KR20190026379A - Grid-off microgrid system capable of maintaining rated voltage and rated frequency - Google Patents

Abstract

Provided is a grid-off microgrid system capable of maintaining and controlling rated voltage and rated frequency. More specifically, the grid-off microgrid system comprises: a microgrid including an energy storage device (ESS) which contains a battery and at least one distributed power source which acquires renewable energy to supply power to at least one load; a power converting device converting power of the distributed power source and the ESS; and a central control unit forming a point of common coupling (PCC) for an interface between the ESS and the distributed power source, and controlling a voltage and frequency of the microgrid to maintain the voltage and frequency to be a rated voltage and a rated frequency in real time. The central control unit controls the voltage of the microgrid by using the reactive power of the power converting device, and controls the frequency by using the active power of the power converting device.

Description

(GRID-OFF MICROGRID SYSTEM CAPABLE OF MAINTAINING RATED VOLTAGE AND RATED FREQUENCY)

The present invention relates to a stand-alone microgrid system, and more particularly, to a stand-alone microgrid system that maintains a rated voltage and a rated frequency of a microgrid by controlling active power and reactive power.

The Micro Grid is a small-scale smart grid system that can self-assemble power in small areas. The Micro Grid is a small, stand-alone power grid that is attracting attention as a next-generation power system that combines renewable energy sources such as solar and wind power and energy storage devices. The microgrid is a collection of many small distributed power sources and loads that can be separated from the main system in the event of a major / minor fault and serious power quality problems, System.

The micro grid is similar to the Smart Grid in that it incorporates technologies for controlling power generation in the power grid. However, there is a difference in that the power grid is close to the power grid and the power grid is small, so no transmission facilities are needed. It is important to secure the power quality and supply stability of new and renewable power generation sources such as solar heat and wind power, because the scope of construction of the power grid is small.

With a conventional microgrid system, Japanese Laid-Open Patent Application No. 10-2016-0077350 discloses an apparatus and method for controlling power grid synchronization of a microgrid. The above-mentioned prior art discloses a structure for measuring the voltage of each of the micro grid side and the power system side, judging the synchronous input availability based on the voltage, and controlling the increase / decrease of the output of active power or reactive power as a result of the determination.

In the conventional micro grid system, the steady-state can not be maintained because the frequency and voltage fluctuations are not maintained at the rated values. In addition, the conventional micro grid system has a problem that reactive power is inaccurately shared due to strong distribution of the line voltage of the distributed power unit units.

 Therefore, Applicant has devised a new micro grid system capable of controlling power quality for stable operation of micro grid system. The present invention utilizes a distributed power plant in the system to propose a system capable of maintaining the voltage and frequency of a stand-alone microgrid at a rated voltage (e.g., 220V) and a rated frequency (e.g., 60Hz).

Japanese Patent Application Laid-Open No. 10-2016-0077350

Accordingly, it is an object of the present invention to provide a stand-alone micro grid system in which a voltage and a frequency can be controlled to be maintained at a rated voltage and a rated frequency in real time in a stand-alone micro grid system.

According to an aspect of the present invention, there is provided a grid-off microgrid system comprising: an energy storage device (ESS) including a battery; at least one distributed power source for acquiring renewable energy; A micro grid for supplying power to the micro grid; A power conversion device for converting power of the distributed power source and the energy storage device; A central control unit for forming a coupling (PCC, Point of Common Coupling) for an interface between the energy storage device (ESS) and the distributed power source and controlling the voltage and frequency of the micro grid to maintain the rated voltage and the rated frequency in real time; Wherein the central control unit controls the voltage of the microgrid by using the reactive power of the power conversion apparatus and controls the frequency by using the active power of the power conversion apparatus.

Preferably, the central control unit obtains the voltage and the frequency of the microgrid measured at the coupling (PCC), obtains the measured active power at the power converter, and adjusts the rated voltage and the rated frequency of the microgrid The power conversion apparatus can be controlled by calculating the reactive power command value and the reactive power command value for maintaining the power consumption.

Preferably, the central control unit calculates a reactive power maximum value that is a maximum available value of the power conversion apparatus, using the acquired voltage of the micro grid and the active power of the power conversion apparatus as input values, And a reactive power controller for calculating the reactive power command value for controlling the voltage of the micro grid using the maximum power value.

Preferably, the central control unit calculates the maximum available electrical power, which is the maximum value in the available range of the power conversion apparatus, based on the obtained frequency of the micro grid and the active power of the power conversion apparatus as an input value, And an active power controller for calculating the active power command value for controlling the frequency of the micro grid using the available maximum available power.

