic side,the coefficient is distributed to the system-side current,is the sum of the currents on the photovoltaic side and the tie system side of each tie,is the transition resistance of the fault point.
Further, it is possible to obtain:
wherein:
in the formula (I), the compound is shown in the specification,is the sum of the resistances at the two sides of the connecting line,is the sum of inductances on both sides of the tie line,for the current distribution coefficient of the photovoltaic side,the coefficient is distributed to the system-side current,in order to obtain the photovoltaic side resistance value of the tie line,in order to obtain a tie line system-side resistance value,for the value of the photovoltaic side inductance of the tie line,is the system-side inductance value of the tie line.
As can be seen from equation (7), when a fault occurs in the interconnection zone, the derivative of the sum of the currents and the sum of the voltages on both sides does not conform to the capacitance circuit model.
The implementation process and effect of the photovoltaic power generation grid-connected tie line pilot protection method of the present application are explained in detail with specific embodiments, and fig. 4 is a schematic diagram of fault simulation of a centralized photovoltaic power generation grid-connected system according to an embodiment of the present invention.
The rated capacity of photovoltaic power generation is 150MW, the box transformer substation adopts Dyn wiring, and the rated voltage is 0.69kV/35 kV; the main transformer adopts YNd wiring, the rated voltage is 35kV/220kV, and the rated capacity is 160 MW. The length of the grid-connected connecting line is 40km, the unit positive sequence impedance is 0.076+ j0.338 omega/km, and the unit zero sequence impedance is 0.284+ j0.824 omega/km. The equivalent positive sequence impedance of the external system is 0.4+ j12.568 omega, and the equivalent zero sequence impedance is 0.6+18.849 omega/km. The photovoltaic side and system side protection devices collect data of the photovoltaic side and transmit the data to the opposite end in real time, and the protection devices calculate correlation coefficients to judge faults and send action instructions. The simulation time length is 3s, and the sampling frequency is 2.5 kHz.Is arranged outside the photovoltaic side area,is an inner outlet of the photovoltaic side area,is the middle point of the connecting line,is an outlet in the side area of the system,outside the system side regionAnd respectively setting a metallic fault and a belt transition resistance fault, and calculating a correlation coefficient.Respectively representing the correlation coefficients of A, B, C three phases ""indicates a protection action and" - "indicates a protection does not. The simulation results of three-phase faults of different fault positions of the photovoltaic power generation grid-connected tie line are directly calculated by taking 5ms and 10ms data windows after the starting element acts are respectively shown in the table 1 and the table 2; table 3 shows simulation results of different types of faults occurring at different positions of the tie line; table 4 shows simulation results of phase a transition resistance ground faults at different fault positions of the tie line; table 5 shows the tie line midpoints under different photovoltaic power generation output conditionsSimulation results of different types of faults are generated; tables 3, 4 and 5 are the results of 10ms delay after starting the element action and then taking the 5ms data window for calculation.
Simulation results in tables 1 and 2 show that when three phases outside the system side area fail, 5ms and 10ms data windows are directly taken for calculation, the similarity coefficients of the B phase are all smaller than 0.85, and misjudgment occurs; the simulation results in tables 3, 4 and 5 show that when the time delay is 10ms after the element is started, and then the data window of 5ms is taken for calculation, the method can reliably judge different types of faults at different positions on the photovoltaic power generation grid-connected connecting line, is not influenced by the magnitude of the output of photovoltaic power generation, and has strong resistance to transition resistance, high sensitivity and reliability.
Referring to fig. 5, a block diagram of a pilot protection system of a photovoltaic power generation grid-connected tie line according to the present application is shown.
As shown in fig. 5, the pv grid-connected tie-line pilot protection system 200 includes a determining module 210, a first calculating module 220, a second calculating module 230, and an executing module 240.
