Photovoltaic power station grid-connected fault model with neutral point grounded through resistor and analysis methodTechnical Field
The invention relates to the technical field of solar photovoltaic power generation and transmission, in particular to a photovoltaic power station grid-connected fault model with a neutral point grounded through a resistor.
Background
With the continuous incorporation of large photovoltaic power stations into power grids, the occurrence rate of power system faults inevitably increases, and the magnitude of short-circuit current of a power transmission line also increases along with the power system faults, and may exceed the maximum current bearing capacity of certain power elements, thereby causing cascading faults. Therefore, the construction and improvement of the power grid must be performed according to the maximum short-circuit current which may occur after the large photovoltaic power station is connected to the grid. Therefore, fault calculation including large photovoltaic power stations becomes one of the primary tasks for developing photovoltaic power generation technology.
The traditional fault analysis has relatively few researches on the condition of grid connection of a large photovoltaic power station, and most of the traditional fault analysis does not consider the fault control strategy of the photovoltaic power station and the condition that a neutral point is grounded through a resistor, so that the limitation of fault calculation is inevitably caused.
Disclosure of Invention
The invention aims to provide a photovoltaic power station grid-connected fault model with a neutral point grounded through a resistor, and the invention also aims to provide an analysis method of the photovoltaic power station grid-connected fault model based on the neutral point grounded through the resistor.
The technical scheme adopted by the invention for realizing the aim is as follows: a photovoltaic power station grid-connected fault model with a neutral point grounded through a resistor comprises a basic model, a system line fault calculation model and a collection line fault calculation model which are established for a photovoltaic power station grid-connected system with the neutral point grounded through the resistor; the details are as follows:
(1) establishing a basic model for a photovoltaic power station grid-connected system with a neutral point grounded through a resistor based on an inverter power supply fault equivalent model with a low-voltage ride-through control strategy; the method comprises the steps of obtaining three-phase output voltage and three-phase output current of a photovoltaic inverter during fault; the current and the voltage output by the photovoltaic inverter are defined according to an instantaneous reactive power theory; three-phase instantaneous active power; three-phase instantaneous reactive power; when the voltage drops, the inverter outputs a current reference value and an active and reactive reference value of any photovoltaic inverter in order to maintain the stability of the output active and reactive power as much as possible.
(2) Aiming at the respective characteristics of two types of lines, namely a system line and an in-station collection line, of a photovoltaic power station grid-connected system with a neutral point grounded through a resistor, a system line fault calculation model and a collection line fault calculation model are correspondingly established.
(3) When a fault occurs on a system line, the whole photovoltaic power station is equivalent to a large-capacity power supply, the characteristics of a voltage-controlled current source are presented, positive and negative zero-sequence network models are respectively established, the photovoltaic current source controlled by a positive sequence only contains a positive sequence component and is injected into a positive sequence network, and the negative sequence network and the zero sequence network do not contain the power supply.
(4) When a fault occurs on a collecting line in a photovoltaic station, the whole photovoltaic station cannot be equivalent to a power supply, and a non-fault collecting line and a fault collecting line need to be equivalent respectively. The failure collection line is equivalent to a controlled current source, the failure collection line is equivalent to two power sources when being disconnected from a failure point, and the failure point is arranged on a cable ZCfUpper, then the bus is collected to the fault cable ZCfBetween the inverter groups is equivalent to a controlled current source, ZCfThe set of inverters between the ends of the collector lines is equivalent to another controlled current source. The whole grid-connected system is equivalent to a systemThe network of a system power supply and three photovoltaic power supplies respectively establishes a positive and negative zero sequence network model, each photovoltaic current source injects respective positive sequence short circuit current into the positive sequence network, and the negative sequence network and the zero sequence network do not contain power supplies.
