CN115882432B - Active injection type harmonic current differential protection method and system for power distribution network containing IIDG - Google Patents

Active injection type harmonic current differential protection method and system for power distribution network containing IIDG Download PDF

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CN115882432B
CN115882432B CN202310186417.0A CN202310186417A CN115882432B CN 115882432 B CN115882432 B CN 115882432B CN 202310186417 A CN202310186417 A CN 202310186417A CN 115882432 B CN115882432 B CN 115882432B
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harmonic current
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characteristic harmonic
differential protection
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CN115882432A (en
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高湛军
于成澳
刘朝
陶政臣
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Shandong University
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Abstract

The invention discloses an active injection type harmonic current differential protection method and system for an IIDG-containing power distribution network, and belongs to the technical field of relay protection of power systems. The method comprises the steps of acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time; judging whether a starting criterion is met, if yes, starting an injection unit, and respectively injecting characteristic harmonic signals into d-axis reference current and q-axis reference current of a current inner loop control module in the inversion type distributed power supply controller, wherein the inversion type distributed power supply outputs characteristic harmonic current; and calculating the difference value of the distortion rate of the negative sequence components of the characteristic harmonic currents at the two sides of the protected line and the difference value of the distortion rate of the A-phase characteristic harmonic currents according to the characteristic harmonic currents, judging whether the differential protection criterion is met, and executing the protection action. The characteristic harmonic current injected into the power distribution network is utilized to strengthen fault characteristics, differential protection of the power distribution network containing IIDGs is achieved, and the problem that the uncertainty of the output current of the IIDGs makes the setting and time delay matching of the traditional passive detection type protection challenging is solved.

Description

Active injection type harmonic current differential protection method and system for power distribution network containing IIDG
Technical Field
The application relates to the technical field of relay protection of power systems, in particular to an active injection type harmonic current differential protection method and system for a power distribution network containing IIDGs.
Background
The statements in this section merely provide background information related to the present application and may not necessarily constitute prior art.
After the distributed power supply (DG) is connected into the power distribution network in a large scale, the power distribution network is converted into a complex multi-power multi-terminal power supply network from a simple single-power radiation type power supply network, so that the power distribution network with the distributed power supply has complex and changeable power flow direction, running mode and short-circuit current fault characteristics, and the traditional three-section current protection is not applicable any more.
The DG can be classified into a rotation type distributed power supply (MTDG) directly connected to the grid and an inversion type distributed power supply (IIDG) connected to the grid through an inverter according to the difference of the grid connection interfaces. Because of the low inertia, high controllability and poor overcurrent capability of the power electronic inverter, the fault characteristics of the IIDG are different from those of the traditional synchronous generator, and in order to prevent the overcurrent damage of the power electronic devices of the inverter, the maximum short-circuit current provided by the IIDG is limited within 2 times of rated current, and the output current is influenced by factors such as an inverter control strategy, low voltage ride through, fault conditions and the like.
In order to cope with the problems, expert scholars at home and abroad apply the current differential protection to the power distribution network, but the change of the IIDG output current phase after the fault is larger, the traditional current differential protection can be refused in a certain fault scene, and the synchronous requirement of the traditional current longitudinal differential protection on the communication is larger. In summary, the uncertainty of the IIDG output current makes the setting and time delay matching of the conventional passive detection protection face a great challenge, especially for the power distribution network with high IIDG permeability. Over time, IIDG permeability has increased, and a new protection method is needed.
Disclosure of Invention
In order to solve the defects of the prior art, the application provides an active injection type harmonic current differential protection method and system for a power distribution network containing IIDGs, which are used for strengthening fault characteristics by utilizing characteristic harmonic current injected into the power distribution network and realizing differential protection of the power distribution network containing the IIDGs.
In a first aspect, the present application provides an active injection type harmonic current differential protection method for a power distribution network including IIDG;
an active injection type harmonic current differential protection method for a power distribution network containing IIDG comprises the following steps:
s1, acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time;
s2, judging whether a starting criterion is met according to current information and voltage information at an outlet of the inversion type distributed power supply, and if so, continuing to execute the following steps; if not, returning to the execution step S1;
s3, starting an injection unit, respectively injecting characteristic harmonic signals into d-axis and q-axis reference currents of a current inner loop control module in the inversion type distributed power supply controller, and outputting characteristic harmonic currents by the inversion type distributed power supply;
and S4, calculating the characteristic harmonic current negative sequence component distortion rate difference values at two sides of the protected circuit and the phase A characteristic harmonic current distortion rate difference values at two sides of the protected circuit according to the characteristic harmonic current, judging whether a differential protection criterion is met, and if so, executing a protection action.
Further, the starting criteria comprise a phase voltage starting criterion and a phase current starting criterion, wherein the phase current starting criterion is expressed as:
Figure SMS_1
in the formula ,
Figure SMS_4
for the sampling point number corresponding to the current time, +.>
Figure SMS_6
Sampling point number for one cycle, +.>
Figure SMS_8
For the number of sampling points of the cycle before the current moment,/-, for the current moment>
Figure SMS_3
For the number of sampling points of the two cycles before the current moment, < +.>
Figure SMS_7
For the sampling value of the phase current at the present time, +.>
Figure SMS_9
For the sampling value of the current of the previous cycle phase at the present moment, is +.>
Figure SMS_10
For the sampling value of the current of the first two cycle phases at the present moment, is +.>
Figure SMS_2
For the start-up coefficient and with a value of 0.1 to 0.3, ">
Figure SMS_5
Is the rated current of the protected feeder.
Further, step S1 further includes:
and if the starting criterion is met, sending an enabling signal to the injection unit to start the injection unit.
Further, the a-phase characteristic harmonic current is expressed as:
Figure SMS_11
wherein ,
Figure SMS_13
for the amplitude of the characteristic harmonic current, +.>
Figure SMS_16
Phase angle of characteristic harmonic signal, +.>
Figure SMS_18
Is the phase angle of power frequency>
Figure SMS_14
For the angular frequency of the characteristic harmonic signal, +.>
Figure SMS_17
Is the angle frequency of the power frequency +.>
Figure SMS_19
For the current moment +.>
Figure SMS_20
For the frequency of the characteristic harmonic signal of the reference current injected into the d-axis and q-axis, +.>
Figure SMS_12
Is power frequency->
Figure SMS_15
Is the initial phase angle of the characteristic harmonic signal.
Further, the amplitude a of the characteristic harmonic current is expressed as
Figure SMS_21
wherein ,IIIDG_d For d-axis reference current, I IIDG_q For q-axis reference current.
