CN115483709B - Island detection method and device of energy grid-connected system - Google Patents

Island detection method and device of energy grid-connected system Download PDF

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CN115483709B
CN115483709B CN202211267662.6A CN202211267662A CN115483709B CN 115483709 B CN115483709 B CN 115483709B CN 202211267662 A CN202211267662 A CN 202211267662A CN 115483709 B CN115483709 B CN 115483709B
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value
axis
direct
quadrature
current
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CN115483709A (en
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胡俊峰
王仕城
徐正国
王启行
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Beijing Suoying Electric Technology Co ltd
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Beijing Suoying Electric Technology Co ltd
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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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • 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]
    • 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
    • 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
    • H02J2300/28—The renewable source being wind energy
    • 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
    • H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
    • 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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Abstract

The application provides an island detection method of an energy grid-connected system, which is characterized by comprising the following steps: acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value; when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to perform island detection; and when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection. According to the island detection method, the corresponding island detection mode is selected based on the current deviation of the current inner ring, the active monitoring mode and the passive detection mode are combined, the island detection efficiency is improved on the basis that the quality of electric energy is not influenced, and the detection blind area is reduced.

Description

Island detection method and device of energy grid-connected system
Technical Field
The application relates to the technical field of power grid safety detection, in particular to an island detection method and device of an energy grid-connected system.
Background
The double-carbon target promotes the increase of the installed capacity of new energy in a new round, the large-scale investment of new energy represented by photovoltaic, energy storage and wind power is realized, the power converter is a connecting bridge of the new energy and a power grid, can work in a rectification mode and an inversion mode, and can realize functions of bidirectional power control, grid-connected and off-grid switching and the like.
With the popularization of new energy power generation, an island effect is always a ubiquitous problem in new energy grid connection, and means that when a main switch is tripped due to reasons such as power supply faults and the like in a main power grid, a grid connection system of each user side cannot timely detect a power failure state and then cannot be timely disconnected with the main power grid, a self-power supply system consisting of the grid connection system and a local load is formed, the island system can cause damage to equipment and maintenance personnel, and therefore the new energy grid connection system needs to timely and accurately detect the island state.
Existing islanding detection is divided into active and passive. The passive island detection is judged by detecting the changes of the voltage, the frequency, the harmonic distortion rate and the unbalance degree of the output end of the power converter, the passive island detection cannot influence the quality of electric energy, but has larger detection blind area and long detection time. Active island detection is amplitude or phase disturbance quantity of current periodically injected into a power grid, voltage or frequency deviation can be triggered when the power grid is powered off, a protection threshold value is triggered to stop the power grid, the power quality can be deteriorated through the active island detection, and certain detection blind areas can exist under certain specific load conditions. Therefore, the existing island detection method can bring the problem of electric energy quality, has the problems of detection blind areas and low detection speed, urgently needs the island detection method of the energy grid-connected system, can overcome the problem that the existing island detection method can bring the problem of electric energy quality, can improve the island detection speed and reduce the detection blind areas.
Disclosure of Invention
In view of this, the application provides an island detection method and device for an energy grid-connected system, which improve island detection efficiency and reduce detection blind areas on the basis of not affecting electric energy.
The technical scheme is as follows:
in a first aspect, an embodiment of the present application provides an island detection method for an energy grid-connected system, where the method includes:
acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to perform island detection;
and when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection.
Optionally, the obtaining a current deviation value of a current inner loop in the energy grid-connected system includes:
acquiring three-phase current of a power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase current to obtain a direct-axis current feedback value and an alternating-axis current feedback value of the current inner ring;
respectively carrying out filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value;
calculating a difference value between the filtered direct-axis current feedback value and a preset direct-axis current reference value to obtain a direct-axis current deviation value;
and/or calculating the difference value of the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain the quadrature axis current deviation value.
Optionally, the selecting the passive detection mode to perform the islanding detection includes: judging whether a first circuit parameter at a PCC (point of common coupling) in the energy grid-connected system exceeds a preset circuit parameter threshold value, and if so, determining that the energy grid-connected system has an island fault, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference.
Optionally, the selecting the active detection mode to perform the islanding detection includes:
acquiring three-phase voltage of a power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase voltage to obtain an alternating-axis voltage value and a direct-axis voltage value;
carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value;
calculating to obtain a direct axis disturbance voltage value according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient;
calculating to obtain a quadrature axis disturbance voltage value according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient;
inputting the direct-axis disturbance voltage value into a direct-axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to a quadrature axis shunt of the current inner loop, and determining whether an islanding state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter includes: at least one of a filtered direct axis voltage value, a voltage at the point of common coupling PCC, and a frequency.
