KR20210126535A - System for operating Direct Current distribution grid, and Method thereof - Google Patents

Abstract

Disclosed is a system for operating a direct current distribution network. The system for operating the direct current distribution network comprises: a direct current (DC) economic power supply planning block (310) calculating an output schedule for power supply only with a demand value and a supply value of electricity regardless of a network structure; a DC network analysis block (320) considering the network structure to calculate an output adjustment value for power output to resolve a voltage violation and using the output schedule and the output adjustment value to calculate an output command value; and an electricity conversion device (330) maintaining a balance of economic power demand and supply of a DC system through constant voltage driving control according to the output command value.

Description

DC distribution network operating system, and method thereof, {System for operating Direct Current distribution grid, and Method thereof}

The present invention relates to a distribution network operating technology, and more particularly, to a DC distribution network operating system and method capable of maintaining a power supply and demand balance while solving a DC system voltage problem.

Various application programs are loaded into the operating system of the power system to provide a solution for economical and stable operation of the system. The generation control program performed by the central operating system generally includes a generator start-up and stop plan (UC), an economic dispatch plan (ED), and an automatic generation control (AGC).

UC decides whether to turn on/off the generator by considering the cost of starting and stopping the generator based on the load prediction result as a unit. ED determines the economical output distribution by considering the load prediction result and power generation cost for the generator that is determined to be On in UC.

ED is usually performed in minutes to hours. AGC is performed every few seconds, and the output adjustment of each generator to maintain the frequency of the system is calculated in real time. If UC and ED establish a power generation plan based on the prediction results, AGC performs a real-time supply and demand control role for output fluctuations such as load fluctuations or generator dropouts in the system.

In the case of a large-scale AC system in which a plurality of generators exist, power generation control is performed as shown in FIG. 1 . UC, ED, and AGC are application programs that are loaded into the EMS (Energy Management System), perform calculations according to the set period, and deliver the output command value to each generator.

Each generator is basically operated based on the output command value of EMS. Although the AGC plays a role in maintaining the frequency of the system at the center, it is difficult to control the frequency for a short term of a few seconds or less at the center. To this end, in a large-scale AC (Alternating Current) system, each generator performs GF (Governor Free) operation so that the rotation speed of the generator is automatically controlled according to the system situation.

GF operation performs output control according to the speed adjustment rate (Droop), which is the ratio of the change in frequency to the change in generator output as a percentage. Each generator in the system maintains the frequency in mSec unit by sharing the amount of change in the output of the system according to the droop curve.

The reason for GF operation in a large-scale system with multiple generators is that one generator has a limit in absorbing the change in output of the entire system.

However, in a small-scale system or micro-grid, it is possible to maintain the frequency of the system and maintain economic balance between supply and demand by one distributed power supply through constant voltage/constant frequency (CVCF) operation. Since one distributed power supply performs real-time power supply and demand control, AGC that adjusts the output of multiple generators is not used.

Since the DC system does not have a frequency, the system supply-demand control can be performed in a manner similar to FIG. 2 by the constant voltage operation of the reference converter instead of the CVCF operation. However, if the network becomes complex such as a loop or mesh, and multiple distributed power sources and/or loads are sporadically connected to the system, the problem of local voltage violations when power supply and demand is controlled with one converter. will occur

In an AC system, voltage has a correlation with reactive power, so when a low voltage occurs, it is possible to control the voltage through an ancestor facility. However, unlike the AC system, since the voltage in the DC system has a correlation with the active power, it is necessary to control the active power. AGC, which adjusts the output of multiple generators based on frequency, is also not applicable to DC systems.

Therefore, an additional technology capable of maintaining a balance between power supply and demand while solving the voltage problem of the DC system is required for the DC distribution network operating system. Recently, with the increase of digital load, DC power such as PV (photovoltaic) and ESS (Energy Storage System) is expanding. In order to efficiently link this to the power distribution network, DC distribution network demonstration projects are underway in areas such as island areas and campuses.

Therefore, DC distribution is also becoming complicated from a simple line concept of power transmission to a grid type, and various distributed power sources, renewable sources, and energy storage devices are connected here. 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, although an application program for DC system operation has not been developed yet, it is an essential element for an operation system for DC distribution.

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

The present invention has been proposed to solve the problems according to the above background art, and the purpose of the present invention is to provide a DC distribution network operating system and method capable of maintaining a balance between power supply and demand while solving the voltage problem of a DC (Direct Current) system. have.

In addition, the present invention is a DC economic dispatch plan (DCED: DC Network Economic Dispatch), DC topology processing (DCTP: DC Network Topology Process), DC state estimation (DCSE: DC Network State Estimation), DC voltage control (DCVC: DC Network) Voltage Control), another object is to provide a DC distribution network operating system and method using four power generation control methods.

