A fast island detection method

Abstract

This invention provides a rapid islanding detection method for distributed generation systems. The method is used to detect islanding in distributed generation systems where distributed generation devices interact with the system and loads after being connected to the grid via a grid-connected circuit breaker (DCB). The method involves the distributed generation device (DG) detecting islanding within 2 seconds after the power supply circuit breaker (SCB) disconnects, controlling the DCB to trip, and stopping external energy transmission, thereby protecting the safety of the system's line operation and maintenance. Compared to traditional islanding detection methods, this method has the advantages of not injecting harmonics into the system, thus avoiding power quality degradation, and not requiring additional detection devices, reducing costs. This method can quickly determine whether the system has entered an islanding state by collecting system voltage and device current. This method features fast islanding detection, no other impact on the system, and high accuracy of detection results. It can be widely applied in the field of distributed generation to improve the safety of power generation systems.

Description

Technical Field

[0001] This invention relates to the field of power generation system safety technology, and in particular to a rapid islanding detection method. Background Technology

[0002] The rapid development of new energy sources has led to the widespread application of distributed generation systems worldwide as an effective means of solving energy and environmental problems. The large-scale application of distributed generation helps the power system reduce energy costs, carbon emissions, transmission distances, and transmission losses, while also bringing about significant changes to the distribution network structure.

[0003] The transformation of the distribution network structure and the various access methods of distributed generation systems have brought many hidden dangers to the safe operation and reliable control of the distribution network, such as unplanned islanding. Therefore, islanding detection technology is of great significance to the safe and stable operation of new energy power systems. Summary of the Invention

[0004] To address the technical problems raised in the background section, this invention provides a rapid islanding detection method. This method can quickly determine whether a system has entered an islanding state by collecting system voltage and device current. This method features fast islanding detection, no impact on the system, and high accuracy. It can be widely applied in distributed generation to improve the security of power generation systems.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A rapid islanding detection method is provided. The method is used to detect a distributed generation system. The distributed generation system structure includes a system power supply Us, a system impedance Xs, a distributed generation device DG, an equivalent impedance Xd of the distributed generation device, a user load impedance XL, a grid-connected circuit breaker DCB for the distributed generation device, and a system power supply circuit breaker SCB. After the distributed generation device is connected to the grid through the grid-connected circuit breaker DCB, it interacts with the system and the load for energy exchange.

[0007] The method described is as follows: when the power supply circuit breaker SCB is disconnected, the distributed generation device DG can detect the islanding within 2 seconds, control the grid-connected circuit breaker DCB to trip, stop the external energy transmission, and thus protect the safety of the system line operation and maintenance.

[0008] Furthermore, the rapid island detection method includes the following steps:

[0009] Step 1: First, use a voltage sensor PT to detect the effective value of the bus voltage Uabc and the frequency Freq of the distributed generation unit (DG).

[0010] Step 2: Based on the operating range U1-U2 set according to the effective voltage value, if the effective value of the system voltage Uabc is detected to exceed the operating range for a duration exceeding T1, the islanding protection action is triggered.

[0011] Step 3: Based on the operating range Freq1-Freq2 set by the voltage frequency, if the system voltage frequency Freq is detected to be outside the stable operating frequency range for a duration exceeding T2, the islanding protection action is triggered.

[0012] Step 4: If the protection action is not triggered by the effective voltage value and frequency, perform FFT calculation on the system voltage Uabc and current Iabc to calculate the impedance X1 of the carrier frequency FC of the distributed generation device DG.

[0013] Step 5: If the impedance X1 is greater than the set value A1, the counter Cnt3 starts timing. If the duration exceeds T3, the islanding protection action is triggered; otherwise, the counter Cnt3 is reset to zero.

[0014] Furthermore, the aforementioned triggering of the islanding protection action is to control the DCB circuit breaker of the grid-connected circuit breaker to trip.

