System Active Power Research Articles

Исследование гиперповерхности мощностей установившихся режимов электрической системы

Absract: The study is given to the normal vector of the power hypersurface of power system steady states. The interrelation of the components of the normal vector is determined through incremental transmission loss coefficients. The analysis of the normal vector components has revealed that in the marginal state of the power system the component of the normal vector of slack bus active power equals zero, and the incremental transmission loss coefficient of the slack bus active power is one. Therefore, any attempts of the slack bus to support the power system active power balance in the marginal state are fully compensated by the associated power losses. In real power systems, variation of slack bus location makes this steady state non-marginal. The only power system where the marginal state does not depend upon a slack bus location is a lossless one.

A multi objective approach for placement of multiple DGs in the radial distribution system

Insertion of distributed generation (DG) in existing distribution system has effectively improved its performance and operation. Many different approaches for the planning of distribution system with DG insertion are presented by researchers. In this paper a multi objective approach has been proposed to maximize the mutual benefits of both the distribution system operator and DG owner. The contradictory relationship between reduction in MVA rating of DGs and reduction of power losses of the system is the motivation for this multi-objective approach. The best compromised size of DGs in MVA, their operating power factors and positions are obtained to reduce the system active power loss along with the reduction of DGs size. The 69-bus and 85-bus radial distribution system are considered as test systems. The Pareto-front of non-dominated solutions is obtained by using multi-objective differential evolution (MODE) optimization algorithm. The performance of MODE algorithm is also compared with that of multi-objective particle swarm optimization (MOPSO) algorithm. The different system operating indices such as active power loss, reactive power loss and voltage deviation are evaluated to show the effect of the best compromised solution of DGs placement in distribution system.

Modeling and Maximum Power Point Tracking Control of Wind Generating Units Equipped with Permanent Magnet Synchronous Generators in Presence of Losses

This paper focuses on the modeling of wind turbines equipped with direct drive permanent magnet synchronous generators for fundamental frequency power system simulations. Specifically, a procedure accounting for the system active power losses to initialize the simulation starting from the load flow results is proposed. Moreover, some analytical assessments are detailed on typical control schemes for fully rated wind turbine generators, thereby highlighting how active power losses play a fundamental role in the effectiveness of the wind generator control algorithm. Finally, the paper proposes analytical criteria to design the structure and the parameters of the regulators of the wind generator control scheme. Simulations performed with Digsilent Power Factory validated the proposed procedure, highlighting the impact of active power losses on the characterization of the initial steady state and that the simplifying assumptions done in order to synthesize the controllers are consistent with the complete modeling performed by the aforementioned power system simulator.

Application of Static Synchronous Compensator (STATCOM) in Improving Power System Performance: A Case Study of The Nigeria 330 KV Electricity Grid

Slow response of the conventional traditional methods for improving power system performance creates the need for adoption of advanced control technologies such as Flexible Alternating Current Transmission System (FACTS) with fast response and low cost for stabilizing electricity grid power and voltage. In this work, we examined the effect of application of Static Synchronous Compensator (STATCOM), a FACTS controller on the performance of the Nigeria 330 kV, 28-bus power system. The conventional and modified Newton-Raphson-based power flow equations describing the steady state conditions before and after compensation was made to the system were presented. Solutions to the developed equations were obtained using Matlab software (Version 7.9.0.529 ‘R2009b’). The results from the analysis showed that before the application of STATCOM, five (5) of the twenty eight ( 28) buses of the sample system have their voltage magnitudes fell outside the statutory limit of 0.95 V i 1.05 p.u, which were improved to 1.0 p.u. each at inclusion of STATCOM. Similarly, the total system active power loss was reduced by 5.88% from 98.21 to 92.44MW. Evidence from this finding is that STATCOM application on the Nigeria electricity grid will stabilise the system’s voltage and reduce the overall transmission active power loss thereby releasing spare capacities for more consumers. http://dx.doi.org/10.4314/njt.v34i3.20

