Browsing by Author "Püvi, Verner"

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  • Analyzing the Impact of EV and BESS Deployment on PV Hosting Capacity of Distribution Networks
    (2022-11) Filip, Robin; Püvi, Verner; Paar, Martin; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The current article analyzes the impact of charging electric vehicles and battery energy storage systems on the photovoltaic hosting capacity of low-voltage distribution networks. A Monte Carlo-based simulation is used to analyze predominantly rural, intermediate and predominantly urban residential regions facing different penetrations of electric vehicles utilizing uncontrolled and controlled charging, and evaluate their impact on photovoltaic hosting capacity. Subsequently, electric vehicles are replaced or supplemented by residential battery energy storage systems, and their combined impact on the hosting capacity is studied. The results revealed that electric vehicles solely do not improve the hosting capacity unless they are connected to the network during sunshine hours. However, controlled storage provides a remarkable increase to the hosting capacity and exceptional contribution in combination with electric vehicles and customers with high loads. Finally, a feasibility analysis showed that controlled charging of the storage has a lower marginal cost of increasing hosting capacity as compared to network reinforcement.
  • Comparison of Different References When Assessing PV HC in Distribution Networks
    (2021-02-01) Fatima, Samar; Püvi, Verner; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The burgeoning photovoltaics’ (PVs) penetration in the low voltage distribution networks can cause operational bottlenecks if the PV integration exceeds the threshold known as hosting capacity (HC). There has been no common consensus on defining HC, and its numerical value varies depending on the reference used. Therefore, this article compared the HC values of three types of networks in rural, suburban, and urban regions for different HC reference definitions. The comparison was made under balanced and unbalanced PV deployment scenarios and also for two different network loading conditions. A Monte Carlo (MC) simulation approach was utilized to consider the intermittency of PV power and varying loading conditions. The stochastic analysis of the networks was implemented by carrying out a large number of simulation scenarios, which led towards the determination of the maximum amount of PV generation in each network case.
  • Comparison of Economical and Technical Photovoltaic Hosting Capacity Limits in Distribution Networks
    (2021-04-23) Fatima, Samar; Püvi, Verner; Arshad, Ammar; Pourakbari-Kasmaei, Mahdi; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Power distribution networks are transitioning from passive towards active networks considering the incorporation of distributed generation. Traditional energy networks require possible system upgrades due to the exponential growth of non-conventional energy resources. Thus, the cost concerns of the electric utilities regarding financial models of renewable energy sources (RES) call for the cost and benefit analysis of the networks prone to unprecedented RES integration. This paper provides an evaluation of photovoltaic (PV) hosting capacity (HC) subject to economical constraint by a probabilistic analysis based on Monte Carlo (MC) simulations to consider the stochastic nature of loads. The losses carry significance in terms of cost parameters, and this article focuses on HC investigation in terms of losses and their associated cost. The network losses followed a U-shaped trajectory with increasing PV penetration in the distribution network. In the investigated case networks, increased PV penetration reduced network costs up to around 40%, defined as a ratio to the feeding secondary transformer rating. Above 40%, the losses started to increase again and at 76–87% level, the network costs were the same as in the base cases of no PVs. This point was defined as the economical PV HC of the network. In the case of networks, this level of PV penetration did not yet lead to violations of network technical limits.
  • Convex Model for Estimation of Single-Phase Photovoltaic Impact on Existing Voltage Unbalance in Distribution Networks
    (2020-12-12) Püvi, Verner; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Due to the increasing adoption of solar power generation, voltage unbalance estimation gets more attention in sparsely populated rural networks. This paper presents a Monte Carlo simulation augmented with convex mixed-integer quadratic programming to estimate voltage unbalance and maximum photovoltaic penetration. Additionally, voltage unbalance attenuation by proper phase allocation of photovoltaic plants is analysed. Single-phase plants are simulated in low-voltage distribution networks and voltage unbalance is evaluated as a contribution of measured background and photovoltaic-caused unbalance. Voltage unbalance is calculated in accordance with EN 50160 and takes into account 10-minute average values with 5% tolerance condition. Results of the optimization revealed substantial unbalance attenuation with optimal phase selection and increased potential of local generation hosting capacity in case of higher background unbalance.
