Real LV Research Articles

Combined unbalanced distribution system state and line impedance matrix estimation

To address the challenges that the decarbonization of the energy sector is bringing about, advanced distribution network management and operation strategies are being developed. Many of these strategies require accurate network models to work effectively. However, distribution network data are known to contain errors, and attention has been given to techniques that allow to derive improved network information. This paper presents a novel method to derive line impedance values from smart meter measurement time series, with realistic assumptions in terms of meter accuracy, resolution and penetration. The method is based on unbalanced state estimation and is cast as a non-convex quadratically constrained optimization problem. Both line lengths and impedance matrix models can be estimated based on an exact nonlinear formulation of the steady-state three-phase network physics. The method is evaluated on both the IEEE European Low Voltage Feeder (906 buses) and a real Belgian LV feeder, showing promising results.

Grid‐aware provision and activation of fast and slow power flexibilities from distributed resources in low and medium voltage grids

AbstractThe intermittencies of renewable generations give rise to situations, which require both slow‐ and fast‐ramping flexibility capability from a variety of resources connected at the medium voltage (MV) andlow voltage (LV) distribution grids. Moreover, this may increase the grid reinforcement costs. To defer this reinforcement, the grid needs to be operated optimally. This paper proposes—(a) such an optimal operational methodology forthe MV and LV grids; and (b) an aggregated flexibility estimation methodology separately for fast and slow services at the primary substation (transmission interface). The methodologies based on model‐based MV grids and sensitivity coefficients‐based LV grids are suitable for LV grids where an up‐to‐date, accurate model and topology are not always available. Besides, the costs and resources associated to create full LV grid model and visibility should be prevented. The approaches, here, use the synchronised and accurate measurements from grid monitoring devices located at the LV distribution grids. They have been validated on a real MV and LV networks of a Swiss distribution grid operator equipped with such devices. The results, in terms of reducing technical losses, reducing grid violation costs,and estimating flexibility capability show the efficacy of the proposed methodologies and therefore, can be easily deployed.

Integration of PV Sources in Prosumer Installations Eliminating Their Negative Impact on the Supplying Grid and Optimizing the Microgrid Operation

This paper concerns the mitigation of voltage disturbances deteriorating power quality and disrupting the operation of LV distribution grids due to the high penetration of PV energy sources in prosumer installations. A novel control strategy for 3-phase 4-wire PV inverters is proposed, which ensures the transmission of PV active power and simultaneous compensation of load unbalance and reactive power, making the prosumer installation balanced and purely active. It results in the balance of phase voltages and the mitigation of their variability. Unlike other methods used for voltage regulation in LV grids, the proposed solution contributes to the reduction in losses, is simple, and does not require additional costs. In the paper, a control algorithm for the PV inverter is described. Its effectiveness was tested by simulation using a model of the real LV distribution grid developed in the PSCAD/EMTDC program. The results of the simulations are presented and evaluated.

Impact on Voltage Regulation in Medium Voltage Distribution Networks Due to the Insertion of Photovoltaic Generators

The objective of this paper was to analyze the impacts caused by the operation of voltage regulators in electrical distribution networks and to evidence the number of operations in the face of short-duration voltage variation caused by the high intermittency of the connected PV generators. A real LV and MV feeder was used, modeled in OpenDSS software, based on normative standards, adjustments, and technical maneuvers strategically used by the local utility. The analyses considered the temporal variations for the photovoltaic generators and different load demand profiles connected to the feeder. The feeder was submitted to the demand curves varying the load percentage, framing it in high and conventional (nominal) load according to the profiles of consumers and prosumers connected. The simulations made it possible to observe the exacerbated elevation in the number of maneuvers performed by the voltage regulators of the network. The single-phase voltage regulators stood out by the elevation of control operations, causing premature wear of the PV generation equipment connected to the most loaded phase. It was observed that discrepancies in the power flow in the lines and the voltage levels at the busbars. The creation of strategies and decisions to correct these impacts caused to transformers and regulators is possible.

