WO2018105990A1 - Microgrid system, and method for managing malfunction - Google Patents

Abstract

A microgrid system according to the present invention is provided with: a plurality of decentralized power sources; a plurality of decentralized subordinates; paths connecting the decentralized power sources and subordinates; and a control apparatus for controlling the operation of the decentralized power sources, wherein at least one among the decentralized power sources converts power generated by a power generator to alternating current power appropriate for the microgrid, and supplies thereto, and is provided with an active PCS having a cut-off means for cutting off connection to the microgrid in abnormal situations, and the control apparatus, when a malfunction is sensed in the microgrid, can gradually increase the voltage outputted from the active PCS and manage the malfunction.

Description

Microgrid System and How to Handle It

The present invention relates to a microgrid system for performing fault handling and a fault handling method using the same. More particularly, the present invention relates to a system and method for shortening a power failure time for a health section that experiences a power failure unnecessarily when a system failure occurs. It is about.

Microgrids are small-scale power supply systems that consist of distributed power sources (solar, wind power, etc.), batteries (power storage devices), etc., to power loads. Microgrids are usually operated in a linked operation mode in which electricity is traded in connection with a large-scale power system, and in the event of a failure in the utility company's line, the microgrid can be switched to an independent operation mode that supplies its own power separately from the power system. It is mainly installed in buildings, university campuses and factories, and aims to reduce electricity bills and improve power supply reliability. On the other hand, microgrids installed in remote areas, such as island areas, can be operated by configuring one system with its own loads without being connected to an external power system.

To improve power supply reliability, one of the goals of installing microgrids, microgrids must be operated uninterrupted. If a fault occurs in the power system, it must be accurately detected and quickly separated from the upper power system and the microgrid. In addition, if a failure occurs in the microgrid, only the corresponding part should be quickly separated to prevent a power failure. On the other hand, the magnitude and direction of the fault current varies depending on the microgrid and the power system connection state, each distributed power supply connection state, fault location, fault occurrence type, and the like. However, conventional circuit breakers (MCCB, ACB, etc.) and fault handling methods cannot adequately cope with various kinds of failures occurring in the microgrid, so that a local failure may affect the entire microgrid, causing a total power failure. In particular, this causes more frequent inconveniences in microgrid systems installed in island areas and the like with independent systems.

FIG. 11 illustrates a power supply section power supply system using a distributed power supply 40 according to the related art. Referring to FIG. 11, a power supply system using a distributed power supply 40 includes a distribution automation IED 100, a distributed power supply IED 200, and a central management device 300.

Distribution automation IED (100) measures the voltage and current of the distribution line, and when a line accident occurs in the distribution system, transmits the line accident event to the central management unit 300 so that the distribution automation system operator can analyze. .

Once a temporary failure occurs, the distribution automation IED 100 determines whether the distribution system is faulty or the direction of the fault current from the fault current, and if it is determined to be a fault, sends FI (Fault Indicator) information to the central management device 300. send.

The central management unit 300 determines the failure section from the failure information provided from the distribution automation IEDs 100 in case of a temporary failure, and transmits a switch 30 operation command to the distribution automation IED 100. The distribution automation IED 100 proceeds with the fault handling procedure by transmitting the result to the central management unit 300 after performing the switch 30 control.

That is, the distribution automation IED (100) measures the overcurrent of the distribution line, and cuts the line through the protection device 20 of the circuit breaker or recloser, through which the protection device 20 When the load stage becomes no voltage, the switchboard detects a failure of the distribution line. In addition, by controlling the closing and opening of the switch on the basis of the control signal of the central management device 300, it serves to control the failure section to be separated from the distribution system.

When a failure occurs in the distribution line, the distribution automation IED 100 transmits the failure occurrence information to the distributed power supply IED 200, so that the distributed power supply IED 200 delivers power to the healthy section through the distributed power supply 40. Make it available.

Further, the distribution automation IED 100 serves to measure the average load current for the load stage existing between the distributed power supply 40 and the distribution automation IED 100. By measuring the load current for the load stage for a predetermined time, the average load current can be calculated. Through this it is possible to calculate the average amount of power consumed by the load stage for each time zone, the information calculated by the distribution automation IED (100) is transmitted to the distributed power supply IED (200), when the distribution system failure occurs distributed power supply (40) It can be used as data to calculate the amount of power to be supplied.

The distributed power source IED 200 is connected to the distributed power source 40 to calculate the amount of power that the distributed power source 40 can supply to the system in the event of a distribution system failure. The distributed power supply IED 200 may calculate the amount of power based on the amount of power generated by the distributed power source 40 and the battery storage amount.

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 associated with the distributed power supply 40, failure from the distribution automation IED (100) Receive occurrence information.

