Title of I nvention : EVALUATION M ETHOD AN D DEVICE FOR AN ELECTRIC POWER SYSTEM

Technical Field

0001

The present invention relates to an evaluation method and an evaluation device for an electric power system, particularly oriented to evaluate an opti mal size of a device that su pplies or absorbs power in the electric power system .

Background Art

0002

Electric power systems have been typically built to transmit power generated by synchronous generation sources using fossil fuels. Due to climate change and energy security concerns, increasing penetration of distributed and Renewable Energy Sources (RES) occurs. RES power supply is variable and intermittent, mostly dependent on weather conditions. For this reason , the increasing penetration of RES affects the power quality and power system stability, but this problem can be alleviated by grid reinforcements or installation of certai n type of devices that supply or absorb power in electric power systems such as Flexible Alternative Current Transmission Systems (FACTS) or storage devices.

0003

New transmission and distribution lines are expensive and require several years in order to be approved and deployed , whi le FACTS and storage devices are less expensive, have less envi ronmental impact, and can be deployed faster improving power quality, power system stability, and accelerating the penetration of RES .

0004

Despite the increasing penetration of RES, Transmission Systems Operators (TSOs) and Distribution Systems Operators (DSOs) need to ensure power supply and need to maintain power quality and power system stability. At the same time, governments and reg ulatory agencies need awareness on the penetration ratio of RES and thei r impact into the stability of power systems to create appropriate policies or recommendations.

0005

I n conventional power system analysis methods, detailed information on the power systems is required in order to assess their robustness, the penetration of RES, and to evaluate the potential relief by installing devices that supply or absorb power in electric power systems such as FACTS and storage devices.

0006

Non Patent Literature 1 consists of a method based on complex network methodology to identify critical lines and buses by employing centrality measures described as net-ability and entropy deg ree, respectively. Combining the net-ability centrality measure to the distri bution of paths for power flow in a power system , the calculation of an overall power system performance index has also been reported . The use of complex network methodologies offers an alternative to evaluate power systems using little information because structural analysis is performed instead of conventional power-flow analysis which requires more details including load profiles and the size of generators.

Citation List

Non Patent Literatu re 0007

Non Patent Literature 1 : E . Bompard , R. Napo!i , and F. Xue, "Extended topological approach for the assessment of structu ral vulnerabil ity in transmission networks", I ET Gener. Transm . Distrib. , vol . 4, No. 6, pp. 71 6-724, 201 0.

Summary of I nvention

Technical Problem

0008

However, the detailed information of power systems, which is owned by power generation companies, TSOs and DSOs, is not publicly available in general . Therefore, it is difficult that manufacturi ng companies evaluate the optimal size of devices that supply or absorb power in electric power systems such as RES , FACTS , and storage. Also, this lack of detailed information makes difficult for governments to assess the status and needs of the regional or national power systems.

0009

It should be noted that problems related to the evaluation of the optimal size of devices that supply or absorb power in electric power systems are encountered by conventional methods owing to the requirement of detailed information such as transmission and distribution lines' properties, buses' properties, load profiles, and the size of generators. As for complex network methodologies described above, their application to evaluate the optimal size of devices that supply or a bsorb power in electric power systems has not been described before.

001 0

Accordingly, it is an object of the present invention to provide an evaluation method and an evaluation device for an electric power system to evaluate an optimal size of a device that supplies or absorbs power i n the electric power system using little information .

Solution to Problem

001 1

I n order to solve the above mentioned problem , an evaluation method for an electric power system to evaluate an optimal size of a device that supplies or absorbs power in the electric power system , based on information about the device's effect on the electric power system and information about the electric power system includi ng a line's impedance, a network topology, and a bus type, comprising the steps of: (a) selecting the device of which evaluating the optimal size is desired ; (b) modifying a cut-set matrix of the electric power system according to an effect of the device selected in the step (a) ; (c) selecting an index to evaluate the optimal size of the device selected in the step (a) according to the step (b) ; (d) calculating a ranking of the index selected in the step (c) for multiple sizes of the device selected in the step (a); and (e) evaluating the optimal size according to the index ranking calculated i n the step (d) .

0012

Moreover, in order to solve the above mentioned problem , an evaluation device for an electric power system to evaluate an optimal size of a device that su pplies or absorbs power in the electric power system , based on information about the device's effect on the electric power system and information about the electric power system including a line's impedance, a network topology, and a bus type, comprises a processing unit for selecting the device of which evaluating the optimal size is desired ; modifying a cut-set matrix of the electric power system according to an effect of the device; selecting an index to evaluate the optimal size of the device; calculating a ranking of the index for multiple sizes of the device; and evaluating the optimal size according to the index ranking.

