CN112421583B - Micro-grid protection method based on two-stage fault regulation and superposition components - Google Patents
Micro-grid protection method based on two-stage fault regulation and superposition components Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
Abstract
The invention discloses a microgrid protection method based on two-stage fault regulation and superposition components, which comprises the following steps of firstly, providing a microgrid fault adjustable frame by utilizing an active filter; secondly, on the basis of the framework, aiming at the fault current characteristics of the distributed power supply, a two-stage fault regulation method is provided, so that the flexible regulation of the microgrid under the fault condition and the consistency of control strategies between strong and weak faults are realized; secondly, on the basis of extracting the direct current component and the fundamental frequency component phase angle which are superposed on each bus, the cosine values of the adjacent bus phase angles are solved to construct a characteristic differential direction; finally, when a number smaller than 0 exists in the characteristic difference direction, the fault state is determined; otherwise, the normal operation state is determined.
Description
Technical Field
The invention belongs to the technical field of relay protection of a power distribution network of a power system, and particularly relates to a micro-grid protection method based on two-stage fault regulation and superposition components.
Background
A distributed power generation technology based on renewable energy is an important technical means for dealing with energy crisis and environmental pollution. In order to more effectively utilize distributed power generation technology, micro-grid technology is in force. The power distribution system is a medium-low voltage power distribution network system consisting of Distributed Generation units (DGs) containing wind energy or solar energy and loads. However, due to the flexible operation mode, topological structure and control method of power electronic devices of the micro-grid, the traditional protection method of the power distribution network is not applicable any more, and therefore, the micro-grid protection method becomes a hot spot of domestic and foreign research in recent years.
At present, protection methods are respectively provided for a line, a DG and a public coupling point in a microgrid by combining directional inverse time-limited overcurrent protection, directional negative sequence current protection, current-voltage harmonic distortion rate and current imbalance degree; calculating the phase change between positive and negative sequence superposed components before and after the fault and the current before the fault to determine the fault direction, and forming inverse time limit overcurrent protection according to the amplitude change; and a closed protection method based on the phase, the current break variable and the DG power reference value break variable is also provided by researching the rule of the equivalent positive sequence fault component under the load condition and the external equivalent impedance change. However, the above methods can adapt to the flexible operation mode of the microgrid, but the construction of the traditional overcurrent protection criterion and the time-limit coordination become more and more complex.
In order to simplify the construction of protection criteria, a method combining a digital signal processing algorithm and an artificial intelligence algorithm is gradually applied to the field of microgrid protection. The currently adopted digital signal processing method mainly comprises discrete Fourier transform, short-time Fourier transform, wavelet transform, S transform, EMD algorithm and the like; the adopted artificial intelligence algorithm comprises a decision tree, K-means clustering, a Bayesian classifier, a support vector machine, a deep learning neural network and the like. Although the combination of the digital signal algorithm and the artificial intelligence algorithm can deeply mine the fault information to a certain extent, the method is very dependent on the accumulation of original samples and lacks theoretical support for feature quantity acquisition.
Disclosure of Invention
The invention aims to provide a microgrid protection method based on two-stage fault regulation and superposition components, and provides a two-stage fault regulation method aiming at the fault current characteristics of a distributed power supply, so that the flexible regulation of a microgrid under the fault condition and the consistency of control strategies between strong and weak faults are realized.
The technical scheme adopted by the invention is that a microgrid protection method based on two-stage fault regulation and superposition components is implemented according to the following steps:
step 5, pair i pn Fourier analysis is carried out to obtain i pn Phase angle C of DC component mn And the phase angle F of the fundamental frequency component mn And find the bus B e Upper characteristic direction D e ；
The invention is also characterized in that:
And 2, step 3, setting the rated current peak value with the current limiting value DG maximum capacity as 200A.
Step 5 and obtain the bus B e Upper characteristic direction D e The formula is as follows:
wherein m is the phase sequence number, and m = a, b, c.
The invention has the beneficial effects that:
the invention relates to a microgrid protection method based on two-stage fault regulation and superimposed components, which is characterized in that from the perspective of utilizing the adjustable characteristic of a microgrid DG, a current limiting strategy based on a capacitor neutral point type three-phase four-wire system parallel active filter (SAPF) is combined to provide a microgrid with adjustable faults, so that each DG can be equivalent to a constant current source in the fault period; then, detailed fault theory analysis is carried out on the fault-adjustable microgrid, and feasibility of using the superposed components as characteristic components is demonstrated; and finally, constructing a protection method according to the corresponding superposed components.
