Distribution System Load Research Articles

Neutral Current Minimization Control for Solid State Transformers Under Unbalanced Loads in Distribution Systems

This paper analyzes the neutral current reduction performance of a three-phase four-leg solid state transformer (SST) under different degrees of unbalanced load. Several kinds of control strategies are presented, such as the neutral current elimination controls that rely on phase shifting, voltage amplitude, phase shifting, and voltage amplitude combination control. A neutral current minimization control, which ensures the SST output voltages complying with the EN 50160 output voltage unbalance standard, is also developed. These control approaches simply build on the balanced voltage control providing voltage references which slightly unbalance the voltage amplitude and phase angle or both. The effectiveness of the proposed strategies is validated through tests on a downscaled prototype. Simulation results for the neutral current minimization control of the SST applied to a real urban distribution network with distributed loads are presented. The results of this analysis show that overall the neutral current minimization results in an energy saving from both reduced losses in the distribution cables and reduced power consumption in the load.

Data-Driven Distribution System Load Modeling for Quasi-Static Time-Series Simulation

This paper presents a data-driven distribution system load modeling methodology targeting quasi-static timeseries (QSTS) simulation. The proposed methodology is appropriate for modeling down to the level of the customer transformer, and it has three main features: 1) both load pattern diversity and intra-second load variability are considered, 2) the load profiles can be populated for multiple nodes on a circuit in such a way that the diversity factor of the feeder can be defined and tuned, and 3) the load aggregation method can be used to populate the profiles for different nodes at various load aggregation levels. As the foundation of the modeling methodology, variability and diversity libraries have been established based on high-resolution load data collected on customer transformers from real utility feeders. The proposed modeling methodology has been used to build load data sets for both the IEEE 123-bus feeder model and a realistic utility feeder model. The QSTS simulation results on the two evaluation feeders have demonstrated that the load data sets established from the proposed modeling methodology can effectively capture the load impact on feeder operations. For the realistic utility feeder, the effectiveness of the proposed methodology has also been validated by comparing the voltage characteristics of the feeder with modeled loads and the voltage characteristics of realistic voltage data from the same feeder.

A Research on Microgrid Technology by Non Conventional and Renewable Sources

Microgrid are little gathering of interconnected power age in charge innovations that can work inside or free of a focal matrix, genuine aggravations and expandingsystem unwavering quality.Distributed resources can give capacity to local loads in the electric distribution system just as advantages,for example improve unwavering quality.Microgrid are capable of operating in grid tied mode and islanded mode.An ideal power system is utilized to decide the ideal allotment of assets utilizing a tranformative programming stratergy,acomplishing the most the minimal expense of providing the interest while representing physical activity.

Investigation and Enhancement of Stability in Grid-Connected Active DC Distribution Systems With High Penetration Level of Dynamic Loads

Nowadays, grid-connected active dc distribution systems are gaining widespread acceptance due to the remarkable development of the dc technology, high penetration levels of dc loads, and the market availability of dc-based distributed generators. One of the main features of dc systems is the elimination of multiple conversion stages required for variable frequency ac loads, such as variable-speed drive applications; therefore, dc distribution systems are considered as an efficient and cost-effective choice for supplying such dynamic loads. Induction motors (IMs) equipped with open-loop constant voltage/frequency $(V/f)$ variable speed drives are considered as the workforce for many industrial loads due to their simplicity and satisfactory dynamic performance. However, $V/f$ IM drives exhibit poor stability dynamics, particularly, at low-speed operation, which might negatively interact with the dc distribution system, leading to further stability degradation. Therefore, this paper investigates the interaction dynamics and the performance of a grid-connected dc distribution system with a high penetration level of dynamic loads. A detailed small-signal model of the entire system is developed to characterize the overall system stability margins with the help of the eigenvalues and impedance-based analysis. Moreover, the uncertainties affecting the marginal stability such as motor operating speed, dc feeder length, and bus capacitance, are thoroughly addressed. It has been found that the dynamic loads in grid-connected dc distribution systems would exhibit instability issues due to various dynamic interactions; therefore, two different stabilizing compensation methods are proposed to mitigate the associating instability issues and enhance the system damping capability. Detailed time-domain non-linear simulations and experimental results are presented to validate the analytical results.