Advantageous Effects of Invention

0013

According to the present invention, evaluation of the optimal size of devices that supply or absorb power in electric power systems can be achieved.

0014

Other objects, features and advantages of the invention will appear from the following description with the accompanying drawings.

Brief Description of Drawings

0015

FIG. 1 is an exemplary flow chart of the procedures defining the evaluation methodology of optimal device size.

FIG. 2 is a flow chart showing an algorithm for evaluating the optimal size of devices.

FIG. 3 shows an example of data used to implement the algorithm.

FIG. 4 is a schematic diagram of a portion of a transmission or distribution system prior to installation of the devices.

FIG.5 is a schematic diagram of single-type buses.

FIG.6 is a schematic diagram of a portion of a transmission or distribution power system illustrating the installation of power system devices.

FIG. 7 is a schematic diagram of a portion of a transmission or distribution system after installation of devices.

FIG. 8 shows an example of hardware configuration and interconnection of the device used to evaluate the size of devices .

FIG . 9 illustrates an example of device user interface.

Description of Embodiments

0016

The disclosed subject matter is now descri bed with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. I n the following description , for purposes of explanation , numerous specific details are set forth in order to provide a thorough understanding of the d isclosed subject matter. However, that the disclosed subject matter may be practiced without these specific details. I n other instances, well-known structures and devices such as processing units and memories are shown in block diagram form in order to facilitate describing the disclosed subject matter.

001 7

As used in this a pplication , the terms "system ," "device," "bus, " "line," "index," and the like, can refer and or can incl ude a computer-related entity or an entity related to and operational machine with one or more specific functionalities. The entities disclosed herein can be either hardware, a combination of hardware a nd software, software , or software in execution . For example, a component may be, but is not limited to being , a process running on a processor, a processor, an object, and executable, a th read of execution , a program and/or a computer.

001 8

By way of illustration , both an application running on a server and the server can be a component. One or more components may reside within a process and/or th read of execution and a component may be localized on one component and/or distributed between two or more computers. Also, these components can execute from various computer readable media havi ng various data structures stored thereon . The components may communicate via local and/or remote processes such as in accordance with signal having one or more data packets.

001 9

The use of complex network methodologies offers an alternative to evaluate the optimal device size because the implemented structural analysis requires little information , contrary to conventional power-flow analysis that require more details including load profiles and the size of the generators. Based on complex network methodologies, the d isclosed subject matter can evaluate the optimal size of the devices.

0020

FI G . 1 is an exemplary flow chart [1 00] of the procedures defining the methodology to evaluate the optimal size of devices that supply or absorb power in electric power systems consisting of a device selection module [1 1 0] selecting each device of which evaluating the optimal size is desired , a cut-set matrix modification module [1 20] modifying the in itial cut-set matrix of the power system by adding line(s) and bus(es) in order to eval uate the optimal size of devices , an index selection module [1 30] selecting indexes based on the properties of the power systems that the device has an effect on , an index ranking calculation module [140] calculating the indexes for each line and bus generating the ranking of optimal sizes, and a merge device sizes module [1 50] determining a final ranking based on each index ranking .

0021

FIG . 2 is a flow chart [200] showing an algorithm for evaluating optimal device size for installing devices that supply or absorb power in electric power systems. A calculation exemplifying a procedure to evaluate the optimal device size for installation is presented as follows.

0022

I n the present detailed example, the evaluation of optimal device size for installing a RES device and a FACTS device are considered according to the flow chart in FI G . 2. RES is an example of a device for which cut-set matrix modifications are implemented to evaluate the optimal device size, while FACTS is an example of a device for which optimal device evaluation can be carried out without cut-set matrix modifications.

0023

First, in the device selection step [S21 0] , a device is selected . Here, in this example, first of all , the RES device is selected .

0024

Then , in the cut-set matrix modification step [S220] , the initial cut-set matrix of the power system is modified by adding line(s) and bus(es) to the location for installing the RES device. Here, in this example, owi ng to the power generation property of RES devices, a line and a generation type bus are added to the location for installing the device as exemplified in Fig .5 ([51 0]) , where, for example, the i nitial power transfer limit of the added li ne is equal to zero. Since a generation type bus is added , the cut-set matrix modification is also applied to all generator buses in the power system , where the power transfer limit of each added line is equal to the sum of the power transfer limits of the lines connected to each generator.