  • Evaluating distribution network optimal structure with respect to solar hosting capacity
    (2023-03) Püvi, Verner; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Optimal design of distribution networks has become an important topic for analysis due to the growing share of photovoltaics (PV). Low and medium voltage networks should undergo structural changes to accommodate widespread PV generation and optimal operation. In this paper, the impact of the network structure on the solar hosting capacity (HC) is analyzed with respect to the role of low and medium voltage networks in power delivery. A given set of load nodes is simulated with multiple feeding substations and varying peak power and number of PV plants. The slime mold algorithm is utilized for numerous topology generations and measured load time series represent regions ranging from rural to urban. The results reveal that networks should go through significant structural changes to cope with larger PV generation and even more so to increase the HC. On the other hand, voltage control measures, such as on-load tap changers, PV reactive power control and curtailment, provide a competitive solution to varying size of distribution networks in hosting solar power. Finally, the analysis in this study provides evidence to a possible need in the change of residential PV policies in order to sustain the current pace of adopting PV plants in Finland.
  • Monte Carlo-based comprehensive assessment of PV hosting capacity and energy storage impact in realistic Finnish low-voltage networks
    (2018-06-01) Arshad, Ammar; Püvi, Verner; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The direction taken towards sustainable power system and renewable energy generation is now irreversible. The power grid needs to host more renewable energy sources, such as solar power, and tackle power quality problems that come along with it. In this paper, firstly, the Hosting Capacities (HCs), of Photo-Voltaic (PV), were found for various regions and their limiting constraints were defined. Afterwards, comparison was made with the HC values obtained for different voltage value standards defined by various countries. Next, single-phase PV connection percentages in the network were defined that makes the voltage unbalance the limiting factor for HC. Lastly, the HC of the solar generation coupled with a Battery Energy Storage System (BESS) was assessed for the Finnish Low-Voltage (LV) grids. Different BESS-based scenarios were employed and their impact on voltage unbalance and HCs were observed. Finally, also the load voltage unbalance was incorporated to make the approach realistic and its impact on HC was analyzed. Results reveal that, depending on the connection strategy, the BESS can increase as well as decrease the HC based on voltage unbalance criteria. However, the load voltage unbalance has little effect on the solar HC values.
  • Network capacity impact on the flexibility of local resources in green energy transition
    (2025-06) Bertè, Emanuele; Püvi, Verner; Jokinen, Ilkka; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This study explores the implications of reducing power capacity limits at the Point of Common Coupling (PCC) on residential energy systems, emphasizing the vital roles of both individual prosumers and energy communities in the transition towards distributed energy landscapes. As the integration of renewable energy sources and Home Energy Management Systems become increasingly common, Distribution System Operators (DSOs) encounter significant challenges in maintaining grid stability and operational efficiency. The analysis is structured to first examine individual users with diverse configurations and installation sizes. This initial focus reveals how limiting the power at the PCC restricts the prosumers’ local energy exports and grid imports, while simultaneously increasing net operating costs. Following this, the research expands to investigate the collective dynamics of an energy community, with a particular focus on the Community Connection Point (CCP). Employing a Mixed Integer Linear Programming optimization framework implemented in Python, the study demonstrates that strategic reductions in PCC capacity can effectively mitigate peak power demands. However, similarly to single households, this is achieved by the expense of the community, as their operating costs increase, while the exports of local generation and grid imports are restricted. The findings highlight the critical need for DSOs to adopt capacity management strategies that not only enhance grid stability but also empower energy communities to fully leverage their resource utilization. Otherwise, the grid may become a bottleneck for the sustainable energy transition, by hindering the adaption of local generation and preventing the flexible prosumer resources to assist the power system.
  • On PV Hosting Capacity of Distribution Networks
    (2023) Lehtonen, Matti; Püvi, Verner; Fatima, Samar; Pourakbari-Kasmaei, Mahdi
     A4 Artikkeli konferenssijulkaisussa
    This paper provides a summary of the research regarding photovoltaic hosting capacity of the distribution networks in Finnish circumstances. Characteristic to these circumstances is high and diverse seasonal variations of electricity demand and photovoltaic generation. The paper presents key findings of the hosting capacity and discusses different methods and approaches when analyzing the hosting capacity questions both from the distribution systems operator and the prosumer point of view.
