KR101904821B1 - MICROGRID SYSTEM and TROUBLE PROCESSING METHOD thereof - Google Patents

Abstract

The microgrid system of the present invention includes a plurality of distributed power sources; Multiple distributed loads; Lines connecting the distributed power sources and the distributed loads; And a controller for controlling operations of the distributed power supplies, the micro grid system comprising:
At least one of the distributed power sources includes a shutoff means for converting power generated by the power generation device into AC power suitable for the microgrid and supplying the generated power to the microgrid and cutting off the connection to the microgrid in an abnormal situation Active PCS. When the micro-grid detects a failure, the control apparatus gradually increases the voltage output from the active PCS and performs the process for the failure.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a micro grid system and a micro-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a micro grid system for performing a failure process and a failure handling method using the same, more specifically, to a system and a method for shortening a power failure time for a non- .

The microgrid is a small-scale power supply system consisting of distributed power (solar power, wind power, etc.), battery (power storage device) and so on. The micro grid operates normally in a linked operation mode in which power is traded in connection with a large-scale power system. In the event of a fault in the power company's line, the micro grid can be switched to a stand-alone operation mode in which power is supplied separately from the power system. It is mainly installed in buildings, university campuses, factories, etc., and aims to reduce electricity costs and improve reliability of power supply. On the other hand, in the case of a micro grid installed in a remote area such as a book area, it can be operated by constructing a system with its own loads without linking with an external power system.

To improve power supply reliability, one of the objectives of microgrid installation, microgrid must be operated uninterruptedly. In the event of a fault in the power system, it should be accurately detected and the upper power system and the micro grid should be separated quickly. In addition, if a fault occurs in the micro grid, it is necessary to quickly separate only the relevant part to prevent power failure. On the other hand, the magnitude and direction of the fault current vary depending on the connection state of the micro grid and the power system, the connection state of each distributed power source, the fault occurrence position, and the fault occurrence pattern. However, existing circuit breakers (MCCB, ACB, etc.) and failure handling methods can not adequately respond to various types of failures occurring in the micro grid, and local failures can affect the entire micro grid, resulting in a total power failure. In particular, this causes frequent inconveniences in micro grid systems installed in island areas having independent systems.

FIG. 11 shows a conventional power supply system using a distributed power supply 40 according to the prior art. 11, a power supply system for a healthy section using a distributed power supply 40 includes an IED 100 for distribution automation, an IED 200 for distributed power supply, and a central management unit 300. [

The IED 100 for distribution automation measures the voltage and current of the distribution line, and when a line accident occurs in the distribution system, the line incident event is transmitted to the central management apparatus 300 so that the distribution automation system operator can analyze it .

Once the temporary fault has occurred, the IED 100 for distribution automation decides the failure of the power distribution system and the direction of the fault current from the fault current. If it is judged that the fault has occurred, the IED 100 informs the central management apparatus 300 of FI (Fault Indicator) send.

The central management apparatus 300 determines a failure section based on the failure information provided from the distribution automation IEDs 100 and temporarily transmits the operation command to the IED 100 for distribution automation. The distribution automation IED 100 performs the failure handling procedure by performing the control of the switch 30 and transmitting the result to the central management unit 300. [

That is, the IED 100 for distribution automation measures the overcurrent of the distribution line and blocks the line through the protection device 20 of the circuit breaker or the recloser, When the negative terminal becomes non-voltage, the failure of the distribution line is detected through the switch. In addition, the control unit 300 controls the closing / opening of the switches based on the control signal of the central management apparatus 300, thereby controlling the failure section to be separated from the power distribution system.

When a failure occurs in the distribution line, the distribution automation IED 100 transmits the failure occurrence information to the distributed power source IED 200, and the distributed power source IED 200 transmits power to the healthy section through the distributed power source 40 To be supplied.

Furthermore, the distribution automation IED 100 measures the average load current with respect to the load end existing between the distributed power source 40 and the distribution automation IED 100. The average load current can be calculated by measuring the load current to the load stage for a predetermined time. The information calculated by the distribution automation IED 100 is transmitted to the distributed power source IED 200, and when the distribution system is out of order, the distributed power source 40 is used to calculate the average power consumed by the time- It can be used as data for estimating the amount of power to be supplied through the network.

The IED 200 for distributed power supply is connected to the distributed power supply 40 to estimate the amount of power that the distributed power supply 40 can supply to the system when the power distribution system fails. The IED 200 for the distributed power source can calculate the amount of power based on the power generation amount of the distributed power source 40 and the battery storage amount.

The distributed power supply IED 200 is connected to the distribution automation IED 100 in a peer-to-peer manner to grasp the amount of power consumed in the distribution line connected to the distributed power supply 40, And receives the occurrence information.

Further, when the failure occurrence and the fault algae information are received from the distribution automation IED 100, it is possible to grasp the healthy section where unnecessary power failure is experienced due to the failure, and to control the switch between the distributed power source 40 and the grid, Allow power to be supplied to the healthy section.

