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This paper proposes to optimally coordinate multiple Energy Storage System (ESS) based stabilizers and Power System Stabilizers (PSS) to increase damping in a multi-machine power system using an improved particle swarm optimization (IPSO). The IPSO has the strong and global searching ability and high efficiency by applying chaos initialization and simulated annealing (SA) algorithm in iteration. All eigenvalues, including both electromechanical and non-electromechanical modes, that meet the stability requirements in a wide range of operating conditions have been included in the objective function. In the 4-machine power system, the power system oscillations are effectively suppressed at different operating conditions by multiple ESS-based stabilizers and PSSs coordinated by IPSO, where the damping effect is better with the stabilizers designed by the IPSO than with the stabilizers tuned individually by the conventional compensation method. The results show the validity, robustness and superiority of the IPSO design.

A fast adaptive power system stabilizer which uses an optimal singul- adaptive observer (OSA) is proposed and investigated. The identical direct (non iteratIve) model identification approach have been used which applied to multimachme power system. In this paper, the implementation ofan adaptive PSS on the base of OSA observer m multtmachine power systems is investigated. The simulation results are corroborated the. correctness, applicableness and effectiveness of the proposed adaptive stabilizer for multimachine power systems.

So far the control of power systems are mostly designed for locally optimized operations and has not been considering information from remotely-located generators. This paper presents a new and novel approach to control power oscillations of generators which are located remotely. First we propose to utilize the GPS (Global Positioning Systems) signals to obtain synchronized measurements of the generators. Under the condition, we propose to design the control of the local generator using a robust decentralized control theory so as to take into account uncertainties arising from unexpected sources. The proposed method is demonstrated using a nine bus system with three generators.

Effectiveness of the fuzzy logic based power system stabilizer in a multi-machine power system environment is investigated in this paper. The power system used to study the performance of the stabilizer exhibits multi-mode oscillation phenomena. Machine speed deviation and accelerating power as the plant's output are used as the inputs to the stabilizer. Results of simulation studies for different operating conditions and disturbances are given in the paper.

The modeling and analysis of the impact of Solar Photovoltaic (PV) on the small signal stability of power system are explored. The analysis provides explanations of the impact of the closed-loop control on the power system stability. Two system models, Single Solar Infinite Bus (SSIB) system and solar connected multi- machine system are considered. In model of PV, module variable are algebraic that is, they change instantaneously and the modeled dynamics are those of the power converter controller. The discussion considers maximum power point tracking, dc link voltage and current controller. In case of SSIB sensitivity to different weather conditions such as irradiance, temperature is studied. Also sensitivity to different power system conditions such as voltage variation, reactive power support from solar is studied. In multi-machine case impact of different active and reactive power injection levels is analyzed. The observations and conclusions obtained from eigenvalue, participation factor analysis suggest that even though the PV generation system dynamic do not participate into low frequency oscillation modes, its control can influence small signal damping depending based on its location in the system.

The main purpose of this paper is to design a non-linear second order sliding mode control for transient stability of two generator system (TGS). Second order sliding mode algorithms such as Twisting Algorithm (TA) and Super Twisting Algorithm (STA) have been applied and their simulation results are compared. The equilibrium point of TGS is maintained after the clearance of fault and the system is in post fault condition. Simulation results verify the proposed controller. The advantage with this type of control is that it does not require linearized model for its implementation and reduced chattering effect.

The design of excitation controllers to improve transient stabilization of power systems is a topic of renewed interest in the control community. Existence of a state– feedback stabilizing law for multi–machine aggregated reduced network models has recently been established. In this paper we extend this result in two directions: first, in contrast with aggregated models, we consider the more natural and widely popular structure–preserving models (SPM) that preserve the identity of the network components and allow for a more realistic treatment of the loads. Second, we explicitly compute a control law that, under a detectability assumption, ensures that all trajectories converge to the desired equilibrium point, provided that they start and remain in the region where the model makes physical sense.

