Showing papers by "Matti Lehtonen published in 2018"
TL;DR: In this article, an energy demand model is proposed for net-zero energy building (NZEB) definitions to represent personal mobility in the building's energy balance, and a mixed-integer linear optimization scheme is developed to address the energy management problem related to the aforementioned energy balance model.
56 citations
TL;DR: The Hosting Capacities (HCs), of Photo-Voltaic (PV), were found for various regions and their limiting constraints were defined, and comparison was made with the HC values obtained for different voltage value standards defined by various countries.
Abstract: 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.
31 citations
TL;DR: In this article, the optimal sizing and control of the hydrogen energy storage system for increased utilization of renewable generation is investigated using a Finnish case study, and sensitivity analyses are conducted to observe the impact of a small share of controllable baseload production as well as the oversizing of renewable power in terms of required hydrogen storage size.
Abstract: From an environment perspective, the increased penetration of wind and solar generation in power systems is remarkable. However, as the intermittent renewable generation briskly grows, electrical grids are experiencing significant discrepancies between supply and demand as a result of limited system flexibility. This paper investigates the optimal sizing and control of the hydrogen energy storage system for increased utilization of renewable generation. Using a Finnish case study, a mathematical model is presented to investigate the optimal storage capacity in a renewable power system. In addition, the impact of demand response for domestic storage space heating in terms of the optimal sizing of energy storage is discussed. Finally, sensitivity analyses are conducted to observe the impact of a small share of controllable baseload production as well as the oversizing of renewable generation in terms of required hydrogen storage size.
23 citations
TL;DR: A two-layer optimization model is introduced, where in the outer layer, an iterative algorithm is applied to determine the optimal set of long-term projects including Distributed Generations (DGs) installation and results show the strong influence of incentive regulation on reliability indices.
Abstract: Incentive regulations of reliability have made a link between distribution companies' revenue and their service reliability. The companies have to decide how much to spend on various projects to provide an acceptable level of reliability while anticipation of load growth. Planners and decision makers require a comprehensive framework to optimally allocate available budgets to different plans with the highest benefits considering implementation of incentive regulation. This paper proposes a decision framework for the optimum share of expansion and reliability oriented plans in presence of reward–penalty mechanisms. A two-layer optimization model is introduced, where in the outer layer, an iterative algorithm is applied to determine the optimal set of long-term projects including Distributed Generations (DGs) installation. A heuristic optimization algorithm is employed in this layer. Considering long-term plans, in inner optimization layer, the optimal set of mid-term plans including feeder reinforcement, and preventive maintenance actions are determined using algorithms such as Branch-and-Cut and dynamic programming techniques. The model is further implemented on a test distribution network and the results are investigated through various case studies. Obtained results show the strong influence of incentive regulation on reliability indices.
16 citations
TL;DR: This work aimed at maximizing the self-consumption of on-site photovoltaic (PV) generation using an electrical storage, as well as demand response solutions, in a building that was also capable of interacting with the main grid.
Abstract: Efficient utilization of renewable generation inside microgrids remains challenging In most existing studies, the goal is to optimize the energy cost of microgrids by working in synergy with the main grid This work aimed at maximizing the self-consumption of on-site photovoltaic (PV) generation using an electrical storage, as well as demand response solutions, in a building that was also capable of interacting with the main grid Ten-minute resolution data were used to capture the temporal behavior of the weather Extensive mathematical models were employed to estimate the demand for hot-water consumption, space cooling, and heating loads The proposed framework is cast as mixed-integer linear programming model while minimizing the interaction with the grid To evaluate the effectiveness of the proposed framework, it was applied to a typical Finnish household Matching indices were used to evaluate the degree of overlap between generation and demand under different PV penetrations and storage capacities Despite negative correlation of PV generation with Finnish seasonal consumption, a significant portion of demand can be satisfied solely with on-site PV generation during the spring and summer seasons
16 citations
TL;DR: An elevator group control scheme to organize the elevator dispatching according to the simulated passenger traffic and enhanced predictions about the energy and power consumption of elevators in a specific type of building with measured or simulated movement of occupants are yielded.