Operational reliability assessment of power systems based on bus voltage

Bus voltage is a direct reliability indicator of a transmission network because it is related to system reactive and active power balance especially during a contingency state. This study proposes a technique to evaluate network operational reliability based on bus voltage. Two new voltage related bus reliability indices are proposed to represent bus reliability. Network reliability levels under various operating conditions and contingency states are evaluated and presented by probabilities of system voltage being in normal, under-voltage, critical and collapse zones. The probabilistic voltage margin to the collapse point for each bus is evaluated to provide information for system operator regarding the risk under system random failures and load uncertainty. The IEEE 30-bus system and a practical 220 kV Taiyuan power system in Shanxi Province of China have been analysed to illustrate the proposed techniques.

Study on Large-Scale Distributed Power Access to Distribution Networks for the Impact of the Loss in the Power

Near the load of distribution network access distributed networks, the entire distribution network load distribution will change, system trend then change, then the trend of the distribution network can also be changed from the original "one-way flow" to "two-way flow". For synchronous generator connected to the power distribution network, the input active power and reactive power at the same time to the system, can reduce the loss and the voltage distribution network can play a supporting role, but for asynchronous induction generator connected to the power distribution network, the input to the system active power and reactive power absorption, reduce the power factor of the grid. By trend analysis found that introducing asynchronous induction generator to increase distribution network loss, deterioration in transmission line voltage level. Distributed generators after introducing the distribution network could reduce may also increase the system network loss.

Multi-objective reactive power optimization strategy for distribution system with penetration of distributed generation

The study investigates multi-objective reactive power optimization (MORPO) of distribution system penetrated with distributed generation (DG). Integrating the reactive power of DG as one type of decision variables, a multi-objective model for RPO has been established to decrease the system active power loss, reduce voltage deviation and minimize the total capacity of reactive power compensation (RPC) devices (or minimize investments on RPC devices). Instead of converting the multiple objectives into a single one, a dynamically adaptive multi-objective particle swarm optimization (DAMOPSO) algorithm with introduction of special adaptive techniques has been proposed and validated and then applied to the MORPO problem with continuous and discrete variables. In order to the proposed MORPO model and the application of DAMOPSO, and to obtain a deep insight into MORPO with different objectives, a series of simulations on IEEE 33-bus system along with analysis and discussion are carried out. The results verified the feasibility and effectiveness of the proposed strategy.

Studies on the Low-Voltage Dynamic Reactive Power Compensation and Switching Control for Capacitors Device

This paper is for the problems of the 400V low voltage power capacitor reactive power compensation and for the problems existing in the transient process, resuming the principle of low-voltage capacitor intelligent technology and its implementation briefly. Propose a synchronization of reactive compensation capacitor switching on-off control system based on the micro controller and adaptive control. Real-time monitoring system is used to access system active and reactive power changes in order to extract the zero voltage signals; intelligent control algorithm is used to realize the intelligence of capacitor reactive power compensation on-spot and cutting, which greatly reduce the over-voltage and flow phenomenon produced by the capacitor in the cutting process. The result checked by actual measured shows that the device is stable, reliable, and can be effective to on-site system reactive power compensation and realize intelligent cutting.

Adaptive neuro‐fuzzy controller for static VAR compensator to damp out wind energy conversion system oscillation

Wind shear and tower shadow produce a periodic pulse reduction in mechanical torque captured from wind energy resulting in wind energy conversion system (WECS) active power oscillations. In this study, an adaptive neuro-fuzzy controller for static VAR compensator, used in power networks integrated with WECS, is presented to address the torque oscillation problem. The proposed controller consists of a radial basis function neural network representing a third-order auto-regressive and moving average system model and performing the prediction, and a main controller with adaptive neuro-fuzzy inference system providing the damping signal. A modified two-area four-machine power network with WECS integration is applied to validate the proposed implementation, compared with conventional lead/lag compensation. Time-domain simulations prove that the proposed controller can provide a damping signal to improve the active power oscillation and system dynamic stability, influenced by torque oscillations under WECSs synchronised operating condition.