Power system stabilizer (PSS) is one of the most important controllers in modern power systems for damping low frequency oscillations. Many efforts have been dedicated to design the tuning methodologies and allocation techniques to obtain optimal damping behaviors of the system. Traditionally, it is tuned mostly for local damping performance, however, in order to obtain a globally optimal performance, the tuning of PSS needs to be done considering more variables. Furthermore, with the enhancement of system interconnection and the increase of system complexity, new tools are required to achieve global tuning and coordination of PSS to achieve optimal solution in a global meaning. Differential evolution (DE) is a recognized as a simple and powerful global optimum technique, which can gain fast convergence speed as well as high computational efficiency. However, as many other evolutionary algorithms (EA), the premature of population restricts optimization capacity of DE. In this paper, a modified DE is proposed and applied for optimal PSS tuning of 39-Bus New-England system. New operators are introduced to reduce the probability of getting premature. To investigate the impact of system conditions on PSS tuning, multiple operating points will be studied. Simulation result is compared with standard DE and particle swarm optimization (PSO).

The researches on decentralised and/or adaptive control of power systems have received a great interest in recent years. In particular, the emphasis of most adaptive approaches towards improved stability has been placed on the utilisation of controller based on single-input/single-output models of single machine systems. Unfortunately, this approach does not guarantee an adequate performance in multi-machine system due to the strong interaction among machines. For this reason, in the paper, a decentralised model reference adaptive control (DMRAC) technique has been used to design a controller for a multi-machine system. In fact, considering as subsystem reference model for each machine the dynamic system determined by an appropriate optimal control law, the proposed DMRAC allows to adjust on line regulator gains in order to compensate the fluctuations in the interconnection. In order to show the performance of the proposed control law, some numerical experiments have been made on a four machines test system.

Electric network is now confronted with market deregulation or overload. Power System Stabilizer (PSS) is used to enhance capacity limits and improve transient stability, and it also make important role in the renewed system. This paper proposes design of excitation control with Fletcher-Powell method, which is non-linear mathematical optimization technique to realize output feedback control. The design procedure and the effectiveness are discussed through 5-machine system models. Scheme of decomposing control matrices for the large network is also discussed for successful application of the method.

The fuzzy control of the super-conducting magnetic energy storage (SMES) is proposed to improve the transient stability and damping requirements of multi-machine power systems. The effects of the SMES control on the line power transfer are considered to design a fuzzy controller. The theoretical realization of the proposed control scheme is presented. The simulation study of the New-England test system is carried out. The practical implementation based on the local measurements is explained. The improvement of the system's critical clearing time and also the system damping requirements are clearly demonstrated Finally a conclusion is provided.

The paper presents an intelligent adaptive turbine control scheme intended to improve the overall control performance of a multi-machine power system. Supplementary rule-based control is applied to the turbine governor, taking account of generator acceleration/deceleration as a measure of the imbalance between mechanical and electrical power. It is shown that this approach is capable of achieving more effective control of frequency transients on multi-machine power systems.

The multi-mode oscillation problem occurs in multi-machine power systems when the rotors of machines, behaving as rigid bodies, oscillate with rcspcct to one another using the electrical transmission path between them to exchange energy [1]. The ability of an adaptive self-tuning stabilizer to damp out the multi-mode power system oscillations is investigated in this paper. The studies show that such a stabilizer is very effective as it damps out the multi-mode oscillations one by one according to their dominance.

A systematic computer-aided procedure for the design of the power system excitation and governor controller, considering the parameter uncertainties, rapid and large load variations the network contingencies and the nonlinearities of the synchronous machine model is presented The design procedure consists in using three layer controllers with the first layer controller guaranteeing the maintenance of the nominal voltage, the nominal frequency and the scheduled powers even in the face of the disturbances, the second layer controller ensuring the desirable damping of the local and inter-tie mode oscillations and the third layer controller improving further the dynamic performance. The controller structure consists in the inclusion of an error driven filter to reject the said disturbances followed by the regulation of the augmented system consisting of the process and the filter using stabilizing compensators. The theoritical justification of the proposed multi-layer control strategy is given using input-output stability and Lyapunov reasoning.