Optionally, the method further includes: and determining a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct-axis disturbance voltage value or the quadrature-axis disturbance voltage value, the filtered quadrature-axis voltage value, the filtered direct-axis voltage value and a preset voltage proportion weighting feedforward coefficient, wherein the PWM signal is used for controlling a power converter in the energy grid-connected system.
In a second aspect, an embodiment of the present application provides an island detection device for an energy grid-connected system, where the device includes:
the acquisition module is used for acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
the island detection module is used for selecting a passive detection mode to carry out island detection when the current deviation value exceeds a preset deviation threshold value;
and the island detection module is also used for selecting an active detection mode to carry out island detection when the current deviation value does not exceed a preset deviation threshold value.
Optionally, the obtaining module includes:
the coordinate conversion submodule is used for acquiring three-phase current at the power grid side in the energy grid-connected system and performing three-phase coordinate conversion on the three-phase current to acquire a direct-axis current feedback value and a quadrature-axis current feedback value of the current inner loop;
the filtering processing submodule is used for respectively carrying out filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value so as to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value;
the deviation calculation submodule is used for calculating the difference value between the filtered direct-axis current feedback value and a preset direct-axis current reference value so as to obtain a direct-axis current deviation value; and/or calculating a difference value between the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain the quadrature axis current deviation value.
Optionally, the island detection module selects a passive detection mode to perform island detection, including: judging whether a first circuit parameter at a PCC (point of common coupling) in the energy grid-connected system exceeds a preset circuit parameter threshold value, and if so, determining that the energy grid-connected system has an island fault, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference.
Optionally, the island detection module selects an active detection mode to perform island detection, including:
acquiring three-phase voltage at the power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase voltage to obtain an alternating-axis voltage value and a direct-axis voltage value;
carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value;
calculating to obtain a direct axis disturbance voltage value according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient;
calculating to obtain a quadrature axis disturbance voltage value according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient;
inputting the direct-axis disturbance voltage value into a direct-axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to a quadrature axis shunt of the current inner loop, and determining whether an islanding state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter includes: at least one of a filtered direct axis voltage value, a voltage at the point of common coupling PCC, and a frequency.
Optionally, the apparatus further comprises:
and the power control module is used for determining a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct axis disturbance voltage value or the quadrature axis disturbance voltage value, the filtered quadrature axis voltage value, the filtered direct axis voltage value and a preset voltage proportion weighting feedforward coefficient, wherein the Pulse Width Modulation (PWM) signal is used for controlling a power converter in the energy grid-connected system.
The technical scheme has the following beneficial effects:
the island detection method of the energy grid-connected system is characterized by comprising the following steps: acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value; when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to perform island detection; and when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection. According to the island detection method, the corresponding island detection mode is selected based on the current deviation of the current inner ring, the active monitoring mode and the passive detection mode are combined, the island detection efficiency is improved on the basis that the quality of electric energy is not influenced, and the detection blind area is reduced.
The embodiment of the application also provides a device corresponding to the island detection method of the energy grid-connected system, and the device has the same beneficial effects as the island detection method of the energy grid-connected system.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an energy grid-connected system according to an embodiment of the present disclosure;
fig. 2 is a schematic flowchart of an island detection method of an energy grid-connected system according to an embodiment of the present application;
fig. 3 is a schematic control strategy flow diagram of an island detection method of an energy grid-connected system according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of an island detection device of an energy grid-connected system according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, a structural schematic diagram of an energy grid-connected system is shown, the system includes a new energy portion (composed of other new energy modules such as photovoltaic, wind power, and energy storage), a power converter, a circuit breaker, a power grid, and a load, where the power converter can be connected to the new energy portion, the power converter is connected to the power grid side, the power converter is connected to the power grid via the circuit breaker, the power converter is connected to the load via a PCC (point of common coupling) connection point, when the grid-connected circuit breaker is disconnected, the new energy portion, the power converter, and the load can perform islanding operation, that is, an islanding fault state occurs, and the islanding state can cause damage to equipment and workers in the system.
