Interconnected Power Systems

Over the past decades, various control techniques (Ibraheem et al., 2005; Omveer Singh et al., 2013) such as classical control, variable structure control, optimal control, and robust control, have been applied to the LFC problem. The classical controllers exhibit poor dynamic performance and are therefore, not suitable for all operating conditions. The variable structure controllers, optimal state feedback controllers, and robust control methods on the other hand show good dynamical response, however, most of them require the availability of all state variables, which seems unrealistic. Therefore, it is not easy to effectively solve the LFC problem depending only on the conventional approaches. The most recent advancement is the application of soft computing techniques (Sathans and Akhilesh Swarup 2011) to the load frequency control of interconnected power systems having nonlinear models and continuously changing operating conditions. In this paper, the Artificial Bee Colony (ABC) algorithm, which mimics the food foraging behavior of swarms of honey bees, has been used for optimizing the controller PI gain values of the proposed interconnected hydro-nuclear power system.

This research presents the load frequency control (LFC) of three interconnected power systems using a Multi- Level Single Linkage algorithm (MLSL) and a proportional-integral-derivative (PID) control approach. The conventional PID controller is developed using MLSL optimization algorithm including the LFC loop to minimize the frequency deviation and regulate the power exchange because of the load disturbance changes in area1 and area2. In order to enhance the dynamic performance, the optimal parameters of the PID scheme which optimized by the proposed MLSL algorithm are compared with that one’s obtained by GA algorithm. Integral Square Error (ISE) is considered as an objective function for both algorithms to determine its performance index value for the same interconnected power system. The results show that the performance of the proposed method is more accurate and faster as well in response to the settling time, maximum deviation, and peak time. The combination algorithms set of MLSL_PID_ISE and GA_PID_ISE are coded and simulated using MATLAB.

dynamic performance of load frequency control for a two area power systems. A SMES device is a dc current device that stores energy in the magnetic field. The dc current flowing through a superconducting wire in a large magnet creates the magnetic field (Chen and Liu, 2006). Since energy is stored as circulating current, energy can be drawn from the SMES unit with almost instantaneous response with energy stored or delivered over periods ranging from a fraction of a second to several hours. In this study, a two area power system using SMES unit is considered to control power flows. In each control area, all generators are assumed to form coherent group. This paper proposes by taking advantage of the superior characteristics inherent in the design of dual mode fuzzy logic load frequency controller, using superconducting magnetic energy storage device for interconnected power systems. An important design concept of dual mode control is incorporated in the proposed controller because it improves the system performance and makes it flexible for application to actual systems (Chen and Liu, 2006). The computer simulation results of application of the proposed controller with inter connected power systems prove that the proposed controller is effective and provides significant improvement in the system performance.

One of the most important control aspects of interconnected power systems is to keep system frequency at scheduled level under the varying load and generation condition. The system frequency has been varying with changing load conditions. With primary speed control action, a change in system load will result in a steady-state frequency deviation, depending upon the governor droop characteristic and frequency sensitivity of the load. All generating units on speed governing will contribute to the overall change in generation, irrespective of the location of the load change. Restoration of system frequency to nominal value requires supplementary control action which adjusts the load reference set point. As system load is continually changing, it is necessary to change the output of generators automatically [2].

In the presented article an attempt has been made to develop a technique for maintaining constant voltage level for a reliable operation of interconnected power system. Modern interconnected power systems have grown in size and complexity in order to satisfy the increasing load demand. Initially the interconnections were means for supporting neigh- boring power systems in case of emergencies and sharing the responsibility for the frequency regulation in normal operation, thus reducing the burden and expenses of each participant. As the generation in one power system tended to be less expensive than in another system, or the load centers were closer to the neighboring power system generation, interchange trans- actions were established, providing for these long-term contracts. As a result, the tie- lines have become internal lines to the entire interconnected grid and are an indispensable part of the entire load supply process. Altogether, interconnections make economical use of the generated power and generally improve the overall reliability of the interconnected systems. Each power system, part of an interconnection, is designed to withstand pre-defined disturbances. To this purpose, all power system components are equipped with dedicated protection schemes, some system protection schemes designed to maintain stability are implemented, and system operators are trained to take measures in order to restore the system to normal conditions following a disturbance.