The IED (200) for distributed power supply analyzes fault information included in the fault information and identifies the fault section or identifies the fault occurrence section through identification information of the distribution automation IED (100) for transmitting the fault information It can be recognized.

The central management apparatus 300 monitors the overall system and analyzes the failure information of the power distribution system received from the distribution automation IED 100 to control the opening and closing of the switch 30. [ Upon receiving the failure information from the distribution automation IED 100, the central management unit 300 analyzes the failure information and transmits a signal for controlling the opening and closing of the switch 30 to the IED 100 for distribution automation , So that the fault line can be separated from the system.

However, the micro grid system shown in Fig. 11 has an IED for each distributed power source and distributed load (distribution). The measurement for the failure is performed by the distribution automation IED 100 installed in the distributed load, The failure is judged by using measured values measured at all points in the system. The failure judgment of this type requires measurement means for all points in the system and transmission means for the measurement values of the respective measurement means must be provided, which leads to a high cost structure.

Further, in the above-described failure determination method, it is not easy to determine the failure of the specific distribution automation IED 100 itself.

Further, in the above-described failure determination method, when the data communication state is not good, the accuracy of the failure determination and / or the determination speed can be lowered.

In addition, the above-described failure determination method requires that each IED has an energy storage device having a considerable capacity for the test power or a diesel generator for producing test power. none.

Korean Patent Publication No. 10-0920113

The present invention seeks to provide a microgrid or a fault handling method capable of promptly detecting and correcting a fault location. More specifically, in the off-grid, when a line failure or a machine failure occurs, a method of locating a fault using a PCS having a fault location determination function and separating the fault location is proposed.

The present invention seeks to improve reliability through stable system operation of the microgrid. To do this, we try to isolate the fault point by analyzing the fault point quickly through PCS.

A microgrid system according to an aspect of the present invention includes: a plurality of distributed power sources; Multiple distributed loads; Lines connecting the distributed power sources and the distributed loads; And a controller for controlling operations of the distributed power supplies, the micro grid system comprising:

At least one of the distributed power sources includes a shutoff means for converting power generated by the power generation device into AC power suitable for the microgrid and supplying the generated power to the microgrid and cutting off the connection to the microgrid in an abnormal situation Active PCS. When the micro-grid detects a failure, the control apparatus gradually increases the voltage output from the active PCS and performs the process for the failure.

Here, the controller may include a step of shutting down the distributed power sources when a failure is detected in the micro grid, Coupling the active PCS to the microgrid; Increasing the voltage output from the connected active PCS gradually and determining the location where the fault occurred; Blocking the location where the fault has occurred and connecting the distributed power sources to the microgrid.

Here, the active PCS can confirm whether or not it is possible to gradually increase the voltage of the power output from the power generation device after the occurrence of the fault.

Here, the active PCS includes energy storage means for outputting to the active PCS that the power generated by the power generation apparatus is temporarily stored, and when performing the operation of gradually increasing the voltage output from the active PCS, The output power of the storage means can be adjusted and output to the microgrid together with the power generated by the power generation apparatus.

Here, the active PCS may increase the voltage output from the active PCS to gradually increase the position of the fault on the microgrid, and may transmit the determined position to the controller.

A fault handling method according to another aspect of the present invention includes a plurality of distributed power sources, a plurality of distributed loads, and lines connecting the distributed power sources and distributed loads, wherein at least one of the distributed power sources includes: A method of processing a microgrid fault in an active PCS having an active PCS having an AC power suitable for a microgrid and supplying a power generated by the power generator to a microgrid in an abnormal state,

Shutting down the distributed power sources when a failure is detected in the microgrid; Coupling the active PCS to the microgrid; Increasing the voltage output from the connected active PCS gradually and determining the location where the fault occurred; And blocking the location where the fault has occurred and connecting the distributed sources to the microgrid.

Here, the step of determining the location where the fault has occurred may include: checking whether the power generation device in charge of the active PCS or the active PCS is faulty; Monitoring the current of the micro grid while gradually increasing the voltage supplied to the system from the active PCS, if it is confirmed that the active PCS is operating normally; Confirming whether the line / load side fault is broken for each load section; And confirming whether or not the line is faulty if a failure is not confirmed in each load section.

Here, after confirming whether or not the active PCS has failed, it may further include checking whether the voltage output after the occurrence of the fault can be gradually increased.

Here, the step of confirming whether or not the line / load side is faulty may include comparing the change of the current according to the gradual increase of the voltage with that of the steady state, and if the change of the current is markedly higher than the steady- It can be judged as a load side failure.

Separating the microgrid system into two or more regions prior to connecting the active PCS to the microgrid; Or assigning a reference time to start the fault position determination operation for each of the two or more active PCSs.

When the micro grid system or the failure processing method of the present invention having the above-described structure is performed, stable system operation can be performed due to the quick failure section removal, thereby improving the reliability of the micro grid system.

Alternatively, the microgrid system of the present invention has the advantage that it is not necessary to provide a separate large-capacity diesel generator for the failure test.

Alternatively, the micro grid system of the present invention has an advantage of minimizing the amount of generated power of a new and renewable source discarded by a power failure.

