An active island detection method for energy storage grid-connected inverters
By using the hardware architecture of the energy storage inverter to verify low-intensity reactive power disturbances and frequency direction consistency, the problems of blind spots and high false positive rates in islanding detection are solved, and fast and reliable islanding detection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI BOKE ELECTRONICS CO LTD
- Filing Date
- 2026-01-21
- Publication Date
- 2026-06-12
AI Technical Summary
Existing islanding detection methods have problems such as detection blind spots, impact on power quality, and high false alarm rates. In particular, it is difficult to detect islanding status quickly and reliably when energy storage inverters are connected to the grid.
The hardware architecture of the energy storage inverter is adopted. Through the frequency sampling module, reactive power disturbance injection module and grid-connected switch control module, low-intensity reactive power disturbance injection, frequency difference judgment and directional consistency verification are realized. Combined with a multi-cycle counter, the accuracy of detection is ensured.
It achieves micro-disturbances that do not affect power quality under normal operating conditions, quickly detects suspected islanding and reduces the false alarm rate through multi-dimensional verification, and adapts to different power levels and complex operating conditions.
Smart Images
Figure CN121602379B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of safe operation technology for grid-connected energy storage inverters, specifically to an active islanding detection method for grid-connected energy storage inverters. Background Technology
[0002] In distributed generation systems (such as photovoltaic energy storage power stations), the energy storage inverter, as the core power conversion device, is responsible for converting the DC power of the energy storage unit into AC power and connecting it to the grid. When the grid unexpectedly loses power due to faults, maintenance, or other reasons, if the energy storage inverter fails to detect and disconnect in time, it will continue to supply power to local loads, forming an unplanned "island." This islanding state can cause inrush currents that damage equipment when the grid restores power, and also poses a risk of electric shock to grid maintenance personnel. Therefore, islanding detection is a core safety technology for the grid-connected operation of energy storage inverters.
[0003] Existing island detection methods are mainly divided into two categories: passive detection methods and active detection methods, but both have obvious drawbacks:
[0004] Passive detection methods identify islanding by monitoring abnormal changes in grid voltage, frequency, harmonics, and other parameters. However, their fatal flaw is the existence of a "detection blind zone"—when the output power of the energy storage inverter is close to matching the local load power, the grid parameters change only slightly after islanding occurs, failing to trigger threshold protection and causing detection failure. Furthermore, this method has difficulty distinguishing between normal grid disturbances and islanding, making it prone to misjudgment.
[0005] Active detection methods inject specific disturbance signals into the power grid, utilizing the grid's rigidity to cancel out disturbances and the amplification of disturbances in islanded states to achieve detection. Traditional active detection methods use fixed-intensity disturbances, which have two major problems: first, continuous disturbances increase grid harmonics and degrade power quality; second, when multiple inverters are operating in parallel, disturbance signals interfere with each other, leading to system instability or false detections. Furthermore, traditional active detection methods only determine islanding based on the magnitude of the disturbance feedback, without verifying the correlation between disturbance and response, making them susceptible to misjudgments due to grid transient fluctuations, load abrupt changes, and other factors.
[0006] Compared with patent [1] (application number 202310987046.6), which adopts a combination of passive and active methods, its active judgment only depends on the magnitude of the disturbance feedback, without verification of direction and period consistency, and is easily interfered with; the passive judgment requires additional impedance measurement and current effective value detection, and the process is complicated. Compared with patent [2] (application number 201810282965.2), which uses a fixed disturbance, has poor adaptability, and judges by a single mathematical operation, which has weak anti-interference ability. Compared with patent [3] (application number 202210894019.X), which does not introduce disturbance-response correlation verification, the misjudgment rate is high in complex scenarios.
[0007] In summary, existing technologies cannot simultaneously address the speed, power quality, and reliability of island detection, necessitating a proactive island detection method with strong adaptability and low false positive rate. Summary of the Invention
[0008] This invention aims to solve the problems of blind spots in passive detection methods and the impact on power quality and high false positive rate of traditional active detection methods in the prior art. It provides an active islanding detection method for grid-connected energy storage inverters, which achieves the goal of "ensuring power quality under normal operating conditions with minor disturbances, improving detection speed for suspected islanding with strong disturbances, and reducing false positive rate through multi-dimensional verification".
[0009] The technical solution of this invention is based on the hardware architecture of an energy storage inverter (including a frequency sampling module, a reactive power disturbance injection module, and a grid-connected switch control module) to implement the technical method: control the hardware module to perform technical actions such as "disturbance injection, frequency acquisition, direction verification, and protection action", and finally solve the technical problem of islanding detection through hardware actions.