The various steps of the proposed methodology have been discussed, explained, and validated using a four bus system and the IEEE fourteen bus interconnected test systems. For validation purposes, the proposed methodology was compared and validated through PSCAD simulation and MathCAD mathematical programming. It is shown that the calculated output of the methodology accurately represents the voltage sag sensed on the various buses. Further work would be accommodate the solution of all the mathematical expressions of the methodology proposed into one common environment to provide a complete package for voltage sag prediction caused by large induction motors for interconnected systems.

are varied from their nominal values in the range of +25% to −25%. The power system parameters and time constants are calculated for the varied condition and used in the simulation model. In all the cases the controller parameters obtained using the objective function J is considered due to its superior performance. The results ob- tained are depicted in Table 1 and Table 2. The system performances are within acceptable change when ±25% changes the operating load condition and system parameters from their nominal values. Hence, it can be con- cluded that the closed loop system is stable when the operating conditions and system parameters vary.

of frequency and power flow [4]. Interconnected multiple- area power systems can be depicted by using circles. A simplified four area interconnected power system used in this study, each area can be represented as equivalent generating unit and interconnected through lossless tie-lines with some reactance. As simplified four-area interconnected power systems as shown in Fig. 1 [6].

An intelligent wavelet neural network (WNN) controller (LFC) is proposed to control the frequency of the two area interconnected thermal–reheat power systems. The integral gains are optimized by the simulation procedures adopted in the two area interconnected thermal reheat power systems. The proposed WNN controller is implemented in a two area interconnected power systems and design implementation of the controller is found that the frequency and tie-line power deviations of the interconnected power systems with WNN controller ensures improved transient response of the system.

AGC plays an important role in the large scale multi-area interconnected power systems to maintain system frequency and tie-line powers at their nominal values. Due to sudden disturbances or some other reasons if the generated active power becomes less than the power demand, the frequency of generating units tends to decrease and vice versa [1-2]. This causes the system frequency to deviate from its nominal value which is undesirable. To damp out the frequency deviation quickly and to keep the tie-line power at its scheduled value, AGC concept is used. However, the constant frequency cannot be obtained by the speed governor alone. So, a control system is essential to cancel the effects of the sudden load changes and to keep the frequency at the nominal value [3–5]. Virtual inertia is thought as an inevitable part of the power systems with high penetration of renewable energy. Recent trend of analysis is orientating in several strategies of emulating the inertia to extend the property of the system. Within the case of dynamic performance of power systems particularly in AGC issue, there area unit considerations considering the matter of virtual inertia. This paper proposes associate degree approach for analyzing the dynamic effects of virtual inertia in three-area AC/DC interconnected AGC power systems. Derivative control technique is employed for higher level management application of inertia emulation [4].

Abstract - As a result of the increasing amount of energy transmission over a long distance, low frequency Inter-area oscillations have been becoming an increasingly important concern in the planning and operation of practical power systems. This undesirable phenomenon may cause very serious results, such as the loss of interconnects, load curtailments and even system blackouts. Abundant of power system stabilizers have been developed by the researchers in the past few years, but the area is still open for the efficient power stabilizer development which can efficiently able to handle the power oscillations without increasing the system controller system complexity. This paper presents a novel way to achieve fast and efficient damping of Inter-area oscillations and improve the dynamic stability of interconnected power systems by designing of an Sugeno type Fuzzy-PID hybrid controller for efficient Inter-area power oscillation damping in two area four machine power system. The most important point for using Sugeno type fuzzy inference over mamdani fuzzy inference is that it is much more suitable for linear PID like controllers. The implementation of the proposed work is with the Simulink of MATLAB 2012(b).This paper also present a complete comparative analysis of Inter-area power oscillation damping capabilities of proposed Sugeno type Fuzzy-PID hybrid controller based power system stabilizer (Hybrid-PSS) and conventional PID controller based power system stabilizer (PID-PSS) and with no controller (No-PSS) at line to ground (LG) fault condition. The obtained results shows that the Inter-area power oscillation damping capability of proposed Sugeno type Fuzzy-PID hybrid controller based power system stabilizer (Hybrid-PSS) is much higher than the conventional PID-controller based PSS. In addition to this the damping time required by proposed Sugeno type Fuzzy- PID hybrid controller.