Furthermore, upon receiving the fault occurrence and fault current information from the distribution automation IED (100), to identify the health section that will experience the power failure unnecessarily due to the failure, by controlling the switch between the distributed power supply 40 and the grid, Allow power to be supplied to the health section.

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

The central management apparatus 300 monitors the entire system and analyzes failure information of the distribution system received from the distribution automation IED 100 to control the input / opening of the switch 30. When 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 input and open of the switch 30 to the distribution automation IED (100) To ensure that the fault line is disconnected from the system.

By the way, the microgrid system shown in FIG. 11 includes an IED for each distributed power supply and distributed load (distribution), and the measurement of the failure is performed by the distribution automation IED 100 installed at the distributed load. The fault is determined using the measured values measured at all points in the system. The failure determination in this manner has to be provided with measurement means for all points of the system and transmission means for measurement values of each measurement means, which is inevitably a costly structure.

In addition, the above-described failure determination method was not easy to determine the failure of the specific distribution automation IED (100) itself.

In addition, the above-described failure determination method can lower the accuracy and / or determination speed of the failure determination when the data communication state is not good.

In addition, in the above-described failure determination method, each IED should have a substantial amount of energy storage device for the test power, or a diesel generator for the production of test power, which may cause an increase in facility cost. none.

The present invention is to provide a microgrid or a fault handling method that can quickly identify the fault location and take action. More specifically, in case of line failure and equipment failure in Off-Grid, we propose a method to identify the location of the failure by using a PCS with a failure location determination function and to recover after separating the failure point.

The present invention seeks to improve reliability through stable grid operation of microgrids. To this end, the PCS will quickly identify the point of failure and isolate the point of failure.

Microgrid system according to an aspect of the present invention, a plurality of distributed power supplies; Multiple distributed loads; Lines connecting the distributed power supplies and distributed loads; And a control device for controlling the operation of the distributed power supplies, the microgrid system comprising:

At least one of the distributed power supplies, converting the power generated by the power generation device to the AC power suitable for the micro grid to supply to the micro grid, but has a blocking means for disconnecting the connection to the micro grid in an abnormal situation The active device may include an active PCS, and when the microgrid detects a failure, the controller may perform a process for the failure while gradually increasing the voltage output from the active PCS.

Here, the control device, the detection of the failure in the micro grid the step of shutting off the distributed power supplies; Coupling the active PCS to the microgrid; Determining a location where the failure occurs while gradually increasing a voltage output from the connected active PCS; Blocking the location where the failure occurs and connecting the distributed power supplies to the microgrid.

Here, the active PCS can check whether the start-up is possible to gradually increase the voltage of the power output from the power generation device after the failure occurs.

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

Here, the active PCS may determine the location of the failure on the microgrid while gradually increasing the voltage output from the active PCS, and transmit the determined location to the control device.

A failure handling method according to another aspect of the present invention includes a plurality of distributed power supplies, a plurality of distributed loads, and lines connecting the distributed power supplies and the distributed loads, wherein at least one of the distributed power supplies includes: A method of handling a failure of a microgrid having an active PCS which converts and generates power generated by a power generation device into an AC power suitable for a microgrid, and has a blocking means for disconnecting the microgrid in an abnormal situation.

Shutting off the distributed power supplies when a failure is detected in the microgrid; Coupling the active PCS to the microgrid; Determining a location where the failure occurs while gradually increasing a voltage output from the connected active PCS; Blocking the location where the failure occurs and connecting the distributed power supplies to the microgrid.

The determining of the location where the failure occurs may include: checking whether the active PCS or the power generation device in charge of the active PCS has failed; If it is determined that the active PCS is operating normally, gradually increasing the voltage supplied from the active PCS to the grid, and monitoring the current of the microgrid to check whether there is a line / load side failure; Checking whether a line / load side fault is detected, each load section; And if the failure is not confirmed in each load section may include checking the line failure.

Here, after the step of checking whether the active PCS side failure, the step of gradually increasing the voltage output after the failure may include the step of checking whether it is possible to start.

Here, the step of checking whether the line / load side failure is, if the increase trend is clearly higher than the current change trend in the steady state, compared to the current change trend due to the gradual increase in voltage, It can be determined by the load side failure.

Wherein before the step of connecting the active PCS to the microgrid, separating the failed microgrid system into two or more regions; Alternatively, the method may further include allocating a reference time for starting the failure location determination task for each of the two or more active PCS.

When the microgrid system or the fault handling method of the present invention having the above-described configuration is implemented, stable system operation is possible due to the rapid failure section removal, thereby improving the reliability of the microgrid system.

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

Alternatively, the microgrid system of the present invention has the advantage of minimizing the amount of power generated by renewable sources discarded by power outages.

Alternatively, the microgrid system of the present invention has an advantage of easy maintenance in a microgrid system that forms an independent system without a separate external power system such as an island area.

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

FIG. 2 is a flowchart illustrating a failure handling method performed in the control device of FIG. 1.