Abstract: This paper proposes a framework for modeling the instantaneous power consumption of individual elevators and elevator groups based on passenger traffic. Though elevators have a key role in the modern urban society, they have remained as rather neglected appliances in the energy efficiency research. To accelerate the energy efficiency studies of elevators, this paper has two major contributions. First, we propose means to model the instantaneous power consumption of individual elevators and elevator groups and analyze the reliability of these means versus the complexity of the modeling. Second, we present an elevator group control scheme to organize the elevator dispatching according to the simulated passenger traffic. When combined, these methods yield enhanced predictions about the energy and power consumption of elevators in a specific type of building with measured or simulated movement of occupants.
15 citations
19 Sep 2018
TL;DR: In this paper, a solution casting method was used to enhance PD activity of polyvinyl chloride (PVC) with the insertion of chemically functionalized silicon dioxide (SiO 2 ) nanoparticles through using solution casting.
Abstract: Partial discharges (PDs) diagnostics are necessary to monitor and detect any abnormal conditions such as; impurities or cavities during the manufacturing process of insulating materials of power cables. This paper aims to enhance PD activity of polyvinyl chloride (PVC) with the insertion of chemically functionalized silicon dioxide (SiO 2 ) nanoparticles through using the solution casting method. The surface functionalization of SiO 2 was performed using amino silane as a coupling agent after activating their surfaces with methanesulfonic acid. Then, PVC/SiO 2 nanocomposites, with different loadings of nanoparticles (0.5, 3%), were synthesized with the aid of ultra-sonication for better dispersion of nanoparticles. After that, the internal discharge measurements were performed using the traditional needle-plane configuration with the help of phase resolved partial discharge analyzer (PRPDA) that analyzes the statistical characteristics of PDs pattern. It is found that the PD activity of PVC/SiO 2 amino-functionalized nanocomposite samples that represented by discharge magnitude, inception voltage, extinction voltage, and the PD generation rate was enhanced compared to that of the PVC/SiO 2 un-functionalized nanocomposites or neat PVC samples. This is because the addition of SiO 2 nanoparticles was increased the trapping sites inside the insulating material and the generation rate of initial electrons will be reduced, resulting in further decrease in PD activities.
13 citations
TL;DR: In this article, an improved methodology for the detailed statistical modeling of wind power generation from multiple new WPPs without measurement data is proposed. But the model is limited to the case of single WPP.
Abstract: In future power systems, a large share of the energy will be generated with wind power plants (WPPs) and other renewable energy sources. With the increasing wind power penetration, the variability of the net generation in the system increases. Consequently, it is imperative to be able to assess and model the behavior of the WPP generation in detail. This paper presents an improved methodology for the detailed statistical modeling of wind power generation from multiple new WPPs without measurement data. A vector autoregressive based methodology, which can be applied to long-term Monte Carlo simulations of existing and new WPPs, is proposed. The proposed model improves the performance of the existing methodology and can more accurately analyze the temporal correlation structure of aggregated wind generation at the system level. This enables the model to assess the impact of new WPPs on the wind power ramp rates in a power system. To evaluate the performance of the proposed methodology, it is verified against hourly wind speed measurements from six locations in Finland and the aggregated wind power generation from Finland in 2015. Furthermore, a case study analyzing the impact of the geographical distribution of WPPs on wind power ramps is included.
11 citations
TL;DR: The results show that the proposed MAS based coordinated RPC and APC of inverters will keep the voltage value of nodes within the statutory limit, with least curtailment possible.
11 citations
9 citations
01 Oct 2018
TL;DR: Investigating the Finnish LV grids of geographically dispersed areas for the voltage flicker problem due to solar irradiance fluctuations and instantaneous-active/reactive power-control methodology for PV, it was observed that the employment of the devised control strategy significantly improved the long-term flicker index at the weakest grid node.