Alternatively, the micro grid system of the present invention is advantageous in that it can be easily maintained in a micro grid system in which independent external power systems such as a book site are not linked to each other.

1 is a block diagram illustrating a microgrid system in accordance with the teachings of the present invention.
Fig. 2 is a flowchart showing a failure processing method performed in the control apparatus of Fig. 1; Fig.
3 is a block diagram illustrating a connection structure for an active PCS microgrid system that may be applied to perform steps S20 and S30 of FIG. 2;
FIG. 4 is a flowchart illustrating an example of a fault location determination method performed in step S50 of FIG. 2. FIG.
5 is a graph showing the measured voltage and current versus off-grid pressurization in steady state.
6 is a graph showing voltage and current measured for off-grid pressurization in a state where a failure occurs in the microgrid.
FIG. 7 is a flowchart illustrating a more detailed process of sequentially checking the connection and failure of distributed power sources installed in the micro grid in step S155 of FIG. 4. FIG.
FIG. 8 is a flowchart illustrating a more detailed process for checking whether a line section is broken in step S189 of FIG. 4. FIG.
9A to 9D are block diagrams showing an action from a failure occurrence to a black start in a micro grid system according to an embodiment of the present invention.
10 is a graph showing voltage and current waveforms according to the progressive step-up start (Soft Start) of the active PCS according to the present invention.
FIG. 11 is a block diagram showing a conventional power supply system using a distributed power source according to the related art; FIG.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In describing the present invention, the terms first, second, etc. may be used to describe various elements, but the elements may not be limited by terms. Terms are for the sole purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being connected or connected to another element, it may be directly connected or connected to the other element, but it may be understood that other elements may be present in between .

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions may include plural expressions unless the context clearly dictates otherwise.

It is to be understood that the term " comprising, " or " comprising " as used herein is intended to specify the presence of stated features, integers, But do not preclude the presence or addition of steps, operations, elements, components, or combinations thereof.

In addition, the shapes and sizes of the elements in the drawings and the like can be exaggerated for clarity.

1 is a block diagram illustrating a microgrid system 700 in accordance with the teachings of the present invention.

The shown microgrid system 700 includes a plurality of distributed power supplies 740 and 750 for powering the grid; A plurality of distributed loads 771, 772, 773 that consume power in the system; And the lines connecting the distributed power supplies 740 and 750 and the distributed loads 771, 772 and 773 to the grid.

According to an aspect of the present invention, at least one of the distributed power sources converts power generated in the distributed power generation device into AC power suitable for the micro grid and supplies the AC power to the micro grid, And an active PCS 730 having a blocking means for disconnecting the grid from the active PCS 730. In order to determine the location of a fault occurring in the micro grid, Can be gradually increased.

All or a portion of the plurality of distributed power supplies 740 and 750 and the distributed loads 771,727 and 773 may be provided with blocking means 781-788 which may selectively connect or disconnect the system . That is, depending on the implementation, the plurality of distributed power supplies 740 and 750 also have respective PCSs 745 and 755, and the plurality of distributed loads 771, 772, The functions according to the principles of the present invention are realized using the blocking means 781 for connecting / disconnecting the active PCS 730 and the active PCS 730 to the system, and the active PCS 730 And the blocking means 781 will be described in more detail.

The lines must ideally have the same electrical characteristics (potential) for the distributed power supplies 740, 750 and distributed loads 771, 772, 773 connected to the grid, (Electric potential, electric current) at each point due to the imbalance of the unbalanced and long-length line itself.

Electrical characteristics detecting means 781 to 783 (e.g., an ammeter, a voltmeter, a flowmeter, and a hall sensor) may be provided at specific points of the lines to monitor the different electrical characteristics.

For example, the detection means may be provided for each of the connection points of the plurality of distributed power sources 740 and 750 and the distributed loads 771, 772, and 773, or the detection means may be provided for each predetermined length unit.

Depending on the implementation, each of all or a portion of the plurality of distributed power supplies 740, 750 and the distributed loads 771, 772, 773 may be provided with a detection means for monitoring their operating state and / Monitoring means may be provided.

In both cases where renewable energy is used or fossil fuel is used, the power produced by the AC generator is not constant in frequency, and the power produced by the DC generator is not easily transmitted. In order to overcome the above problem, the electric power produced by the AC generator is converted into DC by using a converter or a battery charging circuit, and then converted into an AC of a frequency suitable for the system by using an inverter. The generated electric power is charged to an energy storage device such as a battery, and then converted into alternating current of a frequency suitable for the system by using an inverter. On the other hand, even in the case of a DC distribution system, a structure for converting AC into AC using an inverter may be provided in order to mediate a transformer having a flexible transformer and an excellent insulation performance.

