Wind Energy and Power Optimization

Introduction
1. Overview
1.1. Wind energy

The wind energy is one of the sources of renewable energy which has many advantages over the non-conventional sources of energy. There are many topological and economical factors associated with the construction of the wind farm which decide upon the construction design of the wind turbine and the placement of the wind turbines in the farm.The main construction of the wind farm consists of the mechanical, civil costs and electrical costs. In construction of the wind turbines there are different types and designs of turbines used depending on the location, topography and the power output. The wind turbine generators convert kinetic energy of the wind into the electrical energy. Different types of generators are used in the conversion according to the application and the requirements.
1.2. Challenges
A single wind turbine is connected into the array of many wind turbines to form a wind farm which is utilized to generate electrical energy. The main consideration with the wind farm is the cost of installation and the power quality. Due to the non availability of the constant wind at all times the energy was highly unreliable, but due the new power electronic converter devices and manufacturing of the doubly fed induction generators (DFIG) the engineers have been able to overcome the problem. The power quality is the primary concern when the energy generated from the wind farm is connected to the main grid .The voltage unbalance at Bus-Bar, voltage fluctuations and reliability are the issues of prime concern in the power quality.
The main problems related to the power quality in the wind farm are:
1) Steady State voltage impact: It is the most common problem which is mostly related to the source and load of electric power. Due voltage drop in the line because of the presence of impedance there are voltage drops, which must be kept under the limits to avoid failure.
2) Dynamic voltage variations: The cause for the dynamic voltage variations is the same steady state voltage variations but they are studied for a shorter time intervals of seconds or fraction of second. These can be reduced by introducing variable wind speed system or by controlling the reactive power.
3) Harmonic Distortion: In the electric System due to non-linear loads and the power electronic devices there are distortions in the pure sine wave.
4) Voltage Transients: When an induction machine or a capacitor bank is connected in the system, the high currents are observed which might cause disturbance in the grid.
The need of the optimization in the wind farms is a need, to make the technology more efficient and more reliable. There are many tools used for the simulation of the wind farm but the tools used for the wind park grid connection optimization are the PSS/E and Spectrum Power CC which contains a module for the power system optimization.
1.3 Aims and Objectives
“Wind Park Grid Connection Power Optimization”
In the wind farm design a typical on/offshore substation which consists of the switchable reactive components and transformer tap changers should be modeled within a power system simulation package and replicated in the Siemens SCADA (Supervisory control and Data Acquisition) system using the software Spectrum Power CC.
The SCADA contains a module for power system optimization which has not been explored by the Siemens, the software has to be verified for the optimization of the wind farm and then the modeling is to be done which is achieved by proper learning of the software and implementation of the same in the real time SCADA software.
The results obtained from the network optimization algorithm model Vs SCADA system are to be verified and analyzed and based on the analysis the improvements or alternatives are proposed for further enhancement. In the past due to the limited work on the software, exploring of the tools and techniques in the software is another key motive in the process which will not only solve the optimization problem but will be beneficiary for future developments. However there are optimization tools developed using the Generic Algorithm for improving the reliability of the system.
2. LITERATURE REVIEW
2.1. Introduction
The wind energy is now one of the major sources of energy. Different designs of the turbines have been introduced to improve the reliability of the system. The main parameters which are taken into consideration in designing of the wind farms is the energy output, cost efficiency, the impact on the environment and the impact on the electric grid which mainly includes the integration into the existing electrical system and the power quality issues. These factors must be fulfilled before connecting into the main network to keep the existing system operational.
In the process of designing the actual system of the wind farms the modeling of the proposed design which is an important factor in the basic structure of the turbine, type of blades, turbine used etc. The analysis of both the mechanical and electrical properties of the structure of the wind turbine is done using different modeling tools like PSCAD, PSS/E, Dig Silent etc.[7][8]
2.2. Past Achievements
Power quality in the wind turbines is the important area of concern and assurance of the protection from all the disturbances has to be made to ensure the protection of the grid. The main power quality standards are static voltage level, voltage fluctuations, voltage transients, voltage harmonic distortion, voltage unbalance and voltage supply interruptions.
