Local Power Quality Research Articles

A Grid-Wide Comprehensive Evaluation Method of Power Quality Based on Complex Network Theory

To achieve a hierarchical and quantitative evaluation of grid-wide power quality in the distribution network, reflecting the overall power quality level of the distribution network, a comprehensive evaluation method for power quality in a grid-wide system based on complex network theory is proposed. Firstly, based on the propagation characteristics of power quality disturbances, a power quality evaluation index system is constructed. Secondly, to reflect the constraint effect of the local power quality level of nodes on the overall power quality level of the distribution system, corresponding indices such as improved node degree, improved node electrical betweenness, and node self-healing capability are proposed based on complex network theory, and the power quality influence degree of nodes is calculated. Then, the GRA-ANP (Grey Relational Analysis–Analytic Network Process) subjective weight calculation method is improved by introducing grey relational analysis to address the impact of differences in different decision-making results. Based on power quality monitoring data, the entropy weight method is used for objective weighting. To avoid the partiality of a single weight evaluation result, the game equilibrium algorithm is employed to calculate the comprehensive weight of each power quality index. Subsequently, considering the correlation and dependency among indices, the VIKOR (VIseKriterijumska Optimizacija I Kompromisno Resenje) method is used to obtain the power quality grade of each node. Combining this with the calculation of the power quality influence degree of nodes, the overall power quality grade of the distribution network is determined, achieving a hierarchical and quantitative evaluation of power quality in the entire distribution system. Finally, through a case study analysis of an improved 13-node distribution network, it is verified that the proposed method can fully extract data information and produce comprehensive and accurate power quality assessment results by comparing it with other methods. This provides strong support for the safe and stable operation of the distribution system and the subsequent optimization and management of power quality.

Review of electric vehicle (EV) charging using renewable solar photovoltaic (PV) nano grid

This review article gives a comprehensive review of existing research on renewable solar photovoltaic (PV) nanogrid, which is described from small-scale power system with a single domain for reliability, control, and power quality (PQ) for electric vehicle (EV) charging. A primary feeder on the Microgrid is connected to a nanogrid test bed that includes PV as power source, a battery energy storage system (BESS), smart-inverter multiple and EV charging stations (EVCS). The control algorithms are graded on four metrics: (1) voltage profiles, (2) renewable penetration, (3) PV curtailed and (4) net power flows. To investigate the local power quality, a steady-state power flow model of the nano-grid is created. The control algorithms successfully employ the battery to shift the nano-grid peak load while limiting the nano-grid demand to set level. Furthermore, an increasing emphasis is being placed on commonly used strategies for addressing the characteristics of each renewable system. This review paper characterizes the dynamic operation of 4 distinct BESS control algorithms for solar EV charging nanogrid: (1) peak load shifting, (2) reduce peak period impact, (3) cap demand, and (4) photovoltaic capture. These control modes are executed and analyzed on real-world nano-grid site, and optimal BESS control modes are assessed in terms of (1) solar electric vehicle charging, (2) power quality, (3) grid net demand, (4) photovoltaic curtailment, and (5) solar penetration. Finally, the problems highlight research gaps, and discussions on future trends are critical for enhancing the general technology of the renewable solar photovoltaic nano-grid for EV charging.

Hierarchical Energy Management of Networked Flexible Traction Substations for Efficient RBE and PV Energy Utilization Within ERs

The particular split-phase traction power system of AC electrified railways (ERs) restricts its regenerative braking energy (RBE) utilization and photovoltaic (PV) penetration. Networked flexible traction substation (FTSS) operation is a promising paradigm to address this restriction. Therefore, this paper proposes a networked FTSS system architecture that ties adjacent FTSSs via unified power flow controllers (UPFC) at sectioning posts (SPs), which matches the technical characteristics of split-phase ERs obtaining the lower capacity requirement. Correspondingly, a real-time hierarchical energy management strategy is designed. The networked FTSS management level optimizes the energy cooperation among FTSSs, i.e., the exchange power at SPs. It aims at maximizing the global RBE and PV energy utilization and shaving the maximum demand of each FTSS. At the individual FTSS management level, each FTSS autonomously regulates the power outputs of the local back-to-back converter and energy storage system to maximize the local RBE and PV energy utilization and improve the local power quality issues. These two energy management levels operate independently with different time scales, making the networked FTSS system have good extensibility and reliability. Finally, the performance of the proposed scheme is verified via hardware-in-the-loop tests.