Study on output characteristic of bi-direction current source converters

Among the control algorithms of current source pulse-width modulation converter, space vector pulse width modulation (SVPWM) is widely applied for its higher current utilisation factor than sine pulse width modulation (SPWM). However, when the two control methods are applied to active inverters (grid-connected photovoltaic system and current source active power filter (APF) for example), they present a wholly opposite characteristic. The output characteristics are analysed and contrasted in detail between SPWM and SVPWM current source inverters. The whole work is based on energy transfer, area equivalent theorem and different mechanism of the two algorithms when trigger pulses are produced according to the current command. The conclusion is drawn that at the same running condition in inverting operation, SPWM can output higher inverting current than SVPWM. The simulation and test results are presented and a new way of bi-direction current source inverter to obtain higher current utilisation factor is presented.

Reduction of Transmission Losses based on Optimal Power Flow using Genetic Algorithm

This paper presents the application of GeneticAlgorithm (GA) for solving optimal power flow problems. It is animportant tool for performance analysis of many power systemsproblems. Optimal power flow (OPF) is of very muchsignificance in power system operation analysis underderegulated environment of electricity industry. The OPFoptimizes a power system operating objective function, whilesatisfying a set of system operating constraints. The basic OPFsolution is obtained with production cost minimization as theobjective function and the optimal settings of the power systemare determined. OPF can also be formulated for reactive poweroptimization, as minimization of system active power losses andimproving the voltage stability in the system. In the presentpaper objective function is to reduce transmission losses usingGA, a IEEE 30-bus test power system is studied for optimalpower flow. It is described in the paper that GA based optimalpower flow can provide optimal solution

Optimal sizing of photovoltaic distributed generators in a distribution system with consideration of solar radiation and harmonic distortion

This paper presents a probabilistic approach to design an optimal size of photovoltaic distributed generator (PV-DG) in a distribution system. A steady-state voltage stability index is applied to select PV-DG locations. The objective of the proposed technique is to minimize average system active power losses, while considering power quality constraints (i.e., voltage regulation, total harmonic voltage distortion, total demand distortion and harmonic currents). Monte Carlo simulation is applied to acquire solar radiations, ambient temperatures, load demands and substation voltages. The proposed technique is tested on an actual 51-bus medium voltage distribution system in Thailand. From simulations, there is a different solution between selecting the optimal size of PV-DG from with and without considering background harmonics. Also in realistic cases, PV-DGs may improve voltage regulation and decrease losses in distribution systems; however, increase total harmonic voltage distortion values.

Analysis of system frequency and active power control functioning of Serbian power system

This paper is the result of the Master's final project 'Analysis of System Frequency and Active Power Control Functioning of Serbian Power System'. It contains theoretical basis and the basic principles of frequency and active power control. A partial analysis of parameters and simulation of power system of Serbia and neighboring power systems state in three characteristic cases is performed, using a computer program developed at the Electrical Engineering Institute 'Nikola Tesla'. Sensitivity analysis of the obtained results on variations in key parameters of the regulator is also performed. Power system of Serbia and neighboring power systems states are shown by observing the characteristic parameters such as: frequency, active power and regulation errors.

A Simultaneous Estimation of Frequency, Magnitude, and Active and Reactive Power by Using Decoupled Modules

A new practical technique for simultaneous local system frequency, magnitude, and active and reactive power estimation from voltage and current signals is presented. The technique consists of two phases using decoupled modules: the first phase estimates the frequency, and the second one estimates the magnitudes and the active and reactive power. The third important part is the adaptive bandpass and low-pass finite-impulse-response (FIR) filters that extract the fundamental and dc components, respectively. The most important point of this paper is the mathematical model that transforms the problem of estimation into an overdetermined set of linear equations. A very suitable algorithm for the aforementioned parameter estimation has been obtained. The algorithm showed a very high level of robustness and high measurement accuracy over a wide range of frequency changes. The algorithm convergence provided a fast response and adaptability. This technique provides accurate frequency estimates with errors in the range of 0.002 Hz and magnitude and power estimates with errors in the range of 0.03% for SNR = 60 dB in about 25 ms and requires reduced computations.