3 is a block diagram illustrating a connection structure for a microgrid system of an active PCS that may be applied to perform steps S20 and S30 of FIG.

4 is a flowchart illustrating an embodiment of a fault location determining method performed in step S50 of FIG. 2;

Figure 5 is a graph showing the voltage and current measured for Off-Grid pressurization in steady state.

Figure 6 is a graph showing the voltage and current measured for Off-Grid pressurization in the state that a failure occurs in the microgrid.

FIG. 7 is a flowchart illustrating a more detailed process of sequentially connecting and failing distributed power supplies installed in a micro grid in step S155 of FIG. 4.

FIG. 8 is a flowchart illustrating a more detailed process of performing a check of failure of track sections in step S189 of FIG. 4.

9A to 9D are block diagrams showing the action taken from the occurrence of a failure of the microgrid system according to the spirit of the present invention to black start;

FIG. 10 is a graph showing voltage and current waveforms with a gradual soft start in accordance with the inventive concept of an active PCS. FIG.

Figure 11 is a block diagram showing a power supply section power supply system using a distributed power source according to the prior art.

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

In describing the present invention, terms such as first and second may be used to describe various components, but the components may not be limited by the terms. The terms are only for the 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 the second component, and similarly, the second component may also be referred to as the first component.

When a component is referred to as being connected or connected to another component, it may be understood that the component may be directly connected to or connected to the other component, but there may be other components 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. Singular expressions may include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms including or including are intended to designate that there exists a feature, a number, a step, an operation, a component, a part, or a combination thereof described in the specification, and one or more other features or numbers, It can be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

In addition, the shape and size of the elements in the drawings may be exaggerated for more clear description.

1 is a block diagram illustrating a microgrid system 700 according to the spirit of the present invention.

The illustrated microgrid system 700 includes a plurality of distributed power supplies 740 and 750 for powering the grid; Multiple distributed loads 771, 772, 773 consuming power in the system; Lines connecting the distributed power sources 740 and 750 and the distributed loads 771, 772 and 773 to the grid are included.

Here, according to the spirit of the present invention, at least one of the distributed power supplies, by converting the power generated in the distributed generation device in charge to the AC power suitable for the micro grid to supply to the micro grid, in the abnormal situation the micro It includes an active PCS 730 having a blocking means for disconnecting the grid, the active PCS system in the active PCS 730 after the failure occurs to determine the location of the failure occurred in the microgrid The output voltage can be gradually increased.

Each of some or all of the plurality of distributed power sources 740, 750 and distributed loads 771, 772, 773 may include blocking means 781-788 that can selectively connect or disconnect the grid. Can be. That is, depending on the implementation, the plurality of distributed power supplies 740, 750 also have PCS 745, 755, respectively, and the plurality of distributed loads 771, 772, 773 also have their own blocking means 786-788. However, the function according to the spirit of the present invention is realized by using the active PCS 730 and the blocking means 781 which connects / blocks the active PCS 730 to the system. ) And the blocking means 781 will be described in more detail.

The lines should ideally have the same electrical characteristics (potential) for the plurality of distributed sources 740, 750 and distributed loads 771, 772, 773 connected to the grid, but the supply power and / or load Due to the imbalance and the impedance of the long lines themselves, they have different electrical properties (potential, current) at each point.

In order to monitor the different electrical characteristics, specific points of the tracks 781 to 783 (eg, ammeters, voltmeters, current meters, and hall sensors) may be provided at specific points of the lines.

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

Depending on the implementation, each or all of the plurality of distributed power supplies 740, 750 and distributed loads 771, 772, 773 may be provided with detection means for monitoring its running condition and / or electrical characteristics, or Monitoring means.

In the case of using renewable energy or using fossil fuel, the power generated by the AC generator is not constant in frequency, and the power produced by the DC generator is not easy to transmit. In order to overcome the above problems, the power produced in the AC generator is converted to direct current using a converter or a battery charging circuit, and then converted into an alternating current of a frequency suitable for a system using an inverter, The generated power is charged into an energy storage device such as a battery, and then converted into alternating current at a frequency suitable for the system by using an inverter. On the other hand, also in the case of a DC power distribution system, in order to mediate a transformer having a flexible transformer and excellent insulation performance, it may be provided with a structure for converting into an AC using an inverter.

Active PCS 730 according to the spirit of the present invention is provided with an inverter as described above, and in addition, the power phase synchronization function for matching the power phase of the system and the power output from the PCS to the system, which is supplied to the system Perform surge mitigation / protection functions to regulate the amount of power (i.e. the magnitude of voltage and / or current), and to mitigate and / or block the transmission of risk factors to the power generation device 720, such as surges generated at the grid side. It may be equipped with a configuration for this. On the other hand, in the case of the prime mover, while adjusting the amount of power generated by the increase in rpm, the frequency of the output power is fixed, it can perform a function of matching the frequency of the power generated by the prime mover with the frequency of the output power, Configurations for this may be provided. The functions described above have been well known several times as PCS technologies used in the field of renewable energy generation, and detailed descriptions thereof will be omitted.

