KR20190076371A - System for operating Direct Current distribution grid, Method thereof, and Storage medium having the same - Google Patents

Abstract

Disclosed is a direct current (DC) distribution grid operating system capable of maintaining a power supply and demand balance. The DC distribution grid operating system comprises: a DC economic dispatch (ED) block (310) calculating an output schedule for power only having a demand value and a supply value of the power regardless of a network structure; a DC network analysis block (320) calculating an output adjusting value for power output to solve a voltage violation in consideration of the network structure and using the output schedule and the output adjusting value to calculate an output command value; and a power conversion device (330) performing economic power supply and demand balance maintenance of a DC system through constant voltage operation control in accordance with the output command value.

Description

TECHNICAL FIELD The present invention relates to a direct current distribution system, a direct current distribution operating system, a method thereof, and a computer readable storage medium storing the method.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a distribution network operating technique, and more particularly, to a DC distribution network operating system and method capable of maintaining a balance of power supply and demand while solving a voltage problem of a DC system.

The operating system of the power system is equipped with various application programs and provides a solution for economical and stable operation of the system. Generally, power generation control programs executed in the central operating system include generator commutation (UC), economic dispatch (ED), and automatic generation control (AGC).

The UC determines the on / off status of the generator based on the load prediction result based on the start / stop cost of the generator. The ED determines the economic output distribution amount for the generator determined to be On in the UC, considering the load prediction result and the power generation cost.

ED is generally performed in minutes to hours. AGC is performed in units of several seconds and calculates the output adjustment of each generator in real time to maintain the frequency of the system. If the UC and ED establish a power generation plan based on the predicted results, the AGC acts as a real-time supply-demand control for output fluctuations such as load variation in the grid or dropout of the generator.

In the case of a large-scale AC system having a plurality of generators, power generation control is performed as shown in Fig. UC, ED, and AGC are application programs installed in the EMS (Energy Management System), and perform computation according to the determined cycle to transmit the output command value to each generator.

Each generator is basically operated based on the output command value of EMS. Although AGC plays the role of maintaining the frequency of the system in the center, it is difficult to perform the frequency control for the short term in the few seconds. For this purpose, in a large-scale alternating current (AC) system, each generator performs a GF (Governor Free) operation in which the rotation speed of the generator is automatically controlled according to the system conditions.

The GF operation performs output control according to the speed adjustment ratio (Droop), which is a ratio of the frequency change component to the generator output variation as a percentage. Each generator in the system shares the variation of the output of the system according to the Droop curve and maintains the frequency in mSec units.

The reason why GF operation is performed in a large scale system in which a plurality of generators exist is because a generator can not absorb the power variation of the entire system.

However, in a small scale grid or micro grid, a distributed power supply can maintain the system frequency and economic supply / demand balance through Constant Voltage Constant Frequency (CVCF) operation. Since one distributed power supply performs real-time power supply adjustment, AGC for adjusting multiple generator outputs is not used.

Since the DC system does not have a frequency, the supply and demand of the system can be controlled in a manner similar to FIG. 2 by the constant voltage operation of the reference converter instead of the CVCF operation. However, if the DC system becomes complicated due to network complexity such as loops or meshes, and multiple distributed power sources and / or loads are sporadically linked to the grid, if the power supply is adjusted with one converter, .

In the AC system, the voltage is correlated with the reactive power, so that the voltage can be controlled through the ancillary equipment when a low voltage is generated. However, unlike the AC system, the voltage in the DC system has a correlation with the active power, so the control of the active power is necessary. AGC, which regulates multiple generator outputs based on frequency, is also not applicable to DC systems.

Therefore, the DC distribution operating system is required to provide additional technology capable of maintaining the power supply balance while solving the DC voltage problem. In recent years, digital loads have increased and DC power sources such as PV (photovoltaic) and ESS (Energy Storage System) have been expanding. In order to efficiently link this to the distribution network, DC shipments demonstration projects are being conducted in areas such as the island and campus.

