KR20160099914A - Power control apparatus using DC bus signal based on switching frequency modulation type in DC Grid system and method thereof - Google Patents

Abstract

The present invention relates to a power control apparatus using a DC bus signal of a switching frequency modulation type in a DC grid system and a power control method using the same. According to the present invention, the method comprises the following steps of: operating a power value provided to or from a DC line by an energy storage apparatus and a DC power network; selecting a switching frequency value corresponding to the operated power value from power control graph information which defines a switching frequency value fluctuated according to the power value, and an output current values, corresponding to the switching frequency value, of the energy storage apparatus and the DC power network; and providing a DC bus signal loading the selected switching frequency value on a DC bus voltage to the DC line to control the power of the energy storage apparatus and the DC power network. According to the present invention, by using the DC bus signal of a switching frequency modulation type, transmission of power state information and a power flow of each component connected to the DC line in a DC grid system are effectively controlled, and information exchange is smoothly performed by using an existing DC power line without any communication line and an effect of components or operation environment of a load.

Description

[0001] The present invention relates to a power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system, and a power control method using the DC bus signal,

The present invention relates to a power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system and a power control method using the DC bus signal. More particularly, the present invention relates to a control system for controlling a DC grid system, such as a DC micro grid or a DC nano grid, To a power control apparatus using a DC bus signal of a switching frequency variation type and a power control method using the same.

Recently, due to the increasing use of internal combustion engine due to population increase and worldwide industrialization, demand for fossil fuel is increasing. Fossil fuels cause serious environmental pollution such as global warming and fine dust. For this reason, interest in environmentally friendly energy is increasing, and research on the field of Smart Grids is actively being carried out.

Smart grid means power grid upgrading and enables power supply through integration of environmentally friendly factors and local development. According to the Smart Grid, efficient power production and consumption between power producers and power consumers can be realized by using power information collected in real time, and the power grid can be stabilized and high efficiency can be sought by using intelligent power interface devices.

As a method of implementing smart grid, bottom-up approach through advanced micro / nano grid is effective and many researches related thereto are proceeding. Among these advanced micro / nano grids, studies on a DC grid (DC grid) using direct current power rather than AC power have been actively conducted.

When DC power is used instead of AC power, the amount of electric power required for power distribution can be reduced, stable power supply is possible, and a DC power source such as a renewable energy source can be easily connected. Considering that most electronic devices internally use DC power, it is possible to reduce the number of power conversion when DC power is used, thereby achieving high efficiency of the system and unnecessary use of additional parts required for power conversion It can reduce resource consumption and increase price competitiveness of products.

The DC micro / nano grid system corresponding to the DC grid is generally composed of a distributed power source (renewable generator; wind power, solar power), an energy storage device (battery) and a load (DC load) And a small-scale power grid connected to the grid.

For efficient operation of the DC micro / nano grid, the power flow between the distributed power source, the energy storage device, the DC load, and the AC power grid connected to the DC line must be effectively managed. In other words, proper operation point setting and tight power distribution should be made between each component constituting the DC power system according to the consumption of the load in the DC power system, the power storage state of the energy storage device, and the power generation amount of the distributed power supply. To do this, each component needs the power state information of the DC grid system from a power converter that controls the DC voltage of the grid.

In such a DC grid system, power flow must be managed based on the power state information of each component. At this time, information can be transmitted between each elementary device by using an additional communication device, but it is inefficient because it requires an additional communication network in addition to the DC power network.

Recently, a droop control method has been proposed, which is a DC-bus signaling technique in which a DC voltage is varied without using an additional communication network to share basic power information between elements of a power network. This type of droop control system can vary the magnitude of the DC voltage supplied to the DC line based on the power state information of the load and the distributed power source, that is, the amount of power required by the load and the output power produced by the distributed power source, To converge to an appropriate operating point.

However, the droop control method based on the DC voltage fluctuation has an excellent power control performance and a stable advantage, but there is a disadvantage that the operation efficiency is lowered when an error occurs in the measurement of the DC voltage in each component. In addition, the DC voltage may decrease depending on the total length of the power network and the load, and it is difficult to prepare countermeasures at present. As described above, information errors between element devices due to voltage measurement errors and voltage reduction inevitably lead to ineffective operation of the entire DC grid and destruction of stability.