Further, the calculating the difference value of the distortion rates of the negative sequence components of the characteristic harmonic currents at two sides of the protected line is as follows:
respectively calculating negative sequence components in short-circuit currents at two sides of a protected line, wherein the negative sequence components are negative sequence components of characteristic harmonic currents;
according to the negative sequence component of the characteristic harmonic current and the negative sequence component of the power frequency current, calculating the distortion rate of the negative sequence component of the characteristic harmonic current respectively;
calculating the absolute value of the difference value of the negative sequence component distortion rate;
the A-phase characteristic harmonic current distortion rate difference values at two sides of the protected line are calculated as follows:
according to the amplitude of the A-phase characteristic harmonic current and the amplitude of the A-phase power frequency current, respectively calculating the A-phase characteristic harmonic current distortion rate at two sides of the protected line;
and calculating the absolute value of the difference value of the A-phase characteristic harmonic current distortion rate. Further, the judging whether the differential protection criterion is met is as follows:
judging whether the absolute value of the difference value of the negative sequence component distortion rate of the characteristic harmonic current in the short-circuit currents at two sides of the protected line is larger than a first differential protection action threshold value or not;
judging whether the absolute value of the difference value of the A-phase characteristic harmonic current distortion rate in the short-circuit currents at two sides of the protected line is larger than a second differential protection action threshold value or not;
if the difference is larger than the first differential protection action threshold or larger than the second differential protection action threshold, executing differential protection action, and stopping the injection of the characteristic harmonic signals;
the first differential protection operation threshold value and the second differential protection operation threshold value are equal or unequal.
Further, the calculation of the distortion rate of the negative sequence component of the characteristic harmonic current is shown as follows:
Figure SMS_22
wherein h is the number of characteristic harmonics,
Figure SMS_23
amplitude of the negative sequence component of the harmonic current for h order of magnitude, +.>
Figure SMS_24
Is the amplitude of the negative sequence component of the power frequency current.
Further, the frequency of the characteristic harmonic current is not more than 10 times of the power frequency and is an integer multiple of the power frequency.
In a second aspect, the application provides an active injection type harmonic current differential protection system of a distribution network containing IIDG;
an active injection type harmonic current differential protection system for a distribution network containing IIDG, comprising:
a fault detection and harmonic injection control unit configured to: acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time; judging whether a starting condition is met according to current information and voltage information at an outlet of the inversion type distributed power supply, and if so, starting an injection unit;
an injection unit configured to: injecting characteristic harmonic signals into d-axis and q-axis reference currents of a current inner loop control module in the inversion type distributed power supply controller, and outputting characteristic harmonic currents by the inversion type distributed power supply;
a differential protection unit configured to: and calculating the difference value of the distortion rate of the negative sequence components of the characteristic harmonic currents at the two sides of the protected circuit and the difference value of the distortion rate of the A-phase characteristic harmonic currents at the two sides of the protected circuit according to the characteristic harmonic currents, judging whether a differential protection criterion is met, and if so, executing the protection action.
Compared with the prior art, the beneficial effects of this application are:
1. according to the technical scheme, the characteristic harmonic current amplitude injected into the power distribution network adaptively changes along with the IIDG output current amplitude, so that the fault characteristics of the characteristic harmonic current after injection are enhanced, and meanwhile, the harmonic injection regulation of the power distribution network can be guaranteed to be met all the time.
2. According to the technical scheme, the differential protection criterion is constructed by utilizing the harmonic distortion rate, so that the interference of a large number of harmonic waves generated in the moment of faults on protection can be reduced.
3. According to the technical scheme, the active injection type harmonic current differential protection method is simple in action threshold setting, has excellent selectivity and sensitivity, does not need strict communication synchronization requirements, and is strong in transition resistance tolerance.
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The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute an undue limitation to the application.
Fig. 1 is a schematic diagram of a starting detection principle of an IIDG injection unit provided in an embodiment of the present application;
fig. 2 is a schematic diagram of a simple active power distribution network including IIDG access provided in an embodiment of the present application;
fig. 3 is a schematic structural diagram of an IIDG overall control system provided in an embodiment of the present application;
fig. 4 is a schematic flow chart of an active injection type harmonic current differential protection method for a distribution network including IIDG according to an embodiment of the present application;
fig. 5 is a schematic circuit diagram of an outlet of IIDG1 of the IIDG-containing simple active power distribution network in normal operation provided in the embodiment of the present application;
fig. 6 is a schematic diagram of a characteristic harmonic current amplitude and a characteristic harmonic signal waveform injected into a d-axis and a q-axis when the IIDG-containing simple active power distribution network provided in the embodiment of the present application is in normal operation;
fig. 7 is a schematic diagram of a characteristic harmonic current distortion rate at an outlet of an IIDG1 when the IIDG-containing simple active power distribution network provided in the embodiment of the present application is in normal operation;
fig. 8 is a schematic diagram of current at the outlet of IIDG1 when the IIDG-containing simple active power distribution network provided in the embodiments of the present application fails;
fig. 9 is a schematic diagram of characteristic harmonic current amplitude and characteristic harmonic signal waveforms injected into d and q axes when an IIDG-containing simple active power distribution network provided in an embodiment of the present application fails;
fig. 10 is a graph of characteristic harmonic current distortion rate at the outlet of IIDG1 when the IIDG-containing simple active power distribution network provided in the embodiments of the present application fails;
fig. 11 (a) is a schematic diagram of the distortion rate of the characteristic harmonic current negative sequence components on two sides of the feeder line BM when the single-phase grounding short circuit is performed when the point of the point f1 of the simple active power distribution network containing IIDG provided in the embodiment of the present application has a transition resistance of 0.1 Ω;
fig. 11 (b) is a schematic diagram of the distortion rate of the characteristic harmonic current negative sequence components on two sides of the feeder line BM when the two phases are grounded and short-circuited when the transition resistance is 0.1 Ω, which is provided by the embodiment of the present application and includes the point f1 asymmetric fault of the IIDG simple active power distribution network;
fig. 11 (c) is a schematic diagram of the distortion rate of the negative sequence components of the characteristic harmonic currents on two sides of the feeder line BM when the transition resistance is 0.1 Ω and two phases are short-circuited, for the point asymmetric fault of the simple active power distribution network f1 including IIDG provided in the embodiment of the present application;
fig. 12 is a diagram of f in a simple active power distribution network including IIDG provided in an embodiment of the present application 1 When the point symmetry faults and the transition resistance is 0.1 omega, the A-phase characteristic harmonic current distortion rate at two sides of the feeder line BM is shown in the schematic diagram;
fig. 13 (a) shows f in an IIDG-containing simple active power distribution network according to an embodiment of the present application 1 When the point asymmetry faults, the transition resistance is 20Ω, and characteristic harmonic current negative sequence component distortion rate at two sides of the feeder line BM is shown in a schematic diagram when the single-phase grounding is short-circuited;
fig. 13 (b) is a diagram of f in a simple active power distribution network including IIDG according to an embodiment of the present application 1 When the point asymmetry faults and the transition resistance is 20Ω, the distortion rate of the characteristic harmonic current negative sequence components at the two sides of the feeder line BM is shown in the schematic diagram when the two phases are in short circuit;
fig. 13 (c) is a diagram of f in a simple active power distribution network including IIDG according to an embodiment of the present application 1 And when the point asymmetry faults and the transition resistance is 20Ω, the distortion rate of the characteristic harmonic current negative sequence components at the two sides of the feeder line BM is shown in the schematic diagram.
