KR101044631B1 - Synchronization control method for reconnecting microgrid to upstream network - Google Patents

Abstract

PURPOSE: A synchronization control method for reconnecting a micro grid to an upper power system is provided to determine a reference frequency and a voltage by a plurality of micro power, thereby synchronizing with the upper power system. CONSTITUTION: A subtracter(502) calculates the difference between the voltage phase of a power system and the voltage phase of a micro grid. A proportional gain block(503) determines a changed amount of a set effective power value of micro power by multiplying the voltage phase difference with a voltage phase synchronization gain. An adder(506) outputs a set effective power value(507) of micro power modified for voltage phase synchronization by adding the changed amount to the set effective power value. The changed amount is limited in a specific range.

Description

Synchronization Control Method for Reconnecting Microgrid to Upstream Network}

The present invention relates to a synchronization control method for reconnecting a microgrid that can be operated solely by a plurality of micropowers with an upper power system. More specifically, a micropower that is located close to a point of common coupling (PCC) in a microgrid. The present invention relates to a control method of adjusting this output to synchronize the independent voltage phase and magnitude of the microgrid with the voltage phase and magnitude of the upper power system.

Microgrids are defined as small-scale power grids that consist of various types of micropower sources and consumers who are power consumers and consumer groups and are capable of islanded operation.

Microgrids are capable of continuous stand-alone operation by one or more micropower sources, other than an uninterruptible power supply that can supply power during short power outages, and are powered by micropower sources. And a consumer group, consumers can be provided with a high reliability and quality of power as well as a variety of services.

When the power quality is lowered due to an accident in the upper power system, the customer operating with the micro grid can separate and operate the upper power system alone by opening the switch connecting the upper power system and the micro grid. You may not experience power system accidents and reduced power quality.

In addition, the microgrid is described in detail in Patent Application No. 10-2010-0032972 regarding a micro power supply for the microgrid and a control method thereof.

In a microgrid operated alone, the reference frequency and voltage of the microgrid must be provided by one or more micropower sources to maintain the power quality of the microgrid and to supply the power required by the load.

The micropower supplying the reference frequency and voltage to the power system is operated by Grid-Forming control method. Grid-Forming control method outputs phase and magnitude of independent voltage regardless of phase and magnitude of voltage of power system to which micro power is connected.

Unlike the Grid-Forming control method, the Grid-Following control method outputs the phase and magnitude of the voltage relative to the phase and magnitude of the voltage of the power system to which the micro-power is connected. When no reference frequency and voltage are provided to the power system, power cannot be supplied and standalone operation is not allowed.

If the micropower supply providing the reference frequency and voltage has a sufficiently large capacity, it will be able to supply better quality power. However, due to the technical and economic limitations of the micro power supply, the capacity of the micro power supply has to be limited. Therefore, it is necessary to operate a plurality of micro power supplies in parallel to supply enough power for the micro grid.

The droop characteristics of the active power P and the frequency ω of FIG. 1 and the droop characteristics of the reactive power Q and the voltage V of FIG. 2 provide a reference frequency and voltage. One of the control methods of the micro-power source, and using this, there is an advantage that the micro-grid can determine the steady state reference frequency and voltage of the micro grid while properly distributing the power required by the micro grid by operating in parallel without communication. In addition, the droop control method improves the transient stability of the micro power supply.

The droop characteristics as shown in FIGS. 1 and 2 are represented by Equation 1.

[Equation 1]

In Equation 1, P _i ^* and Q _i ^* are the setting values of the active power and the reactive power of the i-th micro power supply in the microgrid operated alone, and P _i (t) and Q _i (t) operate alone. Ω ₀ is the rated frequency, V ₀ is the rated voltage, ω (t) is the common operating frequency of the grid operated alone, V _i (t) is the terminal voltage of the i-th micropower supply, k _P is the static droop gain of the droop characteristic between active power and frequency, k _P <0, and k _Q is the droop characteristic between reactive power and voltage. Proportional gain, k _Q <0, i = 1, 2, ..., n, where n is the number of micropower sources present in the microgrid.

The micropowers in the microgrid operated solely from Equation (1) can supply the active power required by the microgrid using the controller as shown in FIG. 3, and the invalid power required by the microgrid using the controller as shown in FIG. Can supply power

The controller of FIG. 3 is a proportional gain block having a droop characteristic of a difference between the active power set value 300 of the micro power supply and the active power 301 currently output from the micro power supply to supply the power required by the load in the microgrid. Multiply by 302 to determine frequency variation 303, frequency variation 303 is added to frequency variation 308 for synchronization with rated frequency 304 to determine frequency 305 of the output voltage of the micropower source, The frequency 305 of the output voltage of the micropower is integrated by the integrator 306 to determine the phase 307 of the output voltage of the micropower.

The controller of FIG. 4 is a reactive power setpoint 400 of the micropower supply, and a reactive power 401 currently output from the micropower supply to supply reactive power accompanying to supply the active power required by the load in the microgrid. Multiplying the difference by by the proportional gain block 402 of the droop characteristic to determine the magnitude variation 403 of the voltage, and adding the magnitude variation 403 of the voltage and the magnitude 404 of the rated voltage to the magnitude of the output voltage of the micro-power source ( 405).

