Real Voltage Research Articles

Conjugate gradient back-propagation based artificial neural network for real time power quality assessment

This paper proposes conjugate gradient back-propagation based artificial neural network for real time power quality assessment. The novel real time voltage sag and swell detection, classification scheme using artificial neural network is presented. The ANN is trained in MATLAB using voltage sampled signal data and corresponding parameters of the neural network are utilized to implement in LabVIEW in real time sag swell detection and classification. The Levenberg Marquardt, the resilient back-propagation and conjugate back-propagation algorithm performance is evaluated in MATLAB to find the best neural network for real time application. Among these three back-propagation algorithms, conjugate gradient algorithm has better performance for real time power quality monitoring. The mathematical model of Conjugate gradient back-propagation neural network is implemented in LabVIEW. Real time voltage signals of sag and swell for different time duration and magnitude, intensity are acquired from hardware experimental setup. Hardware setup mainly consists of single phase 230V voltage source, microcontroller, dimmerstat and solid state relays. Voltage signals of sag and swell are sensed using high precision voltage sensor. Data acquisition system is used to acquire the signal from voltage sensor. The output of data acquisition system is given to the personal computer with LabVIEW. The proposed monitoring system also detects odd and even harmonic components in the voltage signal acquired using FFT. Real time hardware results obtained using proposed power quality monitoring system for detection of voltage sag, swell and harmonics claims the suitability, robustness and adaptability to monitor power quality issues.

A teaching learning based optimization technique for optimal location and size of DG in distribution network

DGs are placed for the purpose of real power loss minimization and voltage improvement in distribution network system. This paper presents a recent optimization technique, i.e. teaching learning based optimization (TLBO) technique for finding the optimal size and location of Distributed generation (DG) in radial distribution system (RDS). The optimal location and size of DG is analyzed considering voltage stability index as an objective function. The superiority of the proposed approach has been shown by comparing the results with GA and PSO methods in RDS. The comparison is done using system performances such as the real power loss and voltage profile of RDS. In this paper, performance analysis is carried out considering IEEE 33 bus and 69 buses as the test system.

Optimal Reactive Power Dispatch Using Improved Pseudo-gradient Search Particle Swarm Optimization

This article proposes an improved pseudo-gradient search-particle swarm optimization (IPG-PSO) approach for solving the optimal reactive power dispatch (ORPD) problem. This ORPD problem is to determine optimal control variables, such as generator bus voltages, settings of shunt VAR compensators, and tap settings of on-load tap change (OLTC) transformers, for minimizing the real power loss, voltage deviation, and voltage stability index satisfying power balance equations and generator and network operating limit constraints. The proposed method is an improved PSO using a linearly decreasing chaotic inertia weight factor and guided by a pseudo-gradient search, which determines an appropriate direction of particles toward a global optimal solution. The proposed IPG-PSO method is used to minimize three different single-objective functions, including real power loss, voltage deviation, and voltage stability index. Test results on the IEEE 30-bus and 118-bus systems indicate that the proposed IPG-PSO method renders a higher solution quality and faster computing time than other methods. Accordingly, the proposed IPG-PSO for solving ORPD problem is potentially viable for online implementation.

Nonlinear structural joint model updating based on instantaneous characteristics of dynamic responses