[0010] An active islanding detection method for an energy storage grid-connected inverter includes the following steps:
[0011] S1: Initialize settings, clear all status flags and counters, set detection threshold, disturbance period and islanding judgment conditions, and enable islanding detection function; counters include suspected islanding counter, islanding confirmation counter, waiting response counter, recovery counter, forward counter and reverse counter, all with initial values set to 0; disturbance period is set to 1s / time;
[0012] S2: Real-time detection of the operating mode and fault status of the energy storage inverter. Proceed to the next step only when the operating mode is grid-connected, there are no high-priority faults, and the islanding detection function is enabled. High-priority faults include DC-side overvoltage faults, AC-side overcurrent faults, and power module hardware faults. The presence of high-priority faults is determined by reading the fault word register of the energy storage inverter.
[0013] S3: Inject low-intensity reactive power disturbances into the grid at fixed intervals, which are adapted to the current active power. The intensity of the low-intensity reactive power disturbances is dynamically adjusted with the current active power, and the adjusted disturbances will not cause the grid voltage harmonic distortion rate to exceed the limit specified in GB / T14549 "Power Quality - Harmonics in Public Power Grids". At the same time, the periodic disturbance counter is started. The intensity of the low-intensity reactive power disturbances is positively correlated with the current active power output of the energy storage inverter. The higher the active power, the greater the disturbance intensity.
[0014] S4: Continuously collect the current frequency and historical frequency of the power grid voltage, and calculate the absolute value of the frequency difference;
[0015] S5: Determines whether the absolute value of the frequency difference is greater than the preset frequency deviation threshold. The frequency deviation threshold is 0.045Hz. Applicable to 130KW energy storage grid-connected inverters.
[0016] If not, start the recovery counter to decrement. When the recovery counter reaches the set value, clear the suspected island counter and return to step S4.
[0017] If so, increment the suspected island counter, increase the reactive power disturbance intensity according to the size of the suspected island counter, and proceed to step S6;
[0018] S6: Determine if the suspected island counter has reached the first preset number of times. The first preset number of times is 6.
[0019] If not, return to step S4;
[0020] If so, clear the reactive power disturbance, load the wait response counter and decrement it until the wait response counter reaches zero;
[0021] S7: Detect the grid frequency jump value after the disturbance is cleared, and verify whether the frequency jump direction is consistent with the previous reactive power disturbance direction; record the number of times the frequency jump direction is too high using a forward counter, and the number of times the frequency jump direction is too low using a reverse counter; if the injected reactive power disturbance direction is "to make the frequency too high", then the direction is determined to be consistent only when the forward counter count increases; if the disturbance direction is "to make the frequency too low", then the direction is determined to be consistent only when the reverse counter count increases.
[0022] S8: If the frequency jump value is greater than the preset jump threshold and the direction is consistent, increment the island confirmation counter; otherwise, return to step S5. The preset jump threshold is 0.1998Hz.
[0023] S9: Determine if the island confirmation counter has reached the second preset number of times. The second preset number of times is set to 3.
[0024] If not, return to step S4;
[0025] If so, the system is determined to be in islanded mode, triggering a protection action to disconnect the energy storage inverter from the grid.
[0026] S10: After the protection action is executed, delay for a preset time, clear all status flags and counters, update the current frequency to the latest power grid frequency and store it as a historical frequency, and return to step S2 to re-enter the detection loop.
[0027] In a preferred embodiment of the present invention, in step S3, the number of disturbances in one disturbance cycle is 24, and the duration of a single disturbance is 20ms.
[0028] In a preferred embodiment of the present invention, in step S6, the initial loading value of the waiting response counter is 6, corresponding to 6 frequency sampling periods.
[0029] In a preferred embodiment of the present invention, the preset delay time in step S10 is 5s.
[0030] By adopting the above technical solution, the present invention has the following beneficial effects:
[0031] 1. Adaptive Disturbance Strength: The reactive power disturbance strength is related to the current active power. During normal grid connection, only a small disturbance is injected to avoid affecting power quality. When islanding is suspected, the disturbance is automatically amplified by accumulating the number of disturbances, which accelerates frequency shift.
[0032] 2. Directional Consistency Verification: The direction of frequency jump is recorded by a forward / reverse counter. Only when the jump direction is consistent with the direction of disturbance is it considered a valid response, thus eliminating grid fluctuation interference.