The technology of the background of the present invention is disclosed in Korean Patent Publication No. 1431047 (published on Aug. 21, 2014).

An object of the present invention is to provide a power control apparatus using a DC bus signal of a switching frequency variation type and a power control method using the same, in a DC grid system capable of increasing the operation efficiency of a DC grid system.

The present invention relates to a power control method using a power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system including a distributed power source, a load, an energy storage device, and an AC power grid, Calculating a power value to be supplied to the DC line by the energy storage device and the AC power network or a power value to be supplied from the DC line based on the power state and a switching frequency value varying according to the power value, Selecting a switching frequency value corresponding to the calculated power value from power control graph information defining an output current value of the energy storage device and the AC power network corresponding to a DC bus voltage A DC bus signal is provided to the DC line, The present invention provides a power control method using a DC bus signal of a switching frequency variation type in a DC grid system including a base energy storage device and a power control of the AC power grid.

Here, the energy storage device and the AC power network may be driven to analyze the switching frequency value from the DC bus signal provided to the DC line, and to follow the output current value corresponding to the analyzed switching frequency value, respectively.

The power control method may further include a power control graph defining a correspondence between an output current value of each of the energy storage device and the AC power network controlled according to the power value and the switching frequency value on an output current axis and a switching frequency axis, And building the information.

Here, the power control graph information may have a shape in which the switching frequency value decreases with an increase in the output current value, and the first graph, which represents the correspondence between the output current value of the energy storage device and the switching frequency value, And a second graph line representing a correspondence relationship between an output current value of the AC power network and the switching frequency value, wherein an intersection point between the first and second graph lines is located on the switching frequency axis, And can be divided into positive and negative output current sections.

The distributed power source, the load, and the energy storage device may be configured to transmit a DC bus signal including a switching frequency value corresponding to the current power state to a DC bus voltage through a DC line, Wherein the switching frequency values of the switching frequency values are different from each other, and the power control device analyzes the switching frequency value of the DC bus signal received from the distributed power source, the load, and the energy storage device, The power state can be estimated.

The present invention also provides a power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system including a distributed power source, a load, an energy storage device, and an AC power grid, A control power calculator for calculating a power value to be supplied to the DC line by the energy storage device and the AC power network or a power value to be supplied from the DC line; A switching frequency selecting unit for selecting a switching frequency value corresponding to the calculated power value from power control graph information defining an output current value of the energy storage device and the AC power network corresponding to the switching frequency value, A DC bus signal in the bus voltage is applied to the DC line And a power controller for controlling the power of the energy storage device and the AC power grid by providing a power control unit using a DC bus signal of a switching frequency variation type in a DC grid system.

According to the power control apparatus using the DC bus signal of the switching frequency variation type and the power control method using the same, in the DC grid system according to the present invention, the DC bus signal of the switching frequency variation type is used, It is able to effectively control transmission and power flow of power status information of each connected component and it is possible to exchange information smoothly without being influenced by load component or operating environment by using existing DC power line without additional communication line. There is an advantage to be able to perform.

1 is a diagram illustrating a direct current grid system according to an embodiment of the present invention.
2 is a view for explaining a conventional DC voltage fluctuation type droop control method.
3 is a view for explaining a power control method using a DC bus signal of a switching frequency variation type according to an embodiment of the present invention.
4 is a diagram illustrating a configuration of a power control apparatus using a DC bus signal of a switching frequency variation type according to an embodiment of the present invention.
5 is a diagram illustrating a power control method using the power control apparatus shown in FIG.
6 is a time domain representation of a DC bus signal of a switching frequency variation scheme according to an embodiment of the present invention.
7 is a diagram illustrating quantization of a DC bus signal according to frequency resolution when a digital controller is used in an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

The present invention relates to a power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system and a power control method using the DC bus signal and a power control method using the DC bus signal. Device, DC load, and AC power grid) in a power plant.

In an embodiment of the present invention, a DC grid system may refer to a DC microgrid, DC nanogrid form. Hereinafter, for convenience of explanation, the DC micro-grid will be described as an example.