The active PCS 730 according to the present invention includes an inverter as described above. In addition, the active PCS 730 includes a power phase synchronization function for adjusting the phase of the power phase of the system and the power output to the system in the PCS, A surge mitigation / protection function for mitigating and / or preventing a risk factor such as a surge occurring at the grid side from being transmitted to the power generation apparatus 720, a function of adjusting the amount of power (that is, a magnitude of voltage and / or current) And may have configurations for this. On the other hand, in the case of a prime mover, the amount of power generated is controlled by an increase in rpm, while the output power is fixed, so that the frequency of the power generated by the prime mover can be adjusted to the frequency of the output power, And configurations for this can be provided. The functions described above have been known several times as PCS technology used in the field of renewable energy generation, and detailed description will be omitted.

Due to the above-described configurations for the power phase locking function and the surge suppression / protection function of the active PCS 730, when a failure occurs in the micro grid system connected to the active PCS 730, the active PCS 730 can be disconnected from the system for a while have. In order to protect the active PCS 730 itself during the temporary system isolation process and the fault location determination process according to the present invention, the IGBTs (more specifically, the IGBTs included in the inverter) included in the active PCS 730 It is advantageous that the open time is within about several hundred [micro] seconds.

The active PCS 730 in accordance with the teachings of the present invention is advantageously capable of regulating the amount of power with a continuous value as much as possible in the function of regulating the amount of power supplied to the system. Even when the amount of power is adjusted step by step in a discontinuous manner, it is advantageous that the steps are as detailed as possible. For example, the active PCS 730 shown in the figure can be used to determine the rated current or charge current for distributed loads connected to the grid from 0 [A] for a predetermined test time (e.g., a specified period of time ranging from 1 second to 3 seconds) To 80% of the rated rectification according to the maximum power generation capacity of the power generation system (the voltage also rises to a proportional level if it is not a fault).

The active PCS 730 in accordance with the teachings of the present invention is capable of operating in accordance with the state of connection of a plurality of distributed power sources 740, 750 and a plurality of distributed loads 771, 772, 773 to a system of a microgrid system, Which can be implemented by applying the PCS technology to construct a known Smart Grid system.

To gradually increase the voltage output from the active PCS 730 for a predetermined period of time (for example, a period specified by a range of 1 second to 3 seconds), it is necessary to gradually increase the voltage output from the active distributed PCS 730 May be performed at 0V in such a manner that the voltage is sequentially increased to a predetermined voltage level for a predetermined time (for example, a period specified in the range of 1 second to 3 seconds). In this case, it is most preferable that the relationship between time and voltage forms a linear function (straight line of a predetermined slope) continuously. However, in a practical application, and may have the characteristics of a discrete and / or curved time-voltage relationship.

Here, the point at which the voltage and current measurement are to be measured is preferably the output terminal of the active PCS 730 (connection point with the system), but is not limited thereto.

It is not easy to continuously increase the power generation amount of the generator or to increase it to very fine steps in both of the power generation apparatus using the renewable energy and the power generation apparatus using the fossil fuel. On the other hand, in the case of a power generation apparatus using new and renewable energy, an energy storage means for mitigating unevenness of power generation is provided. In the case of a power generation apparatus using fossil fuel, a starter battery is provided. It is possible to further include an energy storing means of a considerable capacity. The energy storage means generally uses a secondary battery such as a lithium ion battery. However, a super capacitor can be used for the purpose of use for smoothing power generation power and for the purpose of increasing the service life.

If the PCS of a fossil fuel generator having a sufficient power supply capacity is provided with the output to the system, a fossil fuel (diesel) generator and an ESS are provided as a power source for the static electricity, Can be regarded as a battery connected to the fossil fuel generator or the active PCS when the smart PCS according to the present invention is implemented.

In all of the above cases, the active PCS may include energy storage means for temporarily storing power generated by the power generation apparatus and outputting the generated power to the active PCS.

That is, in order to gradually increase the voltage of the power outputted to the system by the active PCS 730 according to the idea of the present invention, the energy storage means provided in the active PCS 730, Can be used.

In this case, when the active PCS 730 gradually increases the voltage output from the active PCS 730, the active PCS 730 adjusts the output power of the energy storage means and outputs the generated power to the micro grid system together with the power generated by the power generation device can do.

As described above, three schemes can be exemplified as a method for gradually increasing the voltage output from the active PCS for a predetermined time according to the concept of the present invention.

The first approach is simply to gradually increase the output capacity of the generator. In the case of a fuel cell generator consisting of a large prime mover or a plurality of cells with an adjustable effective rpm range, the output power of the generator can be adjusted continuously (linearly) or progressively in very fine steps. That is, the output power can be adjusted by adjusting the output capacity by rpm for the prime mover generator and by controlling the number of the battery cells contributing in series connection to the output stage for the fuel cell generator.

The active PCS 730 responsible for such a generator may, according to the teachings of the present invention, incrementally increase the voltage output to the grid until the system reaches 80% of the rated current from a value close to 0 .

The second method is to gradually increase the output capacity by using the energy storage means provided in the active PCS 730 at the beginning of the system after the occurrence of the power failure and to increase the output voltage The power generation apparatus can be used to gradually increase the output capacity. This method initially operates in a manner similar to the third method, and may be implemented in a manner that operates in a manner similar to the first method when a predetermined time (level) has elapsed.