This paper proposes a new nonlinear joint model updating method for shear type structures based on the instantaneous characteristics of the decomposed structural dynamic responses. To obtain an accurate representation of a nonlinear system׳s dynamics, the nonlinear joint model is described as the nonlinear spring element with bilinear stiffness. The instantaneous frequencies and amplitudes of the decomposed mono-component are first extracted by the analytical mode decomposition (AMD) method. Then, an objective function based on the residuals of the instantaneous frequencies and amplitudes between the experimental structure and the nonlinear model is created for the nonlinear joint model updating. The optimal values of the nonlinear joint model parameters are obtained by minimizing the objective function using the simulated annealing global optimization method. To validate the effectiveness of the proposed method, a single-story shear type structure subjected to earthquake and harmonic excitations is simulated as a numerical example. Then, a beam structure with multiple local nonlinear elements subjected to earthquake excitation is also simulated. The nonlinear beam structure is updated based on the global and local model using the proposed method. The results show that the proposed local nonlinear model updating method is more effective for structures with multiple local nonlinear elements. Finally, the proposed method is verified by the shake table test of a real high voltage switch structure. The accuracy of the proposed method is quantified both in numerical and experimental applications using the defined error indices. Both the numerical and experimental results have shown that the proposed method can effectively update the nonlinear joint model.

A novel method based on adaptive cuckoo search for optimal network reconfiguration and distributed generation allocation in distribution network

Abstract This paper proposes a new methodology to optimize network topology and placement of distributed generation (DG) in distribution network with an objective of reduction real power loss and voltage stability enhancement. A meta-heuristic cuckoo search algorithm (CSA) inspired from the obligate brood parasitism of some cuckoo species which lay their eggs in the nests of other birds of other species for solving optimization problems is adapted to simultaneously reconfigure and identify the optimal location and size of DG units in a distribution network. The graph theory is used to determine the search space which reduces infeasible network configurations of reconfiguration process and check the radial constraint of each configuration of distribution network. The effectiveness of the proposed method has been validated on three different distribution network systems at seven different scenarios. The obtained results show well the effectiveness and performance of the proposed method in distribution network reconfiguration with optimal location and size of DG problems.

Optimal Power Flow Using Firefly Algorithm with Unified Power Flow Controller

Firefly algorithm is the new intelligent algorithm used for all complex engineering optimization problems. Power system has many complex optimization problems one of which is the optimal power flow (OPF). Basically, it is minimizing optimization problem and subjected to many complex objective functions and constraints. Hence, firefly algorithm is used to solve OPF in this paper. The aim of the firefly is to optimize the control variables, namely generated real power, voltage magnitude and tap setting of transformers. Flexible AC Transmission system (FACTS) devices may used in the power system to improve the quality of the power supply and to reduce the cost of the generation. FACTS devices are classified into series, shunt, shunt-series and series-series connected devices. Unified power flow controller (UPFC) is shunt-series type device that posses all capabilities to control real, reactive powers, voltage and reactance of the connected line in the power system. Hence, UPFC is included in the considered IEEE 30 bus for the OPF solution.

Stability Criterion for Voltage Stability Study of Distributed Generators

This paper proposes a stability criterion for the study of distributed generators equipped with local reactive power regulations. Existing formal methods propose a memory-consuming analysis with some practical issues while dealing with large-scale systems. To cope with this, a novel analytic stability criterion is established in this work. Firstly, a necessary condition for system stability is demonstrated for a feeder hosting a single generator. The approach is illustrated on a real medium voltage feeder. Then, a conjecture is proposed to study the stability of feeders hosting several generators equipped with reactive power regulations. Conjecture validity is proved over several theoretical grids hosting up to four distributed generators thanks to simulations.

Optimal Power Flow with Static VAR Compensator Using Galaxy Based Search Algorithm to Minimize Real Power Losses

In this paper, Galaxy based search algorithm (GbSA) is used to solve multi-objective problem of optimization in power systems. The proposed GbSA resembles the spiral arms of some galaxies to search for the optimal solutions. The GbSA also uses a modified Hill Climbing algorithm as a local search. Simulation results show that the GbSA finds the optimal or very near optimal values in all runs of the algorithm. The weighted sum technique with equal weights has been chosen to solve the multi-objective function. The functions considered are to minimize the power losses in transmission line, cost of the real power generation and voltage deviation. Static VAR Compensator (SVC) is used for the purpose of optimal power flow. L-index is used to identify the optimal location to place SVC. The results have been compared with Genetic algorithm (GA) for IEEE-14 System.