In the embodiment of the present invention, a DC bus signal of a switching frequency variation type is used as a DC bus signal flowing into a DC line (DC line) of a direct current grid system, unlike a conventional DC bus signal of a voltage variation type. Conventionally, the DC bus voltage level itself on the DC line is used as the DC bus signal, whereas the embodiment of the present invention uses the high-frequency switching noise on the DC bus voltage as the substantial DC bus signal.

Each component in the DC grid system analyzes the switching frequency value on the DC bus voltage and can recognize the power state of the current grid system from the analyzed switching frequency value and control the power flow to the corresponding power direction and power amount .

The embodiment of the present invention enables power information exchange and power control using a DC line, which is a conventional DC power network, without a separate communication network. In addition, unlike the conventional voltage fluctuation type, since the switching frequency component rather than the simple voltage level is used as the DC bus signal, each component can perform substantially corresponding operation based on the analyzed frequency. Therefore, in this embodiment, it is possible to overcome the disadvantage of the voltage measurement error due to the error of the DC bus voltage and the distance between the respective components depending on the length of the power network and the load, which have been problems in the conventional voltage fluctuation type.

Hereinafter, a configuration of a direct current grid system according to an embodiment of the present invention will be briefly described. The direct current grid system generally has the form shown in FIG. 1 is a diagram illustrating a direct current grid system according to an embodiment of the present invention.

1, a distributed power source 40, a load 20, and an energy storage device 30 are coupled to a DC line and operate in conjunction with the AC power grid 10. [ The distributed power source 40 may be a wind power generator capable of generating electric power, a solar power generator, etc., and the load 20 may correspond to a direct current load. The AC power grid 10 may correspond to an existing AC grid, an AC distribution system, and the like.

The AC power grid 10 is connected to an AC / DC converter (inverter) capable of bidirectional conversion between AC / DC for connection with a DC grid. The distributed power source 40, the load 20, the energy storage device 30, and the AC power grid 10 are individually connected to bidirectional power converters that perform appropriate power conversion between DC lines. The AC power grid 10 is substantially an AC / DC converter connected to a bi-directional power converter. The configuration of the bidirectional power converter connected to each component is a general matter in a DC grid system, and thus a detailed description thereof will be omitted.

The bi-directional power converter may be implemented as a DAB (Dual Active Bridge) converter, which is one of the isolated bi-directional power DC-DC converters. Such a DAB converter has a merit that the direction of the load current is smooth and the power direction can be easily controlled by the phase shift. Of course, the bi-directional power converter is not necessarily limited thereto and may be implemented in various forms as is known in the art.

The bidirectional power converter connected to each of these components can be controlled to control the power flow. The known voltage-controlled droop control method controls the voltage of the power converter of the component according to the amount of power absorption or emission. Also in the power control method according to the embodiment of the present invention, the power flow of the DC grid for each component can be effectively controlled by using the power converter connected to each component.

The power control apparatus according to an embodiment of the present invention may be directly connected to a DC line to provide a DC bus signal required for power control to the power converter of each component. In addition, the power control device can provide the DC bus signal required for power control to the power converter of each component while being embedded in the power converter of the specific component. For example, a DC bus signal of a switching frequency variation type may be provided to the DC line in a state of being embedded in the bidirectional power converter of the AC power grid 10, so that the power direction and the amount of power in the DC grid can be controlled. As such, the power control device may be directly connected to the DC line, may be included in the bi-directional power converter configuration, and may be installed in various forms within the grid system. A detailed description of the power control will be given later.

The power control device may receive the DC bus signal including the power status information of each component from the power converter of the corresponding component to determine the current power status of each component. The power control apparatus according to the embodiment of the present invention calculates the amount of power to be supplied to or supplied to the DC line based on the current power state of the load and the distributed power source and outputs the switching frequency value corresponding to the calculated power amount to the DC bus By providing the signal to the DC line, the power flow and the power amount of the energy storage device and the AC power network can be effectively controlled.

Of course, in an embodiment of the present invention, each bidirectional power converter may pre-store or share the related control information so that it can perform the agreed control operation corresponding to the switching frequency value recorded in the DC bus signal. In the embodiment of the present invention, control information is represented by power control graph information, and a detailed description thereof will be described later.

