CN111969569A - Micro-grid fault protection method based on improved current phase difference - Google Patents
Micro-grid fault protection method based on improved current phase difference Download PDFInfo
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- H—ELECTRICITY
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- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
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- H—ELECTRICITY
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Abstract
The invention discloses a microgrid fault protection method based on improved current phase difference, which utilizes the fact that the voltage of an IIDG output end can be greatly reduced when a microgrid has a fault and the current phase difference of two ends of a bus as protection criteria, overcomes the problem that the traditional three-section type current protection is possibly rejected due to uncertainty of the direction of the power flow and unobvious change of the current mode value because the microgrid has a bidirectional power flow and independently operates the microgrid, can accurately identify and cut off a fault circuit in two operating states of the microgrid, avoids the problem that the microgrid needs to use two sets of protection devices in the two operating states, reduces the protection cost, and improves the reliability and sensitivity of the microgrid protection. The protection method does not depend on a current module value as a starting criterion, and overcomes the problem that the protection fails because the fault current of the micro-grid containing the IIDG is small.
Description
Technical Field
The invention relates to the technical field of microgrid fault judgment and fault protection, in particular to a microgrid fault protection method based on improved current phase difference.
Background
At present, a distributed power supply mainly based on renewable energy sources such as photovoltaic power generation and wind power generation is more and more applied by organically forming a micro-grid with an energy storage device, a power electronic converter, a load, a monitoring protection device and the like, because the distributed power supply can most effectively utilize the renewable energy sources and meet the requirements of energy conservation and environmental protection.
Because the micro-grid can be operated in a grid-connected mode with the power distribution network, and can also be disconnected from the power distribution network to realize island operation (namely independent operation), in two operation modes, respective fault characteristics and control strategies are different, two sets of protection devices are required to be used frequently, and the maintenance cost is higher. Meanwhile, the existing fault protection mode of the low-voltage distribution network generally adopts a three-section type current protection scheme, but because the bidirectional tide and the independent operation fault current of the micro-grid are smaller, the traditional three-section type current protection often has the condition of protection refusal due to the uncertainty of the tide direction and the change of the current module value, and the problem of protection failure occurs.
Therefore, how to provide a stable and reliable microgrid fault protection method with high sensitivity and lower cost is an urgent problem to be solved by those skilled in the art.
Disclosure of Invention
In view of the above, the invention provides a microgrid fault protection method based on improved current phase difference, which is suitable for a microgrid with an IIDG, and solves the problems that the existing three-section type current protection scheme is high in maintenance cost and prone to failure of protection by using the fact that the voltage of the output end of the IIDG can be greatly reduced and the current phase difference of two ends of a bus is taken as a protection criterion when the microgrid fails.
In order to achieve the purpose, the invention adopts the following technical scheme:
a microgrid fault protection method based on improved current phase difference, the method comprising:
detecting currents on two sides of a fault line, and judging whether the currents exist on the two sides;
when the current is detected on both sides of a fault line, detecting whether the output voltage of each inverter type distributed power supply supplying power for each line section is reduced and whether the voltage reduction value exceeds a preset voltage drop threshold value;
when the output voltage of at least one inverter type distributed power supply is detected to be reduced and the voltage reduction value exceeds a preset voltage drop threshold value, determining a corresponding suspected fault line section according to the detected position of the inverter type distributed power supply;
detecting the current phase difference of buses at two ends of a suspected fault line section, and judging whether the current phase difference is within a preset action current phase difference threshold range;
when the current phase difference is within the range of the action current phase difference threshold, judging that the suspected fault line section is a fault line section, and cutting off the fault line section;
and when the fault line is detected to have current on only one side, the fault line section is cut off through three-section type overcurrent protection.
In consideration of the existing micro-grid, the Distributed power supply mainly comprises an Inverter-type Distributed power supply (IIDG), and the fault current of the Distributed power supply is limited within 2 times of the rated current. The invention takes the output voltage of the inverter distributed power supply and the current phase difference of the buses at two ends of the line section as the basis, carries out fault protection on the line with current at two sides, and carries out fault protection on the line with current at one side by adopting the traditional three-section type overcurrent protection scheme, thereby ensuring the accuracy and reliability of the protection method.
