Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

Design and implementation of hybrid series compensators for smart grid applications

The vision of future modern grids goes through the increase of renewable énergies penetration while providing an efficient, reliable and sustainable power supply to consumers. According to the recent report on climate challenging the way electrical energy is produced and because of the rapid emerging of power electronics based equipment; some serious actions should be engaged. In order to achieve such promoting visions, all power grids are required to become smarter especially at the distribution level. Increasing the application of renewable energy sources and distributed generations assist these vision in the development of a modern power grid where modern equipment are becoming highly sensitive to the supplied voltage quality. Moreover, in this paradigm of design, the traditional power systems based on large concentrated power plants should be able to deal with these unpredictable sources of energy at distribution level. Under these circumstances, considerable activities were carried out aiming to render the grid more flexible and intelligent while taking the power efficiency and its environmental impacts into account. In this way, the power quality issues should be considered for the development of new type of smart grids which are more efficient and sustainable with regards to environmental constraints. Available active and passive compensators are widely involved to improve major power quality issues. Recent trends towards realization of multitasking devices which can solve several power quality issues simultaneously, propose Hybrid active filters or Unified power quality conditioners. These versatile devices should threaten both voltage and current related issues in one place for compensation. They can significantly improve power quality issues, such as voltage distortions, voltage sags, voltage swells, voltage unbalances, and ensure a constant and reliable voltage supply to the load. On the other hand, they compensate for current problems of linear and non-linear loads, such as current harmonics, unbalances, neutral current, and load reactive power. The Hybrid series active filter (HSeAF) is among the most versatile and efficient power electronics based active power compensators. Without the shunt passive filter, the active part could operate solely to rectify for voltage problems and is commonly known as Dynamic voltage restorer. A conventional HSeAF, targeting three-phase system, consists of a three separate series isolation transformer connected to a three-phase converter sharing a common DC link bus. The device is controlled as a variable voltage source in similar but duality manner as of Shunt active power filter. A shunt passive filter tuned for harmonic frequencies is installed to produce an alternative path for load current harmonics and reducing voltage distortions at the load terminals. The existing literature suggests utilizing the hybrid active power filters to compensate for load current related issues only, while due to the complexity and implementation outlays of such devices, it shows a significant drawback of under usage of series compensation to address such power quality problems. The present doctoral research is based on the philosophy of optimal utilization of the available resources in the most efficient way to enhance the product efficiency and to reduce the overall cost. This work proposes a novel control approach for three-phase system in which both the grid’s voltage and load current issues are treated in a co-ordination between the series active and the shunt passive filters without affecting the basic voltage or current compensation capabilities. This eventually results in a better utilization of the series active filter, reduction of the shunt passive filter rating to some extent, and ultimately in the reduction of the overall cost for a unified compensator. Moreover, this thesis also introduces a novel transformerless topology in which the threephase configuration is split into separate devices. It is then possible to extent the Series active power compensation based for three-phase systems with three or four wires to single-phase or bi-phase systems. This newly transformerless hybrid series active filter (THSeAF) is first hosted for single-phase system where appropriate developed controllers ensure adequate operation under low profile power quality systems. The developed single-phase THSeAF concept is successfully validated through digital simulations as well as real-time extensive experimental investigations. The experimental results show that for a given laboratory test conditions with highly polluted nonlinear loads, the active compensator ride of the bulky transformer is capable of compensating load current and correcting the power factor. Moreover, the performance of the THSeAF under polluted grid supply with voltage harmonics, sags, and swells, demonstrates regulated and reduced voltage distortions at the load’s terminals. Following this successful transformerless configuration, and to integrate the series compensation concepts dedicated for power quality improvement of distribution network, the three-phase configuration is anticipated. Three-phase control strategies developed previously for the HSeAF are applied to the proposed topology to make the point of common coupling (PCC) smarter and to decentralize the control of the distribution network. This affordable solution increases the efficiency and sustainability of modern smart power systems and help higher penetration of renewable fluctuating power into the network. The off-line simulations demonstrate that the three-phase THSeAF is capable of healing voltage problems and load current issues simultaneously. The real-time experimental results, carried out on a laboratory prototype, validate successfully the proposed configuration

Investigation of domestic level EV chargers in the Distribution Network: An Assessment and mitigation solution