Therefore, the DC distribution is becoming complicated in the form of a grid network from the concept of a simple line of power transmission, in which various distributed power sources, renewable sources and energy storage devices are linked. In this case, a central operating system for DC distribution is required in order to secure basic power supply and / or stability of the power system.

In addition, application program for DC system operation has not been developed yet, but it is an essential element in DC distribution operating system.

1. Korean Registered Patent No. 10-1780105 (Registered Date: 2017.09.13) 2. Korean Patent Publication No. 10-2016-0081067

Disclosure of Invention Technical Problem [8] The present invention has been proposed in order to solve the above problems, and it is an object of the present invention to provide a DC distribution operating system and method capable of maintaining a balance of power supply and demand while solving a DC (Direct Current) have.

In addition, the present invention can be applied to DC Network Economic Dispatch (DCED), DC Network Topology Process (DCTP), DC Network State Estimation (DCSE), DC Voltage Control (DCVC) Voltage control system, and a voltage control system.

The present invention provides a DC distribution operating system capable of maintaining a balance of power supply and demand while solving a DC (Direct Current) system voltage problem in order to achieve the above-described problems.

The DC distribution operating system includes:

A DC (Direct Current) economic feed planning block 310 for calculating an output schedule for a power source only with a demand value and a supply value of the power irrespective of the network structure;

A DC network analysis block 320 for calculating an output adjustment value for the power output for eliminating a voltage violation in consideration of the network structure and calculating an output command value using the output schedule and the output adjustment value; And

And a power converter (330) for maintaining an economical power supply / demand balance of the DC system through constant voltage operation control according to the output command value.

At this time, the network analysis block 320 includes a DC topology processor 321 for generating bus information according to the network structure; A DC state estimation unit (323) for calculating a correction voltage and an effective power value using the bus information; And a DC voltage control unit 325 for calculating an output adjustment value using the correction voltage.

Also, the DC topology processor 321 may be configured to identify the connection relationship of the DC system equipments and the open / close state of the circuit breakers, group the nodes, and generate bus information.

Here, the bus information tracks a facility link relation of a database set in advance based on the node, and a bus number is assigned to each node having the same potential.

Also, the DC state estimating unit 323 receives the measured voltage and active power data to be used as input data of the system analysis through the bus information as input, and outputs a corrected correction voltage corresponding to the DC power algebraic equation and a valid And calculating a power value.

In addition, the DC voltage controller 325 may adjust the power output when the correction voltage corresponds to a preset voltage violation condition.

In addition, when a voltage violation occurs that deviates from a preset voltage range on a specific bus, the DC voltage controller 325 controls the sensitivity of the DC bus using a sensitivity matrix calculated using a Jacobian matrix of the DC system And the output command value corresponding to the output change amount is calculated.

The output change amount is a voltage sensitivity factor that is set to the largest value among the rows of the Jacobian matrix corresponding to the bus corresponding to the voltage violation, and is a value obtained by dividing the voltage change amount of the power source.

The power source may be a distributed power source or an ESS (Energy Storage System).

The DC economy feed plan block 310 includes a correction data calculation unit 430 for receiving actual data of the new reproduction prediction and load prediction values 410 and 420 and calculating correction data using a predetermined function. And an engine 440 for calculating an output schedule 450 for adjusting the power output for a predetermined time using the correction data.

On the other hand, according to another embodiment of the present invention, (a) a DC (Direct Current) economic feed plan block 310 has only a demand value and a supply value of a power regardless of a network structure, Calculating; (b) The DC network analysis block 320 calculates an output adjustment value for the power supply output for eliminating the voltage violation in consideration of the network structure, and calculates an output command value using the output schedule and the output adjustment value ; And (c) the power conversion apparatus 330 maintains an economical power supply / demand balance of the DC system through the constant voltage operation control according to the output command value.

The step (c) may further include the steps of: (c-1) generating a DC topology processing unit 321 with bus information according to the network structure; (c-2) calculating a correction voltage and an effective power value using the bus information by the DC state estimation unit 323; And (c-3) the DC voltage controller 325 calculates the output adjustment value using the correction voltage.

