KR100856715B1 - Islanding Detection Method for Microgrid and its Device - Google Patents

Abstract

A micro grid for detecting the operation status of the micro grid alone in a micro grid, a form of a new distribution network in which the distributed power generation system is integrated and controlled and operated under the condition that the distributed power generation system is sufficiently distributed to cover a certain area of the distribution system. Disclosed are a single driving detection method and an apparatus thereof. The apparatus includes a micro grid connected to a power grid via a breaker and a micro grid energy management system for integrated management of the micro grid in connection with a power grid, the apparatus comprising: a current detector for detecting current flowing through the breaker; A voltage detector for detecting a voltage across the breaker; An AD conversion circuit for converting the current detection signal and the voltage detection signal from the current and voltage detector into a digital signal; Communicatively coupled to the microgrid energy management system, and upon receiving a single operation detection start signal from the microgrid energy management system, the microgrid based on voltage and current detection digital signals from the AD conversion circuit. And a signal processing processor for detecting single operation.

Description

Single detection method for microgrid and its device {Islanding Detection Method for Microgrid and its Device}

1 is a distribution schematic diagram illustrating an example of a general microgrid.

2 is a block diagram showing a single operation detection device for a micro grid according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating the connection between the single operation detection device and the micro grid energy management system shown in FIG. 2.

4 shows a flow chart of a program executed in the microgrid energy management system as part of the flow chart of single operation detection.

5 is a flowchart of a program for detecting single operation in the single operation detection device.

6 and 7 are waveform diagrams of the line voltage and the phase current of the primary side when the power is turned on while the transformer is unloaded.

Fig. 8 is a waveform diagram of the line voltage and the phase current of the primary side with the transformer unloaded.

9 is a logic diagram for explaining a transformer exciting current determination process.

<Description of the symbols for the main parts of the drawings>

1: power system 2: breaker

3: substation transformer 4: high voltage distribution line

5-1, 2, 3: Cutout switch 6: Distribution transformer

7: static breaker 9: wind generator

10, 11: load 12: solar power generation

13-1, 2: Recloser 20: Microgrid System

50: micro grid energy management system

The present invention relates to a single operation detection method and apparatus for a microgrid, and more particularly, to a new power distribution network in which a distributed power generation system is integrated and controlled and operated on the premise that a distributed power supply system is sufficiently supplied to cover a certain area of a power distribution system. The present invention relates to a microgrid single operation detection method and apparatus for detecting a single operation state of a micro grid in a form of a micro grid.

Microgrid is a new type of distribution network in which distributed generation systems using renewable energy sources are integrated and controlled and operated on the premise that they are sufficiently distributed to cover a certain area of the distribution system. Even if a problem occurs on the main distribution line in the microgrid distribution network, the microgrid can stably supply power to important loads through its own power generation. As such, in order for the micro grid to disconnect from the main power distribution network and supply power to the load independently, the micro grid must detect the single operation of the micro grid, and the micro grid is connected to the main power distribution network by using a breaker between the power distribution systems. By separating and allowing the power supply in the microgrid to continue to operate, the power supply reliability in the microgrid can be increased.

Conventional microgrid detection methods can be classified into active and passive methods. Active type outputs an auxiliary signal using a power conversion device and observes the response characteristics of the power system to the output. Passive type simply uses the voltage, current, or frequency information at a measuring point to obtain higher or lower than the specified value. It is a method of detecting a single operation using a detection or a variation.

However, it is pointed out that the active quality deteriorates the power quality by applying an auxiliary signal to the power system, while the passive type has the advantages of simple implementation, low cost, and no disturbance in power quality. When the non-detection area is large and a large number of distributed power supplies are applied, the detection capability is inferior or impossible.

Referring to the passive single operation detection method that is determined to be more related to the present invention in more detail as follows.

The passive single operation detection method includes a voltage detection method and an overfrequency or low frequency detection method. The method of using voltage detection is a method of detecting overvoltage or undervoltage, and when the output of the effective and reactive power of the distributed power supply is close to the load capacity, there is a disadvantage in that the non-detection area is wide due to poor detection capability. In addition, in the case of detecting the overfrequency or the low frequency, as in the above-described voltage detection method, there is a disadvantage in that the non-detection area is widened when the generation amount and the load are close to each other, because the frequency fluctuation becomes small. As a technique to compensate for these problems, there is a method of using the change rate of the output of the distributed power source or the change rate of the frequency, but the change rate is difficult to determine the size, and similarly, the change rate is minute or gradually changes when the generation amount and the load are close. have.