The third method is to gradually increase the output capacity by using only the energy storage means provided in the active PCS 730 as if it is an ESS or a UPS. For example, in the case of a battery block including a plurality of battery cells, the number of cells used to generate the output power of the buffered battery cells may be sequentially increased. On the other hand, the power generated in the power generation apparatus can be used to charge the battery reel cells discharged from the battery block.

Meanwhile, according to the implementation, the active PCS may gradually increase the voltage output from the active PCS, determine the position of the fault on the micro grid, and transmit the determined position to the controller.

The micro grid system 700 according to an embodiment of the present invention as shown in FIG. 7 is configured to determine a location where a failure occurs in the micro grid system using the active PCS 730, and to perform a black start as a follow- Device 760. < / RTI >

The control device 760 is advantageously installed at the central control site of the microgrid system 700 and positively utilizes the power generation device 720 and the active PCS 730, It is advantageous to be located in the same site (place) or in close proximity.

The control device 760 is connected to the power generation device 720, the active PCS 730, the distributed power sources 740 and 750 and the distributed loads 771, 772 and 773, the detection means 791 To 795) or data (signal) communication with the monitoring means. To this end, the control device 760 may include power line communication means capable of accessing each of the detection means or the monitoring means, or wire / wireless communication means using a separate power line and a separate medium.

In accordance with an implementation, the microgrid system 700 stores power supplied from all or a portion of the distributed power supplies 740, 750 and stores all or part of the distributed loads 771, 772, 773 And an ESS (not shown) that provides power.

The ESS is a configuration for mitigating the power burden due to uneven load demands in the microgrid, and recently, a method using a lithium secondary battery has been implemented, but any well-known energy storage means can be applied.

The ESS includes a PCS (not shown) that converts the power stored in the ESS into AC (or DC) power suitable for the microgrid and supplies the AC (or DC) power to the microgrid system, (Not shown) for interrupting the connection of the battery.

The PCS of the ESS includes a power phase synchronization function for adjusting the phase of the power of the system and the power output to the system in the PCS, a function of adjusting the amount of power (i.e., the voltage and / or current) supplied to the system, And / or a surge mitigation / protection function that mitigates and / or blocks the transmission of the risk factors such as surges generated in the ESS to the ESS. The functions described above have been known several times as PCS technology in the ESS field, and detailed description will be omitted.

In the drawing, PV (photo voltaic) and wind turbine (WT) are exemplified as distributed power sources.

Although the control device 760 is described as driving the blocking means 781 for the countermeasure against the generation of the system failure and the determination of the failure position in the structural explanation and the following method explanation, It is apparent that the active PCS 730 instructs the PCS 730 to operate the blocking means 781 and the blocking means 781 operates in accordance with the instructions.

FIG. 2 is a flowchart showing a failure processing method performed in the control apparatus 760 of FIG.

The illustrated fault processing method includes: detecting a fault in the micro grid system (S10); A grid interception step (S20) of interrupting the distributed power sources; Connecting the active PCS to the micro grid system (S30); (S50) of gradually increasing the voltage output from the connected active PCS (S40) and determining the position where the failure occurs; And closing the fault occurrence position (S60) and connecting the distributed power sources to the micro grid (S70).

The failure detection step S10 may be performed in the PCS of each distributed power sources connected to the microgrid system. In other words, each PCS has its own protection function to protect each dispersed power source mediated by the grid, and can detect faults occurring in the microgrid system. Here, the PCS of each distributed power source includes both the PCS of the prior art and the active PCS of the present invention. The PCS that detects the failure can report it to the control apparatus (760 of FIG. 1) by using the data communication means.

In the system interception step S20, the PCS that has detected the failure may be performed by the PCS function, and the PCS that failed to detect the failure may be performed by the shutdown command of the control device (760 of FIG. 1) have.

In the figure, only the PCSs connected to the system in the system interception step S20 are shown as being shut off from the system. However, in another embodiment, the distributed devices and the distributed power sources, which do not have their own PCS, .

The steps S40 and S50 will be described later.

The step S60 is for separating a section determined as a failure in the step S50 from the system. Specifically, it can be separated by turning off the blocking means for the distributed power supply or the distributed load determined as a failure.

In step S70, the microgrid is restarted in a state where only the faulty part is separated from the system before the fault is completely recovered in the state where the fault has occurred, which may be referred to as Black Start. If it is determined in step S70 that the fault section of the system has been disconnected (S60), first, the active PCS 730 is connected to the micro grid system to supply power to the healthy section, and the distributed power sources PV / WT) can be connected to the microgrid system.

FIG. 3 illustrates an embodiment of a connection structure for an active PCS microgrid system that can be applied to perform steps S20 and S30. The active PCS of the illustrated embodiment includes an inverter including an IGBT.

As a connection structure to the micro grid system of the active PCS shown in the figure, the cutoff means includes a power generation stage switch (G CB) for interrupting the power generation device and the PCS inverter in charge; An AC step switch (AC CB) for interrupting the micro grid and the inverter of the active PCS; And IGBT interrupting means (not shown) for interrupting the IGBT constituting the inverter.

