Distributed power supply island detection method and device and electronic equipment

Abstract

The invention discloses a distributed power supply island detection method, a distributed power supply island detection device and electronic equipment. The method comprises the following steps: under the condition that a distributed power supply is in a stable operation state, performing bidirectional disturbance on a reactive power instruction of an inverter corresponding to the distributed power supply; determining a frequency offset, and controlling the distributed power supply to enter a frequency feedback reactive power disturbance stage when the absolute value of the frequency offset exceeds a preset offset threshold value; controlling the frequency feedback reactive power disturbance stage to last for the maximum allowable island detection time, and controlling bidirectional disturbance to be converted into unidirectional disturbance within the maximum allowable island detection time; and detecting whether the frequency of the distributed power supply within the maximum allowable island detection time reaches a preset protection threshold or not under the condition, and determining whether the distributed power supply has an island phenomenon or not according to a detection result. The technical problem that island detection is inaccurate due to the fact that island detection cannot be compatible with the reactive power disturbance state of the inverter is solved.

Description

Technical Field

[0001] The present invention relates to the field of inverter islanding detection, and in particular, to a distributed power source islanding detection method, device, and electronic device. Background Art

[0002] When the grid is disconnected, the distributed power grid-connected system will form an island that operates independently with loads, which may endanger the safety of equipment, affect fault clearing, and even pose an electric shock hazard, causing a series of potential hazards. Due to the disturbance of the inverter reactive power command and the q-axis reactive current reference, the frequency of the islanding system will deviate from the normal range. However, the islanding detection methods in the related art generally cannot be compatible with the state of the inverter participating in reactive power scheduling and low voltage ride-through, resulting in inaccurate islanding detection.

[0003] In view of the above problems, no effective solution has been proposed yet. Summary of the Invention

[0004] Embodiments of the present invention provide a distributed power source islanding detection method, device, and electronic device to at least solve the technical problem of inaccurate islanding detection caused by the inability of islanding detection to be compatible with the inverter reactive power disturbance state.

[0005] According to an aspect of an embodiment of the present invention, a distributed power source islanding detection method is provided, including: when the distributed power source is in a stable operation state, performing bidirectional disturbance on the reactive power command of the inverter corresponding to the distributed power source, where the stable operation state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power source are within a preset range; determining a frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, controlling the distributed power source to enter a frequency feedback reactive power disturbance stage, where the frequency offset is the difference between the frequency of the distributed power source at a corresponding moment and a dynamic reference frequency; controlling the frequency feedback reactive power disturbance stage to last for a maximum allowable islanding detection time, and within the maximum allowable islanding detection time, controlling the bidirectional disturbance to change to a unidirectional disturbance, where the disturbance amplitude of the unidirectional disturbance has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power disturbance stage and the preset offset threshold; in the case of unidirectional disturbance, detecting whether the frequency of the distributed power source reaches a preset protection threshold within the maximum allowable islanding detection time, and determining whether the distributed power source has an islanding phenomenon according to the detection result, where reaching the preset protection threshold is an over-frequency protection threshold or an under-frequency protection threshold.

[0006] According to another aspect of the embodiments of the present invention, a distributed power source islanding detection device is further provided, including: a bidirectional perturbation module, configured to perform bidirectional perturbation on the reactive power command of the inverter corresponding to the distributed power source when the distributed power source is in a stable operation state, where the stable operation state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power source are within a preset range; an offset determination module, configured to determine a frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, control the distributed power source to enter a frequency feedback reactive power perturbation stage, where the frequency offset is the difference between the frequency of the distributed power source at a corresponding moment and a dynamic reference frequency; a single-direction perturbation module, configured to control the frequency feedback reactive power perturbation stage to last for a maximum allowable islanding detection time, and within the maximum allowable islanding detection time, control the bidirectional perturbation to change to a single-direction perturbation, where the perturbation amplitude of the single-direction perturbation has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power perturbation stage and the preset offset threshold; an islanding determination module, configured to, in the case of single-direction perturbation, detect whether the frequency of the distributed power source reaches a preset protection threshold within the maximum allowable islanding detection time, and determine whether an islanding phenomenon occurs in the distributed power source according to the detection result, where reaching the preset protection threshold is an over-frequency protection threshold or an under-frequency protection threshold.

[0007] According to another aspect of the embodiments of the present invention, a computer program product is further provided, including a computer program, where when the computer program is executed by a processor, the steps of the distributed power source islanding detection method according to any one of the above are implemented.

[0008] In an embodiment of the present invention, when the distributed power supply is in a stable operating state, a bidirectional perturbation is performed on the reactive power command of the inverter corresponding to the distributed power supply. The stable operating state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power supply are within a preset range. A frequency offset is determined, and when the absolute value of the frequency offset exceeds a preset offset threshold, the distributed power supply is controlled to enter the frequency feedback reactive power perturbation stage. The frequency offset is the difference between the frequency of the distributed power supply at a corresponding moment and the dynamic reference frequency. The frequency feedback reactive power perturbation stage is controlled to last for the maximum allowable islanding detection time, and within the maximum allowable islanding detection time, the bidirectional perturbation is controlled to change to a unidirectional perturbation. The perturbation amplitude of the unidirectional perturbation has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power perturbation stage and the preset offset threshold. It is detected whether the frequency of the distributed power supply reaches a preset protection threshold within the maximum allowable islanding detection time, and whether the distributed power supply has an islanding phenomenon is determined according to the detection result. Reaching the preset protection threshold is the over-frequency protection threshold or the under-frequency protection threshold, achieving the purpose of adjusting the reactive power command of the inverter from bidirectional perturbation to unidirectional perturbation according to the frequency offset, thereby achieving the technical effect of better determining the accuracy of islanding detection under the condition of unidirectional perturbation, and further solving the technical problem of inaccurate islanding detection caused by the incompatibility between islanding detection and the reactive power perturbation state of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and the illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0010] Figure 1 is a flowchart of a method for detecting islanding of a distributed power supply according to an embodiment of the present invention;

[0011] Figure 2 is an effect diagram of flipping the reactive power perturbation command Q with the change of the frequency offset according to an embodiment of the present invention;

[0012] Figure 3 is a schematic diagram of the frequency offset - perturbation amplitude curve according to an embodiment of the present invention;

[0013] Figure 4 is a control schematic diagram of the reactive power perturbation command Q according to an embodiment of the present invention ref ;

[0014] Figure 5 is a flowchart of an optional method for detecting islanding of a distributed power supply according to an embodiment of the present invention;

[0015] Figure 6It is a simulation verification system diagram of the island detection method built on a computer-aided design / electromagnetic transient digital simulation platform for a power system according to an embodiment of the present invention;

[0016] Figure 7 It is a broken line graph of the grid connection point frequency changing with time according to an embodiment of the present invention;

[0017] Figure 8 It is a broken line graph of the island detection reactive power command and the inverter reactive power output changing with time according to an embodiment of the present invention;

[0018] Figure 9 It is the 2-7th harmonic amplitudes of the grid connection point phase voltage in the steady state according to an embodiment of the present invention;

[0019] Figure 10 It is a broken line graph of the frequency changing with time in the frequency feedback reactive power disturbance stage according to an embodiment of the present invention;

[0020] Figure 11 It is a broken line graph of the reactive power command and the reactive power output changing with time in the frequency feedback reactive power disturbance stage according to an embodiment of the present invention;

[0021] Figure 12 It is a comparison graph of the reactive power command including island detection interference and the inverter output reactive power according to an embodiment of the present invention;

[0022] Figure 13 It is a comparison graph of the grid connection point voltages in the states of turning on the low voltage ride-through module and blocking the low voltage ride-through module according to an embodiment of the present invention;

[0023] Figure 14 It is a structural schematic diagram of a distributed power source island detection device according to an embodiment of the present invention. Detailed implementation manners

[0024] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] It should be noted that the terms "first", "second", etc. in the specification, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0026] First, for the convenience of understanding the embodiments of the present invention, some terms or nouns involved in the present invention will be explained below:

[0027] The reactive power instruction refers to the control instruction for reactive power. Reactive power refers to the power generated due to the existence of inductive and capacitive elements in an AC circuit, and reactive power does not do work.

