Browsing by Author "Lidula, NWA"

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item: Conference-Full-text
Adaptive droop controller for energy management of islanded ac microgrids
(IEEE, 2023-12-09) Ediriweera, WEPS; Lidula, NWA; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
Distribution feeders with high penetration of renewable power generation can be converted into microgrids for providing more quality power with increased reliability. Virtual synchronous inertia is used to increase the inertia of inverter-based microgrids to provide the same performance as synchronous generators. Frequency stability and power sharing among the distributed energy resources of islanded microgrids would be challenging due to poor transient response with droop controllers and inaccurate selection of droop values. This article proposes an adaptive droop controller for a microgrid in islanded operation that has several distributed energy resources including solar PV, diesel generator, and energy storage. Droop values, and reference values in the droop characteristics curve are decided based on the severity of the frequency disturbance and the state of charge level of the energy storage. The performance of the proposed droop controller is verified using a radial-connected microgrid derived based on a real distribution system. The results illustrate that during a disturbance, the proposed adaptive droop controller can slightly boost the diesel generator's output power with a minimum loss of charge of the energy storage.
item: Conference-Abstract
Behavior of a microgrid during the transition from grid connected to Islanded mode
Lidula, NWA; Rajapakse, AD
Behavior of a microgrid during the control mode transition from grid connected to islanded operation «as studied. A detailed microgrid simulation model was developed. Microgrid frequency and voltage control was designed based on the most generic schemes identified after a thorough literature survey on practical microgrids. The simulation study results reveal the impact of generator inertia and the control mode transition delay on the frequency and voltage deviations and load shedding.
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Designing a Microgrid System Based on Kukuleganga Hydro Power Station
Thiwanka, WAT; Thotabaduge, US; Udageachchi, EH; Undugoda, UANB; Wanniarachchi, WKCU; Lidula, NWA
item: Conference-Abstract
Designing a microgrid test system for transient analysis
Lidula, NWA; Nishshanka, RMMP; Wijesundara, SB; Wijemanna, WLKD; Weerakkody, WNL
A power system test system is designed using PSCAD/EMTDC software for transient analysis, which can be specifically used for transient studies with Distributed Generators (DGs) or this system can be easily developed as a Microgrid test system. The model is developed based on a section of a practical power system that is Kukuleganga area of the Sri Lanka power system. This includes 132kV transmission system, Kukuleganga hydro power station, five grid substations with 33kV distribution buses and DGs. The developed model is verified through comparing the actual fault data obtained from the Ceylon Electricity Board, Sri Lanka with the results obtained from the developed PSCAD/EMTDC model. The Discrete Wavelet Transform is used to identify the degree of accuracy in verification of the model. The test results are demonstrated for both current and voltage waveforms.
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Evaluation of protection coordination violations with the integration of distributed generators
Lidula, NWA; Kodikara, GR
Conventional distribution system is generally passive having a unidirectional power flow from its grid substation to the loads. With the addition of Distributed Generation (DG) in to the system, power flow becomes bidirectional and fault current increases. These can influence the existing protection schemes, which are originally designed for passive networks. This paper proposes a technique, which can be used to assess the protection coordination loss quantitatively, for a DG integrated network allowing the utility to take corrective measures.
item: Conference-Full-text
Evaluation of the impact of integrating pumped-storage systems in a small power system with high wind penetration
(Institute of Electrical and Electronics Engineers, Inc., 2016-12) Peiris, KRD; Kalpage, KMT; Perera, KAIRP; Wickramarathna, MTAP; Siriwardana, MGCI; Lidula, NWA; Rajapakse, A; Prasad, WD
High wind penetration in a small power system can create overwhelming stability issues at contingencies. Hybrid wind and pumped-storage systems are widely adopted to harness the maximum wind energy potential locally. Similarly, integration of pumped-storage power plants can be considered for islands or small power systems to integrate more wind farms while improving stability of the system. A small power system was derived based on the IEEE-12 bus system to evaluate the system behavior with increased wind penetration and pumped-storage integration. The integrated system was simulated in PSCAD/EMTDC to analyze the system transient stability under different scenarios. The studies revealed that the integration of pumped-storage systems into small power systems with high wind penetration not only supports more wind penetration into the system but also improves the transient stability.
item: Conference-Abstract
Grid integration of large scale fixed speed wind farm considering static voltage stability
Lidula, NWA; Mithulananthan, N
This paper addresses the influence of integrating a large-scale wind farm on static voltage stability of a power system based on the factors such as, wind speed, wind farm interconnection bus, interconnection cable length and wind farm size. Using the continuation power flow method effects of each factor were analysed and an index is proposed to locate a large scale fixed speed wind farm in a power system.