[0033] 3. Multi-cycle confirmation: By using a dual counting system of suspected island counter (first set number of times) and island confirmation counter (second set number of times), random fluctuations are filtered out to ensure reliable test results.
[0034] 4. No detection blind spots: Automatically enhances disturbances in suspected islanded states, and can quickly trigger frequency shift even in power-matched scenarios, completely eliminating detection blind spots.
[0035] 5. Ensure power quality: During normal grid connection, use small disturbances that match the active power to avoid harmonic pollution caused by continuous strong disturbances, while taking into account both detection needs and grid stability.
[0036] 6. Low false positive rate: Through triple screening of "frequency deviation threshold judgment + direction consistency verification + multi-cycle counting confirmation", it effectively filters interference from non-islanded scenarios such as power grid transient fluctuations and load changes.
[0037] 7. High adaptability: The disturbance intensity is dynamically adjusted with the active power, which can be adapted to energy storage inverters of different power levels and complex grid connection conditions. Attached Figure Description
[0038] Figure 1 : Schematic diagram of the enable condition judgment for the island detection function of this invention;
[0039] Figure 2 : Schematic diagram of the logic for judging the increasing intensity of reactive power disturbance in this invention;
[0040] Figure 3 : A schematic diagram of the perturbation-response direction consistency verification logic of this invention;
[0041] Figure 4: Schematic diagram of reactive power disturbance and frequency response waveforms of this invention;
[0042] Figure 5 : A schematic diagram of the specific process of this invention. Detailed Implementation
[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0044] Example 1
[0045] This embodiment uses a 130kW energy storage grid-connected inverter as the test object:
[0046] like Figure 1-5 As shown, a specific embodiment of the active islanding detection method for an energy storage grid-connected inverter according to the present invention includes:
[0047] Step S1 (Initialization): After starting the energy storage inverter, clear all counters (set to 0) including the forward counter (PosCnt), reverse counter (NegCnt), suspected islanding counter (SumCnt), islanding confirmation counter (TripCnt), wait-to-respond counter (HopCnt), and recovery counter (RecoverCnt). Clear the "disturbance injection flag" and "islanding confirmation flag". Set the preset frequency deviation threshold to 0.045Hz, the first set number of times to 6, the second set number of times to 3, the initial value of the wait-to-respond counter to 6, and the set value of the recovery counter to 3. Enable the islanding detection function.
[0048] Steps S2 and S3, refer to Figure 1 The details are as follows:
[0049] Step S2 (Mode and Fault Determination): Read the operating mode and fault word through the inverter control unit. If the current mode is grid-connected, there are no high-priority faults such as overvoltage / overcurrent / hardware faults, and the islanding detection enable signal is high, proceed with the detection process; otherwise, continue to wait until the conditions are met.
[0050] Step S3 (Periodic Small Disturbance Injection): Set the "Disturbance Injection Flag" and inject reactive power disturbance at a fixed period of 1 second / time. The disturbance intensity is set according to the current active power. When the active power is 130KW, the disturbance intensity is 0.2%. At the same time, the periodic disturbance counter decrements (initial value 24, after decrementing to 0, the injection is paused once).
[0051] Steps S4, S5, and S6, refer to Figure 2 The details are as follows:
[0052] Step S4 (Frequency Sampling and Difference Calculation): The grid voltage frequency is collected in real time through the voltage frequency sampling unit, the current frequency (CurrLineFreq) and the historical frequency (oldGridLineFreq) are stored, and the absolute value of the difference between the two is calculated.
[0053] Step S5 (deviation threshold judgment): If the difference is ≤ preset frequency deviation threshold of 0.045Hz (normal power grid fluctuation), the recovery counter (RecoverCnt) decrements by itself. When the recovery counter decrements to the set value of 0, the suspected island counter (SumCnt) is cleared and the process returns to step S4 for continuous sampling. If the difference is > 0.045Hz (abnormal fluctuation), the suspected island counter (SumCnt) increments by 1.
[0054] Step S6 (Suspected Island Determination): If the suspected island counter (SumCnt) is less than the first set number of times 6 (not reaching the suspected threshold), return to step S4; if the suspected island counter (SumCnt) is greater than or equal to 6 (6 consecutive abnormalities), clear the "disturbance injection flag" to stop the disturbance, load the wait response counter (HopCnt=6) and decrement it, decrementing by 1 in each sampling period until HopCnt=0 (waiting for frequency response delay).
