CN115078905A - Rapid island detection method - Google Patents

Abstract

The invention provides a fast islanding detection method. The method is used to detect a distributed power generation system, and the distributed power generation device performs energy interaction with the system and the load after being connected to the grid through the grid-connected circuit breaker DCB; the method is: when After the circuit breaker SCB at the power supply side is disconnected, the distributed generation device DG can detect the entry into the island within 2s, control the DCB of the grid-connected circuit breaker to open, and stop the external energy transmission, thereby protecting the safety of system line operation and maintenance. Compared with the traditional island detection method, its advantage is that there is no need to inject harmonics into the system, resulting in a reduction in power quality, no need to add additional detection devices, and lower costs. The method can quickly determine whether the system enters the island state by collecting the system voltage and device current. The method has the advantages of fast island detection speed, no other influence on the system, and high detection result accuracy. It can be widely used in the field of distributed power generation to improve the safety of the power generation system.

Description

A Fast Island Detection Method

technical field

The invention relates to the technical field of power generation system safety, in particular to a fast island detection method.

Background technique

The rapid development of new energy has made distributed power generation systems widely used around the world as an effective means to solve energy and environmental problems. The large-scale application of distributed power generation can help power systems reduce energy costs and reduce carbon emissions. Shorten the transmission distance, reduce the transmission loss, and at the same time have a great change in the structure of the distribution network.

The transformation of the distribution network structure and the multiple access methods of the distributed generation system have brought many hidden dangers to the safe operation and reliable control of the distribution network, such as unplanned islands. Therefore, the island detection technology is very important for the safe and stable operation of the new energy power system. has a very significant meaning.

SUMMARY OF THE INVENTION

In order to solve the technical problem raised by the background art, the present invention provides a fast islanding detection method, which can quickly determine whether the system enters the islanding state by collecting the system voltage and device current. The method has the advantages of fast island detection speed, no other influence on the system, and high detection result accuracy. It can be widely used in the field of distributed power generation to improve the safety of the power generation system.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

A fast island detection method, the method is used to detect a distributed power generation system, the structure of the distributed power generation system includes a system power supply Us, a system impedance Xs, a distributed power generation device DG, an equivalent impedance of the distributed power generation device Xd, and a user load. Terminal impedance XL, distributed generation device grid-connected circuit breaker DCB and system power end circuit breaker SCB; distributed generation device interacts with system and load after grid-connected through grid-connected circuit breaker DCB;

The method is as follows: when the power supply side circuit breaker SCB is disconnected, the distributed power generation device DG can detect entering the island within 2s, control the grid-connected circuit breaker DCB to open, and stop the external energy transmission, thereby protecting the system line operation. dimensional security.

Further, the described rapid island detection method comprises the following steps:

Step 1: First, the effective value of the bus voltage Uabc and the frequency Freq of the distributed generation device DG are detected by the voltage sensor PT;

Step 2: According to the operating range U1-U2 set by the RMS voltage, when it is detected that the RMS value of the system voltage Uabc exceeds the operating range and the duration exceeds T1, the islanding protection action is triggered;

Step 3. According to the operating range Freq1-Freq2 set by the voltage frequency, when it is detected that the system voltage frequency Freq exceeds the frequency range that can be stably operated and the duration exceeds T2, the islanding protection action is triggered;

Step 4. If the protection action cannot be triggered by the effective value of the voltage and the frequency, perform FFT calculation on the system voltage Uabc and current Iabc, and 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 cleared.

Further, the triggering of the islanding protection action is to control the grid-connected circuit breaker DCB to open.

Further, the set value A1 is 1/2 of the value of the impedance X1 calculated under the stable operating conditions of the distributed power generation device DG and the system.

Further, in the operating range U1-U2 set by the voltage effective value, U1 is set to 0.80-0.90pu, or multiple undervoltage thresholds; U2 is set to 1.0-1.5pu, or multiple overvoltage thresholds.

Further, 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.

Further, in the operating range Freq1-Freq2 set by the voltage and frequency, Freq1 is set to 48.0-49.0 Hz, or multiple under-frequency thresholds; Freq2 is set to 50.0-51.0 Hz, or multiple over-frequency thresholds.

Further, 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.

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

1) A fast islanding detection method of the present invention can quickly and accurately detect that the distributed power generation system has entered the islanding state, so as to avoid threats to the life safety of power grid maintenance personnel, affect the protection switch action of the power distribution system, and power grid coincidence. It may cause damage to electrical equipment.

2) Compared with the traditional island detection method, the present invention has the advantage of not needing to inject harmonics into the system, resulting in a reduction in power quality, without adding additional detection devices, and reducing costs.

Description of drawings

FIG. 1 is a schematic structural diagram of a distributed power generation system of the present invention.

FIG. 2 is a block diagram of the fast island detection algorithm of the present invention.

Detailed ways

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

As shown in Figure 1, the structure of the distributed power generation system includes the system power supply Us, the system impedance Xs, the distributed power generation device DG, the equivalent impedance of the distributed power generation device Xd, the user load end impedance XL, and the grid-connected circuit breaker DCB of the distributed power generation device. And the circuit breaker SCB at the power supply side of the system; the distributed generation device interacts with the system and the load after being connected to the grid through the grid-connected circuit breaker DCB;

A fast island detection method, the method is as follows: when the power supply side circuit breaker SCB is disconnected, the distributed power generation device DG can detect entering the island in a short time (within 2s), and control the grid-connected circuit breaker DCB to open, Stop external energy transmission to protect the safety of system line operation and maintenance.