With the above-described configurations for the power phase synchronization function and the surge mitigation / protection function of the active PCS 730, when the microgrid system connected to it fails, the active PCS 730 can be disconnected from the system for a while. have. In order to protect the active PCS 730 itself in such a temporary system separation process and the fault location determination process according to the present invention, the IGBT (more specifically, the IGBT constituting the inverter) provided in the active PCS 730 may be used. The open time is advantageously within about several hundred [us] (microseconds).

Active PCS 730 according to the spirit of the present invention, in the function of adjusting the amount of power supplied to the system, it is advantageous to be able to adjust the amount of power to a continuous value as possible. Even when discontinuously adjusting the amount of power, it is advantageous if the steps are as detailed as possible. For example, the illustrated active PCS 730 may have a rated current or charge specified for distributed loads connected to the grid from 0 [A] for a predetermined test time at startup (e.g., a specified period ranging from 1 second to 3 seconds). It can be gradually increased up to 80% of the rated rectification according to the maximum generating capacity of the generator (in case of failure, the voltage will rise to a level proportional to this).

Active PCS 730 according to the spirit of the present invention, depending on the connection state of the plurality of distributed power sources (740, 750) and a plurality of distributed loads (771, 772, 773) for the system of the microgrid system, The amount of power output can be adjusted, which can be implemented by applying a PCS technology for configuring a known smart grid system.

Incrementally increasing the voltage output from the active PCS 730 for a predetermined time period (e.g., a specified period in the range of 1 to 3 seconds) may be performed by connecting the distributed distributed generation device that was separated from the grid to the grid again. May be performed in a manner of sequentially increasing the voltage up to a predetermined voltage level for a predetermined time (for example, a specified period in a range of 1 to 3 seconds) at 0V. In this case, most preferably, the relationship between time and voltage forms a linear function continuously (a straight line with a predetermined slope), but in actual application, it is a condition that shows a relationship in which the relationship between time and voltage increases proportionally. (discrete) and / or the relationship between the time and voltage of the curve.

Here, the point of reference for measuring the voltage and current is preferably an output terminal (connection point with the system) of the active PCS 730, but is not limited thereto.

Both power plants using renewable energy and power plants using fossil fuels, it is not easy to continuously increase the amount of power generated by the generator or in very fine steps. On the other hand, in the case of a power generation device using renewable energy, it is provided with an energy storage means for alleviating non-uniformity of power generation, a power generation device using fossil fuels also has a starting battery, and serves as a power supply for power failure preparation. In case it can be further provided with a significant amount of energy storage means. A secondary battery such as a lithium ion battery is generally used as the energy storage means, but a supercapacitor may be used for the purpose of smoothing the generated power or for increasing the service life.

On the other hand, as a power supply for power outages, the PCS of the fossil fuel generator is provided with a fossil fuel (diesel) generator and the ESS together, but the PCS of the fossil fuel generator having a sufficient power supply capacity for output to the system If implemented as a smart PCS according to the spirit of the present invention, the ESS can be seen as a battery connected to the fossil fuel generator or active PCS.

In all of the above-described cases, the active PCS may be regarded as having energy storage means for temporarily storing the power generated by the power generation device and outputting the generated power to the active PCS.

That is, in order to gradually increase the voltage of the power output from the active PCS 730 to the system in accordance with the spirit of the present invention, the above-described energy storage means provided in the active PCS 730 or a secondary battery additionally installed separately Can be used.

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

As described above, three methods may be exemplarily presented as methods for gradually increasing the voltage output for a predetermined time in the active PCS according to the inventive concept.

The first solution is simply to gradually increase the output capacity of the generator. In the case of a prime mover generator with a large adjustable effective rpm range or a fuel cell generator consisting of multiple cells, the generator's output power can be adjusted gradually (linearly) or in very fine steps. That is, in the case of the prime mover, the output capacity may be adjusted in rpm, and in the case of the fuel cell generator, the output power may be adjusted by adjusting the number of battery cells contributing to the output terminal in series connection.

The active PCS 730 in charge of such a generator gradually increases the voltage output to the grid from a value close to 0 to 80% of the rated current in the reconnected grid after failure occurs according to the spirit of the present invention. Can be.

The second method is to gradually increase the output capacity by using the energy storage means included in the active PCS 730 after the power failure, and to increase the amount of time (or current, power, and power) for a predetermined time. To increase the output capacity by using a power generation device. This method may be implemented in a manner that initially operates similar to the third scheme below, and operates similarly to the first scheme after a predetermined time (level) elapses.

