CN112117777B - Photovoltaic grid-connected island detection method based on zero sequence current injection - Google Patents
Photovoltaic grid-connected island detection method based on zero sequence current injection Download PDFInfo
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- CN112117777B CN112117777B CN202010710621.4A CN202010710621A CN112117777B CN 112117777 B CN112117777 B CN 112117777B CN 202010710621 A CN202010710621 A CN 202010710621A CN 112117777 B CN112117777 B CN 112117777B
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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
- H02J3/381—Dispersed generators
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
-
- 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
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
-
- 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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Inverter Devices (AREA)
- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention discloses a photovoltaic grid-connected island detection method based on zero sequence current injection, which comprises the steps of building an island detection model; i via DC/AC inverter abc Entering a power grid unit to operate after passing through a transformer; if the signal relay is operated, information is fed back to the DC/AC inverter, which is then injected with I (0) Detecting a zero sequence current value at the public connection point PCC, and judging the island state if the zero sequence current value at the public connection point PCC exceeds a set threshold value. According to the photovoltaic grid-connected island detection method, the signal relay is utilized to send out signals to the photovoltaic power generation unit, so that the problem of high cost of the communication detection method is avoided; only when the alarm starting signal given by the signal relay is received, the zero sequence current disturbance is injected, so that the problem of large dead zone of the passive detection method is avoided, and the influence of the active detection method on the power quality is relieved to a certain extent.
Description
Technical Field
The invention belongs to the field of power system relay protection, and particularly relates to a photovoltaic grid-connected island detection method based on zero sequence current injection.
Background
With the progressive exhaustion of non-renewable energy sources worldwide, solar energy is used as a renewable energy source, and photovoltaic power generation has also become an important power generation mode. The direct current generated by the photovoltaic power generation is converted into alternating current through a grid-connected inverter and then is connected into a power grid. However, when faults such as grounding, disconnection, misoperation and the like occur in the power grid, the power grid can trip the circuit breaker at the first time in order to ensure normal power supply of a normal line. At this time, if the photovoltaic power generation system fails to timely and effectively detect the state of the power grid at this time and continuously operates, the photovoltaic power generation system is in an island operation state and continuously provides electric energy to the power grid.
When the photovoltaic power generation system is in island operation, an unplanned island state can bring serious potential safety hazards to equipment and personnel. Therefore, it is important to be able to timely and effectively judge the island operation state and further take effective control measures.
At present, island detection methods are mainly divided into a communication detection method and a local detection method; local detection methods are also classified into active detection methods and passive detection methods.
The communication detection method transmits fault information to the photovoltaic system through wired or wireless signals, has obvious effect, but has higher manufacturing cost, needs a plurality of communication devices and multi-party verification, and is not suitable for a small photovoltaic power generation system. The passive detection method is used for judging whether the photovoltaic power generation system is in an island state or not by detecting the changes of voltage, current, frequency, phase and the like at the public connection point PCC, and has no influence on the power quality, but has a larger detection blind area. The active detection method is that a small disturbance is sent to the inverter, and in a normal state, the disturbance is very tiny and cannot be detected due to the action of the power grid phase-locked loop, but if the photovoltaic system is in an island operation state, after the regulation action of the power grid is lost, the disturbance is continuously amplified through the positive feedback action of the inverter, and finally exceeds a threshold value. The active detection method has small blind area, but can cause disturbance and influence on the power grid and the power quality.
Disclosure of Invention
The invention aims to provide a photovoltaic grid-connected island detection method based on zero sequence current injection, which solves the problems that the detection blind area of the existing detection method is large and the influence on the power grid and the power quality is easy to occur.
The technical scheme adopted by the invention is that the photovoltaic grid-connected island detection method based on zero sequence current injection comprises the following steps:
step 1, building an island detection model
The island detection model comprises a photovoltaic power generation unit, wherein the photovoltaic power generation unit is connected with a power grid unit through a transformer;
the photovoltaic power generation unit comprises a photovoltaic cell, the photovoltaic cell is sequentially connected with the DC/DC converter and the DC/AC inverter through leads, and the photovoltaic power generation unit also comprises a photovoltaic side equivalent resistor and a photovoltaic side equivalent inductor;
the power grid unit comprises a breaker connected with the transformer through a wire, and the power grid unit comprises a zero-sequence current protection unit, specifically comprises a current transformer, and is also sequentially connected with a zero-sequence current relay, a time relay, a signal relay, an intermediate relay, an auxiliary contact of the breaker, a tripping coil and the breaker; the power grid unit also comprises a power grid side equivalent resistor, a power grid side equivalent inductor and a public connection point PCC; the public connection point PCC is connected with the RLC load unit;
let the alternating current flowing out through the DC/AC inverter be denoted as i abc Ac power i abc Entering a power grid unit to operate after passing through a transformer;
step 2, judging whether the signal relay in the zero sequence current protection acts, if the signal relay acts, feeding information back to the DC/AC inverter, and injecting zero sequence current I into the DC/AC inverter at the moment (0) ；
And step 3, after the processing in the step 2, detecting a zero sequence current value at the public connection point PCC, and if the zero sequence current value at the public connection point PCC exceeds a set threshold value, judging that the island state is achieved.