In the past the fixed speed electric turbines were used but now due to their drawbacks main being the inefficient control of the reactive power and power quality problems the variable speed turbines have been developed. A variable speed turbine keeps the generator torque constant and the speed changes which results in constant power in the system which is the essential requirement. There are many power electronic devices which are used in combination with the induction machine and the synchronous machine.
The structures developed in the modeling of the wind turbines are used in the analysis between the electrical and the mechanical structure of the wind-farm and also help in the dynamics interaction of the wind farm and electrical grid which enables the design engineers and owners to make an adequate study before the installation of the wind- farm. [1][2]
Various models have been developed earlier for specific studies in the wind turbine functioning using the Dig Silent and PSS/E software. Various calculations are performed by the utility engineers like the load flow analysis and the transient analysis of the models developed. The main objective of the load flow calculations is to identify the flows in the transmission lines, transformers and the voltage at different buses or nodes which is an integral planning of the planning and the design of the wind farm. The calculations are done under different scenarios to satisfy the conditions. The transient stability studies are done to calculate the transient response of the system under the disturbances. The synchronism, the damping of the oscillations of the machines are examined which play a vital role in the planning and interconnection of the wind farm. [4][9]
2.3. Current work
Many studies have been conducted on the stability of the wind-farms, but referring to the paper by David T.Johnsen on “Optimisation of the fault ride through strategy of a wind farm” which explains the optimisation and also the dynamic stability of the wind-farm by developing a procedure for an optimal fault ride through strategy for the wind farms. The dynamic simulations are developed and modeled in PSSE which illustrates the possibility of increasing the capacity of the wind farm by optimal fault ride through settings.
“The operational characteristics of the wind farm are optimised by adjusting the parameter settings of a model of a simplified PQ-generator while simulating in PSSE”. From the article it is observed that the “wind-farm consists of radial connection, consisting of two parallel and identical 132 Kv branches which are connected to a high level wind penetration”. Apart from the two wind farms an” additional wind farm (WF2)” is connected which is represented in the network by the “generic PSS/E model of a full converter turbine or a simple P-Q generator which represents as ideal power source.” The settings of the P-Q generator can be modified in the simulation by adjusting the active and reactive power in the system. To increase the stability and the loss of synchronism the “active power injection must be reduced to a low active power level as soon as the voltage dip is detected and a high value of reactive power during the fault increases the transferable limit of the active power during and after the fault. “
In the conclusion of the paper it is seen that the comparisons between the response of the “P-Q generator and generic FCWT model” illustrates that it possible for the “P-Q generator to successfully ride through the fault while the generic FCWT trips.”
“The main concerns regarding the dynamic power response in the process of optimisation are as follows:
1. The active power must be severely constrained during the fault sequence.
2. The maximum reactive power production has to be high and fast responding.”
Hence it is concluded from the paper that the fault ride through strategy can improve the capacity and the electric grid quality in the wind-farm. [3]
In an optimization model developed by the Strategic Energy Institute (Georgia Institute of technology) there are some input parameters like wind speed, Weibull parameter, investment, efficiency of generator and gearbox, speed etc and output parameters as optimal rotor diameter, optimal generator capacity, optimal RPM, torque and power produced. These parameters are drawn into a flowchart which consists of a wind turbine design optimization model. [10]
2.4. Future Prospects
The IEEE research paper on “Optimization of Electrical Connection Scheme for Large Offshore Wind Farm with Genetic Algorithm “at the Sustainable Power Generation and Supply (2009) represents a way of power system optimisation by Generic Algorithm .An analysis on an off-shore wind farm is made in which the optimisation of the electrical connection is converted into the factors of the “voltage level inside the farm, the voltage levels of substation, number of substations, location of substations, connection topology of substation and turbines”. Due to their non-linearity the optimization is done by Generic Algorithm and the analysis is done in the paper. [6]