On the basis of not influencing the electric energy, the island detection efficiency is improved, and the detection blind area is reduced. An embodiment of the present application provides an island detection method for an energy grid-connected system, please refer to fig. 2, where the method may include:
step S100: acquiring a current deviation value of a current inner ring in an energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
specifically, the current inner loop refers to a current feedback system, and is used for generating a control signal for controlling the power converter according to an output feedback value of the energy grid-connected system, so as to adjust and control grid-connected power and a mode. The method comprises the step of obtaining a current deviation value of a current inner ring in a grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value.
In an optional implementation manner, step S100 may be specifically implemented by steps S101 to S103 as follows:
step S101: the method comprises the steps of obtaining three-phase current of a power grid side in an energy grid-connected system, and carrying out three-phase coordinate conversion on the three-phase current to obtain a direct-axis current feedback value and a quadrature-axis current feedback value of a current inner loop.
Specifically, the three-phase current at the power grid side is converted into a current feedback value under a dq coordinate axis according to a three-phase coordinate conversion abc-dq algorithm, that is, the three-phase current at the power grid side is synchronously rotated from a three-phase stationary coordinate system conversion value to a coordinate system, so that a direct-axis current feedback value and a quadrature-axis current feedback value of a current inner loop are obtained, and the abc-dq algorithm can refer to the following formula:
Figure BDA0003894087600000061
namely:
Figure BDA0003894087600000071
wherein, I d As direct axis current feedback value, I q As quadrature axis current feedback value, I a 、I b 、I c The three-phase currents are respectively at the side of the power grid.
Step S102: respectively carrying out filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value to obtain a filtered direct-axis current feedback value I' d And a filtered quadrature-axis current feedback value I' q 。
Specifically, filtering and discrete processing are respectively performed on the direct-axis current feedback value and the quadrature-axis current feedback value to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value, it should be noted that, due to the discrete processing, the filtered direct-axis current feedback value and the filtered quadrature-axis current feedback value are discrete values, the filtering may specifically adopt Low-pass filter (LPF) processing, and the Low-pass LPF processing specifically includes:
y(n)＝y(n-1)*(1-m)+m*(x(n)+x(n-1))；
wherein: x (n) is the current sample value, x (n-1) is the last sample value, y (n) is the result of the current calculation, y (n-1) is the result of the last calculation, and m is the filter coefficient.
Figure BDA0003894087600000072
Wherein, I d (n)、I q (n) is the current sample value, I d (n-1)、I q (n-1) is the last sampled value, I' d (n)、I’ q (n) is the result of the current calculation, I' d (n-1)、I’ q (n-1) is the result of the last calculation, m is the filter coefficient;
step S103: calculating a difference value between the filtered direct-axis current feedback value and a preset direct-axis current reference value to obtain a direct-axis current deviation value; and/or calculating a difference value between the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain a quadrature axis current deviation value.
Specifically, the filtered direct-axis current feedback value and the preset direct-axis current reference value
Figure BDA0003894087600000073
Obtaining the direct axis current deviation value delta I by difference d And/or the quadrature axis current feedback value after filtering and a preset quadrature axis current reference value>
Figure BDA0003894087600000074
Obtaining quadrature axis current deviation value delta I by difference q The calculation is as follows:
Figure BDA0003894087600000075
it should be noted that the preset direct axis current reference value and the preset quadrature axis current reference value may be set according to different grid-connected systems, for example, obtained by calculating according to the requirement of the rated power and the requirement of the rated voltage of the system.
Step S200: when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to carry out island detection;
when the current deviation value obtained by calculation exceeds a preset deviation threshold value, indicating that the energy grid-connected system may have a relatively obvious fault, and therefore, performing island detection on the energy grid-connected system by adopting a passive detection mode, specifically, determining whether a first circuit parameter at a PCC (point of common coupling) in the energy grid-connected system exceeds a preset circuit parameter threshold value, and when the first circuit parameter exceeds the preset circuit parameter threshold value, determining that the energy grid-connected system has an island fault, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference.
Step S300: and when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection.
When the current deviation value obtained by calculation exceeds the preset deviation threshold value, the detection of the island state can be realized by adopting the passive detection mode, and when the current deviation value obtained by calculation does not exceed the preset deviation threshold value, if the passive detection mode is continuously adopted, a larger detection blind area exists.
It should be noted that, in the embodiment of the present application, step S200 and step S300 are only used for distinguishing different execution actions, and do not limit the execution order of the embodiment.