In the step (c-1), the DC topology processor 321 grasps the connection relation of the DC system equipments and the open / close state of the circuit breaker, groups the nodes, and generates bus information And a plurality of pixels.

Also, in the step (c-2), the DC state estimating unit 323 uses the measured voltage and active power data to be used as input data of the systematic analysis through the bus information as an input, And calculating a corrected correction voltage and an effective power value corresponding to the correction value.

In the step (c-3), the DC voltage controller 325 adjusts the power output when the correction voltage corresponds to a preset voltage violation condition.

In the step (c-3), when the DC voltage controller 325 detects a voltage violation that deviates from a predetermined voltage range on a specific bus, the DC voltage controller 325 calculates a DC voltage based on a Jacobian matrix of the DC system Calculating an output change amount of a power source having the highest sensitivity through a sensitivity matrix, and calculating an output command value corresponding to the output change amount.

In the step (a), the correction data calculating unit 430 receives actual data of the new reproduction prediction and the load predicted values 410 and 420 and calculates correction data using a predetermined function. And an output schedule 450 for the engine 440 to adjust the power output for a predetermined time using the correction data.

On the other hand, another embodiment of the present invention can provide a computer-readable storage medium storing the program code for executing the direct current distribution operating method described above.

According to the present invention, the balance of power supply and demand can be maintained while solving the voltage problem of the DC (Direct Current) system.

Another advantage of the present invention is that the technology preemption and the possibility of domestic and overseas business are high in the direct current distribution operating system which can secure the economical and safety of the DC system.

FIG. 1 is a schematic diagram of a general large-scale alternating current (AC) generation control system.
Fig. 2 is a conceptual diagram of power generation control of a general small microgrid system.
3 is a conceptual diagram for DC (Direct Current) system power generation control according to an embodiment of the present invention.
4 is a detailed configuration diagram of the DC Economic Dispatch Block (DC Network Economic Dispatch) shown in FIG.
FIG. 5 is a flowchart illustrating a voltage control process of the DC voltage control block shown in FIG.
6 is a flowchart illustrating a DC power generation control process according to an exemplary embodiment of the present invention.
7 is a block diagram of the configuration of the DC distribution management system shown in FIG.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for similar elements in describing each drawing. The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. The term "and / or" includes any combination of a plurality of related listed items or any of a plurality of related listed items.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Should not. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a DC distribution control system and method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a conceptual diagram for DC (Direct Current) system power generation control according to an embodiment of the present invention. 3, the DC distribution operating system 300 includes a DC DC Economic Dispatch (DCED) 310, a DC Network Analysis (DCNA) 320, a converter 330, and the like.

The DC economy feed plan block 310 performs functions that integrate the functions of the generator commissioning unit (UC) and the economic dispatch plan (ED).

The DC network analysis block 320 calculates a solution to solve the low voltage in the DC system when it occurs. To this end, DC Network Analysis (DCNA) 320 includes DC Network Topology Process (DCTP) 321, DC Network State Estimation (DCSE) 323, DC A DC voltage control unit (DCVC) 325, and the like.

The DC economy feed planning block 310 calculates the output schedule for the power output (distributed power, ESS, etc.) with only the demand value and the supply value of the power irrespective of the network structure, while the DC topology planning block A topology processor 321, a DC state estimator (DCSE) 323, and a DC voltage control unit (DCVC) Calculate the output adjustment value of the output. Accordingly, the DC topology processor (DCTP) 321, the DC state estimator (DCSE) 323, and the DC voltage controller (DCVC) (DC Network Analysis). DCNA operates with a sequence of DCTP> DCSE> DCVC, and the cycle is several seconds.

The DC topology processing unit 321 performs a function of generating bus information by grouping nodes by grasping the connection relationship of the DC system equipments and the open / close state of the circuit breakers. There are nodes at both ends of all facilities such as circuit breaker, line, and power conversion device. The facility link relation of the database is tracked based on this node, and a bus number is assigned to each node having the same potential. In the topology processing algorithm of the existing AC system, processing for the DC system power conversion apparatus is added.