  • Photovoltaic hosting capacity improvement based on the economic comparison between curtailment and network upgrade
    (2023-09) Fatima, Samar; Püvi, Verner; Pourakbari-Kasmaei, Mahdi; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The upcoming network investment decisions and regulatory framework adopted by distribution system operators (DSOs) are most likely to be impacted by the integration of fluctuating distributed generation. The economical hosting capacity (HC) improvement method is investigated in this paper as a trade-off between curtailment and upgrade using a Monte Carlo simulation procedure. The associated costs of both methods are vital indicators for network operators that are trying to maximize the HC and minimize cost. In addition, the breakeven point where curtailment and upgrade costs intersect is the decisive point at which network upgrade becomes sensible as marginal curtailment cost exceeds upgrade cost. A shift in global climate conditions can impact the photovoltaic (PV) levels that motivate network operators to investigate PV penetration, especially in colder climate regions. Thus, the primary objective of this paper is to investigate the shift of the breakeven point to guide DSOs to either adopt PV curtailment as a temporary measure or grid upgrade as a risk aversion strategy considering Finnish climate and load patterns. The real-time load and PV generation data are utilized for the simulations to consider the dynamic performance indication of three Finnish distribution networks. Curtailment remains a low-cost option to obtain a percentage HC rise of 13%, 7%, and 8% for rural, suburban, and urban regions, respectively, beyond which curtailment compensation cost surpasses upgrade cost. In essence, PV curtailment serves as an immediate and least-cost solution to relieve network violations and defer network investment until the HC level (118%, 106%, 97%) making the upgrade a practical option afterwards.
  • Photovoltaic Hosting Capacity Margin due to State Estimation Error
    (2024) Püvi, Verner; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The widespread adoption of distributed Photovoltaics (PV) has sparked a need for more accurate situational awareness in low-voltage distribution networks. This article presents various metering configurations which are compared in balanced and unbalanced conditions and different state estimation frequencies. Smart meter-derived pseudo-measurement configurations are compared to real-time metering in order to address the practical balance between the number of meters and state estimation accuracy. Moreover, a PV safety margin is presented as a margin of injected PV power that is equivalent to a voltage rise, which is derived from the estimation error. The results show a significant need to reduce the PV injected power to hold the estimated voltage below the actual voltage safely. For a network with just a few real-time measurements, the PV margin can reach tens of percentage points relative to the PV peak power. Additional real-time meters reduce the PV margin, however, the estimation accuracy saturates as more meters are added. Alternatively, the inaccuracy, and thus the PV margin, can be countered by the increased granularity of measured data.
  • Photovoltaic Hosting Capacity of Distribution Networks
    (2024) Püvi, Verner
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Due to an increasing share of renewable energy sources and widespread adoption of distributed photovoltaics (PV), the ability of the distribution networks to reliably interconnect new PV installations without hindering the power system's operation gained a lot of interest in the recent decade. Political support and falling prices of the photovoltaics make the panels available for as small as single household installations and some of the network operators have already reported the power quality issues caused by the PVs. To address this issue, this thesis investigates the PV hosting capacity (HC) of low-voltage distribution networks. The thesis is split into two main contributions centered around the power quality limitations of the HC and network structure influence on the HC. The thesis starts with a review of the HC definitions, its most common limiting factors, and reports on the results of a measurement campaign of low-voltage substations. In the first part, a Monte Carlo-based HC evaluation methodology is presented, which is used for the PV-only and energy storage-augmented scenarios. Alongside the single-phase PV installations, a voltage unbalance (VU) mitigation methodology is presented. Despite the VU being a very strict limit, it can be mitigated by relatively low power injections. Moreover, a comparison of PV curtailment and network reinforcement is presented to find the break-even points of the costs of the two. The second part of the thesis presents the distribution network's structure impact on the hosting capacity. A fixed set of customers is simulated with multiple feeding substations and a varying number of PV plants. The slime mold algorithm was proposed to be employed for generating numerous network topologies and its advantages over other algorithms were shown. The results revealed that around one-third of the customers can have PV installations until the HC is depleted. Voltage control can increase the HC, however remains the risk of possible need to change residential PV policies to sustain the current pace of PV installations. Finally, the thesis explores the practical side of the HC and analyzes the accuracy of distribution network state estimation. A PV safety margin is proposed, that represents an equivalent PV power that has to be curtailed in order to keep the estimated values below the actual values of the states.