Further, after detecting the current phase difference of the buses at the two ends of the suspected fault line section, the method may further include:
and judging whether the current phase difference is within a preset holding current phase difference threshold range, and when the current phase difference is within the holding current phase difference threshold range, judging that the suspected fault line section is a non-fault line section.
Because a more reasonable current phase difference threshold range exists when the line is in normal operation and has an out-of-range fault, in order to further improve the reliability of detection, the obtained current phase difference can be respectively compared with the holding current phase difference threshold range and the action current phase difference threshold range, when the holding current phase difference threshold range is met, the line section is indicated to be in normal operation without protection action, when the action current phase difference threshold range is met, the line section is indicated to have a fault, and timely action is required to protect the working safety of the microgrid.
Further, the calculation formula of the current phase difference is as follows:
in the formula,
the phase difference of the currents is represented,
and
and the current values of the buses at the two ends of the suspected fault line section are respectively.
It can be easily found that when the two sides of the fault line are detected to have current, the protection criterion adopted by the invention can be simplified as follows:
protection criterion 1: when a fault occurs, the voltage at the output end of the IIDG can drop greatly and exceeds a preset value Vset(the normal voltage is 0.2 times when the single-phase fault occurs, and the normal voltage is 0.5 times when the three-phase fault or the two-phase fault occurs, and the fault can be adjusted according to actual conditions).
Protection criterion 2: in normal operation and outside fault, the current phase difference at the two ends of the bus is 180 degrees, and in inside fault, the current phase difference at the two ends of the bus is 0 degree. Considering the actual engineering error, in order to improve the reliability and the sensitivity of protection, the selected protection locking angle is
(L represents the line length in km), so the criterion of current phase difference is:
in the above formula, the first and second carbon atoms are,
indicating the current phase difference between the two ends of the bus in normal operation and outside fault,
the phase difference of the current at the two ends of the bus is the fault in the area.
According to the technical scheme, compared with the prior art, the method for protecting the fault of the micro-grid based on the improved current phase difference is disclosed, the method utilizes the fact that the voltage of the output end of the IIDG can be greatly reduced and the current phase difference of two ends of a bus is used as a protection criterion when the micro-grid fails, the problem that the traditional three-section type current protection is possibly rejected due to uncertainty of the direction of the power flow and unobvious change of the current mode value due to the fact that the fault current of the micro-grid in two running states is overcome, meanwhile, the method can accurately identify and cut off a fault line in the two running states of the micro-grid, the problem that the micro-grid needs to use two sets of protection devices in the two running states is solved, the protection cost is reduced, and the reliability and the sensitivity of the micro-grid protection. The protection method does not depend on a current module value as a starting criterion, and overcomes the problem that the protection fails because the fault current of the micro-grid containing the IIDG is small.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic flow chart of a microgrid fault protection method based on improved current phase difference provided by the present invention;
FIG. 2 is a schematic structural diagram of a microgrid according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an equivalent circuit of a grid-connected operation fault of a microgrid in the embodiment of the invention;
FIG. 4 is a schematic diagram of an equivalent circuit of the independent operation fault of the microgrid in the embodiment of the invention;
fig. 5 is a schematic diagram of a current simulation waveform flowing through a breaker QF1 when a point f1 fails during grid-connected operation of a microgrid in the embodiment of the present invention;
FIG. 6 is a schematic diagram of a simulated waveform of current flowing through a breaker QF1 when a point f1 has a fault during independent operation of a microgrid in the embodiment of the invention;
FIG. 7 is a schematic diagram of a voltage simulation waveform of an IIDG output end when a point f1 fails during grid-connected operation of a microgrid in the embodiment of the invention;
FIG. 8 is a schematic diagram of a voltage simulation waveform at the IIDG output terminal when the point f1 fails during independent operation of the microgrid in the embodiment of the present invention;
fig. 9 is a schematic diagram of changes in current phase difference between two ends of a fault bus M, N at point f1 during grid-connected operation of a microgrid in the embodiment of the present invention;
fig. 10 is a schematic diagram of changes in current phase difference between two ends of a fault bus M, N at point f2 during grid-connected operation of a microgrid in the embodiment of the present invention;
fig. 11 is a schematic diagram of current phase difference change at two ends of a fault bus M, N at point f3 during grid-connected operation of a microgrid in the embodiment of the present invention;
fig. 12 is a schematic diagram illustrating changes in current phase difference between two ends of a fault bus M, N at point f1 when a microgrid independently operates according to an embodiment of the present invention;
fig. 13 is a schematic diagram illustrating changes in current phase difference between two ends of a fault bus M, N at point f2 when a microgrid independently operates according to an embodiment of the present invention;
fig. 14 is a schematic diagram of changes in current phase difference between two ends of the fault bus M, N at point f3 when the micro grid operates independently in the embodiment of the present invention.