The present invention is also characterized in that,
in the step 1, the RLC load unit is specifically a user side equivalent resistor, a user side equivalent inductor and a user side equivalent capacitor which are connected in parallel.
The working process of the signal relay in the step 2 is as follows:
if the line has a ground fault, a zero sequence component is generated, and zero sequence current I flows through a current transformer on the line (0) Zero sequence electricityStream I (0) Will continue to flow to the zero sequence current relay, and the zero sequence current I is introduced into the zero sequence current relay (0) When the switch is closed, the action signal will continue to flow to the time relay, and after the time relay is delayed, if the zero sequence current I (0) If the ground fault still exists, the ground fault is proved to not disappear, at the moment, the time relay action switch is closed, the signal flows to the signal relay, the signal relay sends out a signal to the DC/AC inverter, and the zero sequence current I is led to (0) As a perturbation implant.
Zero sequence current I in step 2 (0) The working process of (2) is as follows:
let the given current be i' abc It can be seen that i' abc ＝i' abc(1) +i' abc(0) ＝[i' a i' b i' c ] T Wherein parameter i' abc(1) For a given positive sequence current, parameter i' abc(0) For a given zero sequence current, by giving different i' abc(1) And i' abc(0) I.e. regulating the magnitude of the positive sequence current and the zero sequence current injected into the common connection point PCC.
Given positive sequence current i' abc(1) ＝[i' a(1) i' b(1) i' c(1) ] T Said given zero sequence current i' abc(0) ＝[i' a(0) i' b(0) i' c(0) ] T 。
The beneficial effects of the invention are as follows: according to the photovoltaic grid-connected island detection method based on the injected zero-sequence current, as the zero-sequence current protection device is arranged in the power grid, the signal relay can be directly utilized to send out signals to the photovoltaic power generation unit, and the problem of high cost of the communication detection method is avoided; the disturbance of the zero sequence current can not be automatically injected into the inverter, and the disturbance of the zero sequence current can be injected only when the signal relay gives out a signal, so that the problem of large dead zone of a passive detection method is avoided, and the influence of the active detection method on the power quality is relieved to a certain extent.
Drawings
FIG. 1 is a schematic structural diagram of a model in a photovoltaic grid-connected island detection method based on zero sequence current injection;
FIG. 2 is a flow chart of a photovoltaic grid-connected island detection method based on zero sequence current injection in the invention;
FIG. 3 is a schematic diagram of zero-sequence overcurrent protection in a photovoltaic grid-connected island detection method based on zero-sequence current injection;
fig. 4 is a schematic diagram of zero sequence current injection in a photovoltaic grid-connected island detection method based on zero sequence current injection.