Abstract: In recent years, renewable energy sources, especially Photo- Voltaics (PVs), are being integrated into the Low-Voltage (LV) grid in massive numbers. Inherently, intermittent nature of PVs may cause power quality issues like the voltage rise and the flicker. Firstly, this paper investigates the Finnish LV grids of geographically dispersed areas, for the voltage flicker problem due to solar irradiance fluctuations. Secondly, instantaneous-active/reactive power-control methodology for PV is proposed for flicker problem mitigation. It makes use of the short-circuit impedance value of the feeder from the transformer till the point of PV connection and active power fluctuations, for reactive-power compensation calculation. However, during the peak generation period, the PVs are to be momentarily curtailed to reduce the voltage fluctuation, hence flicker. To support the proposed strategy, simulations are conducted on MATLAB, on various grids differing in topologies. The results reveal the correlation between voltage flicker and solar irradiance fluctuation and it was observed that the employment of the devised control strategy significantly improved the long-term flicker index at the weakest grid node.
TL;DR: The directional distance function and shadow pricing method is used for a case study from Finland with the aim of calculating the cost of one minute of power interruption from the perspective of the distribution network operator.
Abstract: Increasing distributed generation and intermittencies, along with the increasing frequency of extreme weather events, impose a serious challenge for electric power supply security. Understanding the costs of interruption is vital in terms of enhancing the power system infrastructure and planning the distribution grid. Furthermore, customer rights and demand response techniques are further reasons to study the worth of power reliability. In this paper, the authors make use of directional distance function and shadow pricing methods in a case study of Finland. The aim is to calculate the cost of one minute of power interruption from the perspective of the distribution network operator. The sample consists of 78 distribution network operators from Finland, and uses cost and network information between 2013 and 2015.
TL;DR: Novel solution is presented for inductance control of power reactors which is carried out by developing a virtual air gap (VAG) within the core by using simulation environment of finite-element method (FEM).
Abstract: Smart grid technologies require advances in various conventional solutions where efficient control of the inductance of reactors is of a significant interest for utilities. Novel solution is presented for inductance control of power reactors which is carried out by developing a virtual air gap (VAG) within the core. The impact of VAG on the magnetisation behaviour of the transformer core has been analysed by using simulation environment of finite-element method (FEM). Experimental investigation is carried out to observe the performance of VAG for intended inductance variation. Using proposed technique reactor inductance can be tuned in the range of 1 : 20 in less than a millisecond with a significant reduction in harmonics. Implementation of such fast, linear and magnetically controlled inductance along with suitable intelligence can be valuable to enhance smart grid technology for improved integration of renewables and grid optimisation.
25 Jun 2018
TL;DR: In this paper, different open phase conditions (OPCs) and their influence on an induction motor were investigated, including single and double line OPCs on the primary-side of a transformer supplying the motor.
Abstract: Open phase faults can result in motor overloading due to unbalanced voltage. The present paper investigates different open phase conditions (OPCs) and their influence on an induction motor. The considered conditions include single and double line OPCs on the primary-side of a transformer supplying the motor. Several different transformer connections are investigated. The OPCs are first analyzed analytically with symmetrical components, after which the results are compared with simulated values. Measurements are performer to showcase the stator temperature evolution under OPC and to validate the numerical results. The results indicate that in the case of single OPC, only moderate unbalance is observed with YNd and YNyn transformer connection, whereas the highest phase current occurs with Dyn connection.
10 Dec 2018
TL;DR: A stochastic 24-hour ahead rolling window optimal energy scheduling framework to minimize the amount of lost load and lost generation in islanded MG while considering the demand response (DR) potential of heating, ventilation & air-conditioning (HVAC) loads, end user thermal preferences and storage systems.
