Tap Operations Research Articles

Coordinated Strategy for Controlling Multiple SVRs in Distribution Systems with Photovoltaics Using Moving Average Filters

Although the installation of photovoltaic (PV) in distribution systems can contribute to the decarbonization of electricity generation, the PV output fluctuates depending on weather conditions, which in turn complicates power flow and destabilizes the voltage levels in distribution systems. Conventionally, step voltage regulators (SVRs) have been used to maintain voltage profiles within allowable ranges, however, the conventional control strategy might not be enough to successfully mitigate high speed voltage fluctuation caused by PVs. In this study, we focused on the time‐limit characteristic of tap operation in a system with two SVRs located, respectively, upstream near the distribution substation and downstream from the substation. Three methods for the cooperative control of two SVRs using moving average filters were proposed. The effectiveness of the proposed methods was validated through numerical simulation based on a model of a rural distribution system with a PV plant integrated at the end feeder. The performance of the proposed methods was compared with each other using evaluation indices such as the amount of voltage deviation and number of tap operations, and it was shown that the method with band‐pass filter for differential control had the best objective function. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Mid-term operational planning of pre-installed voltage regulators in distribution networks

In this paper, a methodology is presented to maximize the effectiveness of pre-installed Voltage Regulators (VRs) in medium voltage distribution networks. While considering the daily tap operation limitation of VRs, this method contains mid-term operational planning of VRs' settings which is carried out to satisfy voltage constraints in distribution networks and reduce power losses throughout the network. The proposed approach optimizes the settings periodically, leading to Distribution System Operators (DSOs) ' financial benefit because energy losses are reduced by applying the proposed method. Using different combinations of ZIP load model coefficients in the optimization process, the importance and impacts of the load model in the optimization of VRs' settings are also investigated because the operation of a VR directly influences the consumption of voltage-dependent loads (depending on their type of voltage dependency). Due to the discrete nature of the problem, the Genetic Algorithm (GA) has been employed as a tool to attain the previously mentioned goals by optimizing the settings of VRs for forthcoming months. Numerical studies carried out for a 70-bus distribution network show that a reduction of energy loss is achieved by applying the article's proposed method.

Unbalanced Voltage Compensation with Optimal Voltage Controlled Regulators and Load Ratio Control Transformer

Penetration of equipment such as photovoltaic power generations (PV), heat pump water heaters (HP), and electric vehicles (EV) introduces voltage unbalance issues in distribution systems. Controlling PV and energy storage system (ESS) outputs or coordinated EV charging are investigated for voltage unbalance compensation. However, some issues exist, such as dependency on installed capacity and fairness among consumers. Therefore, the ideal way to mitigate unbalanced voltages is to use grid-side equipment mainly. This paper proposes a voltage unbalance compensation based on optimal tap operation scheduling of three-phase individual controlled step voltage regulators (3ϕSVR) and load ratio control transformer (LRT). In the formulation of the optimization problem, multiple voltage unbalance metrics are comprehensively included. In addition, voltage deviations, network losses, and coordinated tap operations, which are typical issues in distribution systems, are considered. In order to investigate the mutual influence among voltage unbalance and other typical issues, various optimization problems are formulated, and then they are compared by numerical simulations. The results show that the proper operation of 3ϕSVRs and LRT effectively mitigates voltage unbalance. Furthermore, the results also show that voltage unbalances and other typical issues can be improved simultaneously with appropriate formulations.

Two-Stage Optimization Strategy for Solving the VVO Problem Considering High Penetration of Plug-In Electric Vehicles to Unbalanced Distribution Networks

This article proposes a two-stage optimization strategy for solving the voltage-var optimization (VVO) problem considering stochastic penetration of plug-in electric vehicles (PEVs) to unbalanced, three-phase power distribution networks (PDN). The optimization strategy considers the prospect of forced active power curtailment at a minimized level, bidirectional PEVs activities. It also includes simple tap operations of shunt capacitor banks, online tap changing transformers, and voltage regulators to achieve optimal economic gain while satisfying the VVO operational constraints. The first stage aims for the optimal decomposition of the PDN into well-defined, cross-checked smaller partitions via a proposed community-based detection particle swarm optimization algorithm. The second stage incorporates a mixed-integer linear programming formulation to solve the VVO problem per partition level. This is done considering the nonlinearity and nonconvexity of the electrical system via applied approximation. This reduces the complexity and computational burdens that usually arise in solving the problem on a larger scale. The proposed two-stage strategy was tested on the modified IEEE 123 bus system with various case scenarios. Economical operation of the PDN is achieved during peak demand hours while maintaining a safe operation within the VVO problem.