FIG. 14 shows the present inventionF in IIDG-containing simple active power distribution network provided by application embodiment 1 When the point symmetry faults and the transition resistance is 20Ω, the phase A characteristic harmonic current distortion rate at two sides of the feeder line BM is shown in the schematic diagram;
fig. 15 (a) shows f in an IIDG-containing simple active power distribution network according to an embodiment of the present application 2 When the point asymmetry faults and the transition resistance is 0.1 omega, the distortion rate of the characteristic harmonic current negative sequence components at the two sides of the single-phase grounding short circuit feeder line MN is shown in the schematic diagram;
fig. 15 (b) shows f in the IIDG-containing simple active power distribution network according to the embodiment of the present application 2 When the point asymmetry faults and the transition resistance is 0.1 omega, the characteristic harmonic current negative sequence component distortion rate at two sides of the two-phase grounding short circuit feeder line MN is shown in a schematic diagram;
fig. 15 (c) is a diagram of f in a simple active power distribution network including IIDG according to an embodiment of the present application 2 When the point asymmetry faults and the transition resistance is 0.1 omega, the distortion rate of the characteristic harmonic current negative sequence components at the two sides of the two-phase short circuit feeder line MN is shown in the schematic diagram;
fig. 16 is a diagram of f in a simple active power distribution network including IIDG provided in an embodiment of the present application 2 When the point symmetry faults and the transition resistance is 0.1 omega, the A-phase characteristic harmonic current distortion rate at two sides of the feeder line MN;
fig. 17 (a) shows f in an IIDG-containing simple active power distribution network according to an embodiment of the present application 2 When the point asymmetry faults, the transition resistance is 20Ω, and the characteristic harmonic current negative sequence component distortion rate of the two sides of the feeder line MN is shown in a schematic diagram when the single-phase grounding is short-circuited;
fig. 17 (b) is a diagram of f in a simple active power distribution network including IIDG according to an embodiment of the present application 2 When the point asymmetry faults and the transition resistance is 20Ω, the distortion rate of the characteristic harmonic current negative sequence components at the two sides of the feeder line MN is shown in the schematic diagram when the two phases are in short circuit;
fig. 17 (c) is a diagram of f in a simple active power distribution network including IIDG according to an embodiment of the present application 2 The point asymmetry fault, when the transition resistance is 20Ω, the characteristic harmonic current negative sequence component distortion rate of the two sides of the feeder line MN is schematic when the two phases are short-circuited;
fig. 18 shows f in a simple active power distribution network including IIDG according to an embodiment of the present application 2 Point symmetry fault, when the transition resistance is 20Ω, the A phase characteristic harmonic current distortion rate at two sides of the feeder line MN is schematically shown。
In the figure: a. positive and negative sequence separation links; b. constant power control links based on positive sequence components; c, suppressing a control link of the negative sequence current; d. a low voltage ride through control link; e. and a fault detection and harmonic injection control link.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, unless the context clearly indicates otherwise, the singular forms also are intended to include the plural forms, and furthermore, it is to be understood that the terms "comprises" and "comprising" and any variations thereof are intended to cover non-exclusive inclusions, such as, for example, processes, methods, systems, products or devices that comprise a series of steps or units, are not necessarily limited to those steps or units that are expressly listed, but may include other steps or units that are not expressly listed or inherent to such processes, methods, products or devices.
Embodiments of the invention and features of the embodiments may be combined with each other without conflict.
Example 1
In the prior art, the uncertainty of the IIDG output current makes the setting and time delay matching of the traditional passive detection type protection face great challenges; therefore, the application provides an active injection type harmonic current differential protection method for the power distribution network containing IIDGs.
Next, a detailed description will be given of an active injection type harmonic current differential protection method for a power distribution network including IIDG disclosed in this embodiment with reference to fig. 1 to 18. The active injection type harmonic current differential protection method for the power distribution network containing IIDG comprises the following steps of:
s1, current information and voltage information at an outlet of an inversion type distributed power supply (IIDG) are obtained in real time, wherein the current information is collected by a current transformer arranged at the outlet of the inversion type distributed power supply (IIDG), and the voltage information is collected by a voltage transformer arranged at the outlet of the inversion type distributed power supply (IIDG).
S2, judging whether a starting criterion is met or not to start the injection unit according to current information and voltage information at an outlet of an inversion type distributed power supply (IIDG), and if so, continuing to execute the following steps; if not, returning to the execution step S1;
specifically, in order to avoid the damage to the user caused by the characteristic harmonic current injected under the normal operation condition of the power distribution network, the embodiment designs a corresponding starting criterion, judges whether to start the injection unit according to whether a fault occurs, and starts to inject the characteristic harmonic current only after the fault occurs.
In this embodiment, the starting detection principle of the IIDG injection unit is shown in fig. 1, and the fault is detected by collecting the voltage or current abrupt change at the outlet of the IIDG, and when the starting criterion is met, an enable signal is injected into the injection unit inside the IIDG controller.
The fault detection based on the current discontinuity at the IIDG outlet (i.e., the phase current discontinuity fault detection algorithm in fig. 1) is represented as:
Figure SMS_25
wherein ,
Figure SMS_28
for the sampling point number corresponding to the current time, +.>
Figure SMS_31
Sampling point number for one cycle, +.>
Figure SMS_33
For the number of sampling points of the cycle before the current moment,/-, for the current moment>
Figure SMS_27
For the first two of the current timeSampling points of each cycle, ++>
Figure SMS_30
For the sampling value of the phase current at the present time, +.>
Figure SMS_32
For the sampling value of the current of the previous cycle phase at the present moment, is +.>
Figure SMS_34
For the sampling value of the current of the first two cycle phases at the present moment, is +.>
Figure SMS_26
For the start-up coefficient and with a value of 0.1 to 0.3, ">
Figure SMS_29
Is the rated current of the protected feeder.