Over/Under Voltage Tripping Circuit for Distributed System Load with GSM alert using Microcontroller

This paper introduces microcontroller based over voltage and undervoltage protection of domestic appliances and monitoring them through GSM. It starts with the importance of using micro controller in controlling voltage condition, it covers up the aspects why this method of protection is better and simpler than conventional method. We used ATmega32 microcontroller and Sim 900A GSM module to get the status of the supply voltage, be it the time of tripping or at any instant by sending specific text to GSM module. We have also added LCD to get voltage value at any time and status during abnormal condition. There is a limit set for a range of voltage that would be considered normal working condition. Microcontroller will check this condition and trip load if it does not satisfy. Under voltage and overvoltage are one of the major issues prevailing at domestic level that can affect electrical appliances. This method of protection can curb this issue significantly.

Two-port network model of fixed-speed wind turbine generator for distribution system load flow analysis

Load flow analysis has always been used in determining the steady-state operation of an electric power or distribution system. For conventional power system without wind turbine generator, the method for load flow analysis has been well established. However, for modern system embedded with wind turbine generator, the investigation of analysis method is still an active research area. This paper proposed a new method to integrate fixed-speed wind turbine generator into distribution system load flow analysis. The proposed method is derived based on two-port network theory where the parameters of induction generator of the wind turbine generator are embedded in general constants of the two-port network. The proposed method has been tested and verified using a representative electric distribution system.

High impedance fault detection in distribution system

<p>High impedance faults (HIFs) present a huge complexity of identification in an electric power distribution network (EPDN) due to their characteristics. Further, the growth of non-linear load adds complexity in HIF detection. One primary challenge of power system engineers is to reliably detect and discriminate HIFs from normal distribution system load and other switching transient disturbances. In this study, a novel HIF detection method is proposed based on the simulation of an accurate model of an actual EPDN study with real data. The proposed method uses current signal alone and does not require voltage signal. Wavelet transform (WT) is used for signal decomposition to extract statistical features and classification of HIF into Non-HIF (NHIF) by Neural Networks (NNs). The simulation study of the proposed method provides good, consistent and powerful protection for HIF.</p>

Economic assessment of non-sinusoidal energy in distorted distribution systems

PurposeThe purpose of this paper is to analyze annual energy expenditure in the presence of non-linear load and substation voltage harmonics in distribution systems. Economic assessment of non-sinusoidal energy is a challenging task that involves complex computations of harmonic load powers and harmonic line losses.Design/methodology/approachThe paper evaluates fundamental and non-sinusoidal components of electrical energy by applying backward/forward sweep technique in distorted distribution systems. This work involves harmonic power computations at the substation by including harmonic losses occurring in various lines of the distribution system.FindingsThe paper found that annual energy expenditure significantly depends upon the non-linear load, supply voltage harmonics and type of tariff structure considered in the distribution system. Impact of individual harmonic orders on the energy billing is also assessed.Originality/valueThe paper concludes that considering harmonic distortions in the distribution system analysis would help electricity regulators formulate adequate pricing structures, which would further generate appropriate economic signals for electricity utility and the consumers.

Scalable Single-Phase Multi-Functional Inverter for Integration of Rooftop Solar-PV to Low-Voltage Ideal and Weak Utility Grid

Integration of rooftop solar-PV (RTSPV) systems and extensive use of nonlinear loads in the low-voltage distribution system (LVDS) leads to poor power quality (PQ). Therefore, it is necessary to address the issues leading to poor PQ at the point of common coupling of the LVDS. In this article, a multi-band hysteresis current control (MB-HCC) for the multi-functional inverter (MFI) is proposed which improves the efficiency of the MFI and also enhances the PQ of the LVDS. The MB-HCC uses simple switching logic and outperforms in its multi-functional tasks such as active power injection and power conditioning. MB-HCC offers better efficiency over variable double-band HCC (VDB-HCC) as it operates at a lower switching frequency. The performance of the proposed system is simulated by using MATLAB/Simulink and validated by OPAL-RT based real-time simulation studies. During the variation of solar irradiation, the proposed MFI has an average efficiency of 98.5% under the ideal grid and 97.34% under the distorted grid. Moreover, the percentage of Total Harmonic Distortion under ideal and distorted grid conditions is brought down to below 5%, and also, reactive power compensation maintains unity power factor operation complying with the IEEE-519-2014 and 1547 standards. These results substantiate the hypothesis of scalability of the single-phase MB-HCC-based MFI for an LVDS contributing to economy and ecology.