Predictive Voltage Control Scheme Based on Estimation of Short‐Time‐Ahead Voltage Fluctuation in Distribution System with PVs

This paper proposes a predictive voltage control scheme baseda on short‐time‐ahead voltage fluctuation estimation in a distribution system for achieving high penetration of photovoltaic generation. In the proposed control scheme, the short‐time‐ahead voltage fluctuation is estimated from the previously measured voltage of the sensor, and the voltage regulator operates to minimize the expected voltage violation risk in the entire distribution system. Because there is no requirement for real‐time sensor‐measured voltage values, as required in centralized voltage control schemes, the proposed scheme is an autonomous control scheme that uses only the present secondary voltage of the voltage regulator. The proposed control scheme was tested on a large‐scale distribution system model to which thousands of customers are connected, and the voltage control performance was evaluated using the monthly measurement data that was in terms of voltage violation amount and number of tap operations. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A Study on Character Input Method for Smartphones Using Back Tap and Tilt Operation

A Study on Character Input Method for Smartphones Using Back Tap and Tilt Operation

Examining the usability of touchscreen gestures for adults with DS

This document is part of a global investigation that aims to establish best practices in usability testing of mobile applications, that fit the specific needs of persons with cognitive disabilities. The motivating factor is to improve the quality of life of people with special needs. As a first step, we want to discover what are the skills of people with DS (DS) when using a mobile device. Thanks to its direct manipulation interaction style, multi-touch technology is the ideal mechanism for learning activities with a view to the social inclusion of people with DS. This paper investigates the most common touchscreen gestures on commercial existing software. A commercial analysis was carried out to discover the touch screen gestures used by 103 free software Apps running on a mobile touch screen tablet of 11 where the applications run”. The commercial analysis showed that most applications support tap and drag operations on multi-touch technology. Additionally, the research sought to discover the adults with DS (19–54 years of age) ability to perform other gestures on multi-touch surfaces. A DS user skill study was performed to assess the ability of this user segment to interact with multi-touch surfaces. The analysis involved 53 participants, aged between 19 and 54 years, from two vocational training centers attended by people with DS in Madrid. Authors used the Gesture Games App for experimenting with multi-touch gestures such as tap, double tap, long press, drag, scale up, scale down, and one-finger rotation. Tap, double tap, and drag were the three gestures that the most participant could use. In contrast, participants had difficulty performing one-finger rotation and long press gesture. Our statistical analysis showed that the ability to perform each gesture was independent of gender, age group, and previous experience with touchscreen of a participant.

An Effective Coordination Strategy for Voltage Regulation in Distribution System Containing High Intermittent Photovoltaic Penetrations

In recent years, with increasing the penetration of renewable-based distributed generations, voltage control plays a vital role in operating distribution systems. Furthermore, the traditional voltage control devices are not fast enough to regulate the voltage due to transient events and the intermittent characteristics of renewable energy sources. On the other hand, because of the fast response of power electronic components, the photovoltaic (PV) inverter can cope with the intermittent and uncertainty of power generation due to weather changes. Therefore, this paper proposes a cooperative voltage control scheme to solve the voltage problems associated with high PV penetration. The scheme is developed based on a multi-agent system (MAS) with a distributed control architecture using time coordination between voltage regulators and reactive power control of the PV inverters. The scheme’s objective is to minimize voltage deviations and reduce the stress on the traditional voltage control devices by utilizing the available reactive power of the PV inverters. Different simulations are carried out and analyzed for various operating conditions over 24 hours using the IEEE 34-bus and 123-bus test feeders. The simulation results show that the proposed control scheme can successfully reduce the total voltage deviation and decrease the number of tap operations of voltage regulators at different sun profiles.