3 and 4, the controller of the micro power source using the droop characteristic may allow the microgrid operated alone to operate at a frequency and voltage lower or higher than the rated frequency and voltage of the power system.

In order for the microgrid, which is operated separately from the upper power system by the micro-power sources, to reconnect with the upper power system, proper synchronization can synchronize the independent grid phase and magnitude of the microgrid with the independent voltage phase and magnitude of the upper power system. Control is required.

If the power system and the microgrid are reconnected without synchronizing control, a transient phenomenon may occur in which a circulating current significantly occurs between them. Such transients can activate multiple protection devices or stress them.

For example, if the reference frequency and voltage of a microgrid operating alone are determined by the droop characteristics of a plurality of micropower sources, the voltage of the microgrid may be due to the following two constraints according to the technical and economic limitations of the micropower source. There is a difficulty in synchronizing the phase and magnitude with the voltage phase and magnitude of the upper power system.

Among the constraints, the first is that fast communication to perform synchronization between the micropower and the integrated control device in a microgrid that operates alone cannot be adopted due to reliability issues. Accordingly, the micro power source capable of synchronizing the voltage phase and magnitude of the microgrid operated alone with the upper power system is located near the point of common coupling (PCC) connecting the micro grid and the upper power system. Only micropower supplies can directly measure the voltage phase and magnitude of the system without fast communication. The second constraint is that if the reference frequency and voltage of a microgrid that is operated solely by multiple micropower sources is determined, a significant output of that micropower or micros in the microgrid when synchronization is performed with only the micropower located close to the PCC A circulating current can occur between the power supplies.

Due to the above constraints, only a micro power source located close to the PCC in the conventionally operated microgrid is able to determine the reference frequency and voltage, thereby performing reconnection after switching and synchronization in single operation. However, in such a method, if the capacity of the micro power supply which determines the reference frequency and voltage is relatively high, another problem arises in that the power required by the micro grid is sufficiently supplied and the transition to single operation can be smoothly performed. .

Another method is to control the microgrid's reference frequency and voltage when the synchronization of the microgrid, except for the micropower located close to the PCC in the microgrid, is performed when the microgrid operating alone is reconnected with the upper power system. The system switches to Grid-Following control method that can't determine the voltage, and only the micro power supply close to PCC can determine the reference frequency and voltage to perform synchronization. However, in such a method, the control method of the micropowers in the microgrid has to be changed, thereby increasing the complexity of the control, and the micropowers also need to support various control methods.

Accordingly, an object of the present invention is to provide a synchronization control method for allowing microgrids to operate independently to reconnect to higher power systems.

In addition, the synchronization control that can be synchronized with the upper power system without changing the control method of other micro power supply with the small effective and reactive power output of the micro power that is located near the PCC among the multiple micro power supplies in the microgrid. To provide a way.

In addition, the reference frequency and voltage of the microgrid can be determined by a plurality of micro-power source irrespective of the geographic location of the micro-power source, to provide a synchronization control method that enables the smooth operation of the micro grid and switching the single operation. have.

First, to summarize the features of the present invention, in accordance with an aspect of the present invention for achieving the object of the present invention, the synchronization control for reconnecting with the upper power system during single operation in a microgrid including a plurality of micro-power source The method adjusts the output of the micropower located close to the PCC connecting the upper grid with the microgrid running alone, thereby synchronizing the voltage phase and voltage magnitude of the microgrid with the voltage phase and voltage magnitude of the upper grid. In order to recover the output of the micropower located near the PCC to '0' or relatively less than other micropowers, the reference frequency and voltage of the microgrid near the frequency and voltage magnitude of the upper power system. A first control step of adjusting; And a second control step of adjusting the output of the micro power supply to synchronize the voltage phase and voltage magnitude of the microgrid with the upper power system.

In addition, the synchronization control method for reconnecting to the upper power system during a single operation in a micro grid including a plurality of micro power source according to another aspect of the present invention, the position close to the PCC connecting the micro grid and the upper power system in a single operation. Adjusting the frequency of the microgrid near the frequency of the upper power system to adjust the output of the micropower to synchronize the voltage phase and voltage magnitude of the microgrid with the voltage phase and voltage magnitude of the upper power system. ; Controlling the active power of the micropower source located close to the PCC for synchronizing the upper power system with the voltage phase; Adjusting the reference voltage of the microgrid to near the voltage level of the upper power system after the voltage phase synchronization is completed to reduce the effective power of the micro-power source located near the PCC; And controlling reactive power of the micropower source located close to the PCC for synchronizing the voltage level with the upper power system.

In addition, the synchronization control method for reconnecting with the upper power system during a single operation in a micro grid including a plurality of micro power supply according to another aspect of the present invention, close to the PCC connecting the micro grid and the upper power system in a single operation In order to adjust the output of the located micro-power source to synchronize the voltage phase and voltage magnitude of the microgrid with the voltage phase and voltage magnitude of the upper power system, the reference frequency and voltage of the microgrid and the frequency of the upper power system and Adjusting to near voltage magnitude; Controlling the active power of the micropower source located close to the PCC for synchronizing the upper power system with the voltage phase; And after the voltage phase synchronization is completed and the active power of the micropower closest to the PCC is reduced, the reactive power of the micropower located close to the PCC for voltage magnitude synchronization with the higher power system is reduced. Controlling.