As shown, the generator is interlocked with the inverter via the generator stage switch G CB, and the inverter is interrupted again with the interrupter CB (781 in Fig. 1) or the micro grid system via the AC stage switch AC CB . The order in which the active PCS, which has been disconnected from the system due to a fault in the system, is reconnected to the system according to the idea of the present invention is that the power stage switch G CB first closes, And the IGBT constituting the inverter is closed according to the DC-AC conversion operation.

The operation process of the switches described above only describes the connection / disconnection structure for the power generation device. When the active PCS is also connected to the energy storage means, the switch operation process for interrupting / connecting with the energy storage means May be performed in a similar manner.

Table 1 below describes a criterion for determining a fault location performed in the fault location determination step (S50).

The criteria described in the above table can be applied to the fault location determination method described later.

In the above table, " before / after current measured ", which is a basis for judging whether or not a line failure occurs, is a line current position of measurement points of each line after occurrence of a fault May refer to a forward point and a backward point of < RTI ID = 0.0 >

Depending on the implementation, the microgrid system may have more than one active PCS. In this case, the microgrid system control device can take measures to prevent each active PCS from interfering with each other in performing the failure position determination after a failure has occurred.

For example, the control apparatus separates (insulates) the micro grid system in which a failure has occurred into two or more areas, and one active PCS can be connected to one separated area. To this end, the microgrid has a system area separating means for separating the area into several points of the lines constituting the system. When a failure occurs in the system, the control system disconnects the system area separating means (Isolated) into two or more regions by control (switching).

Alternatively, the control apparatus may assign different operation times so that the two or more active PCSs perform the fault position determination operation according to the concept of the present invention, so that the execution time does not overlap.

In the former case, the method may further include separating the microgrid system in which the failure has occurred into two or more areas before steps S20 and S30 of FIG.

In the latter case, before the step S30 of FIG. 2, a reference time (a reference time for starting a fault position determination operation) from a fault occurrence point, which is connected to the microgrid system after occurrence of a fault for each of the two or more active PCSs, To the mobile terminal.

4 is a flowchart illustrating an example of a fault location determination method performed in the fault location determination step (S50).

When the active PCS is connected to the micro grid system (S30), it is checked whether the active PCS itself is operating normally (S120). If it is confirmed that the active PCS is normally operated, step S150 of monitoring the current of the micro grid while gradually increasing the voltage supplied from the active PCS to the system to check whether the line / load side is faulty (S150); If the line / load side failure is confirmed, it is checked whether the failure has occurred in each load section (S180); And checking whether the line is broken if the failure is not confirmed in each load section (S189).

The flow chart shown in FIG. 2 is executed as the micro grid system connection step S30 of the active PCS in FIG. 2 is performed, and step S30 in FIG. 2 means step S30 in FIG.

If the active PCS or the connected power generation device does not operate normally in the active PCS normal operation check step (S120), it is determined that the active PCS PCS fails and the procedure is terminated. Since it is a general technology in the PCS to confirm whether the active PCS operates normally, detailed description is omitted.

According to the implementation, after confirming the normal operation of the active PCS itself in the step S120, it is confirmed whether or not the power generation device connected to the active PCS is in a state capable of gradually pressurizing (Off-Grid pressurization) into the system according to the present invention The method comprising the steps of: This is due to the considerable power required to gradually pressurize the system to determine if the entire system has failed. In addition, it is necessary to judge whether solar power generation or wind power generation can produce electricity required for gradual pressurization of the amount of sunshine or wind speed in the system. Of course, even in the case of a fossil fuel power generation device, it can be considered that it is necessary to judge that the amount of fuel is insufficient for the above-mentioned significant power generation.

Increasing the voltage / current to be supplied from the active PCS to the system in step S150 of confirming whether or not the line / load is in failure is performed in step S40 of FIG.

The operation of gradually increasing the voltage supplied to the system from the active PCS performed in step S150 may be called off-grid pressurization. FIG. 5 is a graph showing the voltage and current measured for the off- And FIG. 6 is a graph showing voltage and current measured for off-grid pressurization in a state where a failure occurs in the microgrid.

In the above graphs, the system voltage is 380 V, the total load is 1.5 [M], the capacity of the power generation device in charge of the active PCS is 2.0 [M] ) Assumes the occurrence of a 1-wire ground fault.

It can be seen that 80% (about 2.4 [kA]) of the fault judgment current is approached when the voltage is raised to about 114 [V] in the voltage / current graph in the state of the fault shown in the figure. 3.0 [kA]) In other words, if a fault occurs in the microgrid system, the increase of the grid current due to the increase of the voltage supply is significantly larger than that in the steady state (as a result, ), Which can be attributed to leakage, ground fault, or short circuit in the load or line, which causes the load side impedance of the system to be lower than normal. A method of confirming the fault on the line / load side using the phenomenon shown in the above 2 graph is a method in which the change of the current according to the gradual increase of the voltage is compared with the case of the steady state, If the transition is confirmed, it is determined that there is a line / load side failure. Here, the failure determination current is a reference current amount sufficient to determine a failure, and may be an amount of current that does not hinder the power distribution evenly to the line / load side connected to the system. However, it may generally mean rated current for distributed loads connected to the grid or rated rectification for the maximum generating capacity of the power generating device in charge.