item: Conference-Full-text
Impact of large-scale wind and solar power integration on operating reserve requirements of an islanded power system
(IEEE, 2018-05) Thilekha, MHTT; Siriwardana, KMHD; Siebel, NRD; Waslathanthri, DAD; Lidula, NWA; Siyambalapitiya, T; Wickramasinghe, A; Chathuranga, D
Many nations have shown their support to a battle against environmental pollution by integrating large scale solar and wind energy resources, to their respective grids. Although these commendable efforts have paved the way for a greener future, it has to be noted that non-conventional renewable energy (NCRE) possess their own inherent drawbacks. Their availability is highly dependent on the prevalent weather conditions, which means that they are subjected to uncontrollable variability. With the rise of intermittent renewable resources, it is important to have appropriate amounts of operating reserves to provide backup to the system. This will ensure that the system will be stable under variable power conditions and thus, improve the reliability of the system. This paper is focused in quantifying additional operating reserves requirements to stabilize the system under intermittent conditions with the large penetration of renewables into an islanded power system. It assesses the spinning reserve requirement during the high wind and low wind seasons.
item: Article-Abstract
A New scheme of under frequency load shedding and Islanding operation
Bambaravanage, T; Rodrigo, WDAS; Kumarawadu, SP; Lidula, NWA
Emergency load shedding (LS) for preventing frequency degradation is an established practice all over the world. The objective of LS is to balance load and generation. This paper presents a technique to develop a reliable LS scheme to prevent black-outs, while maintaining stability in power systems (PSs) with high variability and uncertainty under abnormal conditions. Different techniques are available for implementing LS schemes such as traditional, semi-adaptive and adaptive. The LS scheme proposed in this paper has a sequence and conditions of applications of different LS schemes and islanding strategies. The proposed technique comprises with two Phases. During Phase-I, a LS methodology that was based on traditional & semi adaptive LS schemes was implemented and in Phase-II an adaptive LS scheme was implemented. With this methodology, instead of shedding preset loads, the disturbances are shared among the loads. The effectiveness of the developed scheme was investigated by simulating different abnormal conditions in the power system of Sri Lanka. The tendency for a total PS collapse could be eliminated with the suggested scheme which is sensitive to such factors as generation & demand of the PS dynamically, while maintaining stability in PSs with high variability and uncertainty.
item: Article-Abstract
A New scheme of under frequency load shedding and islanding operation
(2015-08-24) Bambaravanage, T; Rodrigo, AS; Kumarawadu, SP; Lidula, NWA
Emergency load shedding (LS) for preventing frequency degradation is an established practice all over the world. The objective of LS is to balance load and generation. This paper presents a technique to develop a reliable LS scheme to prevent black-outs, while maintaining stability in power systems (PSs) with high variability and uncertainty under abnormal conditions. Different techniques are available for implementing LS schemes such as traditional, semi-adaptive and adaptive. The LS scheme proposed in this paper has a sequence and conditions of applications of different LS schemes and islanding strategies. The proposed technique comprises with two Phases. During Phase-I, a LS methodology that was based on traditional & semi adaptive LS schemes was implemented and in Phase-II an adaptive LS scheme was implemented. With this methodology, instead of shedding preset loads, the disturbances are shared among the loads. The effectiveness of the developed scheme was investigated by simulating different abnormal conditions in the power system of Sri Lanka. The tendency for a total PS collapse could be eliminated with the suggested scheme which is sensitive to such factors as generation & demand of the PS dynamically, while maintaining stability in PSs with high variability and uncertainty.