In an optional embodiment, the selecting the active detection mode in step S300 to perform the islanding detection may specifically be implemented by steps S301 to S30 as follows:
step S301: the method comprises the steps of obtaining three-phase voltage on a power grid side in an energy grid-connected system, and carrying out three-phase coordinate conversion on the three-phase voltage to obtain a quadrature axis voltage value and a direct axis voltage value.
Specifically, the three-phase voltage at the power grid side is converted into a quadrature axis voltage value and a direct axis voltage value through a three-phase coordinate conversion abc-dq algorithm, which is as follows:
Figure BDA0003894087600000081
wherein, U d Is the value of the direct-axis voltage, U q Is a quadrature axis voltage value, U a 、U b 、U c The three-phase voltages are respectively at the side of the power grid.
Step S302: and carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value.
Specifically, the quadrature-axis voltage value and the direct-axis voltage value are subjected to low-pass filtering and discrete processing to obtain a filtered quadrature-axis voltage value U' q And a filtered direct-axis voltage value U' d The following formula:
Figure BDA0003894087600000091
wherein, U d (n)、U q (n) is the current sample value, U d (n-1)、U q (n-1) is the last sampled value, U' d (n)、U’ q (n) is the result of the current calculation, U' d (n-1)、U’ q (n-1) is the result of the last calculation, m is the filter coefficient;
step S303: calculating to obtain a direct axis disturbance voltage value delta U according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient d And calculating to obtain a quadrature axis disturbance voltage value delta U according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient q 。
Specifically, disturbance voltage values of a direct axis and a quadrature axis are respectively calculated, and the disturbance voltage values are used for scrambling the circuit inner ring subsequently, so that the detection of the island state is realized. The following formula:
1. direct axis disturbance voltage value delta U d Is calculated by
Firstly aligning the axial current biasThe difference value, the cross-axis voltage value after filtering and a first preset proportionality coefficient k 1 Multiplication is performed as follows:
x(n)＝k 1 *U’ q *ΔI d ，
then, low-pass filtering LPF operation is carried out on the voltage to obtain a straight-axis disturbance voltage value delta U d The following were used:
ΔU d (n)＝ΔU d (n-1) × (1-m) + (x (n) + x (n-1)) × m, where x (n) is the current sample count, x (n-1) is the last sample count, Δ U d (n) result of current calculation, Δ U d (n-1) the result of the last calculation, m being the filter coefficient, k 1 Is a first predetermined scaling factor.
2. Quadrature axis disturbance voltage value delta U q Is calculated by
Firstly, the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient k 2 Multiplication is performed as follows:
x(n)＝k 2 *U’ d *ΔI q ，
then, low pass filter LPF operation is carried out on the voltage to obtain a quadrature axis disturbance voltage value delta U q The following were used:
ΔU q (n)＝ΔU q (n-1) × (1-m) + (x (n) + x (n-1)) × m, where x (n) is the current sample count, x (n-1) is the last sample count, Δ U q (n) result of current calculation, Δ U q (n-1) the result of the last calculation, m being the filter coefficient, k 2 Is a second predetermined scaling factor.
It should be noted that the first preset proportionality coefficient and the second preset proportionality coefficient may be set by comprehensively considering the identification sensitivity and the system stability, and a larger proportionality coefficient may improve the identification rate of the island identification, but an excessively large proportionality coefficient may cause an unstable system power output, and therefore, the proportionality coefficient may be set according to the actual condition of the system.
Step S304: inputting the direct axis disturbance voltage value into a direct axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to the quadrature axis shunt of the current inner loop, and determining whether an island state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter comprises: at least one of a filtered direct axis voltage value, a voltage at the point of common coupling PCC, and a frequency.
Specifically, a direct-axis disturbance voltage value is input into a direct-axis shunt of a current inner loop, and whether an island state occurs in the energy grid-connected system is judged according to at least one parameter information of a filtered quadrature-axis voltage value, a voltage and a frequency at a point of common connection PCC, which are obtained through detection; or inputting the quadrature axis disturbance voltage value into a quadrature axis shunt of the current inner loop, and judging whether an island state occurs in the energy grid-connected system according to at least one parameter information of the filtered direct axis voltage value, the voltage and the frequency at the PCC (point of common coupling) obtained by detection.