[0028] The dynamic reference frequency refers to the processor frequency automatically adjusted according to the system load and demand, and it is dynamically adjusted according to the actual usage of the system.

[0029] The apparent power refers to the power that the device or system is currently consuming or generating. It represents the current electrical energy conversion efficiency and energy usage of the device, and is usually measured in watts (W).

[0030] The margin refers to the ability to measure the richness or breadth of things.

[0031] Based on the above problems, the embodiments of the present invention provide a method embodiment for distributed power island detection. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0032] Figure 1 It is a flowchart of a distributed power island detection method according to an embodiment of the present invention. As Figure 1 shown, the method includes the following steps:

[0033] Step S102, when the distributed power is in a stable operation state, perform bidirectional perturbation on the reactive power instruction of the inverter corresponding to the distributed power, where the stable operation state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power are within a preset range;

[0034] Optionally, when the distributed power source is in a stable operating state, a periodic bidirectional perturbation with positive and negative directions and low amplitude is applied to the reactive power command of the inverter of the inverter-type distributed power source. The stable operation state of the distributed power source means that it can continuously supply power to the load, maintain the voltage and frequency stability of the power system, and at the same time, still maintain the reliability and security of the power system when dealing with external perturbations and emergencies. For example, a solar distributed photovoltaic power generation system can continuously generate electric energy under sufficient sunlight, convert direct current into alternating current through an inverter, and at the same time can achieve a stable connection with the main power grid to maintain the stability of voltage and frequency. Even in the case of sudden weather changes or local faults, the power system can automatically adjust its operating state and maintain stable operation.

[0035] Optionally, a bidirectional perturbation is applied to the reactive power command of the inverter corresponding to the distributed power source. The process is to achieve bidirectional perturbation by adjusting the capacitance of capacitors, inductors or reactive power compensation devices according to the reactive power command. Through the reactive power command, the reactive power in the power system can be controlled to maintain the stable operation of the system and improve energy efficiency. Among them, the reactive power command Q of the inverter ref consists of three parts, namely the reactive power perturbation command Q for island detection ref1 , the reactive power perturbation command Q corresponding to the inverter participating in the bidirectional reactive power scheduling of the main power grid ref2 , and the reactive power perturbation command Qref3 provided by the control when crossing the low voltage outer loop.

[0036] In an optional embodiment, the perturbation period of the bidirectional perturbation is 40 milliseconds. The amplitude of the first half period of the perturbation period is a positive reactive power perturbation command of 0.015 per unit (p.u.) and a width of 10 milliseconds, and the amplitude of the second half period of the perturbation period is a negative reactive power perturbation command of -0.015 p.u. and a width of 10 milliseconds. There is a zero interval between the positive reactive power perturbation command and the negative reactive power perturbation command.

[0037] It can be understood that the bidirectional perturbation period in the steady state is set to 40 milliseconds (ms), that is, 2 power frequency cycle lengths. The first and second half periods respectively correspond to reactive power perturbation commands with amplitudes of 0.015 p.u. and -0.015 p.u., both with a width of 10 ms. There is a zero interval between the positive and negative perturbations. The smaller perturbation period ensures a strong immediate response ability to the islanding phenomenon, and the low amplitude and narrow pulse width perturbation commands ensure that the impact on the steady-state power quality is very limited.

[0038] Optionally, when the distributed power source is in a stable operating state, the reactive power perturbation command Q for island detection is set ref1 with a period of 40 milliseconds (ms), that is, the reactive power perturbation command Q for island detection ref1The period is two power frequency cycle wavelengths. Herein, the power frequency cycle wavelength refers to the power frequency signal in the power system, and the frequency of the power frequency signal is 50 Hertz (Hz) or 60 Hz. The wavelength of the power frequency signal is calculated from the relationship between the speed of light and the frequency. In a vacuum state, the speed of light is approximately 3.00x10^8 meters per second (m / s). Therefore, the wavelengths of the power frequency signals can be calculated respectively as follows: the wavelength of the 50 Hz power frequency signal = 3.00x10^8 m / s / 50 Hz ≈ 6.00x10^6 meters (m); the wavelength of the 60 Hz power frequency signal = 3.00x10^8 m / s / 60 Hz ≈ 5.00x10^6 m.

[0039] Optionally, Q ref1 The first half cycle of Q contains a square wave with a ratio of 0.015 per unit (p.u.) and an amplitude of 10 ms. ref1 The second half cycle of Q contains a square wave with a ratio of -0.015 p.u. and an amplitude of 10 ms. Among them, the reactive power disturbance instruction containing a square wave can effectively regulate the reactive power in the distributed power source, improving the power factor and stability of the distributed power source. The square wave is a special waveform signal that can be used to generate pulses of reactive power, thereby regulating the reactive power in the main power grid. By controlling the frequency and amplitude of the square wave signal, precise adjustment of the reactive power disturbance instruction can be achieved, thereby accurately regulating the reactive power, and further enabling the power system to better adapt to load changes and fluctuations in the power of the main power grid, improving the stability and efficiency of the power system.

[0040] Step S104: Determine the frequency offset, and when the absolute value of the frequency offset exceeds the preset offset threshold, control the distributed power source to enter the frequency feedback reactive power disturbance stage. Herein, the frequency offset is the difference between the frequency of the distributed power source at the corresponding moment and the dynamic reference frequency.

[0041] Optionally, it is necessary to determine whether islanding detection is required before determining the frequency offset. Specifically, by detecting the real-time frequency (f) in the distributed power source, that is, the frequency of the distributed power source at the corresponding moment. If the real-time frequency exceeds the over / under frequency protection range specified in the predetermined programming rule standard, that is, when the real-time frequency is higher than 50.2 Hz or lower than 47.5 Hz, islanding detection is no longer performed, and the inverter is directly triggered to disconnect from the grid connection point, thereby protecting the power system; when the real-time frequency in the distributed power source does not exceed the over / under frequency protection, islanding detection with frequency feedback of the inverter is performed.

[0042] Optionally, in the case where islanding detection is required, first calculate the difference between the real-time frequency and the dynamic reference frequency, and determine it as the frequency offset. When the absolute value of the frequency offset exceeds the preset offset threshold, control the distributed power source to enter the frequency feedback reactive power disturbance stage. When the absolute value of the frequency offset exceeds the preset offset threshold, it indicates that the frequency of the power system has deviated from the normal frequency range. At this time, it may be caused by the formation of an island by the inverter, or it may be caused by a sudden increase or decrease in the load of the power system, or it may also be caused by a failure or unstable operation of the power generation equipment. Regardless of the reason, when the frequency of the power system has deviated from the normal frequency range, it may lead to the instability or even collapse of the power system. To prevent this situation from occurring, by controlling the distributed power source to enter the frequency feedback reactive power disturbance stage, the frequency of the power system can be adjusted to restore it to the normal range. At the same time, the distributed power source can adjust the reactive power by entering the frequency feedback reactive power disturbance stage to help balance the reactive power demand of the power system, thereby improving the stability and reliability of the power system.