The fault detection according to the voltage abrupt change at the IIDG outlet is expressed as:
Figure SMS_35
in the formula ,
Figure SMS_37
for the sampling point number corresponding to the current time, +.>
Figure SMS_40
Sampling point number for one cycle, +.>
Figure SMS_42
For the number of sampling points of the cycle before the current moment,/-, for the current moment>
Figure SMS_38
For the number of sampling points of the two cycles before the current moment, < +.>
Figure SMS_39
For the sampling value of the phase voltage at the present time, +.>
Figure SMS_41
For the sampling value of the voltage of the previous cycle phase at the present moment,/for the sampling value of the voltage>
Figure SMS_43
For the sampling value of the two cyclic phase voltages before the current time,/-, is given>
Figure SMS_36
The value of the starting coefficient is 0.1-0.3, and the starting coefficient is the rated voltage of the protected feeder line.
S3, starting an injection unit, respectively injecting characteristic harmonic signals into d-axis and q-axis reference currents of a current inner loop control module in an inversion type distributed power supply (IIDG) controller, wherein the amplitude of the characteristic harmonic signals adaptively changes along with the amplitude of output current of the inversion type distributed power supply (IIDG), and completing the injection of the characteristic harmonic currents;
wherein, the power frequency current amplitude=iidg output
Figure SMS_44
；
in the formula ,IIIDG_d For d-axis reference current, I IIDG_q For q-axis reference current.
Specifically, most of IIDG in grid-connected operation in an actual power distribution network adopts a constant Power (PQ) control strategy for inhibiting a negative sequence component and has low voltage ride through capability, the IIDG control system is a dual-loop control structure, the outer loop is a power loop, and the inner loop is a current loop. At the moment after the power distribution network faults, characteristic harmonic signals are respectively injected into d-axis and q-axis reference currents of a current inner loop
Figure SMS_45
According to Park conversion, the three-phase current instantaneous value output by IIDG after injection can be obtained as
Figure SMS_46
wherein ,
Figure SMS_48
，/>
Figure SMS_51
，/>
Figure SMS_54
for the instantaneous value of the A-phase current, < >>
Figure SMS_49
For B-phase current transient,/v>
Figure SMS_52
For the instantaneous value of the C-phase current, < >>
Figure SMS_55
For the angular frequency of the characteristic harmonic signal, +.>
Figure SMS_56
Is the angle frequency of the power frequency +.>
Figure SMS_47
Phase angle corresponding to time t for characteristic harmonic signal, +.>
Figure SMS_50
Is the phase angle corresponding to the power frequency at the time t, +.>
Figure SMS_53
To inject the amplitude of the characteristic harmonic signal, I IIDG_d For d-axis reference current, I IIDG_q For q-axis reference current.
From the above, reference currents I are respectively directed to d and q axes IIDG_d 、I IIDG_q After the characteristic harmonic signal is injected, a new characteristic harmonic current exists in the IIDG output current, the new characteristic harmonic current is three-phase symmetrical, A phase output current is taken as an example for analysis, and the new A phase characteristic harmonic current is
Figure SMS_57
wherein ,
Figure SMS_59
is characterized by harmonic electricAmplitude of flow, +.>
Figure SMS_61
Phase angle of characteristic harmonic signal, +.>
Figure SMS_65
Is the phase angle of the power frequency,
Figure SMS_60
for the angular frequency of the characteristic harmonic signal, +.>
Figure SMS_62
Is the angle frequency of the power frequency +.>
Figure SMS_64
For the current moment +.>
Figure SMS_66
For the frequency of the characteristic harmonic signal of the reference current injected into the d-axis and q-axis, +.>
Figure SMS_58
Is power frequency->
Figure SMS_63
Is the initial phase angle of the characteristic harmonic signal.
The amplitude of the novel A-phase characteristic harmonic current is
Figure SMS_67
The frequency is +.>
Figure SMS_68
Hz。
aRepresented as
Figure SMS_69
wherein ,IIIDG_d For d-axis reference current, I IIDG_q For q-axis reference current.
For the selection of the characteristic harmonic current frequency, the characteristic frequency selection is important, and cannot be selected arbitrarily, and the following constraint needs to be considered.
1) The characteristic frequency should not exceed 10 times of the power frequency
The resonance frequency of the IIDG filter is generally widely distributed in the range from 10 times of power frequency to 0.5 time of carrier frequency, and the characteristic frequency is selected according to constraint 1), so that the characteristic harmonic current and the IIDG filter can be avoided from generating resonance, and the IIDG is ensured to run safely and stably. In order to suppress the shunting effect of the non-injection source IIDG on the characteristic harmonic current, the characteristic frequency cannot be much smaller than the resonance frequency.
2) The characteristic frequency should be as far from the power frequency as possible
When the power distribution network is disturbed or fails, harmonic waves are inevitably generated, and low-order harmonic waves are mainly used. If the characteristic frequency is far away from the power frequency, the interference of the generated harmonic wave on the injection type protection can be reduced as much as possible.
3) The characteristic frequency should be an integer multiple of the power frequency
The integer multiple of the power frequency is selected to facilitate the extraction, analysis and treatment of the common time-frequency analysis methods such as the fast Fourier transform, the wavelet transform and the like, shorten the signal processing delay and improve the engineering practicability of the injection type protection method.
And for the selection of the characteristic harmonic current amplitude, according to the latest regulation, when the grid-connected inverter operates at rated power, the total harmonic distortion rate limit value of the current injected into the power grid is 5%, so that the injected characteristic harmonic current amplitude is required to be less than 5% of the output current of the grid-connected inverter.
As described above, in the present embodiment, when 8 harmonic (frequency 400 Hz) signals are injected into the d and q-axis reference currents of the IIDG inverter control system, 7 harmonic (frequency 350 Hz) currents exist in the IIDG output current. The amplitude of the injected harmonic is always kept to be 4% of the amplitude of the output current of the grid-connected inverter under normal operation or various fault scenes.
S4, calculating a characteristic harmonic current negative sequence component distortion rate difference value and an A-phase characteristic harmonic current distortion rate difference value on two sides of the protected line, judging whether a differential protection criterion is met, and if so, executing a protection action.
Specifically, most of the power distribution networks adopt three-phase reclosing, the fault type does not need to be judged, in order to reduce the data volume of communication transmission, the embodiment preferably adopts sequence components to construct a protection criterion, and positive, negative and zero sequence decomposition is carried out on characteristic harmonic current components in IIDG side short-circuit current, wherein the following formula is shown:
Figure SMS_70
wherein ,
Figure SMS_71
zero-sequence current component of characteristic harmonic current, +.>
Figure SMS_72
As a zero sequence current component of the characteristic harmonic current,
Figure SMS_73
negative sequence current component of characteristic harmonic current, +.>
Figure SMS_74
Is the initial phase angle of the characteristic harmonic signal, +.>
Figure SMS_75
For the angular frequency of the characteristic harmonic signal, +.>
Figure SMS_76
Is the current time.
