Browsing by Author "Jayatunga, U"

Now showing 1 - 14 of 14

item: Article-Full-text
Comparative evaluation of solar PV hosting capacity enhancement using Volt-VAr and Volt-Watt control strategies
(Elsevier, 2021) Chathurangi, D; Jayatunga, U; Perera, S; Agalgaonkar, AP; Siyambalapitiya, T
Integration of solar photovoltaic systems to low-voltage distribution networks is witnessing an unprecedented growth in many parts of the world. Although solar photovoltaic generation is of significant benefit from a number of angles, exceedance of hosting capacity levels by such installations in lowvoltage distribution networks continue to cause significant technical challenges in network operation, especially to the management of network voltage. Modern smart inverters are equipped with Volt-VAr and Volt-Watt control capabilities, which can assist in the management of network voltage levels. This paper provides a detailed analysis of the influence of different connection standards which cover these strategies on solar photovoltaic hosting capacity and their applicability in low-voltage distribution networks. Smart inverters with differing Volt-VAr and Volt-Watt control functions are modelled in the DIgSILENT PowerFactory platform. Influence of different connection standards on solar photovoltaic hosting capacity is analysed to investigate the most beneficial connection approach/es to address the issue of voltage violations. Furthermore, the work presented in this paper provides a greater understanding on the hosting capacity improvement by employing advanced inverter control functions where such improvements are subjected to locational aspects of inverters in low-voltage distribution systems.
item: Article-Full-text
Dependancy of three phase induction motor derating aspects on complex voltage unbalance factor: A calorimetric and finite element simulation study
(IEEE, 2021) Sudasinghe, P; Jayatunga, U; Commins, P; Moscrop, J; Perera, S
It is well known that three-phase induction motors have to be derated in the presence of supply voltage unbalance (negative sequence) exceeding a stipulated limit of 1% based on several widely used standards. Generally, voltage unbalance limits are decided based on the magnitude of negative sequence voltage unbalance factor which is quantified as the ratio of negative sequence voltage to positive sequence voltage. However, a specified voltage unbalance magnitude can arise as a result of numerous possibilities of the three phase supply voltages. Therefore, it is hypothesised that the current derating curve, which defines a derating factor that is dependent on the magnitude of the voltage unbalance, is not optimal and may not be economical and/or safe for some voltage unbalance conditions. To examine the validity of this hypothesis, modelling and experimental validation need to be carried out considering motor losses and temperature rise which are the main factors that help determine the derating factor of an induction motor. Realising these requirements, the emphasis of this study is to examine the dependency of losses, temperature rise and torque oscillations of a three-phase induction motor on the complex nature of voltage unbalance through calorimetric and finite element simulation-based studies. The outcomes are expected to assist in the development of suitable derating factors.
item: Article-Full-text
Development of high frequency (Supraharmonic) models of small-scale (< 5 kW), single-phase, grid-tied PV inverters based on laboratory experiments
(Elsevier, 2019) Darmawardana, D; Perera, S; Meyer, J; Robinson, D; Jayatunga, U; Elphick, S
There is a growth of high frequency (HF) emissions in the range of 2–150 kHz (also known as Supraharmonics) in electricity distribution networks, primarily due to the increasing number and capacity of AC grid connected equipment having power electronic interfaces. Although PV inverters are a major HF source in electricity distribution networks, PV inverter models that are suitable for HF emission studies are yet to be developed. To this end, a generic method that can be used to develop HF models of small-scale (< 5 kW), grid-tied, single-phase PV inverters using a black box approach is presented in this paper. Accordingly, HF models of three PV inverters that are commonly used in domestic and commercial installations are developed assuming standard network conditions. It is shown that these HF models are capable of successfully capturing the HF performance of the selected PV inverters under a wide range of operating conditions. The outcomes of this work are expected to broaden the knowledge pertaining to the HF emissions in the frequency range considered.
item: Conference-Full-text
Distribution transformer based smart grids with rooftop solar : a case study for Sri Lanka
(Institute of Electrical and Electronics Engineers, Inc., 2018-09) Amarasinghe, HPP; Jayatunga, U; De Silva, N; Samarasinghe, R; Abeygunawardana, S
Trends on utilizing distributed renewable resources around the world have significantly increased the number of grid connected solar photovoltaic systems in low voltage networks. In Sri Lanka, low voltage systems are now available with the cumulative addition of the installed rooftop solar capacities is exceeding fifty percent of the rated capacity of the connected transformer. Thus, it is of vital importance to understand the technical impacts of solar photovoltaic additions in large scales on the operating performance of the networks and how to mitigate those issues. In this study, a futuristic solution is proposed with the formation of smart grid type operation, to effectively utilize the daytime solar photovoltaic generation in low voltage systems within the distribution transformer service area. Distribution transformer based smart grid, which operates with controlling mechanisms, loads, rooftop solar and battery storage systems is proposed for an urban low voltage distribution network in Sri Lanka which have more than forty percent of solar penetration level based on transformer capacity. The detailed network was modeled in MATLAB/SIMULINK simulation platform in order to develop different operating scenarios. The base model was validated with the field data available with transformer meter.