[0043] In an optional embodiment, the dynamic reference frequency is the average value of the frequencies of the distributed power source within a predetermined number of power frequency cycles before the corresponding moment, and the dynamic reference frequency remains unchanged within the maximum allowable islanding detection time; the positive over-limit threshold of the frequency offset is +0.15 Hz, and the negative over-limit threshold of the frequency offset is -0.15 Hz.

[0044] Optionally, the predetermined number of power frequency cycles can be set to 5 power frequency cycles. The average value of the frequencies of the distributed power source within the predetermined number of power frequency cycles before the corresponding moment is used as the dynamic reference frequency (f base ), and at the same time, it is necessary to keep the dynamic reference frequency unchanged within the maximum allowable islanding detection time of 2 s, that is, to prevent the detection of the frequency offset from being inaccurate due to the change of the dynamic reference frequency. The positive and negative over-limit thresholds of the frequency offset are ±0.15 Hz. The frequency offset (Δf) is the real-time frequency minus the reference frequency. When the absolute value of the frequency offset exceeds 0.15 Hz, that is, |Δf|≥0.15 Hz, trigger the distributed power source to enter the frequency feedback reactive power disturbance stage. By setting the dynamic reference frequency in the above way, the influence of the normal fluctuation of the power grid frequency and the sampling error can be avoided, and the smaller frequency offset over-limit trigger threshold is beneficial to the sensitivity of islanding detection.

[0045] Step S106, control the frequency feedback reactive power disturbance stage to last for the maximum allowable islanding detection time, and within the maximum allowable islanding detection time, control the two-way disturbance to change into a one-way disturbance, where the disturbance amplitude of the one-way disturbance has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power disturbance stage and the preset offset threshold;

[0046] Optionally, the disturbance amplitude of the single disturbance is determined by the reactive power limit of the inverter, where the reactive power limit includes the maximum reactive power output limit value Q of the inverter max and the maximum reactive power absorption limit value Q min ; the maximum reactive power output limit value Q of the inverter max and the maximum reactive power absorption limit value Q min are the reactive power limits when |Δf| just reaches 0.15Hz. It is necessary to keep the maximum reactive power output limit value Q max and the maximum reactive power absorption limit value Q min unchanged within the maximum allowable islanding detection time of 2s. The reactive power limit after the maximum allowable islanding detection time of 2s is the second maximum reactive power output limit value Q max2 and the second maximum reactive power absorption limit value Q min2 , and the reactive power disturbance amplitude in the frequency feedback reactive power disturbance stage is calculated from Q max2 and Q min2 . Determining the reactive power disturbance amplitude through the reactive power limit of the inverter can ensure that the inverter will not experience large fluctuations under single disturbances, thus maintaining the stable operation of the system to ensure that the linear relationship between the disturbance amplitude of the single disturbance and the frequency offset has a constant slope

[0047] It should be noted that the amplitude in the reactive power disturbance command of the inverter needs to be limited by the reactive power limit of the inverter

[0048] In an optional embodiment, controlling the bidirectional disturbance to turn into a single disturbance includes: determining the execution stage of the bidirectional disturbance; in the case where the execution stage is the frequency drop stage, determining the single disturbance as a positive single disturbance; in the case where the execution stage is the frequency rise stage, determining the single disturbance as a negative single disturbance

[0049] Optionally, when Δf < -0.15Hz in the execution stage of the bidirectional disturbance, determine the execution stage of the bidirectional disturbance before this moment, that is, determine whether the disturbance direction in the bidirectional disturbance is a positive disturbance or a negative disturbance. Flip the negative disturbance in the bidirectional disturbance before this moment to a positive disturbance, and keep the square wave interval in the reactive power disturbance command unchanged. The amplitude gradually increases with the increase of the frequency offset, so that the reactive power gradually increases until the reactive power reaches Q max2 and then stop changing the amplitude; when Δf > 0.15Hz, determine the execution stage of the bidirectional disturbance before this moment, flip the positive disturbance in the bidirectional disturbance before this moment to a negative disturbance, keep the square wave interval in the reactive power disturbance command unchanged, and the absolute value of the amplitude gradually decreases with the increase of the frequency offset, so that the reactive power gradually decreases until the reactive power reaches Q min2Stop changing the amplitude when the time is up. Adjust the amplitude during the process of converting bidirectional disturbance to unidirectional disturbance based on the frequency offset, thereby controlling the reactive power process, effectively controlling the reactive power not to exceed the reactive power limit, ensuring that the reactive power is within the normal range, and thus ensuring the stability of the power system.

[0050] Among them, Figure 2 is the effect diagram of the reactive power disturbance power command flipping with the change of frequency offset according to the embodiment of the present invention. Figure 2 In (a), it is the effect diagram of the reactive power disturbance power command flipping when the frequency offset Δf < -0.15 Hz. Figure 2 In (b), it is the effect diagram of the reactive power disturbance power command flipping when the frequency offset Δf > 0.15 Hz.

[0051] In an optional embodiment, in the case of positive unidirectional disturbance, the abscissa of the starting point of the frequency offset - disturbance amplitude curve is 0.15 Hz, and the ordinate is 0.015 p.u. The abscissa of the corresponding end point is the product of the upper limit of the frequency offset and the first predetermined margin, and the ordinate is the difference obtained by subtracting the reactive power commands for the inverter to participate in reactive power scheduling and low - voltage ride - through from the reactive power limit of the inverter before the frequency - feedback reactive power disturbance stage. Among them, the frequency offset - disturbance amplitude curve is obtained based on the linear relationship between the disturbance amplitude and the frequency offset; in the case of negative unidirectional disturbance, the abscissa of the starting point of the frequency offset - disturbance amplitude curve is -0.15 Hz, and the ordinate is -0.015 p.u. The abscissa of the starting point of the frequency offset - disturbance amplitude curve is the product of the lower limit of the frequency offset and the second predetermined margin, and the abscissa of the corresponding end point is the opposite of the difference obtained by subtracting the reactive power commands for the inverter to participate in reactive power scheduling and low - voltage ride - through from the reactive power limit of the inverter before the frequency - feedback reactive power disturbance stage; among them, the reactive power limit of the inverter is obtained by taking the square root of the difference between the apparent power allowed for the inverter to operate within a predetermined time period and the square of the real - time active power.

[0052] Optionally, Figure 3 is the schematic diagram of the frequency offset - disturbance amplitude curve according to the embodiment of the present invention, that is, before the frequency - feedback reactive power disturbance stage, the reactive power disturbance amplitude Q mag changes with the frequency offset. As Figure 3 shown, specifically, the calculation expression of the reactive power disturbance amplitude Q mag is as follows:

[0053]

[0054] Among them, Δf L and Δf H are respectively the lower and upper limits of the frequency offset, and Δf Lis obtained by subtracting the dynamic reference frequency f from the threshold value when the under-frequency protection is triggered base to obtain Δf H is obtained by subtracting the dynamic reference frequency f from the threshold value when the over-frequency protection is triggered base It should be noted that the under-frequency protection threshold is 47.5 Hz, and the over-frequency protection threshold is 50.2 Hz, both of which are determined by the standard specifications. 0.9Δf H is the product of the upper limit value of the frequency offset and the first predetermined margin, and 0.9Δf L is the product of the lower limit value of the frequency offset and the second predetermined margin.