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

The DC distribution network operating system,

DC (Direct Current) economic power supply planning block 310 for calculating an output schedule for power using only the demand and supply values of power regardless of the network structure;

a DC network analysis block 320 for calculating an output adjustment value for the power output for resolving 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 conversion device 330 for maintaining economical power supply and demand balance of the DC system through constant voltage operation control according to the output command value.

In this case, the network analysis block 320 includes a DC topology processing unit 321 for generating bus information according to the network structure; a DC state estimation unit 323 for calculating a corrected voltage and an active power value using the bus information; and a DC voltage control unit 325 for calculating an output adjustment value by using the correction voltage.

In addition, the DC topology processing unit 321 may be characterized in that it generates bus information by grouping the nodes by identifying the connection relationship of the DC system facilities and the opening/closing state of the circuit breaker.

Here, the bus information may be characterized in that a bus number is assigned to each node having the same potential by tracing a relationship of a facility link in a database set in advance based on the node.

In addition, the DC state estimator 323 uses the measured voltage and active power data to be used as input data for system analysis through the bus information as inputs, and the corrected corrected voltage and effective power corresponding to the DC power current equation It may be characterized in that the power value is calculated.

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

In addition, the DC voltage control unit 325, when a voltage violation out of a preset voltage range occurs on a specific bus, a sensitivity matrix calculated using a Jacobian matrix of the DC system through a sensitivity matrix (Sensitivity Matrix). Calculates the output change amount of the largest power and calculates an output command value corresponding to the output change amount.

In addition, the output change amount may be a value obtained by dividing the voltage change amount of the corresponding power source by a voltage sensitivity factor set to the largest value among rows of the Jacobian matrix corresponding to the bus corresponding to the voltage violation.

In addition, the power source may be a distributed power source or an Energy Storage System (ESS).

In addition, the DC economic power supply planning block 310 is a correction data calculation unit 430 for calculating the correction data using a preset function by receiving the actual measurement data of the new regeneration prediction and load prediction values (410, 420) as input; and an engine 440 for calculating an output schedule 450 for adjusting power output for a predetermined time by using the correction data.

On the other hand, another embodiment of the present invention, (a) DC (Direct Current) economic power supply plan block 310, regardless of the network structure, the output schedule for power with only the demand value and supply value of power calculating; (b) the DC network analysis block 320 calculates an output adjustment value for the power output for resolving a voltage violation in consideration of the network structure, and calculates an output command value using the output schedule and the output adjustment value to do; and (c) performing, by the power conversion device 330, an economical power supply/demand balance of the DC system through constant voltage operation control according to the output command value.

In addition, the step (c) includes: (c-1) generating, by the DC topology processing unit 321, bus information according to the network structure; (c-2) calculating, by the DC state estimator 323, a correction voltage and an active power value using the bus information; and (c-3) calculating, by the DC voltage controller 325, an output adjustment value using the correction voltage.

In addition, in the step (c-1), the DC topology processing unit 321 identifies the connection relationship of the DC system equipment and the open/close state of the circuit breaker, and groups the nodes to generate bus information. It may be characterized by including;

In addition, in the step (c-2), the DC state estimator 323 uses the measured voltage and active power data as input data for system analysis through the bus information as input, the DC power current equation Calculating a corrected correction voltage and active power value corresponding to ;

In addition, the step (c-3) may include a step of adjusting the power output when the correction voltage corresponds to a preset voltage violation condition by the DC voltage controller 325 .

In addition, in step (c-3), when the DC voltage control unit 325 generates a voltage violation out of a preset voltage range on a specific bus, the DC-based Jacobian matrix is used to calculate the calculated value. It may be characterized in that the output change amount of the power having the greatest sensitivity is calculated through a sensitivity matrix and an output command value corresponding to the output change amount is calculated.

In addition, the step (a) may include: calculating, by the correction data calculating unit 430, the new regeneration prediction and the actual measurement data of the load prediction values 410 and 420 using a preset function; and calculating, by the engine 440, an output schedule 450 for adjusting the power output for a predetermined time by using the correction data.

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

According to the present invention, while solving the voltage problem of the DC (Direct Current) system, it is possible to maintain the power supply and demand balance.

In addition, as another effect of the present invention, it can be said that the technology preoccupation and domestic and foreign business possibilities are high in the DC distribution network operating system that can secure the economic efficiency and safety of the DC system.

1 is a conceptual diagram of a power generation control of a general large-scale AC (Alternating Current) system.
2 is a conceptual diagram of power generation control of a general small-scale micro-grid system.
3 is a conceptual diagram for control of direct current (DC) system power generation according to an embodiment of the present invention.
4 is a detailed configuration diagram of the DC economic dispatch plan block (DC Network Economic Dispatch) shown in FIG.
5 is a flowchart showing a voltage control process of the DC voltage control block (DC Network Voltage Control) shown in FIG. 3 .
6 is a flowchart illustrating a DC power distribution control process according to an embodiment of the present invention.
FIG. 7 is a block diagram of the DC distribution network operating system shown in FIG. 3 .