In step S30 of FIG. 2, since the distributed power sources are not connected, it can be determined that the failure is not caused by the distributed power source.

If it is determined in step S150 that the off-grid system can be pressurized, that is, there is no fault section in the pressurized system (the part connected to the system in step S30), and in step S155, Failure inspection can be carried out. For example, if a power failure occurs again due to a connected distributed power source, a fault can be determined by the distributed power source. The fact that the off-grid system can be pressurized means that a voltage-current pattern according to the graph shown in FIG. 5 appears.

If the off-grid pressurization is not properly performed in step S150, operations after step S180 of measuring the size and direction of the line section and the load side current are performed.

In step S180, the current value measured at the end of each load section is compared with a predetermined setting value, and if it is measured at a predetermined ratio or more, it is determined that the load section is broken. In other words, in step S180, the current value measured at the end of each load section is compared with a setting value to determine a fault section. For example, if the measured value> Setting X 0.5 (can be changed) . However, when the rated capacity of the ESS is 1M, it is possible to adjust the magnification according to the capacity of the ESS such that 0.8 is applied as the multiplication factor to the setting value and the magnification is set to 0.7 when the rated capacity of the ESS is 2M.

In the step S189, a difference occurs in the current magnitude before and after the measurement in the case of the line failure period. The difference in the magnitude of the current measured before and after the failure can be estimated as the current flowing in the failure point. In the case of the normal line section in which the failure does not occur, the difference in the magnitude of the current before and after the measurement is similar.

FIG. 7 is a flowchart illustrating a more detailed procedure for sequentially checking the connection and failure of distributed power sources installed in the micro grid in step S155 of FIG. FIG. 7 shows the sequential connection of the distributed power sources installed for the post-failure inspection. Assuming that the distributed power sources separated from the micro grid system by the failure are only the solar power (PV) and the wind power (WT) will be.

The illustrated distributed power inspection method comprises: connecting a PCS of a wind power supply (WT) to a system (S210) and checking whether a power failure occurs (S220); If the power failure by the wind power supply WT is not generated, the PCS of the solar power PV is connected to the system (S230) and it is checked whether a power failure occurs (S240); And determining (S250) that an instantaneous failure occurs if a power failure by the solar power source (PV) is not generated.

If it is determined in step S220 that the power failure has occurred, the line failure of the wind power supply WT is determined (S225). If the occurrence of the power failure is confirmed in step S240, the line failure of the solar power PV can be determined )

In the figure, the wind power supply (WT) was inspected and then the PV power was inspected. However, the inspection order may be changed.

FIG. 8 is a flowchart illustrating a more detailed process for checking whether a line section is broken in step S189 of FIG. The figure assumes that the line segments are only 1, 2, and 3.

The illustrated line section checking method is a step S320 of confirming whether the current magnitude before measurement of the line section 3 is similar to the current magnitude after measurement (which means that it belongs to the same range in practical terms) (S320); (S330) if the current magnitude before measurement of the line section 2 is similar to the current magnitude after measurement if the current magnitudes before and after measurement of the line section 3 are similar to each other; If the current magnitudes before and after measurement of the line section 2 are similar to each other, whether the current magnitude before measurement of the line section 1 is similar to the current magnitude after measurement (S340); And checking the reconfiguration and / or the exception interval (excluded interval) if the current magnitudes before and after measurement of the line section 1 are similar to each other (S350).

If it is determined in step S320 that the current magnitudes before and after the measurement are different from each other, the failure of the line section 3 is determined (S325). If it is determined that the current sizes before and after the measurement are different in step S330, (S335). If it is confirmed in step S340 that the current magnitudes before and after measurement are different from each other, it is possible to determine the failure of the line section 1. (S345)

As shown in Table 1, in the "before and after measured currents where the magnitude difference occurs in the line failure section" as a basis for judging whether or not the line is broken, "before / after" May refer to the leading and trailing points of the line image position.

In the figure, the line segments 3, 2, and 1 are checked in this order.

FIGS. 9A to 9D are block diagrams showing an action from a failure occurrence to a black start in the micro grid system according to an embodiment of the present invention. In the figure, the green of each CB means connection, the red means breaking, and in the case of power generators, the gray means a failure.

As shown in FIG. 9A, in the steady state, most of the shutoff means of the microgrid is in a closed state, and the ESS is connected to the micro grid system by the closed shutoff means regardless of the operation. In the drawing, the SCB is a system circuit breaker for isolating (insulating) the microgrid system into two regions. The PCS1 responsible for the diesel generator (DG) and the PCS4 responsible for the fuel cell generator (FC) It is an active PCS according to the idea of the invention.