A photovoltaic power station grid-connected fault model analysis method based on neutral point grounding through a resistor is characterized in that: on the basis of a system line fault calculation model established in the step (2) of the photovoltaic power station grid-connected fault model with the neutral point grounded through the resistor, a photovoltaic power supply is taken as a controlled source to be processed, and a fault network multivariate nonlinear equation set can be obtained by combining boundary conditions of various fault types; and then, an iterative correction equation is constructed by a Newton Raphson iterative method to obtain a convergence solution, so that fault analysis is realized. Taking a typical photovoltaic power station grid connection as an example, a network shown in fig. 1:
(1) when a fault occurs on a system line, a positive zero sequence network and a negative zero sequence network are shown in figure 2, and then the impedances of all the branches in figure 2 are combined in series and parallel to obtain an equivalent network of the positive zero sequence and the negative zero sequence, which is shown in figure 3. When a single-phase earth fault occurs in a system line, combining the boundary conditions of the single-phase earth fault:namely the relation of positive and negative zero sequence voltage currents of the grounding point, obtaining a system line single-phase grounding fault composite sequence network diagram 4, and further obtaining a loop current equation set by a loop current method;whereinFor positive and negative zero sequence voltages of the fault point to ground,positive and negative zero sequence currents of a fault point.
In the formula (1), Ii: loop current of loop i; zS35: a positive sequence equivalent impedance of a 35kV system; zL351: line impedance between the M bus and a fault point K; zT: the photovoltaic source equivalent transformer impedance; eS:35kV system phase voltage;a photovoltaic power supply terminal voltage;a photovoltaic source fault current; z∑0: zero sequence comprehensive impedance; p*And Q*The active and reactive reference values for the inverter control when the fault crosses z.
And then, establishing a nonlinear solving equation set of the single-phase earth fault of the system line by combining the inverter power supply fault equivalent model in the step (1) of the photovoltaic power station grid-connected fault model based on the neutral point grounded through the resistor as follows:
in the formula (2), ZS35A positive sequence equivalent impedance of a 35kV system; zL351Line impedance between M bus and fault point K; zTThe photovoltaic source equivalent transformer impedance; z∑0Zero sequence integrated impedance; eS35kV system phase voltage;a photovoltaic power supply terminal voltage;a photovoltaic source fault current;fault point zero sequence current;
η is the capacity factor of the inverter after the fault,is a positive sequence component of the voltage of the photovoltaic power supply after the fault; i ismaxFor maximum allowable current of inverter, according to latest standard Imax＝1.5In；Sn、UnAnd InRated capacity, voltage and current for the inverter; k is a radical ofqIs a reactive support coefficient; p*And Q*Outputting active and reactive reference values for the inverter during fault;andand outputting active and reactive reference values for the inverter in normal operation.
Equation (2) is a system of equations for solving the single-phase earth fault of the system line, which is shown in the specificationFive unknowns, fx＝[f1f2f3f4f5]TThe five equations can be solved, but the analytic solution cannot be directly solved due to the nonlinear relation of the equations, so that the convergence solution is obtained by constructing an iterative correction equation by a Newton Raphson iteration method, and the single-phase earth fault analysis is realized.
(2) On the basis of the collection line fault calculation model established in the step (2) of the photovoltaic power station grid-connected fault model with the neutral point grounded through the resistor, further performing fault analysis; and (3) carrying out series-parallel connection combination on the impedances of all the branches in the collecting line fault positive and negative zero sequence network topological graph 5 to obtain an equivalent network graph 6 of the positive and negative zero sequences.
When a single-phase earth fault occurs to a collection line in a photovoltaic station, combining boundary conditions:relationship of positive and negative zero sequence current and voltage at fault, whereinFor positive and negative zero sequence voltages of the fault point to ground,positive and negative zero sequence currents of a fault point), namely the relation of the positive and negative zero sequence voltage currents of the grounding point, to obtain a single-phase grounding fault composite sequence network diagram 7 of the collecting line, and obtain a loop current equation set by a loop current method;
in the formula (3), Ii: loop current of loop i; zS35: a positive sequence equivalent impedance of a 35kV system; zL35:35kV line impedance; zT40: equivalent transformer impedance of the non-fault collection line photovoltaic source; zTm,ZTn1: the impedance of the fault collection line photovoltaic source equivalent transformer; eS:35kV system phase voltage;equivalent photovoltaic source end voltage and fault current of a non-fault collection line;collecting the photovoltaic inversion equivalent power source terminal voltage and the fault current between the bus and the fault point;the photovoltaic inversion equivalent power source terminal voltage and the fault current from the fault point to the end of the collecting line; z∑0: zero sequence comprehensive impedance；Z∑2: negative sequence integrated impedance.