Phase Balance Optimization of Customers and Electric Vehicles in a Real Low Voltage Electricity Distribution Network

Abstract Phase unbalance is a common issue encountered in LV electricity distribution networks, caused by uneven allocation of single-phase loads among phases. This paper analyses a part of a real LV distribution network, situated in Bosnia and Herzegovina. The impact of single-phase customers and single-phase charging of electric vehicles was analysed. To reduce unbalance and improve the voltage profiles, Phase Balance Optimization in DIgSILENT PowerFactory software was performed in six scenarios with different customer and electric vehicle unbalance. The goal was to find a method with the least number of changes in the customer and electric vehicle phase connection that fits within defined limits of voltage variations and voltage unbalance of a European norm for power quality (EN 50160). Results showed that all analysed scenarios were improved, with reference to voltage variation and voltage unbalance values, and were found acceptable by the limits from standard EN 50160.

Congestion control strategies for increased renewable penetration of photovoltaic in LV distribution networks

Domestic photovoltaic (PV) installations are increasing their spread due to decreased cost, environmental friendliness, and relatively easy installation. However, the massive domestic PV deployment can bring the LV network (LV) distribution network to its sustained operating limits, as overvoltage and congestion can arise. The overvoltage problems can emerge due to reverse power flows and congestion can be caused if the installed PV capacity is higher than the distribution line loading capacity. The limitations of the LV networks arise especially during the seasons when domestic power demand is minimal, and PVs are generating at their peak. The research presented here incorporates a real suburban LV network with fifteen residential users. The measured load and PV generation data for one year are used to carry out power flow simulations. Several congestion leveraging strategies such as battery energy storage system (BESS) incorporation, reactive power control (RPC), and curtailment of peaks are discussed.

An iterative quota calculation method for congestion management and optimal grid utilization

A quota-based approach can help grid operators deal with congestions in distribution grids in a non-discriminatory way for customers. The quota limits the maximum feed-in or consumption of a group of flexibility providing units (FPU) within a grid cluster. The novel iterative quota calculation (IQC) method is introduced in this paper. In this approach, the maximal active power limits of the FPU are constantly adapted, and the feasible operating region (FOR) of the grid is computed. The quota is computed from the resulting FORs after ensuring that the FPU operation cannot cause grid instability. The proposed method is compared to a previously developed static approach in a real LV grid. Results show the benefits of adding reactive power to the quota calculation, especially in distribution grids with inadequate reactive power compensation.

Benchmarking Various Pseudo-Measurement Data Generation Techniques in a Low-Voltage State Estimation Pilot Environment

Distribution system state estimation (DSSE) is a valuable step for DSOs toward tackling the challenges of transitioning to a more sustainable energy system and the evolution and proliferation of electric cars and power electronic devices. However, on the LV level, implementation has only taken place in a few pilot projects. In this paper, an LV DSSE method is presented and implemented in four real Hungarian LV supply areas, according to well-defined scenarios. Pseudo-measurement datasets are generated from AACs and SLPs, which have been used in different combinations on networks built with different accuracies in terms of load placement. The paper focuses on the critical aspects of finding accurate and coherent information on network topology with automated management of information systems, real LV network implementation for power flow calculation and managing portions of the network characterized by uncertain or inconsistent line lengths. A refining algorithm is implemented for the integrated network information system (INIS) models. The published method estimates node voltages with a relative error of less than 1% when using AACs, and a meter-placement method to reduce the maximum value of relative errors in future scenarios is also presented. It is shown that the observation of node voltages can be improved with the usage of AACs and SLPs, and with optimal meter placement.

Experimental Validation of a Dynamic Equivalent Model for Microgrids

The goal of this paper is the experimental validation of a gray-box equivalent modeling approach applied to microgrids. The main objective of the equivalent modeling is to represent the dynamic response of a microgrid with a simplified model. The main contribution of this work is the experimental validation of a two-step process, composed by the definition of a nonlinear equivalent model with operational constraints, adapted to the microgrid environment, and the identification procedure used to define the model parameters. Once the parameters are identified, the simplified model is ready to reproduce the microgrid behavior to voltage and frequency variations, in terms of active and reactive power exchanges at the point of common coupling. To validate the proposed approach, a set of experimental tests have been carried out on a real LV microgrid considering different configurations, including both grid-connected and islanded operating conditions. Results show the effectiveness of the proposed technique and the applicability of the model to perform dynamic simulations.

