R.P. Kumudini Devi

Optimal reconfiguration of radial distribuion system using artificial intelligence methods

Reconfiguration of radial distribution system is the significant way of altering the flow of power through lines. This altered flow changes the real power losses, reactive power losses and voltage profiles. Privatized RDS need to operate profitably with minimum operational losses and power quality. Envisaging such a prospect, this paper focuses on the aspects of loss minimization and voltage enhancement of RDS by artificial intelligence methods. A sample 33-bus system and 69-bus system are chosen for the study and the results are being compared..

Analysis of the Impact of Interconnecting Wind Turbine Generators to the Utility Grid

A preliminary analysis on the impact of wind power penetration into the grid is presented. This develops consistent simulation tools to analyze the steady-state impact of the interconnection of wind turbine generators to the utility grid for (i) power flow analysis, and (ii) reactive power compensation. Simulation results show that parallel compensation improves the effective power-factor of the wind farm, whereas series compensation improves the power developed by the induction machines. The advantages of both series and parallel compensation with AC capacitors are utilized by ‘series-parallel’ compensation. Simulation studies done on a 9-bus radial system, using the C++ programming language, show that this combination produces a very satisfactory voltage profile at the point of common coupling.

Optimal Siting and Sizing of UPFC Control Settings in Grid Integrated Wind Energy Conversion Systems

The depletion of fossil fuel reserves, emission of greenhouse gases and the uneven distribution of existing reserves led the countries to look for sustainable alternatives, especially wind power. In India mostly Squirrel cage induction generators (SCIG) are used for extracting energy from the wind. Induction generators inject real power to the grid and absorb reactive power from grid. Normally, fixed capacitors of rating equal to no-load compensation are installed at the wind-turbine. Reactive power absorbed by the SCIG over and above the no-lad compensation is dependent on the operating condition. To compensate for the reactive power (over and above the no-load compensation) dynamic VAR compensator can be installed at the point of common coupling. When the wind-farm is connected to a weak grid there may be a problem with wind penetration into the grid. UPFC (a versatile FACTS controller) will be able to alleviate the problems associated with fixed speed wind-farms that are connected to a weak grid. In this paper finding the location and capacity of the UPFC for minimisation of power generation cost is posed as a non-linear optimization problem. An efficient Primal-Dual Interior Point algorithm in conjunction with second order sensitivity analysis is made use for solving the above problem. The optimal line placement for wind penetration in terms of marginal values of UPFC variables are identified using first order sensitivity analysis. Second order sensitivity analysis has been employed to identify the optimal line placement for highest cost savings. Further actual cost savings and optimal control settings of UPFC are evaluated by actually placing UPFC in each line. The proposed approach is tested on a sample 9-bus system using the program developed in Matlab and the results are encouraging. The results indicate that the estimation of optimal placement of UPFC for a large system is possible reducing the computation time involved.

Performance Evaluation of Different ANN Models for Medium Term Wind Speed Forecasting

Wind power generation is characterized by its variability and uncertainty in the wind speed. Thus, the integration of wind farms to utility grids has several impacts on the optimum power flow, transmission congestion, load dispatch, economic analysis, and electricity market clearing prices. Due to the irregular nature of wind power production, accurate prediction of wind speed poses a major challenge to researchers. Wind speed of a wind farm is affected by conditions of the environment in which the wind farm is built, such as temperature, humidity, dew point, atmospheric pressure and wind direction. In this paper, five ANN techniques namely FFBP, CFBP, PNN, GRNN and KNN are considered to predict the wind speed using MATLAB. The feasibility of the proposed techniques is evaluated using the performance measures such as MSE, MAPE and linear regression and it is observed that GRNN is superior amongst the other methods that are used.

A sliding mode controller for SSSC to delay Hopf bifurcation in a differential-algebraic power system model

A novel sliding mode controller (SMC) is proposed for static synchronous series capacitors (SSSCs) to delay Hopf bifurcation (HBF) in a differential-algebraic power system model. The proposed controller consists of an equivalent control term and a switching term. The major drawback of SMC approach, viz., the undesired chattering is eliminated by introducing a continuously changing switching term instead of the conventional switching function. The effectiveness of the controller is demonstrated in a bifurcation perspective. Steady state bifurcation diagrams are constructed by the application of an algorithm based on continuation method for the entire Jacobian matrix of structure preserving power system model. From the bifurcation diagram, existence of HBF is identified with the help of eigen value analysis. Occurrence of HBF is confirmed through computation of HBF index. The effectiveness of the proposed SMC over the conventional PI controller for SSSC in delaying HBF and maintaining load voltage constant for higher reactive power loading is illustrated for a 3 machine, 9-bus system.

