An island identification method based on detecting injection voltage ratio

Abstract

A method for island identification by detecting the ratio of injected voltage belongs to the technical field of active island detection. It is characterized by comprising the following steps: step 1001, monitoring voltage and current signals; step 1002, judging whether there is a pre-synchronization signal injected by other island detection devices in the system; step 1003, judging whether the degree of voltage waveform distortion of the system exceeds a set threshold; step 1004, judging whether the voltage positive zero crossing is captured; step 1005, injecting a synchronization signal; step 1006, judging whether the voltage positive zero crossing is captured; step 1007, injecting an island identification signal; step 1008, calculating the voltage ratio; step 1009, judging whether it is in an island operation state; step 1010, issuing a tripping command. In the island identification method for detecting the ratio of injected voltage, the bus voltage is used as a reference for synchronous signal injection. With the assistance of the pre-synchronization injection signal, it is ensured that each distributed power source injects the island detection signal at the same time, thereby improving the reliability of the measurement result.

Description

Technical Field

[0001] The invention discloses an island identification method for detecting an injection voltage ratio, belonging to the technical field of active island detection. Background Art

[0002] Distributed power sources connected to the distribution network need to be equipped with anti-islanding protection function to avoid the formation of unplanned islands in the distribution lines due to power outages, endangering the personal safety of maintenance personnel, and affecting the automatic reclosing and power supply quality. At present, there are two main types of anti-islanding protection applied to distributed power sources: passive method and active method. The passive method realizes the protection function by monitoring whether the voltage, frequency and other electrical quantities of the distributed power supply grid connection point (PoC) are out of limit. The principle is simple, easy to deploy, and does not affect the power supply quality. However, there is a detection blind spot in principle, and it is easy to malfunction when the power grid is disturbed. The active method is divided into frequency\power disturbance method and impedance measurement method. The former injects frequency / power disturbance signals to promote the protection of electrical quantities such as frequency and voltage when the island is out of limit; the latter realizes protection by injecting signals to measure the changes in system impedance. The active method effectively improves the detection blind spot problem of the passive method, and the impedance measurement method is increasingly concerned because of its small voltage disturbance and not easy to malfunction. However, the signal injection strategy and protection criterion of the impedance measurement method in a multi-distributed power system are difficult to effectively deal with the protection failure problem caused by mutual interference of the injected signals.

[0003] In order to solve the signal interference problem of impedance measurement method, current research focuses on three aspects: coordinated injection signal between devices, centralized injection signal at the point of common connection (PCC), and synchronous injection signal of each distributed power source. Although some progress has been made, the effect is still not ideal. At the same time, the impact of the change in the number of distributed power sources on the injection signal and island protection criteria is rarely mentioned.

[0004] The impedance measurement method generally injects a current signal of a specific frequency through a distributed power source, and solves the system impedance based on the voltage response generated by the system, thereby determining whether it is currently operating in an island state. However, in a multi-distributed power system, the signal injection time of each distributed power source is relatively independent, resulting in mutual interference between signals, making it impossible for the distributed power source to accurately measure the impedance of the system. Fig.15 Take the medium voltage distribution line with two distributed power sources and its equivalent circuit as an example. Fig.15 In the figure, T1 is a transformer, and distributed power source 1 and distributed power source 2 are distributed power sources with the ability to inject island detection signals in the distribution line. Fig.16 Middle Z G is the grid impedance, which is mainly composed of the leakage impedance of transformer T1, Z L is the equivalent impedance of the load in the system, They are the island detection signals injected into the system by distributed generation 1 (DG1) and distributed generation 2 (DG2); for The voltage response generated on the system impedance. Then the measured impedance Z when the distributed power source 1 is connected to the grid grid1 The measured impedance Z when isolated island1 for:

[0005]

[0006] The above formula shows that the measured impedance of distributed generation 1 (DG1) depends not only on the grid-connected and islanded operation status, but also on the phasor relationship of the injected signals between distributed generation sources. Island Time Grid-connected and island-connected and The phasor relationship of Z grid1 With Z island1 They are:

[0007]

[0008] Since the signal injection process of each distributed power source is relatively independent, there is a certain uncertainty in the amplitude and phase relationship between the signals. Therefore, in the above formula The value of is arbitrary, so that Z grid1 With Z island1 The measurement results are randomly distributed in a circular area, such as Fig.17 As shown. Among them, Z grid1 With Z island1 The intersection between the distribution areas makes it impossible for the distributed power source to identify the grid-connected and islanded states based on the measured impedance, resulting in the failure of the method.