Other passive single operation detection methods include a voltage phase detection method and a voltage harmonic detection method, but these methods may also be applied to the instantaneous phase change of the voltage depending on whether a power system is connected or the magnitude of harmonics included in the voltage. As a method of determining whether there is a power failure, there are problems such as a possibility of malfunction due to load or variation of distributed power output or an excessive amount of calculation.

Accordingly, the present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a single operation detection device and method for a microgrid, which are simpler and more reliable than conventional single operation methods.

The single operation detection device for a micro grid according to the first aspect of the present invention for achieving the above object is a micro grid energy management system for integrated management of the micro grid and the micro grid connected to the power grid through a power grid. 12. A current detector comprising: a current detector for detecting current flowing through the breaker; A voltage detector for detecting a voltage across the breaker; An AD conversion circuit for converting the current detection signal and the voltage detection signal from the current and voltage detector into a digital signal; Communicatively coupled to the microgrid energy management system, and upon receiving a single operation detection start signal from the microgrid energy management system, the microgrid based on voltage and current detection digital signals from the AD conversion circuit. And a signal processing processor for detecting single operation.

Advantageously, said signal processing processor receives a single operation detection start signal from said microgrid energy management system, and wherein the voltage across said breaker is one or more of overvoltage, undervoltage, low frequency and overfrequency, or said voltage or When the variation in the harmonic content of the current is equal to or greater than a predetermined reference value, it is determined that the single operation of the microgrid is detected.

Preferably, the micro grid energy management system generates the single operation detection start signal in preparation for the generation amount and load amount of the micro grid.

According to a second aspect of the present invention, there is provided a method of detecting a single operation of a micro grid, in a micro grid connected to a power grid through a circuit breaker, and a micro grid energy management system integrating and managing the micro grid in connection with a power grid. CLAIMS 1. A method for detecting sole operation of a circuit, the method comprising: detecting a current and a voltage flowing through the breaker, respectively; Receiving a single operation detection start signal from the micro grid energy management system; And when receiving a single operation detection start signal from the micro grid energy management system, detecting single operation of the micro grid based on the voltage and current detected by the detection step.

Preferably, the step of detecting the sole operation of the micro-grid is when the voltage between the circuit breaker is at least one of overvoltage, undervoltage, low frequency and overfrequency, or when the variation in harmonic content of the voltage or current is above a predetermined reference value. Next, it is determined that the single operation of the microgrid is detected.

Preferably, the single operation detection start signal is generated according to the result of the generation and load of the microgrid.

1 is a distribution schematic diagram illustrating an example of a general microgrid.

1 is a diagram illustrating an example of a low-pressure micro grid for protecting a critical load on a campus or a part of an industrial complex of a university.

In general, the distribution voltage of Korea is 22.9kV, but in the case of large-scale customers, there are also ultra-high voltages such as 154kV, and in the case of less than 100kW, low-voltage (220, 380V). If a certain part of the load is expected to cause fatal losses due to voltage fluctuations or power outages, an uninterruptible power supply (UPS) or an emergency generator can be installed and used. This goal can be achieved by constructing a grid.

Referring to FIG. 1, in the case of a low voltage microgrid, a stationary circuit breaker 7 which operates at a high speed on the secondary side of a transformer 6, that is, a distributed power system grid connection point (PCC), is installed and includes an anti-operation device at both ends. By installing a protective relay to detect an accident such as a power outage occurring in the power distribution system to cut off the stationary circuit breaker 7 at a high speed, the distributed power supply (not a commercial power supply) to the loads 10 and 11 of the portion composed of the microgrid 20 is used. 9, 12) to supply power. This operation is called single operation or isolated operation. In this case, the distributed generation amount of the part operated alone must be larger than the load. In case of greater load than the generation amount, the non-critical load can be cut off to supply stable power to the important load. Do it.

On the other hand, as described above, when the system power is restored during the single operation, the microgrid 20 is connected to the power system again, it is necessary to re-inject the load that was interrupted to continue the normal operation. It is necessary to re-synchronize the static circuit breaker by synchronizing the voltage, frequency, and phase of the microgrid that was operated alone with the voltage, frequency, and phase of the power system. Therefore, the microgrid single operation detection device should not only detect single operation but also be able to perform the procedure of returning to grid linked operation again after single operation.