In the figure, a photovoltaic cell, a 2 DC/DC converter, a 3 DC/AC inverter, a 4 photovoltaic side equivalent resistor, a 5 photovoltaic side equivalent inductor, a 6 transformer, a 7 grid side equivalent resistor, a 8 grid side equivalent inductor, a 9 circuit breaker, a 10 trip coil, a 11 circuit breaker auxiliary contact, a 12 intermediate relay, a 13 signal relay, a 14 time relay, a 15 zero sequence current relay, a 16 current transformer, a 17 common connection point PCC, a 18 user side equivalent resistor, a 19 user side equivalent inductor, and a 20 user side equivalent capacitor.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The invention discloses a photovoltaic grid-connected island detection method based on zero sequence current injection, which comprises the following steps of:
step 1, building an island detection model
As shown in fig. 1, the island detection model comprises a photovoltaic power generation unit, and the photovoltaic power generation unit is connected with a power grid unit through a transformer 6;
the photovoltaic power generation unit comprises a photovoltaic cell 1, the photovoltaic cell 1 is sequentially connected with a DC/DC converter 2 and a DC/AC inverter 3 through wires, and the photovoltaic power generation unit also comprises a photovoltaic side equivalent resistor 4 and a photovoltaic side equivalent inductor 5;
the power grid unit comprises a breaker 9 connected with the transformer 6 through a wire, the power grid unit comprises a zero sequence current protection unit, and particularly comprises a current transformer 16, and the current transformer 16 is also connected with a zero sequence current relay 15, a time relay 14, a signal relay 13, an intermediate relay 12, an auxiliary contact 11 of the breaker, a tripping coil 10 and the breaker 9 in sequence; the power grid unit also comprises a power grid side equivalent resistor 7, a power grid side equivalent inductor 8 and a public connection point PCC17; the common connection point PCC17 is connected with the RLC load unit;
the specific operation process of the model is as follows: the photovoltaic cell 1 generates electric energy, and the electric energy is converted into qualified direct current through the DC/DC converter 2 and is converted into alternating current i through the DC/AC inverter 3 abc 。i abc The current flows through the transformer 6 to be converted into a ratio and then is integrated into a power grid unit. The open-close state of the circuit breaker 9 may reflect whether the photovoltaic power generation unit is in an island state, and is assumed to be an RLC load unit, and is connected to the common connection point PCC 17.
As shown in fig. 2, let i be the alternating current flowing out through the DC/AC inverter 3 in step 1 abc Ac power i abc Entering a power grid unit to operate after passing through a transformer 6;
step 2, judging whether the signal relay 13 acts in the zero sequence current protection, if the signal relay 13 acts, feeding information back to the DC/AC inverter 3, and at the moment, injecting zero sequence current I into the DC/AC inverter 3 (0) ；
As shown in fig. 3, taking phase a as an example, if a line fails to ground, a zero sequence component will be generated on the line, and a zero sequence current I will flow through the current transformer 16 on the line (0) Zero sequence current I (0) The flow will continue to the zero sequence current relay 15. Zero sequence current I is led into the zero sequence current relay 15 (0) The switch is closed, the action signal will continue to flow to the time relay 14, and after a certain time delay, if the zero sequence current I (0) If the ground fault still exists, the ground fault is not disappeared, the time relay 14 acts to switch on, and the signal flows to the signal relay 13. At this time, it is proved that a non-transient grounding short-circuit fault exists on the line, and the signal relay 13 sends a signal to the DC/AC inverter 3 to make the zero sequence current I (0) As a perturbation implant.
As shown in FIG. 4, let the given current be i' abc It can be seen that i' abc ＝i' abc(1) +i' abc(0) ＝[i' a i' b i' c ] T Wherein parameter i' abc(1) For a given positive sequence current, parameter i' abc(0) For given purposesBy giving different i' abc(1) And i' abc(0) The magnitude of the positive sequence current and the zero sequence current injected into the common connection point PCC17 can be regulated. Wherein a given positive sequence current i' abc(1) ＝[i' a(1) i' b(1) i' c(1) ] T Given zero sequence current i' abc(0) ＝[i' a(0) i' b(0) i' c(0) ] T C is the ratio of the given positive sequence current amplitude to the given zero sequence current amplitude.
And step 3, after the processing in the step 3, detecting a zero sequence current value at the public connection point PCC17, and if the zero sequence current value at the public connection point PCC17 exceeds a set threshold value, judging that the island state is achieved.
The invention relates to a photovoltaic grid-connected island detection method based on zero sequence current injection, which comprises the following steps:
the direct current converted by the photovoltaic power generation unit through the DC/DC converter 2 is converted into alternating current meeting the power grid requirement through the DC/AC inverter 3, and then is merged into the normal operation of the power grid through the transformer 6. At this time, the grid generates a zero sequence component, i.e. a zero sequence current and a zero sequence voltage, due to the occurrence of the ground fault. Therefore, the zero-sequence current protection will open the breaker 9, and as the zero-sequence current protection is not affected by oscillations and the like and reacts more sensitively to ground faults, whether zero-sequence components occur in the power grid is used as a "starting criterion" for island detection, and then a disturbance of zero-sequence current is injected into the DC/AC inverter, and if the zero-sequence current detected at the common connection point PCC exceeds a threshold value, the island state is determined.
According to the photovoltaic grid-connected island detection method based on the zero sequence current injection, the signal relay is utilized to send out signals to the photovoltaic power generation unit, and the problem of high cost of the communication detection method is avoided; the disturbance of the zero sequence current can not be automatically injected into the inverter, and the disturbance of the zero sequence current can be injected only when the signal relay gives out a signal, so that the problem of large dead zone of a passive detection method is avoided, and the influence of the active detection method on the power quality is relieved to a certain extent.