[0009] At the same time, the relatively independent signal injection strategy of each distributed power source makes it difficult to achieve the ideal effect of impedance measurement. Therefore, an external synchronization signal is introduced into the distributed power source, so that each distributed power source can realize synchronous signal injection and island detection under the same time reference benchmark. Fig.15 The equivalent circuit of the distribution line shown in the figure is as follows: Fig.18 As shown, at this time, each distributed power source can simultaneously inject a current signal with the same amplitude and phase for island detection, that is:

[0010]

[0011] Under the conditions shown in the above formula, the grid-connected measurement impedance Z of distributed generation 1 (DG1) grid1 With island measurement impedance Z island1 Then:

[0012]

[0013] If the above formula is extended to a power distribution system containing n distributed power sources, the measured impedance of distributed power source 1 is:

[0014]

[0015] The coefficient n in the above formula is determined by the number of distributed power sources actually operating in the system, and causes the amplitude of the measured impedance to change continuously with the input and output of distributed power sources in the system, making it difficult to directly use the impedance criterion for island identification.

[0016] In the prior art: A Chinese invention patent with application number 202211227393.0, application date October 9, 2022, and patent name "A method for island detection based on signal collaborative injection" discloses a technical solution, in which it is proposed to use 25Hz interharmonic modulated industrial frequency current signal to realize synchronous injection of island detection signal based on voltage synchronization, but this method does not mention the synchronization problem of the 25Hz modulation signal of each distributed power source, and the coded pulse therein is only used to calibrate the strength of the island detection signal, and cannot solve the synchronous injection of the signal.

[0017] The Chinese invention patent with application number 201911096482.4, application date November 11, 2019, and patent name "A microgrid non-destructive island detection method based on harmonic current injection and harmonic impedance measurement", and the Chinese invention patent with application number 201711353275.3, application date December 15, 2017, and patent name "Island detection system and detection method based on interharmonic impedance", respectively disclose technical solutions that propose a method for island detection by measuring the rate of change of impedance amplitude during grid connection and islanding. The present method uses the voltage response ratio of the system power frequency voltage and the detection signal on the system impedance during islanding and grid connection to identify the island, and does not involve the issue of impedance change rate.

[0018] In summary, the prior art generally has the following defects:

[0019] (1) Difficulty in synchronous signal injection: Whether introducing an external synchronization signal or using a voltage signal as the synchronous injection time of a distributed power supply island detection signal, it is impossible to ensure that the distributed power supplies in the system inject signals at the same time.

[0020] (2) Difficulty in setting the criteria: The complex operating environment of the distribution network and the operation of the island detection device make it difficult for the existing impedance criterion design method to give a unified island identification criterion.

[0021] (3) Difficulty in signal extraction: The island detection signal is much smaller than the power frequency signal in the system, and the existing methods are difficult to propose the influence of the power frequency signal without affecting the detection signal. Summary of the invention

[0022] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide an island identification method for detecting the injection voltage ratio, which uses the bus voltage as a reference for signal synchronous injection and, with the assistance of a pre-synchronous injection signal, ensures that each distributed power source injects an island detection signal at the same time, thereby improving the reliability of the measurement result.

[0023] The technical solution adopted by the present invention to solve the technical problem is: the island identification method for detecting the injection voltage ratio is characterized by comprising the following steps:

[0024] Step 1001, real-time monitoring of voltage and current signals in the system, and recording and storing the sampled data;

[0025] Step 1002, determining whether there is a pre-synchronization signal injected by other island detection devices in the system, if yes, executing step 1007, if no, executing step 1003;

[0026] Step 1003, determining whether the voltage waveform distortion of the system exceeds a set threshold, if so, executing step 1004, if not, returning to step 1001;

[0027] Step 1004, determine whether the voltage is captured to be positively crossing zero, if the voltage is captured to be positively crossing zero, execute step 1005, if the voltage is not captured to be positively crossing zero, continue to execute this step;

[0028] Step 1005, the pre-synchronization signal is a one-cycle high-frequency sinusoidal voltage signal, and the injection is completed when the system voltage zero crossing point is captured;

[0029] Step 1006, determining whether the voltage is positively crossing zero, if the voltage is positively crossing zero, executing step 1007, if the voltage is not positively crossing zero, continuing to execute this step;

[0030] Step 1007, when the device completes the injection of the pre-synchronization signal, or detects the pre-synchronization signal injected by other devices, injects the island identification signal at the positive zero crossing point of the voltage captured subsequently;

[0031] Step 1008, capturing voltage and current detection signals, and completing the calculation of the voltage ratio;

[0032] Step 1009, determine whether it is in an island operation state; if it is in an island operation state, execute step 1010; if it is not in an island operation state, return to step 1001;

[0033] Step 1010: issue a trip command to control the distributed power source to exit operation.