item: Article-Abstract
Prototype implementation of an islanding detection relay based on pattern classification of current and voltage transients
Lidula, NWA; Rajapakse, AD; Pham, JP; Denboer, N
A prototype islanding detection relay, which uses decision tree classifier to categorize the transient generating events as ‘islanding’ or ‘non-islanding’ was implemented and tested. It consisted of two basic stages of signal processing to extract the required feature vectors for the classification. The first stage involved signal filtering and in the second stage signals were processed by rectifying, summing, and lowpass filtering to get the energy content in the three phases during a selected time-frame. A simple radial medium voltage distribution system having a single distributed generator was simulated in PSCAD/EMTDC to obtain the transient waveforms, and the performance of the relay was tested with signals generated using an RTP real-time waveform playback instrument. The experimental results showed high accuracy in detecting islanding events within a response time of less than two cycles. The proposed relay can be implemented with a very low cost and is simple in construction. Therefore, this could be an acceptable low cost substitute for the expensive and complex transfer trip schemes, which are commonly in use with the distributed generation. loads and distributed energy resources (DER) remains energized while isolated from the remainder of the utility system’ (IEEE, 2003). Unintentional islanding resultsin several safety and power quality' issues including abnormal variations in frequency and voltage, possibility of creating ungrounded systems, and potential safety hazards for repair crews. In formulating guidelines and/or rules for interconnecting DGs in the distribution systems, the most common practice is to adopt the IEEE standard 154 (IEEE, 2003). These otional practice standards have been developed with an underlying assumption that thepower system is radial. In the past, the power available from DGs was not essential to support the load on the system. Hence, the standards suggest to disconnect the DGs for any ‘significant’ fault (a fault that could require the protection to be provoked) on the distribution system and thus, maintaining the radial nature of the system. Consequently, the islanding detection relays are designed to avoid power islanding, and these relays are referred to as anti-islanding relays (Xu et al., 2004; Mahat et al., 2008). However, there is a change in the approach towards islanding with the initiatives on microgrids (Chowdhury et al., 2009; Lidula & Rajapakse, 2011). The performance of the power-islanding detection methods in a microgrid setup is more demanding as the microgrid is designed to operate as a stable power island. Many powerislanding detection methods in practice would find it difficult to meet the qualities demanded by micorgrids (Katiraei et al., 2005) without the use of expensive telecommunication facilities. Keywords: Active filters, decision tree classificat
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Prototype implementation of an islanding detection relay based on pattern classification of current and voltage transients
Lidula, NWA; Rajapakse, AD; Pham, JP; Denboer, N
A prototype islanding detection relay, which uses decision tree classifier to categorize the transient generating events as ‘islanding’ or ‘non-islanding’ was implemented and tested. It consisted of two basic stages of signal processing to extract the required feature vectors for the classification. The first stage involved signal filtering and in the second stage signals were processed by rectifying, summing, and lowpass filtering to get the energy content in the three phases during a selected time-frame. A simple radial medium voltage distribution system having a single distributed generator was simulated in PSCAD/EMTDC to obtain the transient waveforms, and the performance of the relay was tested with signals generated using an RTP real-time waveform playback instrument. The experimental results showed high accuracy in detecting islanding events within a response time of less than two cycles. The proposed relay can be implemented with a very low cost and is simple in construction. Therefore, this could be an acceptable low cost substitute for the expensive and complex transfer trip schemes, which are commonly in use with the distributed generation.
item: Conference-Abstract
SoC based multi-mode battery energy management system for dc microgrids
Jayasena, KNC; Jayamaha, DKJS; Lidula, NWA; Rajapakse, AD
Renewable based DC microgrids are being widely deployed due to its increased efficiency compared to AC networks. An energy storage system helps to cater power flow imbalances due to the intermittent nature of renewable energy sources and varying load conditions. An adaptive Battery Energy Management System (BEMS) to ensure efficient operation of the battery storage system is proposed in this study. The state of charge (SoC) level management is of great importance for the prolong battery life, minimizing the capacity fade and avoiding over draining of the battery storage. Monitoring SoC level, DC bus voltage regulation and ability to provide backup power are the main considerations in designing the proposed BEMS. Performance of the proposed control algorithm was evaluated using PSCAD/EMTDC simulation results, and is presented in this paper.
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Solid state transformer technologies are cost estimation
Jayarathna, CU; Binduhewa, PJ; Lidula, NWA; Samaranayake, L; Ekanayake, JB
Local direct current (dc) grids, supports by local storage and local renewables in residential and commercial buildings are identified as the key enablers for demand reduction and demand flexibility (demand response). It would be advantageous if the prevailing alternating current (ac) networks can be used to integrate dc networks. Solid state transformer (SST) has been proposed as of more efficient and reliable way to incorporate dc networks with the ac distribution network. SST is based on semiconductor devices and has the capability to replace the conventional transformer. The control circuitry of the SST provides two-way power flow with flexible control to power distribution networks utilizing both ac and dc simultaneously. Besides SST could overcome disadvantages of conventional distribution transformer such as voltage regulation, environmental concerns and power quality issues. However the downside of SSTs is the cost and efficiency compared to its conventional counterparts. Thus it is important to design a cost effective SST that provides connectivity for both ac and dc systems. Number of SST topologies are available in the literature. This study focused on developing a method to estimate the cost of a SST considering most commonly proposed three SST architectures. A database, with important ratings and cost of their commercially available semiconductor devices was created. The method developed was able to identify the cheapest semiconductor devices which match the given power rating, and input and output voltage values of the SST. With this method, it is possible to find the minimum cost 0f the SST considering the semiconductor devices.