Claims (5)
1. The photovoltaic grid-connected island detection method based on the injected zero sequence current is characterized by comprising the following steps of:
step 1, building an island detection model
The island detection model comprises a photovoltaic power generation unit, wherein the photovoltaic power generation unit is connected with a power grid unit through a transformer (6);
the photovoltaic power generation unit comprises a photovoltaic cell (1), the photovoltaic cell (1) is sequentially connected with a DC/DC converter (2) and a DC/AC inverter (3) through wires, and the photovoltaic power generation unit further comprises a photovoltaic side equivalent resistor (4) and a photovoltaic side equivalent inductor (5);
the power grid unit comprises a breaker (9) connected with a transformer (6) through a wire, the power grid unit comprises a zero sequence current protection unit, and particularly comprises a current transformer (16), and the current transformer (16) is further connected with a zero sequence current relay (15), a time relay (14), a signal relay (13), an intermediate relay (12), an auxiliary contact (11) of the breaker, a tripping coil (10) and the breaker (9) in sequence; the power grid unit further comprises a power grid side equivalent resistor (7), a power grid side equivalent inductor (8) and a public connection point PCC (17); the public connection point PCC (17) is connected with an RLC load unit;
let the alternating current flowing out through the DC/AC inverter (3) be denoted as i abc Ac power i abc Entering a power grid unit to operate after passing through a transformer (6);
step 2, judging whether the signal relay (13) acts in the zero sequence current protection, if the signal relay (13) acts, feeding information back to the DC/AC inverter (3), and at the moment, injecting zero sequence current I into the DC/AC inverter (3) (0) ；
And step 3, after the processing in the step 2, detecting a zero sequence current value at the public connection point PCC (17), and if the zero sequence current value at the public connection point PCC (17) exceeds a set threshold value, judging that the island state is realized.
2. The method for detecting the grid-connected island of the photovoltaic power grid based on the zero sequence current injection according to claim 1, wherein the RLC load units in the step 1 are specifically a user side equivalent resistor (18), a user side equivalent inductor (19) and a user side equivalent capacitor (20) which are connected in parallel.
3. The photovoltaic grid-connected island detection method based on zero sequence current injection according to claim 1, wherein the working process of the signal relay (13) in the step 2 is as follows:
if the line has a ground fault, a zero sequence component is generated, and zero sequence current I flows on a current transformer (16) on the line (0) Zero sequence current I (0) Will continue to flow to the zero sequence current relay (15), and the zero sequence current I is led into the zero sequence current relay (15) (0) When the switch is closed, the action signal will continue to flow to the time relay (14), after the time relay (14) is delayed, if the zero sequence current I (0) If the ground fault still exists, the ground fault is not disappeared, at the moment, the action switch of the time relay (14) is closed, the signal flows to the signal relay (13), the signal relay (13) sends out a signal to the DC/AC inverter (3), and the zero sequence current I is generated (0) As a perturbation implant.
4. The method for detecting the grid-connected island of the photovoltaic system based on the zero-sequence current injection according to claim 1, wherein the zero-sequence current I in the step 2 (0) The working process of (2) is as follows:
let the given current be i' abc It can be seen that i' abc ＝i' abc(1) +i' abc(0) ＝[i' a i' b i' c ] T Wherein parameter i' abc(1) For a given positive sequence current, parameter i' abc(0) For a given zero sequence current, by giving different i' abc(1) And i' abc(0) I.e. regulate the magnitude of the positive sequence current and the zero sequence current injected into the common connection point PCC (17).
5. The method for detecting the grid-connected island of the photovoltaic system based on the zero-sequence current injection according to claim 4, wherein the given positive-sequence current i' abc(1) ＝[i' a(1) i' b(1) i' c(1) ] T Said given zero sequenceCurrent i' abc(0) ＝[i' a(0) i' b(0) i' c(0) ] T 。
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| WO2014000359A1 (en) * | 2012-06-29 | 2014-01-03 | 京东方科技集团股份有限公司 | Islanding detection method and system |
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| WO2014000359A1 (en) * | 2012-06-29 | 2014-01-03 | 京东方科技集团股份有限公司 | Islanding detection method and system |
| CN104502795A (en) * | 2014-11-26 | 2015-04-08 | 国家电网公司 | Intelligent fault diagnosis method suitable for microgrid |
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