From the above, the characteristic harmonic current only contains a negative sequence component and does not contain a positive sequence component and a zero sequence component after positive and negative sequence decomposition.
Next, taking the simple active distribution network with IIDG access as an example in fig. 2, the characteristic harmonic current negative sequence component in the short-circuit current at both sides of the protected feeder section is analyzed, in fig. 2, L 1 、L 2 、L 3 、L 4 For load, K 1 、K 2 、K 3 、K 4 Is a circuit breaker, f 1 、f 2 Is the failure point.
Let f 1 After the point fails, the short-circuit current provided by the system power supply and the short-circuit current provided by DG both flow to the failure pointThe short-circuit current provided by DG contains an injected characteristic harmonic current component, while the short-circuit current provided by the system power supply does not or less contain this characteristic harmonic component. Therefore, fault location and removal can be achieved according to the magnitude of the negative sequence component of the characteristic harmonic current in the short-circuit current on both sides of the protected section BM. Meanwhile, in order to reduce the interference of a large number of harmonic waves generated in the moment of faults on protection, the embodiment constructs a differential protection criterion based on the distortion rate of the negative sequence component of the characteristic harmonic current.
Calculating the distortion rate of the negative sequence component of the characteristic harmonic current:
Figure SMS_77
wherein h is the number of characteristic harmonics,
Figure SMS_78
for the magnitude of the negative sequence component of the h-harmonic current,/->
Figure SMS_79
Is the amplitude of the negative sequence component of the power frequency current.
Calculating the A-phase characteristic harmonic current distortion rate:
Figure SMS_80
wherein h is the number of characteristic harmonics,
Figure SMS_81
amplitude of h-th A-phase harmonic current, < >>
Figure SMS_82
Is the amplitude of the phase A power frequency current.
When an asymmetric fault occurs, the system power supply provides a larger power frequency current negative sequence component, so that the distortion rate of the system side characteristic harmonic current negative sequence component can be further weakened, and because the IIDG adopts a control strategy for inhibiting the negative sequence current, the output power frequency negative sequence current is smaller, so that the distortion rate of the feeder line IIDG side characteristic harmonic current negative sequence component is larger, and based on the distortion rate difference value of the feeder line side characteristic harmonic current negative sequence component, the feeder line differential protection can be realized.
When a symmetrical fault occurs, the power frequency current negative sequence component is about 0 in a short time after the fault, and the characteristic harmonic current negative sequence component distortion rate differential protection criterion is not applicable any more. The A-phase characteristic harmonic current distortion rate difference values at two sides of the protected feeder line are used as auxiliary criteria, so that the problem of the characteristic harmonic current negative sequence component distortion rate differential protection criteria dead zone during three-phase short circuit can be effectively eliminated.
In summary, the characteristic harmonic current differential protection criterion is
1) In case of asymmetrical failure
Figure SMS_83
wherein ,
Figure SMS_84
for the characteristic harmonic current negative sequence component distortion rate of the power supply side of the protected feeder system, +.>
Figure SMS_85
For the distortion rate of the negative sequence component of the harmonic current of the distributed power supply side, < >>
Figure SMS_86
Is the first differential protection action threshold.
2) In the event of a symmetrical fault
Figure SMS_87
wherein ,
Figure SMS_88
harmonic current distortion rate of phase A characteristic of power supply side of protected feeder system, < ->
Figure SMS_89
Harmonic current distortion rate for A-phase characteristic of distributed power supply side, +.>
Figure SMS_90
Is the second differential protection action threshold.
Specifically, the threshold value of the differential protection action is generally 0.3-0.5 times of the total harmonic current distortion rate at the IIDG outlet, and in this embodiment, the first differential protection action threshold value is equal to the second differential protection action threshold value, which is 0.4 times of the total harmonic current distortion rate at the IIDG outlet.
FIG. 3 is a block diagram of the overall control system for IIDG, with the letter numbers in the upper right hand corner of each module representing the meaning: a positive and negative sequence separation step a, namely realizing positive and negative sequence separation of electric quantity by adopting a signal delay method; a constant power control link b based on a positive sequence component, wherein the outer ring is power control, and the inner ring is current control; a control link c for suppressing the negative sequence current; a low voltage ride through control step d; and e, fault detection and harmonic injection control step. When the power distribution network breaks down, a fault detection and harmonic injection control link e in the IIDG control system detects the fault, and an enabling signal is injected into a constant power control link b based on a positive sequence component; after receiving the enabling signal, the constant power control link b based on the positive sequence component injects characteristic harmonic current into d and q axis reference currents of the current inner loop control link respectively, the characteristic harmonic current amplitude adaptively changes along with the IIDG output current amplitude, the characteristic harmonic current is always kept to be 4% of the output current amplitude, the fault characteristic of the characteristic harmonic current after injection is enhanced, meanwhile, grid-connected regulation can be met under the fault condition, and finally, the characteristic signal injection is completed. The implementation flow of the injection type harmonic current differential protection of the distribution network containing IIDG is shown in figure 4.
In order to verify the feasibility of the active injection type harmonic current differential protection method for the distribution network with the IIDG, a 10kV simple active distribution network with the IIDG shown in the figure 2 is built by using PSCAD/EMTDC simulation software, the lengths of feeder lines BM and MN are 4km, and the line parameters are (0.13+i0.402) omega/km; DG1 and DG2 are inverter distributed power supplies, and rated capacities are 1MW; the load capacity is 1MW and the load power factor is 0.9.
1) Verifying correctness of characteristic harmonic current injection
Calculation example 1: normal operation, 0.3s injection of characteristic harmonics
And (3) the distribution network with the IIDG normally operates, the IIDG1 and the IIDG2 are manually started to inject characteristic harmonic current according to an injection strategy at 0.3s, current waveforms at the exit of the IIDG1 before and after injection are shown in a graph 5, amplitudes of the phase A power frequency current and the characteristic harmonic current are extracted by utilizing fast Fourier transformation, and the characteristic harmonic current distortion rate at the exit of the IIDG1 is calculated. The amplitude of the phase A characteristic harmonic current at the outlet of IIDG1 and the characteristic harmonic signal waveforms injected into d and q axes are shown in figure 6, and the distortion rate of the characteristic harmonic current at the outlet is shown in figure 7.