Dynamic Optimization of SVR Control Parameters for Improving Tap Operation Efficiency of Voltage Control in Distribution Networks

In this study, we propose a new optimization method to determine the control parameters of a step voltage regulator (SVR) to maximize its voltage control characteristic in distribution networks (DNs) with photovoltaic systems. Considering the service life of an SVR, the proposed method evaluates the expected number of tap operations and the voltage control performance based on the past voltage measurements obtained with sensors in the DN. Subsequently, the time series of two control parameters, that is, the reference voltage and the dead bandwidth, are determined for the most improved voltage control characteristic of the SVR, maintaining the number of tap operations within the upper limit. Voltage control simulation using a realistic 6.6‐kV DN model is conducted to show that the proposed method significantly reduces the voltage violation compared with the conventional SVR control using fixed parameters, as well as the alternative SVR operation developed in our previous study, in which the reference voltage was temporally updated. In addition, the simulation results demonstrate that the proposed method realizes efficient tap operations to mitigate the voltage violation, whereas the conventional method requires a much larger number of tap operations to mitigate the voltage violation to the same degree. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Dynamics of high penetration photovoltaic systems in distribution circuits with legacy voltage regulation devices

Concerns for criteria pollutant emissions and air quality, as well as greenhouse gas emissions, have resulted in stringent energy and environmental rules and regulations mandating deployment of renewable resources. Moreover, increased frequency of extreme weather events highlighted the need for increased reliability and resiliency of the grid further encouraging deployment of distributed energy resources. This has resulted in an increasing deployment of solar PV in the distribution system. While many studies focus on analyzing the impact of increased penetration of PV on smart circuits or systems with upgraded infrastructure, it is necessary to assess impacts on existing circuits with legacy devices. In this study, the impacts of high penetration of PV are investigated for two distribution circuits (one residential and one commercial) located in northern California, equipped with legacy voltage regulation devices including on-load tap changer (OLTC) transformers and switched capacitor banks.The dynamics of circuit operation and bus voltage profiles are studied by developing time-resolved three-phase balanced feeder models of the two circuits. Using connectivity and load demand measurements provided by the utility, the models are validated and calibrated to the point of the substation. In order to help generalize the results associated with the two circuits, a set of circuit design metrics are developed to characterize the distribution of the load demand and generation, load center (LC) and generation center (GC). The load center and generation center metrics are weighted averages of the total consumed and total produced bus energy relative to the distance from the substation.Various scenarios are simulated in order to quantify generation limits necessary to conform to various standards including ANSI C84.1 voltage standards while maintaining reliable circuit operations. In these scenarios, location of the PV installation as well as PV penetration (from baseline to 100%) are varied. Simulation results indicate that high PV penetrations have a direct impact on OLTC transformer operation but only marginal impact on capacitor switching. Tap operation is found to increase approximately linearly with PV penetration for both of the circuits and specific Load Drop Compensation (LDC) controller settings greatly affect the sensitivity of OLTC operation to PV penetration. It is also concluded that not only the location of PV installation relative to loads and substation affects the performance, the metrics developed are a powerful tool to describe high PV circuits and to help utilities better plan for deployment of PV in their distribution network.

Smoothing control of solar photovoltaic generation using building thermal loads

Distributed energy resources such as solar photovoltaic (PV) systems are seeing significant expansion in power grids worldwide. However, serious system integration issues have arisen including voltage fluctuations and accelerated aging of voltage regulation devices, when adopting mass amounts of volatile energy resources onto legacy distribution networks originally designed for unidirectional power flow. Building heating, ventilation and air-conditioning (HVAC) systems, collocated with the distributed generation, can be considered as flexible loads due to the inherent building thermal inertia. HVAC systems can be proactively controlled to improve voltage regulation of distribution networks with high PV penetrations. This paper presents a smoothing solution that modulates HVAC power in response to volatile PV generation as a means to mitigate fluctuations in the net demand and generation. To demonstrate the effectiveness and evaluate performance gains, hardware-in-the-loop (HIL) tests were carried out using a 3-ton variable-speed heat pump. The HIL tests leveraged a building thermal dynamic model and a steady-state power flow model for a 33-bus distribution network to capture realistic indoor thermal responses and distribution voltage variations during PV smoothing control. Test results showed that the developed strategy was effective in reducing variations of net demand and generation with negligible impact on indoor comfort. More than 55% reductions of voltage fluctuation were achieved and tap operations of voltage regulators could be fully or partially eliminated with proactive PV smoothing.

Advanced voltage control based on short-time ahead voltage fluctuation estimation in distribution system

Distributed energy resources such as photovoltaic generation (PV) have negative impacts on the voltage regulation in distribution networks. This paper proposes an advanced predictive voltage control scheme based on short-time-ahead voltage fluctuation estimation in a distribution system with high PV penetration. In the proposed scheme, the short-term voltage fluctuation is predicted based on the past sensor measurements of voltage, and a voltage regulator is operated to mitigate the expected voltage violation risk in a distribution system. The proposed scheme is an autonomous control scheme requiring only the present secondary voltage of the voltage regulator, because there is no need for real-time sensor-measured voltage values as in centralized voltage control schemes. The proposed scheme is tested on a hardware testbed constructed in Waseda University, and the experimental simulation results clearly show that the proposed scheme can prevent voltage violation without significantly increasing the number of tap operations and achieve superior voltage-control performance compared to that of the centralized scheme.

