Study on Adaptive Harmonic Extraction Approaches in Active Power Filter Applications

Active power filter (APF) has now become a mature technology for harmonic and reactive power compensations in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) ac power networks with nonlinear loads. This paper presents a study on three different adaptive algorithms for active power filtering applications. These algorithms are adaptive linear combiner (ADALINE), least mean square adaptive notch filter (ANF-LMS), and recursive least square adaptive notch filter (ANF-RLS). In this paper, these approaches are employed for extracting load harmonic currents. The important issues associated with adaptive methods are accuracy and prediction speed. These issues will be addressed in the paper. Simulations using MATLAB/Simulink are presented to clarify the algorithms

Fuzzy Approach for Online Coordination of Plug-In Electric Vehicle Charging in Smart Grid

This paper proposes an online fuzzy coordination algorithm (OL-FCA) for charging plug-in electric vehicles (PEVs) in smart grid networks that will reduce the total cost of energy generation and the associated grid losses while maintaining network operation criteria such as maximum demand and node voltage profiles within their permissible limits. A recently implemented PEV coordination algorithm based on maximum sensitivity selection (MSS) optimization is improved using fuzzy reasoning. The proposed OL-FCA considers random plug-in of vehicles, time-varying market energy prices, and PEV owner preferred charging time zones based on priority selection. Impacts of uncoordinated, MSS, and fuzzy coordinated charging on total cost, gird losses, and voltage profiles are investigated by simulating different PEV penetration levels on a 449-node network with three wind distributed generation (WDG) systems. The main advantage of OL-FCA compared with the MSS PEV coordination is the reduction in the total cost it introduces within the 24h

Online optimal variable charge-rate coordination of plug-in electric vehicles to maximize customer satisfaction and improve grid performance

© 2016 Elsevier B.V. Participation of plug-in electric vehicles (PEVs) is expected to grow in emerging smart grids. A strategy to overcome potential grid overloading caused by large penetrations of PEVs is to optimize their battery charge-rates to fully explore grid capacity and maximize the customer satisfaction for all PEV owners. This paper proposes an online dynamically optimized algorithm for optimal variable charge-rate scheduling of PEVs based on coordinated aggregated particle swarm optimization (CAPSO). The online algorithm is updated at regular intervals of Δt = 5 min to maximize the customers’ satisfactions for all PEV owners based on their requested plug-out times, requested battery state of charges (SOCReq) and willingness to pay the higher charging energy prices. The algorithm also ensures that the distribution transformer is not overloaded while grid losses and node voltage deviations are minimized. Simulation results for uncoordinated PEV charging as well as CAPSO with fixed charge-rate coordination (FCC) and variable charge-rate coordination (VCC) strategies are compared for a 449-node network with different levels of PEV penetrations. The key contributions are optimal VCC of PEVs considering battery modeling, chargers’ efficiencies and customer satisfaction based on requested plug-out times, driving pattern, desired final SOCs and their interest to pay for energy at a higher rate

Optimal operation of multiple unbalanced distributed generation sources in three-phase four-wire LV distribution networks

Distributed Generation (DG) in the form of residential roof top photovoltaic installations is driven by consumer action. The placement of DG in the distribution network is not controlled by the network operator. Power quality issues, especially voltage rise and unbalance, is restricting ability of networks to accommodate further connections. There is a growing interest in utilizing the latent capacity of DG inverters to provide reactive power, or to integrate storage into DG systems, to increase the renewable power fraction. This paper presents an optimization method that is able to simultaneously manage the operation of many arbitrary located residential DG sources to reduce system losses and improve power quality. The optimization model is solved by a Sequential Quadratic Programming (SQP) based approach and the validity is tested on an accurate three-phase four-wire unbalanced distribution network model developed during the Perth Solar City trial

Application of SVC and single-phase shunt capacitor to improve voltage profiles and reduce losses of unbalanced multiphase smart grid with PEV charging stations