2 is a block diagram showing a single operation detection device 39 for a micro grid according to an embodiment of the present invention.

Referring to FIG. 2, the standalone operation detecting apparatus for a microgrid according to the present invention integrates and manages a microgrid 20 and the microgrid 20 connected to a power grid through a circuit breaker 7. It is associated with a micro grid energy management system 50.

The micro-grid single operation detection device includes a current detector 32, a voltage detector 30 and 31, a filter 33, a buffer 34, an A / D conversion circuit 35, a display and an operation unit 36, and a signal. A processing processor 37, a memory 38, and a communication port 40.

The current detector 32 detects the current flowing through the breaker 7 and provides the detected current to the A / D conversion circuit 35 through the filter 33.

The voltage detectors 30 and 31 detect the voltage across the breaker 7 and provide the detected voltage to the A / D conversion circuit 35 through the filter 33.

The A / D conversion circuit 35 converts the current detection signal and the voltage detection signal from the current and voltage detectors 30, 31, and 32 into digital signals, and converts the converted digital signals into a signal processing processor 37. to provide.

The signal processing processor 37 controls the opening and closing of the breaker 7 through the buffer 34. The signal processing processor 37 is communicatively coupled with the microgrid energy management system 50 via a communication port 40. The signal processing processor 37 receives the voltage from the A / D conversion circuit 35 when receiving the single operation detection start signal from the micro grid energy management system 50 through the communication port 40. And sole operation of the micro grid 20 based on current detection digital signals.

Further, when the signal processing processor 37 receives the single operation detection start signal from the micro grid energy management system 50, the voltage between the circuit breaker 7 is one of overvoltage, undervoltage, low frequency and overfrequency. In the case of abnormality or when the harmonic content of the voltage or current is more than a predetermined reference value, it is determined that the single operation of the microgrid is detected.

On the other hand, the micro grid energy management system 50 will be described in detail below, but generates the single operation detection start signal in preparation for the amount of power generation and load of the micro grid 20.

Hereinafter, with reference to the accompanying drawings, it will be described in more detail the operation of the microgrid alone driving apparatus according to the present invention.

The basic input and output of the single operation detection device 39 according to the present invention are the voltages 30 and 31 and the current 32 across the stationary circuit breaker 7 and the output 41 is the input / disconnect signal of the stationary circuit breaker. First, current and voltage are detected by current detector 32 and voltage detectors 30 and 31, respectively, and these signals are input to analog-to-digital conversion circuit 35 via a filter 33 for noise attenuation. The analog-digital converted value is performed by the signal processing processor 37 to perform arithmetic operations such as an effective value and the like. The detected result is displayed on the display and the operation unit 36, and outputs the closing or breaking signal 41 of the stationary circuit breaker 7 as necessary. In addition, the single operation detection device 39 has a communication port 40 for exchanging information with the microgrid energy management device through which the single operation possibility information is received.

FIG. 3 is a diagram illustrating the connection between the single operation detection device 39 and the micro grid energy management system 50 shown in FIG. 2. The micro grid 20 is characterized by being able to operate independently from the power system, which requires a means for controlling power generation and load demand, and integrated control between them is essential. The subject performing such integrated control and monitoring is the micro grid energy management system 50, and each of the distributed generation systems 9, 10, 60, load groups 11, 12, and standalone operation detection devices 39 This function is performed through linkage of. A detailed control scheme will be described later and an interface scheme with each device or load will be presented here. The micro grid energy management system 50 must first be able to detect the amount of power generation and the amount of load, and the amount of power generation can obtain current generation amount information using the communication linkage 52 with each of the distributed generation devices 9, 10, and 60. The loads 11 and 12 may obtain the information through the electricity meters of the feeders 55 and 56. Therefore, the micro grid energy management system 50 can know the current operation state, that is, the relationship between the amount of power generation and the load amount, and can use this to determine the action to be taken when the single operation state occurs. As a representative measure, when the load is large compared to the amount of power generation, the power may be discharged from the energy storage device 61 in the microgrid 20, and the load 12 which is not important may be cut off. It is also possible to issue commands to control the power quality in stand-alone operation, that is, active power and reactive power for maintaining voltage and frequency.