It should be noted that, the obtained disturbance voltage is applied to the grid-connected system current inner ring in a scrambling manner, the scrambled system parameters are detected, whether the system is in an island state or not is judged according to the detected system parameters, and the specific mode of judging whether the system is in the island state or not according to the detected system parameters can refer to a passive island detection mode, and whether the circuit parameters exceed a preset threshold value or not is determined to judge the island state.
As can be seen from the above discussion, in the embodiment of the present application, the scrambling voltage used for the scrambling process of the energy grid-connected system is calculated according to the current deviation value of the current inner loop, the current deviation value of the current inner loop changes along with the state of the grid-connected system and time, and under a condition of a strong power grid, that is, under a condition that a fault does not occur in normal operation of the power grid, the filtered quadrature axis voltage value is almost equal to zero, the calculated direct axis disturbance voltage value is small, and the disturbance influence on the power grid can be ignored, so that compared with the method for realizing island detection by periodically injecting a constant disturbance quantity into the power grid, the method is not easy to influence the power quality of the power grid.
In an optional implementation manner, the method provided in the embodiment of the present application may further include the following steps:
step S400: and determining a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct axis disturbance voltage value or the quadrature axis disturbance voltage value, the filtered quadrature axis voltage value, the filtered direct axis voltage value and a preset voltage proportion weighting feedforward coefficient, wherein the Pulse Width Modulation (PWM) signal is used for controlling a power converter in the energy grid-connected system.
Fig. 3 is a schematic control strategy flow diagram of an islanding detection method of an energy grid-connected system, where fig. 3 includes three control strategy flows of islanding detection, current loop control, and phase-locked loop PLL, and step S400 is described below with reference to fig. 3.
(1) The current loop control strategy carries out abc/dq coordinate conversion on the sampled three-phase current, and converts the three-phase current into a direct-axis current feedback value I under the dq coordinate d And quadrature axis current feedback value I q (ii) a For the feedback value I of the axial current d And quadrature axis current feedback value I q Low-pass filtering and discretizing to obtain filtered direct-axis current feedback value I' d And a filtered quadrature-axis current feedback value I' q (ii) a Filtered direct-axis current feedback value I' d And a preset direct axis current reference value
Figure BDA0003894087600000112
Obtaining the direct axis current deviation value delta I by difference d And a quadrature-axis current feedback value I 'after filtering' q And a preset quadrature axis current reference value->
Figure BDA0003894087600000113
Obtaining quadrature axis current deviation value delta I by difference q 。
(2) The phase-locked loop PLL control strategy performs abc/dq coordinate conversion on the sampled three-phase power grid voltage to obtain a direct-axis voltage value U under the dq coordinate d And quadrature axis voltage value U q And aligning the axial voltage value U d And quadrature axis voltage value U q Low pass filtering and discretizingProcessing to obtain a filtered direct axis voltage value U' d And a filtered quadrature axis voltage value U' q 。
(3) Island detection control strategy enables direct axis current deviation value delta I d And a filtered quadrature axis voltage value U' q A first predetermined proportionality coefficient k 1 Multiplying, low-pass filtering and discretizing to obtain the direct axis disturbance voltage value delta U d 。
It should be noted that, the calculation formulas of the above steps (1) to (3) are described above.
(4) Current loop control strategy for alignment axis current deviation value delta I d Outputting direct axis current I through proportional-integral PI regulator regulation and discrete processing dout And quadrature axis current I qout The following:
Figure BDA0003894087600000111
kp is a proportional coefficient of the PI regulator, and Ki is an integral coefficient of the PI regulator.
(5) Perturbing the direct axis by a voltage value delta U d Adding to the current inner ring quadrature-axis shunt, and direct-axis current I dout And a filtered direct-axis voltage value U' d Feedforward coefficient k weighted in proportion to preset voltage f Adding the products to obtain a direct-axis voltage modulation signal V under a rotating coordinate system d (ii) a Will be quadrature axis current I qout And a filtered quadrature axis voltage value U' q Feedforward coefficient k weighted in proportion to preset voltage f Adding the products to obtain quadrature axis voltage modulation signal V under the rotating coordinate system q The following are:
Figure BDA0003894087600000121
it should be noted that the voltage proportional weighted feedforward coefficient k f The method can be set according to the working power condition of an energy grid-connected system, and the quadrature axis voltage value after filtering under the condition of a strong power grid is almost equal to zero, so that disturbance can be ignored, and therefore a weak power grid is consideredIn this case, the voltage modulation signal may be pre-modulated by setting a value smaller than 1, and as an alternative, the voltage proportional weighted feedforward coefficient k f Set to 0.6.