[0055] When Δf is lower than 0.9 times Δf L , the reactive power disturbance amplitude takes the lower limit Q maglim1 ; when Δf is between 0.9 times Δf L and -0.15 Hz, the reactive power disturbance amplitude performs linear feedback linearly with the frequency offset; when between 0.15 Hz and 0.9 times Δf H , the reactive power disturbance amplitude performs linear feedback linearly with the frequency offset; when Δf is higher than 0.9 times Δf H , the reactive power disturbance amplitude takes the upper limit Q maglim2 ; when Δf is between ±0.15 Hz, the disturbance mode is converted to the two-way disturbance mode when the distributed power source is in a stable operating state.

[0056] Optionally, Q maglim1 is the amplitude limit of the negative disturbance, and Q maglim2 is the amplitude limit of the positive disturbance. Both are determined by Q max2 , Q min2 , Q ref2 and Q ref3 together to exclude the occupation of the reactive power capacity of the inverter by reactive power scheduling and low-voltage ride-through. Among them, Q maglim1 and Q maglim2 The expressions are as follows:

[0057] Q maglim1 = Q min2 + Q ref2 + Q ref3

[0058] Q maglim2 = Q max2 - Q ref2 - Q ref3

[0059] Optionally, the reactive power output limit value Q max and the reactive power absorption limit value Q minIt is obtained based on the square difference between the apparent power allowed for the inverter to operate within a preset time period and the square of the real-time active power, and by taking the square root of the square difference, Q max and Q min has the following expression:

[0060]

[0061] S is the rated apparent power of the inverter. Generally, the inverter is allowed to operate short-term at 1.1 times the apparent power. P is the active power output by the inverter in real time.

[0062] Step S108, in the case of unidirectional perturbation, detect whether the frequency of the distributed power source reaches the preset protection threshold within the maximum allowable islanding detection time, and determine whether the distributed power source has an islanding phenomenon according to the detection result, where reaching the preset protection threshold is the over-frequency protection threshold or the under-frequency protection threshold.

[0063] Optionally, if it is determined that the distributed power source has an islanding phenomenon, immediately disconnect the inverter to complete the anti-islanding protection, and restore the unidirectional perturbation to bidirectional perturbation. If it is determined that the distributed power source has not had an islanding phenomenon, directly restore the unidirectional perturbation to bidirectional perturbation, where the reactive power perturbation command Q for islanding detection ref1 restores the unidirectional perturbation to bidirectional perturbation. Specifically, within the maximum allowable islanding detection time, if the system frequency reaches the set over / under-frequency protection threshold, disconnect the inverter; if it does not reach the over / under-frequency protection threshold, it is considered that no islanding phenomenon has occurred, but rather a normal range of frequency change, restore to the steady-state bidirectional perturbation, and update the reference frequency. According to whether the frequency touches the over / under-frequency protection threshold within the maximum allowable islanding detection time, determine whether an islanding phenomenon has occurred, or whether the frequency deviation belongs to the normal range of frequency change. The latter requires updating the reference frequency to avoid the continuous frequency feedback - reactive power perturbation from affecting the power quality.

[0064] Optionally, the derivation process of the reactive power perturbation command Q for islanding detection ref1 is as follows, Figure 4 is based on the reactive power perturbation command Q of the embodiment of the present invention ref control schematic diagram, as Figure 4 shown, specifically including:

[0065] S1081, determine Q ref1The first square wave starting from the end: When it is determined that islanding protection is completed or no islanding phenomenon occurs, a reference pulse is generated by a pulse generator, and the positive initial trigger square wave InP0 in the end of the reference pulse is delayed by one power frequency cycle through a monostable multivibrator to obtain a negative initial trigger square wave InN0; among them, the positive initial trigger square wave InP0 is a positive disturbance square wave with a width of 10 ms in the reference pulse, and the values used for the positive disturbance square wave are 1 and 0; the negative initial trigger square wave InN0 is a negative disturbance square wave with a width of 10 ms in the reference pulse, and the values used for the negative disturbance square wave are -1 and 0.

[0066] S1082, determine Q ref1 The remaining square waves after the first square wave: When the frequency offset Δf > 0.15 Hz, set the first frequency offset flag F1 to 1; when Δf < -0.15 Hz, set the second frequency offset flag F2 to 1; F1 and F2 pass through an exclusive-OR gate and interval limiting to obtain a third frequency offset flag F3. If F3 is set to 1, it indicates that |Δf| exceeds 0.15 Hz; at this time, F3 and F1 pass through a first AND gate and then through a first single-input comparator to obtain a disturbance flip signal Flip; among them, when Δf < 0.15 Hz, the negative disturbance is flipped to a positive disturbance, and the trigger square wave InN1 with values of 1 and 0 is obtained after multiplying Flip by InN0. When Δf > 0.15 Hz, the positive disturbance is flipped to a negative disturbance, and the trigger square wave InP1 with values of -1 and 0 is obtained after multiplying Flip by InP0. Among them, the interval limit is T1 < t < T2, T1 is 20 ms, effectively avoiding the change of the flip signal value during a single disturbance square wave; T2 is 2 s, making the single-round frequency feedback reactive power disturbance not exceed the maximum allowable islanding detection time, which is beneficial to preventing misjudgment of non-islanding frequency fluctuations caused by load switching, etc.

[0067] S1083, similarly, the negative disturbance flip signal F lipN and I nN0 are multiplied to obtain a trigger square wave I with values of 1 and 0 nN1 , multiplied by the disturbance amplitude Q mag2 and then Q is also obtained ref1 .

[0068] In an optional embodiment, when the detection result indicates that the frequency of the distributed power supply reaches the preset protection threshold within the maximum allowable islanding detection time, it is determined that the distributed power supply has an islanding phenomenon; when the detection result indicates that the frequency of the distributed power supply does not reach the preset protection threshold within the maximum allowable islanding detection time, it is determined that the distributed power supply has no islanding phenomenon.

[0069] Optionally, within the maximum allowable islanding detection time, if the frequency of the distributed power source reaches the preset protection threshold, that is, when the set over / under frequency protection threshold is reached, it is determined that an islanding phenomenon has occurred. Then, the inverter is disconnected to complete the anti-islanding protection. If within the maximum allowable islanding detection time, the frequency of the distributed power source does not reach the set over / under frequency protection threshold, it is determined that no islanding phenomenon has occurred. Therefore, the absolute value of the frequency offset in step S104 exceeding the preset offset threshold is not caused by the islanding phenomenon. It may be caused by a sudden increase or decrease in the power system load, or by a fault or unstable operation of the power generation equipment. In both of the above situations, the power system can adjust itself, which is a normal frequency fluctuation within the range. Then, the dynamic reference frequency f base is adjusted to within ±0.15 Hz, and the bidirectional disturbance of the reactive power command of the inverter corresponding to the distributed power source is restored.