REACTIVE POWER COMPENSATION ASSESSMENT USING SELF-ORGANIZING FEATURE MAP

In the present work a self-organizing neural network is used for reactive power compensation assessment. The optimal reactive power sources planning are solved using a genetic algorithm. A genetic algorithm is proposed to optimize an objective function which is a linear combination of several factors, such as, overall system active power loss, cost incurred from the installation and use of VAR devices, enhance voltage profile. A self-organizing feature map is trained to compare the power system state once without optimization, then with optimization, first taking account of voltage constraints, and secondly without voltage constraints.

Maximum wind energy contribution in autonomous electrical grids based on thermal power stations

Greek islands cover their continuously increasing electricity demand on the basis of small autonomous thermal power stations. This electrification solution is related with increased operational cost and power insufficiency, especially during summer. On the other hand, the stochastic behaviour of the wind and the important fluctuations of daily and seasonal electricity load in almost all Greek islands pose a substantial penetration limit for the exploitation of the high wind potential of the area. In this context, the present study is concentrated on developing an integrated methodology which can estimate the maximum wind energy contribution to the existing autonomous electrical grids, using the appropriate stochastic analysis. For this purpose one takes into account the electrical demand probability density profile of every island under investigation as well as the operational characteristics of the corresponding thermal power stations. Special attention is paid in order to protect the existing internal combustion engines from unsafe operation below their technical minima as well as to preserve the local system active power reserve and the corresponding dynamic stability. In order to increase the reliability of the results obtained, one may use extensive information for several years. Finally, the proposed study is integrated with an appropriate parametrical analysis, investigating the impact of the main parameters variation on the expected maximum wind energy contribution.

A new symbolic analysis approach to the DC load flow method

A new symbolic analysis approach is proposed to the DC load flow method. The power system network parameters are given by symbols and the system active line power flows are derived analytically as closed-form symbolic expressions. An original program SALF is presented as a universal tool to find the line powers by an automated computer-aided algorithm. The theory of the DC load flow method is reviewed. The approach is illustrated by standard network examples. The approach exposed is targeted at researchers and experts dealing with analysis, planning and operation of transmission power system networks.

Hydro-thermal stochastic optimal power dispatch: A Newton's based approach

A technique that deals with the power system hydro-thermal optimal power dispatch problem accounting for the effects of uncertainty in predicting active power demand is presented. The method relates the probability distribution of the uncertain factors in the system active power generation, bus voltages, and phase angles to the probability distribution of the errors resulting from the forecast of the active power demand. The equality constraints considered are the power flow equations in the polar co-ordinates, using the nodal admittance matrix formulation. A comparison of stochastic results with the conventional dispatch is offered for the 14-bus system. The differences in voltage profiles are minimal, but the corresponding differences in power, and energy losses can be noticeable. The authors also discuss the potential for using the proposed technique to supplement spinning reserve allocation as a tool for catering to uncertainty in demand.

Probabilistic Load Flow Considering Dependence Between Input Nodal Powers

This paper presents a new method for obtaining a probabilistic load flow solution when dependence between the input nodal powers is considered. Such dependence is modeled in order to account for the criteria used to balance the system active power and also the correlation between loads due-mainly to environmental and social factors. The proposed technique is applied to a typical power system and the results discussed.

Status of power-system research at ENEL

The main trends of research underway at ENEL in the field of power system analysis and control are described. Topics covered include stability analysis, dynamic equivalents, reconstruction of real incidents, disturbance detection, emergency control, centralized system control, load forecasting, reactive and active power dispatching, scheduling of hydroresources, optimization techniques and power station control.