Control Topologies for Induction Micro-Hydroelectric Power Plant - Report Example

Control Topologies for Induction Micro-hydroelectric Power plant Name Institution Date Course Control Topologies for Induction Micro-hydroelectric Power plant Introduction Hydropower is one of the renewable sources of energy that has been utilised for several years now. The operation of the plant is based on the principle that when moving water is directed towards and moves a turbine that is coupled to a generator, the generator is caused to spin and generates electricity. Several other components will be required to make the plant operational, but the source of energy is the moving water. It is a mechanism that has been used for several years to convert the mechanical energy of the turbine to electrical energy. Micro-hydropower systems are smaller generation stations that are developed for individual users or small groups of users who are not connected to the main electricity supply grid. In this research work, the development of an independent induction generator hydro-electric power plant (or MHPP) is investigated. The system is expected to involve improved parallel operation of two MHPPs with properly designed frequency and voltage regulations. The system will also accommodate management of active and reactive power so that cost efficiency and reliable power supply can be achieved to rural residents. Research Problem Definition Electric power continues to draw great demand all over the world. Electric power generating stations have therefore been developed to meet this demand, with micro-hydropower systems continuing to attract great interest. As Sing and Tiwari (2013) point out, the demand for electrical energy has been rising in recent years around the world. The authors further say that interested parties have realised that sources for renewable energy can be used to supplement available energy and have continued to be used provide useful options within a broad range of applications. These sources have played a critical role in contributing towards the solution to the increasing demand. Research Performance Criteria A micro-hydropower system will usually be composed of a water turbine that will convert the kinetic energy of the water to mechanical energy which is then converted to electrical energy by the generator. A control mechanism will also be required to ensure that the energy produced is stable while the transmission system will deliver the power to the consumers. Several considerations must be made to ensure that reliable power gets to the consumer at the right voltage and frequency. There is need to understand the various control mechanisms employed for such micro-hydroelectric systems that will ensure that this requirements are met by the system. Developers of small and micro-hydropower plant have commonly used the induction generators for establishment of power generation projects due to the advantages associated with the generators. These generators, generally, are robust, low cost and readily available, making them the preferred selections for these projects (Ekanayake, 2002). But even for these generators, costs incurred for every kW generated in a single-phase system are generally higher compared to three-phase systems. As a result, three-phase generator systems that produce single-phase power have been used (Ekanayake, 2002). This brings great convenience to the process, and is one of the centres of focus for this research. Specific Objective The research will investigate the operation of these generators and analyse how the single-phase power generation is achieved and to understand how a stand-alone three-phase induction generator can be used to supply single-phase load Other Objectives To investigate whether it is possible to implement control mechanisms that can improve the parallel operation of two micro-hydropower plants To investigate how the development of control systems can be optimized to combine robustness and single-point operation of the generators To learn about the functioning of the micro-hydropower scheme induction generator and the control system This will therefore be an intensive research that will seek to find information regarding the various factors that contribute to the optimal performance of the micro-hydropower plant with emphasis of how the control systems could be used to achieve this. The research will involve an investigation of the available literature material on the subject. Literature Review Micro-hydropower plants are small hydropower plants that could be used to meet the demands of small local consumers like lighting and charging batteries for local uses (Tanbhir et al, 2011). These projects are becoming more acceptable due to the environmentally friendly generation process and the availability of water in several locations (Gaius-obaseki, 2010). They have therefore played a significant role in meeting the energy demand that is already on the rise over the last few years. Micro-hydropower projects are also preferred due to their lower costs, ease of establishment and the minimal disturbance to the environments compared to huge hydropower projects (Tanbhir et al, 2011). The induction generator is preferred for such projects due to its dominant and rugged advantages like low cost, brushless construction and low maintenance requirements (Ion, Serban & Marinescu, 2006). Usually, three-phase squirrel cage units are used. In the rural setting, however, the demand for power will usually be below 10 kW within single-phase networks. Although single-phase generation units could be used for these cases, these units may not give the best performance and they may not supply powers that exceed 3 kW. To meet these design requirements, three-phase induction machines have been deployed to supply the demands within these isolated systems, but with necessary adjustments to enable