[0070] In an optional embodiment, it is detected whether the frequency offset within the maximum allowable islanding detection time is within the preset offset range; when the frequency of the distributed power source does not reach the preset protection threshold within the maximum allowable islanding detection time and the frequency offset within the maximum allowable islanding detection time is within the preset offset range, it is determined that no islanding phenomenon has occurred in the distributed power source; when the frequency of the distributed power source reaches the preset protection threshold within the maximum allowable islanding detection time, or the frequency offset within the maximum allowable islanding detection time is not within the preset offset range, it is determined that no islanding phenomenon has occurred in the distributed power source.

[0071] Optionally, to avoid the inaccurate detection situation that may occur when only detecting whether the frequency of the distributed power source reaches the preset protection threshold, it is necessary to detect whether the frequency offset is within the preset offset range thereafter. This method effectively enhances the detection effect and better ensures the accuracy of islanding phenomenon detection.

[0072] In an optional embodiment, when an islanding phenomenon occurs in the distributed power source, the inverter is disconnected; when no islanding phenomenon occurs in the distributed power source, the unidirectional disturbance is switched back to the bidirectional disturbance, and the dynamic reference frequency is updated.

[0073] Optionally, when it is detected that an islanding phenomenon occurs in the distributed power source, since this islanding phenomenon will pose a safety hazard to the power system, the inverter corresponding to the distributed power source that generates the islanding phenomenon is directly disconnected to ensure the safe and stable operation of the power system; if it is detected that no islanding phenomenon occurs in the distributed power source, the reactive power command of the inverter corresponding to the distributed power source is restored from unidirectional disturbance to bidirectional disturbance, and the distributed power source returns to the stable operation state.

[0074] Through the above steps S102 to S108, the purpose of adjusting the reactive power command of the inverter from bidirectional disturbance to unidirectional disturbance according to the frequency offset is achieved, thereby realizing the technical effect of better determining the islanding detection accuracy under the condition of unidirectional disturbance, and further solving the technical problem of inaccurate islanding detection caused by the incompatibility between islanding detection and the reactive power disturbance state of the inverter.

[0075] Based on the above embodiments and alternative embodiments, the present invention proposes an alternative implementation manner. Figure 5 It is a flowchart of an alternative distributed power source islanding detection method according to an embodiment of the present invention, as Figure 5 shown, the method includes:

[0076] S1. During steady state, perform positive and negative, low-amplitude periodic bidirectional disturbances on the reactive power command of the inverter corresponding to the inverter-type distributed power source.

[0077] Among them, the bidirectional disturbance period during steady state is 40 milliseconds (ms), that is, 2 power frequency cycle lengths. The first half cycle corresponds to an amplitude of 0.015 p.u., and the second half cycle corresponds to an amplitude of -0.015 p.u. The first half cycle and the second half cycle are both reactive power disturbance commands with a width of 10 ms. The bidirectional disturbance includes a positive disturbance and a negative disturbance, and there is a zero interval period between the positive disturbance and the negative disturbance. The smaller disturbance period ensures a strong immediate response ability to the islanding phenomenon, and the low-amplitude, narrow pulse-width reactive power disturbance command ensures that the impact on the steady-state distributed power source is very limited. It should be noted that p.u. is a dimensionless unit used in the power system to represent the ratio or proportion of variables. For example, the transformation ratio of a transformer is represented by p.u.

[0078] S2. When the frequency offset based on the dynamic reference frequency exceeds the preset offset threshold, trigger the distributed power source to enter the frequency feedback reactive power disturbance stage. Among them, the dynamic reference frequency is the average value of the distributed power source frequency within 5 power frequency cycles and remains unchanged within the maximum allowable islanding detection time of 2 s specified by the standard; it should be noted that the preset offset threshold is from -0.15 Hz to +0.15 Hz. Calculating the frequency offset using the dynamic reference frequency can effectively avoid the influence brought by the normal fluctuation of the main grid frequency and sampling error. This preset offset threshold is smaller than the preset offset threshold in the related technology, which is beneficial to the sensitivity of islanding phenomenon detection.

[0079] S3. The duration of the frequency feedback reactive power disturbance stage is the maximum allowable islanding detection time, i.e., 2 s. During this time period, the bidirectional disturbance in the inverter corresponding to the distributed power source is converted into a unidirectional disturbance. Among them, the disturbance amplitude of the unidirectional disturbance has a linear relationship with the frequency offset. This linear curve is obtained from the inverter reactive power limit and the frequency offset before the frequency feedback reactive power disturbance stage. Specifically, the method for converting the bidirectional disturbance into a unidirectional disturbance is as follows: during the frequency decrease stage, i.e., when Δf < -0.15 Hz, the negative unidirectional disturbance in the bidirectional disturbance is flipped to a positive unidirectional disturbance; during the frequency increase stage, i.e., when Δf > -0.15 Hz, the positive unidirectional disturbance in the bidirectional disturbance is flipped to a negative unidirectional disturbance.

[0080] Among them, when performing a positive disturbance, the abscissa of the starting point of the slant line segment of the frequency offset - disturbance amplitude curve is -0.15 Hz, and the ordinate is 0.015 p.u.; the abscissa of the end point is the product of the upper limit of the frequency offset multiplied by the first predetermined margin, and the ordinate is the difference obtained by subtracting the reactive power disturbance instruction for the inverter to participate in reactive power scheduling and low-voltage ride-through from the inverter reactive power limit determined before the frequency feedback reactive power disturbance stage; when performing a negative disturbance, the abscissa of the starting point of the slant line segment of the frequency offset - disturbance amplitude curve is -0.15 Hz, and the ordinate is 0.015 p.u.; the abscissa of the end point is the product of the lower limit of the frequency offset multiplied by the second predetermined margin, and the ordinate is the opposite of the difference obtained by subtracting the reactive power disturbance instruction for the inverter to participate in reactive power scheduling and low-voltage ride-through from the inverter reactive power limit determined before the frequency feedback reactive power disturbance stage; it should be noted that the inverter reactive power limit is obtained by taking the square root of the difference between the short-time allowable apparent power of the inverter and the square of the real-time active power.

[0081] S4. During the maximum allowable islanding detection time, when the frequency reaches the set over / under frequency protection threshold, the inverter is disconnected; when the frequency does not reach the over / under frequency protection threshold, it is considered that no islanding phenomenon has occurred, but rather a frequency change within the normal range. The inverter corresponding to the distributed power source is restored to the steady-state bidirectional disturbance, and the reference frequency is updated.

[0082] Among them, according to whether the frequency touches the over / under frequency protection threshold during the maximum allowable islanding detection time, it is judged whether an islanding phenomenon has occurred, or whether the frequency offset belongs to the frequency change within the normal range. When it is confirmed that the frequency change is within the normal range, the reference frequency needs to be updated, effectively avoiding the influence of the continuous frequency feedback reactive power disturbance stage on the power supply quality of the distributed power source.

[0083] This embodiment makes full use of the output capacity of the inverter's reactive power, changes the disturbance direction in the frequency feedback reactive power disturbance stage, thereby changing the effect of the frequency amplitude in the islanding phenomenon, and effectively realizes the accurate detection of the islanding phenomenon; this embodiment can efficiently complete the islanding detection of a distributed power generation system with an inverter, including the most severe islanding phenomenon conditions specified by the Institute of Electrical and Electronics Engineers (IEEE), and also has excellent immediate islanding response ability, can correct the misjudgment of islanding occurring within the normal frequency change range in a timely manner, has a very limited impact on the quality of the steady-state distributed power supply, reduces the steady-state harmonic interference brought by active islanding detection, and at the same time enables the system to have the ability to participate in two-way reactive power scheduling and low-voltage ride-through ability without complex and active strategy switching.