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

In describing each figure, like reference numerals are used for like elements. The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

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

Unless defined otherwise, 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 a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. shouldn't Hereinafter, a DC distribution network operating 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 direct current (DC) system power generation control according to an embodiment of the present invention. Referring to FIG. 3 , the DC distribution network operating system 300 includes a DC economic dispatch plan block (DCED: DC Network Economic Dispatch) 310, a DC network analysis block (DCNA: DC Network Analysis) 320, a converter ( 330) and the like.

DC economic dispatch plan block 310 performs a function of integrating the functions of a generator start-up stop plan (UC: Unit Commitment) and an economic dispatch plan (ED: Economic Dispatch).

The DC network analysis block 320 performs a function of calculating a solution for solving the occurrence of a low voltage in the DC system. To this end, the DC network analysis block (DCNA: DC Network Analysis) 320 is a DC topology processing unit (DCTP: DC Network Topology Process) 321, DC state estimation unit (DCSE: DC Network State Estimation) (323), DC It is configured to include a voltage control unit (DCVC: DC Network Voltage Control) 325 and the like.

While the DC economic power supply planning block 310 calculates the output schedule for power output (distributed power, ESS, etc.) with only the demand and supply values of power regardless of the network structure, the DC topology processing unit (DCTP: DC Network) Topology Process) 321, DC Network State Estimation (DCSE) 323, and DC Voltage Control Unit (DCVC: DC Network Voltage Control) 325 are power sources for resolving voltage violations in consideration of the network structure. Calculate the output adjustment value of the output. Therefore, the DC topology processing unit (DCTP: DC Network Topology Process) (321), DC state estimation unit (DCSE: DC Network State Estimation) (323), DC voltage control unit (DCVC: DC Network Voltage Control) (325) DCNA (DC Network Analysis). DCNA operates in the sequence of DCTP>DCSE>DCVC, and the execution cycle is several seconds.

The DC topology processing unit 321 performs a function of generating bus information by grouping nodes by identifying the connection relationship of the DC system equipment and the opening/closing state of the circuit breaker. Nodes exist at both ends of all facilities such as circuit breakers, lines, and power conversion devices. Based on this node, the facility link relationship of the database is traced, and a bus number is assigned to each node having the same potential. In the existing AC system topology processing algorithm, processing for the DC system power conversion device is added.

In general, actual measurement data contains errors to some extent due to various field conditions, such as errors in communication equipment or problems in unsynchronization. Therefore, it is difficult to use such acquired data as input data for systematic analysis as it is without purification. Accordingly, the DC state estimator 323 serves to generate meaningful data by correcting it.

To this end, the DC state estimation unit 323 uses the DC system network model and bus information (ie, bus information) configured in the DC topology processing unit 321 . Using the measured voltage and active power data as inputs, a corrected correction voltage and active power value corresponding to the DC power flow equation are calculated. That is, an objective function is constructed to minimize the cost, which is expressed by the following equation.

Here, w denotes a weight matrix, and H denotes a DC power flow equation matrix. If w is higher than the preset accuracy value, it is applied high, and if it is lower than the accuracy value, it is applied low.

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

Here, x is the desired data.

In the above equation, when the partial derivative is 0, it becomes the minimum value.

Therefore, it is repeated until Δx becomes smaller than a tolerance. Since this has been described in various literatures and papers, a further description thereof will be omitted.

The overall performance process is similar to the AC system estimation, but the DC current equation is used instead of the AC power equation. The DC current equation is as follows.

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

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

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

FIG. 4 is a detailed configuration diagram of FIG. 3 . The DC economic dispatch plan block 310 integrates the functions of a generator start-up stop plan (UC: Unit Commitment) and an economic dispatch plan (ED: Economic Dispatch).

Referring to FIG. 4 , the optimal output schedule of the distributed power supply is calculated based on the predicted values 410 and 420 of the renewable load. To this end, the correction data calculation unit 430 that receives the actual measurement data of the predicted values 410 and 420 of the renewable load as an input and calculates the correction data using a preset function, and an output schedule 450 using the correction data. and an engine 440 that calculates.

The preset function may be composed of an objective function and a constraint function. The objective function is to minimize the power generation cost, and the constraint function is similar to that of the existing AC (Alternating Current) system, but a constraint function related to the efficiency of the power converter of the DC system is added. In other words, the constraint function includes a start/stop state constraint, a minimum stop time constraint, and the like.