Large scale energy storage in Uppsala, Sweden: an analysis of voltage fluctuations and a service stacked portfolio

Extensive electrification has created an increased demand of electric energy and power. Congestion issues are expected to become more common as transmission and distribution grids reach their capacity limits. One of the regions in Sweden that has experienced this already is Uppsala. The distribution system operator, Vattenfall Distribution has initiated an R&D project that connects a 5 MW/20 MWh Li-ion battery energy storage system to temporarily ease the grid congestion. This study covers an analysis of grid voltage fluctuations using a largescale battery in a distribution grid. The power quality is examined at the 10 kV connection point of the storage, where voltage and power flow are presented. Also, an example of how value stacking may be implemented is illustrated by adding a secondary service during the year. The test results indicate no significant distortion of the voltage level at the measurement point during smooth ramping. It can be concluded that smooth ramping of the BESS has very low or no impact on the local power quality, and additional services should be provided during the year to create several revenue streams. Future studies could focus on fast ramping of the BESS and stacking services in an intra-season perspective.

Experimental Verification of Self-Adapting Data-Driven Controllers in Active Distribution Grids

Lately, data-driven algorithms have been proposed to design local controls for Distributed Generators (DGs) that can emulate the optimal behaviour without any need for communication or centralised control. The design is based on historical data, advanced off-line optimization techniques and machine learning methods, and has shown great potential when the operating conditions are similar to the training data. However, safety issues arise when the real-time conditions start to drift away from the training set, leading to the need for online self-adapting algorithms and experimental verification of data-driven controllers. In this paper, we propose an online self-adapting algorithm that adjusts the DG controls to tackle local power quality issues. Furthermore, we provide experimental verification of the data-driven controllers through power Hardware-in-the-Loop experiments using an industrial inverter. The results presented for a low-voltage distribution network show that data-driven schemes can emulate the optimal behaviour and the online modification scheme can mitigate local power quality issues.

Power factor corrected level‐1 DC public green‐charging infrastructure to promote e‐mobility in India

With the growing popularity of electrified transportation across the world, there have been extensive reports of research involving plug-in electric vehicles (PEVs), electric vehicle charging facilities (EVCFs) and their integration to the main electric grid, besides sustainable energy resources for powering these vehicles. This study proffers a power factor corrected level-1 DC public green-charging infrastructure accompanied by an integrated control, for electric light motor vehicles, compliant with recently formulated Indian charging standards. Power factor correction of plug-in electric vehicle charging current, solar photo-voltaic grid integration and charging of energy storage system is achieved using control of bidirectional AC/DC converters. A firmware and user interface for multimode off-board DC charging, with green, fast and semi-fast charging modes are investigated. Intelligent control for fast charging is also presented to reduce its pernicious impact on the grid. The simulation and hardware results verify the prime performance objectives of improving the local power quality and renewable energy utilisation with multimode charging, in the Indian context. The effectiveness of the proposed infrastructure is further demonstrated by a simulated use case, where 30 PEVs are randomly charged, in various modes, at this EVCF during busy commute hours.

Dynamics of an integrated solar photovoltaic and battery storage nanogrid for electric vehicle charging

In this paper, the performance of a renewable Solar Photovoltaic (PV) nanogrid — here defined as a small-scale power system, which comprises a single domain for control, reliability, and power quality — is assessed for Electric Vehicle (EV) charging. A nanogrid testbed, containing PV as the power supply, twenty EV charging stations, a Battery Energy Storage System (BESS), and a smart-inverter is connected to a primary feeder on the University of California, Irvine (UCI) Microgrid. We present four different smart-inverter control algorithms that govern battery dispatch for different energy management goals. The control algorithms were evaluated with respect to four figures of merit: (1) Renewable Penetration, (2) Voltage Profiles, (3) Net Power Flows, and (4) PV curtailed. A steady-state power flow model of the nanogrid was developed to study the local power quality. The control algorithms were able to successfully use the battery to shift the nanogrid peak load and also limit the nanogrid demand to a given threshold. It is shown that the nanogrid was able to offset the EV daily charging loads completely. In this same mode, the renewable contribution to EV charging was 80%, and the overall solar penetration (accounting for export and battery charge) was 89%.