[0034] Preferably, step 1007 includes the following steps:

[0035] Step 1007-1, the device completes the injection of the pre-synchronization signal, or captures the pre-synchronization signal injected by other devices;

[0036] Step 1007-2, determine whether the voltage zero-crossing point is captured, if captured, execute step 1007-3, if not captured, continue to execute step 1007-2;

[0037] Step 1007-3, complete the phase calculation of the island identification signal through the internal crystal oscillator: θ t2 (n) = θ t2 (n-1)ω2Δt,

[0038] Where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, and ω2 is the angular frequency of the injected signal;

[0039] Step 1007-4: if the power frequency current amplitude of the line where the device is located is I0, generate and inject an island identification signal i s1 (n) = I p1 sin(θ t2 (n)), where I p1 =kI0, and 0.05≤k≤0.1;

[0040] Step 1007 - 5 , when the signal injection of three cycles is completed, the island identification signal injection procedure ends.

[0041] Preferably, step 1005 includes the following steps:

[0042] Step 1005-1, after the controller captures the voltage zero crossing point, it completes the phase angle calculation of the pre-synchronized injection signal through the internal crystal oscillator: θ t1 (n) = θ t1 (n-1)ω1Δt,

[0043] Where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, ω1 is the angular frequency of the injected signal, and ω1 / 2π>300Hz;

[0044] Step 1005-2: If the current system voltage amplitude is U0, then set the injection signal amplitude to U p1 =m1U0, and m1>0.1;

[0045] Step 1005-3, generate and inject a pre-synchronization injection signal: u s1 (n) = U p1 sin(θ t1 (n));

[0046] Step 1005-4, after completing one cycle signal injection, the pre-synchronization signal injection ends.

[0047] Preferably, step 1008 includes the following steps:

[0048] Step 1008-1, detection signal extraction;

[0049] Step 1008-2, generating a voltage prediction signal;

[0050] Step 1008 - 3 , calculating the voltage ratio λ.

[0051] Preferably, step 1008-2 includes the following steps:

[0052] Step 1008-2-1, collect the system power frequency voltage u o ;

[0053] Step 1008-2-2, system power frequency voltage u o Connect to the phase-locked loop to give the angular frequency ω of the current system voltage;

[0054] Step 1008-2-3, the angular frequency ω is calculated by integrating θg=∫ωdt to obtain the phase angle θg of the current system voltage;

[0055] Step 1008-2-4, obtaining the predicted voltage cosine waveform cos(θg) of the current voltage signal through cosine calculation;

[0056] Step 1008-2-5, system voltage modulus |u o | and predicted system voltage modulus value |u m The difference e of | is introduced into the PID controller to find the current predicted voltage amplitude U m ;

[0057] Step 1008-2-6, the current predicted voltage amplitude U m The product of the predicted voltage cosine waveform cos(θg) is the current predicted voltage u m ;

[0058] Step 1008-2-7, extracting island identification signal u e =u0-u m .

[0059] Preferably, step 1008-3 includes the following steps:

[0060] Step 1008-3-1, the injection device configures the current island identification signal strength coefficient k;

[0061] Step 1008-3-2: the injection device collects the current on the current line

[0062] Step 1008-3-3, setting the current island identification signal strength

[0063] Step 1008-3-4, using the DFT algorithm to identify the voltage island signal u e The island detection voltage signal strength is obtained from

[0064] Step 1008-3-5, using the DFT algorithm to obtain the power frequency voltage signal strength from the acquired system power frequency voltage u0

[0065]

[0066] Step 1008-3-6, obtain voltage ratio

[0067] Preferably, when executing step 1009, the basis for determining whether the voltage ratio λ is in the island operation state is:

[0068]

[0069] When λ is equal to 1, it is determined to be in an island operation state, and when λ is much less than 1, it is determined to be in a grid-connected operation state. are the power frequency current flowing through the injection device, are the island identification signals injected by the injection devices respectively, for The voltage response produced across the system impedance is To obtain the power frequency voltage signal strength from the acquired system power frequency voltage u0, Z Load It is the total load after all loads are equivalent.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] 1. In the island identification method for detecting the injection voltage ratio, the bus voltage is used as the reference benchmark for the synchronous signal injection. With the assistance of the pre-synchronous injection signal, it is ensured that each distributed power source injects the island detection signal at the same time, thereby improving the reliability of the measurement result.