Controlling the power of each component in the following description may be equivalent to controlling the power converter connected to each component. Therefore, the configuration of the bidirectional power converter will be omitted for convenience of explanation. The AC / DC converter connected to the AC power grid 10 is located substantially in the same position as each component and can be seen as a component of the AC power grid 10, which is referred to as the AC power grid 10 for convenience of explanation.

Before describing the DC bus signal of the switching frequency variation type according to the embodiment of the present invention, a control method using the DC bus signal according to the conventional voltage variation method will be briefly described in order to facilitate understanding of the present invention.

2 is a view for explaining a conventional DC voltage fluctuation type droop control method. This figure 2 shows a droop control graph of a voltage variation type of the known type defined in the current axis and the voltage axis.

If the output power of the distributed power supply 40 is greater than the consumed power of the load 20, surplus power is generated, so that the AC power supply network 10 and the energy storage device 30 absorb (charge) the power from the DC line, In the opposite case, since the electric power is insufficient, the AC power grid 10 and the energy storage device 30 control the discharge (discharge) of electric power to the DC line. The two components 10, 30 are preferably designed to handle charging and discharging within their power capacity limits.

As described above, the two components 10 and 30 share the operation of charging or discharging the energy through the DC line as much as the difference between the amount of power the load 20 desires to receive and the amount of power produced by the dispersed power source 40 . The specific operation thereof is according to the graph of Fig.

One of the two graphs shown in FIG. 2 is a control graph for the energy storage device 30, and the other graph shows a control graph for the AC power grid 10. FIG. These graphs are shown in relation to the DC bus voltage applied to the DC line and the corresponding output current value.

The difference in the slopes of the two graphs within the same operating voltage range is related to the difference in power capacity that the two components 10,30 take up. It can be seen that the smaller the slope, the larger the output current range, which means the greater the available power capacity. In the case of FIG. 2, the power capacity of the AC power grid 10 is larger than that of the energy storage device 30.

Referring to the graph of FIG. 2, a conventional droop control method using a DC bus signal of a voltage variation method will be briefly described as follows. The DC bus signal flowing into the DC line has a voltage level within the operating voltage range (V _{ref , L} to V _{ref , H} ).

If a DC bus signal having a voltage level of a certain level flows into the DC line, each of the components 10 and 30 performs an operation according to an output current value corresponding to (mapped) the corresponding voltage value in the graph corresponding to the DC bus signal . At this time, if the mapped output current value is a positive number, energy corresponding to the corresponding voltage value and the current value mapped thereto is discharged (discharged) to the DC line. Conversely, if the output current value is negative, (Charges) the energy equivalent to the amount of electric power by the current value from the DC line.

As a simple example, if the DC bus signal of a large V _{ref, H} larger than V _ref flowing into the DC line energy storage device 30 and the AC power grid 10 corresponds to Fig. V _{ref, H} in each of the graphs of the two And the corresponding power amount is charged according to -I _{1 , max} and -I _{2 , max} , respectively. Since the voltage values are equal to V _{ref , H} , while the mapped output current values are different from -I _{1 , max} and -I _{2 , max} , the power to be charged is determined by the AC power grid 10 in the energy storage device 20, . This charging operation is performed on the same principle for a DC bus signal having a magnitude larger than V _ref .

On the contrary, in the case of the DC bus signal having a magnitude smaller than V _ref , since the mapped current value is positive, the discharging operation in which the power flow in the opposite direction is performed is performed. Of course, if the DC bus of the signal V _ref size flows to the DC line because the two components (10,30), all of the output current value that is mapped to the V _ref 0 does not need to perform charging and discharging.

The embodiment of the present invention uses a frequency variation type power control method using a fixed voltage level, unlike the voltage variation type control method described above.

The embodiment of the present invention described below also allows the AC power grid 10 and the energy storage device 30 to absorb (charge) power from the DC line when the output power of the distributed power source 40 is greater than the consumed power of the load 20, And the opposite case is based on a principle that the AC power grid 10 and the energy storage device 30 control the discharge (discharge) of power to the DC line. Also, the AC power grid 10 and the energy storage device 30 are designed to handle charging and discharging within their power capacity limits.

However, in the embodiment of the present invention, the level of the DC bus voltage is fixed, unlike the DC bus signal of the conventional voltage variation method. Embodiments of the present invention also control the flow and dispersion of power in a direct current grid system through a DC bus signal carrying a switching frequency value to the DC bus voltage.