4 shows a flowchart of a program executed in the microgrid energy management system 50 as part of the flowchart of the single operation detection.

When the program is started (70), first, the power generation amount and load amount which are the current operating states are received from each distributed power source (9, 10, 60) and the load (11, 12).

The difference between the amount of power generated and the amount of load is calculated and examined whether it is within a predetermined set value (for example, 5% of the rating of the total microgrid) (72).

If the difference is smaller than the set value, since the operation area is likely to be operated alone, the start time is checked (73), and when a predetermined time elapses, the single operation detection start command is set (75).

Then, the release time is set to 0 (76) so that the release is delayed. If it is larger than the set value (77), the release time is checked to release the single operation detection (78), and when the predetermined time has elapsed, the detection is released (80), and the start time for the next detection start is set to 0 ( 81).

The detection start or release information of the single operation is transmitted to the single operation detection device 39 (82) and returns to the beginning (83) to repeat execution. The reason for the time check for starting and releasing the single operation detection is to avoid unnecessarily changing the detection mode.

5 is a flowchart of a program for detecting single operation in the single operation detection device.

First, the overvoltage or undervoltage 90 is detected and one of the two cases (92) and the low frequency or the overfrequency (91) are detected and one of the two cases (93) is considered. If abnormality occurs (94), it is determined that there is a possibility of single operation.

Up to this point, it is the same as the method of the conventional single operation detection device, but the following procedure becomes a special matter of the present invention. Next, when the harmonic content of the voltage and current is detected and the value is above the set value (95) or when one of the above voltage-frequency abnormality detections (96) occurs, it is determined that the operation is a single operation. It is determined (99) that only the operation 98 is detected when the grid energy management system 50 simultaneously meets the detection start 97 condition sent out.

As such, the reason for applying the complex algorithm is that any existing detection algorithm has its disadvantages. In particular, when power generation and load are very close to each other in the event of a power failure, the voltage and frequency fluctuation hardly occur or progress too slowly. This is because a single operation cannot be detected by a change in voltage and frequency within a desired time, and in the case of harmonic detection, it is difficult to distinguish between generation of harmonics by a load and generation of harmonics by a distributed power supply. Furthermore, unnecessarily detecting single operation when the system power is sound and shutting off the power may result in deterioration of power quality. Therefore, activate this function only in the operating area where single operation may occur. Can be prevented.

6 is an oscillogram of the line voltage and the phase current of the primary side when the power is turned on under no load, and when the power is turned on (112), the transformer terminal voltage 110 remains constant, but the starting current of the transformer remains constant. As indicated by the numeral 111 in FIG. 6, the value is changed over time. However, the transient current at the time of power supply of the transformer is not necessarily the waveform as shown in FIG. 6, but may appear as shown in FIG.

When the power is turned on, the starting current 123 changes with time, but not the same as the starting current 111 of FIG. 6. That is, when the portion A 121 of the starting current 123 of FIG. 7 is enlarged (122), as shown below in FIG. 7, the DC component is small and the AC component is large.

8 is a no-load current waveform of a steady state measured after the transient time has elapsed as shown in FIGS. 6 and 7, and it can be seen that the waveform is a distorted waveform that is distinguished from a sine wave. A detailed detection method is shown in FIG. 9 to distinguish the characteristics of the current waveform from the load current.

FIG. 9 illustrates an algorithm for detecting a quiescent current of a transformer among currents detected by a single operation detection device. The three components are obtained through the direct current component detection 130, the third harmonic component detection 131, and the crest factor calculation 132. Only when the condition is satisfied at the same time (133) is determined as the no-load current of the transformer (95). The detection of DC current, the detection of third harmonic and the calculation of crest factor are as follows.

In this case, after calculating the DC component of the current, the magnitude of the third harmonics, and the crest factor, the load current is equal to or higher than the reference value obtained from the excitation current waveform of a typical transformer. It is determined that contains the exciting current of the transformer.