A research paper presented in the Nordic workshop on Power and industrial electronics (2004) on Optimization of electrical system for a large DC offshore wind farm by Generic Algorithm” proposes an optimization based on Generic Algorithm where the input parameters are used as technical data and are optimised for minimum cost and maximum reliability. Based on the theory of natural evolution a Generic is developed which consists of “population of bit strings transformed into three genetic operators’ selection, crossover and mutation.” An optimization model is developed which computes cost and the reliability. The model consists of the input data, some rules, cost calculation, reliability evaluation and an optimum configuration with the help of generic algorithm. In the genetic optimization the “encoding and decoding of the chromosomes” is done which leads to computation of the cost and reliability, finally the mutation operator is used to improve the execution of the Generic Algorithm. [14]
In another IEEE paper by Kusiak.A et al (2010) “Optimization of Wind Turbine Performance With Data-Driven Models” a multi objective optimisation function is made which represents the wind power output, the vibrations in the train and the vibration in the tower to determine the wind turbine functioning. The concept of neural networks, an ES algorithm “the Strength Pareto Evolutionary Algorithm (SPEA)” is used solving the model. The results obtained state that the vibration mitigation and power maximization can be done by adjusting the generator torque and blade pitch angle. [5]
In the “Small Wind Off-Grid System Optimization Regarding Wind Turbine Power Curve” paper by Simic.Z and Mikulicic.V (IEEE) there is another small hybrid off-grid system in which there is discussion on the impact of the power curve on the cost of the energy and amount of energy produced. The “HOMER micro power optimizing tool “was used for the optimisation, wind speed data was varied and the results were analyzed.
3. METHODODLOGY
3.1. Description
In the project as the simulations of the wind farm are to be carried out in the software package, the studying of the wind model layout is the prime important step which includes the components and specifications. The layout of the wind farm design mainly consists of an array of wind turbines, the electrical connections, on/off shore substation, transformer, On -Load Tap changers, Phase -to -Phase voltage controllers and shunt capacitor banks to improve the voltage quality of the system.
3.2. PSS/E
The optimal power flow software PSS/E is used in the analysis in which all the components are modeled and all the results are recorded. A brief description of the software is as follows:
PSS/E (Power System Simulation for Engineering):
“Power System Simulation for Engineering (PSS/E) is the major tool used in the course of the project which consists of a set of programs for studies of power system transmission and generation behavior in both steady state and dynamic situations. It can be used as a tool to analyze the power flow and the related network functions, the optimal power flow, balanced and unbalanced faults, network equivalent construction, as well as dynamic simulation.
The main software used is the Power System Simulator for engineering optimal power flow from Siemens which improves the overall efficiency and output of the system in addition to the normal power flow.
The software is mainly used for the today’s challenges of the regulated power supply which are as follows:
Reactive power scheduling
Voltage collapse analysis
Transfer capability investigation
Location based marginal cost assessment
Ancillary service opportunity cost assessment
Impact assessment
Base case development
Congestion analysis”
*The Above content is taken from the user manual of the Software PSS/E. [11]
As the software has been used earlier in the analysis of the power system so learning and implementing the software would not be a very difficult task and the analysis can be carried out using the manuals and other research material provided on the internet.
3.3. Spectrum Power CC
In the second and the important part of the project the same wind farm simulation model is modeled in the Siemens Spectrum Power CC software using the SCADA, the Distribution Network Analysis (DNA) which consists of Distribution system power flow (DSPF), Distribution System State Estimator (DSSE), Short Term Load Scheduler (STLS), Fault Management and Volt-Var Control(VCC).
The brief description of the software from the Siemens software reference manual of the Power Spectrum CC is as follows:
“Distribution Network Analyses (DNA) supports the following features:
Effective and efficient control of distribution networks
Increased supply quality and reliability
Optimal use of network equipment
Minimization of network losses
Detection and elimination of overloads in time
Efficient fault management
The elements which are to be used in the software for the analysis of the system along their main functions which are an integral part of the Spectrum Power CC Distribution Network Analysis are:
1) Distribution System Power Flow(DSPF):
“DSPF is mainly used to calculate the network status in the system configuration. The power flow solution calculates the voltages at all the bus-bars, the power and the reactive power at all the buses. The flows in the network are the most important parameters in the simulation. The limits of the system are analyzed and suitable optimization technique is used.”