9B, when the dropout occurs in the load 2, the ESS having its own PCS and the respective distributed power sources PV and WT are disconnected from the micro grid system by the CB (Circuit Breaker) and / or the PCS self protection function . In the drawing, the SCB is also expressed as blocked, but in the field, the CBs connected to the PCS immediately detecting the failure can be blocked first, and then the SCB can be blocked by the control of the control device detecting the failure somewhat later.

Next, in FIGS. 9C and 9D, in which an accident response measure according to the present invention is performed, the SCB is interrupted to separate (isolate) the micro grid system into two regions SR1 and SR2, In each of the divided regions, the distributed power sources PV and WT are disconnected from the system as they are, and the active PCSs PCS1 and PCS4 are connected to the separated regions SR1 and SR2 of the microgrid system, (DG, FC) are operated to gradually increase the voltage of the separated regions (SR1, SR2).

Figure 10 shows the voltage and current waveforms according to the progressive step-up soft start according to the present invention of the active PCS.

For example, it shows the voltage / current waveform of the active PCS output stage as the soft start function of the PCS in charge of the prime mover, gradually increasing the output voltage from 0 V to the rated voltage over a period of about one second.

The Soft Start operation of the active PCS described above can be associated with the Black Start, which blocks the faulty part in the system and again activates the microgrid. As a system condition for Black Start, the VCB-side UVR relay may be required to deactivate the function during Black Start, deactivate the UVR relay, and then activate the active PCS after all circuit breakers have been switched on.

It should be noted that the above-described embodiments are intended to be illustrative, not limiting. In addition, it will be understood by those of ordinary skill in the art that various embodiments are possible within the scope of the technical idea of the present invention.

700: Micro Grid System
730: Active PCS
740, 750: Distributed power supplies
760: Control device
771, 772, 773: Distributed loads
781 to 788:
781 to 785: Detection means

Claims (10)

A plurality of distributed power sources;
Multiple distributed loads;
Lines connecting the distributed power sources and the distributed loads; And
A controller for controlling the operation of the distributed power sources
The micro grid system comprising:
At least one of the distributed power sources includes a shutoff means for converting power generated by the power generation device into AC power suitable for the microgrid and supplying the generated power to the microgrid and cutting off the connection to the microgrid in an abnormal situation An active PCS,
Wherein the control unit performs a process for the failure while gradually increasing a voltage output from the active PCS when a failure is detected in the micro grid,
The active PCS,
Wherein the control unit determines the position of the fault on the micro grid while gradually increasing the voltage output from the active PCS, and transmits the determined position to the control unit.
The method according to claim 1,
The above-
Shutting down the distributed power sources when a failure is detected in the microgrid;
Coupling the active PCS to the microgrid;
Increasing the voltage output from the connected active PCS gradually and determining the location where the fault occurred;
Blocking the location where the fault occurred and connecting the distributed power sources to the microgrid
The microgrid system.
The method according to claim 1,
Wherein the active PCS checks whether the voltage of the power output from the power generation device can be gradually increased after the occurrence of the fault.
The method according to claim 1,
Wherein the active PCS comprises an energy storage means for temporarily storing power generated by the power generation apparatus and outputting the generated power to the active PCS,
Wherein the output power of the energy storage means is adjusted and output to the microgrid together with the power generated by the power generation device when the operation of gradually increasing the voltage output from the active PCS is performed.
delete A plurality of distributed power sources,
A plurality of distributed loads,
And lines connecting the distributed power sources and the distributed loads,
At least one of the distributed power supplies includes at least one of a microprocessor having an active PCS having an AC power supply for converting electric power generated in the power generator into AC power suitable for a micro grid and for interrupting connection with the micro grid in an abnormal situation, In a failure processing method for a grid,
Shutting down the distributed power sources when a failure is detected in the microgrid;
Coupling the active PCS to the microgrid;
Increasing the voltage output from the connected active PCS gradually and determining the location where the fault occurred;
Blocking the location where the fault occurred and connecting the distributed power sources to the microgrid
And a failure handling method.
The method according to claim 6,
The step of determining the location where the failure has occurred,
Confirming whether the power generation device in charge of the active PCS or the active PCS is faulty;
Monitoring the current of the micro grid while gradually increasing the voltage supplied to the system from the active PCS, if it is confirmed that the active PCS is operating normally;
Confirming whether the line / load side fault is broken for each load section; And
If the failure is not confirmed in each load section, check the failure of the line
And a failure handling method.
8. The method of claim 7,
After confirming whether the active PCS has failed,
Checking whether the voltage output after the occurrence of the fault is gradually increased
Further comprising the steps of:
8. The method of claim 7,
The step of confirming whether or not the line /
The failure is judged to be a line / load side failure when a trend of a current change due to a gradual increase of the voltage is compared with a steady state transition and an increase trend of a predetermined value or more is confirmed than a steady state current change.
The method according to claim 6,
Prior to connecting the active PCS to the microgrid,
Dividing the microgrid system into two or more regions; or
Assigning a reference time to start a fault position determination operation for each of the two or more active PCSs
Further comprising the steps of:

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