The judging module 210 is configured to respond to three-phase voltage data and three-phase current data acquired by the pilot protection device, and judge whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, where an expression of the first condition is:in the formula (I), wherein,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side and the tie-line system side of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side and the tie-line system side of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side and the tie-line system side of the sampling points of the individual,the first three at a certain momentPeriodic the firstThe sum of the currents on the photovoltaic side and the tie line system side of the sampling points of the individual;
the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,unbalanced voltage for normal operation;
the first calculation module 220 is configured to control the pilot protection device to start pilot protection if a certain phase current mutation in the three phases meets a first condition or zero-sequence voltage meets a second condition, select a data window of a preset time period based on the pilot protection device in a delayed manner, and calculate the sum of the current and the sum of the voltage of the tie line photovoltaic side and the tie line system side respectively according to the phases;
the second calculating module 230 is configured to perform zero sequence compensation on the sum of the voltages at the photovoltaic side and the system side of each tie line, obtain a derivative thereof, and calculate a correlation coefficient of each phase based on the sum of the currents at the photovoltaic side and the system side of each tie line, where an expression of the correlation coefficient of each phase is:
in the formula (I), the compound is shown in the specification,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,for the start of a sampling point for a window of data,the number of the sampling points is,andthe following were used:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentThe sum of the currents on the photovoltaic side and the tie-line system side of the sampling points of the individual,is the first momentSampling point ofThe sum of the currents on the photovoltaic side and on the tie-line system side,is the first momentThe sum of the voltages of the photovoltaic side and the tie line system side after zero sequence compensation of the photovoltaic grid-connected inverter,is the first momentThe sum of the voltages of the photovoltaic side and the tie line system side of the sampling points after zero sequence compensation;
and the execution module 240 is configured to compare the calculated correlation coefficient of each phase with a setting threshold value, and execute a corresponding protection action based on the comparison result.
It should be understood that the modules recited in fig. 5 correspond to various steps in the method described with reference to fig. 1. Thus, the operations and features described above for the method and the corresponding technical effects are also applicable to the modules in fig. 5, and are not described again here.
In other embodiments, the present invention further provides a computer-readable storage medium, where computer-executable instructions are stored, where the computer-executable instructions may execute the method for pilot protection of a photovoltaic power generation grid-connected tie line in any of the above method embodiments;
as one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions configured to:
responding to the three-phase voltage data and the three-phase current data acquired by the pilot protection device, and judging whether a certain phase current break variable in the three phases meets a first condition or whether zero-sequence voltage meets a second condition;
if the sudden change of a certain phase current in the three phases meets a first condition or the zero sequence voltage meets a second condition, controlling a pilot protection device to start pilot protection, selecting a data window of a preset time period based on the pilot protection device in a delayed mode, and respectively calculating the current sum and the voltage sum of the photovoltaic side of the tie line and the system side of the tie line according to the phases;
performing zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each connecting line, then obtaining the derivative of the voltage, and calculating the correlation coefficient of each phase based on the sum of the currents of the photovoltaic side and the system side of each connecting line;
and comparing the calculated correlation coefficient of each phase with a setting threshold value, and executing corresponding protection action based on the comparison result.
The computer-readable storage medium may include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required for at least one function; the storage data area may store data created from use of the photovoltaic power generation grid-connected tie line pilot protection system, and the like. Further, the computer-readable storage medium may include high speed random access memory, and may also include memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid state storage device. In some embodiments, the computer readable storage medium optionally includes memory remotely located from the processor, and the remote memory may be connected to the pv tie pilot protection system via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
Fig. 6 is a schematic structural diagram of an electronic device according to an embodiment of the present invention, and as shown in fig. 6, the electronic device includes: a processor 310 and a memory 320. The electronic device may further include: an input device 330 and an output device 340. The processor 310, the memory 320, the input device 330, and the output device 340 may be connected by a bus or other means, such as the bus connection in fig. 6. The memory 320 is the computer-readable storage medium described above. The processor 310 executes various functional applications and data processing of the server by running the nonvolatile software program, instructions and modules stored in the memory 320, that is, the method for protecting the pilot of the photovoltaic power generation grid-connected tie line according to the embodiment of the method is implemented. The input device 330 may receive input numeric or character information and generate key signal inputs related to user settings and function control of the pv grid tie pilot protection system. The output device 340 may include a display device such as a display screen.