item: Article-Abstract
Estimation of voltage unbalance attenuation caused by three-phase induction motors: An extension to distribution system state estimation
(IEEE, 2019) Kahingala, TD; Perera, S; Jayatunga, U; Agalgaonkar
With the increased interest in controlling and managing voltage unbalance (VU), network operators are now increasingly being motivated to obtain the state of their networks with greater details. Distribution system state estimation (DSSE) is a prominent tool which enables network operators to estimate the level, location and related impacts of VU. DSSE techniques developed to date which use the polynomial or exponential load models are deficient in recognising VU attenuation associated with three-phase induction motors (IMs) that are directly connected to the AC network. Adoption of adequate three-phase models of IMs, that are used in full unbalanced load flow, into the existing DSSE techniques is not feasible due to several factors including requirement of extensive data, additional computational efforts and major constraints related to incorporating the necessary modifications. As a solution, this paper proposes a novel formulation for post processing the results of current DSSE techniques to reflect the aforementioned behaviour of IMs. Simulations are carried out using the IEEE 13 bus distribution network, for a range of scenarios to verify the developed methodology. The work presented in relation to VU attenuation in interconnected networks also complements the existing treatise in IEC documentation which only deals with radial networks.
item: Thesis-Full-text
Impact of high penetration of solar PVS on harmonics in LV distribution networks
(2018) Anurangi, RO; Rodrigo, WDAS; Jayatunga, U
Present trend of using solar photovoltaic (PV) technology for generating electricity has marked a rapid growth in the number of grid connected solar PV systems which has been reported to make a considerable impact on the power quality in the grid. With comparison of power quality (PQ) problems such as voltage unbalance, local voltage rise and voltage fluctuations, the increase of network harmonic levels has been identified as a potential PQ concern with the grid connected solar PVs. PV inverters are source of harmonics that produces low order and high order harmonics at the switching frequency and its side bands. Low order harmonics present at the inverter output due to the inability of producing pure sinusoidal waveform. Varying solar irradiance, inverter characteristics, inverter capacity, multi-inverter interactions and background harmonic level are examples of factors which influence the amount of harmonic generation of a PV system. This research focuses on the effect of high levels of harmonic injection and propagation of current harmonics in distribution network with solar PV integrations. A methodology is discussed in this thesis to achieve the aforementioned matter with the detailed modeling of PV inverters in a typical distribution network using PSCAD/EMTDC simulation platform. From the analysis of simulation results, the current harmonics injected by single phase inverters has been found substantial and influential with regard to the energy transmission and increase losses with compared to the three phase inverters. Unbalance occurred due to single phase inverters results in triplen harmonics to propagate to the upstream grid via the distribution transformer. Moreover, current harmonics superimposition were recorded as a result of multi-inverter operation. It was found that the Point of connection (POC) of the PV inverter affects the voltage harmonic levels at the inverter output.
item: Thesis-Full-text
Impacts of maximizing plug-in electric vehicle penetration on urban power distribution network
Wanigasuriya, RM; Jayatunga, U; Achchige, LW
Electrified vehicles are a recent developing trend in transportation. It is a good solution for the reduction of fossil fuel usage on the transportation and hence the reduced CO2 emission. Plug-in Electric Vehicles (PEVs) are driven by the electricity stored in its battery and therefore zero tailpipe emission. Thus, PEVs attract much interests of public due to its environmental friendliness and they will possibly emerge widely in city areas in the short-term future mainly for short distance travels. Most of the countries provide incentives (tax credits, grants) to purchase plug-in electric vehicles as promotion of green vehicle. During last two years usage of PEVs was increased in Sri Lanka. PEVs are becoming more popular due to the reduction of importing tax and the developing infrastructure in Sri Lanka. However, in worldwide, increasing number of PEVs will become a substantial load to the existing power grid which can be characterized as an unusual type of load. Therefore, it is essential to pre-investigate the inevitable impacts on the power system. Lot of studies has been carried out worldwide to investigate the both positive and negative impacts on power grid. But in Sri Lankan context, a proper study had not been carried out to examine the challenges we have to face due to the increasing penetration of PEVs. Thus this research study is aimed to evaluate the level of impact due to the residential and fast charging of increasing number of PEVs. Anticipated impacts on power system such as voltage drop, voltage unbalance, transformer overloading, line losses and current harmonic effect are addressed in this study. Charging behavior of PEVs is unpredictable due to the variation of travel needs and the driving patterns. This study basically evaluates the impacts on distribution network due to this uncoordinated charging of increasing number of PEVs. It also addresses the mitigation methods and the maximum number of PEVs can be charged during off-peak hours from the distribution feeder modeled.