As can be seen from fig. 5, there is a characteristic harmonic component in the current at the IIDG1 outlet after 0.3 s. Due to the inherent delay of the fast Fourier transform operation, the amplitude of the extracted characteristic harmonic current is stable after one cycle, and the stable value is approximately equal to the amplitude of the characteristic harmonic signal injected into the current inner loop to control the d and q axes, as shown in fig. 6. As shown in FIG. 7, the characteristic harmonic current distortion rate at the IIDG outlet is stabilized to be 4% after one cycle, and the simulation result is consistent with the theoretical analysis, so that the correctness of the characteristic harmonic injection system can be verified under the normal operation condition.
Calculation example 2: f (f) 2 Point AB interphase short circuit fault, transition resistance 0.1 Ω
time t=0.3 sf 2 And after the point is subjected to AB interphase short circuit fault, the transition resistance of the fault point is 0.1Ω, and IIDG1 and IIDG2 detect the fault, the characteristic harmonic current is started to be injected according to an injection strategy. The current waveform at the IIDG1 outlet before and after the fault is shown in fig. 8, the amplitude of the A-phase characteristic harmonic current at the IIDG1 outlet and the waveform of the characteristic harmonic signals injected into d and q axes are shown in fig. 9, and the characteristic harmonic current distortion rate is shown in fig. 10.
As shown in fig. 8, IIDG1 performs low voltage ride through at 0.3s, the current at the outlet increases by 1.5 times as compared with the original current, and the IIDG adopts a negative sequence current control strategy for suppressing the fault, so that the output current is still three-phase symmetrical. Due to the inherent delay of the fast Fourier transform operation, the amplitude of the characteristic harmonic current after the fault is stabilized after one cycle, and the stable value is approximately equal to the amplitude of the characteristic harmonic signal injected into the current inner loop to control the d and q axes, as shown in fig. 9. As shown in fig. 10, the characteristic harmonic current distortion rate at the IIDG outlet is stabilized to be 4% after one cycle, and it is known that the characteristic harmonic current amplitude after the fault is always kept to be 0.04 times of the IIDG output current, and the simulation result is consistent with the foregoing theoretical analysis, so that the correctness of the characteristic harmonic injection system under the fault condition can be verified.
2) Verifying correctness of characteristic harmonic current differential protection method
Calculation example 1: f (f) 1 Point asymmetric short-circuit fault, transition resistance 0.1 omega
Assume t=0.3 s time f 1 The point generates single-phase grounding, two-phase grounding and two-phase short circuit faults, the transition resistance of the fault point is 0.1Ω, and after faults are detected by IIDG1 and IIDG2, the characteristic harmonic current is started to be injected according to an injection strategy. The distortion rate of the characteristic harmonic current negative sequence components on both sides of the feeder line BM after the fault is shown in fig. 11 (a) -11 (c).
Fig. 11 (a) -11 (c): i jm 、I jb Characteristic harmonic current negative sequence component distortion rates of a feeder BM distributed power supply side and a system power supply side respectively. The characteristic harmonic current negative sequence component distortion rate differential protection action threshold value is set to be 2%. As can be seen from fig. 11 (a) -11 (c), when a single-phase grounding fault occurs in the feeder BM region, the difference of distortion rates at two sides of the feeder is about 0.45 after one cycle, and the difference of distortion rates at two-phase grounding and two-phase short-circuit faults is about 0.06 after one cycle, so as to sum up, f 1 The characteristic harmonic current differential protection under various asymmetric faults can reliably act.
Calculation example 2: f (f) 1 Point symmetric short-circuit fault, transition resistance 0.1 omega
Based on the calculation example 1, f 1 The point fault type is changed into a three-phase short circuit fault, the transition resistance of the fault point is 0.1 omega, and the characteristic harmonic current distortion rate of the A phase at two sides of the feeder line BM after the fault is shown in figure 12.
In fig. 12: i jma 、I jba And B, feeding line BM distributed power supply side and system power supply side A phase characteristic harmonic current distortion rate respectively. The characteristic harmonic current distortion rate differential protection operation threshold is set to be 2%. As can be seen from the view of figure 12,the difference of the harmonic current distortion rate of the phase A characteristics at the two sides of the feeder line is about 4% after being stabilized, which is consistent with the theoretical analysis, thus f 1 The characteristic harmonic current differential protection under the point-symmetrical fault can reliably act.
Calculation example 3: f (f) 1 Point asymmetric short-circuit fault, transition resistance 20Ω
Based on the calculation example 1, f 1 After the point transition resistance is changed to 20Ω, IIDG1 and IIDG2 detect the fault, the characteristic harmonic current is started to be injected according to the injection strategy. The distortion rate of the characteristic harmonic current negative sequence components on both sides of the feeder line BM after the fault is shown in fig. 13 (a) -13 (c).
As can be seen from fig. 13 (a) -13 (c), when a single-phase grounding fault occurs in the BM region of the feeder line, the difference between the distortion rates at two sides of the feeder line is about 1.58 after one cycle, the difference between the distortion rates at two-phase grounding and two-phase short-circuit faults is about 1.00 and 0.41 after one cycle, and the difference between the distortion rates at high-resistance asymmetric faults is far greater than the action threshold, which is due to the fact that the power frequency negative sequence component at the distributed power supply side is very small caused by the large transition resistance of the fault point, so that the distortion rate of the characteristic harmonic current negative sequence component at the distributed power supply side is very large.
Calculation example 4: f (f) 1 Point symmetric short-circuit fault, transition resistance 20Ω
Based on the calculation example 2, f 1 The point fault transition resistance is changed to 20Ω, and the distortion rate of the a-phase characteristic harmonic currents at two sides of the feeder line BM after the fault is shown in fig. 14.
As can be seen from fig. 14, the difference between the distortion rates of the a-phase characteristic harmonic currents on both sides of the feeder line is about 3.8% and slightly lower than 4% after being stabilized, because the transition resistance of the fault point is large, so that most of the characteristic harmonic currents flow to the fault point, and the other small part flows to the system power supply downstream of the fault point. To sum up, f 1 The characteristic harmonic current differential protection under the point high-resistance symmetrical fault can reliably act.
Calculation example 5: f (f) 2 Point asymmetric short-circuit fault, transition resistance 0.1 omega
Based on the calculation example 1, the fault point is changed to f 2 And the point, the transition resistance of the fault point is 0.1Ω, and the IIDG1 and the IIDG2 start to inject characteristic harmonic current according to an injection strategy. The distortion rate of the characteristic harmonic current negative sequence components on both sides of the feeder MN after the fault is shown in fig. 15 (a) -15 (c).