[0072] 2. In the island identification method for detecting the injection voltage ratio, the power frequency signal prediction technology is used to effectively filter out the power frequency component in the detection signal, thereby ensuring the quality of the detection signal and the reliability of the island identification result.

[0073] 3. In the island identification method for detecting the injected voltage ratio, the proposed voltage ratio identification criterion does not depend on the system's operating environment and the number of island detection devices involved, which improves the universality of the method and is easy to promote and apply.

[0074] 4. Use phase-locked loop and PID control to predict the power frequency signal in the system, and use the difference between the predicted signal and the actual signal to accurately extract the island detection signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 Flowchart of the island identification method for detecting the injection voltage ratio.

[0076] Figure 2 Generate schematic for pre-synchronized injection signal.

[0077] Figure 3 Schematic diagram for signal generation for islanding identification.

[0078] Figure 4 Schematic diagram of the detection signal extraction process.

[0079] Figure 5 Schematic diagram of the voltage prediction signal generation process.

[0080] Figure 6 Design schematic for voltage ratio criterion.

[0081] Figure 7 Schematic diagram of the integrated signal injection and measurement device.

[0082] Figure 8 Schematic diagram of independent measurements for common connection points.

[0083] Fig. 9 Schematic diagram of the integrated signal injection and measurement device for island protection at distributed power sources.

[0084] Fig.10 Schematic diagram of the integrated signal injection and measurement device for island protection at the common connection point.

[0085] Fig.11 Schematic diagram of the hardware structure of an independent measuring device.

[0086] Fig.12 Schematic diagram of the integrated signal injection and measurement device for island protection at distributed power sources.

[0087] Fig.13 Schematic diagram of the integrated signal injection and measurement device for island protection at the common connection point.

[0088] Fig.14 This is a functional block diagram of an independent measuring device controller.

[0089] Fig.15 The figure is a medium voltage power distribution circuit diagram containing two distributed power sources in the prior art.

[0090] Fig.16 for Fig.15 Equivalent circuit diagram of .

[0091] Fig.17 The impedance Z is measured when the distributed power source is connected to the grid in the prior art. grid1 With islanding, the impedance Z is measured island1 Schematic diagram of the distribution characteristics of .

[0092] Fig.18 The equivalent circuit diagram of two distributed power distribution lines connected to the synchronization signal in the prior art. DETAILED DESCRIPTION

[0093] Figures 1 to 18 The best embodiment of the present invention is shown below in conjunction with the attached Figures 1 to 18 The present invention is further described.

[0094] like Figure 1 As shown, an island identification method for detecting an injection voltage ratio (hereinafter referred to as the island identification method) comprises the following steps:

[0095] Step 1001, sampling and recording voltage and current signals;

[0096] The device monitors the voltage and current signals in the system in real time, and records and stores the sampled data.

[0097] Step 1002: whether a pre-synchronization injection signal is detected;

[0098] It is determined whether there is a pre-synchronization signal injected by other island detection devices in the system. If yes, step 1007 is executed; if no, step 1003 is executed.

[0099] Step 1003, determining whether the voltage distortion exceeds a threshold;

[0100] It is determined whether the voltage waveform distortion degree of the system exceeds a set threshold value. If it exceeds the set threshold value, step 1004 is executed; if it does not exceed the set threshold value, the process returns to step 1001.

[0101] Step 1004, determining whether the capture voltage is positively crossing the zero point;

[0102] Determine whether the voltage is captured to be positively crossing zero. If the voltage is captured to be positively crossing zero, execute step 1005. If the voltage is not captured to be positively crossing zero, continue to execute this step.