In general, actual data includes some errors due to various field conditions, such as faulty or asynchronous communication equipment. Therefore, it is difficult to use such acquired data as input data of the system analysis without refining. Therefore, the DC state estimation unit 323 corrects the DC state to generate meaningful data.

To this end, the DC state estimation unit 323 uses the DC system network model and bus information (i.e., bus information) configured in the DC topology processing unit 321. [ Using the measured voltage and active power data as inputs, calculate the corrected correction voltage and the active power value that meet the DC power algebraic equation. That is, an objective function is constructed to minimize the cost, which is expressed by the following equation.

Where w is a weighting matrix and H is a DC power algebraic equation matrix. w is applied higher than a preset accuracy value, and applied lower than an accuracy value.

Then, a partial differential equation is constructed, which is expressed by the following equation.

Here, x is the data to be obtained.

In the above equation, it becomes the minimum value when the partial derivative is zero.

Therefore, it is repeated until? X becomes smaller than the tolerance. This is described in various documents and papers, and the description thereof will be omitted.

The overall performance process is similar to the AC system estimation, but uses the DC current equation, not the AC power equation. The DC current equation is given by the following equation.

Where P is power, V is voltage, I is current, Y is admittance, and dc is direct current.

3, DC Topology Processor (DCTP) 321 and DC Network State Estimation (DCSE) 323 perform functions for modeling and error processing, Is a voltage control by a DC voltage control unit (DCVC: DCVC) When a voltage violation occurs in the DC system during operation, it is necessary to adjust the output of a controllable distributed power supply or an ESS (Energy Storage System). The DC voltage control unit 325 calculates the output adjustment value. A drawing showing this is shown in Fig. 5 and will be described later.

3, the power converter 330 maintains the economical power supply balance of the DC system through the constant voltage operation control according to the output power adjustment value of the distributed power and / or ESS. The power converter 330 may be a converter or the like.

FIG. 4 is a detailed configuration diagram of FIG. 3. FIG. The DC economy feed plan block 310 incorporates the functions of the generator commissioning unit (UC) and the economic dispatch plan (ED).

Referring to FIG. 4, the optimal output schedule of the distributed power source is calculated based on the predicted values 410, 420 of the renewal / load. To this end, a correction data calculating section 430 for receiving actual data of the predicted values 410, 420 of the new reproduction / load as inputs and calculating correction data by using a predetermined function, and an output schedule 450 using the correction data And the like.

The preset function may consist of an objective function and a constraint function. The objective function is to minimize the power generation cost. The constraint function is similar to that of the existing AC (Alternating Current) system, but adds a constraint function related to the power system efficiency of the DC system. More specifically, the constraint function may include a start / stop state constraint, a minimum stop time constraint, and the like.

The output schedule 450 is information for adjusting the output (80 kW, -50 kW, etc.) of the power sources (Source A, B, ... N) for a certain period of time. For example, Source A is output at 80 kW for 15 minutes and Source B at -50 kW for 15 minutes.

FIG. 5 is a flowchart illustrating a voltage control process of the DC voltage control block shown in FIG. Referring to FIG. 5, when a low voltage is generated on a bus line k, a sensitivity matrix is calculated using a DC Jacobian matrix (steps S510, S520, and S530). The sensitivity matrix is [ΔV] = [J] ^-1 [ΔP]. Here, J is a Jacobian matrix, and AP represents an output change amount.

Thereafter, a power source having the highest sensitivity to the bus k is selected, and the output variation of the selected power source is calculated (step S550). The output change amount is expressed by the following equation.

Here, VSF represents the voltage sensitivity factor, and VSF (Voltage Sensitivity Factor) is set to the largest value among the rows of the Jacobian matrix corresponding to the voltage violation bus (i.e., bus).