  • Probabilistic Assessment of Hosting Capacity in Distribution Networks Considering Varying References and Network Losses
    (2021-06-14) Fatima, Samar
     Sähkötekniikan korkeakoulu | Master's thesis
    The transitioning of power distribution networks from passive towards active paradigm by integration of distributed generation gives rise to concerns regarding network stability due to operational bottlenecks. Therefore, maximum photovoltaic penetration, known as hosting capacity, is limited in distribution networks concerning technical and economical constraints. However, hosting capacity is case specific considering varying reference definitions and selection of performance constraints. A probabilistic approach has been adopted in this thesis to analyze the hosting capacity of three Finnish distribution networks depending on different references and economical constraints. The stochastic network analysis is based on Monte Carlo simulations to consider the random probability distribution of loads. The idea of hosting capacity is further extended towards finding economical hosting capacity subject to the performance constraint of network losses. An optimal network formation in terms of cables and transformer selection is carried out in the context of cost and benefit analysis. The inability of deterministic methods for assessing the probabilistic loads has been resolved by employing a large number of simulation scenarios for optimal modelling of network components. In addition, the influence of the amount of PV penetration on network losses is investigated in the context of finding the point of violation of network losses before and after the addition of PVs. Finally, a sensitivity analysis is carried out to consider the uncertainties in certain decisive parameters for network analysis and results are concluded.
  • A review of electric vehicle hosting capacity quantification and improvement techniques for distribution networks
    (2024-03) Fatima, Samar; Püvi, Verner; Lehtonen, Matti; Pourakbari-Kasmaei, Mahdi
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The electrification of the transport sector to control the carbon footprint has been gaining momentum over the last decade with electric vehicles (EVs) seen as the replacement for conventional internal combustion engines. Economic incentives, subsidies, and tax exemptions are also paving the way for rising EV penetration in the power distribution networks. However, the exponential EV adoption requires careful technical and regulatory analysis of traditional networks to satisfy the network reliability constraints. Therefore, it would be vital to find EV hosting capacity (HC) limits of networks from a multifaceted approach involving various market players, mainly distribution system operators and EV owners. This review provides a systematic categorization of EV hosting capacity evaluation and improvement methods, thus enabling researchers and industry personnel to navigate the advancing landscape of EVs. This novel framework extends beyond the theoretical implication of diverse objective functions and HC improvement methods to the actual numerical values of EV HC across varying geographical settings. Therefore, this unique synthesis of varying aspects of EV HC facilitates the in-depth understanding of the integration of sustainable energy and transport sector.
  • Review on the PV hosting capacity in distribution networks
    (2020-09) Fatima, Samar; Püvi, Verner; Lehtonen, Matti
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The increasing penetration of Photovoltaic (PV) generation results in challenges regarding network operation, management and planning. Correspondingly, Distribution Network Operators (DNOs) are in the need of totally new understanding. The establishment of comprehensive standards for maximum PV integration into the network, without adversely impacting the normal operating conditions, is also needed. This review article provides an extensive review of the Hosting Capacity (HC) definitions based on different references and estimated HC with actual figures in different geographical areas and network conditions. Moreover, a comprehensive review of limiting factors and improvement methods for HC is presented along with voltage rise limits of different countries under PV integration. Peak load is the major reference used for HC definition and the prime limiting constraint for PV HC is the voltage violations. However, the varying definitions in different references lead to the conclusion that, neither the reference values nor the limiting factors are unique values and HC can alter depending on the reference, network conditions, topology, location, and PV deployment scenario.
  • Slime Mold Inspired Distribution Network Initial Solution
    (2020-11-28) Püvi, Verner; Millar, Robert; Saarijärvi, Eero; Hayami, Ken; Arbelot, Tahitoa; Lehtonen, Matti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Electricity distribution network optimisation has attracted attention in recent years due to the widespread penetration of distributed generation. A considerable portion of network optimisation algorithms rely on an initial solution that is supposed to bypass the time-consuming steps of optimisation routines. The aim of this paper is to present a nature inspired algorithm for initial network generation. Based on slime mold behaviour, the algorithm can generate a large-scale network in a reasonable computation time. A mathematical formulation and parameter exploration of the slime mold algorithm are presented. Slime mold networks resemble a relaxed minimum spanning tree with better balance between the investment and loss costs of a distribution network. Results indicate lower total costs for suburban and urban networks.