It can be understood that the scrambling quantity involved in the active island detection in the embodiment of the present application is the product of the calculated current inner loop tracking error and the quadrature axis voltage value, that is: k is a radical of 1 *U’ q *ΔI d The disturbance quantity is added into the direct-axis shunt of the current inner ring, the value of the disturbance quantity is very small when the power grid is normal, the disturbance influence on the power grid can be ignored, when the power grid has island fault, the disturbance quantity can be increased after time accumulation due to the fact that clamping of power grid voltage is avoided, the changed disturbance quantity can influence voltage and frequency, positive feedback is further formed, the system can rapidly detect the island state conveniently, island protection is triggered, the island detection speed is increased, and the weighted feedforward coefficient K is weighted through the voltage proportion f The method is used for pre-modulating the voltage modulation signal and avoiding the adverse effect on the stability of the energy grid-connected system caused by the operation of scrambling the current inner ring under the condition of a weak power grid.
(6) For direct axis voltage modulation signal V d And quadrature axis voltage modulation signal V q Carrying out dq/alpha beta coordinate conversion, and converting the voltage modulation signal under the synchronous rotating coordinate system to obtain a voltage modulation signal V under a two-phase static alpha beta coordinate α And V β The conversion formula is as follows:
Figure BDA0003894087600000122
(7) Modulating signal V based on voltage α And V β And determining a Pulse Width Modulation (PWM) signal for controlling the power converter through a space vector modulation (SVPWM) algorithm.
The above steps (4) to (7) correspond to a specific implementation manner of the step S400, it is understood that the above steps adopt an island detection manner in which current inner loop direct axis shunt is scrambled, and correspondingly, an island detection manner in which current inner loop quadrature axis shunt is scrambled may be adopted, and reference may be made to the implementation manner of the island detection manner in which current inner loop direct axis shunt is scrambled, which is not described herein again.
The analysis is convenient, and a loop equation of a power converter in the energy grid-connected system under a dq axis can be obtained based on kirchhoff voltage KVL law:
Figure BDA0003894087600000131
wherein, L is the output inductive reactance of the power converter in the system, and R is the output impedance of the power converter in the system.
Filtered quadrature axis voltage value U' q The phase angle ω t of the grid-connected point voltage is obtained through integration of the PI regulator, and the phase angle ω t can be obtained through separation processing of the phase angle ω t:
Figure BDA0003894087600000132
when the power grid is normal, the filtered quadrature axis voltage value U' q And a filtered direct axis voltage value U' d Substantially constant and filtered quadrature axis voltage value U' q Essentially zero, U 'when the grid fails' q And Δ I d U 'is obtained from the derivation formula of ω t' q The frequency change can be caused, the change of the frequency further influences the change of the system voltage output value to form voltage frequency disturbance positive feedback, and the disturbance quantity delta U d The effective value of the grid-connected point voltage can be known by calculation along with the increase of the disturbance quantity
Figure BDA0003894087600000133
And increasing, and after a certain time accumulation, the filtered quadrature axis voltage value, the voltage at the PCC and the frequency exceed preset thresholds, so that the system identifies the island state.
To sum up, when the island detection method of the energy grid-connected system provided by the embodiment of the application is executed, a current deviation value of a current inner loop in the energy grid-connected system is obtained, wherein the current deviation value includes at least one of a direct axis current deviation value and an alternating axis current deviation value; when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to carry out island detection; and when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection. According to the island detection method and device, the corresponding island detection mode is selected based on the current deviation of the current inner loop, the active monitoring mode and the passive detection mode are combined, the island detection efficiency is improved on the basis that the electric energy quality is not influenced, and the detection blind area is reduced.
Corresponding to the above method, an embodiment of the present application further provides an islanding detection device for an energy grid-connected system, please refer to fig. 4, which shows a schematic structural diagram of the device, and the islanding detection device may include:
the obtaining module 401 is configured to obtain a current deviation value of a current inner loop in an energy grid-connected system, where the current deviation value includes at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
an island detection module 402, configured to select a passive detection mode for island detection when the current deviation value exceeds a preset deviation threshold value;
the islanding detection module 402 is further configured to select an active detection mode for islanding detection when the current deviation value does not exceed a preset deviation threshold value.