The present invention also provides a control method of a grid-off microgrid system, comprising: an energy storage device (ESS) including a battery; at least one distributed power source for acquiring renewable energy; (A) measuring a voltage and a frequency of the microgrid supplying the plasma; (B) measuring active power or reactive power from a power conversion apparatus that converts the power of the distributed power source and the energy storage device; And a coupling (PCC, Point of Common Coupling) for an interface between the energy storage device (ESS) and the distributed power source, and controlling the voltage and frequency of the microgrid to maintain the rated voltage and the rated frequency in real time The control unit controls the voltage of the micro grid by using the reactive power of the power conversion apparatus and controls the frequency by using the active power of the power conversion apparatus.

According to the present invention, it is possible to control the voltage by using the reactive power of the power conversion device of the distributed power plant and to control the frequency by utilizing the active power. At this time, since the active power and the reactive power can not exceed the rating of the facility, the set values of the active power and the reactive power for maintaining the rated voltage and the rated frequency of the microgrid are calculated in consideration of the maximum allowable value. Thus, the present invention has an effect of enabling stable operation of a poison-hip type micro grid system which is difficult to maintain in a steady state.

1 shows a schematic diagram of a stand-alone microgrid system according to an embodiment of the present invention.
2 schematically shows a configuration of an energy storage device according to an embodiment of the present invention.
3 schematically shows the configuration of a photovoltaic system (PVS) as a distributed power supply according to an embodiment of the present invention.
FIG. 4 shows an execution algorithm of a reactive power controller according to an embodiment of the present invention.
5 illustrates an execution algorithm of an active power controller according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the exemplary embodiments. Like reference numerals in the drawings denote members performing substantially the same function.

The objects and effects of the present invention can be understood or clarified naturally by the following description, and the purpose and effect of the present invention are not limited by the following description. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 shows a schematic diagram of a stand-alone microgrid system 1 according to an embodiment of the present invention.

1, a stand-alone microgrid system 1 according to the present embodiment includes an energy storage device 10, a microgrid including a distributed power supply 30, a power conversion device 50, a central control unit 90, And the like.

Microgrid is a small-scale power network that supplies power and heat independently. Recently, it is a next generation power system composed of a small distributed power generator using a renewable energy source.

The microgrid may supply power to at least one load 70, including an energy storage device (ESS) 10 including a battery 101 and one or more distributed power sources 30 for acquiring renewable energy. In this embodiment, the renewable energy acquired by the distributed power source 30 may be solar energy or wind energy. In the present specification, a photovoltaic system branch for acquiring solar energy is described as an example of a distributed power source 30. [ It is preferable that the micro grid is configured with an energy storage system (ESS) 10 because it is important to secure the power quality of the new and renewable power generation source of the solar power generation and stability of the supply.

The energy storage device 10 may include a battery 101 and a bi-directional DC-AC inverter 50a, which is a power conversion device. In this case, the power conversion device 50 may be configured together in the ESS system to convert the power of the energy storage device 10.

2 schematically shows the configuration of an energy storage device 10 according to an embodiment of the present invention. Referring to FIG. 2, the energy storage device 10 may be provided as a battery strain system (BSS) brunch. The BSS may include an inverter 50a, a power conversion device including a transformer, an inverter controller, and a battery controller. The battery model can be designed based on the Randle's model, and the battery controller controls the charging and discharging of the battery in a bidirectional three-phase inverter model.

One or more distributed power sources 30 may be provided in the microgrid and include a photovoltaic system (PVS) including a photovoltaic array 301, a DC-DC converter 50b and a DC-AC inverter 50c, ). FIG. 3 is a schematic diagram of the configuration of a photovoltaic system (PVS) as a distributed power source 30 according to an embodiment of the present invention.

Referring to FIG. 3, the photovoltaic system PVS includes a photovoltaic PV array, a DC-DC converter 50b, a DC-AC inverter 50c, an inverter controller, and a converter controller. In this case, the power inverter 50 may be configured together in the PVS system to convert the power of the distributed power supply 30.

The central control unit 90 forms a coupling (PCC, Point of Common Coupling) 93 for the interface between the energy storage device 10 and the distributed power supply 30, and controls the voltage and frequency of the micro grid, And the rated frequency can be maintained in real time.

The PCC 93 refers to the wiring for various branch interfaces and can refer to the line impedance (RL) of the microgrid.

The central control unit 90 can control the voltage of the micro grid using the reactive power of the power conversion apparatus 50 and control the frequency using the active power of the power conversion apparatus 50. [

The central control unit 90 acquires the voltage and frequency of the microgrid measured by the PCC 93 and obtains the measured active power at the power inverter 50 to maintain the rated voltage and the rated frequency of the microgrid The power conversion device 50 can be controlled by calculating the reactive power command value and the reactive power command value.

For this, the central control unit 90 may include a configuration of an active power controller 901 and a reactive power controller 903. [

The reactive power controller 903 calculates the reactive power maximum value that is the maximum available value of the power conversion device 50, using the acquired voltage of the micro grid and the active power of the power conversion device 50 as input values, It is possible to calculate the reactive power command value for controlling the voltage of the micro grid using the maximum reactive power value.