2) Distribution State Estimator(DSSE):
“DSSE is mainly used for the real-time monitoring, control and optimization of the model. It estimates the active and reactive power values and corrects the data by using the techniques of mismatching of information. “
DSSE integrates the optimization process with the optimal power flow to calculate the flows which are then used to monitor the real time operation of the network.
3) Short Term Load Scheduler(STLS):
“STLS tracks the active and reactive power management of the power system loads and maintains the consumption for the loads in the network into a database. “
4) Fault Management:
“The main application of the Fault management is location of the fault, the fault isolation and service restoration.
The fault management consists of:
Fault location
Locating the faulty section or area of the network as closely as possible
Fault isolation
Isolating the faulty section or area of the network
Service restoration
Restoring power to de-energized non-faulty areas of the network
5) Volt-Var Control(VVC):
“Volt-Var Control (VCC) deals with the operations on the transformer with on-load tap changers, phase-to phase voltage controllers and shunt capacitors to improve the network operations. The main task is to improve the overall reliability and quality of the network.
VCC works on two operating modes:
Open loop: The settings after running the flow are not automatically executed; they are reviewed by the user.
Closed Loop: The settings after running the flow are automatically executed after VCC calculation.”
The main objectives which are to be fulfilled after the optimization of the system mainly consists of:
1) Minimize limit violations.
2) Minimize power losses and limit violations.
3) Minimize active power consumption and limit violations.
4) Minimize reactive power consumption and limit violations.
5) Maximize power revenue and minimize limit violations.
*(The description of the software has been taken from the reference manuals provided by Siemens .It has been edited and modified according to the data required, but still Quoted to be on safer side.)[12]
The above tools in the software are studied and then analyzed as the software is used for the optimal power flow for the first time, so understanding the software is a difficult task which may consume a lot of time and may require a lot of help from the external sources. If the results are required results not obtained on the software then if will become more challenging, and have to take the help of the specific team involved in creation of the power system optimisation tool in the software, which may include taking help from Siemens, Germany. Replicating the power system model on the software won’t be a challenging task, if all the main functions are studied and learned in detail. The results may be then obtained if the simulation is successfully modeled in the software.
3.4. Comparison
In the last step results of both the simulations will be compared and the analysis of the results obtained is done separately for both the softwares. The drawbacks of the Distribution Network Analysis software will be studied based on the results obtained from the comparison of the data obtained after running the simulations. A suitable alternative is then proposed, supporting the simulation and improvements in the design are implemented to obtain the desired results.
The proper explanations of the improvements supporting the outcomes are made as the improvements proposed in the software are then implemented by the engineers without the power system background.
4. PLANNING
4.1. Overview:
The project work has been planned and divided into a timeline which has been shown in the Gantt chart as attached in the report.
The project plan is made keeping in mind some delays due to the unavoidable circumstances and will be effective from the initiation till the completion of the project.
4.2. Project Risks:
In the Project as the modeling tools have to be used in the simulation of the wind farm so the availability of the software is a major concern. The power system optimization software PSS/E is available which won’t be a concern. As the software is complex and difficult to understand so it may take a longer time to understand the working. The help of the PhD students will be taken and the simulation will be made as simple as possible to remove the complexity from the model as it has to be modeled in a short duration. If necessary the use of simple optimization tools would be done like Dig SILENT, Power world Simulator etc.
In the another modeling software Spectrum Power CC provided by Siemens, the power optimization module in the software on which the simulation is mainly based is new, which may consume a lot of time learning the software, therefore suitable training will be taken by the experts so that, I can easily adapt the software and proceed with the work. The difficulties faced will be rectified by the Siemens Technical Team and PhD students at The University Of Manchester which will lead to the success of the project.
4.3. Gantt Chart
Risk Assessment Form
Dissertation Project: “Wind Park Grid Connection Power Optimization”
Risk DescriptionEffect on the projectAction Required
Non Availability of PCThe postponement of the project
Immediate availability of another PC
Non Availability of Software
Difficulty in modeling.
Immediate availability or some alternative modeling tool.
Data CrashA data backup is created.
A backup has to be created.
Power system optimization software use
Due to the non-familiarity longer time to learn the software.
Modeling will be kept simple and the help of PhD students would be taken for modeling.
SCADA software interfaceDue the first time use of optimization module there may be delays.