[0103] Step 1005, injecting a synchronization signal;

[0104] The pre-synchronization signal is a high-frequency sinusoidal voltage signal with one cycle. The injection is completed when the system voltage zero crossing point is captured. The pre-synchronization signal injection process is as follows: Figure 2 As shown, the specific steps include:

[0105] Step 1005-1, after the controller captures the voltage zero crossing point, it completes the phase angle calculation of the pre-synchronized injection signal with the help of the internal crystal oscillator: θ t1 (n) = θ t1 (n-1)ω1Δt, where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, ω1 is the angular frequency of the injected signal, and ω1 / 2π>300Hz;

[0106] Step 1005-2: If the current system voltage amplitude is U0, then set the injection signal amplitude to U p1 =m1U0, and m1>0.1;

[0107] Step 1005-3, generate and inject a pre-synchronization injection signal: u s1 (n) = U p1 sin(θ t1 (n));

[0108] Step 1005-4, after completing one cycle signal injection, the pre-synchronization signal injection ends.

[0109] Step 1006, determining whether the capture voltage is positively crossing the zero point;

[0110] Determine whether the voltage is captured to be positively crossing zero. If the voltage is captured to be positively crossing zero, execute step 1007. If the voltage is not captured to be positively crossing zero, continue to execute this step.

[0111] Step 1007, injecting an island identification signal;

[0112] When the device completes the injection of the pre-synchronization signal, or detects the pre-synchronization signal injected by other devices, the island identification signal is injected at the positive zero crossing point of the subsequently captured voltage, such as Figure 3 As shown, the generation of the island identification signal specifically includes the following steps:

[0113] Step 1007-1, the device completes the injection of the pre-synchronization signal, or captures the pre-synchronization signal injected by other devices;

[0114] Step 1007-2, determine whether the voltage zero-crossing point is captured, if captured, execute step 1007-3, if not captured, continue to execute step 1007-2;

[0115] Step 1007-3, with the help of the internal crystal oscillator, complete the phase calculation of the island identification signal θ t2(n) = θ t2 (n-1)+ω2Δt, where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, ω2 is the angular frequency of the injected signal, and ω2 / 2π=75 Hz;

[0116] Step 1007-4: if the power frequency current amplitude of the line where the device is located is I0, generate and inject an island identification signal i s1 (n) = I p1 sin(θ t2 (n)), where I p1 =kI0, and 0.05≤k≤0.1;

[0117] Step 1007 - 5 , when the signal injection of three cycles is completed, the island identification signal injection procedure ends.

[0118] Step 1008, calculating the voltage ratio;

[0119] Capture voltage and current detection signals and complete the calculation of system voltage ratio, which includes the following steps:

[0120] Step 1008-1, detection signal extraction;

[0121] When extracting the detection signal from the system voltage and current signal, it is necessary to filter out the interference of the power frequency component in the original signal. The traditional filter will introduce greater interference into the detection signal while filtering out the power frequency signal. Therefore, a detection signal extraction method based on power frequency signal prediction is designed. Taking the extraction of voltage island identification signal as an example, the extraction process is as follows: Figure 4 shown. Figure 4 System voltage prediction signal u m The generation of a single-phase signal phase-locked loop and a PID controller are required to track the system voltage in real time. Figure 5 shown.

[0122] Step 1008-2, generating a voltage prediction signal;

[0123] The specific process is as follows:

[0124] Step 1008-2-1, collect the system power frequency voltage u o ;

[0125] Step 1008-2-2, system power frequency voltage u o Connect to the phase-locked loop to give the angular frequency ω of the current system voltage;

[0126] Step 1008-2-3, the angular frequency ω is calculated by integrating θg=∫ωdt to obtain the phase angle θg of the current system voltage;

[0127] Step 1008-2-4, obtaining the predicted voltage cosine waveform cos(θg) of the current voltage signal through cosine calculation;

[0128] Step 1008-2-5, system voltage modulus |u o | and predicted system voltage modulus value |u m The difference e of | is introduced into the PID controller to find the current predicted voltage amplitude U m ;

[0129] Step 1008-2-6, the current predicted voltage amplitude U m The product of the predicted voltage cosine waveform cos(θg) is the current predicted voltage u m ;

[0130] Step 1008-2-7, extracting island identification signal u e =u0-u m .

[0131] Step 1008 - 3 , calculating the voltage ratio.

[0132] The operation status of the island detection device in the actual operation system will change continuously. Therefore, the amplitude of the injection signal of each island detection device will affect the island identification, making the traditional impedance amplitude criterion unable to be applied to island identification. Therefore, a voltage ratio identification criterion is designed. Fig.15 The system shown is taken as an example. Figure 6 In the example, the power frequency currents flowing through the injection devices 1 and 2 are The island identification signals injected are According to the generation process of the island identification signal, the island identification signal injected by the injection device 1 and 2 must meet for The voltage response generated in the system impedance. Island Time Z Load It represents the total load after all loads are equivalent, and Zs is the grid impedance.