An Improved Three-Phase AMB Distribution System State Estimator

State estimators (SEs) are required to enable the evolving and increasingly important role of communications and control in smart distribution systems. In this context, this paper presents an improved three-phase admittance matrix-based (AMB) SE for medium voltage systems to tackle issues related to zero injections, consistency, and the inclusion of voltage measurements. Here, the state variables are the real and imaginary parts of the complex bus voltages, while power and voltage measurements are converted into equivalent currents and voltages, respectively. The key improvements include: 1) considering zero injections through a linear nonweighted procedure, 2) using phasor rotation for calculation of the equivalent voltage measurements, and 3) including the covariance between real and imaginary parts of equivalent current measurements. Despite these new characteristics, the proposed improved AMB SE (ISE) features constant coefficient matrices, thus resulting in reduced computational times. The performance of the ISE is assessed considering a real UK medium voltage system. Its consistency is assessed via a Monte Carlo analysis. Comparisons with other AMB SEs demonstrate that the proposed three-phase ISE is more robust, statistically more consistent, and computationally very competitive.

Order Reduction of Lithium-Ion Battery Model Based on Solid State Diffusion Dynamics via Large Scale Systems Theory

A simple and accurate model is essential for the model-based control design. The 1D electrode-averaged battery model maintains the prediction accuracy and depth of physical interpretations. The most critical and complicated dynamics in the system is solid phase concentration diffusion, which has a direct impact on battery status. The finite difference method based on uneven discretization benefits to reduce the complexity. Then, the simplification theory of large scale systems is applied to retain the dominant variable and make the model more compact. The simplification process meets the requirements of fast computation and retention of electrochemical diffusion dynamics. This approach was experimentally verified under 0.2C to 2Cdischarge tests. The simulation output converges to the real terminal voltage within an error of ±0.1V. The simplified model enjoys advantages including high accuracy, low computational cost, and therefore is suitable for deployment and use in real-time embedded battery management systems (BMSs).

Microgeneration Impact on LV Distribution Grids: A Review of Recent Research on Overvoltage Mitigation Techniques

Nowadays, due to the increasing rate of microgeneration penetration in Low Voltage distribution networks, overvoltage and power quality issues are more likely to occur in a more and more bidirectional operating grid. This paper offers a recent review on the main techniques available to mitigate and regulate feeder voltage profile, such as, PV generation active curtailment, reactive power support, On-Load Tap Changer transformers, or even recurring to Battery Energy Storage systems. Whenever possible, published results in real and test Low Voltage grids are called to support each given example.

Evaluation of Measures to Operate Urban Low Voltage Grids Considering Future PV Expansion

Abstract: The Swiss federal government set forth its energy policy, titled ”Energiestrategie 2050,” in which photovoltaics (PV) production would reach 20% of the total yearly electrical energy production by the year 2050. Such a drastic expansion rate of PV and the resulting excess energy thereof, however, can lead to technical challenges for the infrastructure of the power system. In this paper, the impact of the future PV penetration on a real urban low voltage (LV) area is presented. To this end, two PV scenarios are devised and implemented, and quasi dynamic load flow simulations are conducted for every fifteen minutes interval of a whole year. To generate the input data, a load profile generator is developed based on smart meter measurement data. It is concluded that the examined urban area appears to be prepared for a certain amount of further PV integration as there were no violations detected for the medium PV production scenario (43% of the total consumption in the area). However, for the maximum PV penetration scenario to be implemented, violations such as over voltage and transformer overloading are detected. To resolve these issues, different mitigation measures such as battery energy storage system, active power curtailment and short-term overloading of the transformer are implemented and examined with the aid of appropriate mathematical models. As a result, at least 20% of the PV energy needs to be stored, curtailed or used by demand side management, in order to run the low voltage grid as it is. In a further work, an intelligent combination of different measures could be examined to fully utilize the excess energy.