Simultaneous Removal of NO and SO2 with a Novel Oxidation-Absorption Process Based on Air Microbubble Water System

Microbubbles (MBs) can spontaneously generate hydroxyl radicals (·OH) with high oxidizing capacity. In this study, a novel oxidation-absorption process based on a microbubble system in the indirect removal mode was proposed for the simultaneous removal of nitric oxide (NO) and sulfur dioxide (SO2). In this process, an air microbubble water system (AMBW) was produced by a microbubble generator (MBG) inhaling air and tap water and injected into an oxidation-absorption column reactor by the MBG, meanwhile the mixed gas composed of NO and SO2 passed through a micron-sized gas distributor at the bottom of the reactor and flowed into the AMBW. Important parameters including initial pH and temperature of tap water, operation time, NO concentration, SO2 concentration, and NaCl concentration were assessed to investigate the feasibility of the AMBW for the simultaneous removal of NO and SO2. The results showed that ·OH generated from the collapsed MBs played a critical role in the removal and the simultaneous removal of NO and SO2 was successfully achieved with the AMBW. Even with only tap water used as the absorbent, the removal efficiencies of NO and SO2 reached 92.7% and above 99%, respectively, when the experiment conditions were initial water pH 11.5, initial water temperature 298 K, 600 ppm NO, and 3,000 ppm SO2. Compared with the microbubble system in the direct removal mode, this new system is more suitable for the treatment of flue gases with low NO concentration and high volume. Moreover, this novel process should have a good prospect of industrial application in the flue gas treatment due to its high efficiencies of desulfurization and denitration and some advantages such as low usage cost of the reagents, simple system, and small occupation space.

Coordination of OLTC and smart inverters for optimal voltage regulation of unbalanced distribution networks

Photovoltaic (PV) smart inverters can improve the voltage profile of distribution networks. A multi-objective optimization framework for coordination of reactive power injection of smart inverters and tap operations of on-load tap changers (OLTCs) for multi-phase unbalanced distribution systems is proposed. The optimization objective is to minimize voltage deviations and the number of tap operations simultaneously. A novel linearization method is proposed to linearize power flow equations and to convexify the problem, which guarantees convergence of the optimization and less computation costs. The optimization is modeled and solved using mixed-integer linear programming (MILP). The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced modified IEEE 37 bus test system and a large California utility feeder. Simulation results show that the proposed method accurately estimates feeder voltage, significantly reduces voltage deviations, mitigates over-voltage problems, and reduces voltage unbalance while eliminating unnecessary tap operations. The robustness of the method is validated against various levels of forecast error. The computational efficiency and scalability of the proposed approach are also demonstrated through the simulations on the large utility feeder.

Cooperative Voltage Control in MV Distribution Networks With Electric Vehicle Charging Stations and Photovoltaic DGs

The proliferation of distributed generators (DGs) and electric vehicle charging stations (EVCSs) has brought voltage regulation challenges to distribution networks. This article proposes a distributed control algorithm to dispatch surplus reactive power from EVCSs and DGs for proper voltage regulation without violating their converters' capacities or stressing conventional voltage control devices, such as on-load tap changers (OLTCs). Further, an active power curtailment strategy is proposed for DGs to properly integrate OLTCs in voltage regulation when the reactive power support is deficient. The proposed control algorithms rely on the average consensus theory and sensitivity analysis to provide optimized voltage support while satisfying the agents' self-objectives. Simulation results of a typical distribution network confirm the effectiveness of the proposed distributed control algorithms in maintaining proper voltage regulation with minimum voltage support from EVCSs and DGs, and reduced daily tap operation for OLTC.

An Excessive Tap Operation Evaluation Approach for Unbalanced Distribution Networks With High PV Penetration

Recently, utility-scale photovoltaic (PV) plants in remote areas are drastically increasing due to abundant and low-priced land. These remote areas are usually connected to zone substations through long weak feeders with open-delta step voltage regulators (SVRs) installed in the middle to regulate downstream voltages. However, frequent PV and load power fluctuations can lead to undesirable voltage variations and hence excessive tap operation issues. Currently, it is not clear about the percentage of responsibility by load or PV fluctuations to excessive tap operations. In this article, a novel method based on line-to-line voltage sensitivity and time series evaluation is proposed to respectively quantify the interactions between PV/load fluctuations and tap operations. The accuracy of this method is firmly validated with the measured data from a real-life unbalanced distribution network with high PV penetration. Further, this proposed method is implemented to statistically quantify the causes of excessive tap operations with half-year field data under the support of the local utility and the PV plant owner. The investigation results can provide valuable insights for utilities to better manage the voltage profiles and tap maintenance for remote distribution networks with high PV penetration.