[0055] Steps S7, S8, and S9, refer to Figure 3 The details are as follows:
[0056] Step S7 (Directional Consistency Verification): After the response counter decreases to 0, collect the frequency jump value after clearing the disturbance. Record the number of high jumps using the forward counter (PosCnt) and the number of low jumps using the reverse counter (NegCnt) to verify whether the jump direction is consistent with the previous disturbance direction. If the jump value is greater than the preset jump threshold of 0.1998Hz and the direction is consistent, proceed to step S8; otherwise, return to step S5.
[0057] Step S8 (Confirmation Count): The island confirmation counter (TripCnt) increments by 1 to record the number of valid confirmations.
[0058] Step S9 (Final Islanding Determination): If the islanding confirmation counter (TripCnt) is less than or equal to the second set number of times 2, return to step S4 to continue the detection; if TripCnt > 2 (3 consecutive valid confirmations), it is determined to be an island, and the protection action of disconnecting the grid-connected switch is triggered.
[0059] Step S10 (Fault Reset): After the protection action is executed, delay for 5 seconds to wait for the power grid to recover, clear all counters and flags, update the current frequency (CurrLineFreq) to the latest power grid frequency and store it as the historical frequency (oldGridLineFreq), and return to step S2 to re-enter the detection loop.
[0060] While the specific embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and modifications or variations without creative effort are still within the protection scope of the present invention.
Claims
1. An active islanding detection method for an energy storage grid-connected inverter, characterized in that, Includes the following steps: S1: Initialization settings, clear status indicators and count data that affect detection accuracy, avoid historical data from interfering with detection results, set detection threshold, disturbance period and island determination conditions, and enable island detection function; S2: Real-time detection of the operating mode and fault status of the energy storage inverter. Proceed to the next step only when the operating mode is grid-connected, there are no high-priority faults, and the islanding detection function is enabled. S3: Inject reactive power disturbances adapted to the current active power into the power grid at fixed intervals. The intensity of the reactive power disturbances is dynamically adjusted according to the current active power, and a periodic disturbance counter is started at the same time. S4: Continuously collect the current frequency and historical frequency of the power grid voltage, and calculate the absolute value of the frequency difference; S5: Determine if the absolute value of the frequency difference is greater than the preset frequency deviation threshold. If not, start the recovery counter to decrement. When the recovery counter reaches the set value, clear the suspected island counter and return to step S4. If so, increment the suspected island counter, increase the reactive power disturbance intensity according to the size of the suspected island counter, and proceed to step S6; S6: Determine if the count of the suspected island counter has reached the first preset number: If not, return to step S4; If so, clear the reactive power disturbance, load the wait response counter and decrement it until the wait response counter reaches zero; S7: Detect the grid frequency jump value after the zeroing disturbance, and verify whether the frequency jump direction is consistent with the previous reactive power disturbance direction; S8: If the frequency jump value is greater than the preset jump threshold and the direction is consistent, increment the island confirmation counter; otherwise, return to step S5. S9: Determine if the island confirmation counter has reached the second preset number of times. If not, return to step S4; If so, the system is determined to be in islanded mode, triggering a protection action to disconnect the energy storage inverter from the grid. S10: After the protection action is executed, delay for a preset time, clear all status flags and counters, update the current frequency to the latest power grid frequency and store it as a historical frequency, and return to step S2 to re-enter the detection loop.
2. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S1, the counters include a suspected island counter, an island confirmation counter, a wait-for-response counter, a recovery counter, a forward counter, and a reverse counter, all with initial values set to 0; the disturbance period is set to 1 second / time.
3. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S2, the high-priority faults include DC-side overvoltage faults, AC-side overcurrent faults, and power module hardware faults. The presence of a high-priority fault is determined by reading the fault word register of the energy storage inverter.
4. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S3, the reactive power disturbance is a low-intensity reactive power disturbance, and the intensity of the low-intensity reactive power disturbance is positively correlated with the active power currently output by the energy storage inverter.
5. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S3, the number of disturbances in one disturbance cycle is 24, and the duration of a single disturbance is 20ms.
6. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S5, the preset frequency deviation threshold is 0.045Hz, which is applicable to a 130KW energy storage grid-connected inverter.
7. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S6, the first set number of times is 6 times; in step S9, the second set number of times is 3 times.
8. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S6, the initial loading value of the waiting response counter is 6, corresponding to 6 frequency sampling periods.
9. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S7, the number of times the frequency transition direction is too high is recorded by a forward counter, and the number of times the frequency transition direction is too low is recorded by a reverse counter.
10. The active islanding detection method for a grid-connected energy storage inverter according to claim 1, characterized in that: In step S8, the preset transition threshold is 0.1998Hz; in step S10, the preset delay time is 5s.