Management of Charging Load of Electric Vehicles for Optimal Capacity Utilisation of Distribution Transformers

A de-centralised load management technique exploiting the flexibility in the charging of Electric Vehicles (EVs) is presented. Two charging regimes are assumed. The Controlled Charging Regime (CCR) between 16:30 hours and 06:00 hours of the next day and the Uncontrolled Charging Regime (UCR) between 06:00 hours and 16:30 hours of the same day. During the CCR, the charging of EVs is coordinated and controlled by means of a wireless two-way communication link between EV Smart Charge Controllers (EVSCCs) at EV owners’ premises and the EV Load Controller (EVLC) at the local LV distribution substation. The EVLC sorts the EVs batteries in ascending order of their states of charge (SoC) and sends command signals for charging to as many EVs as the transformer could allow at that interval based on the condition of the transformer as analysed by the Distribution Transformer Monitor (DTM). A real and typical urban LV area distribution network in Great Britain (GB) is used as the case study. The technique is applied on the LV area when its transformer is carrying the future load demand of the area on a typical winter weekday in the year 2050. To achieve the load management, load demand of the LV area network is decomposed into Non-EV load and EV load. The load on the transformer is managed by varying the EV load in an optimisation objective function which maximises the capacity utilisation of the transformer subject to operational constraints and non-disruption of daily trips of EV owners. Results show that with the proposed load management technique, LV distribution networks could accommodate high uptake of EVs without compromising the useful normal life expectancy of distribution transformers before the need for capacity reinforcement.

Adaptive coordination of sequential droop control for PV inverters to mitigate voltage rise in PV-Rich LV distribution networks

This paper introduces an adaptive sequential droop control strategy for PV inverters to mitigate voltage rise problems in PV-rich LV distribution networks. To facilitate the effective coordination of sequential (Q−V and P−V) droop control of PV inverters, multiple control areas with the strong coupling nature of PV systems are identified based on the ε-decomposition technique. The droop control parameters are tuned and adapted, based on a consensus among PV inverters within each control area. This proposed control strategy inherits the autonomous feature of the droop control for coping with voltage rise issues while being able to avoid curtailing a significant amount of PV production. To evaluate the effectiveness of the proposed control strategy, simulations using MATLAB/Simulink are performed on a real European LV distribution network, considering a PV penetration level of about 150%. The obtained results highlight that the proposed control strategy successfully mitigates voltage rise problems while significantly reducing the amount of curtailed PV generation by approximately 35.6% and 76.2% when compared with the static sequential droop control and the static Q−V droop control and adaptive P−V droop control, respectively. Simultaneously, the effective contribution among all the PV systems towards voltage rise mitigation is obtained.

Management Information Systems and Data Science in the Smart Grid – Inner Class Area Capacity Distribution of the iSHM Class Maps of Overhead Low-Voltage Broadband over Power Lines Topologies

On the basis of the initial Statistical Hybrid Model (iSHM), the iSHM class maps, which are 2D contour plots and may graphically classify the real and virtual OV LV BPL topologies into five class areas, are upgraded in this paper by exploiting the third dimension of the capacity so that the upgraded class maps can provide additional information concerning the inner class area capacity distribution. The comprehension of the behavior of the inner class area capacity distribution is critical in order to deeper understand the extent and the position of iSHM class map footprints when various operation conditions of OV LV BPL topologies occur. Two inner class area capacity distribution rule of thumbs that deal with the OV LV BPL topology classification and capacity estimation are proposed thus supporting the management information system of OV LV BPL networks. Citation:  Lazaropoulos, A. G. (2020). Management Information Systems and Data Science in the Smart Grid – Inner Class Area Capacity Distribution of the iSHM Class Maps of Overhead Low-Voltage Broadband over Power Lines Topologies. Trends in Renewable Energy, 6(3), 245-265. DOI: 10.17737/tre.2020.6.3.00122

Business Analytics and IT in Smart Grid – Part 1: The Impact of Measurement Differences on the iSHM Class Map Footprints of Overhead Low-Voltage Broadband over Power Lines Topologies