[0084] Based on the above embodiments and alternative embodiments, the present invention proposes an alternative implementation manner, taking a distributed photovoltaic power generation system as an example for illustration, specifically:

[0085] Figure 6 It is a simulation verification system diagram of the islanding detection method built on the power system computer-aided design / electromagnetic transient digital simulation platform according to the embodiment of the present invention. The main parameters of the distributed photovoltaic power generation system are shown in Table 1. The case with a load quality factor of 2.5, which is the most difficult to detect in the Institute of Electrical and Electronics Engineers, is selected to verify this islanding detection strategy.

[0086] Table 1 Main parameters of the photovoltaic simulation system

[0087]

[0088]

[0089] The inverter in the distributed photovoltaic power generation system operates in a steady state and outputs the rated output power. Figure 5 The active power P output by the inverter in PV = 200 kW, that is, 1 p.u., and the reactive power Q PV = 0 kVar, that is, 0 p.u. The parallel load includes: a 500 Ω resistor in parallel with a 643 mH inductor, and then in parallel with a 15.91549 μF capacitor. At steady state, the output power of the load matches that of the inverter. Combining with the grid-connected transformer, at this time, the resonant frequency of the load is 49.95 Hz, and the total load quality factor is 2.495. It should be noted that the resonant frequency of the load depends on the inductance and capacitance of the load. Generally, the resonant frequency of the load can be calculated by the following formula:

[0090] f = 1 / (2π√(LC))

[0091] where f represents the resonant frequency, L represents the inductance of the load, and C represents the capacitance of the load.

[0092] At steady state, it is a two-way positive and negative disturbance. At 3.0396 s, the frequency offset exceeds -0.15 Hz, and the distributed photovoltaic power generation system automatically enters the frequency feedback reactive power disturbance stage. The negative disturbance flips to a positive disturbance, and the reactive power disturbance amplitude is calculated in real time according to the frequency offset. When the frequency touches the under-frequency protection threshold, the islanding detection is completed. At 3.0 s, Figure 5 As shown, circuit breaker 1 disconnects to form an islanding system. If the method in the related technology uses 49.5 Hz as the standard for successful islanding detection, this embodiment takes 0.12 s to complete the islanding detection; if the specified 47.5 Hz is used as the standard, this embodiment takes 0.43 s, and at 3.43 s, circuit breaker 3 of the inverter can be triggered to disconnect, completing the anti-islanding protection. Among them, during this process, the grid connection point frequency, the islanding detection reactive power command, and the inverter reactive power output are as Figure 7 and Figure 8 shown. Figure 7 is the broken line graph of the grid connection point frequency changing with time according to the embodiment of the present invention. Figure 8 is the broken line graph of the islanding detection reactive power command and the inverter reactive power output changing with time according to the embodiment of the present invention.

[0093] Figure 9 are the 2-7th harmonic amplitudes of the grid connection point phase voltage at steady state according to the embodiment of the present invention. As Figure 9 shown, this embodiment benefits from the low amplitude of the disturbance at steady state, and the total harmonic distortion rate THD is only 0.345%. The reactive power output by the inverter at steady state is only between ±0.005 p.u., and hardly affects the AC voltage quality and steady-state reactive power in the distributed photovoltaic power generation system during grid connection.

[0094] Figure 10 is the broken line graph of the frequency changing with time during the frequency feedback reactive power disturbance stage according to the embodiment of the present invention. Figure 11 is the broken line graph of the reactive power command and the reactive power output changing with time during the frequency feedback reactive power disturbance stage according to the embodiment of the present invention. As Figure 10 and Figure 11 shown, at 3 s, it changes from 50 Hz to 49.84 Hz. Since f base is still 50 Hz, at 3.021 s subsequently, it is detected that |Δf| exceeds 0.15 Hz, thus triggering the frequency feedback reactive power disturbance stage. After about 2 s of the frequency feedback reactive power disturbance stage, f base is updated to 49.84 Hz, and the disturbance returns to the two-way disturbance at steady state. During the feedback disturbance, due to the stable effect of the main power grid, the frequency and reactive power of the distributed photovoltaic power generation system do not change much. This embodiment is not affected by the misjudgment of the steady-state normal frequency change and has the ability to cope with the misjudgment of the steady-state normal frequency change.

[0095] Figure 12 It is a comparison chart of the reactive power command including island detection interference and the reactive power output of the inverter according to an embodiment of the present invention. As shown by Figure 12 in the figure, two working conditions of the reactive power scheduling command rising and falling are set in this embodiment. Among them, the rising of the reactive power scheduling command is working condition A, and the falling of the reactive power scheduling command is working condition B. When the inverter is in a steady state, the active power output is 0.8 p.u. Working condition A is that at 3.0 s, when the inverter participates in the two-way reactive power scheduling of the main power grid, the corresponding reactive power disturbance command Q ref2 gradually rises from 0 to 0.35 p.u. in 1 s; working condition B is that at 3.0 s, Q ref2 gradually drops from 0 to -0.35 p.u. in 1 s. In this embodiment, the island detection strategy can be compatible with the two-way reactive power scheduling of the inverter participating in the main power grid, can support the reactive power demand of the load and the main power grid, and can also absorb the excess reactive power of the power grid.

[0096] Figure 13 It is a comparison chart of the grid connection point voltage in the state of the low voltage ride-through module being put into operation and the low voltage ride-through module being blocked according to an embodiment of the present invention. As shown by Figure 13 in the figure, the circuit breaker in Figure 5 is closed at 3.0 s, and the main power grid voltage drops by 0.6 V in amplitude and lasts for 2 s due to the voltage dip simulation impedance. On the premise that the island detection control remains put into operation, after the low voltage ride-through control in this embodiment, the grid connection point voltage rises from 0.574 p.u. to 0.593 p.u., and the rising amplitude is about 0.019 p.u. This embodiment can support the inverter to simultaneously put into the island detection strategy and the low voltage ride-through strategy, and maintain grid-connected operation during the voltage dip to achieve low voltage ride-through.

[0097] In summary, the embodiments of the present invention can achieve at least one of the following effects: (1) During steady state, the reactive power is disturbed bidirectionally, both positive and negative, ensuring that islands with resonant frequencies slightly lower or slightly higher than the power frequency can generate a tendency to change the system frequency, thereby making the frequency offset reach the trigger threshold of frequency feedback - reactive power disturbance; after the frequency offset exceeds the threshold, both the disturbance direction and the disturbance amplitude perform frequency feedback, and the effect of influencing the frequency of the island system is gradually enhanced after the frequency offset reaches the threshold, making full use of the current reactive power capacity of the system based on the dynamic reactive power limit. (2) The steady-state disturbance period is extremely short, with each cycle corresponding to a positive or negative reactive power disturbance pulse, having a strong ability to respond promptly to islands occurring at any unknown time; the extremely small steady-state disturbance amplitude greatly reduces the impact on the steady-state power quality of the system. (3) The reference frequency is taken as the average value of the past several cycles and remains unchanged within the maximum allowable island detection time, which can not only avoid the influence of frequency sampling errors but also help correct the misjudgment of islands occurring within the normal frequency change range in a timely manner. (4) It only affects the outer-loop reactive power command of the inverter and does not directly act on the inner-loop current controller, enabling the inverter to participate in two-way reactive power scheduling of the power grid and perform low-voltage ride-through without complex strategy adjustment, having good compatibility in reactive power type control.