In addition, in the microgrid operated alone by a plurality of micro-power source that is the control base of the droop characteristics according to another aspect of the present invention, for managing the energy storage device provided in a specific micro-power source that is the control base of the droop characteristics Setting an active power setpoint P ₁ ^* of the micropower to a desired output setpoint to adjust the output of the powerpoint to a desired value; And based on [Equation 2], the active power setting value P ₁ ^* and the active power output P ₁ (t) of the corresponding micro power supply, the active power output P _i (t) of the i-th micro power source of the remaining micro power sources in the microgrid. And using the proportional gain k _p of the droop characteristic between the active power and the frequency, to change the active power set value _Pi ^* of the other micropowers in the microgrid.

In addition, in a microgrid operated with a plurality of micropowers based on droop characteristics according to another aspect of the present invention, an active power controller of a micropower based on droop characteristics may include a variation ΔP of the active power setpoint in the active power setpoint P ₁ ^* . in order to determine the ₁ ^* plus modified active power set value P ₁ ^'*, limit the active power output variation of the micro-power in accordance with the effective variation ΔP ₁ of the power set point ^- within the specified range (ΔP ^min ~ ΔP ^max) To adjust the output of the micro power supply by setting the threshold ΔP ₁ ^{max *} or ΔP ₁ ^{min *} of the variation ΔP ₁ ^* to the hard limiter, the limit ΔP ₁ ^{max *} or ΔP ₁ ^{min *} is represented by [Equation 12] is determined based on where, k _p1 is within the i-th power micro-loop gain, k _pi micro grid of the active power and frequency between the droop characteristic of the micro-power Proportional gain of the droop characteristic between effective power and frequency, P ₁ ^max is a minimum active power tolerance of the micro-power to perform synchronization is maximum active power limit, P ₁ ^min of the micro-power, P _i ^* is the micro-grid within the rest of the micro- Each active power setpoint of the power supplies, P _L is characterized in that the active power required by the load in the microgrid.

According to the synchronization control method of the present invention, a reference frequency and voltage are determined through a plurality of micro power supplies, and when a microgrid operating alone performs synchronization for reconnecting with a higher power system, a PCC of a plurality of micro power supplies in the micro grid is performed. It is possible to perform synchronization with the upper power system without changing the control method of other micro power supply with the small effective and reactive power output of the micro power supply which is located close to perform synchronization.

In addition, the output limitation of the micropower that performs the synchronization in the synchronization control enables the micropower to be operated in a stable range.

And, the reference frequency and voltage of the microgrid can be determined by a plurality of micropower sources irrespective of the geographic location of the micropower source, thereby enabling smooth single-run and single-run switching of the microgrid.

1 is a view for explaining the droop characteristics of a typical frequency and the active power.
2 is a view for explaining the droop characteristics of a typical voltage and reactive power.
3 is a configuration diagram of an active power controller of a conventional micro-power source based on droop characteristics of frequency and active power.
4 is a configuration diagram of a reactive power controller of a conventional micro-power source due to droop characteristics of voltage and reactive power.
5 is a relationship between the microgrid and the upper power system according to an embodiment of the present invention.
6 is a view for explaining the reference frequency change and the operating point change of the micro grid according to the active power set value according to an embodiment of the present invention, (a) is a steady state operating point at the reference frequency, (b) is a reference Steady state operating point change with increasing frequency, (c) shows steady state operating point change with decreasing reference frequency.
7 is a block diagram of a voltage phase synchronization controller according to an embodiment of the present invention.
8 is a block diagram of a voltage magnitude synchronization controller according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

Hereinafter, according to the present invention, a preferred embodiment of a synchronization control method for reconnecting a microgrid, which is operated with a plurality of micro power sources and capable of independent and grid linkage operation, to a higher power system will be described in detail.

The synchronization control method according to the present invention may be applied in synchronization control for connecting a microgrid, which is operated solely, with a reference frequency and voltage determined by a predetermined droop characteristic among a plurality of micro power supplies. Can be.

Considerations for the synchronization control method in the microgrid include:

First, because of reliability problems of fast communication for synchronization, only a micropower located close to a point of common coupling (PCC) among a plurality of micropowers in a microgrid may perform synchronization control with a higher power system. Under these constraints, if the reference frequency and voltage of the microgrid are determined only by the microsupply located close to the PCC, the microsupply must be sufficiently sensitive to the sensitive loads in the microgrid for smooth single run and single run switching of the microgrid. It must have sufficient capacity to provide power. However, depending on the technical and economic limitations of micropower sources, there are limitations in their implementation.

Accordingly, in the present invention, the reference frequency and voltage of the microgrid are determined by a plurality of micropower sources located close to the PCC regardless of the geographic location of the micropower, thereby ensuring smooth operation of the microgrid and switching of single operation. It was. When the reference frequency and voltage of the microgrid are determined by the plurality of micro-power sources as described above, when the micro-grid can perform synchronization with the upper power system, that is, only the micro-power located close to the PCC performs synchronization. A circulating current can occur between a significant output of the power supply or between micropowers in the microgrid.