Integrating demand side management into EU electricity distribution system operation: A Dutch example

The EU goals for renewable electricity cause significant changes of electrical loads in distribution systems, in which most renewable electricity sources are integrated. This poses a challenge for distribution system operators (DSOs) as their networks are not designed for such load changes. DSOs could use networks more efficiently with demand side management (DSM), where consumers of electricity alter their consumption patterns, shifting (production/consumption) loads in the distribution system. In such a setting, consumers would trade DSM services with the DSOs. However, currently, DSOs follow the ‘copper plate approach’, which assumes the system should have sufficient capacity to ensure that the desired volumes of electricity can be transported. This seeks to guarantee regulated third party access (rTPA) for all system users. Next to rTPA, based on regulated tasks, DSOs should ensure secure, reliable and efficient systems. In doing so, the DSOs are bound by unbundling requirements, which do not allow them to be involved in any activities other than those related to distribution. Therefore, especially production and supply are not allowed. Still, it seems debatable whether EU law allows DSOs to apply DSM, as it has an impact on both the access conditions to the electricity system, and the production, supply and trade of electricity. This article further analyses how DSM relates to the legal framework of DSOs, which obstacles are present, and how DSM could be traded between DSOs and system users.

Optimal distribution system restoration using PHEVs

Power outages cost billions of dollars every year and jeopardise the lives of hospital patients. Traditionally, power distribution system takes a long time to recover after a major blackout, due to its top-down operation strategy. New technologies in modern distribution systems bring opportunities and challenges to distribution system restoration. As fast response energy resources, plug-in hybrid electric vehicles (PHEVs) can accelerate the load pickup by compensating the imbalance between available generation and distribution system load. This study provides a bottom-up restoration strategy to use PHEVs for reliable load pickup and faster restoration process. The optimisation problem of finding load pickup sequence to maximise restored energy is formulated as a mixed integer linear programming (MILP) problem. Moreover, the coordination between transmission and distribution restoration is developed to efficiently restore the entire system back to normal operating conditions. Simulation results on one 100-feeder test system demonstrate the efficiency of MILP-based restoration strategy and the benefit from PHEVs to restore more energy in given restoration time. The proposed restoration strategy has great potential to facilitate system operators to achieve efficient system restoration plans. It also provides incentives to deploy a large amount of PHEVs to improve system resiliency.

Influence of distributed photovoltaic power generation on distribution network and the design of optimal access scheme

Distributed photovoltaic (PV) access to distribution network will affect the line loss and voltage of the system, and affect the reliability and economic operation of the distribution system. Therefore, in this study, firstly, node analysis models of distribution network system with four different typical load distribution is established. Secondly, the changes of voltage and network loss caused by distributed PV access to distribution network systems with four typical load distribution are analysed, and the formula of optimal access position and optimal access capacity of distributed PV system under different load distribution system is derived. Thirdly, on the basis of the work data of a distribution line with 43 distributed PV access in Tongchuan city, Shaanxi Province, China, the influence of distributed PV power generation on line loss and voltage of distribution network under different weather conditions are analysed. Finally, an optimal PV access scheme for distribution network based on ant colony algorithm is proposed to ensure the reliable and economical operation of distribution network after distributed PV access. The simulation model of distribution system with distributed PV access is established under Matlab, and the simulation results show the correctness and effectiveness of the proposed formula and the optimisation scheme.