them supply singe-phase networks (Ion, Serban & Marinescu, 2006). As Ekanayake (2002) further points out, minimization of further capital costs is achieved through crude voltage and frequency control techniques. The system frequency and voltage are kept within permissible limits by connecting resistive ballast. This ensures that the sum of consumer load and the ballast load are maintained at a fixed value (Ekanayake, 2002). As shown in the figure below, the three-phase generator is successfully converted to a single-phase source by connecting two capacitors across its terminal (Ekanayeke, 2002). Fig1: Three-phase induction generator supplying single-phase load. Ion, Serban & Marinescu (2006) also agree that using a load controller, one that is used to feed a dump load to the generator, enables the total power supplied by the generator to equal the total between the dump load and the consumer. When the active power gets balanced effectively, the system frequency is also satisfactorily regulated. According to Chan (1998), coupling capacitors across the terminals B and C of the generator as shown in figure 2 below, results in establishment of a reliable operating point for the unbalanced configuration so that the generator delivers nominal power under nominal voltage. In this way, it is possible to obtain a balanced between the phases of the generator. This balance, when achieved, becomes fundamentally important when this generator has to be paralleled with a single-phase voltage source (Chan, 1998). Fig2: capacitor couling for stabling system power This is therefore one of the most important processes in construction of the single phase supply and if not properly done, the generator is likely to operate in an unbalanced condition which is undesired (Ekanayake, 2002). When the micro-hydropower plants are developed, there may be need for interconnections of the new systems and other plants that supply the distribution network. The interconnections of units within the network must, however, be achieved in a manner that will ensure that power quality of the energy supplied, the capacity of the system to respond in time to the consumer demands and minimum disturbance on the grid are realised (Ion & Marinescu, 2010). The distributed generating units will, therefore, need to accommodate state of the art equipment for measurement, communication, control and protection. When generation of power within a micro-hydroelectric plant employs two units of synchronous and a synchronous type, regulation of certain parameters may be achieved through the use of the synchronous unit. When the system is operated on an isolated grid, there may be witnessed challenges relating to stabilization of the main power parameters: voltage and frequency. When a synchronous generating unit is paralleled with an induction generating unit, voltage control could be achieved by the synchronous unit through its voltage regulator. In this case, the frequency regulation will also need to be done. The frequency could be controlled using the governor of one of the generators. It may also be controlled through introduction of an additional load within the circuit damp load (Ion & Marinescu, 2010). While several topologies have been developed over the past few years, modern solutions have incorporated an uncontrolled bridge rectifier that feeds a resistance through the chopping power transistor. The transistor’s duty cycle is then controlled so that the active power can be modified. This solution has been used for three-phase induction generation with three-phase loads. It can however, be modified with much ease so that it is applied to single-phase systems. This has been achieved by replacing the three-phase uncontrolled bridge with a single-phase one. It should be noted that this arrangement results in injection of current harmonics into the system whose actual levels will depend upon the charging of the dump load (Ion, Serban & Marinescu, 2006). An isolated micro-hydropower system will always have to overcome challenges like integration of other renewable sources, management of intermittent energy resources, real time response to demand and stabilization of the network parameters (Singh & Surjan, 2014). Recent advancements in ICTs, however, have resulted to more effective methods of system monitoring and control, modelling and performance improvements. Voltage and frequency controllers have been classified into several categories. For self exited induction generation units, static compensators have been used to achieve control (Singh & Tiwari, 2013). A static compensators is an equipment that can be used to maintain reactive power in the system. It is made up of voltage source converters that are connected to an energy storage device on one side and to the micro-hydropower system on the other. It can be considered a voltage source behind a reactance which supplies reactive power to the system and also absorbs the same by means of electronic processing of currents and voltage in a Voltage Source Converter (VSC). A DC capacitor bank is used to stabilize the controlled direct current voltage required for the operation of the VSC. Effective control of voltage and frequency has also been achieved using an electronic load controller as has already been mentioned above. Through this method, it is possible to maintain a fixed electrical load on the generator terminals despite the changing conditions on the consumer side (Singh & Tiwari, 2013). When this is achieved, it is possible to use turbine without the need to regulate the flow rate or the governor control system. This control mechanism uses an uncontrolled rectifier and chopper together with a series “dump” load. It is important to ensure that proper design considerations are made when selecting the rectifier, chopper, and dump load so as to ensure that trouble free operation is achieved. Several