The electronic device can execute the method provided by the embodiment of the invention, and has the corresponding functional modules and beneficial effects of the execution method. For technical details that are not described in detail in this embodiment, reference may be made to the method provided by the embodiment of the present invention.
As an embodiment, the electronic device is applied to a pilot protection system of a photovoltaic power generation grid-connected tie line, and used for a client, and includes: at least one processor; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor to cause the at least one processor to:
responding to the three-phase voltage data and the three-phase current data acquired by the pilot protection device, and judging whether a certain phase current break variable in the three phases meets a first condition or whether zero-sequence voltage meets a second condition;
if the sudden change of a certain phase current in the three phases meets a first condition or the zero sequence voltage meets a second condition, controlling a pilot protection device to start pilot protection, selecting a data window of a preset time period based on the pilot protection device in a delayed mode, and respectively calculating the current sum and the voltage sum of the photovoltaic side of the tie line and the system side of the tie line according to the phases;
performing zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each connecting line, then obtaining the derivative of the voltage, and calculating the correlation coefficient of each phase based on the sum of the currents of the photovoltaic side and the system side of each connecting line;
and comparing the calculated correlation coefficient of each phase with a setting threshold value, and executing corresponding protection action based on the comparison result.
The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. A pilot protection method for a photovoltaic power generation grid-connected tie line is characterized by comprising the following steps:
responding to three-phase voltage data and three-phase current data acquired by a pilot protection device, and judging whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, wherein the expression of the first condition is as follows:in the formula (I), wherein,for the purpose of the rated current, the current,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first three periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and the system side of the tie line of each sampling point;
the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,unbalanced voltage for normal operation;
if the sudden change of a certain phase current in the three phases meets a first condition or the zero sequence voltage meets a second condition, controlling a pilot protection device to start pilot protection, selecting a data window of a preset time period based on the pilot protection device in a delayed mode, and respectively calculating the current sum and the voltage sum of the photovoltaic side of the tie line and the system side of the tie line according to the phases;
obtaining a derivative of the voltage of the photovoltaic side of each connecting line and the voltage of the system side of each connecting line after zero sequence compensation, and calculating a correlation coefficient of each phase based on the sum of the currents of the photovoltaic side of each connecting line and the system side of each connecting line, wherein the expression of the correlation coefficient of each phase is as follows:
in the formula (I), the compound is shown in the specification,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,for the start of a sampling point for a window of data,the number of the sampling points is,andthe following were used:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentPhases of sampling points ofThe sum of the currents on the photovoltaic side of the tie and on the system side of the tie,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side and the system side of each tie line after zero sequence compensation of each sampling point;
and comparing the calculated correlation coefficient of each phase with a setting threshold value, and executing corresponding protection action based on the comparison result.
2. The grid-connected tie line pilot protection method for photovoltaic power generation according to claim 1, wherein the expression for performing zero sequence compensation on the sum of the voltages of the photovoltaic side and the tie line system side of each tie line is as follows:
in the formula (I), the compound is shown in the specification,the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the sum of the voltages on the photovoltaic side of each tie line and on the system side of the tie line,is a phase A, a phase B or a phase C,for zero sequence voltage on two sides of the grid-connected tie line,is a zero-sequence compensation coefficient, and the zero-sequence compensation coefficient,the zero sequence capacitor is a grid-connected tie line unit length zero sequence capacitor, and the grid-connected tie line unit length positive sequence capacitor.