As shown in Figure 2, the rapid island detection method of the present invention comprises the following steps:

Step 1: First, the effective value of the bus voltage Uabc and the frequency Freq of the distributed generation device DG are detected by the voltage sensor PT;

Step 2: According to the operating range U1-U2 set by the RMS voltage, when it is detected that the RMS value of the system voltage Uabc exceeds the operating range and the duration exceeds T1, the islanding protection action is triggered;

Step 3. According to the operating range Freq1-Freq2 set by the voltage frequency, when it is detected that the system voltage frequency Freq exceeds the frequency range that can be stably operated and the duration exceeds T2, the islanding protection action is triggered;

Step 4. If the protection action cannot be triggered by the RMS voltage and frequency, perform FFT calculation on the system voltage Uabc and the system current Iabc (detected by the current sensor CT), and calculate the impedance X1 of the carrier frequency FC of the distributed generation device DG. ;

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.

The set value A1 is 1/2 of the value of the impedance X1 calculated under the stable operation condition of the distributed power generation device DG and the system.

The triggering of the islanding protection action is to control the grid-connected circuit breaker DCB to open.

In the operating range U1-U2 set by the voltage RMS, U1 is set to 0.80-0.90pu, or multiple undervoltage thresholds; U2 is set to 1.0-1.5pu, or multiple overvoltage thresholds. In this embodiment, U1 is set to 0.85pu, and U2 is set to 1.1pu.

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.

In the operating range Freq1-Freq2 set by the voltage and frequency, Freq1 is set to 48.0-49.0Hz, or multiple underfrequency thresholds; Freq2 is set to 50.0-51.0Hz, or multiple overclock thresholds. In this embodiment, Freq1 is set to 48.5 Hz, and Freq2 is set to 50.5 Hz.

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. In this embodiment, the time T2 is 0.2s.

The rapid islanding detection method of the present invention can quickly and accurately detect that the distributed power generation system enters the islanding state, so as to avoid threats to the life safety of power grid maintenance personnel, affect the protection switch action of the power distribution system, and the possibility of power grid reclosing. cause damage to electrical equipment. Compared with the traditional islanding detection method, its advantage is that it does not need to inject harmonics into the system, resulting in the reduction of power quality, no need to add additional detection devices, and lower costs.

The above embodiments are implemented on the premise of the technical solutions of the present invention, and provide detailed embodiments and specific operation processes, but the protection scope of the present invention is not limited to the above-mentioned embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims (8)

1. a fast island detection method, is characterized in that, described method is used for detecting distributed generation system, and distributed generation system structure comprises system power supply Us, system impedance Xs, distributed generation device DG, distributed generation device etc. Effective impedance Xd, user load end impedance XL, distributed generation device grid-connected circuit breaker DCB and system power end circuit breaker SCB; distributed generation device interacts with the system and load after grid-connected through the grid-connected circuit breaker DCB; The method is as follows: when the power supply side circuit breaker SCB is disconnected, the distributed power generation device DG can detect entering the island within 2s, control the grid-connected circuit breaker DCB to open, and stop the external energy transmission, thereby protecting the system line operation. dimensional security. 2. a kind of fast island detection method according to claim 1, is characterized in that, comprises the steps: Step 1: First, detect the effective value of the system voltage Uabc and the frequency Freq of the distributed power generation device DG through the voltage sensor PT; Step 2: According to the operating range U1-U2 set by the RMS voltage, when it is detected that the RMS value of the system voltage Uabc exceeds the operating range and the duration exceeds T1, the islanding protection action is triggered; Step 3. According to the operating range Freq1-Freq2 set by the voltage frequency, when it is detected that the system voltage frequency Freq exceeds the frequency range that can be stably operated and the duration exceeds T2, the islanding protection action is triggered; Step 4. If the protection action cannot be triggered by the effective value of the voltage and the frequency, perform FFT calculation on the system voltage Uabc and the system current Iabc, and calculate the impedance X1 of the carrier frequency FC of the distributed power 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 cleared. 3 . A fast islanding detection method according to claim 2 , wherein the triggering of the islanding protection action is to control the grid-connected circuit breaker DCB to open. 4 . 4. A fast islanding detection method according to claim 2, wherein the set value A1 is 1/1 of the calculated impedance X1 value under the stable operation condition of the distributed generation device DG and the system 2. 5. A kind of fast islanding detection method according to claim 2, is characterized in that, in the operating range U1-U2 that the voltage effective value is set, U1 is set to 0.80-0.90pu, or is a plurality of undervoltage thresholds; U2 is set to 1.0-1.5pu, or multiple overvoltage thresholds. 6 . A fast island detection method according to claim 2 , wherein the time T1 is set to 0.1-0.3s, and if there are multiple detection thresholds, different time detection thresholds are set according to each threshold. 7 . 7. A fast islanding detection method according to claim 2, characterized in that, in the operating range Freq1-Freq2 set by the voltage frequency, Freq1 is set to 48.0-49.0Hz, or multiple under-frequency thresholds; Freq2 Set to 50.0-51.0Hz, or multiple overclocking thresholds. 8 . A fast island detection method according to claim 2 , wherein the time T2 is usually set to 0.1-0.3s, and if there are multiple detection thresholds, different time detection thresholds are set according to each threshold. 9 .

Images