Thereafter, the output of the corresponding power supply is changed according to the amount of change of the output, and the low voltage of the bus line k is removed (steps S560 and S570). In addition, in the event that a voltage violation occurs in the DC system during operation, the DC voltage controller 325 calculates the adjusted value because the output power of the controllable distributed power supply or ESS is required.

6 is a flowchart illustrating a DC power generation control process according to an exemplary embodiment of the present invention. 6, when the execution manager 60 executes the control on the distribution view, the DC (Direct Current) economy feed planning block 310 and the DC network analysis block 320 are executed (steps S610, S620, S650). Of course, the load forecast value 420 and the renewal predicted value 410 are input to the DC (Direct Current) economic power supply planning block 310. Basically, the output schedule of the distributed power source and the charge / discharge schedule of the ESS are calculated while the direct current (DC) economic power supply planning block 310 performs water units.

Thereafter, it is confirmed whether the correction voltage calculated by the DC topology processing unit 321 and the DC state estimation unit 323 of the DC network analysis block 320 corresponds to a voltage violation (step S630). If it is determined that the voltage is out of the range of the minimum voltage and the maximum voltage range, the DC voltage control unit 325 calculates the output adjustment value (step S640). Otherwise, steps S610 to S630 are performed again if the voltage violation is not satisfied.

On the other hand, an output schedule is calculated by a DC (Direct Current) economic power supply planning block 310, and an output command value is calculated by reflecting an output schedule and an output adjustment value (step S660). Thereafter, the power conversion device 330 is controlled through the output command value. In other words, DCCP> DCSE> DCVC is repetitively performed every several seconds. When DCSE bus voltage result is out of voltage range, DC voltage controller 325 operates to calculate the real time distributed power output adjustment value. The output command value of the actual distributed power and ESS is the sum of the "output value calculated by DCED" and the "adjustment value calculated by DCVC".

FIG. 7 is a block diagram of the configuration of the DC distribution operating system 700 shown in FIG. 7, the DC distribution operation server 700 is connected to the actual system 720 to acquire the field values and store them in the field database 711. The field database 711 and the power operation program 713, (Application programming interface) interface 712 is connected.

The terms " part, "" block," and the like, which are described in the specification, refer to a unit for processing at least one function or operation, and may be implemented by hardware or software or a combination of hardware and software.

(DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

Furthermore, the steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied in the form of a program form which may be performed via a variety of computing means, and recorded in a computer-readable medium. The computer-readable medium may include a program (command) code, a data file, a data structure, and the like, alone or in combination.

The program (command) codes recorded on the medium may be those specially designed and constructed for the present invention or may be those known to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape, optical media such as CD-ROMs, DVDs, Blu-ray and the like, and ROMs, RAM), flash memory, and the like, which are specifically configured to store and execute program (instruction) codes.

Here, examples of program (command) codes include machine language codes such as those produced by a compiler, as well as high-level language codes that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

310: Direct Current (DC) Economy Feed Planning Block
320: DC network analysis block
321: DC topology processor 323: DC state estimator
325: DC voltage control unit
330: Power converter

Claims (20)