Hereinafter, a power control method using a DC bus signal of a switching frequency variation type according to an embodiment of the present invention will be described with reference to FIG. 3 is a view for explaining a power control method using a DC bus signal of a switching frequency variation type according to an embodiment of the present invention.

FIG. 3 shows a new type of power control graph information defined in the current axis and the switching frequency axis. In FIG. 3, a switching frequency value varying according to a power value requiring control in the current grid system and an angle corresponding to the switching frequency value And the output current values of the components 10 and 30 are defined.

Referring to FIG. 3, there is shown a first graph line showing a correspondence relationship between the output current value and the switching frequency value of the energy storage device 30, and a second graph line showing a correspondence relationship between the output current value and the switching frequency value of the AC power network 10. [ And a graph line. That is, one of the two graphs is a control graph for the energy storage device 30, and the other graph represents a control graph for the AC power grid 10. [ These graphs represent the relationship between the switching frequency value selected based on the current power state and the corresponding output current value.

Here, the difference in the slopes of the two graphs within the same operating frequency range is related to the difference in the power capacity that the two components 10 and 30 assume. The two components 10, 30 operate with a fixed size DC bus voltage, but their output current ranges are different. It can be seen that the smaller the slope, the larger the output current range, which means the greater the available power capacity. 3 illustrates a case where the power capacity of the AC power network 10 is twice as large as that of the energy storage device 30. [

The range (band) of the switching frequency value is defined as the value between f _{sw , L} and f _{sw , H} based on the reference values f _{sw , ref} . The frequency range can be selected to have a value that is less affected by the grid system in question.

The graph of FIG. 3 has a form in which the switching frequency value decreases as the output current value increases. The switching frequency value varies up and down with reference to the reference frequency ( _{fsw , ref} ) in accordance with the transmission direction of electric power (charging, discharging). In this embodiment, the frequency of the ripple applied to the DC bus voltage varies depending on the switching frequency value.

In FIG. 3, the intersection point between the two graph lines is located at the reference frequency value ( _{fsw , ref} ) on the switching frequency axis. The output current direction is reversed with respect to the switching frequency axis. It can be seen that the graph is divided into left and right output current sections based on the switching frequency axis.

A power control method according to an embodiment of the present invention will be described with reference to the graph of FIG. The DC bus signal flowing into the DC line has a form in which the switching frequency value is switched by the switching noise to the DC bus voltage. This DC bus voltage may correspond to a predetermined reference voltage V _ref as a fixed level voltage.

Further, in constructing the DC bus signal in the embodiment of the present invention, after calculating the power value to be supplied to or supplied to the DC line based on the current power state of the load 20 and the distributed power source 40, So that the switching frequency value corresponding to the value is stored in the DC bus voltage.

In the graph of FIG. 3, multiplying the current value at each point by the DC bus voltage results in a power value corresponding to each point. The points of the two graphs that meet the same switching frequency value are the points corresponding to the power values that each component takes. The embodiment of the present invention selects the switching frequency value in FIG. 3 such that the sum of the power values of the two components becomes equal to the calculated power value. In the case of FIG. 3, the power value attained by the AC power grid 10 for the same switching frequency value is twice as large as that of the energy storage device 30.

When the DC bus signal containing the switching frequency component flows into the DC line, each of the components 10 and 30 analyzes the corresponding switching frequency value included in the DC bus signal and then calculates a corresponding switching frequency value (Mapped) to the output voltage value. In this case, if the mapped output current value is a positive value, the DC bus voltage value and the energy amount corresponding to the corresponding current value are discharged (discharged) to the DC line. Conversely, if the output current value is negative, (Charges) the energy of the amount of power by the value from the DC line.

For example, when a DC bus signal containing f _{sw , H} higher than f _{sw , ref} is inputted to the DC line, the energy storage device 30 and the AC power grid 10 are connected to f _{sw , H} And charges the corresponding power amount according to the corresponding -I _{1 , max} and -I _{2 , max} , respectively. The DC bus voltage value is a handle (charging) electric power is AC power grid 10, the energy storage device 20, because the output current value that is mapped to the same, while V _ref are different in -I _{1, max} and -I _{2, max} . This charging operation is performed on the same principle for a DC bus signal having frequencies higher than f _{sw , ref} .