Resilience-Oriented Distribution System Restoration Considering Mobile Emergency Resource Dispatch in Transportation System

After major outages, local power sources, including mobile power sources (MPSs), can be coordinated to serve critical loads in distribution systems (DSs). Repair crews (RCs) are sent to repair faulted components. Both mobile emergency resources, i.e., MPSs and RCs, need to travel through the transportation system (TS) before they reach the destination for service. However, traffic congestion may happen after natural disasters and impact the dispatch of the MPSs and RCs. Therefore, the dynamic traffic state in the TS should be considered for efficient dispatch of mobile emergency resources. This paper proposes a framework to determine critical load restoration strategy for the DS, considering the dispatch strategy of the MPSs and RCs in the TS. The cell transmission model (CTM) is used to formulate the weighted dynamic traffic assignment problem (WDTA) in the TS as a linear program (LP), aiming at minimizing the total prioritized travel time of the MPSs and RCs. For the DS, the multi-period critical load restoration problem (CLR-DS) is formulated as a mixed-integer linear program (MILP) to maximize the cumulated service time to critical loads. Unbalanced three-phase power flow and time-varying topological constraints are considered. Case studies validate the effectiveness of the proposed method.

Distributed Finite-Time Secondary Control for DC Microgrids With Virtual Impedance Arrangement

In direct current (DC) microgrids, the accurate current sharing could be achieved by regulating the virtual impedance (droop coefficient) and the output voltage average value of each distributed generator (DG) could be restored by regulating the voltage reference value with a secondary controller. However, there is a coupling relationship between the current sharing and the voltage restoration process. In this paper, a distributed finite-time secondary control strategy is proposed aiming at overcoming the coupling effect. The proposed controller consists of four control loops, which are the current sharing controller (CSC), the virtual impedance average value restoration controller (AIRC), the reference voltage consensus controller (RVCC), and the voltage average value restoration controller (AVRC). With the proposed controller, the coupling effect is eliminated and the virtual impedance of each DG is only determined by the system load distribution. Besides, a simplified control strategy is also proposed which only contains the CSC and AIRC, and the reference voltage value can be calculated using the local information. The stability of the proposed controller is analyzed using the Lyapunov method. At last, the proposed controller is simulated in MATLAB/Simulink to verify its effectiveness.

Modeling the Impact of the Vehicle-to-Grid Services on the Hourly Operation of the Power Distribution Grid

Electric Vehicles (EVs) impact on the grid could be very high. Unless we monitor and control the integration of EVs, the distribution network might experience unexpected high or low load that might exceed the system voltage limits, leading to severe stability issues. On the other hand, the available energy stored in the EVs can be utilized to free the distribution system from some of the congested load at certain times or to allow the grid to charge more EVs at any time of the day, including peak hours. This article presents dynamic simulations of the hour-to-hour operation of the distribution feeder to measure the grid’s reaction to the EV’s charging and discharging process. Four case scenarios were modeled here considering a 24-h distribution system load data on the IEEE 34 bus feeder. The results show the level of charging and discharging that were allowed on this test system, during each hour of the day, before violating the limits of the system. It also estimates the costs of charging throughout the day, utilizing time-of-use rates as well as the number of EVs to be charged on an hourly basis on each bus and provide hints on the best locations on the system to establish the charging infrastructure.

Passive harmonic filter planning considering daily load variations and distribution system reconfiguration

Although distribution system reconfiguration is usually implemented for grid loss reduction, it can affect many other indices of the grid such as voltage profile and power quality indices. Therefore, harmonic filter planning studies which ignore different configurations of the system cannot achieve optimal solutions. In other words, when the filter planning study is carried out with respect to a single grid topology, power quality constraints satisfaction isn’t guaranteed while the real-world loss-reduction-based reconfigurations are applied to the system. In order to incorporate different configurations of the grid in planning study, this paper proposes an aggregate model for passive harmonic filter planning and loss-reduction-based reconfigurations in primary distribution systems. In this method, in order to incorporate distribution system operator decisions, reconfiguration for loss minimization is carried out as a lower level problem in pre-determined hours of each day type. The passive harmonic filter planning (as the higher level problem) is then studied with respect to the daily load profiles and different system configurations. Two separate Genetic-Algorithm (GA) cores are implemented to solve the main passive harmonic filter planning problem and reconfigurations. The proposed method is then applied to a modified 33-bus system with high penetration of nonlinear loads. The simulation results verified that ignoring the system reconfigurations in planning process may result in power quality constraints violation in some specified hours during the planning horizon. On the other hand, incorporating different system topologies in the planning study guarantees to maintain the system Total Harmonic Distortion (THD) levels within the standard limits and results in lower energy loss, capacity occupation and filter investment cost.