And then combining a photovoltaic inverter power supply fault equivalent model in the step (1) of a photovoltaic power station grid-connected fault model based on neutral point grounding through a resistor, wherein a collection line fault calculation model comprises a system power supply and three photovoltaic power supplies, each photovoltaic power supply has a current equation and an active and reactive equation, and a nonlinear solution equation set of the photovoltaic collection line single-phase grounding fault is established as follows:
in the formulae (4) to (7),fault point zero sequence current; zS35: a positive sequence equivalent impedance of a 35kV system; zL35:35kV line impedance; zT40: equivalent transformer impedance of the non-fault collection line photovoltaic source; zTm,ZTn1: the impedance of the fault collection line photovoltaic source equivalent transformer; zmCollecting positive and negative sequence impedance of the cable between the bus and the fault point; zCf1Line impedance of the faulty cable; eS:35kV system phase voltage;
the collection line fault calculation model comprises three photovoltaic current sources, and each photovoltaic source has a current equation and an active and reactive equation:
equivalent photovoltaic source terminal voltage and fault current of non-fault collector line η40SIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
Voltage and fault current of equivalent power source of photovoltaic inversion between collection bus and fault point ηmSIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
Voltage and current of equivalent power source of photovoltaic inversion from fault point to end of collecting line ηnSIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
The equations (4) to (7) have thirteen equations andthirteen unknowns are also used for constructing an iterative correction equation by using a Newton Raphson iteration method to obtain a convergence solution, so that the single-phase earth fault analysis of the photovoltaic collection line is realized.
The invention solves the line fault calculation modeling problem of a photovoltaic power station grid-connected system which is grounded through a resistor, particularly provides possibility for completely analyzing line faults by establishing a gathered line fault calculation model in a photovoltaic power station, fully considers the influence of neutral grounding resistance on a zero sequence network of the grid-connected system, can conveniently obtain short-circuit current, particularly zero sequence current and node voltage under various fault conditions, provides basis for subsequent protection scheme design, particularly provides basis for setting and checking zero sequence protection of the line, and solves the problem that the photovoltaic station grid-connected system quickly cuts off the grounding fault to avoid large-area photovoltaic off-network caused by fault expansion.
Drawings
FIG. 1 is a photovoltaic station grid-connected system with a neutral point grounded via a resistor, which is studied in an embodiment of the method of the present invention;
wherein ZS330: a 330kV system impedance; zL110: a 110kV line impedance; zL35:35kV line impedance; l is1～L5: five photovoltaic station internal collection lines; t is1: a 330kV main transformer; t is2: a 110kV step-up transformer; rg: a neutral point ground resistor; zC1～ZC10: the impedance of the first section to the tenth section of the cable of the collecting line; 1: protection of collection line, 2: and protecting the system line.
FIG. 2 is a system line fault positive and negative zero sequence network topology diagram in an embodiment of the method of the present invention;
(a) (b) and (c) are positive and negative zero sequence topological graphs respectively; whereinA 330kV system impedance;impedance of a 110kV positive and negative zero sequence line;positive and negative zero sequence line impedance between the M bus and a fault point K;positive sequence line impedance between fault point K and N bus;the positive and negative zero sequence impedances of the 330kV main transformer;the 330kV main transformer is zero-sequence impedance to the ground branch;positive and negative zero sequence impedance of the 110kV booster transformer;the 110kV boosting transformer is used for zero-sequence impedance of a ground branch circuit;positive and negative zero impedance of the tank transformer;a terminal voltage of the photovoltaic current source;a photovoltaic source positive sequence fault current;and the fault point is positive and negative zero sequence voltage of the ground.
FIG. 3 is a diagram of an equivalent network of system line faults in each sequence in accordance with an embodiment of the method of the present invention;
wherein,a positive sequence equivalent impedance of a 35kV system;negative sequence equivalent impedance of a 35kV system;zero-sequence equivalent impedance of a 35kV system; rg is a neutral point grounding resistor;positive and negative zero sequence currents of fault points.
FIG. 4 is a composite sequence network diagram of a line single phase to ground fault in an embodiment of the method of the present invention;
wherein Ii: loop current of loop i;positive and negative sequence impedances are equal, and a 35kV system positive and negative sequence equivalent impedance;positive and negative sequence impedances of the photovoltaic power equivalent transformer;zero sequence synthetic impedance.