[0133] The specific steps include:

[0134] Step 1008-3-1, the injection device 1 configures the current island identification signal strength coefficient k;

[0135] Step 1008-3-2: the injection device collects the current on the current line

[0136] Step 1008-3-3, setting the current island identification signal strength

[0137] Step 1008-3-4, using the DFT algorithm to identify the voltage island signal u e The island detection voltage signal strength is obtained from

[0138] Step 1008-3-5, using the DFT algorithm to obtain the power frequency voltage signal strength from the acquired system power frequency voltage u0

[0139]

[0140] Step 1008-3-6, obtain voltage ratio

[0141] Step 1009, determining whether it is in an island operation state;

[0142] Step 1009, determine whether it is in an island operation state, and the determination basis is:

[0143]

[0144] That is, when λ is approximately equal to 1, it is determined to be in an island operation state, and when λ is much less than 1 (such as less than 0.5), it is determined to be in a grid-connected operation state. If it is in an island operation state, execute step 1010, and if it is not in an island operation state, return to step 1001.

[0145] Step 1010: issue a trip command to control the distributed power source to exit operation.

[0146] As an island protection solution for distributed power sources or public connection points, considering the diversity of actual on-site needs, its specific implementation method will be different in different application scenarios. The following is a further explanation of the island protection examples in several typical scenarios from three aspects: device configuration method, implementation scheme and its judgment criteria.

[0147] (1) Application scenarios. The core of this island identification method consists of two modules: signal injection and voltage ratio calculation. When the two functional modules are combined into a single integrated application, it can be inherited from the existing distributed power supply as part of the control to achieve the island protection of the distributed power supply, or it can be installed as an independent device at the common connection point to complete the island protection of the common connection point. Figure 7 The two installation points 1 and 2 are shown in the figure. Alternatively, the island detection device can be installed only at the common connection point, and the signal injection can be completed by the local distributed power supply. The two cooperate with each other to realize the protection of the common connection point, such as Figure 8 shown.

[0148] (2) Hardware Example: Since this island identification method includes two steps: signal injection and island detection, its specific hardware configuration will vary in different application scenarios.

[0149] 1) When signal injection and island detection are integrated into a single device, the existing mainstream inverter configuration scheme can be used whether it is used as distributed power supply island protection or to achieve island protection of public connection points, such as Figures 9-10 As shown. The controller needs to collect the inductor current i of the inverter circuit labc , output current i oabc And output voltage u oabc , and gives the corresponding switch tube PWM drive signal, as well as the circuit breaker drive signal for island protection. The difference is that the distributed power supply island protection drives the grid-connected switch, and the common connection point protection drives the circuit breaker at the common connection point.

[0150] 2) If the island detection is completed only at the common connection point, the controller only needs to measure the voltage u inside the circuit breaker oabc and current i oabc , and give the driving signal of the circuit breaker, such as Fig.11 shown.

[0151] (3) Software examples.

[0152] The functions of the island protection at the distributed power source and the common connection point are similar when the signal is injected. The only difference is that the island protection of the distributed power source needs to superimpose the injection signal for island detection on its original power frequency control command. Figure 12-13 For an island protection device that only implements island detection at the common connection point, its control function only needs to complete island detection and implement island protection action based on the voltage and current signals measured at the access point. Fig.14 shown.

