Developed software tool for distribution energy systems simulation ...

2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

Developed Software Tool for Distribution Energy Systems Simulation and Analysis Basma Othman1, Student MIEEE, Mamdouh Abdel-Akher1, MIEEE, Ahmad M. Eid1, MIEEE, Mohamed M. Aly1, Hassan El-Kishky2, SMIEEE Department of Electrical Engineering Aswan University, 81542 Aswan, EGYPT

The University of Texas at Tyler, 3900 University Blvd, Tyler, TX 75799, USA The developed simulation tool is based on visual C++ programming unlike other research software [4] which uses MATLAB. Therefore the proposed software will not need any additional software to run and it will work directly under windows environment. Hence using this software reduces the cost of running and analysis. Moreover, the speed of C++ program is better than that using MATLAB [5]. The GUI software is designed to be user friendly, simple and provide visualization charts. In this paper, based on the power system analysis requirements (radial load flow, voltage stability, continuation power flow and transient stability) and GUI requirements (simplicity, friendly using, clarity and general appearance) a simulation GUI software for distributed power system behavior and analysis is designed. The designed software includes the required C++ classes, Windows forms and data base structure as well as the relationships and links between them. After the design step, the code is implemented using C++. The designed software is used for a 33-bus distribution system analysis and the output curves are demonstrated.

Abstract— Power-system calculations and studies are considering an essential issue to study the behavior of the distributed power system networks. In this paper development GUI software is used for stability studies of distribution power networks with distributed energy resources. The software is based on multi- tier architecture. The multi-tier architecture consists of different layers which perform different functions in the program and provide advantages of reusability and extendibility. The proposed developed GUI software deploys Microsoft.Net framework, Microsoft visual C++ and the SQL server as data base management system to manage the application database. The developed GUI software is designed and applied for the analysis of three-phase radial load flow, voltage stability, continuation power flow and transient stability. Specific case studies are considered and demonstrated in this work. Keywords GUI software; distribution syetem;voltage stability; multi-tier; C++

I.

INTRODUCTION

Distributed energy resources have become an important part of electrical generation in many countries worldwide and its importance is continuing to increase. Especially, some believe that the most significant changes for deregulated power systems will occur in the distribution business since the cost to serve commercial and residential customers is higher than the cost to serve industrial customers [1]. Software helps in designing and planning distributed energy systems. It is appreciated that most of the computer simulation studies require a GUI that makes user interaction easier and more effective when compared with classical text based approaches [2]. Computer simulation is an essential engineering tool used by both students and practitioners to gain insight into a system's behavior. Simulation tools allow students to model a system, understand it, and then explore alternate designs [3]. Because the evaluation of competitive power system structures is a topic of great interest and importance, there are several groups creating simulations of electricity markets. These simulations offer a range of Capabilities, with some modeling various aspects of the system better than others

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II. A.

MATHMATICAL MODEL

Componnets modeling The model of the power system elements as well as distributed energy resources (DERs) is considered in the developed software. The modeling process is based on specific requirements which as follows: 1) representing multi-phase connections which include multi-phase distribution elements as well as DERs, 2) Relationships among distribution system elements, and finally, 3) distribution systems characteristics. The following models are considered: 1) Lines In the line model, the actual phasing of the line and the correct spacing between conductors are considered. Distribution lines employ phase coordinates for the solution of the unbalanced distribution systems. 2) Transformers The developed transformer model is reliable and has good convergence characteristics with the backward/forward radial power-flow method [6].

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2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

M is the set of line sections connected downstream to node j In the case of using power summation instead of current summation, the injected powers at node l are calculated as follows:

3) Loads Load model is a very important aspect for distribution power systems. The loads are represented as constant complex power, constant current, constant impedance, or any combination of the three types. The load may comprise of any number of phases connected as delta or Star. 4) Photovoltaic generation system As the proposed software is modeling the conventional power system elements, it also modeling distributed power energy resources. The photovoltaic generator is usually connected via inverter circuit to the grid, hence, it is modeled as constant complex power load with a negative sign. 5) Wind geneartion The wind generation is considering one of the most used distributed energy resources in both transmission and distribution system level. When the wind energy system is connected through converter circuit, it is modeled as constant complex power load with negative sign. However, when the wind energy system is directly connected to the system, internal details must be fully exploited in the solution process resulting in iterative solution process of the wind energy system model [7].