Detailed Description
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 only a part of the embodiments of the present invention, and not all of the embodiments. 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, an embodiment of the present invention discloses a microgrid fault protection method based on improved current phase difference, including:
s1: detecting currents on two sides of a fault line;
s2: judging whether both sides have current or not;
s3: when the current is detected on both sides of the fault line, detecting whether the output voltage of each inverter type distributed power supply supplying power for each line section is reduced and whether the voltage reduction value exceeds a preset voltage drop threshold value (namely a protection criterion 1);
s4: when the output voltage of at least one inverter type distributed power supply is detected to be reduced and the voltage reduction value exceeds a preset voltage drop threshold value, determining a corresponding suspected fault line section according to the detected position of the inverter type distributed power supply;
s5: detecting the current phase difference of buses at two ends of a suspected fault line section, and judging whether the current phase difference is within a preset action current phase difference threshold range (namely a second formula in a current phase difference criterion);
s6: when the current phase difference is within the range of the action current phase difference threshold, judging that the suspected fault line section is a fault line section, and cutting off the fault line section;
s7: and when the fault line is detected to have current on only one side, the fault line section is cut off through three-section type overcurrent protection.
After detecting the current phase difference of the buses at the two ends of the suspected fault line section, the method further comprises the following steps:
s8: and judging whether the current phase difference is within a preset holding current phase difference threshold range, and when the current phase difference is within the holding current phase difference threshold range, judging that the suspected fault line section is a non-fault line section (namely a first formula in a current phase difference criterion).
The following describes the implementation process of the protection method in detail with reference to a specific microgrid structure:
as shown in fig. 2, the microgrid is connected with a power distribution network through a common connection point PCC and boosting by a transformer T; wherein M, N, P, Y is bus, L1, L2 and L3 are lines, QF1, QF2, QF3, QF4, QF5 and QF6 are circuit breakers (namely protection devices), I is a circuit breakerm、InThe fault current is a fault current flowing through a breaker QF1 and a fault current flowing through a breaker QF2, wherein f1, f2 and f3 are fault points, Load1 and Load2 are loads, IIDG1, IIDG2 and IIDG3 are inverter type distributed power supplies, I is an inverter type distributed power supply, and I is a power supply voltage of the inverter type distributed power supplyg1、Ig2、Ig3The fault current is output for IIDG1, IIDG2 and IIDG3 respectively.
In the embodiment, when the micro-grid is connected to the power grid and runs, the inverter type distributed power supply adopts PQ control; the independent operation micro-grid adopts master-slave control, wherein the IIDG1 and the IIDG2 controlled by PQ are slave power supplies, and the IIDG3 is switched to V/f control by PQ control to be used as a master power supply. The micro-grid can be operated in a grid-connected mode with a power distribution network, and can also be disconnected from the power distribution network to realize isolated island operation (independent operation).
The fault current modulus characteristic is analyzed as follows:
supposing that a three-phase short-circuit fault occurs at point f1 in fig. 2, equivalent circuits of grid-connected operation and independent operation faults are respectively shown in fig. 3 and fig. 4, when a fault occurs, the PQ control inversion type distributed power supply is equivalent to a current source controlled by the voltage of a grid-connected point, the V/f control inversion type distributed power supply is equivalent to a voltage source controlled by the output current of the grid-connected point, the micro-grid performs independent operation by disconnecting the PCC, and in order to improve the fault ride-through capability of the independent operation micro-grid, the fault current output by the V/f control inversion type distributed power supply is 3-5 times of the rated current.