In contrast _{, in} the case of a DC bus signal having a switching frequency lower than f _{sw , ref ,} the discharging operation is performed in such a manner that power flow occurs in the opposite direction. Of course, since the DC line f _sw, when the syringe _ref DC bus signal flows in the two components (10,30), both f _sw, the output signal value is mapped to 0 _ref is not necessary to perform a charge and discharge .

As such, embodiments of the present invention differently determine the switching frequency value carried by the DC bus voltage according to the amount of power computed based on the current power state of the load 20 and the distributed power supply 40. The energy storage device 30 and the AC power network 10 are operated to analyze the switching frequency value in the DC bus signal and to follow the output current value corresponding to the analyzed switching frequency value.

This embodiment of the present invention varies the frequency component of the DC bus voltage without changing the voltage level of the DC bus signal, The power absorbing or discharging operation can be performed.

Hereinafter, a power control method using a DC bus signal of a switching frequency variation method in a DC grid system according to an embodiment of the present invention will be described in detail. FIG. 4 is a diagram illustrating a configuration of a power control apparatus using a DC bus signal of a switching frequency variation type according to an embodiment of the present invention, and FIG. 5 is a diagram illustrating a power control method using the power control apparatus shown in FIG. 4 .

The power control apparatus 100 according to the embodiment of the present invention includes a power state receiver 110, a control power calculator 120, a frequency selector 130, a power controller 140, and a control information generator 150 do.

First, before performing the power control corresponding to the current grid state in the DC grid, the embodiment of the present invention preliminarily constructs the power control graph information as shown in FIG. 3 through the control information construction unit 150. FIG. 3 shows the relationship between the output current value of each of the energy storage device 30 and the AC power network 10 controlled according to the power value and the switching frequency value for the corresponding output current value on the output current axis and the switching frequency axis . The information of FIG. 3 is constructed considering the current grid communication network environment and the capacity of each component.

The following embodiments of the present invention effectively control the power flow between each component using the DC bus signal of the switching frequency variation type shown in FIG. To do this, we first collect the current power state from each component.

That is, the power state receiving unit 110 receives the respective current power states from the distributed power source 40 and the load 20 via the DC line (S510). In this step S510, the distributed power source 40 and the load 20 can transmit the DC bus signal including the DC bus voltage to the switching frequency value corresponding to the current power state through the DC line. That is, in step S510, the power state receiving unit 110 receives a signal having a switching frequency value corresponding to the power state for each component loaded on the DC bus voltage, thereby determining the current power state of each component have.

Here, the distributed power source 40 and the load 20 may have different switching frequency bands of the switching frequency values used for transmission in the power state. The load 20 can send a switching frequency value corresponding to the amount of power to be supplied to the DC voltage, and the distributed power supply 40 can send the switching frequency value corresponding to the produced amount of power information to the DC voltage. In addition, the embodiment of the present invention can also transmit the switching frequency value corresponding to the stored energy amount of the energy storage device 30 to the DC voltage.

At this time, the voltage signals transmitted by the respective elements as the power state information can use different frequency bands as described above. More specifically, each component may select a switching frequency value corresponding to the current power state within a predetermined frequency band of its own, and transmit the selected switching frequency value by placing the selected switching frequency value on a preset DC bus voltage. The switching frequency can be controlled via a converter.

Since the switching frequency bands used for transmission of the power state are different from each other, the power state receiving unit 110 analyzes the switching frequency value included in the DC bus signal received from each component, And the current power state of the corresponding component can be estimated by using the analyzed switching frequency value.

In addition, since each component transmits a power state using different frequency bands, it is possible to simultaneously transmit a plurality of power state information at the same time, as well as to transmit individual information among the elements. On the receiving side, it is obvious that even if several frequency components are simultaneously received, they can be individually analyzed and judged. However, the frequency band used by each component may be set to be spaced by a certain range (interval) between used frequency bands so that the frequency value can be read more easily. In addition, the frequency band that each component uses to transmit the current power state may be set to a band that is also separated from the frequency band in which the power control is used.

On the other hand, based on the current power state of each component obtained in the step S510, the control power calculation unit 120 calculates a control power based on the power value supplied from the energy storage device 30 and the AC power grid 10 to the DC line or from the DC line And calculates a power value (S520).