 

S labc  V ja J la 

I

  

*

 S ib  b  Vi

  

*

 S ic  c  Vi

  

*

  

J abc l

Where:

J abc l is

(3)

 a S   la  V j 

   

*

 Sb  l  V jb 

   

*

 Sc  l  V jc 

   

*

  

t

(5)

(6)

After the above three steps are executed every iteration, the power mismatches at each node for all the three phases are calculated as follows:

ΔS iabc

(1)

     

V a I a *   i i *  Vib I ib   S iabc  c c * Vi I i   

(7)

If the real or imaginary part (real or reactive power) of any of these power mismatches is greater than a preset convergence criterion, the solution process is repeated until convergence is occurred [8].

scheduled power injection vector, and Viabc is the phase voltages, ‘i’ is a subscript refers to system nodes, and ‘a’, ‘b’, and ‘c’ are superscripts refer to system phases. 2) Backward sweep: The total current at the source node can be calculated based on the fact that the line currents are known at the laterals of the feeder. Hence, the current flows in a line segment l are calculated as follows:

mM

t

(4)

Viabc  Vjabc  Z abc J abc l l

t

m  J abc

 

* V jc J lc  

Then, the voltages at the receiving end of line segment are calculated by:

where I iacb is the current injection vector, S iabc is the

J labc  I abc j 

*

3) Forward sweep: After calculating the branch currents/powers in the previous step, the receiving end voltages are calculated using based on the knowledge of the voltage at the root node. In the current summation method, the line current of each line segment are updated using the entering powers as follows:

Radial load Flow anaylsis The radial power flow technique is based on the fact that the voltage at the root node is known and the current at the lateral is zero [8].Consequently, an iterative process is developed for solving the power-flow problem. For a line segment l connected between nodes i, j, the iterative solution includes the following main steps [9]. 1) Nodal Current Calculations: The load currents are initially calculated by assuming initial voltages at all nodes. The injected currents due to loads at node i are expressed as follows [6]:

 S a   ia  Vi

 

V jb J lb

V abc  Viabc  Z labc J labc j

B.

abc i

*

C.

Stability index calcuations The installation of DG units to the distribution system helps to reduce the line losses, improve the voltage stability and improve the power quality [9]. The location and size of DG units to enhance the voltage stability are different from that of loss reduction purpose. In the visible literature, there is no a specified direct formula to determine the size and location of the DG units. The steady state voltage stability index at bus j is defined by [10]:

(2)

Lj 

the current flow into the line section l

173





1 Pi X  Qi R 2  Vi 2 Pj R  Q j X Vi 4



(8)

2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

where

bus bar table as a relation. To retrieve data from data base, queries and stored procedure are used. The design of the developed software is based on the data modeling of power system element. The database is mainly consisting of the tables of power system elements and distributed power energy resources (DERs) having relationships between them. A server stores and maintains the developed software data. It comprises data base which is created using Microsoft SQL server. The relationship data base design of the proposed software is as following

Lj is the voltage stability index, Pi, Qi, Pj and Qj are active and reactive power injections at nodes ‘i’ , R, X are the resistance and the reactance of branch connecting nodes ‘i’

D.

Continuation Load Flow Anaylsis the continuation power flow component is the responsible for calculate continuation for three phase power system network .The continuation power flow can be described as a power flow solution that can maintain the stability of the power system under normal and disturbances conditions. Therefore the main purpose of Continuation Power Flow is to find the continuity of power flow solution for a given load change. The solution process for the continuation power flow process is summarized in the following sections [12]. 1) Initially solve two successive load flows 2) Calculate slope3) Estimate predicted solution 4) Calculate the corrected solution 5) Check if the critical point is detected when step is smaller than a preset tolerance, if not go to step 2. 6) Print solution.

III.

The data base implements each power system elements and distributed power energy resources (DERs) in an individual table such as bus bar and PV element. The bus bar element considers the main table and all power elements tables have a foreign key from bus bar table to its table. And as shown in figure 1 each table will contain the attributes of the power system element such as the regulator table will contain the data of the regulator such as the sendbusid, the value of tap for each phase tapa, tapb and tapc and this is for all the elements The data base constrains are:1)Not Null constrains are applied for all necessary data of the power system element such as the resistant of the line data table 2) unique constrains are made for the data fields which is distinctive in the power element data table like 3)check constrains is applied for the field in power system element data table which need only specified values such as the type of connection in load data table this field have specific value which is star or delta

SOFTWARE DESIGN

Most of the available commercial software uses a multi-tier architecture. The multi-tier architecture provides a flexible, modular approach for programming and development. Every application tier provides a certain function and gives this functionality to its former tier and uses the functionality provided by its successor to carry out its part of the overall processing of the application [13]. This software methodology is used here in the development of a power system software application. The multi-tier architecture divides application processing across multiple machines (client and server). Such that non-critical data and functions are processed on the client, while critical functions and data are processed on the server. The multi-tier is consisting of the following layers [10]: 1) Data Layer 2)Data access Layer 3)Business Layer 4)Presentation Layer

B. Data Access Layer The data access layer classes are designed and implemented as shown in Fig. 3. The design includes DBManager class which is the main class responsible for connection to database and executing the stored procedures (data manipulated, data query). For each table in the database, a class manager is created to be responsible for dealing and manipulating data. Each class manager consists of four operations; add new data entry, delete data entry, update data entry, and get data according to specific conditions C. The Business Rules Layer The business layer encapsulates the business rules and the business logic of the developed software. As seen from Fig. 2, this layer consists of two parts; power system calculations and the GUI and visualization. Any changes in the business rules can be handled in this layer. This layer is also responsible for passing the data from the GUI forms to the data access layer. 1) Comutational Engine The computational engine is implements the object oriented programming. Each power system analysis is implementing by a class such as radial load flow calculation which perform the calculations. 2) Visualization Handling

Data baselayer The first layer in multi-tier architecture which the software adopts is the data layer. This layer is basically the server that stores and maintains software data. It comprises data base components such as database files, tables, views, and sorted procedures. The actual database could be created using SQL server, Oracle, and flat files. The implementation of data layer consists of the following steps:1)Using SQL server and flat files to maintain the data, 2) Data base structure showing links between the data of the different elements Each element in the power system network is represented in a table. Noting that the bus bar is the main element and each other element has a foreign key from the A.