In this project, a novel decentralized SMLFC with PI switching surface is designed to solve the Load frequency control (LFC) problem of multi-area interconnected power systems with matched uncertainties and unmatched uncertainties. This controller uses the Local state measurements to regulate the frequency deviation of each area. The controller design process has been theoretically proved in this project based on Lyapunov stability theory to assure that frequency deviation reaches zero. Robustness of the controller against the uncertainties and nonlinearities is tested in the three-area interconnected system. Fast frequency responses and insensitive to parameter variations and load disturbance show that the performance of the proposed control strategy is effective and reliable. In future the proposed controller can be applied to multi area interconnected power system containing renewable energy.

One of the most important non-linearities in AGC of power systems is the presence of generation rate constraints (GRC). A due space has been given by researchers in this area also. A considerable number of articles have been reported to propose AGC schemes for power systems incorporating GRCs [19, 23,24, 159, 160,146,149]. The researchers [158] have reported their work for the dynamic stability analysis of a two-area power system consisting of non-reheat turbines. They have studied the damping effect on frequency and tie line power oscillations by varying the load characteristics and excitation stabilizer parameters. Recently the application of superconducting magnetic energy storage [136] and capacitive energy storage [154] devices to improve AGC performance has been proposed. Investigations carried by Tripathi et al [153, 154] revealed that improved dynamic performance of the system could be achieved by simultaneous control of steam turbine and energy storage device. However, due to limited energy storage capacity, cost and complicated control, these devices may play very limited role in AGC of large interconnected power systems.

This work forwarded a novel way to achieve fast and efficient damping of Inter-area power oscillations. By the development of the project work an improved dynamic stability of interconnected power systems has been achieved by designing of an Sugeno type Fuzzy-PID hybrid controller for efficient Inter-area power oscillation damping in two area four machine power system. The basic aim was to exploit unique advantage of the fuzzy based advance control structure.

This paper presents a comprehensive study on dynamic performance of two-area interconnected power systems when subjected to Time constant parametric uncertainties. Power system model consists of one area with reheat thermal power plants and other area with hydro power plants having identical capacity. the system interconnection considered as namely EHVAC transmission link only, HVDC transmission link with ∆Pdc taken as state variable, HVDC transmission link with ∆Pdc taken as control variable, EHVAC in parallel with HVDC transmission link with ∆Pdc taken as state variable and EHVAC in parallel with HVDC transmission link with ∆Pdc taken as control variable. The dynamic model of incremental power flow through HVDC transmission link is derived based on frequency deviation at rectifier end only. Moreover, the HVDC link is considered to be operating in constant current control mode. To carry out the investigations, optimal AGC regulators are designed using proportional-plus-integral

The widespread increase of non-linear loads nowadays, significant amounts of harmonic currents are being injected into power systems. Harmonic currents flow through the power system impedance, causing voltage distortion at the harmonic currents’ frequencies. The distorted voltage waveform causes harmonic currents to be drawn by other loads connected at the point of common coupling (PCC). The existence of current and voltage harmonics in power systems increases losses in the lines, decreases the power factor and can cause timing errors in sensitive electronic equipments.