Help of specialized team is expected.
CONCLUSION
In the feasibility study above the methodology of the dissertation project is explained. The literature review highlights all the work done and the future prospects of the work that can be done in the research are. The project planning consists of the Gantt chart which is a layout of the working of the project which includes all the risks and different challenges during the project.
REFERENCES:
1)Eriksson.K .et al.(n.d.), “ System Approach On Designing An Offshore Wind Power Grid Connection” http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/34ec041beda66334c1256fda004c8cc0/$file/03mc0132%20rev.%2000.pdf
2)Hanson.J and Hunger.T (n.d.) “Network Studies for Offshore Wind Farm Grid Connections – Technical Need and Commercial Optimization “ http://www.2004ewec.info/files/23_1400_juttahanson_01.pdf
3) Johnsen.D .et al. (n.d.) “Optimisation of the fault ride through strategy of a wind farm” http://www.frontwind.com/Paper%20Master%20Thesis.pdf
4) Kazachkov.Y and Stapleton.S (2004), “Modeling Wind Farms for Power System Stability Studies” https://www.ptius.com/pti/company/eNewsletter/2004April/Modeling%20Wind%20Farms%20for%20Power%20System%20Stability%20Studies.pdf
5)Kusiak.A .et al. (2010) “Optimization of Wind Turbine Performance With Data-Driven Models” IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, VOL. 1, NO. 2, JULY 2010 http://www.icaen.uiowa.edu/~ankusiak/Journal-papers/IEEE_2010_2.pdf
6) Lingling.H, Yang.F and Xiaoming.G(2009) “Optimization of Electrical Connection Scheme for Large Offshore Wind Farm with Genetic Algorithm” Sustainable Power Generation and Supply, 2009. SUPERGEN ’0910.1109/SUPERGEN.2009.5348118 http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5348118
7) Petru.T (2001), “Modeling of Wind Turbines for Power System Studies” http://webfiles.portal.chalmers.se/et/Lic/PetruTomasLic.pdf
8) Petru.T and Thiringer.T (2002) “Modeling of Wind Turbines for Power System Studies” IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 17, NO.4 http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1137604
9) Sayedi.M (2009),”Evaluation of the DFIG Wind Turbine Built-in Model in PSSE” http://webfiles.portal.chalmers.se/et/MSc/SeyediMohammadMSc.pdf
10)Schmidt.M “Wind Turbine design Optimization” Strategic Energy Institute(Georgia Institute of Technology) . http://www.clemson.edu/scies/wind/Poster-Schmidt.pdf
11) “Siemens Energy manual Guide for PSS/E “(Available on internet)
http://www.energy.siemens.com/us/en/services/power-transmission-distribution/power-technologies-international/software-solutions/pss-e.htm
12) “Spectrum Power CC Manual”, Siemens Germany
13) Simic.Z and Mikulicic.V (n.d.) “Small Wind Off-Grid System Optimization Regarding Wind Turbine Power Curve” an IEEE paper.
http://bib.irb.hr/datoteka/309501.Small_Wind_OffGrid_ZS_final.pdf
14) Zhao.M, Chen.Z and Blaabjerg.F (2004) “Optimization of Electrical System for a Large DC Offshore Wind Farm by Genetic Algorithm “ NORDIC WORKSHOP ON POWER AND INDUSTRIAL ELECTRONICS 2004 – 037
APPENDIX:
General Risk Assessment Form
Date: (1)
11/5/2011Assessed by: (2)
Rajat Aggarwal
Checked / Validated* by: (3)Martin LorimerLocation: (4)
Siemens, ManchesterAssessment ref no (5)
Review date: (6)

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Task / premises: (7)
Wind Park Grid Connection Power Optimization :Modeling of Power system
Activity (8)Hazard (9)Who might be harmed and how (10)Existing measures to control risk (11)Risk rating (12)Result (13)
Continuous use of computer Eyes pain , back pain , HeadacheMyself , May lead to fatigueProper Precautions while using computerLowT
Computer crashData crashDelay in projectData backupMediumA
FireDamage to the companyCompany working may be harmedFire Safety EquipmentsMediumA

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