item: Conference-Full-text
Techno-economic feasibility of using 400 kV for the 2032 transmission system of Sri Lanka
(Institute of Electrical and Electronics Engineers, Inc., 2016-12) Alahendra, GB; Banda, HMW; Lidula, NWA; Rajapakse, A; Prasad, WD
Congestion occurs on the nation’s electric transmission grids with the addition of new generation to meet the increasing electricity demand. Therefore, reliable, efficient and better quality of supply urge introduction of new higher voltage levels for power transmission. However, it has to be technically feasible and economically justifiable for the country. Technical feasibility and economic justification of introducing a higher voltage than that of existing voltage to transmit bulk power to load centers from bulk power generating stations in Sri Lanka is discussed in detail in this research.
item: Conference-Abstract
Under-Frequency load shedding for power systems with high variability and uncertainty
Bambaravanage, T; Rodrigo, WDAS; Kumarawadu, S; Lidula, NWA
Abstract−Emergency load shedding for preventing frequency degradation is an established practice all over the world. The objective of load shedding is to balance load and generation. This paper presents a methodology to develop a reliable load shedding scheme, to prevent black-outs while maintaining stability in power systems with high variability and uncertainty under any abnormal condition. The technique proposes the sequence and conditions of applications of different load shedding schemes and islanding strategies. The effectiveness of the developed scheme was investigated by simulating different abnormal conditions in the power system of Sri Lanka
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Voltage balancing and synchronization of microgrids with highly unbalanced loads
Lidula, NWA; Rajapakseb, AD
Microgrids can operate in parallel with the grid or as a power-island. They are thus, expected to perform seamless transition from islanded to parallel operation and vice versa. This paper reviews the existing DG interconnection standards for microgrid resynchronization, investigates possible simple solutions for voltage balancing, and shows that the existing synchrocheck relay with a circuit breaker is sufficient to reconnect an islanded, highly unbalanced microgrid back to the utility grid.
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Wavelet-Multi resolution analysis based ANN architecture for fault detection and localization in DC microgrids
(IEEE, 2019) Jayamaha, DKJS; Lidula, NWA; Rajapakse, AD
DC microgrids present an effective power system solution for increased integration of renewable sources while providing clear benefits, such as high efficiency and simpler control. However, the protection of DC networks still remains a challenge due to strict time limits for fault interruption imposed by fast rising fault currents in DC systems, and absence of frequency and phasor information. This paper introduces a technique for fast detection and isolation of the faults in the DC microgrids without de-energizing the whole network. In the proposed algorithm, branch current measurements are sampled and Wavelet transform is applied to capture the characteristic changes in the current signals caused by network faults. The temporal variations in the relative wavelet energy within the frequency bands are acquired to construct the feature vector for classification. Artificial neural networks are used as the classifier as it provides a soft criterion for fault detection, featuring smart fault detection capability. The relatively fast calculation time of artificial neural networks makes it a good candidate for this application, due to the strict time restrictions inherited in DC fault isolation. To evaluate the performance, a comprehensive study on the proposed scheme is presented. The results demonstrate the effectiveness of the proposed scheme in terms of fast and reliable fault detection and inbuilt accurate fault localization capability.
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Wind resource assesment and turbine selection : case study for Mannar, Sri Lanka
Kalpage, KMT; Peiris, KRD; Perera, KAIRP; Siriwardana, MGCI; Lidula, NWA
In deploying a large scale wind power plant, there are several aspects that have to be assessed. Among them the initial site screening for wind power plants, wind data assessment and proper selection of wind turbines are vital for the success of the project. This paper presents a step by step analysis in selecting a wind turbine, as a case study for Sri Lanka, where it has a substantial amount of wind energy that can be harnessed for power generation. Mannar area is identified as the candidate site with the high wind potential it exhibits throughout the year. After a detailed analysis of the wind resource in Mannar area, Gamesa-114 2 MW wind turbine is selected as the most suitable wind turbine for this particular area of Sri Lanka.
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Wind resource assesment and turbine selection: case study for Mannar, Sri Lanka
(Electrical Engineering Society (EESoc) of Department of Electrical Engineering, University of Moratuwa, 2015) Kalpage, KMT; Peiris, KRD; Perera, KAIRP; Siriwardana, MGCI; Lidula, NWA; Wickramarathna, MTAP; Jayasekara, AGBP
In deploying a large scale wind power plant, there are several aspects that have to be assessed. Among them the initial site screening for wind power plants, wind data assessment and proper selection of wind turbines are vital for the success of the project. This paper presents a step by step analysis in selecting a wind turbine, as a case study for Sri Lanka, where it has a substantial amount of wind energy that can be harnessed for power generation. Mannar area is identified as the candidate site with the high wind potential it exhibits throughout the year. After a detailed analysis of the wind resource in Mannar area, Gamesa-114 2 MW wind turbine is selected as the most suitable wind turbine for this particular area of Sri Lanka.