The third solution is to gradually increase the output capacity using only the energy storage means provided in the active PCS 730, as if it were 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 output power among the fully charged battery cells may be sequentially increased. Meanwhile, the power generated by the power generation device may be used to charge the battery cells discharged from the battery block.

In some implementations, the active PCS may determine the location of the failure on the microgrid while gradually increasing the voltage output from the active PCS, and transmit the determined location to the control device.

In the microgrid system 700 according to the spirit of the present invention, a control is performed using the active PCS 730 to determine a location where a failure occurs in the microgrid system and to perform a black start as a follow-up measure according to the failure. The device 760 may further include.

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

The monitoring device 760 includes a detection unit 791 installed in the power generation device 720, the active PCS 730, the distributed power sources 740 and 750, the distributed loads 771, 772 and 773, and the tracks. 795 or data (signal) communication with the monitoring means. To this end, the control device 760 may include a power line communication means that can access each detection means or monitoring means or a wired / wireless communication means that uses a separate medium from the power line.

Depending on the implementation, the microgrid system 700 stores power supplied from all or part of the distributed power sources 740 and 750 and is stored as all or part of the distributed loads 771, 772, 773. It may further include an ESS (not shown) for providing power.

The ESS is a configuration to alleviate the power burden due to uneven load requirements in the microgrid, and although a method using a lithium secondary battery has recently been implemented, any known energy storage means may be applied.

The ESS is a PCS (not shown) that converts the power stored in the ESS into an alternating current (or direct current) suitable for the microgrid, and supplies the microgrid to the microgrid system, and the microgrid system in an abnormal situation such as a power failure or an electrical leak. Blocking means (not shown) for blocking the connection of the.

The PCS of the ESS has a power phase synchronization function for matching the power phase of the system with the power output from the PCS, a function of adjusting the amount of power supplied to the system (that is, the magnitude of the voltage and / or current), and the system side. A surge mitigation / protection function for mitigating and / or blocking transmission of a risk factor such as a surge generated in the ESS can be performed, and configurations for this can be provided. Since the above functions have been known several times as PCS technology in the ESS field, detailed descriptions will be omitted.

The drawings illustrate a solar cell (PV: Photo Voltaic) and a wind turbine (WT) as distributed power sources.

In the structure description and the method description below, the control device 760 is expressed as driving the shut-off means 781 in order to respond to the system failure occurrence and determine the location of the failure. It is apparent that the PCS 730 is instructed to operate the blocking means 781, and the active PCS 730 operates the blocking means 781 according to the instruction.

2 is a flowchart illustrating a failure handling method performed in the control device 760 of FIG. 1.

The illustrated failure handling method includes: detecting a failure in the microgrid system (S10); A system shutdown step of shutting off the distributed power supplies (S20); Coupling the active PCS to the microgrid system (S30); Gradually increasing the voltage output from the connected active PCS (S40), and determining a location where the failure occurs (S50); And blocking the location where the failure has occurred (S60) and connecting the distributed power supplies to the microgrid (S70).

The failure detection step S10 may be performed by the PCS of each distributed power source connected to the microgrid system. In other words, as a self-protection function to protect each distributed power source that each PCS intersects with the system, it is possible to detect failures occurring in the microgrid system. Here, the PCS of each distributed power source is meant to include both the PCS of the prior art and the active PCS according to the spirit of the present invention. The PCS that has detected a failure may report it to the control device 760 of FIG. 1 using data communication means.

The system shutdown step S20 may be performed by a PCS detecting a failure by a function of the PCS itself, and a PCS not detecting a failure by a blocking command of the control device 760 of FIG. have.

Although the drawing shows that only the PCSs connected to the grid are disconnected from the grid in the grid breaking step (S20), in another implementation, distributed loads and distributed power supplies that do not have their own PCS are also blocked by the grid by the control device. Can be.

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, the step S60 may be performed by turning off a disconnected power source or a cutoff means of the distributed load.

In the step S70, the microgrid is restarted with only the failure part removed from the system before the complete recovery of the failure in the state where the failure has occurred, and may be referred to as a black start. In the step S70, when it is confirmed that the fault section of the system is separated (S60), first, the active PCS 730 is connected to the micro grid system to supply power to the healthy section, and sequentially cut off the distributed power supplies (PV) / WT) 's PCS can be connected to the microgrid system.

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

As a connection structure to the microgrid system of the active PCS shown in the figure, the disconnecting means includes: a power generation stage switch (G CB) for intermitting a power generating device and a PCS inverter in charge; An AC stage switch (AC CB) intermittent between the inverter and the microgrid of the active PCS; And an IGBT interrupting means (not shown) which interrupts the IGBT constituting the inverter.