Abstract: The integral variability of electricity demand and intermittency of renewable energy resources (RERs) pose special challenges in the operation of islanded Microgrid (MG). The uncertainty associated with load and generation data further magnifies the problem resulting in huge energy curtailments in real time thus making MG operation expensive. Hence, this paper proposes a stochastic 24-hour ahead rolling window optimal energy scheduling framework to minimize the amount of lost load and lost generation in islanded MG while considering the demand response (DR) potential of heating, ventilation & air-conditioning (HVAC) loads, end user thermal preferences and storage systems. These thermal characteristics are modeled via two-capacity building model. The proposed methodology is formulated as a stochastic linear programming problem. The effectiveness of the framework is validated by simulation for the entire winter season using realistic data. Ultimately, the results are used to calculate and control loss of load probability (LOLP) and loss of load expectation (LOLE) in islanded MG at minimum cost.
TL;DR: In this paper, a framework from the distribution system operator's perspective for the optimal utilization of demand response (DR) between DG curtailment mitigation and network management is proposed. But, the application of the developed framework to a generic Finnish distribution system demonstrates that the benefits of DR should be envisioned for network management as long as the wind curtailment rate is below a certain level.
Abstract: In power systems today, considerable developments are being made in the energy transition from centralized fossil fuels to renewable distributed generation (DG) sources. However, this ongoing progress has presented several challenges to the operation and planning of distribution systems due to the variability of intermittent renewable generation. Demand response (DR) is widely regarded as a feasible tool to provide a seamless transition by altering the load profiles according to the intermittent generation profile. However, the resultant volatile power flows can be taxing for network capacity. This paper offers a framework from the distribution system operator's perspective for the optimal utilization of DR between DG curtailment mitigation and network management. The application of the developed framework to a generic Finnish distribution system demonstrates that the benefits of DR should be envisioned for network management as long as the wind curtailment rate is below a certain level. This means that, beyond the threshold energy curtailment rate, the distribution system operator would be more economically efficient by making network reinforcements.
10 Dec 2018
TL;DR: The mitigation possibilities of the VU caused by single-phase-connected photovoltaics (PV) are analysed with Tesla Powerwall 2 battery energy storage systems (BESS) added to the grid.
Abstract: Modern electrical power system is evolving to a smarter and agile system, which will support society's sustainable development. The low voltage grid should be capable of withstanding new challenges such as reverse power flows and voltage unbalance (VU) caused by distributed generation. In this paper, the mitigation possibilities of the VU caused by single-phase-connected photovoltaics (PV) are analysed with Tesla Powerwall 2 battery energy storage systems (BESS) added to the grid. Three different BESS phase connection strategies are modelled and the VU is assessed with Monte Carlo Simulation (MCS). A low voltage distribution grid in Sweden is considered with different PV and BESS penetration levels and the applied method for VU assessment is validated. Simulation results reveal the effectiveness of VU mitigation by connecting PV and BESS to the same phase.
10 Dec 2018
TL;DR: This paper makes use of two existing cost estimation techniques and suggests a simple and straightforward methodology which will provide sound and reliable estimations in an objective manner by relying solely on publicly available analytical data.
Abstract: Basic There is increasing attention on the estimation of the customer interruption costs. The existing studies adopt indirect analytical methods, customer surveys and case studies to evaluate these costs. This paper makes use of two existing cost estimation techniques and suggests a simple and straightforward methodology which will provide sound and reliable estimations in an objective manner by relying solely on publicly available analytical data, The study is based on 78 Finnish Distribution System Operators' 2016 energy and reliability data. In addition, the standard customer compensation scheme in Finland is briefed and the results are compared with the power interruption cost estimations.
TL;DR: It is shown that the best way to control the frequency response is to adjust the distance between LV and HV windings while maintaining other clearances as short as possible; realizing limitations enforced by other insulation constraints.