Drawings
FIG. 1 is a flow chart of a method for microgrid protection based on two-stage fault regulation and superimposed components in accordance with the present invention;
FIG. 2 is an equivalent circuit of the microgrid employed in the present invention;
FIG. 3 is a block diagram of the voltage-current dual-loop control of the microgrid employed in the present invention;
FIG. 4 is a diagram of a microgrid fault adjustment framework employed in the present invention;
FIG. 5 is a block diagram of SAPF control as employed in the present invention;
FIG. 6 (a) is a diagram of an equivalent circuit before a three-phase fault and after a fault superimposed component fault in a microgrid zone in accordance with the present invention;
FIG. 6 (b) is an equivalent circuit diagram of a superimposed component after fault and a superimposed component before fault and after fault in a microgrid area according to the present invention;
fig. 7 (a) is an equivalent circuit diagram of a superimposed component before and after a three-phase fault outside a microgrid zone according to the present description;
fig. 7 (b) is an equivalent circuit diagram of superimposed components after a fault before and after a fault of three phases outside a micro-grid area according to the description of the present invention;
FIG. 8 illustrates a microgrid model according to an embodiment of the present invention;
fig. 9 (a) is a superimposed component diagram of a bus bar 1 and a bus bar 2 under the condition of the embodiment of the present invention;
fig. 9 (b) is an amplitude-frequency diagram of the bus bar 1 and the bus bar 2 under the condition of the embodiment of the present invention;
FIG. 9 (c) is a phase-frequency diagram of bus 1 and bus 2 under the condition of the first embodiment of the present invention;
FIG. 10 is the DG1 output current under case two conditions in accordance with the embodiment of the present invention;
fig. 11 (a) is a graph of the superimposed components of bus bar 1 and bus bar 2 under case two conditions according to the embodiment of the present invention;
fig. 11 (b) is an amplitude-frequency diagram of the bus bar 1 and the bus bar 2 under case two conditions according to the embodiment of the present invention;
fig. 11 (c) is a phase-frequency diagram of the bus 1 and the bus 2 under the case two condition according to the embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention discloses a micro-grid protection method based on two-stage fault regulation and superposition components, which is implemented according to the following steps as shown in figure 1:
the specific process of judging whether to start the current limiting strategy based on the fault adjustable framework is as follows: when the absolute value of the differential zero-sequence current of each DG output current in the microgrid is greater than 10A, or the absolute value i of the instantaneous value of each phase output current of each DG in the microgrid jn And (t) when the output current rating of each DG is 1.5 times larger than that of the microgrid during full-load operation, starting a current limiting strategy based on the fault adjustable framework, otherwise, not starting.
In the invention, the peak value of the stable current output by the DGs is 83A, the starting current of the current limiting strategy is set to be 124A, the maximum capacity of a single DG is 100kW, the peak value of the current under the maximum capacity is 203.6A, and the current limiting value is 200A in consideration of the transient characteristic of fault current.
Step 5, pair i pn Fourier analysis is carried out to obtain i pn Phase angle C of DC component mn And the phase angle F of the fundamental frequency component mn And find the bus B e Upper characteristic direction D e ；
Obtaining a bus B e Upper characteristic direction D e The formula is as follows:
wherein m is the phase sequence number, and m = a, b, c.
The working principle of the microgrid protection method based on two-stage fault regulation and superposition components is as follows:
1. fault-adjustable microgrid framework
Fig. 2 shows an equivalent circuit of the microgrid used in the present invention, and fig. 3 shows a voltage-current double loop control diagram. In FIG. 2, L f 、R f And C f The inductor, the resistor and the capacitor are sequentially used for filtering; l is c 、R c Coupled inductors and resistors; l is line 、R line Inductance and resistance of the circuit; i.e. i L Is a filter inductor current; u. of dc Is a direct current side voltage; u. of 0 、i 0 Voltage, current, rated value u, for DG output E 、i E (ii) a m is a controllable sinusoidal modulation signal. In fig. 3, s is laplacian; k is a radical of up 、k ui The proportional and integral coefficients of the voltage outer ring; i all right angle c Is the filter capacitor current;
is a reference inductor current; k is a radical of ip 、k ii The current inner loop proportion and integral coefficient.
In FIG. 3, in order
Is input, i 0 For output, and consider u 0 The formula (1) can be obtained.