[0015] Furthermore, the set value A1 is half of the impedance X1 value calculated under the conditions of stable operation of the distributed generation device DG and the system.

[0016] Furthermore, in the operating range U1-U2 of the effective voltage value setting, U1 is set to 0.80-0.90 pu, or multiple undervoltage thresholds; U2 is set to 1.0-1.5 pu, or multiple overvoltage thresholds.

[0017] Furthermore, the time T1 is set to 0.1-0.3s. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold.

[0018] Furthermore, in the operating range of voltage frequency setting Freq1-Freq2, Freq1 is set to 48.0-49.0Hz, or multiple underfrequency thresholds; Freq2 is set to 50.0-51.0Hz, or multiple overfrequency thresholds.

[0019] Furthermore, time T2 is usually set to 0.1-0.3s. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) The present invention provides a rapid islanding detection method, which can quickly and accurately detect when a distributed generation system enters an islanding state, so as to avoid threatening the life safety of grid maintenance personnel, affecting the operation of protection switches of the power distribution system, and causing damage to electrical equipment when the grid recloses.

[0022] 2) Compared with traditional island detection methods, the present invention has the advantage of not needing to inject harmonics into the system, which would reduce power quality, and not needing to add additional detection devices, thus reducing costs. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the distributed generation system structure of the present invention.

[0024] Figure 2 This is a block diagram of the fast island detection algorithm of the present invention. Detailed Implementation

[0025] The specific embodiments provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the distributed generation system structure includes system power supply Us, system impedance Xs, distributed generation device DG, equivalent impedance of distributed generation device Xd, user load impedance XL, distributed generation device grid-connected circuit breaker DCB and system power supply circuit breaker SCB; after the distributed generation device is connected to the grid through the grid-connected circuit breaker DCB, it interacts with the system and load for energy exchange.

[0027] A rapid islanding detection method is described as follows: when the power supply circuit breaker SCB is disconnected, the distributed generation device DG can detect the islanding within a short time (within 2 seconds), control the grid-connected circuit breaker DCB to trip, and stop the external energy transmission, thereby protecting the safety of system line operation and maintenance.

[0028] like Figure 2 As shown, the fast island detection method of the present invention includes the following steps:

[0029] Step 1: First, use a voltage sensor PT to detect the effective value of the bus voltage Uabc and the frequency Freq of the distributed generation unit (DG).

[0030] Step 2: Based on the operating range U1-U2 set according to the effective voltage value, if the effective value of the system voltage Uabc is detected to exceed the operating range for a duration exceeding T1, the islanding protection action is triggered.

[0031] Step 3: Based on the operating range Freq1-Freq2 set by the voltage frequency, if the system voltage frequency Freq is detected to be outside the stable operating frequency range for a duration exceeding T2, the islanding protection action is triggered.

[0032] Step 4: If the protection action is not triggered by the effective voltage value and frequency, perform FFT calculation on the system voltage Uabc and system current Iabc (detected by the current sensor CT) to calculate the impedance X1 of the carrier frequency FC of the distributed generation device DG.

[0033] Step 5: If the impedance of X1 is greater than the set value A1, the counter Cnt3 starts timing. If the duration exceeds T3, the islanding protection action is triggered; otherwise, the counter Cnt3 is cleared.

[0034] The set value A1 is half of the impedance X1 value calculated under the conditions of stable operation of the distributed generation device (DG) and the system.

[0035] The aforementioned triggering of the islanding protection action is to control the DCB circuit breaker of the grid-connected circuit breaker to trip.

[0036] Within the operating range U1-U2 of the effective voltage value setting, U1 is set to 0.80-0.90 pu, or multiple undervoltage thresholds; U2 is set to 1.0-1.5 pu, or multiple overvoltage thresholds. In this embodiment, U1 is set to 0.85 pu, and U2 is set to 1.1 pu.

[0037] The time T1 is set to 0.1-0.3s. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold. In this embodiment, the time T1 is 0.2s.