FIG. 5 is a topological diagram of a collecting line fault positive and negative zero sequence network in an embodiment of the method of the present invention;
(a) (b) and (c) are positive and negative zero sequence topological graphs respectively; whereinA 330kV system impedance;impedance of a 110kV positive and negative zero sequence line;impedance of a 35kV positive and negative zero sequence line;the positive and negative zero sequence impedances of the 330kV main transformer;the 330kV main transformer is zero-sequence impedance to the ground branch;positive and negative zero sequence impedance of the 110kV booster transformer;the 110kV boosting transformer is used for zero-sequence impedance of a ground branch circuit;fault cable line impedance upstream of the fault point;fault cable line impedance downstream of the fault point;collecting positive and negative zero sequence impedance of the cable between the bus and the fault point;positive and negative zero sequence impedances of the cable from a fault point to the end of the collecting line;the positive sequence impedance of the equivalent transformer of the non-fault collection line photovoltaic source;the positive sequence impedance of the equivalent transformer of the line concentration photovoltaic source at the upstream of the fault point;the positive sequence impedance of the equivalent transformer of the line concentration photovoltaic source at the downstream of the fault point;equivalent photovoltaic source end voltage and fault current of a non-fault collection line;collecting the photovoltaic inversion equivalent power source terminal voltage and the fault current between the bus and the fault point;the photovoltaic inversion equivalent power source terminal voltage and the fault current from the fault point to the end of the collecting line; rg: a neutral point ground resistor;and the fault point is positive and negative zero sequence voltage of the ground.
FIG. 6 is a diagram of an equivalent network for each sequence of a feeder line fault in an embodiment of the method of the present invention;
wherein,a positive sequence equivalent impedance of a 35kV system;negative sequence equivalent impedance of a 35kV system;zero-sequence equivalent impedance of a 35kV system;positive and negative zero sequence currents of fault points.
Fig. 7 is a single-phase-to-ground composite sequence net diagram for a feeder fault in an embodiment of the method of the present invention.
Wherein Ii: loop current of loop i;positive and negative sequence impedances are equal, and a 35kV system positive and negative sequence equivalent impedance;35kV line impedance;collecting positive and negative sequence impedance of the cable between the bus and the fault point;positive and negative sequence impedance of a fault cable line upstream of a fault point;the downstream convergent line photovoltaic source equivalent transformer positive sequence impedance;zero sequence comprehensive impedance;negative sequence integrated impedance.
Detailed Description
A photovoltaic power station grid-connected fault model with a neutral point grounded through a resistor comprises a basic model, a system line fault calculation model and a collection line fault calculation model which are established for a photovoltaic power station grid-connected system with the neutral point grounded through the resistor; the method specifically comprises the following steps:
(1) establishing a basic model for a photovoltaic power station grid-connected system with a neutral point grounded through a resistor based on an inverter power supply fault equivalent model with a low-voltage ride-through control strategy; the method comprises the steps of obtaining three-phase output voltage and three-phase output current of a photovoltaic inverter during fault; the current and the voltage output by the photovoltaic inverter are defined according to an instantaneous reactive power theory; three-phase instantaneous active power; three-phase instantaneous reactive power; when the voltage drops, the inverter outputs a current reference value and an active and reactive reference value of any photovoltaic inverter in order to maintain the stability of the output active and reactive power as much as possible.
(2) Aiming at the respective characteristics of two types of lines, namely a system line and an in-station collection line, of a photovoltaic power station grid-connected system with a neutral point grounded through a resistor, a system line fault calculation model and a collection line fault calculation model are correspondingly established.
(3) When a fault occurs on a system line, the whole photovoltaic power station is equivalent to a large-capacity power supply, the characteristic of a voltage-controlled current source is presented, modeling is carried out according to a positive and negative zero sequence network, wherein the photovoltaic power station respectively injects positive and negative zero sequence components of short-circuit current into the positive and negative zero sequence network.
(4) When the fault occurs on a collecting line of the photovoltaic station, the whole photovoltaic station can not be equivalent to a power supply, and a collecting line fault calculation model is reestablished; if the fault point is located at one section of cable Z of the junctionCfThe above. The faultless collecting line is equivalent to a controlled current source, the faulted collecting line is equivalent independently, and the collecting bus is connected to the fault cable ZCfBetween the inverter groups is equivalent to a controlled current source, ZCfThe inverter group between the tail ends of the collecting lines is equivalent to a controlled current source, the whole system is equivalent to a network with multiple power sources, the system power source and the impedance of each part are converted to the side of the collecting bus, modeling is carried out according to a positive and negative zero sequence network, and the photovoltaic power station injects positive and negative zero sequence components of short-circuit current into the positive and negative zero sequence networks respectively.