Therefore, according to the above configuration, a sensor for detecting a voltage and a current is installed at both ends of the breaker of the power grid connection point (PCC) of the microgrid and observes the current and the state of the voltage to cut out the power in the high voltage distribution line. Detect an accident. In addition, the detection method does not depend on one method such as observing fluctuations in voltage and frequency or using harmonic state information, but adds a method of observing a quiescent current waveform of a distribution transformer to these existing methods. The non-detection area is narrowed by detecting single operation. In other words, a power distribution transformer for stepping down the distribution high voltage to low voltage is used to supply power to the low voltage microgrid. Usually, the primary side becomes the extra high voltage (22.9 kV) and the secondary side low voltage becomes 220/380 V. Even when no load is connected to the secondary side, no-load current (magnetization current) flows.However, if the recloser is shut off due to a ground fault in a special high-voltage distribution line, the primary side of the transformer becomes a no-pressure state and the secondary side is a microgrid. The magnetization current flows by the distributed power supply in the magnetization current, and the magnetization current has a current waveform of a form different from that of the load current. Detected status information of single operation is sent to the microgrid operating system and grid connection breaker to isolate the breaker and immediately disconnect the microgrid from the power distribution system.The microgrid operating system provides the defined voltage and frequency of distributed power supplies in the microgrid. The control command will be sent to maintain. In order to reconnect to the power system again according to the power system restoration, the microgrid that has been operated alone requires a synchronous re-entry function, which is also provided by the single operation detection device according to the present invention.

Therefore, the present invention has the following effects.

First, according to the present invention, independent operation can be detected independently regardless of the type of distributed power supply or the number of connections of the distributed power supply.

Second, in connection with the micro grid operating system, it is possible to continuously supply power to critical loads in the micro grid even in the event of power failure in the distribution system, thereby improving the reliability of power.

Third, by applying the passive single operation detection technique, the detection quality of the single operation is improved because the non-detection zone (NDZ) is narrower than the existing single operation detection algorithm without affecting the power quality.

Fourth, the present invention checks the possibility of single operation by always detecting the generation amount of distributed power supply and the load in the micro grid using the communication function in the micro grid, and performs the single operation detection function only in the deduction operation where the single operation may occur. By activating it, it is possible to prevent unnecessary malfunctions in advance, thereby improving the quality of power and improving the utilization of distributed power.

As described above, according to the present invention, it is possible to realize a single-grid operation detection device for a microgrid and a method thereof that are simpler and more reliable than the conventional single operation.

Although the present invention has been described in detail by the above embodiments, the present invention is not limited thereto, and variations and improvements can be made without departing from the ordinary knowledge of those skilled in the art.

Claims (8)

delete In the micro grid connected to the power grid via a circuit breaker and the micro grid energy management system for integrated management in connection with the power grid, A current detector for detecting current flowing through the breaker; A voltage detector for detecting a voltage across the breaker; An AD conversion circuit for converting the current detection signal and the voltage detection signal from the current and voltage detector into a digital signal; Communicatively coupled to the microgrid energy management system, and upon receiving a single operation detection start signal from the microgrid energy management system, the microgrid based on voltage and current detection digital signals from the AD conversion circuit. A signal processing processor for detecting single operation, The signal processing processor Receives an independent operation detection start signal for the generation amount and load amount of the micro grid from the micro grid energy management system, and the voltage between the received signal and the circuit breaker is one of overvoltage, undervoltage, low frequency and overfrequency The single operation detection device for microgrids is characterized in that it is determined that the single operation of the microgrid has been detected at the same time or when the change in the harmonic content of the voltage or current is equal to or greater than a predetermined reference value. 3. The signal processing processor of claim 2, wherein the signal processing processor is

Single operation detection device for a micro grid, characterized in that to calculate the harmonic content of the current according to the above formulas. delete delete In a micro grid connected to a power grid through a circuit breaker and a micro grid energy management system integrating and managing the micro grid in connection with the power grid, A method for detecting the sole operation of the micro grid, Detecting current and voltage flowing through the breaker, respectively; Receiving a single operation detection start signal from the micro grid energy management system; And When receiving a single operation detection start signal from the micro grid energy management system, detecting single operation of the micro grid based on the voltage and current detected by the detecting step, Detecting alone operation of the micro grid When the voltage between the circuit breaker is at least one of overvoltage, undervoltage, low frequency and overfrequency, or when the change in harmonic content of the voltage or current is above a predetermined reference value, and the amount of generation of the microgrid from the microgrid energy management system And determining that single operation of the micro grid has been detected when simultaneously satisfying the case of receiving the single operation detection start signal in preparation for the load amount. 7. The method of claim 6, wherein calculating the harmonic content of the current

A method for detecting single operation of a micro grid, characterized in that performed according to the above formulas. delete

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