[0098] In this embodiment, a distributed power source island detection device is also provided. This device is used to implement the above embodiments and preferred implementation manners, and those that have been described will not be repeated. As used hereinafter, the terms "module" and "device" can be a combination of software and / or hardware that can achieve a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation in hardware, or a combination of software and hardware is also possible and contemplated.

[0099] According to an embodiment of the present invention, an apparatus embodiment for implementing the above distributed power source island detection method is also provided. Figure 14 It is a schematic structural diagram of a distributed power source island detection device according to an embodiment of the present invention, as Figure 14 shown, the above-mentioned distributed power source island detection device includes: a bidirectional disturbance module 700, an offset determination module 702, a single disturbance module 704, and an island determination module 706, where:

[0100] The bidirectional perturbation module 700 is used to perform bidirectional perturbation on the reactive power command of the inverter corresponding to the distributed power source when the distributed power source is in a stable operation state, where the stable operation state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power source are within a preset range; the offset determination module 702 is connected to the bidirectional perturbation module 700 and is used to determine the frequency offset, and when the absolute value of the frequency offset exceeds the preset offset threshold, control the distributed power source to enter the frequency feedback reactive power perturbation stage, where the frequency offset is the difference between the frequency of the distributed power source at the corresponding moment and the dynamic reference frequency; the single-direction perturbation module 704 is connected to the offset determination module 702 and is used to control the frequency feedback reactive power perturbation stage to last for the maximum allowable islanding detection time, and within the maximum allowable islanding detection time, control the bidirectional perturbation to change to single-direction perturbation, where the perturbation amplitude of the single-direction perturbation has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power perturbation stage and the preset offset threshold; the islanding determination module 706 is connected to the single-direction perturbation module 704 and is used to detect whether the frequency of the distributed power source reaches the preset protection threshold within the maximum allowable islanding detection time in the case of single-direction perturbation, and determine whether the distributed power source has an islanding phenomenon according to the detection result, where reaching the preset protection threshold is the over-frequency protection threshold or the under-frequency protection threshold.

[0101] It should be noted that the above-mentioned various modules can be implemented by software or hardware. For example, for the latter, it can be implemented in the following way: the above-mentioned various modules can be located in the same processor; or, the above-mentioned various modules are located in different processors in any combination.

[0102] It should be noted here that the above-mentioned bidirectional perturbation module 700, offset determination module 702, single-direction perturbation module 704, and islanding determination module 706 correspond to steps S102 to S108 in the embodiment. The examples and application scenarios implemented by the above modules and the corresponding steps are the same, but are not limited to the content disclosed in the above embodiment. It should be noted that the above modules can run in a computer terminal as part of the device. It should be noted that the optional or preferred implementation manners of this embodiment can refer to the relevant descriptions in the embodiment, which will not be elaborated here.

[0103] The above-mentioned distributed power source islanding detection device may further include a processor and a memory. The above-mentioned bidirectional perturbation module 700, offset determination module 702, single-direction perturbation module 704, islanding determination module 706, etc. are all stored in the memory as program modules, and the corresponding functions are implemented by the processor executing the above program modules stored in the memory.

[0104] The processor contains a kernel, which retrieves the corresponding program module from the memory. One or more kernels can be set. The memory may include non-permanent memory in a computer-readable medium, in the form of random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. The memory includes at least one memory chip.

[0105] According to an embodiment of the present application, an embodiment of a non-volatile storage medium is also provided. Optionally, in this embodiment, the non-volatile storage medium includes a stored program, wherein when the program runs, it controls the device where the non-volatile storage medium is located to execute any one of the above-mentioned distributed power island detection methods.

[0106] Optionally, in this embodiment, the non-volatile storage medium can be located in any one of the computer terminals in a computer terminal group in a computer network, or in any one of the mobile terminals in a mobile terminal group. The non-volatile storage medium includes a stored program.

[0107] Optionally, when the program runs, it controls the device where the non-volatile storage medium is located to execute the following functions: when the distributed power is in a stable operating state, perform bidirectional perturbation on the reactive power command of the inverter corresponding to the distributed power, where the stable operating state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power are within a preset range; determine the frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, control the distributed power to enter the frequency feedback reactive power perturbation stage, where the frequency offset is the difference between the frequency of the distributed power at the corresponding moment and the dynamic reference frequency; control the frequency feedback reactive power perturbation stage to last for the maximum allowable island detection time, and within the maximum allowable island detection time, control the bidirectional perturbation to turn into a unidirectional perturbation, where the perturbation amplitude of the unidirectional perturbation has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power perturbation stage and the preset offset threshold; in the case of unidirectional perturbation, detect whether the frequency of the distributed power reaches a preset protection threshold within the maximum allowable island detection time, and determine whether the distributed power has an islanding phenomenon according to the detection result, where reaching the preset protection threshold is the over-frequency protection threshold or the under-frequency protection threshold.

[0108] According to an embodiment of the present application, an embodiment of a processor is also provided. Optionally, in this embodiment, the processor is used to run a program, wherein when the program runs, it executes any one of the above-mentioned distributed power island detection methods.

[0109] According to an embodiment of the present application, an embodiment of a computer program product is further provided. Optionally, in this embodiment, the above computer program product includes a computer program, and when the computer program is executed by a processor, it implements the program steps of any one of the above distributed power island detection methods.

[0110] Optionally, when the above computer program product is executed on a data processing device, it is adapted to execute a program initialized with the following method steps: when the distributed power is in a stable operating state, perform bidirectional perturbation on the reactive power command of the inverter corresponding to the distributed power, where the stable operating state is used to indicate that the fluctuation ranges of the output voltage and frequency of the distributed power are within a preset range; determine the frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, control the distributed power to enter the frequency feedback reactive power perturbation stage, where the frequency offset is the difference between the frequency of the distributed power at the corresponding moment and the dynamic reference frequency; control the frequency feedback reactive power perturbation stage to last for a maximum allowable island detection time, and within the maximum allowable island detection time, control the bidirectional perturbation to change to a unidirectional perturbation, where the perturbation amplitude of the unidirectional perturbation has a linear relationship with the frequency offset, and the linear relationship is determined based on the reactive power limit of the inverter before entering the frequency feedback reactive power perturbation stage and the preset offset threshold; in the case of unidirectional perturbation, detect whether the frequency of the distributed power reaches a preset protection threshold within the maximum allowable island detection time, and determine whether the distributed power has an islanding phenomenon according to the detection result, where reaching the preset protection threshold is an over-frequency protection threshold or an under-frequency protection threshold.

[0111] An embodiment of the present invention provides an electronic device, which includes a processor, a memory, and a program stored on the memory and executable on the processor. When the processor executes the program, it implements any one of the above distributed power island detection methods.

[0112] The above order of the embodiments of the present invention is only for description and does not represent the advantages or disadvantages of the embodiments.

[0113] In the above embodiments of the present invention, the descriptions of the various embodiments have their own emphases. For the parts not detailed in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0114] In several embodiments provided in the present application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are merely illustrative. For example, the above-mentioned module division can be a logical function division. In actual implementation, there can be other division methods. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of modules or modules can be electrical or other forms.

[0115] The modules described above as separate components may or may not be physically separated. The components shown as modules may or may not be physical modules, that is, they can be located in one place, or they can be distributed to multiple modules. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in each embodiment of the present invention, the functional modules can be integrated in a processing module, or each module can exist physically alone, or two or more modules can be integrated in one module. The above-mentioned integrated modules can be implemented in the form of hardware or in the form of software functional modules.