As shown, the power generation device is interrupted with the inverter through the power generation switch (G CB), and the inverter is again interrupted with the breaking device (CB, 781 in FIG. 1) or the microgrid system through the AC end switch (AC CB). Can be. The order in which the active PCS, which has been separated from the system due to a fault occurring in the system, is reconnected to the system in accordance with the spirit of the present invention, is first closed by the generator switch (G CB) and then by the AC switch (AC CB). Is closed, and the IGBT constituting the inverter is closed according to the DC-AC conversion operation.

The operation process of the switches described above describes only the connection / blocking structure for the power generation device. When the active PCS is also connected to the energy storage means, the operation of the switch for interrupting / connecting the energy storage means is also described above. The process can be performed similarly.

Table 1 below describes the criteria of the failure location determination performed in the failure location determination step (S50).

The criteria described in the above table may be applied to the failure location determination method described below.

In the above table, "measured before and after the current difference in magnitude in the line fault section", which is the basis for judging whether there is a line fault, "before / after" means the position on the line of the measuring points of each line after the fault occurs. It can mean the point before and after.

Depending on the implementation, the microgrid system may be provided with two or more active PCS. The control device of the microgrid system in this case can take measures so that each active PCS does not interfere with each other in performing the failure position determination after the failure occurs.

For example, the control device separates (insulates) the failed microgrid system into two or more regions, and allows one active PCS to be connected to one separated region. To this end, the microgrid has a system area separation blocking means for separating the area at several points of the tracks constituting the system, and the control device is provided with a disconnecting means for separating the system area when a failure occurs in the system. It can be controlled (switched) to separate (insulate) into two or more regions.

Alternatively, the control device may allocate different working hours so that the two or more active PCSs perform the failure location determination work according to the spirit of the present invention, so that the times performed by each other do not overlap each other.

In the former case, after the step S20 in FIG. 2 and before the step S30, the method may further include separating the microgrid system in which the failure occurs into two or more regions.

In the latter case, before the step S30 of FIG. 2, the reference time from the time of the failure (reference time to start the failure position determination operation), which is connected to the microgrid system after the failure for each of the two or more active PCSs, occurs. It may further comprise the step of assigning.

4 is a flowchart illustrating an embodiment of a fault location determining method performed in the fault location determining step S50.

The illustrated failure location determination method, when the active PCS is connected to the microgrid system (S30), checking whether the active PCS itself is normal operation (S120); If it is confirmed that the active PCS is operating normally, by gradually increasing the voltage supplied from the active PCS to the system, by monitoring the current of the microgrid, to check whether the line / load side failure (S150); If the line / load side failure is confirmed, checking whether the failure for each load section (S180); If the failure is not confirmed in each load section, it may include a step (S189) to determine whether the line failure.

The flowchart shown is executed as the microgrid grid connection step S30 of the active PCS in FIG. 2 is performed, and step S30 in the figure means step S30 in FIG.

If the active PCS or the connected power generation device does not operate normally in the step S120 of checking whether the active PCS is normally operating, it is determined that the active PCS PCS is broken and the procedure ends. Checking whether the active PCS operates normally is a general technique of the PCS, and thus detailed description thereof will be omitted.

According to the implementation, after confirming the normal operation of the active PCS itself in step S120, it is confirmed whether the power generation device connected to the active PCS is capable of gradual pressurization (Off-Grid pressurization) to the system according to the spirit of the present invention. It may further comprise the step. This is due to the fact that significant power is required for the gradual pressurization into the system to check the overall system for failure. In addition, in the case of photovoltaic power generation and wind power generation, it is necessary to determine whether the amount of sunshine or wind speed can generate power for gradual pressurization to the system. Of course, in the case of the fossil fuel generator, it is also possible to consider the need to determine that the fuel amount is insufficient for the considerable power generation.

Gradually increasing the voltage / current supplied from the active PCS to the grid in the step S150 of checking whether the line / load side is faulty means performing the step S40 of FIG. 2.

The step of gradually increasing the voltage supplied to the grid from the active PCS performed in step S150 may be referred to as off-grid pressurization. FIG. 5 is a graph showing measured voltage and current with respect to off-grid pressurization in a normal state. 6 is a graph showing voltage and current measured with respect to off-grid pressurization in a state where a failure occurs in the microgrid.

In the above graphs, the grid voltage is 380 [V], the total load is 1.5 [M], the capacity of the power generation unit in charge of the active PCS is 2.0 [M], and the load 2 (772) of FIG. ) Assumes a ground fault accident.

It can be seen from the voltage / current graph in the state where the fault has occurred that when the voltage rises to about 114 [V], 80% (about 2.4 [kA]) of the fault determination current is close. 3.0 [kA]) In other words, when a microgrid system fails, the increase in the grid current due to the increase in the voltage supply is significantly greater than in the normal state (as a result, the failure determination current reaches 80%). This may be due to leakage, ground fault, or short circuit in the load or line, resulting in lower load-side impedance of the system. In the method of checking whether the line / load side fault is detected by using the phenomenon shown in the graph 2, the change in current due to the gradual increase in voltage is significantly higher than that in the steady state, compared to the case of the steady state. If the trend is confirmed, it is determined as a line / load side failure. Here, the failure determination current may be a reference current amount sufficient to determine the failure, and may be a current amount that does not interfere with the power distribution evenly to the line / load side connected to the grid. However, in general, it may mean a rated current according to the rated current specified for the distributed loads connected to the grid or the maximum power generation capacity of the power generator in charge.