electronic control methods exist including the binary weighted-switched resistor method, controlled rectifier feeding dump load method, phase-controlled thyristor-based load controllers method among other methods (Singh & Tiwari, 2013). Several other control mechanisms exist for the regulation of various parameters within micro-hydropower plants, but the major parameters are voltage and frequency. The literature materials depict presence of several approches that have been used to achieve stability and reliability within these systems. Research approach, methodology and planning This is a highly technical research study that seeks to investigate critical components in the design and control of micro-hydropower plants. Since the study involves investigation of operational characteristics of the power plants, like the determination of three-phase induction motors can be used to supply single-phase consumers, the study must be designed to be as practical as possible. The centres of interest of the study demands that the investigation include physical interactions with the components and processes since this will be the easiest way through which these concepts can be learned. During this physical presence, a huge amount of learning will be achieved through observations and recording. This will be The study will also involve face to face interviews and discussions with the field experts who have deep understanding of the concepts and principles regarding design development and implementation of micro-hydropower projects. These face to face discussions will target individuals who have great experience in small power projects and those who will be ready to share information. Proper selection of respondents will be done by reviewing their past experiences and selecting individuals who seem to have content and practical knowledge. All interview information will be collected and written down and at the same time, explanations recorded for further analysis. The most important approach will be to try and ask as many questions as possible on site and have the answers recorded or written down. Face to face interviews is the selected method of data collection and as ... states, this method motivates the respondent to give even more information due to both verbal and non-verbal cues used during interviews. In this sense, face to face interviews are much more preferable to telephone interviews or mailed questionnaires. Once the study is complete, all the collected information will be organized and then studied so that the processes are understood. An investigation into available literature material will also be done to consolidate and supplement the information collected from the study. Once this has been done, final findings, lessons and ideas learnt will be compiled and organized into a single piece. Justification  Preliminary investigation into the relevant literature material reveals presence of several works that provide explanations about the subject. Critical information about the rising demand of electrical energy and the increasing interest in micro-hydropower indicate a growing industry that needs to be explored. The literature materials also give explanations about the various considerations that must be put in place to ensure that the generated power is maintained in a stable and reliable condition. Also explained are the importance of use of three-phase generating units to supply single-phase power and the associated technical requirements. With these background concepts already explored, it will not be difficult to carry out the study as efficiently as possible. The objectives of this study therefore, will be achieved and the findings used to enhance the understanding of micro-hydropower plants. List of References Singh A, & Surjan, BS, 2014, Microgrid: A review, IJRET: Intenational Journal of Research in Engineering and Technology, 3(2): 185 - 198 Tanbhir et al, 2011, Micro Hydro Power: Promising Solution for Off-grid Renewable Energy Source, International Journal of Scientific & Engineering Research, 2(12): 1 – 5 Gaius-obaseki T, 2010, Hydropower opportunities in the water industry, International journal of environmental science, 1(3): 392 – 402 Chan, TF, 1998, Performance Analysis of a Three-Phase Induction Generator Connected to a Single-phase Power System, IEEE – Transactions on Energy Conversion, 13 (3), pp 205-213. Surendra, KC, Khanal SK, Shrestha, P & Lamsal, B, 2011, Current status of renewable energy in Nepal: Opportunities and challenges, Renewable and Sustainable Energy Reviews, 15: 4107 - 4117 Ion, CP, Serban, I & Marinescu, C, 2006, A single-phase dump load for stand-alone Generating units with induction generator, Annals of the University of Craiova, Electrical Engineering series, No. 30 < http://elth.ucv.ro/fisiere/anale/2006/4_8.pdf> Ekanayake, JB, 2002, Induction generators for small hydro schemes, Power engineering journal, 16(2), pp. 61 – 67 Marquez JL, Molina MG & Pacas JM, 2010, Dynamic modeling, simulation and control design of an advanced micro-hydro power plant for distributed generation applications, International journal of hydrogen energy, 35: 5772–5777 Singh, S & Tiwari, AN, 2013, Voltage and frequency controller for self excited induction generator in micro hydro power plant: review, International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE), 2(2): 214 – 219 Ion, C. P. & Marinescu, C., 2010. Control of parallel operating micro hydro power plants. Brasov, Romania, IEEE Min et al, 2011, Renewable energy potential from micro hydro for techno-economic uplift – a brief review, IJRRAS, 7(4): 368 – 372 Holbrook, AL, Green, MC, & Krosnick JA, 2003, Telephone versus face-to-face interviewing of national probability samples with long questionnaires: Comparisons of respondent satisficing and social desirability response bias, Public Opinion Quarterly, 67: 79 - 125 Read More