0025

As afore-mentioned , a modification of a property of a transmission or distri bution line or a bus modified by the device are considered in addition to a modification of the cut-set matrix in the step [S220] . The property is a change in an impedance, or a power transfer limit, or a power absorption , or a power delivery.

0026

Then , in the index selection step [S230] , index(es) according to step [S220] are selected . The index is based on a structure of a network topology of the electric power system . Here, in this example, an index related to effect of power generation by the instal lation of RES at a bus is selected as follows. The i ndex is defined as increased net-ability (I NA,) index by using the following equation [MATH 1 ].

0027

[MATH 1 ] INAi = ( ^NAi~ " ^A °)

0028

I n [MATH 1 ] , NA ₀ is the net-ability of the power system without the RES device, and NA, is the net-ability of the power system when installing the RES device of size i .

0029

The net-ability in [MATH 1 ] is defined in the above-mentioned Non Patent

Literatu re 1 by using the following equation [MATH 2] .

0030

[MATH2] NA = ^∑ _5eG ∑ _d=(d≠a)eD ¾

0031

I n [MATH2] , N _G is the number of generators, N _D is the number of loads, C _gd is the power transfer capacity for each generator "g " and load "d" pair, and A _{g d} is the equivalent impedance between each "g" and "d" pair. The power transfer capacity in [MATH 2] is defined in the above-mentioned Non Patent Literature 1 by usi ng the following equation [MATH 3] .

0032 [MATH 3] max

C _gd = min _iei

0033

I n [MATH 3] , "L" is the ensemble of lines in the network, "I" is one of the lines, Pmax 's the power transfer limit of the line "I", and f _gd is the PTDF (Power Transfer Distribution Factor) of the line "I" considering the power injection withdrawal at a "g" and "d" pair. The PTDF and Z matrices are calculated based on dc-power flow approximation. The equivalent impedance in [MATH 2] is defined in the above-mentioned Non Patent Literatu re 1 by using the following equation [MATH 4].

0034

[MATH 4] A _gd = Z _gg - 2Z _gd + Z _dd

0035

I n [MATH 4] , Z _gd is the g-row and d-column of the impedance matrix, Z, of the network. Z _gg and Z _dd are d riving-point impedances of nodes "g" and "d", respectively.

0036

Additionally, other indexes related to a line impedance with the installed devices corresponding to the size of the device can be selected in the step [S230] . For example, Average-Equivalent-I mpedance (AE I) by using the following eq uation [MATH 5] . 0037

[MATH 5] AEI = ( ∑ _geG A _gl )

0038

I n [MATH 5] , A _{g i} is the equivalent impedance between each "g" and "i" pair, where "i" is any potential bus location to install a device. 0039 Then , in the index ranking calculation step [S240] index rankings corresponding to multiple device sizes are calculated em ploying the power system data [300] in FIG .4. Here, in this example, the I NA, index is calculated for each RES device size. In step [S240] for each device size, the I NAj index is calculated [241 ] and the results [242] are obtained in the form of a ranking . Here, in this example, the I NA, index results depend on the RES device size, so a ranking of device sizes is obtained . At the cut-set modification step [S220] , the in itial power system is modified so that the RES device and all the generator type buses become connected to the power system through one line of specific power transfer li mit. Also, the initial power transfer limit of the line connected to the RES device is set to zero.

0040

Then , gradually, the power transfer limit of the line connected to the RES device is increased and the I NA, index is calculated until reaching the sum of the power transfer limits of the lines connected to the location for installing the RES device. Each incremental power transfer limit value represents an increase of the RES device size. The increase of the RES device size is compensated by reducing proportionately or distributary the power transfer limit of the lines connected to each generator resulting i n slightly smaller generators. The gradual reduction of all generators size with the gradual RES device size increase ensures that the RES device replaces existing generators and that the effective reduction of C0 ₂ emissions or reduction of energy dependence on fossil fuels can be evaluated . 0041

When there is an index [241 ] for which the calculation has not been ca rried out yet (step [S250] : NO) , the process returns to step [S240] . On the other hand , when the rankings of all indexes have been calculated (step [S250] : YES) , the process progresses to next step [S260]. When there is a device for which the cut-set matrix modifications have not been carried out yet (step [S260] : NO), the process retu rns to step [S21 0] . On the other hand , when the cut-set matrix modifications of all devices have been selected (step [S260] : YES), the process progresses to next step [S270] .