3. The method for the pilot protection of the grid-connected photovoltaic power generation tie line according to claim 1, wherein the step of calculating the derivative of the sum of the voltages at the photovoltaic side and the tie line system side of each tie line after zero sequence compensation comprises the steps of:
and after carrying out zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each connecting line, calculating a derivative of the voltage through a differential derivative method, wherein the expression of calculating the derivative is as follows:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,the sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side and the tie line system side after zero sequence compensation of the photovoltaic grid-connected inverter,is the first momentAnd the sum of the voltages of the photovoltaic side and the tie line system side after zero sequence compensation of the sampling points.
4. The method for pilot protection of the grid-connected tie line for photovoltaic power generation according to claim 1, wherein the setting rule of the setting threshold value is as follows: and (4) considering the sensing error of the mutual inductor, and obtaining the sensing error based on simulation training.
5. The method according to claim 1, wherein the performing of the corresponding protection action based on the comparison result comprises:
if the correlation coefficient of one of the three phases is smaller than a setting threshold value, judging that the single-phase fault exists in a photovoltaic power generation grid-connected tie line area, and protecting the action from jumping to the single phase;
if the correlation coefficient of a certain two phases is smaller than a setting threshold value or the correlation coefficients of the three phases are smaller than the setting threshold value, judging that two-phase faults and three-phase faults in a grid-connected tie line area exist, and protecting the action from jumping the three phases;
if the correlation coefficients of the three phases are all larger than the setting threshold value, the fact that no fault occurs inside the grid-connected tie line is judged, and the protection does not act.
6. The utility model provides a photovoltaic power generation tie-in line pilot protection system that is incorporated into power networks which characterized in that includes:
the judging module is configured to respond to three-phase voltage data and three-phase current data acquired by the pilot protection device, and judge whether a phase current break variable in three phases meets a first condition or whether a zero-sequence voltage meets a second condition, wherein an expression of the first condition is as follows:in the formula (I), wherein,for the purpose of the rated current, the current,for a certain amount of the phase current burst,,is a phase A, a phase B or a phase C,is the number of sampling points in one period,is the maximum value of the unbalance amount of a certain phase current,,the serial numbers of the sampling points are shown,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first period of a timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first two periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,the first three periods of a certain timeThe sum of the currents on the photovoltaic side of each tie line and the system side of the tie line of each sampling point;
the expression of the second condition is:in the formula (I), wherein,for zero sequence voltage on two sides of the grid-connected tie line,taking the sample at 0.5V to 1V,taking 1.2-1.5 as a reliable coefficient,unbalanced voltage for normal operation;
the first calculation module is configured to control the pilot protection device to start pilot protection if a certain phase current mutation in the three phases meets a first condition or zero-sequence voltage meets a second condition, select a data window of a preset time period based on the pilot protection device in a delayed mode, and calculate the sum of the current and the sum of the voltage of the tie line photovoltaic side and the tie line system side respectively according to the phases;
the second calculation module is configured to perform zero sequence compensation on the sum of the voltages of the photovoltaic side and the system side of each tie line, obtain a derivative of the voltage, and calculate each phase correlation coefficient based on the sum of the currents of the photovoltaic side and the system side of each tie line, wherein the expression of each phase correlation coefficient is as follows:
in the formula (I), the compound is shown in the specification,is the correlation coefficient of each phase and is,is a phase A, a phase B or a phase C,starting sampling point for data window,The number of the sampling points is,andthe following were used:
in the formula (I), the compound is shown in the specification,the serial numbers of the sampling points are shown,in order to be the sampling interval of the sample,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the currents on the photovoltaic side of each tie line and on the system side of the tie line of the sampling points of the individual,is the first momentThe sum of the voltages of the photovoltaic side of each connecting line and the system side of the connecting line after zero sequence compensation,is the first momentThe sum of the voltages of the photovoltaic side and the system side of each tie line after zero sequence compensation of each sampling point;
and the execution module is configured to compare the calculated correlation coefficient of each phase with a setting threshold value and execute corresponding protection actions based on the comparison result.
7. An electronic device, comprising: at least one processor, and a memory communicatively coupled to the at least one processor, wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method of any of claims 1 to 5.
8. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the method of any one of claims 1 to 5.
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