Analytical Study on the Loss Reduction of Static Var Generator for Power Grid Based on the Soft Switch Technology

With SVG technology becoming more and more mature, chain SVG is also installed in some power grid substations to solve local power quality problems, and certain effect has been achieved. Compared with other compensators in the substations, for example, capacitor bank, SVQC, SVC etc, actual loss of SVG is above average level, this limits its practicability.This paper puts forward a method that utilizes soft switch technology to reduce IGBT on/off loss in SVG device, gives main circuit topology of the designed soft switch PWM inverter, and the comparative analysis with on/off loss of hard switch, proves effectiveness of this method.

Distributed Control Systems for Small-Scale Power Networks: Using Multiagent Cooperative Control Theory

Existing electric power distribution networks are operating near full capacity and facing rapid changes to address environmental concerns and improve their reliability and sustainability. These concerns are satisfied through the effective integration and coordination of distributed generators (DGs), which facilitate the exploitation of renewable energy resources, including wind power, photovoltaics, and fuel cells [1]. Although DGs can be of rotating machinery type, more recently, DGs have been designed to support renewable energy resources by electronic interfacing through voltage source inverters (VSI). Each DG corresponds to one energy source, and its control inputs are given to the interface VSI [1]-[5]. The successful coordination of DGs can be realized through microgrids, which are small-scale power systems consisting of local generation, local loads, and energy storage systems. Microgrids are autonomous subsystems with dedicated control systems that provide guaranteed power quality for local loads such as hospitals, economic centers, apartments, and universities. The microgrid concept, with its local control and power quality support, allows for the scalable integration of local power resources and loads into the existing power grid and enables a high penetration of distributed generation [5]-[10].

Ecodesign of Ever Net-Load Microgrids

The European Union has promoted the process of electrical market liberalization, extended to residential/commercial buildings, and a strong encouragement toward the rational use of energy. The European energetic policy aims to promote the installation of small renewable power sources, the use of highly efficient cogeneration, and the Nearly Zero-Energy Buildings (NZEBs) that have to be pursued as much as possible by local generation sufficient to supply the residual amount of energy. To avoid future chaotic phenomena in the existing distribution network, this paper highlights that the power flow of local generators has to be maintained locally: The users have to remain net-loads organized in ever net-load microgrids at least in a first evolution. The actual distribution network for low-voltage customers appears inadequate to comply with these improvements, and it has to change in order to accept microgrids organized by the union of customer groups. The authors suggest the ecodesign of the microgrids able to constitute the NZEB and to accomplish the goals of enhanced safety, high local power quality, dc distribution systems, common emergency systems, efficient load shedding, and energy management. The microgrids guarantee a reduced impact as ever net-load on the net supply.

Load-following active power filter for a solid oxide fuel cell supported load

While the integration of base-load fuel cells into the built environment is expected to provide numerous benefits to the user, the steady-state and dynamic behavior of these stationary fuel cell systems can produce an undesirable impact on the grid distribution circuit at the point of connection. In the present paper, a load-following active power filter (LFAPF) is proposed to mitigate the grid impact of such systems and instead improve overall local power quality. To evaluate the strategy, the LFAPF is integrated into a SOFC system inverter with one-cycle control (OCC) to provide the fundamental benefits of a traditional active power filter (APF) while also damping out short-term line current transients. The LFAPF benefit is illustrated through simulation of an SOFC interconnected with the utility electric distribution system and a building electricity demand that is modeled as a dynamic non-linear load. Three installation cases are examined: (1) a load-following SOFC, (2) a base-loaded SOFC, and (3) an offline SOFC. Without LFAPF, the load-following SOFC causes load transients due to the finite SOFC response time, and the base-loaded SOFC case has transients that appear more severe because they represent a larger overall percentage of the grid-provided load. The integration of an LFAPF improves the steady-state behavior over the base case and mitigates voltage sags and step changes. Thus integrating an LFAPF can, by providing useful services to both the utility and the end-user, facilitate the integration of an SOFC into the distribution system.

An electronic solution for the direct connection of a three-phase induction generator to a single-phase feeder

This paper proposes a solution for the direct connection of a three-phase induction generator to a single-phase feeder. This high power quality system is intended to be used in micro-hydro power plants applications with control of the water flow. It is employed to maintain the speed of the induction generator greater than its synchronous value. The difference between the generated power and the power consumed by the local load flows through the single-phase feeder. The power flow control is provided by a three-phase PWM inverter that additionally guarantees the local power quality. A system with good power quality must have sinusoidal and constant amplitude voltages, fixed frequency operation, balanced induction generator voltages and currents, harmonics and reactive power compensation. The paper describes the inverter control strategy, presents design criteria of the controllers, and shows experimental results.