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2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

Figure 1 Software class Diagram power system elements data depend on it. Then enter the line data and the other power system elements .after the completion of data entering the user will select which calculation he want to solve and our system offer three calculation which are radial load flow ,stability index and continuous power flow and after the system calculate the chosen calculation . The user will view the results either in tables or charts

The visualization is part of the business rules layer .and its function is to handling the process of the visualization and user interfacing. D. The Presentation Layer The last layer to the client in multi-tier architecture is The presentation layer. It called the client layer and comprises the components that are dedicated to presenting and showing the data and results to the user such as windows forms, labels, textbox, etc. E. Usage Scenarios The principle medium for capturing requirements is the use case diagram. Use case diagrams illustrate the relationship between a software system and its users. These diagrams describe all the ways in which each type of user will interface with the system. the set of all use case diagrams and their associated use case description constitute the use case model, the use case captures the intended behavior of the system you are developing without having to specify how that behavior is implemented. It provides a way for your developers to come to a common understanding with your system end users and domain expert The system user (Engineer) as shown in Figure: 2 is the main actor in the system -who initiates and uses the system- The use case in the diagram represent the action which the software and the actor will do First the actor engineer will initiate using the system by a login to the system then he begin to enter the power system elements data and it should begin with the bus data as the other

Figure 2 Software Use Case Diagram Operation which does authentication the user against data base for users. After successful login the user will add the main data for the system which is the bus bar data and line data which are consider the main data of any power

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2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

system network. Adding Bus bar data and line data will include all data of the bus bar and line such as bus bar name, bus bar voltage level, a bus bar angle degree and bus bar type and for line data such as line length and line kilovolt, when we do analysis we obtain this constrain that the data of bus bar and the data of line should be added before any element of the network as this data especially the bus bar will be used in adding the flowing elements.

to the data base, each element will be saved to its data base table. The system will go to calculation stage which is stage which the user will choose what calculation he needs and as shown in diagram 4 use case the system will first calculate the Radial load flow. The stability index calculations include the calculation of Radial load flow. And continuation load flow calculation should include the Radial load flow in balanced but in the balanced analysis it included the Newton Raphson load flow not Radial load flow. IV.

NUMERICAL EXAMPLE

A. Data imput The developed software enables the user to input the case system which will be analyzed .The user enters the data of the distribution system. The data entering process is designed to be user friendly as shown in Fig. 3 for the wind input data. The required input data forms for all the elements are implemented using visual C++ and Microsoft.Net framework. And also the developed Software provide other option, to input the system data is through loading standard text files for the system .

Figure 3 Wind turbine data input

B. Results visulizations After the computational engine calculated its routine the user can see the results of the studied system. And according to the output one of the following methods will be used 1) Charts The charts visualization is used for this purpose as

Then adding the data of the other network elements and as shown in Figure 3: that PVs, winds, loads and distributed loads will be associated with the bus bar and the transformers, regulators and capacitor banks will be associated with the line. The system will go to the next operations which is saving all the entered data by the user

Figure 4 Charts representation of P-V curves

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2012 IEEE International Conference on Power and Energy (PECon), 2-5 December 2012, Kota Kinabalu Sabah, Malaysia

shown in Fig 4 The chart shows the P-V curve of Bus 18 of the studied system. The software provides additional features like saving, copying and printing the output chart in a simple way. 2) Tables The one of the visualization method used in the developed software if table method. And as shown in Fig.5 the results of radial load flow of 33 bus system is represented in the output windows form.

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[2]

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[9]

[10]

[11] Figure 5 Sample of the power-flow solution in tables [12]

V.

CONCLUSIONS

This paper presents flexible and user friendly GUI Multi-tier software for power distribution system analysis with distributed energy resources. The paper presents the mathematical modeling for both the power system elements and for the computational calculations and also it shows the methodology used in the software design which is multitier architecture. The developed software runs under Microsoft Windows and hence no need for additional cost to buy other software. Due to the nature of the architecture of the software, the developer can extend and reuse the software modules for new analysis or applications.

[13]

ACKNOWLEDGMENT The authors gratefully acknowledge the contribution the USA-Egypt Joint Science and Technology Fund and the Science and Technology Development Fund (STDF) under the project no. 839 for providing research funding to the work reported in this paper.

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