As can be seen from the formula (1), when the micro-grid operates stably, i can be controlled by adjusting the control parameters 0 Remain stable and, in case of failure, i 0 Will follow u 0 Is changed by i 0 Stabilization can be achieved by injecting an additional component, as shown in equation (2).
In order to realize the dynamic tracking of Q when the micro-grid fails, a capacitor-containing medium-point three-phase four-wire system parallel active filter (SAPF) can be utilized to enable the SAPF to generate compensation current, and therefore the purpose of fault regulation is achieved. The microgrid fault adjustment framework is shown in figure 4.
In FIG. 4, i 0j Is an output current; l is ff And R ff A filter inductor and a resistor of the SAPF are respectively; c f1 And C f2 A direct current side capacitor; they all have a value of C ff ；V dc1 And V dc2 Is a direct current side voltage; i.e. i Lj (i La , i Lb ,i Lc ) Is the load current; i.e. i fj (i fa ,i fb ,i fc ) Is the output current of the APF; i.e. i Ln and i fn Zero sequence currents of the load and the APF are respectively; s j And
is the switching function:
selecting an inductive current i at the output side of the SAPF according to the kirchhoff law and a state space averaging method fj Voltage difference Δ V of capacitor on DC side dc (ΔV dc ＝V dc1 -V dc2 ) And the total voltage sigma V on the DC side dc (∑V dc ＝ V dc1 +V dc2 ) For state variables, the mathematical model of the SAPF under the three-phase stationary abc coordinate system can be obtained as follows:
according to the coordinate transformation theory, the mathematical model of SAPF in the dq coordinate system of synchronous rotation can be obtained from the formula (4) by adopting the equal power transformation, see formula (5), wherein i fd ,i fq ,i f0 ,S d ,S q ,S 0 And V Ld ,V Lq ,V L0 Respectively are d, q and 0 components of the SAPF output side inductance current, the switching function and the PCC voltage under a dq coordinate system; ω is the supply angular frequency.
Further, the SAPF control block diagram shown in fig. 5 can be derived, which employs a dual-loop cascade structure of a voltage outer loop and a current inner loop. Wherein:
1) By dq0 harmonic detection method, i can be obtained Ldh ，i Lqh And i and L0h ；
2) Obtaining Δ i dv : will V dc1 And V dc2 The summed total voltage ∑ V dc Is related to the expected value ∑ V dcr After comparison, the delta i can be generated after passing through a 2-order low-pass filter dv ；
3) Obtaining Δ i 0v Will V dc1 And V dc2 After the difference is found, and compared with the expected 0, the Δ i can be generated by a 2-step low-pass filter 0v ；
4) Obtaining i fdr : by i Ldh And Δ i dv Is obtained by addition;
5) Obtaining i f0r : through i L0h And Δ i 0v Is obtained by addition;
2. empirical wavelet transform
Taking the discrete time domain integrated current signal as an example, the specific process of the transformation is realized as follows:
the method comprises the following steps: signal i to be decomposed n (t) performing a fourier transform;
step two: at omega N As a boundary, for a range of [0, π]The Fourier spectrum of i (t) of (a) is divided into N sections in succession, wherein, omega 0 ＝0，ω N And N-1 remaining paragraphs are divided according to local spectral maxima, and the arrangement order is arranged in descending order. If the number of the maximum values is M, when M is more than or equal to N, retaining the first N-1 maximum values, when M is less than N, retaining all the maximum values and correcting N, and finally omega n Determining according to the intermediate frequency of two local maxima;
step three: constructing N empirical wavelets for the obtained N Fourier spectrum paragraphs
The expression is shown in formula (6), and the scale function thereof
See formula (7), formula (8) and formula (9) give expressions of β and γ in formula (6) and formula (7);
step four: calculating a detail correlation coefficient W i (N, t), expression thereofThe formula is shown as formula (10).
In the formula (I), the compound is shown in the specification,
is an empirical wavelet function;
is composed of
Complex conjugation of (a);
and
are respectively i and
fourier transform of (d).