In this embodiment, the reactive power controller 903 can calculate the reactive power maximum value by the calculation according to the following equation (1).

[Equation 1]

Here, DG denotes a distributed power source, Q ^max _{j, DG} denotes a reactive power maximum value, S ^max _{j, DG} denotes an apparent power of the distributed power source (DG), P ^meas _jDG denotes a power source Means the measured active power. The variable j means the number of distributed power sources installed.

Thereafter, the reactive power controller 903 calculates the reactive power command value by the calculation according to the following expression (2), and when the calculated reactive power command value is larger than the reactive power maximum value, the reactive power maximum value is set as the reactive power command Value.

&Quot; (2) "

Here, Q ^set _{j, DG} means a reactive power command value, set is a value commanded to the power converter controller of each distributed power source (j-th DG), Q ^max _{j, DG} means the maximum reactive power , n denotes the total number of distributed power sources, and _{ΔQ cont} denotes the amount of reactive power required for voltage control calculated by the reactive power controller.

4 shows an execution algorithm of the reactive power controller 903 according to an embodiment of the present invention. That is, Fig. 4 can be understood as the voltage control logic of the microgrid. Referring to FIG. 4, Step 2 is a step in which the reactive power controller 903 calculates a reactive power maximum value, and Step 3 is a step in which the reactive power controller 903 calculates a reactive power command value. Step 4 is a step in which the reactive power controller 903 compares the reactive power command value calculated in step 3 with the reactive power maximum value. In step 4, the reactive power controller 903 finally controls the power inverter 50 by setting the reactive power maximum value as the command value when the reactive power command value is larger than the reactive power maximum value. The reactive power controller 903 considers the rating of the facility and finally determines the command value in consideration of the maximum value available, as in this embodiment.

On the other hand, the active power controller 901 receives the frequency of the acquired micro grid and the active power of the power inverter 50 as an input value, and obtains the maximum available active power, which is the maximum value in the usable range of the power converter 50 And the active power command value for controlling the frequency of the micro grid can be calculated using the calculated maximum available available power.

In this embodiment, the active power controller 901 can calculate the active power maximum value which becomes the maximum allowable value by an operation according to the following expression (3).

&Quot; (3) "

P ^max _{j, DG} means the maximum available active power available for the jth _DG , P ^max _{j, DG} means the maximum installed capacity active power of the j th DG, P ^meas _{j, DG} Means the measured active power of the power conversion device.

Thereafter, the active power controller 901 calculates the active power command value by an operation according to the following expression (4), and when the calculated active power command value is larger than the available active power maximum value, It can be set as a power command value.

&Quot; (4) "

Where P ^set _{j, DG} means the active power command value commanded to the power converter of the j th DG, ΔP ^max _{j, DG} means the maximum available active power available for the j th DG, P ^max _{j, DG} denotes the maximum installed capacity of the j th DG, n denotes the total number of distributed power sources, and ΔP ^cont denotes the amount of active power required for frequency control calculated by the active power controller.

5 shows an execution algorithm of the active power controller 901 according to an embodiment of the present invention. That is, FIG. 5 can be understood as the frequency control logic of the microgrid. Referring to FIG. 5, step 2 is a step of calculating the available maximum active power value by the active power controller 901, and step 3 is a step of calculating the active power command value by the active power controller 901. Step 4 is a step in which the active power controller 901 compares the active power command value calculated in Step 3 with the maximum available reactive power. In Step 4, the active power controller 901 finally controls the power converter 50 by setting the maximum available electric power as the command value when the active power command value is larger than the available active power maximum value. The active power controller 901, as in the present embodiment, considers the rating of the facility, and finally determines the command value in consideration of the maximum usable value.

The present embodiment can be understood as a technique applicable to voltage and frequency control utilizing the power conversion device 50, having technical features that can be applied generally regardless of the number of distributed power sources 30. [

The control method of the independent microgrid system 1 described above can be summarized as follows. A control method of the micro grid system includes an energy storage device (ESS) 10 including a battery, at least one distributed power source 30 for acquiring renewable energy, and a voltage of a micro grid (A) measuring frequency and frequency; (B) measuring active power or reactive power from a power conversion device (50) for converting the power of the distributed power source (30) and the energy storage device (10); And a point of common coupling (PCC) 93 for the interface between the energy storage device (ESS) 10 and the distributed power supply 30 and controls the voltage and frequency of the micro grid to control the rated voltage and the rated voltage A central control unit 90 for maintaining a frequency in real time controls the voltage of the micro grid by using the reactive power of the power conversion device 50 and controls the frequency by using the effective power of the power conversion device 50 ) Step.