To solve this problem, the control method of other micropowers in the microgrid is changed to the Grid-Following control method so that only the micropower located near the PCC can determine the reference frequency and voltage when performing the synchronization. The finite capacity of the micro power source must be considered, and there is a problem that a switching function of the control method of other micro power sources in the microgrid must be supported.

In order to solve this problem, the synchronization control method according to the present invention includes the following two control steps.

1. First Control Stage

The first control step of the synchronization control method according to the present invention performs the synchronization, that is, considering the instantaneous output limit according to the finite capacity of the micropower located close to the PCC, the corresponding state in the normal state of the microgrid before performing the synchronization Restores the microgrid's reference frequency and voltage magnitude, restoring the active and reactive power of the micropower to zero or a relatively low output (relatively less than that of a micropower other than the micropower located close to the PC). To recover near the rated frequency (ω ₀ ) and rated voltage (V ₀ ) of the upper power system.

Here, restoring the effective and reactive power of the corresponding micropower that performs the synchronization control to '0' or a relatively small output is considered to be effective and effective for synchronizing the micropower in consideration of the finite energy and instantaneous capacity of the micropower. This is to allow a margin in the reactive power output.

In a microgrid operated solely by a plurality of micropower sources that are the control base of droop characteristics, a reference frequency recovery according to the present invention is also used to manage the state of charge of an energy storage device (battery, etc.) included in a specific micropower source within the microgrid. Using the procedure, you can adjust the active power of the micropower to the desired output.

(1) reference frequency recovery

For the micropowers using the droop characteristic, the steady state frequency ω (t) and voltage V _i (t) are determined according to [Equation 1]. When the terminal voltage of each micro power supply is operating at V _i (t) in a microgrid that is operated alone at a specific frequency ω (t), the active power setting value (P _i ^* ) and the reactive power setting value (Q) of each micro power source are operated. _{When i} ^* ) is set to the active power (P _i (t)) and reactive power (Q _i (t)) currently output from each micro power supply, each micro power supply is rated at the rated frequency and rated voltage ω ₀ and V _0. Can be driven.

To restore the output of a micropower located close to the PCC to '0' or to a specific output, the active and reactive power settings of the micropower located close to the PCC must be set to '0' or to the value of the specific output.

Therefore, from the droop characteristic in which the frequency in the microgrid operating alone distributes the effective power at a common reference frequency, the frequency recovery during the first control step of the synchronization control method according to the present invention except for the micro power source located close to the PCC. Set the active power setpoint of the micropowers (P _i ^* ) as shown in [Equation 2] and set the active power setpoint (P ₁ ^* ) of the micropower placed near the PCC to the desired output setpoint ('0' or relatively less output). To restore the reference frequency of the microgrid near the rated frequency. In Equation 2, subscript 1 denotes a micro power source that is located close to the PCC and can perform synchronization by quickly and simply measuring the voltage of the upper power system without data transmission by communication. That is, the micro power source located close to the PCC does not mean a micro power source whose geographical position is located closest to the PCC, but is a micro power source located near the connection point (PCC) connecting the micro grid and the upper power system. In other words, it refers to a micro power source located at a place where voltage can be quickly measured through a directly connected signal line without a process of transmitting and receiving digital data through communication according to a predetermined communication method.

[Equation 2]

Where P ₁ (t) is the steady state active power output of the micropower near the PCC before restoring the reference frequency of the microgrid near the rated frequency, and P _i (t) is the reference of the microgrid near the rated frequency. It is the steady state active power output of the i-th micropower before restoring frequency, and P ₁ ^* is the active power output setpoint of the micropower close to the PCC when it is restored to a frequency near its rated. In addition, each k _P is a proportional gain of the droop characteristic between the effective power and the frequency of the micro power supplies in the micro grid, and k _P <0. k _P is expressed as an absolute value in [Equation 2] because the sign can be changed according to the configuration of the controller.

When the control method is performed, the flow of active power in the microgrid may be changed, and the terminal voltage of each micro power source may be changed to change the total effective power required in the microgrid. Therefore, it is difficult to recover to the rated frequency exactly by the above method. However, since it is required to assist the synchronization control, the above method is sufficient, and frequency recovery can be easily performed by changing a single set point.

The method of the present invention as described above, in the microgrid that is operated alone by a plurality of micro-power source that is the control base of the droop characteristics, by using [Equation 2], the energy storage device of a specific micro-power source that is the control base of the droop characteristics You can also adjust the micropower to the desired output for management purposes.

Set the active power setpoint (P ₁ ^* ) of the micropower, which is the control base of the droop characteristic to adjust the output, to the desired output setpoint, and set the active power setpoint (P _i ^* ) of the other micropowers in the microgrid to [Equation 2]. If set by using it, you can adjust the output of the micropower to the desired output.

In this case, the subscript 1 in [Equation 2] means the micro power supply to adjust the output. Also, P ₁ (t) is the steady state active power output of the micropower to adjust the output, P ₁ ^* is the active power setting of the micropower to adjust the output, and P _i (t) is the current of the other micropowers in the microgrid. Active power output.