The calculation of the control power values of the energy storage device 30 and the AC power network 10 based on the power state of the load 20 and the distributed power supply 40 corresponds to a known method. For example, the power capacity equivalent to the difference between the output power of the distributed power supply 40 and the consumed power of the load 20 is calculated.

Next, from the power control graph information of FIG. 3 which defines the output current values of the energy storage device 30 and the AC power network 10 corresponding to the switching frequency value and the switching frequency value varying according to the power value, The switching frequency value corresponding to the value is selected (S530). That is, the switching frequency value corresponding to the calculated power value is selected by referring to the power control graph information.

As an example, if the energy storage device 30 and the AC power grid 10 need to supply energy to the DC line as much as the calculated power value as a result of the calculation of the power value in step S520, The power storage device 30 and the AC power grid 10 for power consumption.

For example, if the total capacities of the AC power network 10 and the energy storage device 30 are 2 kW and 1 kW, respectively, and the current value to be supplied to the DC line is 2 kW, then the two components 10, According to the graph, it is possible to divide the capacity in proportion to its own capacity. That is, the AC power grid 10 can support 1.33 kW in 2 kW, and the energy storage device a can afford the remaining 0.67 kW. This can vary depending on the design, and the ratio of the mutually sharing capacity is reflected in the slope element of the graph line. In FIG. 3, the points of the two graphs meeting the same switching frequency value have been described above as points corresponding to the power values that each component receives. Therefore, the switching frequency value corresponding to the power value shared for each component can be selected from the graph.

Then, the power control unit 140 controls the power of the energy storage device 30 and the AC power grid 10 by providing a DC bus signal containing the selected switching frequency value to the DC bus voltage at step S540. The power control principle according to the switching frequency value has been described in detail while defining the graph of FIG. In an embodiment of the present invention, the DC bus voltage may correspond to the rated voltage of the DC line and may simply correspond to V _ref .

6 is a time domain representation of a DC bus signal of a switching frequency variation scheme according to an embodiment of the present invention. DC bus signal may be transmitted to put the switching frequency value corresponding to the current grid state to V _ref. In the powering mode, which requires energy release for the component, a lower switching frequency value is used than in the Generating mode, which requires absorption. In addition, each component can perform power control corresponding to the corresponding power by following the current value corresponding to the switching frequency value analyzed in the DC bus signal alone.

As described above, in the embodiment of the present invention, by changing the switching frequency value not the voltage level of the DC bus signal provided to the DC line to a value suitable for the current power state, each component in the grid system can converge to an appropriate operating point .

7 is a diagram illustrating quantization of a DC bus signal according to frequency resolution when a digital controller is used in an embodiment of the present invention. FIG. 7 illustrates quantization of a DC bus signal generated when a bidirectional power converter is controlled using a digital controller.

Unlike an analog controller, it is clear that the performance of a digital controller is determined by the frequency resolution (resolution). In Fig. 7, the frequency resolution is represented by? _Fsw . The graph of FIG. 3 can be quantized in the form of FIG. 7 according to this frequency resolution. That is, the current resolution of the AC / DC converter of the AC power network 10 is determined as ΔI _REC and the current resolution of the energy storage device 30 is determined as ΔI _ESS according to the frequency resolution Δf _sw .

According to the embodiment of the present invention as described above, it is possible to smoothly exchange power information and control power flow between each component by using the switching frequency variation of the converter without a separate communication line between each element equipment in the direct current grid system, Compared with the conventional voltage fluctuation type control system, it is possible to construct an information transmission system which is robust against disturbance or fluctuation of operating environment.