Fig. 15 (a) -15 (c): i jm 、I jn And characteristic harmonic current negative sequence component distortion rates of a power supply side and a distributed power supply side of the feeder line MN system respectively. As can be seen from fig. 15 (a) -15 (c), when a single-phase grounding fault occurs in the MN region of the feeder line, the difference of distortion rates at two sides of the feeder line is about 0.18 after one cycle, and the difference of distortion rates at two-phase grounding and two-phase short-circuit faults is about 0.06 and 0.055 after one cycle, compared with the simulation result of the calculation example 1, the difference of distortion rates at two sides of the feeder line is slightly reduced, but is larger than the action threshold, so that reliable action is protected. In addition, it should be noted that a part of the characteristic harmonic current provided by IIDG1 flows into the fault point, and another part flows into the system power supply side, but the characteristic harmonic current flowing into the fault point is far smaller than the short-circuit current provided by the system power supply, and the influence on the differential protection of the characteristic harmonic current of the feeder line MN can be ignored.
Calculation example 6: f (f) 2 Point symmetric short-circuit fault, transition resistance 0.1 omega
Based on the calculation example 2, the fault point is changed tof 2 The point, the transition resistance of the fault point is 0.1Ω, and the characteristic harmonic current distortion of the a-phase on both sides of the feeder MN after the fault is shown in fig. 16.
In fig. 16: i jma 、I jna And the characteristic harmonic current distortion rates of the phase A of the power supply side and the distributed power supply side of the feeder line MN system are respectively. As can be seen from fig. 16, the difference of the distortion rate of the a-phase characteristic harmonic currents on both sides of the feeder line MN is about 4% after being stabilized, and the accuracy of the deduction of "neglecting the effect of the characteristic harmonic current injected by IIDG1 on the differential protection of the characteristic harmonic current of the feeder line MN" in example 5 is further verified, therefore, f 2 The characteristic harmonic current differential protection under the point-symmetrical fault can reliably act.
Calculation example 7: f (f) 2 Point asymmetric short-circuit fault, transition resistance 20Ω
Based on the calculation example 3, the fault point is changed to f 2 Point, fault point is crossedThe crossover resistance is 20Ω, and the distortion rate of the characteristic harmonic current negative sequence components on both sides of the feeder line MN after the fault is shown in fig. 17 (a) -17 (c).
From fig. 17 (a) -17 (c), it can be seen that, after a single-phase earth fault, two-phase earth fault, and two-phase short circuit fault occur in the MN region of the feeder, the difference between distortion rates at two sides of the feeder is stabilized at 0.52, 0.34, and 0.15, thus f 2 The difference of distortion rates at two sides of the protected feeder line under the point high-resistance asymmetric fault is far greater than an action threshold value, and the characteristic harmonic current differential protection can reliably act.
Calculation example 8: f (f) 2 Point symmetric short-circuit fault, transition resistance 0.1 omega
Based on the calculation example 4, the fault point is changed to f 2 And the point, the transition resistance of the fault point is 20Ω, and the distortion rate of the A-phase characteristic harmonic currents on both sides of the feeder line MN after the fault is shown in figure 18.
As can be seen from fig. 18, the difference of the harmonic current distortion rate of the a-phase characteristic on both sides of the feeder MN is about 3.5% after being stabilized, and is slightly lower than 4%, which is consistent with the analysis of example 4, therefore, f 2 The characteristic harmonic current differential protection under the point high-resistance symmetrical fault can still reliably act.
Example two
The embodiment discloses an active injection type harmonic current differential protection system of an IIDG-containing power distribution network, which comprises the following components:
a fault detection and harmonic injection control unit configured to: acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time; judging whether a starting condition is met according to current information and voltage information at an outlet of the inversion type distributed power supply, and if so, starting an injection unit;
an injection unit configured to: injecting characteristic harmonic signals into d-axis and q-axis reference currents of a current inner loop control module in the inversion type distributed power supply controller, and outputting characteristic harmonic currents by the inversion type distributed power supply;
a differential protection unit configured to: and calculating the difference value of the distortion rate of the negative sequence components of the characteristic harmonic currents at the two sides of the protected circuit and the difference value of the distortion rate of the A-phase characteristic harmonic currents at the two sides of the protected circuit according to the characteristic harmonic currents, judging whether a differential protection criterion is met, and if so, executing the protection action.
It should be noted that the fault detection and harmonic injection control unit, the injection unit and the differential protection unit correspond to the steps in the first embodiment, and the above units are the same as examples and application scenarios implemented by the corresponding steps, but are not limited to the disclosure in the first embodiment. It should be noted that the above-described elements may be implemented as part of a system in a computer system, such as a set of computer-executable instructions.
The foregoing embodiments are directed to various embodiments, and details of one embodiment may be found in the related description of another embodiment.
The foregoing description is only of the preferred embodiments of the present application and is not intended to limit the same, but rather, various modifications and variations may be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims (7)

1. An active injection type harmonic current differential protection method for a distribution network containing IIDG is characterized by comprising the following steps:
s1, acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time;
s2, judging whether a starting criterion is met according to current information and voltage information at an outlet of the inversion type distributed power supply, and if so, continuing to execute the following steps; if not, returning to the execution step S1;
s3, starting an injection unit to inject characteristic harmonic signals into d-axis and q-axis reference currents of a current inner loop control module in the inversion type distributed power supply controller respectively
Figure QLYQS_1
The inversion type distributed power supply outputs characteristic harmonic current; the amplitude of the characteristic harmonic signal adaptively changes along with the amplitude of the output current of the inversion type distributed power supply;
inversion classificationPower frequency current amplitude = of cloth type power supply output
Figure QLYQS_2
；
The amplitude a of the characteristic harmonic current is expressed as
Figure QLYQS_3
wherein ,IIIDG_d For d-axis reference current, I IIDG_q Reference current for q-axis;
s4, calculating the characteristic harmonic current negative sequence component distortion rate difference values at two sides of the protected circuit and the phase A characteristic harmonic current distortion rate difference values at two sides of the protected circuit according to the characteristic harmonic current, judging whether a differential protection criterion is met, and if so, executing a protection action;
the judging whether the differential protection criterion is met is as follows:
judging whether the absolute value of the difference value of the negative sequence component distortion rate of the characteristic harmonic current in the short-circuit currents at two sides of the protected line is larger than a first differential protection action threshold value or not;
judging whether the absolute value of the difference value of the A-phase characteristic harmonic current distortion rate in the short-circuit currents at two sides of the protected line is larger than a second differential protection action threshold value or not;
if the difference is larger than the first differential protection action threshold or larger than the second differential protection action threshold, executing differential protection action, and stopping the injection of the characteristic harmonic signals;
the first differential protection action threshold value and the second differential protection action threshold value are equal or unequal;
the absolute value of the difference of the distortion rate of the negative sequence component is
Figure QLYQS_4
wherein ,
Figure QLYQS_5
to be protectedCharacteristic harmonic current negative sequence component distortion rate of feeder system power supply side, < ->
Figure QLYQS_6
For the distortion rate of the negative sequence component of the harmonic current of the distributed power supply side, < >>
Figure QLYQS_7
A first differential protection action threshold;
the absolute value of the difference of the A-phase characteristic harmonic current distortion rate is
Figure QLYQS_8
wherein ,
Figure QLYQS_9
harmonic current distortion rate of phase A characteristic of power supply side of protected feeder system, < ->
Figure QLYQS_10
Harmonic current distortion rate for A-phase characteristic of distributed power supply side, +.>
Figure QLYQS_11
Is the second differential protection action threshold.