[0153] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. An island identification method for detecting an injection voltage ratio, characterized in that: The steps include: Step 1001, real-time monitoring of voltage and current signals in the system, and recording and storing the sampled data; Step 1002, determining whether there is a pre-synchronization signal injected by other island detection devices in the system, if yes, executing step 1007, if no, executing step 1003; Step 1003, determining whether the voltage waveform distortion of the system exceeds a set threshold, if so, executing step 1004, if not, returning to step 1001; Step 1004, determine whether the voltage is captured to be positively crossing zero, if the voltage is captured to be positively crossing zero, execute step 1005, if the voltage is not captured to be positively crossing zero, continue to execute this step; Step 1005, the pre-synchronization signal is a one-cycle high-frequency sinusoidal voltage signal, and the injection is completed when the system voltage zero crossing point is captured; Step 1006, determining whether the voltage is positively crossing zero, if the voltage is positively crossing zero, executing step 1007, if the voltage is not positively crossing zero, continuing to execute this step; Step 1007, when the device completes the injection of the pre-synchronization signal, or detects the pre-synchronization signal injected by other devices, injects the island identification signal at the positive zero crossing point of the voltage captured subsequently; Step 1008, capturing voltage and current detection signals, and completing the calculation of the voltage ratio; Step 1009, determine whether it is in an island operation state; if it is in an island operation state, execute step 1010; if it is not in an island operation state, return to step 1001; Step 1010, issuing a trip command to control the distributed power source to exit operation; Step 1007 includes the following steps: Step 1007-1, the device completes the injection of the pre-synchronization signal, or captures the pre-synchronization signal injected by other devices; Step 1007-2, determine whether the voltage zero-crossing point is captured, if captured, execute step 1007-3, if not captured, continue to execute step 1007-2; Step 1007-3, complete the phase calculation of the island identification signal through the internal crystal oscillator: θ t2 (n) = θ t2 (n-1)ω2Δt, Where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, and ω2 is the angular frequency of the injected signal; Step 1007-4: if the power frequency current amplitude of the line where the device is located is I0, generate and inject an island identification signal i s1 (n) = I p1 sin(θ t2 (n)), where I p1 =kI0, and 0.05≤k≤0.1; Step 1007-5, when the signal injection of three cycles is completed, the island identification signal injection procedure ends; Step 1008 includes the following steps: Step 1008-1, detection signal extraction; Step 1008-2, generating a voltage prediction signal; Step 1008-3, calculating the voltage ratio λ; Step 1008-2 includes the following steps: Step 1008-2-1, collect the system power frequency voltage u o ; Step 1008-2-2, system power frequency voltage u o Connect to the phase-locked loop to give the angular frequency ω of the current system voltage; Step 1008-2-3, the angular frequency ω is calculated by integrating θg=∫ωdt to obtain the phase angle θg of the current system voltage; Step 1008-2-4, obtaining the predicted voltage cosine waveform cos(θg) of the current voltage signal through cosine calculation; Step 1008-2-5, system voltage modulus |u o | and predicted system voltage modulus value |u m The difference e of | is introduced into the PID controller to find the current predicted voltage amplitude U m ; Step 1008-2-6, the current predicted voltage amplitude U m The product of the predicted voltage cosine waveform cos(θg) is the current predicted voltage u m ; Step 1008-2-7, extracting island identification signal u e =u0-u m ; Step 1008-3 includes the following steps: Step 1008-3-1, the injection device configures the current island identification signal strength coefficient k; Step 1008-3-2: the injection device collects the current on the current line Step 1008-3-3, setting the current island identification signal strength Step 1008-3-4, using the DFT algorithm to identify the voltage island signal u e The island detection voltage signal strength is obtained from Step 1008-3-5, using the DFT algorithm to obtain the power frequency voltage signal strength from the acquired system power frequency voltage u0 Step 1008-3-6, obtain voltage ratio 2. The island identification method for detecting the injection voltage ratio according to claim 1, characterized in that: Step 1005 includes the following steps: Step 1005-1, after the controller captures the voltage zero crossing point, it completes the phase angle calculation of the pre-synchronized injection signal through the internal crystal oscillator: θ t1 (n) = θ t1 (n-1)ω1Δt, Where n is the nth sampling or control cycle of the device, Δt is the duration of a single sampling or control cycle inside the controller, ω1 is the angular frequency of the injected signal, and ω1 / 2π>300Hz; Step 1005-2: If the current system voltage amplitude is U0, then set the injection signal amplitude to U p1 =m1U0, and m1>0.1; Step 1005-3, generate and inject a pre-synchronization injection signal: u s1 (n) = U p1 sin(θ t1 (n)); Step 1005-4, after completing one cycle signal injection, the pre-synchronization signal injection ends.

3. The island identification method for detecting the injection voltage ratio according to claim 1, characterized in that: When executing step 1009, the basis for determining whether the voltage ratio λ is in an island operation state is: When λ is equal to 1, it is determined to be in an island operation state, and when λ is much less than 1, it is determined to be in a grid-connected operation state. are the power frequency current flowing through the injection device, are the island identification signals injected by the injection devices respectively, for The voltage response produced across the system impedance is To obtain the power frequency voltage signal strength from the acquired system power frequency voltage u0, Z Load It is the total load after all loads are equivalent.

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