(2) reference voltage recovery

Voltage recovery in the first control step of the synchronization control method according to the present invention can also recover the reference voltage of the microgrid to near the rated in a similar manner to the frequency recovery.

In the voltage recovery, set the reactive power setpoint (Q _i ^* ) of the remaining micropowers except for the micropower placed near the PCC as shown in [Equation 3], and set the reactive power setpoint of the micropower placed near the PCC (Q ₁ ^* ). Is set to the desired output set point ('0' or relatively low output) to restore the reference voltage of the microgrid to near the rated voltage. In Equation 3, subscript 1 denotes a micro power source which is located close to the PCC and can perform synchronization by quickly and simply measuring the voltage of the upper power system without data transmission by communication.

&Quot; (3) &quot;

Where Q ₁ (t) is the steady state reactive power output of the micropower near the PCC before restoring the reference voltage of the microgrid near the rated voltage, and Q _i (t) is the reference of the microgrid near the rated voltage. It is the steady state reactive power output of the i-th micropower before voltage recovery, and Q ₁ ^* is the reactive power setpoint of the micropower close to the PCC when it returns to the voltage near its nominal power. In addition, each k _Q is a proportional gain of the droop characteristic between reactive power and voltage of the micro power supplies in the microgrid, and k _Q <0. k _Q is represented as an absolute value in [Equation 3] because the sign can be changed according to the configuration of the controller.

In the reference voltage recovery, it is difficult to recover to the rated reference voltage accurately because of the local characteristics of the voltage, but the reference voltage recovery for the synchronous control is enough to recover only near the rated voltage. In addition, even in the upper system, a voltage magnitude in which a certain voltage drop occurs rather than an accurate voltage may be provided. If the reference voltage of the microgrid is restored, some frequency reduction may occur due to the loads having constant impedance characteristics. However, even frequency recovery for synchronous control does not require a completely accurate rated frequency.

2. Second control step

The second control step of the synchronization control method according to the present invention is to adjust the effective and reactive power of the micro power supply located close to the PCC in order to synchronize with the upper power system by changing the voltage phase and magnitude of the microgrid in operation alone. .

6 is a view for explaining a change in the reference frequency of the microgrid according to the active power set point, according to an embodiment of the present invention, (a) is at the reference frequency, (b) when the reference frequency increases, (c) Indicates the steady state operating point when the reference frequency decreases. Here, for the sake of simplicity, one embodiment of n = 2 is shown, and even when a plurality of micro power sources exist, the same characteristics as in the case of n = 2 may be exhibited.

As shown in the graph of FIG. 6 (a) showing a steady state operating point at a reference frequency, when the microgrid is operating alone, the first control step is performed in the synchronization control method according to the present invention to evaluate the frequency of the microgrid. It can be operated by recovering to the frequency ω ₀ .

Fig 6 (a) in the P ₁ and P ₂ are each real power of the micro-power located closer to the PCC (P ₁₎ and the active power of the different micro-power in the micro-grid (P _2), P ₁ ^* and P ₂ ^* are each active power set value of the micro-power located closer to the PCC (P ₁ ^*) with the active power set value of the other micro power (P ₂ ^*) is, ω _0, ω, ω _min were rated frequency, the synchronization control before the normal State operating frequency, minimum operating frequency, k _P1 and k _P2 are proportional gains (k _P1 ) of the droop characteristics between the active power and frequency of the micropower close to the PCC, respectively, and droop characteristics between the active power and the frequency of the other micropower. Is the proportional gain of k _P2 .

6 (b) and 6 (c) show that the micro-power source located near the PCC is located close to the PCC as shown in [Equation 4] to synchronize the phase of the voltage of the microgrid with the phase of the voltage of the upper power system. When the active power setting value of the micro power supply is changed from P ₁ ^* to P ₁ ' ^* , the reference frequency increases and the reference frequency decreases.

&Quot; (4) &quot;

Here, P ₁ ' ^* is a modified active power setpoint for phase synchronization, and ΔP ₁ ^* is a change in active power setpoint required for P ₁ ' ^* .

As shown in [Equation 4], as the active power setting value of the micro power source located near the PCC is changed to P ₁ ' ^* , the steady state operation of the micro grid as shown in FIGS. 6 (b) and 6 (c). As the reference frequency at e varies from ω ₀ to ω ₀ ± Δω, the outputs of the micropower and other micropowers located close to the PCC change from P ₁ and P ₂ to P ₁ 'and P ₂ ', respectively. Accordingly, the steady state active power P of the entire micropower, including the power required by the loads in the microgrid and the micropower (i = 1) and other micropowers (i = 2,3, ..) located close to the PCC. _load satisfies [Equation 5].

[Equation 5]

Hereinafter, a voltage phase synchronization controller (FIG. 7) and a voltage magnitude synchronization controller (FIG. 8) for adjusting the voltage phase and magnitude of the microgrid and synchronizing with the upper power system in the second control step as described above will be described. .

(1) voltage phase synchronization

7 is a diagram illustrating a voltage phase synchronization controller according to an embodiment of the present invention. Referring to FIG. 7, a voltage phase synchronization controller according to an embodiment of the present invention includes a subtractor 502, a proportional gain block 503, and a summer 506.