item: Conference-Full-text
Lagrange multiplier based solution for optimizing dg sizes in distribution networks
(IEEE, 2021-07) Anuradha, KBJ; Jayatunga, U; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
Integration of Distributed Generation (DG) has occupied a great interest in modern power engineering due to its significant merits over the conventional power generation techniques. However, several aspects such as climatic conditions, land and fuel availability, DG location and DG size need to be carefully considered to harness the best results from integrating DG units for power networks. Among them, sizing of DG units has taken a prominent place as it affects the network operation as well as the cost aspect. Optimizing the sizes of prospective DG units that are intended to be integrated for a given network will facilitate in gaining the expected merits such as minimizing active power losses and voltage deviations without causing any stability, protection and power quality issue. The existing methodologies for determining optimal DG sizes are rather sophisticated. This paper presents a robust mathematical solving approach based on Lagrange Multiplier Method (LMM) for determining the optimal DG sizes for minimizing the active power losses and voltage deviations. The problem is formulated and solved as a multi objective function. Validation of the proposed mathematical solution strategy was tested using the IEEE-6 and IEEE-33 standard test bus systems. Results demonstrate the effectiveness of the proposed methodology.
item: Article-Full-text
Loss-Voltage Sensitivity Analysis Based Battery Energy Storage Systems Allocation and Distributed Generation Capacity Upgrade
(Elsevier, 2021) Anuradha, KBJ; Jayatunga, U; Perera, HYR
Distributed Generation (DG) has become a key component in modern power industry due its significant advantages over the traditional power generation methods. Nevertheless, best expected outcomes can only be achieved with optimal allocation of DG resources where inappropriate allocation may impose problems in power system stability, protection and quality. This paper presents analytical approaches for optimizing the DG size, BESS (Battery Energy Storage Systems) capacities and power dispatch in Medium Voltage (MV) networks. Since most of the existing analytical approaches related to optimizing DG sizes for minimizing network losses and voltage deviations have considered individual objective function separately, both parameters may not be minimized simultaneously. Thus, in this paper, an analytical methodology was formulated based on an objective function built on new parameter Loss-Voltage Sensitivity Index (LVSI) that evaluates both minimum impact of network loss and voltage variations for optimizing the DG size. The results obtained from this approach were compared with a conventional Genetic Algorithm (GA) formulated by the authors. The BESS capacities are determined considering the effects of Load Proportionality Factor (LPF), State of Charge limits (SOC) of battery storages, number of load areas and the portion of daily off-peak solar generation period energy consumption expected to be served by each BESS unit. The significance of this BESS capacity determination methodology is highlighted as the BESS capacities can be numerically calculated whereas in existing work, they are heavily relying on conventional optimization techniques which do not give an idea about the internal behavior of parameters which determine the capacities of BESS units. Moreover, an optimal BESS dispatch algorithm is also presented in this paper for minimizing the energy losses and voltage deviations. The applicability of the proposed methodologies are verified using the standard IEEE-33 and IEEE-69 test bus systems. Simulations carried out in MATLAB is used to illustrate the accuracy and the appropriateness of the proposed approaches.
item: Article-Full-text
Network-Wide influence of a STATCOM configured for voltage unbalance mitigation
(IEEE, 2020) Kahingala, TD; Perera, S; Jayatunga, U; Agalgaonkar, AP
This letter proposes an analytical approach to estimate local and the network wide influence of a static compensator (STATCOM), configured for voltage unbalance (VU) mitigation. In addition, it provides guidelines for determining the most appropriate location for active mitigation. The proposed generalised formulation is able to demonstrate the VU mitigation provided by a STATCOM regardless of the control strategy used or the network conditions.