0042

For example, there is a FACTS device for which evaluating the optimal device size is desired and has not been evaluated yet. I n this example, secondly, the FACTS device is selected . Then , in the cut-set matrix modification step [S220] for the case of a FACTS device, the cut-set matrix of the power system is not modified by adding line(s) and bus(es) , but the properties of the lines connected to the location for installing the FACTS device are modified .

0043

Then , in the index selection step [S230], index(es) according to step [S220] are selected . Here, in this example, an index related to the effect of the installation of a FACTS device is selected as follows. The i ndex is defined as increased net-ability (I NAi) index by using the Equation [MATH 1 ] , where NAi is the net-ability of the power system when installing the FACTS device of size "i".

0044

Then , in the index ranking calculation step [S240] index rankings corresponding to multi ple device sizes are calculated employing the power system data [300] in Fig .3. Here, in this example, the I NA, index is calculated for each FACTS device size.

0045

I n step [S240] for each device size the I NA, index is calculated [241 ] and the results [242] are obtained i n the form of a ranking . Here, in this exam ple, the I NA, index results depend on the FACTS device size so a ranking of device sizes is obtained . The FACTS device reduces the impedance of the lines connected to the location for installing the FACTS device. The reduction of line's impedance is dependent on the FACTS device size and it increases the net-ability resulting in a I NAj index ranking , where the maximum I NA, value corresponds to the best potential location for installation .

0046

For the calculation of the indexes and the ranking , more detailed information about the device characteristics or about the power system , such as transmission and distribution line's capacity, operation states, etc. can be used .

0047

When there is a device for which the cut-set matrix modifications have not been carried out yet (step [S260J: NO) , the process returns to step [S21 0] . On the other hand , when the cut-set matrix modifications of all devices have been selected (step [S260] : YES), the process progresses to next step [S270]. Here, the cut-set matrix modifications have been evaluated for all desired devices. Then , in the merge device size step [S270] , the rankings of all i ndexes for each device size are merged i n order to evaluate the optimal device size for installation . Here, in this example, the I NA, index has been calculated for multiple sizes and for RES and FACTS devices, where two ra nkings are generated and for example the top locations of both rankings are selected to generate the summarized optimal sizes of both devices i n step [S270] . 0048

I n the step [S220] (cut-set matrix modification) , a complex network methodology can be applied for selecti ng an optimal position of the installed devices in the electric power system . I n this case, a calculation like the above-mentioned I NA, or AE I can be performed .

0049

FIG . 3 shows an example of data [300] used to implement the algorithm for evaluating the optimal sizes of devices that supply or absorb power in electric power systems. The reference character [31 0] in FI G . 3 represents an example of the format of data regarding the lines in power systems. The line number, from-to buses, and impedance value are stored in the data in the PU (per unit) representation .

0050

The reference character [320] in F IG . 3 represents an example of the format of data regarding the buses in power systems. The data regarding each bus includes the bus number and the bus type including generator, load , and substation .

0051

The reference character [330] in FIG . 3 represents an example of the format of data regarding the devices of which evaluating optimal device sizes are desired . The data regarding each device includes the device number and the bus type including energy storage systems, photovoltaic devices, wind turbines, FACTS , and storage devices.

0052

The power system information prior to installing the devices ([31 0] , [320]) as well as the device information ([330]) are required to implement an algorithm for evaluating optimal device size for installing devices that supply or absorb power in electric power systems.

0053

F I G . 4 is a schematic diagram of a portion of a transmission or distribution power system prior to instal lation of the devices and a number of devices to be installed consisting of generator buses [400] , substation buses [41 0] , load buses [420] , transmission and distribution lines in the power system (herei nafter referred to as "lines") [430], and the devices to be i nstalled [440] including energy storage systems, photovoltaic devices, wind turbines, FACTS, and storage devices represented for example by the reference character [450] . Here, in this example, three devices are shown but the number of devices to be installed is not limited .

0054

I n accordance with various aspects, in complex network methodology, the bus classification shown in F IG . 4 is used to consider the allowable structural power flow th rough the lines between all buses. Depending on the device properties , the device installation , which FIG. 5 shows, for exam ple, on single-type buses [500] could be done with or without cut-set matrix modifications.

0055

With cut-set matrix modifications, new line(s) and bus(es) are added , where tuning of the new line properties is used to evaluate the optimal device sizes resulting in large [530] or small [540] devices. On the other hand , without cut-set matrix modifications, depending on the device properties, the initial bus may turn into a multiple-type bus [550] . Additionally, in Fig . 5, the size of rectangle indicates the size of device, and the thickness of solid line indicates the capacity of distribution or transmission line.