The subtractor 502 calculates a voltage phase error that is the difference between the voltage phase δu 500 and the microgrid voltage phase δm 501 of the upper power system, and the proportional gain block 503 calculates the voltage phase error from the subtractor 502. Multiply the voltage phase synchronization gain (k _δ ) to determine the variation ΔP ₁ ^* (504) of the active power setpoint of the micropower supply. Accordingly, the summer 506 adds the variation ΔP ₁ ^* 504 of the active power setpoint and the active power setpoint P ₁ ^* 505 of the micropower, and the active power setpoint P ₁ ′ of the micropower modified for voltage phase synchronization. ^* outputs 507. The variation ΔP ₁ ^* 504 of the effective power setpoint may be limited to a specific range ΔP ^min ΔP ^max to protect the device in consideration of the finite capacity of the micro power source.

Here, the active power set point P ₁ ' ^* (507) of the modified micro-power source can be expressed as shown in [Equation 6].

&Quot; (6) &quot;

(2) voltage magnitude synchronization

The voltage magnitude synchronization control of the synchronization control method according to the present invention also uses the droop characteristic principle for reactive power and voltage in a similar manner to the voltage phase synchronization control.

8 is a configuration diagram illustrating a voltage magnitude synchronization controller according to an embodiment of the present invention. Referring to FIG. 8, a voltage magnitude synchronization controller according to an embodiment of the present invention includes a subtractor 602, an integration controller 603, and an adder 606.

The subtractor 602 calculates a voltage magnitude error that is the difference between the voltage magnitude V _u 600 and the microgrid voltage magnitude V _m 601 of the upper power system, and the integral controller 603 calculates the voltage magnitude from the subtractor 602. Multiply the error by the voltage magnitude synchronization gain (k _V ) and integrate to determine the variation ΔQ ₁ ^* 604 of the reactive power setpoint of the micropower supply. Accordingly, the summer 606 adds the variation ΔQ ₁ ^* 604 of the reactive power set value and the reactive power set value Q ₁ ^* 605 of the micro power supply, and the reactive power set value P ₁ ′ of the micro power source modified for voltage magnitude synchronization. ^* outputs 607. The variation ΔQ ₁ ^* 604 of the reactive power setpoint may be limited to a specific range ΔQ ^min to ΔQ ^max to protect the device according to the finite capacity of the micropower.

Here, the modified reactive power set value Q ₁ ' ^* 607 of the micro-power source can be expressed as shown in [Equation 7].

 [Equation 7]

In Fig. 8, the variation ΔQ ₁ ^* 604 of the reactive power set point is initialized when the microgrid in stand-alone operation is reconnected with the upper power system after synchronization is completed, which causes the integral controller 603 to reset the reset signal. It can be made by initialization.

As shown in FIG. 6 and [Equation 4], when the effective power setpoint is changed to P ₁ ' ^* , the reference frequency of the microgrid can be changed. However, when the phase difference between the upper power system and the voltage in the microgrid is large, many frequencies If a change is required and ΔP ₁ ^* becomes large in Equation 4, the output of the micro power source located near the PCC may exceed the limit. Therefore, by appropriately limiting ΔP ₁ ^* , the output of the micropower source located close to the PCC should be limited.

The output P _i (t) of the i-th micropower supply performing synchronization control from Equation 1 is expressed by Equation 8, and the outputs of the n micropowers in the microgrid are expressed by Equation 9 .

[Equation 8]

[수학식 9]

[Equation 9]

Considering the variation ΔP ₁ ^* (504) of the set value for the active power required for performing synchronization, [Expression 8] and [Formula 9] in P ₁ ^* is [Equation 10] P ₁ 'equal to the ^* , leaving the active power variation of the micro-power by ΔP ₁ ^* as ΔP ₁ (t), [expression 8] and of formula 9] [formula 11] P ₁ (t) in the P ₁ '(t )

[Equation 10]

[Equation 11]

Using Equations 8 to 11, the maximum and minimum limits ΔP ₁ ^{max *} and ΔP ₁ ^{min *} of the active power setpoint variation of the micro-power source performing synchronization control are obtained as shown in [Equation 12]. As shown in [Equation 12], the maximum and minimum limits ΔP ₁ ^{max *} and ΔP ₁ ^{min *} of the change of the active power set value of the corresponding micro power supply are set in the hard limiter so that the effective power output of the micro power supply is appropriately limited.

[Equation 12]

Here, P ₁ ^max is the maximum active power allowance of the micro power supply performing synchronization, P ₁ ^min is the minimum effective power allowance of the micro power supply performing synchronization, and P _L is the active power required by the load in the microgrid. The minimum active power allowable value P ₁ ^min of the micro power supply may be set as a limit value of the active power absorbing power by being expressed as a negative number.

When the micro power supply performing synchronization to synchronize the voltage phase injects the active power into the micro grid, the flow of reactive power from the change of the voltage of each bus (node) in the micro grid according to the change of the active power flow in the micro grid. Will change. Such interference of active power and reactive power may result in the following in synchronization control.

When synchronizing with the upper system, assuming that the voltage magnitude synchronization by the injection of reactive power is completed before the voltage phase synchronization, when the voltage phase synchronization is completed and the active power flow changes, the voltage magnitude synchronization should be performed again.