Abstract: A wind turbine transformer resonance can occur due to high frequency transients at its terminal i.e.; under its energization through a length of cable. Occurrence of resonance can be addressed by a sophisticated transformer design procedure. The goal is to obtain an optimum design capable of controlling the frequency response of the winding in such a way to avoid occurrence of any resonance under transient conditions. Three insulation clearances parameters which are employed for the wind turbine transformer winding design have been investigated in design of a (800 kVA, 690/20,000 V) wind turbine transformer to determine effect of their variation on its frequency response. It is shown that the best way to control the frequency response is to adjust the distance between LV and HV windings while maintaining other clearances as short as possible; realizing limitations enforced by other insulation constraints. Multiple-design algorithm is also investigated and found to be effective in control of the amplification factor under resonance frequency condition. Finally a 20 kV/690 V-400 kVA dry type wind turbine transformer is employed to verify the promising features of this design methodology, through comparison of the frequency responses of the real transformer against the model.
22 May 2018
TL;DR: An adaptive de-noising technique based on discrete wavelet transform (DWT), capable of de- noising the measured signals automatically without any human intervention is presented in this paper and proves that it is simple, effective and reliable in terms of run time which makes it more useful for online monitoring application.
Abstract: Partial Discharge (PD) detection and measurement are considered as reliable source of information related to early signs of insulation degradation in order to avoid complete breakdown and longer power outages. During the last decade, the online PD measurements and self healing networks gained significant interest over the periodic maintenance. However, online measured signals are suppressed by high frequency noise, therefore, de-noising of measurements is of paramount importance to get reliable information about a fault. An adaptive de-noising technique based on discrete wavelet transform (DWT), capable of de-noising the measured signals automatically without any human intervention is presented in this paper. The major challenges in using DWT such as wavelet function selection and reconstruction of de-noised signals are addressed. A simple criteria about selection of decomposition coefficients based on dominant frequency and amplitude is used in the presented algorithm. The de-noising performance is evaluated by comparing with other techniques such as correlation based wavelet selection and energy based wavelet selection methods. The results prove that adaptive de-noising is simple, effective and reliable in terms of run time which makes it more useful for online monitoring application.
20 Sep 2018
TL;DR: The paper estimates the potential contribution of elevators to a VPP-provided service as well as the adverse impact on traffic performance f or different elevator types in hourly granularity for weekdays and weekends.
Abstract: This paper analyzes the potential of applying elevators in power system frequency containment reserves (FCR). As an example, the study employs the Finnish FCR market structure. The markets are split into two segments: frequency containment reserves for normal operation (FCR-N) and for disturbances (FCR-D). Both of the markets have distinct minimum bid sizes and thresholds for the maximum allowed delay for activating the reserves. The paper uses a unique elevator simulator to assess the power consumption profiles of common elevator setups. Then, the elevators are aggregated into a virtual power plant (VPP) and controlled with a variety of approaches to rank the effectiveness of each control method. As a result, the paper estimates the potential contribution of elevators to a VPP-provided service as well as the adverse impact on traffic performance f or different elevator types in hourly granularity for weekdays and weekends.
20 Sep 2018
TL;DR: The cost of demand response for vertical transports by means of speed reduction for elevators and escalators in terms of lost customer hours is analyzed to indicate positive applicability of such strategy in vertical transportation.
Abstract: Vertical transportation systems are designed to enhance the people flow. T he power c onsumption of escalators and elevators depends on applied technology, control strategies and passenger flow. Vertical transports are often e quipped with energy saving technologies and are eligible for demand response (DR). DR for vertical transports results in induced costs related to increased passenger travel and waiting times. In this article, we analyze the cost of DR by means of speed reduction for elevators and escalators in terms of lost customer hours. We use modeling approaches to simulate passenger time delays and aggregated power consumption of a large number of escalators and elevators. The results further indicate positive applicability of such strategy in vertical transportation.
10 Dec 2018
TL;DR: The results indicate that vertical transportation is able to contribute to the frequency support with little impact on the aggregate travel time of passengers, however, the capability is limited during the most likely periods of low system inertia, which, in the Nordic power system, occur during summer nights.