[0116] If the above-mentioned integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable non-volatile storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a non-volatile storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in each embodiment of the present invention. And the aforementioned non-volatile storage medium includes: USB flash drives, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), mobile hard disks, magnetic disks, or optical discs and other media that can store program codes.

[0117] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A distributed power supply island detection method, characterized in that: include: When the distributed power source is in a stable operation state, bidirectionally disturbing the reactive power instruction of the inverter corresponding to the distributed power source, wherein the stable operation state is used to indicate that the fluctuation range of the output voltage and frequency of the distributed power source is within a preset range; Determine a frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, control the distributed power source to enter a frequency feedback reactive disturbance phase, wherein the frequency offset is a difference between the frequency of the distributed power source at a corresponding moment and a dynamic reference frequency; Controlling the frequency feedback reactive disturbance stage to last for a maximum allowable islanding detection time, and controlling the bidirectional disturbance to be transformed into a unidirectional disturbance within the maximum allowable islanding detection time, wherein the disturbance amplitude of the unidirectional disturbance is linearly related to the frequency offset, and the linear relationship is determined based on the reactive limit of the inverter before entering the frequency feedback reactive disturbance stage and the preset offset threshold; In the case of the unidirectional disturbance, it is detected whether the frequency of the distributed power source reaches a preset protection threshold within the maximum allowable islanding detection time, and it is determined whether an islanding phenomenon occurs in the distributed power source based on the detection result, wherein reaching the preset protection threshold is an overfrequency protection threshold or an underfrequency protection threshold.

2. The method according to claim 1, characterized in that The disturbance period of the bidirectional disturbance is 40 milliseconds, the amplitude of the first half of the disturbance period is 0.015 per unit pu, the width is 10 milliseconds, and the positive reactive power disturbance instruction is in the form of a positive reactive power disturbance instruction; the amplitude of the second half of the disturbance period is -0.015 pu, the width is 10 milliseconds, and the negative reactive power disturbance instruction is in the form of a negative reactive power disturbance instruction; there is zero interval between the positive reactive power disturbance instruction and the negative reactive power disturbance instruction.

3. The method according to claim 1, characterized in that The dynamic reference frequency is the average value of the frequency of the distributed power source within a predetermined number of power frequency cycles before the corresponding moment, and the dynamic reference frequency remains unchanged within the maximum allowable island detection time; the positive threshold of the frequency offset is +0.15Hz, and the negative threshold of the frequency offset is -0.15Hz.

4. The method according to claim 1, characterized in that: The controlling the bidirectional disturbance to be transformed into a unidirectional disturbance comprises: Determining an execution phase for executing the bidirectional perturbation; In a case where the execution phase is a frequency reduction phase, determining that the unidirectional disturbance is a positive unidirectional disturbance; When the execution phase is a frequency increase phase, it is determined that the unidirectional disturbance is a negative unidirectional disturbance.

5. The method according to claim 4, characterized in that In the case of the forward unidirectional disturbance, the frequency offset-disturbance amplitude curve has a horizontal coordinate of 0.15 Hz and a vertical coordinate of 0.015 pu corresponding to the starting point, and a horizontal coordinate of the corresponding end point is the product of the upper limit value of the frequency offset and the first predetermined margin, and a vertical coordinate is the difference between the reactive power limit of the inverter before the frequency feedback reactive disturbance stage and the reactive power instruction of the inverter participating in reactive scheduling and low voltage ride-through, wherein the frequency offset-disturbance amplitude curve is obtained based on the linear relationship between the disturbance amplitude and the frequency offset; In the case of the negative unidirectional disturbance, the abscissa of the frequency offset-disturbance amplitude curve corresponding to the starting point is -0.15 Hz and the ordinate is -0.015 pu, the abscissa of the frequency offset-disturbance amplitude curve corresponding to the starting point is the product of the lower limit of the frequency offset and the second predetermined margin, and the abscissa of the corresponding end point is the inverse of the difference between the reactive power limit of the inverter before the frequency feedback reactive disturbance stage and the reactive power instruction of the inverter participating in reactive scheduling and low voltage ride-through; The reactive power limit of the inverter is obtained by taking the square root of the square difference between the apparent power allowed to operate the inverter and the real-time active power within a predetermined period of time.

6. The method according to any one of claims 1 to 5, characterized in that The determining, according to the detection result, whether the distributed power source has an islanding phenomenon comprises: When the detection result indicates that the frequency of the distributed power source reaches the preset protection threshold within the maximum allowable islanding detection time, determining that the distributed power source has the islanding phenomenon; When the detection result indicates that the frequency of the distributed power source does not reach the preset protection threshold within the maximum allowable islanding detection time, it is determined that the distributed power source does not have the islanding phenomenon.

7. The method according to any one of claims 1 to 5, characterized in that The method further comprises: When the islanding phenomenon occurs in the distributed power source, disconnecting the inverter; When the islanding phenomenon does not occur in the distributed power source, the unidirectional disturbance is switched back to the bidirectional disturbance, and the dynamic reference frequency is updated.

8. The method according to any one of claims 1 to 5, characterized in that The determining, according to the detection result, whether the distributed power source has an islanding phenomenon comprises: Detecting whether the frequency offset within the maximum allowable islanding detection time is within a preset offset range; If the frequency of the distributed power source does not reach the preset protection threshold within the maximum allowable islanding detection time, and the frequency offset within the maximum allowable islanding detection time is within the preset offset range, it is determined that the distributed power source does not have the islanding phenomenon; When the frequency of the distributed power source reaches the preset protection threshold within the maximum allowable islanding detection time, or the frequency offset within the maximum allowable islanding detection time is not within the preset offset range, it is determined that the distributed power source does not experience the islanding phenomenon.

9. A distributed power supply island detection device, characterized in that: include: A bidirectional disturbance module, used for bidirectionally disturbing the reactive power instruction of the inverter corresponding to the distributed power source when the distributed power source is in a stable operation state, wherein the stable operation state is used to indicate that the fluctuation range of the output voltage and frequency of the distributed power source is within a preset range; An offset determination module, used to determine a frequency offset, and when the absolute value of the frequency offset exceeds a preset offset threshold, control the distributed power source to enter a frequency feedback reactive disturbance phase, wherein the frequency offset is a difference between the frequency of the distributed power source at a corresponding moment and a dynamic reference frequency; A unidirectional disturbance module, used for controlling the frequency feedback reactive disturbance phase to last for a maximum allowable islanding detection time, and controlling the bidirectional disturbance to be transformed into a unidirectional disturbance within the maximum allowable islanding detection time, wherein the disturbance amplitude of the unidirectional disturbance is linearly related to the frequency offset, and the linear relationship is determined based on the reactive limit of the inverter before entering the frequency feedback reactive disturbance phase and the preset offset threshold; The island determination module is used to detect whether the frequency of the distributed power source reaches a preset protection threshold within the maximum allowable island detection time under a unidirectional disturbance, and determine whether an island phenomenon occurs in the distributed power source based on the detection result, wherein reaching the preset protection threshold is an overfrequency protection threshold or an underfrequency protection threshold.

10. An electronic device, characterized in that: It includes one or more processors and a memory, wherein the memory is used to store one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the distributed power supply island detection method as described in any one of claims 1 to 7.

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