Wherein E isSIs system electricitySource, Ig1、Ig2、Ig3Respectively IIDG1 output fault current, IIDG2 output fault current, IIDG3 output fault current, ImFor fault currents flowing through the circuit breaker QF1, InFor fault currents flowing through the circuit breaker QF2, UgControlling the equivalent voltage of the inverter type distributed power supply IIDG3 for V/f; zS、Z2、Z3、ZM1、ZN1System equivalent impedance, line impedance of line L2, line impedance of line L3, line impedance of bus M to fault point f1, and line impedance of bus N to fault point f1, respectively.
As can be seen from fig. 3 and 4, when the microgrid is connected to the grid, the fault current flowing through the breaker QF1 is provided by the grid and the inverter type distributed power supply IIDG 3; the fault current flowing through the circuit breaker QF1 during independent operation of the microgrid is only provided by the inverter type distributed power supply IIDG3, and meanwhile due to the current limiting reason of the power electronic converter, the fault current flowing through the circuit breaker QF1 during independent operation can be smaller than the fault current flowing through the circuit breaker QF1 during grid-connected operation. In both operating states, it is therefore difficult to achieve effective fault protection using the same protection scheme that depends only on the current modulus.
The characteristics of the current phase difference were analyzed as follows:
the tidal current direction has bidirectionality when the micro-grid operates normally, and as can be seen from fig. 1, the two conditions can be divided into 2 cases: the case 1 is that the current direction flows from the bus M to the bus N, and the case 2 is that the current direction flows from the bus N to the bus M. The predetermined current is a positive current when flowing from the bus to the line, and a negative current when flowing from the line to the bus.
As can be readily seen from fig. 1, no matter what the direction of the power flow is in the normal operation of the microgrid, the current flows across the bus M, N
And
equal in size and opposite in direction, the phase difference is 180 °, namely:
when a micro-grid fails, the following two situations can be specifically distinguished:
(1) line MN in-zone failure
When f1 point in the line MN is in fault, no matter what state the microgrid operates in and the direction of the power flow, the current flows at two ends of the bus M, N
And
the size is indefinite, but the same direction is all from generating line to circuit, and the phase place is the same under the ideal condition, and the phase difference is 0, promptly:
(2) line MN out-of-area fault
When f2 point or f3 point has fault, current flows to the fault point, and no matter what state the microgrid operates in and what direction the microgrid operates in normal operation is, current flows to the two ends of the bus M, N
And
the phase difference is 180 degrees, and the calculation formula is the same as the current phase difference formula when the micro-grid normally operates.
According to the phase difference change of the current at two ends of the bus M, N when the micro grid is in normal operation and faults occur at different positions, the analysis conclusion is as shown in the following table 1:
TABLE 1 bus M, N variation in current phase difference across
As can be seen from table 1, the phase difference between the currents at both ends of the bus M, N is 0 ° only when the fault occurs in the MN region, and the phase difference between the currents at both ends of the bus M, N is 180 ° during normal operation and MN out-of-zone fault.
The characteristics of the voltage at the output end of the inverse distributed power supply in two running states of grid-connected running and independent running of the micro-grid are analyzed as follows:
(1) grid-connected operation
When the microgrid is connected to the power grid, no matter which point f1, f2 and f3 in fig. 1 fails, because the support of a large power grid is lacked after the failure and the capacity of the inverter type distributed power supply is limited, the voltage at the output end of the inverter type distributed power supply at the fault line side drops greatly, that is:
wherein,
the voltages of the output end of the inverter type distributed power supply on the fault line side after the fault and before the fault are respectively.
(2) Operate independently
When the independently operated micro-grid fails, the voltage at the output end of the inverter type distributed power supply drops greatly due to the current limiting function of the power electronic converter in the inverter type distributed power supply, and the situation is consistent with that during grid-connected operation.
Therefore, when the micro-grid fails, the voltage of the output end of the grid-connected operation fault line side inversion type distributed power supply can drop greatly, and the voltage of the output end of the inversion type distributed power supply of the same feeder line or the adjacent feeder lines can drop greatly when the micro-grid operates independently. Therefore, a suspected fault line can be selected by monitoring the voltage drop of the output end of the inverter-type distributed power supply, namely, low-voltage protection can be used as starting protection.