Оценка быстродействия энергоблоков «синхронный генератор – ОРПМ» при регулировании напряжения в схемах выдачи мощности электростанций

The main method of voltage and reactive power control is to change the excitation current of synchronous generators. This method requires a complex excitation system that can provide a necessary control range. In addition, response performance of such control is constrained by a long time constant of the excitation circuit. One of the alternative control methods is the use of power units including synchronous generators with a non-controlled excitation system and unified power flow controllers (UPFC). The MATLAB Simulink software package enabled research of mode control performance of such power units and comparison with the thyristor excitation systems. Furthermore, a real voltage change was analyzed at short-circuit in the power system. The synchronous generator - UPFC power units are proved to implement a high-speed voltage control, which can significantly increase flexibility and adaptability of mode control in the power distribution circuits of the power plants.

Optimizing real power loss and voltage stability limit of a large transmission network using firefly algorithm

This paper proposes a Firefly algorithm based technique to optimize the control variables for simultaneous optimization of real power loss and voltage stability limit of the transmission system. Mathematically, this issue can be formulated as nonlinear equality and inequality constrained optimization problem with an objective function integrating both real power loss and voltage stability limit. Transformers taps, unified power flow controller and its parameters have been included as control variables in the problem formulation. The effectiveness of the proposed algorithm has been tested on New England 39-bus system. Simulation results obtained with the proposed algorithm are compared with the real coded genetic algorithm for single objective of real power loss minimization and multi-objective of real power loss minimization and voltage stability limit maximization. Also, a classical optimization method known as interior point successive linear programming technique is considered here to compare the results of firefly algorithm for single objective of real power loss minimization. Simulation results confirm the potentiality of the proposed algorithm in solving optimization problems.

Optimum placement of shunt capacitors in a radial distribution system for substation power factor improvement using fuzzy GA method

Abstract In this work a combination of fuzzy multiobjective and genetic algorithm (GA) based approach is proposed for optimal shunt capacitor placement to improve the substation power factor near unity, reduce the real power loss, and reduce the burden on the substation and to improve the voltage profile of the distribution network. In order to obtain best nodes for capacitor placement, a sensitivity index based on real power loss reduction and voltage profile improvement is considered. In the present work, an attempt is made to make reactive current component drawn by distribution network through substation is nearly zero such that power factor at the substation will be near unity. A fuzzy multiobjective function is formed considering substation reactive current component reduction, real power loss reduction, branch current constraint limit, minimum and maximum voltage limit satisfaction. The fuzzy multiobjective function is maximized using GA for obtaining the optimum sizing of fixed and switched shunt capacitors. Simulation results are shown to demonstrate the advantage of the proposed method compared to optimal shunt capacitor placement based on annual energy savings method.

Hybridization of Firefly and Water Wave Algorithm for Solving Reactive Power Problem

In this paper, a hybrid algorithm as the combination of Firefly and Water Wave algorithm (FWW) has been proposed to solve the Reactive power problem. The firefly algorithm is a meta-heuristic technique which is widely used for solving the optimization problems. The water wave optimization algorithm is also a nature inspired based algorithm. Both algorithms collectively improved the performance of search. The water wave algorithm is work on the combinatorial optimization and utilized as application of firefly algorithm. Hence we merge these two algorithms and make a hybrid algorithm. Proposed FWW algorithm has been tested in standard IEEE 30 Bus test system and simulation results reveal the better performance of the proposed algorithm in reducing the real power loss and voltage profiles were found to be within the limits.