In operation S30 of FIG. 2, since the distributed power supplies are not connected, it may be determined that the distributed power supplies are not malfunctioned.

When it is determined that the off-grid system is pressurized in step S150, that is, it is determined that there is no failure section in the pressurized system (part connected to the system in step S30), and in step S155, the distributed power supply installed is sequentially linked and Failure checks can be carried out. For example, when a power failure situation occurs again due to the associated distributed power source, failure due to the distributed power source may be determined. Pressurization of the off-grid system means that the voltage-current pattern according to the graph shown in FIG. 5 appears.

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

In step S180, when the current value measured at each end of each load section is measured at a predetermined ratio or more by comparing with a preset setting value, it is determined as a failure of the corresponding load section. In other words, in step S180, a failure section is determined by comparing a current value measured at the end of each load section with a setting value. For example, when the measured value> Setting X 0.5 (may be changed.), The corresponding section fails. Can be determined. However, when the rated capacity of the ESS is 1M, 0.8 may be applied as the magnification multiplied by the setting value. When the rated capacity of the ESS is 2M, the magnification may be adjusted according to the capacity of the ESS, such as setting the magnification to 0.7.

In the step S189, a difference occurs in the measured before and after current magnitudes in the case of a line failure section, and the difference in the measured magnitudes before and after the current may be estimated as the current flowing through the failure point. In the case of a normal line section where no fault has occurred, the difference in the magnitude of the measured current before and after appears similar.

FIG. 7 is a flowchart illustrating a more detailed process of sequentially connecting and failing distributed power supplies installed in a micro grid in step S155 of FIG. 4. 7 is a diagram illustrating sequentially connecting distributed power supplies installed for inspection after a failure, assuming that only the solar power power (PV) and the wind power power (WT) are distributed power sources separated from the corresponding microgrid system due to a failure. will be.

The illustrated distributed power test method includes connecting the PCS of the wind power source (WT) with the grid (S210) and checking whether a power failure occurs (S220); If the power failure by the wind power source (WT) does not occur, connecting the PCS of the solar power source (PV) with the grid (S230) and checking whether the power failure occurs (S240); If the power failure by the solar power supply PV does not occur, it may include a step (S250) for determining a momentary failure.

When the power failure is confirmed in step S220, a line failure of the wind power supply (WT) is determined (S225). When the power failure is confirmed in step S240, the line failure of the solar power PV may be determined. )

In the drawing, the wind power source (WT) is first inspected and then the solar power source (PV) is inspected. This inspection order may be changed.

FIG. 8 is a flowchart illustrating a more detailed process of checking whether line sections have failed in step S189 of FIG. 4. The drawings assume that there are only 1, 2, 3 track sections.

The illustrated line section inspection method includes: checking whether the current magnitude before measurement in line section 3 is similar to the magnitude of current after measurement (meaning that it is within the range considered to be practically the same) (S320); If the current magnitudes before / after measurement in line section 3 are similar to each other, checking whether the current magnitudes before measurement in line section 2 are similar to the current magnitudes after measurement (S330); If the current magnitudes before / after measurement in line section 2 are similar to each other, checking whether the current magnitudes before measurement in line section 1 are similar to the current magnitudes after measurement (S340); If the current magnitudes before / after measurement of the line section 1 are similar to each other, the method may include re-checking and / or checking an exception section (excluded section) (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 in step S335 and in step S340 that the current magnitudes before and after the measurement are different from each other, the failure of the line section 1 may be determined. (S345)

As described above in Table 1, in the "measured before / after currents in which the size difference occurs in the line fault section," which is the basis for judging whether a line has failed, "before / after" is a measurement point of each line after the failure. It may mean the front point and the back point of the position on the track.

In the drawings, the inspection was performed in the order of track sections 3, 2, and 1. However, the inspection order may be changed.

9A to 9D are block diagrams illustrating actions taken from a failure of a microgrid system to a black start according to the spirit of the present invention. In the figure, green for each CB means connection, red for disconnection, and gray for power generation devices, means stop functioning.

As shown in FIG. 9A, most of the blocking means of the microgrid is in the closed state, and the ESS is connected to the microgrid system by the closing means, regardless of whether the ESS is also operating. In the figure, SCB is a system circuit breaker for separating (insulating) the microgrid system into two areas, and PCS1 responsible for diesel generators (DG) and PCS4 responsible for fuel cell generators (FC) are seen. It is an active PCS according to the spirit of the invention.