The authenticity of the characteristic analysis result of the current phase difference and the characteristic analysis result of the output terminal voltage of the inverter-type distributed power supply is verified through a specific example as follows:
according to the method, a 10kV micro-grid system is built according to the graph 1, and rated capacities of inverter type distributed power sources IIDG1, IIDG2 and IIDG3 are 0.3WM, 0.6WM and 0.9WM respectively; in actual engineering, a power distribution network line accessed by a power source such as wind energy, photovoltaic and the like is short, the capacitance to the ground can be not considered, an equivalent PI circuit is used for a transmission line, the line length L1 is 3km, the line length L2 is L3 is 1km, and the positive sequence impedance Z of the unit length is1＝(0.6+j0.86)Ω/km，Z1＝Z2，Z0＝1.5Z1(wherein Z is1、Z2、Z0Respectively representing the positive sequence impedance, the negative sequence impedance and the zero sequence impedance of unit length, multiplying the parameters set in simulation by the length of the corresponding line to obtain the impedance of the corresponding line); the end loads are respectively as follows: sLd1＝0.6MV·A，
SLd2＝0.25MV·A，
The middle point of the line is set as a fault point, a three-phase metallic short-circuit fault occurs at 0.4s after the system stably operates, the fault time is 0.1s, and the grid-connected operation and independent operation current simulation wave diagrams flowing through the protection QF1 at the point f1 are respectively shown in fig. 5 and fig. 6.
As can be seen from fig. 5 and 6, the fault current flowing through the breaker QF1 during independent operation of the microgrid is smaller than the fault current flowing through the breaker QF1 during grid-connected operation, and the result of characteristic analysis of the current phase difference is consistent with the result of characteristic analysis of the current phase difference.
The micro-grid is in grid-connected operation and independent operation, and voltage simulation wave forms of the output end of the inverter type distributed power supply are shown in fig. 7 and 8 when f1 point fails. As can be seen from fig. 7 and 8, when the microgrid has a fault, the voltage at the output end of the inverter-type distributed power supply drops greatly, and the result of characteristic analysis of the voltage at the output end of the inverter-type distributed power supply is consistent with the result of characteristic analysis of the voltage at the output end of the inverter-type distributed power supply.
In conclusion, the analysis and verification results can obtain the protection criterion of the microgrid as follows:
protection criterion 1: when a fault occurs, the voltage of the output end of the inverter type distributed power supply can drop greatly and exceed a preset value Vset(the normal voltage is 0.2 times when the single-phase fault occurs, and the normal voltage is 0.5 times when the three-phase fault or the two-phase fault occurs, and the fault can be adjusted according to actual conditions).
Protection criterion 2: in normal operation and in an out-of-range fault, the phase difference between the currents at the two ends of bus M, N is 180 °, and in an in-range fault is 0 °. Considering the actual engineering error, in order to improve the reliability and the sensitivity of protection, the selected protection locking angle is
(L represents the line length in km), so the criterion of current phase difference is:
No matter the micro-grid is in grid-connected operation or independent operation, the voltage at the output end of the inverter type distributed power supply at the fault line side drops greatly during fault, the problem that the short-circuit current of the inverter type distributed power supply after fault does not change obviously due to the current limitation of power electronic devices is effectively solved, and the fault can be used as a starting criterion for protection; the current phase difference does not depend on the modulus of the fault current, the problem that the fault current is small when the micro-grid operates independently is avoided, and meanwhile, the faults inside and outside the area can be distinguished correctly.
When the microgrid is in normal operation or failure, a single power supply condition occurs, and then only one-side current may flow through the line during the failure, so that the protection scheme in the embodiment fails.
With reference to fig. 1, the whole protection scheme flow is briefly described as follows:
(1) detecting whether both sides of the line have current, if both sides have current, executing the protection criterion 1, selecting a suspected fault line when the protection criterion 1 is met (when a fault occurs, the voltage of the IIDG output end of the fault line side can drop greatly, so that the suspected fault line can be selected by monitoring the drop of the voltage of the IIDG output end), starting a current phase difference detection element (a current transformer beside a circuit breaker), and if the current phase difference criterion is met
If so, judging the line as a fault line, outputting a tripping signal to a breaker, and cutting off the fault line;
(2) if only one side has current, the fault line is cut off by overcurrent protection. Overcurrent protection is traditional three-section type current protection, fault current can be increased when a fault occurs, and a fault line is cut off through current amplitude change.