3. High-resistance detection method based on empirical wavelet transform
step 1.1 of obtaining three-phase current i on each bus of micro-grid an (t)、i bn (t) and i cn (t), a, b and c are phase sequences;
step 1.2 obtaining d-axis current i on each bus dn (t) and q-axis current i qn (t), the calculation formula is as follows:
wherein, f s To a rated frequency, f s ＝50Hz；
Step 1.3 obtaining the comprehensive current i on each bus n (t), calculated as follows:
wherein i Dn (t) and i Qn (t) is the differential d-axis current and the differential q-axis current on each bus, and w is the number of sampling points in one period;
step 2.1 for i n (t) normalizing to obtain i gn (t)；
Step 2.2 for i gn (t) performing a fourier transform;
step 2.3 Pair in the range of [0, π]I of (a) gn (t) dividing the Fourier spectrum into N segments, wherein ω is 0 ＝0，ω N = pi, the rest N-1 paragraphs are divided according to the local spectrum maximum, the arrangement order is arranged according to the descending order, and N is 10 in the invention;
step 2.4, calculating empirical wavelet transform component W of each segment in (N, t), the specific calculation formula is as follows:
in the formula (I), the compound is shown in the specification,
is an empirical wavelet function;
is composed of
Complex conjugation of (a);
and
are respectively i and
ω is the angular frequency.
Step 2.5 selecting W in (10, t) as the highest frequency component i on the bus n Hn (t)；
step 3.1 to find i Hn 10 pairs of maximum and minimum points of (t);
step 3.2 the variance between these 20 points is found and defined as the mutation variance v rn ；
Step 3.3 when v rn >c, judging that disturbance occurs in the microgrid, and turning to the step 4; when v is rn <And c, judging that the microgrid is in a normal operation state, and ending the detection program, wherein c is 50 -6 ；
step 4.1 when v rn >When p, judging the fault state to be a strong fault state, and ending the detection program; when v is rn <When p is detected, the normal disturbance operation state or the high-resistance fault state is judged, the step 4.2 is carried out, and p is taken as 50;
step 4.2 obtaining i Hn Energy E of (t) n (t), the calculation formula is as follows:
E n (t)＝i Hn (t)×i Hn (t) (15)
step 4.3 mixing E n (t) normalizing to obtain normalized g n (t), the calculation formula is as follows:
step 4.4 mixing of g n Setting the value less than 0.2 in (t) as 0 to obtain new energy sequence G n (t)；
Step 4.5 obtaining the weight value j of the abrupt change quantity rn The calculation formula is as follows:
in the formula, T is the number of sampling points.
Step 4.6 when j rn >Lambda, judging that the microgrid is in a high-resistance fault state at the moment, and ending the detection program; when j is rn When the lambda is less than or equal to lambda, judging the normal disturbance running state, and ending the detection program; in the invention, the lambda is 1000.
4. Microgrid fault analysis based on superimposed components
In the low-voltage microgrid, a three-wire four-wire system wiring mode is often adopted, so that when a fault occurs, the neutral voltage is 0, and even if an asymmetric fault occurs, the neutral voltage can force each phase to be relatively independent, and therefore, the phase a analysis is taken as an example below.
According to the superposition theorem, when a three-phase fault occurs in a section of a microgrid with the current limiting strategy, the equivalent circuit of the fault and the superposed components before the fault is shown in fig. 6 (a) and 6 (b), wherein U is a (t) and U b (t) voltages of the distributed power supplies a and b before the fault are sequentially obtained; u shape fa (t) and U fb (t) voltage superposition components of the distributed power supplies a and b after the fault are sequentially generated; l is inv The equivalent inductance of the distributed power supply; r fa And L fa Resistance and inductance between a fault point and a line terminal A; r is fb And L fb Resistance and inductance between a fault point and a line terminal B; u shape f (t) is the voltage at the point of failure F before failure; delta U f (t) is the voltage superposition component of the fault point F after the fault; i.e. i A (t) and Δ i fA (t) is the current flowing through the end point of line A before the fault and the superposed component of the current after the fault; u. of A (t) and. DELTA.u fA (t)The voltage at the end point of the line A before the fault and the voltage after the fault are superposed to form a component.
Equations (18) to (22) can be obtained from fig. 6 (b) and KVL.
Δi fA (t)＝Δi fa (t)-Δi fb (t) (19)
L s ＝L inv +L fa (22)
Similarly, when the microgrid with the current limiting strategy has an out-of-area three-phase fault, the equivalent circuits of the superposed components before and after the fault are shown in fig. 7 (a) and 7 (b). In FIG. 8, R ab And L ab Resistance and inductance between line end A and line end B; Δ i FA (t) is the current superposition component flowing through the line A endpoint after the fault; Δ u FA And (t) is a voltage superposition component of the line A endpoint after the fault.
Equations (23) to (28) can be obtained from fig. 7 (b) and KVL.