Steady State Analysis of Wind Turbine Generators Interconnected to the Grid

A preliminary analysis on the impact of wind power penetration into the grid is presented. The purpose of the work is to develop consistent simulation tools in order to analyze the steady state impact of the interconnection of wind turbine generators (WTG) to the utility grid. Conclusions regarding the impact are drawn from the power flow analysis, in which the steady state model of the induction machine is considered. The usual N-R method of power flow is modified to include the WTG bus. The convergence characteristics of this modified N-R method (simultaneous method) is compared with the usual sequential methods of power flow and it is found that the simultaneous method is faster and results in less number of iterations. The impact of increasing the number of wind turbines in the wind farm is studied. A method is suggested to strengthen the given network between the point of common coupling (PCC) and the rest of the grid. Simulation results show that this helps in accommodating more wind turbines in the wind farm. Simulation studies are done on a 9-bus radial system, using C++ programming language and the results obtained are presented

Optimal control of grid connected variable speed wind energy conversion system

This paper presents an optimum design procedure for the coordinated tuning of rotor side converter (RSC) and grid side converter (GSC) controllers of grid connected doubly fed induction generator (DFIG) wind turbine system. The RSC and GSC controller parameters are determined to optimize the performance indices. The performance indices considered are maximum peak overshoot (MPOSωr), settling time (Tssωr) of the generator speed and the maximum peak overshoot (MPOSVdc), maximum peak undershoot (MPUSVdc) and settling time (TssVdc) of DC link voltage. The sum squared error deviation of the dc link voltage and the generator speed is considered as the objective function. The constrained optimization problem is solved using particle swarm optimization (PSO). Simulations are performed on a sample system with DFIG based WECS. The effectiveness of the designed parameters using PSO is then compared with that obtained using simulated annealing (SA).

Tracing of stable and unstable steady state periodic solutions of autonomous systems: algorithm and bifurcation analysis

This paper describes a numerical algorithm and its computer implementation for the tracing of stable and unstable steady state periodic solutions of autonomous systems of ordinary differential equations. The problem is posed as an initial value problem. The autonomous system considered is a function of n state variables. The period is unknown for autonomous systems. The total number of unknowns to be determined at each step is n+1, i.e., n state variables plus the time period T. Since autonomous systems admit an infinite number of periodic solutions each one differing from the others by a translation in time, to have a unique solution, an appropriate value for one of this n+1 variables is assumed. The recasted system of n nonlinear algebraic equations in n unknowns is solved iteratively using Newton-Raphson method. This will give one periodic solution and its period. To have a continuum of solutions, a locally parameterised continuation procedure is adopted. Stability of periodic solutions along the continuous branch of solutions is determined by computing characteristic multipliers. The effectiveness of the algorithm is demonstrated by conducting bifurcation analysis on a three-node power system

Small signal stability analysis of grid connected Photo Voltaic distributed generator system

Distributed Generation is a small source of electric power conversion from non-conventional energy sources such as Photo Voltaic system (PV), wind, Fuel cell etc. Small signal stability analysis is very much essential to study the inter-area and intra area oscillations which normally exist in a power system. But, it leads to unstable operation when small disturbances are applied. Normally, mechanical part of a synchronous system is intrinsically prone to weakly damped oscillations and the damping of these oscillations must come from other sources, such as damper windings and the machines controllers. Because power system oscillations have frequencies in the order of a few Hz and of rather small amplitude, hardly any damping is provided by the damper windings, leaving the controllers and the rest of the power system as the main contributors to the damping of the rotor speed oscillations. So in this paper, Power system stabilizer (PSS) is used for providing damping torque. This paper examines the effect of PV sources on small signal stability conditions of conventional power system with Synchronous Generators (SG) along with PSS. Eigen value analysis is conducted after developing a Differential-Algebraic model (DAE) in power balance form and tested on a modified 3 synchronous machine − 9 bus system [10] with PV converters.

Rotor Speed Stability of Grid Connected Wind Energy Conversion Systems

This paper examines the dynamics of grid connected wind energy conversion systems under the concept of ‘rotor speed stability’. The majority of wind turbines installed in India have induction generators, which are directly connected to the grid. Consequently, wind turbines interact with the power system in a way that differs from synchronous generators. Therefore, it is more appropriate to study the impacts in terms of rotor speed stability that focuses on torque-speed dependence of asynchronous generators, similar to the rotor-angle stability that focuses on the torque-angle dependence of synchronous generators. In this paper, the rotor-speed stability of the system considered is analysed for step change in wind velocity, gust speed and for three-phase faults at key locations in the system. Simulation studies are done on an 11-bus radial system, using C++ programming language and the results obtained are presented. The results help to understand the rotor-speed stability phenomena in fixed speed windfarms and could help in designing the rotor-speed stability requirements of such systems.