 The control method of the independent microgrid system 1 is performed by the central control unit 90. Steps (a) and (b) refer to a process of acquiring measurement values through a sensor. (C) Step < / RTI > refers to the process of performing the operational logic in the active power controller 901 and the reactive power controller 903.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined by all changes or modifications derived from the scope of the appended claims and equivalents of the following claims.

1: Stand-alone Micro Grid System
10: Energy storage device
101: Battery
30: Distributed power supply
301: photovoltaic array
50: power converter
70: Load
90:
93: PCC
901: Active power controller
903: reactive power controller

Claims (9)

In a grid-off microgrid system,
A micro grid for powering at least one load including an energy storage device (ESS) including a battery and at least one distributed power source for acquiring renewable energy;
A power conversion device for converting power of the distributed power source and the energy storage device;
A central control unit for forming a coupling (PCC, Point of Common Coupling) for an interface between the energy storage device (ESS) and the distributed power source and controlling the voltage and frequency of the micro grid to maintain the rated voltage and the rated frequency in real time; Lt; / RTI >
The central control unit,
Wherein the voltage of the microgrid is controlled using the reactive power of the power conversion device, and the frequency is controlled using the active power of the power conversion device.
The method according to claim 1,
The central control unit,
Obtaining a voltage and frequency of the microgrid measured at the coupling (PCC)
Obtaining the measured active power at the power conversion device,
Wherein the power control device controls the power conversion device by calculating an active power command value and a reactive power command value for maintaining the rated voltage and the rated frequency of the microgrid.
3. The method of claim 2,
The central control unit,
Calculating a reactive power maximum value which is an available maximum value of the power conversion apparatus by using the acquired voltage of the micro grid and the active power of the power conversion apparatus as an input value, And a reactive power controller for calculating the reactive power command value for controlling the voltage of the microgrid.
The method of claim 3,
The reactive power controller includes:
And calculates the reactive power maximum value by an operation according to the following equation (1).
[Equation 1]

Here, DG denotes a distributed power source, Q ^max _{j, DG} denotes a reactive power maximum value, S ^max _{j, DG} denotes an apparent power of the distributed power source (DG), P ^meas _jDG denotes a power source Means the measured active power. The variable j means the number of distributed power sources installed.
The method of claim 3,
The reactive power controller includes:
The reactive power command value is calculated by an operation according to the following expression (2), and when the calculated reactive power command value is larger than the reactive power maximum value, the reactive power maximum value is set as the reactive power command value A stand-alone micro-grid system.
&Quot; (2) "

Here, Q ^set _{j, DG} means a reactive power command value, set is a value commanded to the power converter controller of each distributed power source (j th DG), Q ^max _{j, DG} means the maximum reactive power , n denotes the total number of distributed power sources, and _{ΔQ cont} denotes the amount of reactive power required for voltage control calculated by the reactive power controller.
3. The method of claim 2,
The central control unit,
Calculating a maximum usable active power which is a maximum value in a usable range of the power conversion apparatus based on the obtained frequency of the micro grid and the active power of the power conversion apparatus as an input value, And an active power controller for calculating the active power command value for controlling the frequency of the microgrid using the control signal.
The method according to claim 6,
Wherein the active power controller comprises:
And calculates an active power maximum value which is the maximum allowable value by an operation according to the following equation (3).
&Quot; (3) "

P ^max _{j, DG} means the maximum available active power available for the jth _DG , P ^max _{j, DG} means the maximum installed capacity active power of the j th DG, P ^meas _{j, DG} Means the measured active power of the power conversion device.
Wherein the active power controller comprises:
Calculates a valid electric power command value by an operation according to Equation (4) below, and sets the available available electric power maximum value as the effective electric power command value when the calculated effective electric power command value is larger than the available available electric power maximum value Wherein the microgrid system is a stand-alone microgrid system.
&Quot; (4) "

Where P ^set _{j, DG} means the active power command value commanded to the power converter of the j th DG, ΔP ^max _{j, DG} means the maximum available active power available for the j th DG, P ^max _{j, DG} denotes the maximum installed capacity of the j th DG, n denotes the total number of distributed power sources, and ΔP ^cont denotes the amount of active power required for frequency control calculated by the active power controller.
A method of controlling a grid-off microgrid system,
(a) measuring the voltage and frequency of a microgrid that supplies power to at least one load including an energy storage device (ESS) including a battery and at least one distributed power source for acquiring renewable energy;
(b) measuring active power or reactive power from a power conversion apparatus for converting the power of the distributed power source and the energy storage device; And
(c) forming a coupling (PCC, Point of Common Coupling) for the interface between the energy storage device (ESS) and the dispersed power source, and controlling the voltage and frequency of the microgrid to maintain a real- Wherein the central control unit controls the voltage of the microgrid by using the reactive power of the power conversion apparatus and controls the frequency by using the active power of the power conversion apparatus. / RTI >

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