Δi FA (t)＝Δi Fa (t)+Δi Fb (t) (24)
L A ＝L inv +L fa +L ab (27)
R A ＝R fa +R ab (28)
As can be seen from equations (19) and (24), the superimposed component of the current flowing through line terminal a is composed of a constant current and an alternating current regardless of an in-zone or out-of-zone fault.
As can be seen from the observation of the expressions (20) and (25), the denominators thereof are both positive numbers, that is, Δ i fa (t) and Δ i FA The sign of (t) depends on their molecules, and their key portions are shown by the formulas (29) and (30).
Since the output impedance of the distributed power supply based on droop control is inductive, but the impedance value is almost 0, the expressions (29) and (30) can be further reduced to expressions (31) and (32).
In the formula, R F And L F Resistance and inductance values for each kilometer of line; x is the number of fa And x FA The distance between the fault point and the line end point A when the fault occurs in the zone and the zone.
In view of R F And L F Is a fixed value, and R is in the microgrid F And L F Typically 0.642 omega/km and 0.083H/km, and therefore, may be usedWhen both the formula (20) and the formula (21) are greater than 0, the initial phase angle range of the fault point voltage is 0-88.59 degrees, that is, in the range, both the formula (20) and the formula (21) are positive, and further both the formula (5) and the formula (10) are negative. When the initial phase angle range is 88.59-90 deg., L is s ωU fa Is much greater than R fa U m In this range, both of the formulae (20) and (21) are positive, that is, the formulae (9) and (14) are positive and negative in this order. Therefore, when a short-circuit fault occurs, the equations (9) and (14) always maintain a positive-negative characteristic regardless of the change of the fault initial phase angle, the short-circuit resistance and the amplitude of the distributed power supply, and the equations (10) and (15) also maintain a positive-negative characteristic in the same way.
Examples
A microgrid model is built as in fig. 8, and in fig. 8, note: DG 1-DG 4 are 4 identical DG units controlled by droop, the capacity is 100kW, the switching frequency is 6kHz, and the direct current voltage is 800V; the resistance and inductance parameters of the line are 0.642 omega/km and 0.083H/km in sequence, and the length of the line is 0.3km, 0.2km and 0.5km in sequence. The load parameters are shown in Table 1.
TABLE 1 load parameters
Case one: the three-phase short-circuit fault occurs in line 1 of the microgrid at 0.1s, wherein the fault distance is 200m.
Due to the three-phase short circuit fault, the instantaneous value of each phase current reaches the starting condition of the first phase of fault regulation, and the next judgment is not needed. Fig. 9 (a) -9 (c) show the superimposed components of the bus bar 1 and the bus bar 2, and their amplitude-frequency diagram and phase-frequency diagram. The dc component phase angle, fundamental frequency component phase angle and characteristic direction on each bus are given in table 2. In fig. 9 (a), the trend of change between the superimposed components of the busbar 1 and the busbar 2 after the fault is inversely related, as can be seen from fig. 9 (b) and 9 (c), the amplitudes of the dc component and the fundamental frequency component of the busbar 1 and the busbar 2 are not 0, the phase angles of the dc component are 180 ° and 0 ° respectively, the directions are completely reversed, the phase angles of the fundamental frequency component are-111.4 ° and 46.1 ° respectively, the phase angle difference is greater than 90 °, and the sign of the amplitude is positive-negative, which is consistent with the theoretical derivation of the description.
TABLE 2 DC COMPONENT PHASE ANGLE, BASE-FREQUENCY COMPONENT PHASE ANGLE AND CHARACTERISTIC DIRECTIONS ON BUS LINES
Case two: the a-phase single-phase grounding short circuit occurs on the line 1 of the microgrid at 0.05s, wherein the grounding resistance is 10 omega, and the fault distance is 200m.
Fig. 10 shows the output current of DG1, and it can be known from simulation that the phase a of bus 1 and bus 2 will not reach the current limiting strategy, and the phase a is started immediately, and related documents and practice show that the ground resistance of 0-600 Ω in 10kV distribution network is equivalent to the ground resistance of 0-30 Ω in 500V network, therefore, the ground resistance of 10 Ω in 400V network is equivalent to about 250 Ω in 10kV distribution network, and belongs to large ground resistance fault. Then, through a fault-adjusted second stage calculation, the variance v of the variables is determined r 0.05, mutation amount weight j r At 1384, the current limit strategy was initiated at 0.12s due to the detection of the last cycle of weak fault.