Due to the smart grid (SG) operation, the power utilities are dealing with a cataclysm of big data that demands advanced information technology (IT) infrastructure and business analytics while one cause of this growth is the nature of the power grid operation that demands real-time measurements. In [1], [2], the theoretical framework and the numerical results for the interoperability of Deterministic Hybrid Model (DHM), initial Statistical Hybrid Model (iSHM), the definition procedure and the class maps have been presented for the overhead low-voltage broadband over power lines (OV LV BPL) networks as well as the iSHM footprints. On the basis of the five real indicative OV LV BPL topologies of [1], [2], the impact of measurement differences that follow either continuous uniform distributions (CUDs) or normal distributions (NDs) of different intensities is first highlighted on iSHM footprints. Citation: Lazaropoulos, A. G. (2020). Business Analytics and IT in Smart Grid – Part 1: The Impact of Measurement Differences on the iSHM Class Map Footprints of Overhead Low-Voltage Broadband over Power Lines Topologies. Trends in Renewable Energy, 6, 146-176. DOI: 10.17737/tre.2020.6.2.00117

Statistical Channel Modeling of Overhead Low Voltage Broadband over Power Lines (OV LV BPL) Networks – Part 1: The Theory of Class Map Footprints of Real OV LV BPL Topologies, Branch Line Faults and Hook-Style Energy Thefts

Due to the significant volatility of Broadband over Power Lines (BPL) networks regarding their circuital and topological characteristics, channel statistical modeling recently gains special attention from the BPL communications engineers. Among the recently presented channel attenuation statistical models, initial statistical hybrid model (iSHM) and modified statistical hybrid model (mSHM) have been theoretically defined and applied to overhead medium voltage (OV MV), underground medium voltage (UN MV) and overhead high voltage (OV HV) BPL networks so far. Apart from the iSHM and mSHM definition and application, the theory of the definition procedure of new virtual distribution and transmission BPL topologies, which describes the phases towards defining statistically equivalent BPL topologies and topology subclasses to the real indicative ones, has been demonstrated as well as the class maps, which are 2D capacity contour plots with respect to the channel attenuation statistical distributions (CASDs) parameters of iSHM and mSHM. In this pair of papers, iSHM, mSHM, the definition procedure of new virtual BPL topologies and the class mapping are first applied to overhead low voltage (OV LV) BPL networks. Based on the class maps and the BPL topology database of Topology Identification Methodology (TIM), the required theory for illustrating the footprint of the real OV LV BPL topologies is first presented on class maps in this paper. On the basis of the class maps and the BPL topology database of Fault and Instability Identification Methodology (FIIM), the required theory for illustrating the footprint of the OV LV BPL topologies with branch line faults is first identified on class maps in this paper. On the basis of the class maps and the BPL topology database of hook style energy theft detection method (HS-DET method), the required theory for illustrating the footprint of the OV LV BPL topologies with a hook style energy theft is first demonstrated on class maps in this paper. Citation: Lazaropoulos, A. G. (2020). Statistical Channel Modeling of Overhead Low Voltage Broadband over Power Lines (OV LV BPL) Networks – Part 1: The Theory of Class Map Footprints of Real OV LV BPL Topologies, Branch Line Faults and Hook-Style Energy Thefts. Trends in Renewable Energy, 6, 61-87. DOI: 10.17737/tre.2020.6.1.00112

New analytical method for analysing the effectiveness of infrastructure reinforcement in electric power distribution systems

Technical problems are emerging in electric power distribution systems caused by the recent widespread deployment of new technologies of load, as the plug-in electric vehicles, and generation, as the photovoltaic generators. This fact has increased the volume of studies to evaluate the effectiveness of solutions based on infrastructure reinforcement. In this context, this work proposes an analytical method to update values of voltage magnitude in distribution systems when transformers and/or conductors are replaced. This analytical formulation can be implemented in spreadsheets for single-case analyses or it can be integrated in more-complex approaches, which demand multiple solutions, such as in optimization-based or Monte Carlo-based approaches. For the more-complex approaches the main objective is to speed up the process, as it is not necessary to run several power flows. In this work, the analytical formulation is integrated into a Monte Carlo-based process with two objectives: (a) to supply a wide-scale assessment of reinforcements to increase the electric vehicles hosting capacity in low voltage distribution systems analysing 25,000 real LV systems of a local utility; (b) to supply a systematic and wide validation of the analytical formulation. The results showed that it speeds up the process keeping relatively high accuracy.