Therefore, the two control steps of the synchronization control may be divided into detailed steps as follows.

1) Restore the microgrid's reference frequency near the rated frequency of the upper power system (ω ₀ ) (see '(1) Reference Frequency Recovery' in '1.First Control Step')

2) Start of voltage phase synchronization control to synchronize the upper power system and voltage phase (see '(1) Voltage Phase Synchronization' in '2. Second Control Stage')

3) After the voltage phase synchronization is completed and the active power of the micro power supply performing the synchronization is reduced, the reference voltage of the micro grid is restored to near the rated voltage (V ₀ ) of the upper power system (see '1.First Control Step'). Refer to '(2) Reference Voltage Recovery')

4) Start voltage magnitude synchronization to synchronize voltage magnitude with the upper power system (see '(2) Voltage magnitude synchronization' in '2. Second control stage')

5) Once the voltage phase and magnitude synchronization is complete, reconnect to the upper power system and terminate the voltage phase and magnitude synchronization control.

The above procedure may be briefly applied as follows.

1) Restore the reference frequency and voltage of the microgrid to the frequency and voltage of the upper power system (refer to '(1) Reference Frequency Recovery' and '(2) Reference Voltage Recovery' in '1.First Control Step')

2) Start of voltage phase synchronization control to synchronize the upper power system and voltage phase (see '(1) Voltage Phase Synchronization' in '2. Second Control Stage')

3) After the voltage phase synchronization is completed and the active power of the micro power supply performing the synchronization is reduced, the voltage magnitude synchronization starts to synchronize the voltage magnitude with the upper power system ('2 voltage in' 2. Second Control Phase '). Size sync ”)

4) Once the voltage phase and magnitude synchronization is complete, reconnect to the upper power system and terminate the voltage phase and magnitude synchronization control.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

Subtractor (502)
Proportional Gain Block (503)
Summer (506)
Subtractor (602)
Integral Controller (603)
Summer (606)

Claims (12)

A synchronization control method for reconnecting to an upper power system during a single operation in a microgrid including a plurality of micro power sources,
In order to adjust the output of the micro power source located close to the PCC connecting the upper power system and the micro grid in operation alone, to synchronize the voltage phase and voltage magnitude of the micro grid with the voltage phase and voltage magnitude of the upper power system.
The reference frequency and voltage of the microgrid are the frequency and voltage magnitude of the upper power system while restoring the active power and the reactive power of the micropower located near the PCC to a relatively smaller output than '0' or other micropower, respectively. A first control step of adjusting each to near; And
And adjusting a output of the micro power supply to synchronize the voltage phase and voltage magnitude of the micro grid with the upper power system.
The second control step may include: controlling an active power of the micropower source located close to the PCC for synchronizing the upper power system with the voltage phase; And
Controlling reactive power of the micropower located close to the PCC for synchronizing voltage magnitude with the upper power system
Synchronization control method of a microgrid comprising a. A synchronization control method for reconnecting to an upper power system during a single operation in a microgrid including a plurality of micro power sources,
In order to adjust the output of the micro power source located close to the PCC connecting the upper power system with the micro grid in operation alone, to synchronize the voltage phase and voltage magnitude of the micro grid with the voltage phase and voltage magnitude of the upper power system.
Adjusting the reference frequency of the microgrid to near the frequency of the upper power system while recovering the active power of the micropower located near the PCC to an output less than '0' or other micropower;
Controlling the active power of the micropower source located close to the PCC for synchronizing the upper power system with the voltage phase;
After the voltage phase synchronization is completed and the active power of the micropower located close to the PCC is reduced, outputting less reactive power of the micropower located near the PCC to zero or other micropower. Adjusting the reference voltage of the microgrid to near the voltage level of the upper power system while recovering to; And
Controlling reactive power of the micropower located close to the PCC for synchronizing voltage magnitude with the upper power system
Synchronization control method of a microgrid comprising a. A synchronization control method for reconnecting to an upper power system during a single operation in a microgrid including a plurality of micro power sources,
In order to adjust the output of the micro power source located close to the PCC connecting the upper power system with the micro grid in operation alone, to synchronize the voltage phase and voltage magnitude of the micro grid with the voltage phase and voltage magnitude of the upper power system.
The reference frequency and voltage of the microgrid are the frequency and voltage magnitude of the upper power system while restoring the active power and the reactive power of the micropower located near the PCC to a relatively smaller output than '0' or other micropower, respectively. Adjusting each to near;
Controlling the active power of the micropower source located close to the PCC for synchronizing the upper power system with the voltage phase; And
After the voltage phase synchronization is completed and the active power of the micropower closest to the PCC is reduced, the reactive power of the micropower close to the PCC is controlled to synchronize voltage magnitude with the higher power system. Steps to
Synchronization control method of a microgrid comprising a. The method of claim 1,
In the first control step,
Equation

Based on
Active power setpoint P ₁ ^* and active power output P ₁ (t) of the micropower located close to the PCC, active power output P _i (t) of the i-th micropower of the remaining micropowers in the microgrid, and effective By using the proportional gains k _p of the droop characteristic between power and frequency, each effective power set point P _i ^* of the remaining micro power supplies in the microgrid is changed,
And controlling the reference frequency of the microgrid to be close to the frequency of the upper power system. The method of claim 1,
In the first control step,
Equation