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

5 is a flowchart showing a voltage control process of the DC voltage control block (DC Network Voltage Control) shown in FIG. 3 . Referring to FIG. 5 , when a low voltage occurs in the bus (ie, bus) k, a sensitivity matrix is calculated using a DC-based Jacobian matrix (steps S510, S520, and S530). The sensitivity matrix is [ΔV] = [J] ^-1 [ΔP]. Here, J is a Jacobian matrix, and ΔP is an output change amount.

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

Here, VSF represents a 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 (ie, bus).

Thereafter, the low voltage of the corresponding bus bar k is resolved by changing the output of the corresponding power source according to the output change amount (steps S560 and S570). In other words, when a voltage violation in the DC system occurs during operation, it is necessary to adjust the output of a controllable distributed power source or ESS, and the DC voltage control unit 325 calculates this adjustment value.

6 is a flowchart illustrating a DC power distribution control process according to an embodiment of the present invention. Referring to FIG. 6 , when the execution manager 60 executes control on the distribution network, a DC (Direct Current) economic power supply planning block 310 and a DC network analysis block 320 are executed (steps S610, S620, S650). Of course, the DC (Direct Current) economic power supply planning block 310 is input to the load predicted value 420, the new regeneration predicted value (410). The basic distributed power output schedule and ESS charge/discharge schedule are calculated while the DC (Direct Current) economic power supply plan block 310 performs in minutes.

Thereafter, it is checked 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 ). As a result of the check, if it corresponds to a voltage violation (out of the minimum voltage and maximum voltage range), an output adjustment value is calculated by the DC voltage control unit 325 (step S640). On the other hand, if it does not correspond to a voltage violation, steps S610 to S630 are performed again.

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

FIG. 7 is a block diagram of the DC distribution network operating system 700 shown in FIG. 3 . Referring to FIG. 7 , the DC distribution network operation server 700 is connected to the actual system 720 to acquire field values and store them in the field database 711 , and the field database 711 and the power operation program 713 . API (application programming interface) interface 712 is connected.

Terms such as “…unit” and “…block” described in the specification mean a unit that processes at least one function or operation, which may be implemented as hardware or software or a combination of hardware and software.

In hardware implementation, an application specific integrated circuit (ASIC), digital signal processing (DSP), programmable logic device (PLD), field programmable gate array (FPGA), processor, controller, microprocessor designed to perform the above-described functions , 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 the memory unit and executed by the processor. The memory unit or processor may employ various means well known to those skilled in the art.

In addition, the steps of the method or algorithm described in relation to the embodiments disclosed herein may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable medium. The computer-readable medium may include program (instructions) codes, data files, data structures, etc. alone or in combination.

The program (instructions) code recorded on the medium may be specially designed and configured for the present invention, or may be known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs, DVDs, Blu-rays, and the like, and ROM, RAM ( A semiconductor memory device specially configured to store and execute program (instruction) code such as RAM), flash memory, and the like may be included.

Here, examples of the program (instruction) code include not only machine language codes such as those generated by a compiler but also 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: DC (Direct Current) economic dispatch plan block
320: DC network analysis block
321: DC topology processing unit 323: DC state estimation unit
325: DC voltage control unit
330: power conversion device

Claims (2)

DC (Direct Current) economic power supply planning block 310 for calculating an output schedule for power with only the predicted values 410 and 420 of renewables and loads;
a DC network analysis block 320 for calculating an output adjustment value for the power output for resolving 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
The power conversion device 330 for maintaining the economical power supply and demand balance of the DC system through constant voltage operation control according to the output command value; includes;
The DC economic dispatch plan block 310 is,
a correction data calculation unit 430 that receives the measured data of the predicted values 410 and 420 of the reproduction and load as input and calculates correction data using a preset objective function and a constraint function; and
an engine 440 for calculating the output schedule by using the correction data; and
The objective function is an objective function related to the minimization of power generation cost is added,
The constraint function is added with a constraint function related to the efficiency of the power conversion device 330 of the DC system,
The output schedule is information for controlling the output of the power for a predetermined period of time.
(a) DC (Direct Current) economic power supply planning block 310 calculating the output schedule for the power supply with only the predicted values 410 and 420 of the renewable and load;
(b) the DC network analysis block 320 calculates an output adjustment value for the power output for resolving a voltage violation in consideration of the network structure, and calculates an output command value using the output schedule and the output adjustment value step to ; and
(c) performing, by the power conversion device 330, economical power supply and demand balance maintenance of the DC system through constant voltage operation control according to the output command value;
The step (a) is,
calculating, by the correction data calculating unit 430, the correction data using the objective function and the constraint function preset by receiving the measured data of the predicted values 410 and 420 of the reproduction and load as input; and
Calculating, by the engine 440, the output schedule using the correction data;
The objective function is an objective function related to the minimization of power generation cost,
The constraint function is added with a constraint function related to the efficiency of the power conversion device 330 of the DC system,
The output schedule is information for adjusting the output of the power for a predetermined time.

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