Use of demand response for voltage regulation in power distribution systems with flexible resources

In low-voltage power distribution systems with high penetration of photovoltaics (PVs) generation and electric vehicles (EVs), the over-voltage problem arises at times because of large PV generation, and under-voltage problem also arises sometimes because of simultaneous charging of massive EVs. Over- and under-voltage problems lead to more difficulties in achieving voltage regulation. Demand response (DR) is expected to be promising and cost-effective in promoting smart grids, and hence, the utilisation of flexible resources (FRs) through DR can be helpful for distribution system voltage regulation. This study introduces a hierarchical control structure of a community energy management system (CEMS) and multiple sub-CEMSs to apply an FR-based two-stage voltage regulation technique. In the first stage, i.e. the day-ahead scheduling stage, each sub-CEMS optimises the FRs' schedules for minimising customers' electricity cost and network voltage violation times. In the second stage, i.e. the real-time operation stage, the voltage sensitivity-based FRs' shifting method is proposed to eliminate network voltage violations caused by errors of estimated day-ahead data. The proposed models and methods are verified based on a realistic distribution system in Japan, where voltage violations, customer electricity cost and a number of on-load tap changer tap operations are proved to be reduced.

An approach to torque and temperature thread by thread on tapping

During internal threading, small alterations in cutting parameters, tool geometry, or process characteristics produce considerable effects on torque and temperature behavior. Understanding these effects is critical to the design and development of new taps. In this work, the torque behavior for a tap operation is evaluated as a function of the number of threads, tool manufacturer, and angle of the taper region of the tool. The chip–tool interface temperature was analyzed, considering the influence of cutting speed and number of threads. Experimental tests were carried out using M10x1.5 taps and cutting speeds of 10 m/min and 25 m/min. Taps with two different geometries were considered in this analysis. The results show a difference in the distribution of the torque along the threads of the conical part between the tools. The presence of adhered material increased the torque during the reverse stage. The torque during the reverse stage for a tap with a damaged tooth was approximately 50% of the torque during the cutting stage. The temperature showed an increase with the number of threads stabilizing between the fourth and fifth threads and increasing again in the sixth filled due to adhesion of workpiece material.

A Voltage Smoothing Algorithm Using Energy Storage PQ Control in PV-Integrated Power Grid

Changes in solar irradiance cause variations in photovoltaic (PV) power generation and thus affect customer voltage. Load tap changers in substations are used to mitigate voltage variations, but they are relatively slow and cannot regulate the voltage adequately. Furthermore, abrupt voltage changes induced by PVs could greatly cause mechanical wear and reduce their lifetime. This letter develops a novel voltage smoothing control algorithm for distributed energy storage systems to reduce the impact of PV generation on voltage quality. Different from other works, the proposed control can improve the performance by having both active and reactive power control and monitoring voltage directly. The technique's performance is verified through simulation and modeling of the IEEE 4-bus test system. The proposed technique can effectively smoothen the voltage and reduce the number of tap operations by approximately 50%.

Moth Search Optimization for Optimal DERs Integration in Conjunction to OLTC Tap Operations in Distribution Systems

In this paper, a newly developed moth search optimization (MSO) technique is introduced to solve the complex distributed energy resources (DER) integration problems of distribution systems. In order to overcome some of the limitations observed in the standard variant of MSO, minor corrections are also suggested. On the other hand, a new optimization problem is formulated for optimal deployment of dispatchable distributed generations and shunt capacitors while simultaneously optimizing the tap positions of on-load tap-changing transformers, already deployed in grid substations. The objective of this work is to minimize the cost of annual energy loss and node voltage deviations over multiple load levels. The proposed model is implemented and solved for two benchmark test distribution networks of 33 and 118 buses. The suggested corrections are also validated by comparing the performance of the proposed approach with standard MSO and other available optimization methods. The simulation results show that the developed model optimally utilizes the existing distribution system resources and generates higher deployment benefits at lesser DER penetration as compared to the planning model which ignores these resources.