This research focuses on the electrification of the transport sector. Such electrification could potentially pose challenges to the distribution system operator (DSO) in terms of reliability, power quality and cost-effective implementation. This thesis contributes to both, an Electrical Vehicle (EV) load demand profiling and advanced use of reactive power compensation (D-STATCOM) to facilitate flexible and secure network operation. The main aim of this research is to investigate the planning and operation of low voltage distribution networks (LVDN) with increasing electrical vehicles (EVs) proliferation and the effects of higher demand charging systems. This work is based on two different independent strands of research. Firstly, the thesis illustrates how the flexibility and composition of aggregated EVs demand can be obtained with very limited information available. Once the composition of demand is available, future energy scenarios are analysed in respect to the impact of higher EVs charging rates on single phase connections at LV distribution network level. A novel planning model based on energy scenario simulations suitable for the utilization of existing assets is developed. The proposed framework can provide probabilistic risk assessment of power quality (PQ) variations that may arise due to the proliferation of significant numbers of EVs chargers. Monte Carlo (MC) based simulation is applied in this regard. This probabilistic approach is used to estimate the likely impact of EVs chargers against the extreme-case scenarios. Secondly, in relation to increased EVs penetration, dynamic reactive power reserve management through network voltage control is considered. In this regard, a generic distribution static synchronous compensator (D-STATCOM) model is adapted to achieve network voltage stability. The main emphasis is on a generic D-STATCOM modelling technique, where each individual EV charging is considered through a probability density function that is inclusive of dynamic D-STATCOM support. It demonstrates how optimal techniques can consider the demand flexibility at each bus to meet the requirement of network operator while maintaining the relevant steady state and/or dynamic performance indicators (voltage level) of the network. The results show that reactive power compensation through D-STATCOM, in the context of EVs integration, can provide continuous voltage support and thereby facilitate 90% penetration of network customers with EV connections at a normal EV charging rate (3.68 kW). The results are improved by using optimal power flow. The results suggest, if fast charging (up to 11 kW) is employed, up to 50% of network EV customers can be accommodated by utilising the optimal planning approach. During the case study, it is observed that the transformer loading is increased significantly in the presence of D-STATCOM. The transformer loading reaches approximately up to 300%, in one of the contingencies at 11 kW EV charging, so transformer upgrading is still required. Three-phase connected DSTATCOM is normally used by the DSO to control power quality issues in the network. Although, to maintain voltage level at each individual phase with three-phase connected device is not possible. So, single-phase connected D-STATCOM is used to control the voltage at each individual phase. Single-phase connected D-STATCOM is able maintain the voltage level at each individual phase at 1 p.u. This research will be of interest to the DSO, as it will provide an insight to the issues associated with higher penetration of EV chargers, present in the realization of a sustainable transport electrification agenda

Improvement Of Power Quality Using Shunt Active Power Filter In An Electrical Distribution System Using Eerl-Smc

In this paper a three phase Shunt Active Power Filter (ShAPF) is proposed to address the current related issues in a three phase Electrical Distribution System (EDS). A sliding mode controller (SMC) and an Enhanced Exponential Reaching Law based SMC (EERL-SMC) is proposed for a ShAPF to compensate the load current. The controller’s performance is tested by injecting the current harmonics into the system. A non-linear load along with different loads on the distribution side is connected in parallel in a distribution network at Point of common coupling (PCC). Modelling of the system is done using state space analysis. Stability of the system is analyzed using the state feedback approach. The reference source currents are generated using instantaneous PQ theory. For variations in the load, the THD in the source current is realized. It is found that EERL-SMC is more effective for a ShAPF in reducing the high frequency oscillations and settling time for convergence. The source voltage and current waveforms are observed to be sinusoidal in nature. Both the controllers are effective in reducing the THD levels in the source current as per the IEEE standards. A comparison between the controllers is presented in terms of settling time, THD in source current. PSCAD v4.6 is used for simulation works

Grid-Connected Renewable Energy Sources

The use of renewable energy sources (RESs) is a need of global society. This editorial, and its associated Special Issue “Grid-Connected Renewable Energy Sources”, offers a compilation of some of the recent advances in the analysis of current power systems that are composed after the high penetration of distributed generation (DG) with different RESs. The focus is on both new control configurations and on novel methodologies for the optimal placement and sizing of DG. The eleven accepted papers certainly provide a good contribution to control deployments and methodologies for the allocation and sizing of DG

An overview of power quality enhancement techniques applied to distributed generation in electrical distribution networks

It is obvious that power quality is an important characteristic of today's distribution power systems as loads become more sensitive on the other hand nonlinear loads are increasing in the electrical distribution system. Considering the distributed nature of harmonic loads, the need for distributed power quality improvement (PQI) is inevitable. From years ago, researchers have been working on various kinds of filters and devices to enhance the overall power quality of power system, but today the nature of distribution system has been changed and power electronic based DGs play an important role in distribution grids. In this paper, a thorough survey is done on power quality enhancement devices with emphasis on ancillary services of multi-functional DGs. A literature review is also done on microgrids concept, testbeds and related control methods. Although there were some applications of DGs for PQI improvement these applications were not defined multi-functional DGs. Various control methods are studied and categorized regarding different viewpoints in the literature. Finally, a couple of thorough comparisons are done between the available techniques considering the nature, capabilities, advantages and implementation costs

Nonlinear loads model for harmonics flow prediction, using multivariate regression

This paper describes a method for obtaining a model of a single or a set of nonlinear loads (NLL) connected to a certain point of an electrical network. The basic assumption is that the network supplying the NLL has significant series impedances and is disturbed by other parallel, random, and unknown neighbor loads, sharing part of the supply system with the NLL. The main interest for obtaining the model is its further use to predict the amount and flow of harmonic currents generated by the NLL, in the case of adding a filter to reduce the harmonics distortion. The modeling technique used in the paper is based on multivariate multiple outputs regression and leads to a set of equations giving the NLL behavior (one for each of the harmonic currents). The model is obtained from data taken at measuring point and is only valid to predict the NLL behavior when new loads are connected at this point. The modeling method was first tested with V, I data coming from simulations using a MATLAB-Simulink SimPowerSystems toolbox. Finally, the method has been validated using V, I data taken in a real installation with different neighbor loads and under different load conditions.Postprint (published version

A review on power electronics technologies for power quality improvement

Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.This work has been supported by FCT-Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017 and by the FCT Project newERA4GRIDs PTDC/EEIEEE/30283/2017