2. The method for protecting the active injection type harmonic current differential of the distribution network containing the IIDG according to claim 1, wherein the starting criteria comprise a phase voltage starting criterion and a phase current starting criterion, wherein the phase current starting criterion is expressed as:
Figure QLYQS_12
in the formula ,
Figure QLYQS_15
for the sampling point number corresponding to the current time, +.>
Figure QLYQS_20
Sampling point number for one cycle, +.>
Figure QLYQS_21
For the number of sampling points of the cycle before the current moment,/-, for the current moment>
Figure QLYQS_14
For the number of sampling points of the two cycles before the current moment, < +.>
Figure QLYQS_16
For the sampling value of the phase current at the present time, +.>
Figure QLYQS_18
For the sampling value of the current of the previous cycle phase at the present moment, is +.>
Figure QLYQS_19
For the sampling value of the current of the first two cycle phases at the present moment, is +.>
Figure QLYQS_13
For the start-up coefficient and with a value of 0.1 to 0.3, ">
Figure QLYQS_17
Is the rated current of the protected feeder.
3. The method for active injection type harmonic current differential protection of a distribution network containing IIDG according to claim 1, wherein step S1 further comprises:
and if the starting criterion is met, sending an enabling signal to the injection unit to start the injection unit.
4. The active injection type harmonic current differential protection method for the distribution network containing IIDG according to claim 1, wherein the a-phase characteristic harmonic current is expressed as:
Figure QLYQS_22
wherein ,
Figure QLYQS_24
for the amplitude of the characteristic harmonic current, +.>
Figure QLYQS_28
Phase angle of characteristic harmonic signal, +.>
Figure QLYQS_30
Is the phase angle of power frequency>
Figure QLYQS_25
For the angular frequency of the characteristic harmonic signal, +.>
Figure QLYQS_27
Is the angle frequency of the power frequency +.>
Figure QLYQS_29
For the current moment +.>
Figure QLYQS_31
For the frequency of the characteristic harmonic signal of the reference current injected into the d-axis and q-axis, +.>
Figure QLYQS_23
Is power frequency->
Figure QLYQS_26
Is the initial phase angle of the characteristic harmonic signal.
5. The method for protecting the active injection type harmonic current differential of the distribution network containing the IIDG according to claim 1, wherein the calculating the difference of the distortion rates of the negative sequence components of the characteristic harmonic current on both sides of the protected line is as follows:
respectively calculating negative sequence components in short-circuit currents at two sides of a protected line, wherein the negative sequence components are negative sequence components of characteristic harmonic currents;
according to the negative sequence component of the characteristic harmonic current and the negative sequence component of the power frequency current, calculating the distortion rate of the negative sequence component of the characteristic harmonic current respectively;
calculating the absolute value of the difference value of the negative sequence component distortion rate;
the A-phase characteristic harmonic current distortion rate difference values at two sides of the protected line are calculated as follows:
according to the amplitude of the A-phase characteristic harmonic current and the amplitude of the A-phase power frequency current, respectively calculating the A-phase characteristic harmonic current distortion rate at two sides of the protected line;
and calculating the absolute value of the difference value of the A-phase characteristic harmonic current distortion rate.
6. The method for protecting the active injection type harmonic current differential of the distribution network containing the IIDG according to claim 1, wherein the frequency of the characteristic harmonic current is not more than 10 times of the power frequency and is an integer multiple of the power frequency.
7. An active injection type harmonic current differential protection system of a distribution network containing IIDG is characterized by comprising:
a fault detection and harmonic injection control unit configured to: acquiring current information and voltage information at an outlet of an inversion type distributed power supply in real time; judging whether a starting condition is met according to current information and voltage information at an outlet of the inversion type distributed power supply, and if so, starting an injection unit;
an injection unit configured to: injecting characteristic harmonic signals into d-axis and q-axis reference currents of current inner loop control modules in inversion type distributed power supply controllers
Figure QLYQS_32
The inversion type distributed power supply outputs characteristic harmonic current; the amplitude of the characteristic harmonic signal adaptively changes along with the amplitude of the output current of the inversion type distributed power supply;
power frequency current amplitude = of inverter type distributed power supply output
Figure QLYQS_33
；
The amplitude a of the characteristic harmonic current is expressed as
Figure QLYQS_34
wherein ,IIIDG_d For d-axis reference current, I IIDG_q Reference current for q-axis;
a differential protection unit configured to: according to the characteristic harmonic currents, calculating the characteristic harmonic current negative sequence component distortion rate difference values at two sides of the protected circuit and the phase A characteristic harmonic current distortion rate difference values at two sides of the protected circuit, judging whether a differential protection criterion is met, and if so, executing a protection action; the judging whether the differential protection criterion is met is as follows:
judging whether the absolute value of the difference value of the negative sequence component distortion rate of the characteristic harmonic current in the short-circuit currents at two sides of the protected line is larger than a first differential protection action threshold value or not;
judging whether the absolute value of the difference value of the A-phase characteristic harmonic current distortion rate in the short-circuit currents at two sides of the protected line is larger than a second differential protection action threshold value or not;
if the difference is larger than the first differential protection action threshold or larger than the second differential protection action threshold, executing differential protection action, and stopping the injection of the characteristic harmonic signals;
the first differential protection action threshold value and the second differential protection action threshold value are equal or unequal;
the absolute value of the difference of the distortion rate of the negative sequence component is
Figure QLYQS_35
wherein ,
Figure QLYQS_36
for the characteristic harmonic current negative sequence component distortion rate of the power supply side of the protected feeder system, +.>
Figure QLYQS_37
For the distortion rate of the negative sequence component of the harmonic current of the distributed power supply side, < >>
Figure QLYQS_38
A first differential protection action threshold;
the absolute value of the difference of the A-phase characteristic harmonic current distortion rate is
Figure QLYQS_39
wherein ,
Figure QLYQS_40
harmonic current distortion rate of phase A characteristic of power supply side of protected feeder system, < ->
Figure QLYQS_41
Harmonic current distortion rate for A-phase characteristic of distributed power supply side, +.>
Figure QLYQS_42
Is the second differential protection action
A threshold value.
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