Based on
Reactive power setpoint Q ₁ ^* and reactive power output Q ₁ (t) of the micropower located close to the PCC, reactive power output Q _i (t) of the i-th micropower of the remaining micropowers in the microgrid, and invalid By using the proportional gain k _Q of the droop characteristic between power and voltage, each reactive power set point Q _i ^* of the remaining micro power supplies in the micro grid is changed to shift the reference voltage of the micro grid to near the voltage of the upper power system. A method for controlling synchronization of a microgrid, characterized in that for adjusting. The method of claim 1,
The second control step, in order to change the voltage phase of the microgrid,
Calculating a voltage phase error that is a difference between the voltage phase δ _u of the upper power system and the voltage phase δ _m of the microgrid;
Multiplying the voltage phase error by a voltage phase synchronization gain k _δ to determine a variation ΔP ₁ ^* of the active power setpoint of the micropower source located close to the PCC; And
Outputting the modified active power setting value P ₁ ' ^* of the micro power supply for voltage phase synchronization by adding the change ΔP ₁ ^* of the active power setting value and the active power setting value P ₁ ^* of the micro power supply;
Synchronization control method of a microgrid comprising a. The method of claim 6,
The variation ΔP ₁ ^* of the set value of the active power is limited to a specific range (ΔP ^min to ΔP ^max ) for protection based on the finite capacity of the micro power supply. The method of claim 6,
The limit value ΔP ₁ ^{max *} or ΔP ₁ ^{min *} of the variation ΔP ₁ ^* of the active power set value is
Equation

Is determined based on the hard limiter of the corresponding micropower that performs the synchronization,
Where k _p1 is the proportional gain of the droop characteristic between the active power and the frequency of the micropower to perform the synchronization, k _pi is the proportional gain between the droop characteristic between the active power and the frequency of the i-th micropower in the microgrid and P ₁ ^max is the synchronization P ₁ ^min is the minimum active power allowance of the micropower to perform the synchronization, P _i ^* is the respective active power set value of the remaining micropowers in the microgrid, P _L is the microgrid in the microgrid A microgrid synchronous control method, characterized in that the active power required by the load. The method of claim 1,
In the second control step, in order to change the voltage magnitude of the microgrid,
Calculating a voltage magnitude error that is a difference between the voltage magnitude V _u of the upper power system and the voltage magnitude V _m of the microgrid;
Multiplying the voltage magnitude error by a voltage magnitude synchronization gain k _V and integrating the voltage magnitude error to determine a variation ΔQ ₁ ^* of the reactive power setpoint of the micro-power source located near the PCC; And
Adding the variation ΔQ ₁ ^* of the reactive power setpoint and the reactive power setpoint Q ₁ ^* of the micropower to output the modified reactive power setpoint Q ₁ ' ^* of the micropower for voltage magnitude synchronization.
Synchronization control method of a microgrid comprising a. 10. The method of claim 9,
The variation ΔQ ₁ ^* of the reactive power set value is limited to a specific range (ΔQ ^min to ΔQ ^max ) for protection based on the finite capacity of the micro power supply. In microgrids operated solely by multiple micropower sources, which are the control base of droop characteristics,
In order to adjust the output of the micropower to the desired value for the management of the energy storage device provided in the specific micropower which is the control base of the droop characteristic,
Setting an active power set point P ₁ ^* of the corresponding micro power supply to a desired output set point; And
Equation

Based on the active power setting value P ₁ ^* and the active power output P ₁ (t) of the corresponding micropower, the active power output P _i (t) of the i-th micropower of the remaining micropowers in the microgrid, and Changing the active power setpoint _Pi ^* of the other micropowers in the microgrid, using the proportional gains k _p of the droop characteristics between frequencies;
Output adjustment method of the micro power source comprising a. In a microgrid operated with a plurality of micropowers based on droop characteristics, an active power controller of a micropower based on droop characteristics,
Determining the active power set value P ₁ ^* for the addition to the variation of the active power set value ΔP ₁ ^* corrected active power set value P ₁ ^'-, and
In order to limit the active power output variation of the micro power supply according to the variation ΔP ₁ ^* of the active power set value within a specific range (ΔP ^min to ΔP ^max ),
Adjust the output of the micro power supply by setting the threshold ΔP ₁ ^{max *} or ΔP ₁ ^{min *} of the variation ΔP ₁ ^* to the hard limiter,
The threshold ΔP ₁ ^{max *} or ΔP ₁ ^{min *} is
Equation

Is determined based on
Here, k _p1 is a proportional gain of the droop characteristics between the active power and the frequency of the micro-power source, k _pi is a proportional gain of the droop characteristics between the active power and the frequency of the i-th micropower in the microgrid, P ₁ ^max is the Maximum active power allowance, P ₁ ^min is the minimum active power allowance of the micropower to perform the synchronization, P _i ^* is the active power setting of each of the remaining micropowers in the microgrid, P _L is the active power required by the load in the microgrid The output adjustment method of a micro power supply characterized by the above-mentioned.

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