A uniform laminar air plasma plume with large volume excited by an alternating current voltage

Using a plasma jet composed of two needle electrodes, a laminar plasma plume with large volume is generated in air through an alternating current voltage excitation. Based on high-speed photography, a train of filaments is observed to propagate periodically away from their birth place along the gas flow. The laminar plume is in fact a temporal superposition of the arched filament train. The filament consists of a negative glow near the real time cathode, a positive column near the real time anode, and a Faraday dark space between them. It has been found that the propagation velocity of the filament increases with increasing the gas flow rate. Furthermore, the filament lifetime tends to follow a normal distribution (Gaussian distribution). The most probable lifetime decreases with increasing the gas flow rate or decreasing the averaged peak voltage. Results also indicate that the real time peak current decreases and the real time peak voltage increases with the propagation of the filament along the gas flow. The voltage-current curve indicates that, in every discharge cycle, the filament evolves from a Townsend discharge to a glow one and then the discharge quenches. Characteristic regions including a negative glow, a Faraday dark space, and a positive column can be discerned from the discharge filament. Furthermore, the plasma parameters such as the electron density, the vibrational temperature and the gas temperature are investigated based on the optical spectrum emitted from the laminar plume.

Electrical treeing behavior at high temperature in XLPE cable insulation samples

This paper reports on investigations aiming to understand the behavior of electrical trees formed in XLPE cable insulation at elevated temperatures. Samples cut from a real high voltage cable equipped with an embedded electrode system and composed of a needle separated by 2 mm from counter electrode were used. The temperature was varied between 50 and 90 °C and the range of voltage changed between 9 and 18 kV. The electrical treeing process was followed by means of microscopic observation from the moment of initiation until the leading branches connected the counter electrode and partial discharge (PD) activity was monitored simultaneously. The shape and fractal dimension of the resulting trees were analyzed. It was found that temperature and voltage level had pronounced effect on the process of electrical tree formation. At lower voltages different type of trees could be formed, whereas at higher voltages branch trees dominated. Increase of test temperature reduced the time for tree initiation, whereas the tree growth time was less affected, except for the lowest voltage level at which the slowest tree development was observed at the highest test temperature. It is postulated that the impeding effect of elevated temperature on tree growth is due to a change of tree channel sidewall conductivity, whereas the observed reduction of tree initiation time with the increase of temperature and voltage level is attributed to lowering of the threshold energy for damage at higher temperature as well as increasing of the injection current at higher voltage level.

Novel Phasor Transformation for Feedback Control Design of Induction Heating Systems With Experimental Results

For analyzing the transients of induction heating (IH) systems, time-dependent phasor transformations were proposed so far in the literature. Applying these transformations to linear R, L, C circuit equations leads to differential equations in the complex domain from which equivalent circuits modeling the envelopes of sinusoidal waveforms were derived. This paper proposes a phasor transformation, which is based on fictitiously replacing the real voltage and current signals of a system by complex voltage and current signals. It leads to transformed system equations in the real domain where instantaneous amplitudes, phases, and frequencies explicitly appear, which makes the transformed equations suitable for the feedback control design. The methodology is applied to a parallel IH system to design a sliding-mode controller. The theory is supported by simulations, experiments, and comparisons.

A two-point estimate method for uncertainty modeling in multi-objective optimal reactive power dispatch problem

Abstract Due to nonlinear and discrete variables and constraints, optimal reactive power dispatch (ORPD) is a complex optimization problem in power systems. In this paper, the purpose is to solve multi objective ORPD (MO-ORPD) problem considering bus voltage limits, the limits of branches power flow, generators voltages, transformers tap changers and the amount of compensation on weak buses. The objectives of this paper are real power losses and voltage deviations from their corresponding nominal values, which are conflicting objectives. Because of the stochastic behavior of loads, the MO-ORPD problem requires a probabilistic approach. Hence, in this paper, a two-point estimate method (TPEM) is proposed to model the load uncertainty in MO-ORPD problem. Moreover, the proposed method is compared with some other methods such as deterministic approaches and Monte Carlo simulations (MCS). The obtained results approve the efficiency of the proposed methodology. The proposed models are implemented and solved using GAMS optimization package and verified using IEEE 14-bus and IEEE 30-bus standard test systems.