Fig. 11 shows the superposed currents of the phases a and the amplitude frequency diagram and the phase frequency diagram of the superposed currents of the phases a and b in 1 period after the fault of the bus 1 and the bus 2. It can be known from fig. 11 that the trend of the change between the superimposed components on the buses at both ends of the fault section is opposite, and as can be known from fig. 11 (b) and 11 (c), the amplitudes of the dc component and the fundamental frequency component of the bus 1 and the bus 2 are not 0, and the phase angles of the dc component are 0 ° and 180 ° respectively, and are completely reversed, the phase angles of the fundamental frequency components are-36.3 ° and 125.5 ° respectively, the phase angle difference is greater than 90 °, and the sign of the amplitude is one positive, one negative. In addition, it should be noted that, since the fault existed in the previous cycle, the phase angle of the dc component caused by the calculation of the superimposed component is opposite to that of fig. 9.
As can be seen from table 3, the solution by the protection method provided by the present invention still only has the negative value in the characteristic direction of the bus 1, and therefore, it is determined that a fault occurs between the bus 1 and the bus 2, which is consistent with the actual fault.
TABLE 3 DC COMPONENT PHASE ANGLE, BASE-FREQUENCY COMPONENT PHASE ANGLE AND CHARACTERISTIC DIRECTIONS ON BUS LINES
Through the mode, the invention discloses a microgrid protection method based on two-stage fault regulation and superposition components, which comprises the steps of firstly, providing a microgrid fault adjustable frame by utilizing an active filter; secondly, on the basis of the framework, aiming at fault current characteristics of a Distributed Generation (DG), a two-stage fault regulation method is provided, so that the flexible regulation of the microgrid under a fault condition and the consistency of control strategies between strong and weak faults are realized; secondly, on the basis of extracting the direct current component and the fundamental frequency component phase angle which are superposed on each bus, the cosine values of the adjacent bus phase angles are solved to construct a characteristic differential direction; finally, when a number smaller than 0 exists in the characteristic difference direction, the fault state is determined; otherwise, the normal operation state is determined.
Claims (3)
1. A micro-grid protection method based on two-stage fault regulation and superposition components is characterized by being implemented according to the following steps:
step 1, collecting a differential zero sequence current of each DG output current in a microgrid and each phase output current instantaneous value of each DG in the microgrid;
step 2, judging whether to start a current limiting strategy based on a fault adjustable frame according to the differential zero sequence current of each DG output current and each phase output current instantaneous value of each DG; if the starting is finished, setting the current limiting value as the rated current peak value of the DG maximum capacity, and executing the step 4; if not, executing the step 3;
the specific process of judging whether to start the current limiting strategy based on the fault adjustable frame is as follows: when the absolute value of the differential zero-sequence current of each DG output current in the microgrid is greater than 10A, or the absolute value i of the instantaneous value of each phase output current of each DG in the microgrid jn (t) when the output current rating of each DG is 1.5 times greater than that of the microgrid during full-load operation, starting the fault-based adjustable frameworkOtherwise, not starting;
step 3, judging whether a high-resistance fault occurs in the microgrid, if so, starting a current limiting strategy based on a fault adjustable frame, and setting a current limiting value as a rated current peak value of the maximum DG capacity; if not, stopping executing the subsequent steps, and enabling the micro-grid to be normal;
step 4, obtaining each bus B of the microgrid n Each phase current superimposed component i pn The time window is 1 cycle, wherein N is the bus number, N =1,2,3, …, e, e +1, …, N;
step 5, pair i pn Fourier analysis is carried out to obtain i pn Phase angle C of DC component mn And the phase angle F of the fundamental frequency component mn And find the bus B e Upper characteristic direction D e ；
The bus B is obtained by the summation e Upper characteristic direction D e The formula is as follows:
wherein m is a phase sequence number, and m = a, b, c;
step 6, if D e If the value of any element in the bus bar is less than 0, the bus bar B is judged e And bus B e+1 A fault section is arranged between the two sections, the signal is sent to a microgrid relay protection device, and the action is tripped; otherwise, the micro-grid relay protection device is judged to be a healthy section, no signal is sent, and the micro-grid relay protection device does not act.
2. The microgrid protection method based on two-stage fault regulation and superposition components of claim 1, wherein in the step 4, each bus B of the microgrid is obtained n Each phase current superimposed component i pn The sampling frequency of (2) is 10kHz, and the number of sampling points is 200.
3. The microgrid protection method based on two-stage fault regulation and superposition components is characterized in that rated current peak values with the set current limiting values being DG maximum capacity in the steps 2 and 3 are 200A.
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