In an alternative embodiment, the obtaining module 401 includes:
the coordinate conversion sub-module 4011 is configured to obtain three-phase currents on a power grid side in the energy grid-connected system, and perform three-phase coordinate conversion on the three-phase currents to obtain direct-axis current feedback values and quadrature-axis current feedback values of the current inner loop;
the filtering processing sub-module 4012 is configured to perform filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value respectively to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value;
the deviation calculation submodule 4013 is configured to calculate a difference between the filtered direct-axis current feedback value and a preset direct-axis current reference value, so as to obtain a direct-axis current deviation value; and/or calculating a difference value between the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain a quadrature axis current deviation value.
In an optional implementation, the islanding detection module 402 selects a passive detection mode for islanding detection, including: judging whether a first circuit parameter at a PCC (point of common coupling) in an energy grid-connected system exceeds a preset circuit parameter threshold value, and if so, determining that an island fault occurs in the energy grid-connected system, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference.
In an alternative embodiment, the islanding detection module 402 selects the active detection mode for islanding detection, which includes:
the method comprises the steps of obtaining three-phase voltage of a power grid side in an energy grid-connected system, and carrying out three-phase coordinate conversion on the three-phase voltage to obtain a quadrature axis voltage value and a direct axis voltage value;
carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value;
calculating to obtain a direct axis disturbance voltage value according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient;
calculating to obtain a quadrature axis disturbance voltage value according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient;
inputting the direct axis disturbance voltage value into a direct axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to the quadrature axis shunt of the current inner loop, and determining whether an island state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter comprises: at least one of a filtered direct axis voltage value, a voltage at the point of common coupling PCC, and a frequency.
In an alternative embodiment, the apparatus further comprises:
and the power control module 403 is configured to determine a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct axis disturbance voltage value or the quadrature axis disturbance voltage value, the filtered quadrature axis voltage value, the filtered direct axis voltage value, and the preset voltage proportion weighted feedforward coefficient, where the Pulse Width Modulation (PWM) signal is used to control a power converter in the energy grid-connected system.
It should be noted that, steps executed by each module in the islanding detection device of the energy grid-connected system provided by the embodiment of the present application and related technical features correspond to the method provided by the embodiment of the present application, and for descriptions of the device portion, reference may be made to the foregoing method portion embodiments, which are not described herein again.
To sum up, the embodiment of the present application provides an island detection device of an energy grid-connected system, including: the acquisition module is used for acquiring a current deviation value of a current inner ring in an energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value; the island detection module is used for selecting a passive detection mode to carry out island detection when the current deviation value exceeds a preset deviation threshold value; and the island detection module is also used for selecting an active detection mode to carry out island detection when the current deviation value does not exceed a preset deviation threshold value. According to the island detection method and device, the corresponding island detection mode is selected based on the current deviation of the current inner loop, the active monitoring mode and the passive detection mode are combined, the island detection efficiency is improved on the basis that the electric energy quality is not influenced, and the detection blind area is reduced.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
Those skilled in the art will appreciate that the flowchart shown in the figure is only one example in which the embodiments of the present application can be implemented, and the application scope of the embodiments of the present application is not limited in any way by the flowchart.
In the several embodiments provided in the present application, it should be understood that the disclosed method, apparatus, and device may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of devices or units through some communication interfaces, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment. In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. An island detection method of an energy grid-connected system is characterized by comprising the following steps:
acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
when the current deviation value exceeds a preset deviation threshold value, selecting a passive detection mode to perform island detection;
when the current deviation value does not exceed a preset deviation threshold value, selecting an active detection mode to carry out island detection;
the selecting the passive detection mode for island detection comprises: judging whether a first circuit parameter at a PCC (point of common coupling) in the energy grid-connected system exceeds a preset circuit parameter threshold value, and if so, determining that the energy grid-connected system has an island fault, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference;
the selecting the active detection mode for island detection comprises:
acquiring three-phase voltage at the power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase voltage to obtain an alternating-axis voltage value and a direct-axis voltage value; carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value; calculating to obtain a direct axis disturbance voltage value according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient; calculating to obtain a quadrature axis disturbance voltage value according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient; inputting the direct axis disturbance voltage value to a direct axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to a quadrature axis shunt of the current inner loop, and determining whether an islanding state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter includes: at least one of a filtered value of the direct axis voltage, a voltage at the point of common coupling PCC, and a frequency.