That is, according to the power control apparatus using the DC bus signal of the switching frequency variation type and the power control method using the DC bus signal according to the present invention, the DC bus signal of the switching frequency variation method is used, It is possible to effectively control transmission and power flow of power state information of each component and perform smooth information exchange without being influenced by load component or operating environment by using existing DC power line without a separate communication line There is an advantage to be able to.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: power control device 110: power state reception unit
120: Control power calculation unit 130: Frequency selection unit
140: power control unit 150: control information construction unit

Claims (10)

A power control method using a power control device using a DC bus signal of a switching frequency variation type in a DC grid system including a distributed power source, a load, an energy storage device, and an AC power grid,
Computing a power value to be supplied to the DC line by the energy storage device and the AC power network or a power value to be supplied from the DC line based on the current power state of the distributed power source and the load;
A switching frequency value corresponding to the calculated power value is calculated from power control graph information defining a switching frequency value varying according to the power value and an output current value of the energy storage device and the AC power network corresponding to the switching frequency value, Selecting; And
And controlling the power of the energy storage device and the AC power grid by providing a DC bus signal that includes the selected switching frequency value to the DC bus voltage to the DC line, A power control method using the power control method. The method according to claim 1,
Wherein the energy storage device and the AC power grid comprise:
And a DC bias control unit for controlling the DC bias signal of the DC grid signal based on the switching frequency of the DC bus signal, Control method. The method according to claim 1,
And constructing the power control graph information defining a corresponding relationship between the output current value of each of the energy storage device and the AC power network controlled based on the power value and the switching frequency value on an output current axis and a switching frequency axis A power control method using a DC bus signal with a switching frequency variation method in a DC grid system. The method of claim 3,
The power control graph information includes:
A first graph line representing a relationship between an output current value of the energy storage device and the switching frequency value and having a shape in which the switching frequency value decreases with an increase in the output current value; And a second graph line representing a correspondence relationship between the switching frequency values,
A power control using a DC bus signal of a switching frequency variation type in a DC grid system in which an intersection point between the first and second graph lines is located on the switching frequency axis and is divided into positive and negative output current sections based on the switching frequency axis; Way. The method according to claim 1,
The distributed power source, the load, and the energy storage device,
Wherein a DC bus signal carrying a switching frequency value corresponding to the current power state is transmitted through a DC line in a DC bus voltage, the switching frequency bands of switching frequency values used for transmission in the power state differ from each other,
The power control device includes:
A DC bus signal of a switching frequency variation type in a DC grid system that analyzes a switching frequency value of a DC bus signal received from the distributed power source, the load, and the energy storage device, respectively, and estimates each of the current power states corresponding thereto, Power control method using. A power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system including a distributed power source, a load, an energy storage device, and an AC power grid,
A control power calculator for calculating a power value to be supplied to the DC line by the energy storage device and the AC power network or a power value to be supplied from the DC line based on the current power state of the distributed power source and the load;
A switching frequency value corresponding to the calculated power value is calculated from power control graph information defining a switching frequency value varying according to the power value and an output current value of the energy storage device and the AC power network corresponding to the switching frequency value, A switching frequency selection unit for selecting the switching frequency; And
And a power control unit for controlling the power of the energy storage device and the AC power grid by providing a DC bus signal including the selected switching frequency value to a DC bus voltage on the DC bus line. In the DC grid system, Power control device using signal. The method of claim 6,
Wherein the energy storage device and the AC power grid comprise:
And a DC bias control unit for controlling the DC bias signal of the DC grid signal based on the switching frequency of the DC bus signal, controller. The method of claim 6,
A control information construction unit for constructing the power control graph information defining the correspondence between the output current values of the energy storage device and the AC power network and the switching frequency value on the output current axis and the switching frequency axis, A power control apparatus using a DC bus signal of a switching frequency variation type in a DC grid system further including a power control unit. The method of claim 8,
The power control graph information includes:
A first graph line representing a relationship between an output current value of the energy storage device and the switching frequency value and having a shape in which the switching frequency value decreases with an increase in the output current value; And a second graph line representing a correspondence relationship between the switching frequency values,
A power control using a DC bus signal of a switching frequency variation type in a DC grid system in which an intersection point between the first and second graph lines is located on the switching frequency axis and is divided into positive and negative output current sections based on the switching frequency axis; Device. The method of claim 6,
The distributed power source, the load, and the energy storage device,
Wherein a DC bus signal carrying a switching frequency value corresponding to the current power state is transmitted through a DC line in a DC bus voltage, the switching frequency bands of switching frequency values used for transmission in the power state differ from each other,
The power control device includes:
A DC bus signal of a switching frequency variation type in a DC grid system that analyzes a switching frequency value of a DC bus signal received from the distributed power source, the load, and the energy storage device, respectively, and estimates each of the current power states corresponding thereto, Power control apparatus using power.

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