The protection method is simulated as followsIn the simulation process, the parameter setting is the same as that in the above example of verifying the authenticity of the analysis result, wherein in fig. 1, f1 is a fault point in the section MN, f2 is a fault point of the same feeder line outside the section MN, f3 is a fault point of an adjacent feeder line outside the section MN, the fault point is set as the middle point of the line, the fault occurs 0.4s after the system operates stably, the duration is 0.1s, and the L1 equals 3km so that the blocking angle is equal to
And simulating 4 fault types of the A-phase grounding short circuit, the B, C two-phase short circuit, the B, C two-phase grounding short circuit and the A, B, C three-phase short circuit by using PSCAD/EMTDC simulation software respectively so as to verify the effectiveness and reliability of the micro-grid protection method based on the current phase difference. In the present embodiment, simulation and analysis are performed only by taking the metallic ground short circuit occurring in the a phase as an example, and the current phase difference changes at both ends of the bus M, N when the microgrid grid-connected operation is at f1 point fault, at f2 point fault, and at f3 point fault are respectively shown in fig. 9, 10, and 11, and the current phase difference changes at both ends of the bus M, N when the microgrid independent operation is at f1 point fault, at f2 point fault, and at f3 point fault are respectively shown in fig. 12, 13, and 14.
The specific data related to the current phase difference change are shown in table 2:
TABLE 2 simulation results of single-phase earth faults of microgrid
As can be seen from Table 2, no matter whether the microgrid is in grid-connected operation or independent operation, the current phase difference between the two ends of the bus M, N is only satisfied
Protection at both ends of the microgrid bus M, N is active.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (5)
1. A microgrid fault protection method based on improved current phase difference is characterized by comprising the following steps:
detecting currents on two sides of a fault line, and judging whether the currents exist on the two sides of the fault line;
when the current is detected on both sides of a fault line, detecting whether the output voltage of each inverter type distributed power supply supplying power for each line section is reduced and whether the voltage reduction value exceeds a preset voltage drop threshold value;
when the output voltage of at least one inverter type distributed power supply is detected to be reduced and the voltage reduction value exceeds a preset voltage drop threshold value, determining a corresponding suspected fault line section according to the detected position of the inverter type distributed power supply;
detecting the current phase difference of buses at two ends of a suspected fault line section, and judging whether the current phase difference is within a preset action current phase difference threshold range;
when the current phase difference is within the range of the action current phase difference threshold, judging that the suspected fault line section is a fault line section, and cutting off the fault line section;
and when the fault line is detected to have current on only one side, the fault line section is cut off through three-section type overcurrent protection.
2. The microgrid fault protection method based on an improved current phase difference as claimed in claim 1, characterized in that after detecting the current phase difference of the buses at the two ends of the suspected fault line section, the method further comprises:
and judging whether the current phase difference is within a preset holding current phase difference threshold range, and when the current phase difference is within the holding current phase difference threshold range, judging that the suspected fault line section is a non-fault line section.
3. The microgrid fault protection method based on an improved current phase difference as claimed in claim 1 or 2, characterized in that the calculation formula of the current phase difference is as follows:
in the formula,
the phase difference of the currents is represented,
and
and the current values of the buses at the two ends of the suspected fault line section are respectively.
4. The microgrid fault protection method based on improved current phase difference as claimed in claim 2, characterized in that the holding current phase difference threshold range is
To
Wherein the protection locking angle
The calculation formula of (2) is as follows:
in the formula, L represents a line length in km.
5. The microgrid fault protection method based on improved current phase difference as claimed in claim 1, characterized in that the action current phase difference threshold range is 0 ° to
Wherein the protection locking angle
The calculation formula of (2) is as follows:
in the formula, L represents a line length in km.
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| CN112713576A (en) * | 2020-12-21 | 2021-04-27 | 西安理工大学 | Short-circuit protection method for radiation direct-current micro-grid |
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