2. The method according to claim 1, wherein the obtaining of the current deviation value of the current inner loop in the energy grid-connected system comprises:
acquiring three-phase current at the power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase current to obtain a direct-axis current feedback value and an alternating-axis current feedback value of the current inner loop;
respectively carrying out filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value;
calculating a difference value between the filtered direct-axis current feedback value and a preset direct-axis current reference value to obtain a direct-axis current deviation value;
and/or calculating the difference value of the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain the quadrature axis current deviation value.
3. The method of claim 1, further comprising:
and determining a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct axis disturbance voltage value or the quadrature axis disturbance voltage value, the filtered quadrature axis voltage value, the filtered direct axis voltage value and a preset voltage proportion weighted feedforward coefficient, wherein the Pulse Width Modulation (PWM) signal is used for controlling a power converter in the energy grid-connected system.
4. An island detection device of an energy grid-connected system is characterized by comprising:
the acquisition module is used for acquiring a current deviation value of a current inner ring in the energy grid-connected system, wherein the current deviation value comprises at least one of a direct-axis current deviation value and a quadrature-axis current deviation value;
the island detection module is used for selecting a passive detection mode to carry out island detection when the current deviation value exceeds a preset deviation threshold value;
the island detection module is further used for selecting an active detection mode to perform island detection when the current deviation value does not exceed a preset deviation threshold value;
the island detection module selects a passive detection mode to perform island detection, and comprises: judging whether a first circuit parameter at a PCC (point of common coupling) in the energy grid-connected system exceeds a preset circuit parameter threshold value, and if so, determining that the energy grid-connected system has an island fault, wherein the first circuit parameter comprises: at least one of voltage, frequency, and phase difference;
the island detection module selects an active detection mode to perform island detection, and comprises the following steps: acquiring three-phase voltage at the power grid side in the energy grid-connected system, and performing three-phase coordinate conversion on the three-phase voltage to obtain an alternating-axis voltage value and a direct-axis voltage value; carrying out filtering processing and discrete processing on the quadrature axis voltage value and the direct axis voltage value to obtain a filtered quadrature axis voltage value and a filtered direct axis voltage value; calculating to obtain a direct axis disturbance voltage value according to the direct axis current deviation value, the filtered quadrature axis voltage value and a first preset proportionality coefficient; calculating to obtain a quadrature axis disturbance voltage value according to the quadrature axis current deviation value, the filtered direct axis voltage value and a second preset proportionality coefficient; inputting the direct-axis disturbance voltage value into a direct-axis shunt circuit of the current inner ring, and determining whether an island state occurs in the energy grid-connected system according to a second circuit parameter, wherein the second circuit parameter comprises: at least one of a filtered quadrature axis voltage value, a voltage at the point of common coupling, PCC, and a frequency; or, inputting the quadrature axis disturbance voltage value to a quadrature axis shunt of the current inner loop, and determining whether an islanding state occurs in the energy grid-connected system according to a third circuit parameter, wherein the third circuit parameter includes: at least one of a filtered direct axis voltage value, a voltage at the point of common coupling PCC, and a frequency.
5. The apparatus of claim 4, wherein the obtaining module comprises:
the coordinate conversion submodule is used for acquiring three-phase current at the power grid side in the energy grid-connected system and performing three-phase coordinate conversion on the three-phase current to acquire a direct-axis current feedback value and a quadrature-axis current feedback value of the current inner loop;
the filtering processing submodule is used for respectively carrying out filtering processing and discrete processing on the direct-axis current feedback value and the quadrature-axis current feedback value so as to obtain a filtered direct-axis current feedback value and a filtered quadrature-axis current feedback value;
the deviation calculation submodule is used for calculating the difference value between the filtered direct-axis current feedback value and a preset direct-axis current reference value so as to obtain a direct-axis current deviation value; and/or calculating a difference value between the filtered quadrature axis current feedback value and a preset quadrature axis current reference value to obtain the quadrature axis current deviation value.
6. The apparatus of claim 4, further comprising:
and the power control module is used for determining a Pulse Width Modulation (PWM) signal based on a space vector modulation (SVPWM) algorithm according to the current deviation value, the direct axis disturbance voltage value or the quadrature axis disturbance voltage value, the filtered quadrature axis voltage value, the filtered direct axis voltage value and a preset voltage proportion weighting feedforward coefficient, wherein the Pulse Width Modulation (PWM) signal is used for controlling a power converter in the energy grid-connected system.
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