In smart grids, the conventional approach of locating compensation devices based on the forecasted daily load curves is not realistic as the locations, times and durations of some loads such as plug-in electric vehicles (PEVs) and smart appliances are randomly changing during the 24 hour period. This paper proposes a new approach to improve the performance of unbalanced multiphase distribution systems consisting of single-, two- and three-phase networks with PEV charging stations. The approach is designated to perform online VRI ranking, place SVCs and single-phase capacitors at the weakest three-phase and single-phase buses, respectively; and then switch these devices in and out of the service according to the lowest voltage ranking index (VRI) values in order to improve voltage profiles and reduce total system losses. Simulation results are performed and compared for an unbalanced multiphase 13 node test feeder with PEV charging stations using DIgSILENT PowerFactory software

Impacts of symmetrical and asymmetrical voltage sags on DFIG-based wind turbines considering phase-angle jump, voltage recovery, and sag parameters

This paper presents a new analysis into the impacts of various symmetrical and asymmetrical voltage sags on doubly fed induction generator (DFIG)-based wind turbines. Fault ride-through requirements are usually defined by the grid codes at the point of common coupling (PCC) of wind farms to the power network. However, depending on the network characteristics and constraints, the voltage sag conditions experienced at the wind generator terminals can be significantly different from the conditions at the PCC. Therefore, it is very important to identify the voltage sags that can practically affect the operation of wind generators. Extensive simulation studies are carried out in MATLAB/Simulink to investigate the transient overshoots and ripples that appear in the rotor current and dc-link voltage when the DFIG is subjected to various types of (a)symmetrical faults. For the first time, the impacts of phase-angle jump and operational constraints of circuit breakers are examined. Furthermore, the influences of sag parameters including type, initial point-on-wave instant, depth, and impedance angle are investigated. Complementary theoretical analyses are also presented to support the validity of observations made in the simulation studies

Different Techniques for Simultaneously Increasing the Penetration Level of Rooftop PVs in Residential LV Networks and Improving Voltage Profile

Utilization of rooftop photovoltaic cells (PVs) in residential feeders without controlling their ratings and locations may deteriorate the overall grid performance including power flows, losses and voltage profiles. This paper investigates different methods for regulating the voltage profile and reducing the voltage unbalance at low voltage residential feeders. The algorithm considers reactive power exchange and active power curtailment of the single-phase rooftop PVs. In addition, it is assumed that the distribution transformers have on-load tap changers and can automatically control the voltage to prevent voltage rise in the feeder. The main objectives of the discussed methods are to regulate the voltage profiles and reduce the voltage unbalance. MATLAB-based simulation results demonstrate effectiveness of the discussed approaches

Coordination of single-phase rooftop PVs to regulate voltage profiles of unbalanced residential feeders

Installation of single-phase rooftop Photovoltaic (PV) systems in low voltage distribution networks is gaining increasing popularity in many countries including Australia. Utilization of rooftop PVs in residential feeders without controlling their ratings and locations may deteriorate the overall grid performance including power flows, losses and voltage profiles. This paper investigates the effectiveness and limitations of two different methods for regulating the voltage profile at low voltage residential feeders with single-phase rooftop PVs. These methods are based on the availability of voltmeters at each phase at each bus along the low voltage feeder which transmit their measurements to the controllers of the PV inverters. The main objective is to regulate the voltage profiles and reduce the voltage unbalance using drool control. The algorithm considers reactive power exchange and active power curtailment of the single-phase rooftop PVs. MATLAB-based simulation results demonstrate effectiveness of the proposed approach

Online Transformer Internal Fault Detection Based on Instantaneous Voltage and Current Measurements Considering Impact of Harmonics

This paper investigates the performance of a recently proposed online transformer internal fault detection technique and examines impact of harmonics through detailed nonlinear simulation of a transformer using three-dimensional finite element modelling. The proposed online technique is based on considering the correlation between the instantaneous input and output voltage difference (ΔV) and the input current of a particular phase as a finger print of the transformer that could be measured every cycle to identify any incipient mechanical deformation within power transformers. To precisely emulate real transformer operation under various winding mechanical deformations, a detailed three-dimensional finite-element model is developed. Detailed simulations with (non)sinusoidal excitation are performed and analysed to demonstrate the unique impact of each fault on the ΔV-I locus. Impact of harmonic order, magnitude and phase angle is also investigated. Furthermore, practical measurements have been performed to validate the effect of winding short circuit fault on the proposed ΔV-I locus without and with the impact of system harmonics