  • Stochastic Assessment of Voltage Unbalance Mitigation by Battery System in case of Single-Phase Solar Generation
    (2018-02-12) Püvi, Verner
     Sähkötekniikan korkeakoulu | Master's thesis
    The political decisions and environmental problems apply a pressure on the research to utilize environmentally friendly energy sources and bring them to masses. However, the vast spread of renewable energy generation, such as solar power, adds an additional strain to electric power grid and damage the quality of the supplied electrical energy. In this thesis, stochastic assessment of the voltage unbalance mitigation by home battery system in low voltage grid with single-phase solar generation is analysed. The stochastic voltage unbalance assessment method based on Monte Carlo Simulation technique was utilised for two algorithms: time independent and time dependent. Both models were presented and results of each were compared. Three different battery phase connection strategies were modelled and voltage unbalance mitigation efficacy of each was evaluated. Three low voltage distribution grids are considered - rural, intermediate and urban - each grid representing different regions in Finland. The voltage unbalance at different solar and battery penetration levels was assessed and the most efficient battery connection strategy was revealed. Lastly, various aspects of the topic were discussed in the end.
  • Survey of a power quality measurement campaign in low-voltage grids
    (2019-06-01) Püvi, Verner; Tukia, Toni; Lehtonen, Matti; Kütt, Lauri
     A4 Artikkeli konferenssijulkaisussa
    With an increasing share of renewable energy generation becoming connected to distribution grids, power quality has attracted the attention of grid operators and academia. However, to obtain a realistic picture, power quality distortions caused by renewables should be superimposed on already existing emissions in grids. Measured household load data is tedious to acquire and is not publicly available. This paper presents the data from a low-voltage feeder measurement campaign and it is divided into voltage and feeder current analyses. The voltage parameters are validated as per EN 50160. The measured data includes measurements from feeders supplying single-family homes as well as one apartment building. A total of 24 weeks of 10-second mean values were recorded in the Helsinki region of Finland. Results indicate that the voltage quality is within the acceptable limits. The feeder currents show load unbalance in single-family homes and high utilisation rate of feeders supplying multiple customers.
  • Travel activity based stochastic modelling of load and charging state of electric vehicles
    (2021-02-02) Iqbal, Muhammad Naveed; Kütt, Lauri; Lehtonen, Matti; Millar, Robert John; Püvi, Verner; Rassõlkin, Anton; Demidova, Galina L.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The uptake of electric vehicles (EV) is increasing every year and will eventually replace the traditional transport system in the near future. This imminent increase is urging stakeholders to plan up-gradation in the electric power system infrastructure. However, for efficient planning to support an additional load, an accurate assessment of the electric vehicle load and power quality indices is required. Although several EV models to estimate the charging profile and additional electrical load are available, but they are not capable of providing a high-resolution evaluation of charging current, especially at a higher frequency. This paper presents a probabilistic approach capable of estimating the time-dependent charging and harmonic currents for the future EV load. The model is based on the detailed travel activities of the existing car owners reported in the travel survey. The probability distribution functions of departure time, distance, arrival time, and time span are calculated. The charging profiles are based on the measurements of several EVs.
  • Urban medium-voltage distribution network planning under a complete back-up regime
    (2020-09) Püvi, Verner; Millar, Robert; Saarijärvi, Eero; Anttila, Jaakko; Lepistö, Juhani; Loukkalahti, Mika; Hayami, Ken; Arbelot, Tahitoa; Klein, Martin; Lehtonen, Matti
     A4 Artikkeli konferenssijulkaisussa
    The thrust of this paper is to show how the reach of a planning algorithm can be extended to provide backup for urban distribution networks from adjacent primary substations, while also treating the planning constraints of thermally constrained networks with the likely increase in almost coincident loads such as electric vehicle charging, and the possible increase in coincident DER generation from increased roof-top photovoltaic production. An innovation is to use the slime mould algorithm to aid in producing a good initial network. The initial network is then passed to the planning algorithm to refine the final solution. The simulation results are based on realistic networks for target horizon Greenfield planning scenarios. The hypothetical (but relevant to consider) reduction in network investments that would result if the inter-primary substation back-up requirement is relaxed will also be explored.