A control mechanism will also be required to ensure that the energy produced is stable while the transmission system will deliver the power to the consumers. Several considerations must be made to ensure that reliable power gets to the consumer at the right voltage and frequency. There is need to understand the various control mechanisms employed for such micro-hydroelectric systems that will ensure that this requirements are met by the system. Developers of small and micro-hydropower plant have commonly used the induction generators for establishment of power generation projects due to the advantages associated with the generators.

These generators, generally, are robust, low cost and readily available, making them the preferred selections for these projects (Ekanayake, 2002). But even for these generators, costs incurred for every kW generated in a single-phase system are generally higher compared to three-phase systems. As a result, three-phase generator systems that produce single-phase power have been used (Ekanayake, 2002). This brings great convenience to the process, and is one of the centres of focus for this research.

Specific Objective The research will investigate the operation of these generators and analyse how the single-phase power generation is achieved and to understand how a stand-alone three-phase induction generator can be used to supply single-phase load Other Objectives To investigate whether it is possible to implement control mechanisms that can improve the parallel operation of two micro-hydropower plants To investigate how the development of control systems can be optimized to combine robustness and single-point operation of the generators To learn about the functioning of the micro-hydropower scheme induction generator and the control system This will therefore be an intensive research that will seek to find information regarding the various factors that contribute to the optimal performance of the micro-hydropower plant with emphasis of how the control systems could be used to achieve this.

The research will involve an investigation of the available literature material on the subject. Literature Review Micro-hydropower plants are small hydropower plants that could be used to meet the demands of small local consumers like lighting and charging batteries for local uses (Tanbhir et al, 2011). These projects are becoming more acceptable due to the environmentally friendly generation process and the availability of water in several locations (Gaius-obaseki, 2010). They have therefore played a significant role in meeting the energy demand that is already on the rise over the last few years.

Micro-hydropower projects are also preferred due to their lower costs, ease of establishment and the minimal disturbance to the environments compared to huge hydropower projects (Tanbhir et al, 2011). The induction generator is preferred for such projects due to its dominant and rugged advantages like low cost, brushless construction and low maintenance requirements (Ion, Serban & Marinescu, 2006). Usually, three-phase squirrel cage units are used. In the rural setting, however, the demand for power will usually be below 10 kW within single-phase networks.

Although single-phase generation units could be used for these cases, these units may not give the best performance and they may not supply powers that exceed 3 kW. To meet these design requirements, three-phase induction machines have been deployed to supply the demands within these isolated systems, but with necessary adjustments to enable them supply singe-phase networks (Ion, Serban & Marinescu, 2006). As Ekanayake (2002) further points out, minimization of further capital costs is achieved through crude voltage and frequency control techniques.

The system frequency and voltage are kept within permissible limits by connecting resistive ballast. This ensures that the sum of consumer load and the ballast load are maintained at a fixed value (Ekanayake, 2002).

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