Models for characterising the final electricity demand

Nowadays the consumption and generation profile estimation is of the greatest importance. New loads characterized by coincident peak of consumption (e.g., home charging of electric vehicles) or by high absorption peaks (heat pumps) are increasingly frequent. The presence of such loads must be carefully considered for network investments and for the optimization of asset management. Moreover, the massive diffusion of non-programmable renewable sources gives a leading role to the flexibility of demand, which is crucial for the success of the energy transition. The variety and difference of the electrical behaviour of LV customers, even nominally homogeneous, need stochastic methods for estimating the load profile on the LV/MV interfaces for the planning and the operation of distribution network, and for estimating the flexibility potential of demand. In this paper different techniques for modelling the demand composition are compared to evaluate the quality of the DSO models on real customers. In particular, the power peak of a given network section is calculated as key indicator for estimating the risk of overloading of lines and secondary substation transformers. Different methods of calculation have been applied on a dataset gathered with a recent measurement campaign in Italy by considering real LV distribution networks.

Smart Meter Data-Based Three-Stage Algorithm to Calculate Power and Energy Losses in Low Voltage Distribution Networks

In this paper, an improved smart meter data-based three-stage algorithm to calculate the power/energy losses in three-phase networks with the voltage level below 0.4 kV (low voltage—LV) is presented. In the first stage, the input data regarding the hourly active and reactive powers of the consumers and producers are introduced. The powers are loaded from the database of the smart metering system (SMS) for the consumers and producers integrated in this system or files containing the characteristic load profiles established by the Distribution Network Operator for the consumers, which have installed the conventional meters non-integrated in the SMS. In the second stage, a function, which is based on the work with the structure vectors, was implemented to easily identify the configuration of analysed networks. In the third stage, an improved version of a forward/backward sweep-based algorithm was proposed to quickly calculate the power/energy losses to three-phase LV distribution networks in a balanced and unbalanced regime. A real LV rural distribution network from a pilot zone belonging to a Distribution Network Operator from Romania was used to confirm the accuracy of the proposed algorithm. The comparison with the results obtained using the DigSilent PowerFactory Simulation Package certified the performance of the algorithm, with the mean absolute percentage error (MAPE) being 0.94%.

A novel methodology for the management of distribution network based on neutral losses allocation factors

A multi-phase losses allocation method is proposed to provide explicit information about losses allocated to the neutral conductor. This information from the proposed methodology can be utilized by distribution system operators in the identification of highly unbalanced nodes in a network and consequently, allows them to implement suitable unbalance compensation schemes at these nodes in order to improve network balancing. The newly developed approach, based upon neutral losses allocation factors, reduces the unbalance in a network by switching single-phase loads across phases of highly unbalanced nodes. Two-phase switching algorithms, based upon individual and combined load commutation, are proposed to achieve this objective. The developed technique is implemented on a real LV Italian distribution network by adopting real customer’s power profiles. Results indicate a significant improvement in network balancing and losses reduction, which clearly represent the positive active role that neutral losses allocation factors can play in the assessment and management of distribution networks.

Effectiveness of BPSK Modulation With Peak Noise Avoidance Algorithm in Smart Street Lighting Communications Based on PLC

Abstract This work reports the measurement results of long-terms tests obtained in real smart street lighting LV networks and in lab test bed. The measurements results are presented in the form of PER vs. SNR characteristics for BPSK coded and BPSK coded with peak noise avoidance algorithm. The surprising results obtained from real LV networks prompted the Authors to carry out detailed lab tests. The setup for lab tests is also presented in this work. To carry out lab tests a suitable software was prepared, it allowed to obtain results in 72 times shorter time comparing to real conditions; it is why this work can present characteristics of PER vs. SNR even for the values of PER at the level of 10−9. The work concludes with disadvantages of using the peak noise avoidance algorithm in PLC communication for smart street lighting.

THE APPLICATION OF SEMI-EMPIRICAL METHODS OF SOUND PRESSURE LEVELS EVALUATION FOR THE ANALYSIS OF LOADS ON BAYS IN SLV

The problem of sound spectra evaluation around the bays of an LV during the supersound flight is considered in the article. In order to perform the evaluation four different evaluation methods of pressure pulsations spectral density proposed by Efimtsev, Laganelli, Robertson and Chase-Howe are used.After the sound power spectra calculated by each of four evaluation methods have been compared with the measured sound power values on the real LV, the Chase-Howe method has been chosen as the most accurate one in the matter of describing the actual physical processes.The initial data for the calculation of sound power spectra have been obtained from the results of finite-element modeling of super-sound flow around the fairing, performed in the Ansys 17.0. (Fluent module).