The following is a specific application example of the photovoltaic power station grid-connected fault model analysis method based on the neutral point grounded through the resistor.
Taking a typical large photovoltaic station (50MW) grid-connected system with a neutral point grounded through a resistor as an example, the network topology is shown in fig. 1. The photovoltaic power supply presents the characteristic of a controlled current source in a fault, and in engineering, all power generation units in the same photovoltaic station are very high in consistency, and the illumination intensity and the temperature of the power of the photovoltaic cells are determined to be basically consistent in the same photovoltaic station, so that all parameters of all the power generation units are assumed to be equal, and the power sent by all the power generation units at the same time is assumed to be consistent.
Therefore, when a fault occurs on a 35kV system line, the whole photovoltaic power station can be equivalent to a large-capacity power supply. When a ground fault occurs, the photovoltaic source presents the characteristic of a voltage-controlled current source, the photovoltaic inverter adopts a positive sequence control strategy, and the positive sequence component of the short-circuit current is injected into the network, as shown in fig. 2, so that a positive and negative zero sequence network model of the system line fault is established.
When the faults occur on the collection line in the photovoltaic station, the whole photovoltaic station can not be equivalent to a power supply, and a collection line fault calculation model needs to be established again. One section of cable Z with fault point positioned on collection lineCfThe above. The non-failed 4 collector lines are equivalent to a 40MW controlled current source I40SThe faulted collecting line is equivalent independently, and a 35kV collecting bus is connected to a fault cable ZCfM 1MW inverter groups in between are equivalent to one mMW controlled current source ImS，ZCfThe n 1MW inverter groups to the end of the collector line are equivalent to a nMW controlled current source InSAnd (3) wherein m + n is 10, the whole system is equivalent to a multi-power-supply network, the system power supply and the impedance of each part are converted to the 35kV side, and a positive and negative zero sequence network model of the photovoltaic collection line fault is established as shown in figure 5.
Further performing fault analysis based on the established system line fault calculation model; and (3) carrying out series-parallel connection combination on the impedances of all the branches in the system line fault positive and negative zero sequence network topological diagram 2 to obtain an equivalent network diagram 3 of positive and negative zero sequences.
When the system line is generatedAnd when the phase earth fault occurs, combining the boundary conditions of the single-phase earth fault:namely the relation of positive and negative zero sequence voltage currents of the grounding point, obtaining a system line single-phase grounding fault composite sequence network diagram 4, and further obtaining a loop current equation set by a loop current method;whereinFor positive and negative zero sequence voltages of the fault point to ground,positive and negative zero sequence currents of a fault point.
In the formula (1), Ii: loop current of loop i; zS35: a positive sequence equivalent impedance of a 35kV system; zL351: line impedance between the M bus and a fault point K; zT: the photovoltaic source equivalent transformer impedance; eS:35kV system phase voltage;a photovoltaic power supply terminal voltage;a photovoltaic source fault current; z∑0: zero sequence comprehensive impedance; p*And Q*The active reference value and the reactive reference value are controlled by the inverter during fault ride-through.
And establishing a nonlinear solving equation set of the system line single-phase earth fault by combining the inverter power supply fault equivalent model as follows:
in the formula (2), ZS35A positive sequence equivalent impedance of a 35kV system; zL351Line impedance between M bus and fault point K; zTThe photovoltaic source equivalent transformer impedance; z∑0Zero sequence integrated impedance; eS35kV system phase voltage;a photovoltaic power supply terminal voltage;a photovoltaic source fault current;fault point zero sequence current;
η is the capacity factor of the inverter after the fault,is a positive sequence component of the voltage of the photovoltaic power supply after the fault; i ismaxFor maximum allowable current of inverter, according to latest standard Imax＝1.5In；Sn、UnAnd InRated capacity, voltage and current for the inverter; k is a radical ofqIs a reactive support coefficient; p*And Q*Outputting active and reactive reference values for the inverter during fault;andand outputting active and reactive reference values for the inverter in normal operation.