A DC (Direct Current) economic feed planning block 310 for calculating an output schedule for a power source only with a demand value and a supply value of the power irrespective of the network structure;
A DC network analysis block 320 for calculating an output adjustment value for the power output for eliminating a voltage violation in consideration of the network structure and calculating an output command value using the output schedule and the output adjustment value; And
A power converter (330) for maintaining an economical power supply / demand balance of the DC system through constant voltage operation control according to the output command value;
Wherein the direct current distribution system comprises:
The method according to claim 1,
The DC network analysis block 320,
A DC topology processor 321 for generating bus information according to the network structure;
A DC state estimation unit (323) for calculating a correction voltage and an effective power value using the bus information; And
And a DC voltage control unit (325) for calculating an output adjustment value using the correction voltage.
3. The method of claim 2,
Wherein the DC topology processing unit (321) obtains bus information by grouping the nodes by grasping the connection relationship of the DC system equipments and the open / close state of the circuit breakers.
The method of claim 3,
Wherein the bus information tracks a facility link relationship of a database set in advance based on the node, and a bus number is assigned to each node having the same potential.
5. The method of claim 4,
The DC state estimating unit 323 receives the measured voltage and active power data to be used as input data of the systematic analysis through the bus information as inputs and outputs a corrected correction voltage and a reactive power value corresponding to the DC power algebraic equation Of the direct current distribution system.
6. The method of claim 5,
Wherein the DC voltage controller (325) adjusts the power output when the correction voltage corresponds to a preset voltage violation condition.
3. The method of claim 2,
When a voltage violation occurs that deviates from a predetermined voltage range on a specific bus, the DC voltage controller 325 controls the DC voltage controller 325 such that sensitivity is maximized through a sensitivity matrix calculated using a Jacobian matrix of a DC system And calculates an output command value corresponding to the amount of change in the output of the direct power distribution system.
8. The method of claim 7,
Wherein the output variation amount is a voltage sensitivity factor that is set to a largest value among rows of a Jacobian matrix corresponding to a bus corresponding to a voltage violation, and is a value obtained by dividing a voltage variation amount of the power source.
The method according to claim 1,
Wherein the power source is a distributed power source or an ESS (Energy Storage System).
The method according to claim 1,
The DC economy feed plan block 310 includes a correction data calculation unit 430 for receiving actual data of the new reproduction prediction and load prediction values 410 and 420 and calculating correction data using a predetermined function. And an engine (440) for calculating an output schedule (450) for adjusting the power output for a predetermined time using the correction data.
(a) calculating an output schedule for a power source using only a demand value and a supply value of a power regardless of a network structure;
(b) The DC network analysis block 320 calculates an output adjustment value for the power supply output for eliminating the voltage violation in consideration of the network structure, and calculates an output command value using the output schedule and the output adjustment value ; And
(c) the power converter (330) performing the constant voltage operation control according to the output command value to maintain the economical power supply balance of the DC system;
Wherein the direct current distribution operating method comprises the steps of:
12. The method of claim 11,
The step (c)
(c-1) the DC topology processing unit 321 generating bus information according to the network structure;
(c-2) calculating a correction voltage and an effective power value using the bus information by the DC state estimation unit 323; And
(c-3) calculating an output adjustment value using the correction voltage by the DC voltage controller (325).
13. The method of claim 12,
The step (c-1)
And a DC topology processor (321) for acquiring the connection relationship of the DC system equipments and the opening and closing states of the circuit breakers and grouping the nodes to generate bus information. How to operate.
14. The method of claim 13,
Wherein the bus information tracks a facility link relationship of a database set in advance based on the node, and a bus number is assigned to each node having the same potential.
15. The method of claim 14,
In the step (c-2), the DC state estimating unit 323 uses the measured voltage and active power data to be used as the input data of the systematic analysis through the bus information as an input, And calculating a corrected correction voltage and an effective power value for the direct current power supply.
16. The method of claim 15,
And adjusting the power output when the DC voltage controller (325) meets a voltage violation condition in which the correction voltage is set in advance, in the step (c-3).
13. The method of claim 12,
In the step (c-3), when a voltage violation occurs in which the DC voltage controller 325 is out of a predetermined voltage range on a specific bus, the sensitivity matrix calculated using the Jacobian matrix of the DC system Wherein the output command value corresponding to the output change amount is calculated by calculating an output change amount of the power source having the highest sensitivity through the sensitivity matrix.
18. The method of claim 17,
Wherein the output change amount is a voltage sensitivity factor that is set to a largest value among rows of a Jacobian matrix corresponding to a bus corresponding to a voltage violation, and is a value obtained by dividing a voltage change amount of the power source.
12. The method of claim 11,
The step (a)
Calculating correction data by using a function that is preset and receiving actual data of the new and reproduction prediction and load predicted values (410, 420) as a correction data calculation unit (430); And
And calculating an output schedule (450) for the engine (440) to adjust the power output for a predetermined time using the correction data.
A computer readable storage medium storing a program code for executing a method of operating a DC distribution according to any one of claims 11 to 19.

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