Abstract: Displacement of conventional generation with inverter-fed renewable generation hampers power system stability due to a decrease in rotating masses and spinning reserves. This reduction in inertial response capability requires more advanced power system design and innovations in frequency control technology and related power system balancing markets. This paper investigates the potential of applying vertical transportation devices to provide the system with virtual inertia to maintain the frequency quality. The study focuses on the Nordic power system and considers the demand response from both elevators and escalators. The results indicate that vertical transportation is able to contribute to the frequency support with little impact on the aggregate travel time of passengers. However, the capability is limited during the most likely periods of low system inertia, which, in the Nordic power system, occur during summer nights.
01 Nov 2018
TL;DR: In this paper, the authors analyzed the customer interruption cost (CIC) evaluation techniques and presented some results of CIC due to unexpected outages, obtained by different methods, including direct worth estimation, willingness to pay and willingness to accept methods.
Abstract: Supply reliability is an important factor to be considered when planning and developing modern power distribution systems. If reliability value is expressed in monetary terms, it can be used as one input parameter when optimizing the electrical distribution systems and when developing regulation. This paper analyses the customer interruption cost (CIC) evaluation techniques and presents some results of CIC due to unexpected outages, obtained by different methods. The methods first discussed are customer surveys including direct worth estimation, willingness to pay and willingness to accept methods. As another group of methods, different indirect analytical methods are considered. The cases explored are residential, industrial, commercial and public customers in Finland.
12 Feb 2018
TL;DR: The voltage unbalance (VU) caused by single-phase connected photovoltaics (PV) in residential low voltage grid are assessed by Monte Carlo Simulation (MCS) and battery energy storage system (BESS) mitigation possibilities are evaluated.
Abstract: The electric power system face big challenges today. Environmental concerns and political decisions that follows, are up to reshape electrical energy industry and change the way how energy is managed. One of the key ideas of forthcoming changes is to utilise renewable energy sources, such as solar. However, solar generation, as any other distributed generation, sets strain on the power system and power quality properties can be negatively affected. In this paper, the voltage unbalance (VU) caused by single-phase connected photovoltaics (PV) in residential low voltage grid are assessed by Monte Carlo Simulation (MCS). The voltage unbalance mitigation possibilities by battery energy storage system (BESS) are evaluated, by connecting the battery in a three different phase connection strategies. Two different stochastic assessment models will be tested: time independent and time series models. The results of the two models are presented and discussed in depth.
TL;DR: In this article, the authors presented a simple and straightforward methodology which can provide credible and objective estimations utilizing only publicly available analytical data, and highlighted regional differences in CIC estimations in different parts of Finland and provided a critical overview of the existing standard customer compensation scheme in Finland.
Abstract: Estimating the worth of continuity of electricity supply is of interest to industry, governments, regulators and the research community. There are numerous methods to calculate the Customer Interruption Costs (CICs). Each method has its advantages and disadvantages. We approach the problem from the Distribution System Operator (DSO) point of view and employ two existing analytical models. One model is used by the Finnish Energy Market Authority and the second one was proposed by some of the authors in a previous study. Our model offers a simple and straightforward methodology which can provide credible and objective estimations utilizing only publicly available analytical data. We made use of cost and reliability indices data of 78 DSOs in Finland from the 2016. In addition to cost estimations, we highlight regional differences in CIC estimations in different parts of Finland and provide a critical overview of the existing standard customer compensation scheme in Finland.
TL;DR: For the IN region, the constraints of E4 (−5% and 0% MV changes) and E3 (+5% MV rise case) were violated as discussed by the authors, and the same constraints were violated as in the balanced feed-in scenario.
Abstract: Moreover, on page 10 the paragraph describing table 6 findings, also requires one line change. The correct expressions are given as “For the IN region, the constraints of E4 (−5% and 0% MV changes) and E3 (+5% MV rise case) were violated.” Instead of “For the IN region for all MV values, the same constraints of E3 and E7 were violated as in the balanced feed-in scenario.” The manuscript will be updated, and the original one will remain available on the article webpage.