0056 FIG 6 shows that simultaneous multiple cut-set matrix mod ifications allow the evaluation of power system devices that interconnect more than one bus in the initial power system such as High Voltage Direct Current (HVDC) devices [600] and transmission or distribution lines [61 0] . The devices to be i nstalled are selected one by one by the device selection module [ 1 1 0] in Fig .1 and the procedure to evaluate the optimal device size is carried out according to the procedure of flow chart [1 00] in Fig .1 .

0057

FIG . 7 is a schematic diagram of a portion of a transmission or distribution system after installation of the devices. As examples, devices are installed with cut-set matrix modifications at the location of a substation [700], with cut-set matrix modifications between an existing line [71 0], and without cut-set matrix modifications together at the location of a load [720] .

0058

F IG . 8 shows an example of hardware configu ration of evaluation device for an electric power system [800] . The evaluation device for an electric power system [800] has the function for evaluating an optimal size of a device that supplies or absorbs a power in the electric power system as mentioned above. The hardwa re is composed of an optimal device size evaluation device [810] , a processing unit [820] , a system memory [830], a disk storage [840] , an operati ng system [851 ] , a data [852], applications [853], modules [854], an input-output interface [860] , and a network interface [870] . These are connected by a bus or the like [890] . The network interface [870] has a function of sending and receiving information to and from the remote computers [880] .

0059 The optimal device size evaluation device [810] is composed of disk storages or the like and loaded with programs for realizing functions of a device selection module [811], a cut-set matrix modification module [812], an index selection module [813], an index ranking calculation module [814] and a merge device sizes module [815] corresponding to [110], [120], [130], [140] and [150] in Fig. 1, respectively.

0060

The processing unit [820] realizes the various functions by performing processing for reading the aforementioned programs from the optimal device size evaluation device [810] into the system memory [830] and running the programs. The aforementioned functions may be implemented in hardware. Furthermore, the programs for realizing the functions may be shifted to other storage mediums or downloaded from other device via a network.

0061

FIG. 9 illustrates an example of an optimal device size evaluation device user interface [900]. The user interface [900] includes a menu [910], a data interface area [920], and a power systems and devices display area [930]. Functions may be performed via menu selections. The menu [910] includes a number of menu elements including "home" [911], "projects" [912]," tools" [913], "configuration" [914], and "help" [915]. The data interface area [920] comprises interface elements [921-928] for managing data, including uploading, downloading, selecting devices from a database and saving and creating new projects.

0062

The power systems and devices display area [930] includes a power system (initial state) display area [940], a devices to be installed display area [950], and a power system (with devices) display area [960]. The power systems and devices display area [930] comprises interface elements [931 -935] for carrying out functions, including zoom-i n , zoom-out, update, run and change the number of devices .

0063

Additionally, a size of a mark of the device in the power system (with devices) display area [960] represents the optimal size of the device as mentioned above on Fig . 5 and Fig . 7.

0064

According to the above-mentioned embodiments, evaluation of the optimal size of devices, such as FACTS and storage devices, that supply or absorb power in electric power systems can be achieved using little i nformation by employing complex network methodologies to modify the cut-set matrix and calculate indexes that generate rankings of the lines and buses according to the properties of power systems that the device modifies . Therefore, the power quality and power system stability are improved for the increasing penetration of RES devices. Additionally, evaluating the optimal RES device size for each potential con nection point minimizes the negative effect on power quality and power system stability.

0065

According to the above-mentioned embodiments, manufacturers of RES , FACTS or storage devices can evaluate the optima l device size in any given power system , which is needed to make installation proposals. Additionally, prior to installing RES , evaluating the optimal device size for each connecting point reduces the negative effect and avoids power quality or power system stability problems.

0066

Additionally, governments and regulatory agencies, which do not have access to detailed information about the power systems in their territory, can evaluate the potential increase in RES penetration ratio with respect to the combination of devices and sizes including RES, FACTS or storage devices. Their evaluation can be used to provide incentives for those installations.

0067 It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation .

Reference Signs List

0068

300 Example of data

31 0 Example of data regarding the lines

320 Example of data regarding the buses

330 Example of data regarding the devices

400 generator buses , 410 substation buses, 420 load buses

430 Transmission and distribution lines

440 Devices to be installed , 450 Storage devices

500 Single-type buses, 51 0 , 520 New lines and buses,

530, 540 Optimal device size, 550 Multiple type bus

600 H igh voltage direct cu rrent devices

61 0 Transmission and distribution lines

700 Substation , 71 0 Existing line, 720 Load

800 Evaluation device