item: Thesis-Full-text
Neutral current mitigation in low voltage installations
Ameer, MIS; Fernando, R; Jayatunga, U
Power quality problems with the ever increasing use of electrical and electronic loads has risen to a greater extent. It is quite common to blame the supply authority for lower power quality issues. CEB and LECO the main utilities in Sri Lanka are blamed of this problem. But what the consumers do not understand is that power generation is not low in power quality. It is the consumer himself, who makes the network a poor quality one. The bitter part is that consumers are in the losing side due to this poor network quality, which they take time to realize. This research was intended to consider the energy loss caused due to unbalance and heavy neutral currents. Heavy neutral currents can be for two reasons. First may be due to unbalance in the network and second could be due to presence of harmonics. This current is a loss to the system in terms of cable losses, over capacity network requirement and added operation and maintenance cost. In turn presence of harmonics and unbalance currents distorts the voltage supplied to other equipment which in turn produces unbalance currents. Several solution has been found by engineers to this problem. Finding the correct solution is important in this concept. The solution can be easily divided into two categories as energy efficient solutions and energy inefficient solution. For an example if a facility is having high neutral current with high temperature in the neutral current, one solution will be to overate the neutral cable to accommodate the extra current. But on the other hand this will be an inefficient solution, which is trying to accommodate the waste energy comfortably. But if a solution is looked into reducing the neutral current by phase balancing or reducing harmonics, this will be an energy efficient solution. I have extensively discussed energy efficient solutions as a rectification to this problem and other solutions should be discouraged. The case studies done at varying consumer location proved a much promising solution to, this problem with a sustainable saving from the bills. I have also implemented a logical unit which will reduce the time consumed for manual phase swapping by fast load flow analysis of the network.
item: Article-Full-text
A nomographic tool to assess solar PV hosting capacity constrained by voltage rise in low-voltage distribution networks
(Elsevier, 2022) Chathurangi, D; Jayatunga, U; Perera, S; Agalgaonkar, AP; Siyambalapitiya, T
Proliferation of solar photovoltaic (PV) generation in low voltage (LV) distribution networks has imposed a set of challenges in network operation and control. Voltage rise is currently the main constraint that limits solar PV capacity increase in LV networks. Together with this, there is a growing need for a generalised and versatile tool which utilities can use to deal with customer requests for new solar PV connections. This paper proposes a generalised approach to assess solar PV hosting capacity (HC) subjected to over-voltage curtailment based on a Nomogram representation, which facilitates reasonable modeling insights for HC assessment in LV networks. In addition, solar PV connection criteria are further developed using the Nomogram representation of HC evaluation. The proposed Nomogram based approach for HC assessment and connection criteria will contribute to further improvement of available guidelines on solar PV connections in LV networks.
item: Conference-Full-text
Three phase asymmetrical power flow algorithm using current injection technique
(Institute of Electrical and Electronics Engineers, Inc., 2016-12) De Vas Gunawardena, APSG; Ranatunga, NT; Samarathunga, LL; Weerawansha, SDT; Jayatunga, U; Rajapakse, A; Prasad, WD
Load flow studies play a vital role in planning the future expansion of power system as well as for deciding the optimum operation of the existing power system. Three phase asymmetrical power flow studies are recommended for unbalanced power systems such as distribution networks. Unbalanced loading, single phase and two phase shunts make the system operation unbalanced leaving the application of conventional load flow techniques away from the scene. The paper presents an unbalanced power flow algorithm based on the current injection technique with full Newton-Raphson formulation. The proposed method is validated using IEEE four bus test network.
item: Thesis-Full-text
Three phase state estimation techniques for network voltage unbalance assessment
Manmatharajan, S; Jayatunga, U
Voltage unbalance is an important aspect of power quality. Unbalance can damage power equipment in a power system network, affect the operation of sensitive customer equipment and increase losses. Conventional Power system state estimation (PSSE) which assumes the network to be fully balanced does not capture the information related network voltage unbalance. Although, the single line representation of the network is good enough for most of the cases when it comes to transmission level, there can be certain locations in the power system, especially in the distribution network, which are prone to high voltage unbalance (VU) levels over which network operators wish to have full three-phase details in real time. To address this issue, completely switching into three phase model of the network which will add a significant computational burden, is not a feasible solution at all. As a feasible remedy, this thesis introduces a novel methodology for voltage unbalance state estimation extending the conventional state estimation which can be selectively applied only for the locations of interest to capture the information related to network voltage unbalance, with minimum additional computational effort. The proposed three phase estate estimation make use of Singular Value Decomposition method to work out the estimation of three phase voltages and hence the complex voltage unbalance factor (VUF) at the locations of interest. Proposed methodology is verified using IEEE 4 bus and 14 bus test networks simulating them using a three phase unbalanced power flow program written in MATLAB environment.