As originally introduced in Popp et al. (2016a), CoSimMA, a modular simulation framework, uses mCCM as theoreti- cal core for performing studies on the efficient simulation of large interconnected dynamical systems. The basic con- cept behind CoSimMA and its modular structure is graphi- cally outlined in Fig. 2. After setting up the connected com- ponent, several types of model manipulation and simulation such as linearization, model aggregation, linear and nonlin- ear order reduction as well as static and transient simula- tions can be performed in a modular manner. The key of the implementation concept is, that the result of each manip- ulation is a connected component or a component, respec- tively. This is enabled by strictly utilizing the object oriented programming paradigm within the problem solving environ- ment MATLAB (The MathWorks, Inc., 2015). Using MAT- LAB’s interfaces for other programming languages such as C or FORTRAN allows the convenient usage of sophisticated software packages for simulation purposes such as SUN- DIALS (Hindmarsh et al., 2005) as an alternative to MAT- LAB’s own numerical solvers for ordinary differential equa- tions (Shampine et al., 2003; Shampine, 2002). On the one hand, due to the unified module interfaces within CoSimMA, it becomes completely transparent from a users point of view, which specific algorithm and software package is used for simulation purposes. On the other hand, the development of new simulator modules, such as the model order reduction methods treated in this paper, are easily implemented, since already existing modules are interfaced in an abstract and therefore very clear manner. All simulation results presented in the following section have been obtained with CoSimMA.

A typical example of two area power system is considered for the simulation and the values of the different parameters of the system are given in Appendix-I. The initial values of the performance indices were obtained by carrying simulation of the system over a period of 100 sec with automatic generation controller gain parameters obtained from randomly selected initial population. These values were used to produce next generation of individuals and procedure is repeated until the population has converged to some minimum value of the performance index. The parameters for PSO process are given in Appendix-II. The two area system with diverse sources of power generation is simulated for different cases with 1% step load perturbation in either of the areas. The scheduled generations from each of the sources for different nominal loading conditions for both areas are given in Table T1 in Appendix-I. The transient responses of the system are given below for optimum values of PID gains which are evaluated using ISE+ITAE criterion. Finally, complete content and organizational editing before formatting. Please take note of the following items when proofreading spelling and grammar:

Abstract--- The Nigerian power system is afflicted with continuous load shedding due to inadequate generation and transmission capacities. The power transmission capability available from transmission line design is limited by technological and economic constraints. To maximize the amount of real power that can be transferred over a network, reactive power flow must be minimized. Consequently, sufficient reactive power should be provided locally in the system to keep bus voltages within normal ranges to satisfy customers’ equipment voltage ratings. Currently, less than 40% of the population is connected to the national grid and less than 50% of the available installed capacity is used in meeting demand. This paper presents an overview in reactive power compensation technologies which remains as research challenges in this area. Newton-Raphson’s solution method was used to carry out the analysis because of its fast convergence, sparsity, and simplicity attributes when compared to other solution methods, with relevant data obtained from Power Holding Company of Nigeria (PHCN). MAT LAB/SIMULINK was used to carry out the simulation analysis. It is observed that the application of compensation on the interconnected system jointly has side effect on the other buses. This is confirmed by a step-by-step application of compensation at 5percent intervals. The effects were noticed in Bus (20) where voltage decreased from 0.9568p.u to 0.9329p.u about 2.39percent, bus (19) from 0.998p.u to 1.1035p.u and others. These results indicate undershoot and overshoot that will cause damage to the system, and may lead to system collapse if no contingency control is installed. It is also observed that compensation should be done on weak buses only for better results. The results also showed that control of active and reactive power greatly influence the Nigeria electricity grid, hence need adequate attention with the recent advent of renewable energy and its integration into the grid.

In the present scenario, due to very fast and rapid development of electronic device or equipment which support the concepts of the conventional controller in a very efficient way which lead to raise the new concepts of the control design and analysis in the power system. One such device is thyristor control phase shifter (TCPS) which change the relative phase angle between the system voltage and thus the real power flow can be maintained and eliminate the frequency deviation and finally enhance the power system stability [20].