[0038] Within the operating range of voltage frequency setting Freq1-Freq2, Freq1 is set to 48.0-49.0Hz, or multiple underfrequency thresholds; Freq2 is set to 50.0-51.0Hz, or multiple overfrequency thresholds. In this embodiment, Freq1 is set to 48.5Hz and Freq2 is set to 50.5Hz.

[0039] The time T2 is typically set to 0.1-0.3 seconds. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold. In this embodiment, the time T2 is 0.2 seconds.

[0040] This invention provides a rapid islanding detection method that can quickly and accurately detect when a distributed generation system enters an islanded state, thus preventing threats to the safety of grid maintenance personnel, interference with the operation of protective switches in the distribution system, and potential damage to electrical equipment during grid reclosing. Compared to traditional islanding detection methods, its advantages include not injecting harmonics into the system, thus avoiding a reduction in power quality, and eliminating the need for additional detection devices, thereby reducing costs.

[0041] The above embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the above embodiments. Unless otherwise specified, the methods used in the above embodiments are conventional methods.

Claims

1. A fast island detection method, characterized in that, The method described above is used to detect a distributed generation system. The distributed generation system structure includes a system power supply Us, a system impedance Xs, a distributed generation device DG, an equivalent impedance Xd of the distributed generation device, a user load-side impedance XL, a grid-connected circuit breaker DCB for the distributed generation device, and a system power supply-side circuit breaker SCB. After the distributed generation device is connected to the grid through the grid-connected circuit breaker DCB, it interacts with the system and the load for energy exchange. The method described is as follows: when the power supply circuit breaker SCB is disconnected, the distributed generation device DG can detect the islanding within 2 seconds, control the grid-connected circuit breaker DCB to trip, stop the external energy transmission, thereby protecting the safety of system line operation and maintenance. Includes the following steps: Step 1: First, use a voltage sensor PT to detect the effective value of the system voltage Uabc and the frequency Freq of the distributed generation unit (DG). Step 2: Based on the operating range U1-U2 set according to the effective voltage value, if the effective value of the system voltage Uabc is detected to exceed the operating range for a duration exceeding T1, the islanding protection action is triggered. Step 3: Based on the operating range Freq1-Freq2 set by the voltage frequency, if the system voltage frequency Freq is detected to be outside the stable operating frequency range for a duration exceeding T2, the islanding protection action is triggered. Step 4: If the protection action is not triggered by the effective voltage value and frequency, perform FFT calculation on the system voltage Uabc and system current Iabc to calculate the impedance X1 of the carrier frequency FC of the distributed generation device DG. Step 5: If the impedance X1 is greater than the set value A1, the counter Cnt3 starts timing. If the duration exceeds T3, the islanding protection action is triggered; otherwise, the counter Cnt3 is reset to zero. The set value A1 is half of the impedance X1 value calculated under the conditions of stable operation of the distributed generation device (DG) and the system.

2. The rapid island detection method according to claim 1, characterized in that, The aforementioned triggering of the islanding protection action is to control the DCB circuit breaker of the grid-connected circuit breaker to trip.

3. The rapid island detection method according to claim 1, characterized in that, Within the operating range U1-U2 of the effective voltage value setting, U1 is set to 0.80-0.90 pu, or multiple undervoltage thresholds; U2 is set to 1.0-1.5 pu, or multiple overvoltage thresholds.

4. The rapid island detection method according to claim 1, characterized in that, The time T1 is set to 0.1-0.3s. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold.

5. The rapid island detection method according to claim 1, characterized in that, Within the operating range of voltage frequency setting Freq1-Freq2, Freq1 is set to 48.0-49.0Hz, or multiple underfrequency thresholds; Freq2 is set to 50.0-51.0Hz, or multiple overfrequency thresholds.

6. The rapid island detection method according to claim 1, characterized in that, The time T2 is usually set to 0.1-0.3s. If there are multiple detection thresholds, different time detection thresholds are set according to each threshold.

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