Equation (2) is a system of equations of the single-phase earth fault of the system line, which is shown in the specificationFive unknowns, fx＝[f1f2f3f4f5]TThe five equations can be solved, but the analytic solution cannot be directly solved due to the nonlinear relation of the equations, so that the convergence solution is obtained by constructing an iterative correction equation by a Newton Raphson iteration method, and the single-phase earth fault analysis is realized.
Similarly, based on the fault calculation model of the collecting line, further carrying out fault analysis; and (3) carrying out series-parallel connection combination on the impedances of all the branches in the collecting line fault positive and negative zero sequence network topological graph 5 to obtain an equivalent network graph 6 of the positive and negative zero sequences.
When a single-phase earth fault occurs to a collection line in a photovoltaic station, combining boundary conditions:relationship of positive and negative zero sequence current and voltage at fault, whereinFor positive and negative zero sequence voltages of the fault point to ground,positive and negative zero sequence currents of a fault point), namely the relation of the positive and negative zero sequence voltage currents of the grounding point, to obtain a single-phase grounding fault composite sequence network diagram 7 of the collecting line, and obtain a loop current equation set by a loop current method;
in the formula (3), Ii: loop current of loop i; zS35: positive sequence equivalent impedance of 35kV system；ZL35:35kV line impedance; zT40: equivalent transformer impedance of the non-fault collection line photovoltaic source; zTm,ZTn1: the impedance of the fault collection line photovoltaic source equivalent transformer; eS:35kV system phase voltage;equivalent photovoltaic source end voltage and fault current of a non-fault collection line;collecting the photovoltaic inversion equivalent power source terminal voltage and the fault current between the bus and the fault point;the photovoltaic inversion equivalent power source terminal voltage and the fault current from the fault point to the end of the collecting line; z∑0: zero sequence comprehensive impedance; z∑2: negative sequence integrated impedance.
And combining the photovoltaic inverter power supply fault equivalent model, wherein the collection line fault calculation model comprises a system power supply and three photovoltaic power supplies, each photovoltaic power supply has a current equation and an active and reactive equation, and a nonlinear solving equation set of the single-phase earth fault of the photovoltaic collection line is established as follows:
in the formulae (4) to (7),fault point zero sequence current; zS35: a positive sequence equivalent impedance of a 35kV system; zL35:35kV line impedance; zT40: equivalent transformer impedance of the non-fault collection line photovoltaic source; zTm,ZTn1: the impedance of the fault collection line photovoltaic source equivalent transformer; zmCollecting positive and negative sequence impedance of the cable between the bus and the fault point; zCf1Line impedance of the faulty cable; eS:35kV system phase voltage;
the collection line fault calculation model comprises three photovoltaic current sources, and each photovoltaic source has a current equation and an active and reactive equation:
equivalent photovoltaic source terminal voltage and fault current of non-fault collector line η40SIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
Voltage and fault current of equivalent power source of photovoltaic inversion between collection bus and fault point ηmSIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
Voltage and current of equivalent power source of photovoltaic inversion from fault point to end of collecting line ηnSIs the capacity coefficient of the equivalent photovoltaic inverter power supply,andoutputting active and reactive reference values for the equivalent photovoltaic inverter power supply in case of failure;andand outputting active and reactive reference values for the inverter in normal operation.
The equations (4) to (7) have thirteen equations andthirteen unknowns are also used for constructing an iterative correction equation by using a Newton Raphson iteration method to obtain a convergence solution, so that the single-phase earth fault analysis of the photovoltaic collection line is realized.
In order to obtain a complete grid-connected fault protection scheme of a photovoltaic power station with a neutral point grounded through a resistor, the characteristics of various symmetric and asymmetric faults at different fault positions of a system line and a collection line under the condition that the neutral point grounding resistor Rg has different resistance values must be completely researched, and the mutual matching relation of the protection 1 and the protection 2 shown in the graph 1 must be fully considered. The fault short-circuit phase currents and sequence currents of the system lines and the collector lines under different conditions need to be calculated respectively. When a fault occurs on a system line, only positive sequence current generated by the photovoltaic power supply flows through the collection line, and zero sequence current is not contained.
Based on the calculation result of the example, the relay protection scheme of the 35kV system line and the photovoltaic collection line of the typical network can be researched.