In FIG. 9B, when a drop occurs in load 2, the ESS having its own PCS and each of the distributed power supplies PV and WT are disconnected from the microgrid system by a circuit breaker (CB) and / or the PCS self-protection function. . In the figure, the SCB is also expressed as blocked, but in the field, the CBs connected to the PCS that immediately detect a failure may be blocked, and then the SCB may be blocked by the control of a control device that detects the failure somewhat later.

Next, in FIGS. 9C and 9D in which an incident response measure according to the spirit of the present invention is performed, the SCB is continuously blocked to separate (insulate) the microgrid system into two regions SR1 and SR2, and In each of the separated regions, the distributed power supplies PV, WT are connected to the active PCS PCS1 and PCS4 with the separated regions SR1 and SR2 of the microgrid system, while the distributed power supplies PV and WT are disconnected from the system. (DG, FC) is operated to gradually increase the voltage of the divided regions SR1 and SR2.

FIG. 10 shows voltage and current waveforms with a gradual soft start in accordance with the inventive idea of the active PCS.

For example, as a soft start function of a PCS in charge of a prime mover, it shows the voltage / current waveform of the active PCS output stage as the output voltage gradually rises from 0V to the rated voltage over about 1 second.

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

It should be noted that the above embodiment is for the purpose of illustration and not for the purpose of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

* Explanation of the sign

700: microgrid system

730: active PCS

740, 750: distributed power supplies

760: control device

771, 772, 773: distributed loads

781 ~ 788: blocking means

781 ~ 785: detection means

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microgrid system for performing fault handling and a fault handling method using the same, which can be used in the field of power systems.

Claims (10)

Multiple distributed power supplies; Multiple distributed loads; Lines connecting the distributed power supplies and distributed loads; And Control device for controlling the operation of the distributed power supplies In the microgrid system comprising: At least one of the distributed power supplies, converting the power generated by the power generation device to the AC power suitable for the micro grid to supply to the micro grid, but has a blocking means for disconnecting the connection to the micro grid in an abnormal situation With active PCS, The control device, when detecting the failure in the microgrid, the microgrid system, characterized in that for processing the failure while gradually increasing the voltage output from the active PCS. The method of claim 1, The control device, Shutting off the distributed power supplies when a failure is detected in the microgrid; Coupling the active PCS to the microgrid; Determining a location where the failure occurs while gradually increasing a voltage output from the connected active PCS; Disconnecting the faulted location and connecting the distributed power supplies to the microgrid; Microgrid system to carry out. The method of claim 1, And wherein the active PCS checks whether the start-up is possible by gradually increasing the voltage of the power output from the power generation device after the failure occurs. The method of claim 1, The active PCS includes energy storage means for temporarily storing power generated by the power generation device and outputting the generated power to the active PCS. And gradually increasing the output voltage of the active PCS, and adjusting the output power of the energy storage means to output the microgrid together with the power generated by the power generation device. The method of claim 1, The active PCS, And gradually determine the location of the fault on the microgrid while gradually increasing the voltage output from the active PCS, and transmit the determined location to the control device. Multiple distributed power supplies, Multiple distributed loads, Including lines connecting the distributed power supplies and distributed loads, At least one of the distributed power supplies, the microcomputer having an active PCS that converts the power generated by the power generation device into an alternating current power suitable for the microgrid, and has a blocking means for disconnecting the connection to the microgrid in an abnormal situation In the failure handling method of the grid, Shutting off the distributed power supplies when a failure is detected in the microgrid; Coupling the active PCS to the microgrid; Determining a location where the failure occurs while gradually increasing a voltage output from the connected active PCS; Disconnecting the faulted location and connecting the distributed power supplies to the microgrid; Failure processing method comprising a. The method of claim 6, Determining the location where the failure occurs, Checking whether the active PCS or the power generation device in charge of the active PCS has failed; If it is determined that the active PCS is operating normally, gradually increasing the voltage supplied from the active PCS to the grid, and monitoring the current of the microgrid to check whether there is a line / load side failure; Checking whether a line / load side fault is detected, each load section; And If the fault is not confirmed in each load section Failure processing method comprising a. The method of claim 7, wherein After checking whether the active PCS side failure, Checking whether the start-up to gradually increase the output voltage after the failure occurs is possible Failure processing method further comprising. The method of claim 7, wherein Checking whether the line / load side failure, A failure handling method that determines a line / load side failure if a trend of increase of the current due to a gradual increase in voltage is compared with the case of a steady state, and if an increase trend is markedly higher than that of the steady state current. The method of claim 6, Prior to connecting the active PCS to the microgrid, Separating the faulty microgrid system into two or more regions; or Allocating a reference time for starting the failure location determination operation for each of the two or more active PCS; Failure processing method further comprising.

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