A Short-Term and High-Resolution Distribution System Load Forecasting Approach Using Support Vector Regression With Hybrid Parameters Optimization

This paper proposes an approach for distribution system load forecasting, which aims to provide highly accurate short-term load forecasting with high resolution utilizing a support vector regression (SVR) based forecaster and a two-step hybrid parameters optimization method. Specifically, because the load profiles in distribution systems contain abrupt deviations, a data normalization is designed as the pretreatment for the collected historical load data. Then an SVR model is trained by the load data to forecast the future load. For better performance of SVR, a two-step hybrid optimization algorithm is proposed to determine the best parameters. In the first step of the hybrid optimization algorithm, a designed grid traverse algorithm (GTA) is used to narrow the parameters searching area from a global to local space. In the second step, based on the result of the GTA, particle swarm optimization is used to determine the best parameters in the local parameter space. After the best parameters are determined, the SVR model is used to forecast the short-term load deviation in the distribution system. The performance of the proposed approach is compared to some classic methods in later sections of this paper.

Design of PI and Fuzzy Logic Controllers for Distribution Static Compensator

<span>This paper presents study of distribution static compensator (D-STATCOM) for compensation of reactive power, harmonic distortion mitigation and load balancing in three phase three wire nonlinear load distribution system. The proposed control algorithm is developed based on synchronous reference frame theory using PI and FUZZY logic controller. The obtained reference current signal from control algorithm is compared in hysteresis band current controller for better switching of D-STATCOM. The performance of DSTATCOM with PI and fuzzy logic controller is also analysed and compared for DC voltage regulation and harmonic distortion mitigation .The proposed method is provided effective compensation for reactive power, harmonic distortion mitigation and load voltage balancing. The simulation results are obtained using MATLAB/SIMULINK soft ware.</span>

An Efficient Load Flow Algorithm for AC–DC Distribution Systems

The AC–DC distribution systems have recently gained huge popularity due to advancements in power converters, high penetration of renewable energy resources and widespread use of DC loads. However, load flow in such systems is a challenging task, due to non-linear characteristics of power converters. This paper presents a new and computationally efficient load flow algorithm for AC distribution systems using graphical search technique along with matrix algebra and has been further extended for solving AC–DC distribution systems load flow problem by making use of proposed per-unit equivalent model of various power converter devices. In contrast with traditional methods, the proposed technique does not require any LU decomposition, matrix inversion and forward backward substitution of admittance matrix or Jacobian matrix. The significant feature of the proposed algorithm lies in formulation of path impedance matrix and loads beyond branch matrix, which will remain unaltered for the entire operation. Reconfiguration of these matrices takes place automatically in accordance with the change in input data. Because of the aforementioned reasons, the developed technique is computationally potent when applied on large sized distribution systems. The proposed method has been validated on various standard test systems. Results show feasibility and authenticity of the proposed method.

Load Distribution of Semi-Central Evaporative Cooling Air-Conditioning System Based on the TRNSYS Platform

Evaporative cooling is a green, energy-efficient cooling technology adopted in hot and dry regions, which has wider application in the field of air-conditioning systems. Outdoor meteorological parameters have a great influence on the operation mode and control strategy of evaporative cooling air-conditioning systems, and the system load distribution and system configuration will be affected. This paper aims at investigating the load distribution of semi-central evaporative cooling air-conditioning systems under the condition of hourly outdoor meteorological parameters. Firstly, this paper introduced the design partition, operation mode, controlling strategy and load distribution method on semi-central evaporative cooling air-conditioning system. Then, taking an office building in Lanzhou (China) as an example, the evaporative cooling air-conditioning system was divided into five regions and the load distribution was simulated by TRNSYS (The Transient Energy System Simulation Tool) under the condition of hourly outdoor meteorological parameters. Finally, the results have shown that the evaporative cooling air-conditioning system can provide 25.46% of the building loads, which was of great significance to reduce the energy consumption of air-conditioning system.