In this paper we apply the decentralized H∞ control theory to interconnected multi-machine power systems. The idea is to design a local controller for each generator model so as to globally stability and optimal performance with consideration to interactions among multi-machine systems. The proposed excitation controller enables a power system to remain stable over a wide range of operating conditions. We also propose the design method of the advanced type of multi-input PSS(Power System Stabilizer) on the basis of H∞ theory.

Stabiliser faults in multi-machine power systems are examined in this paper where fault-masking and system reconfiguration of the nonlinear system are obtained using a virtual actuator approach. Phasor Measurement Units, which can be integrated in wide-area transmission grids to improve the performance of power system stabilisers, are utilised when reconfiguring remaining stabilisers after a local failure has made one inoperable. A stability-preserving reconfiguration is designed using absolute stability results for Lure type systems. The calculation of a virtual actuator that relies on the solution of a linear matrix inequality (LMI) is detailed in the paper. Simulation results of a benchmark transmission system show the ability of the fault-tolerant reconfiguration strategy to maintain wide-area stability of a power system despite failure in one of the stabilisers.

This paper considers the application of the supervisory discrete-time LQG control as a wide-area multi-machine power system controller subjected to unknown communication time-delays. These unknown time-delays are estimated using the Extended Kalman Filter algorithm and their estimates are then used to re-design LQG controller. The resulting LQG controller is then compared with the conventional LQG controller which ignores the presence of time-delays. The comparison is carried out on a non-linear simulation of a 2-area, 4-machine, 8-bus power system with a control objective of damping the electromechanical oscillations in the presence of unknown time-delays.

Power systems are highly n onlinear systems th at ex hibit undesirable oscillatio ns following disturbances. Power system stabilizers (PSS) are usually incorporated to provide auxiliary excitation signals to dam p these oscillations. Our objective is to im prove the PSS performance via the use of fuzzy logic and LMI techniques. A power system is viewed as a polytopic model that can be adequately represented by a Takagi-Sugeno fuzzy system. A power system stabilizer based on the parallel distributed c ontrol principle i s suggested. Ty pically, speed measurements are used as feedback signals. Consequently, a fuzzy observer is included to estimate the unmeasured states. LMI conditions that guarantee the stability and robust pole clustering of the closed loop system are derived. Simulation results of both single-machine an d multi-machine m odels co nfirm the effectiv eness of the propo sed algorithm. �

Based on a Neuro-Fuzzy Controller (NFC) architecture, two approaches are presented for the design of a Power System Stabilizer (PSS) with adaptive input scaling. In the first approach, input link weights (ILWs) are introduced and the NFC is made adaptive by the online modification of the ILWs and the consequent parameters (CPs) through the gradient descent method. In the second approach, nonlinear functions (NLFs) are used in the first layer of the NFC and both NLFs and CPs are modified online by using a hybrid adaptation process. Comparison studies on a one machine-infinite bus system and a multi-machine power system show the ability of the proposed PSSs to improve the system dynamic performance.

In this paper we provide a solution to the long-standing problem of transient stabilization of multi machine power systems with non-negligible transfer conductances. More specifically, we consider the full 3 n -dimensional model of the n -generator system with lossy transmission lines and loads and prove the existence of a nonlinear static state feedback law for the generator excitation field that ensures asymptotic stability of the operating point with a well-defined estimate of the domain of attraction provided by a bona fide Lyapunov function. Our derivations underscore the deleterious effects of resistive elements which, as is well-known, hamper the assignment of simple “gradient” energy functions and compel us to include non-standard cross terms. A key step in the construction is the modification of the energy transfer between the electrical and the mechanical parts of the system that play the role of multipliers in classical passivity theory.

UPFC which is one of the FACTS devices, can control transmission line reactances and ph~se angles. In this paper we propose a method for determining the optimal allocation of UPFC devices. In this method, for a multi-machine power system first through numerical simulations severe fault conditions are found. Then a UPFC device is allocated to different buses and behaviors of the control inputs under the severe fault conditions are studied. The less control effort for the system equipped with UPFC means the most efficient UPFC allocation. The effectiveness of the proposed method is shown using a four-machine eleven bus power system model.

To analyze and solve the problem of long-term low damping oscillation phenomena, a method is presented to find the best allocation and to design a power system stabilizer (PSS) for damping inter-area power oscillations. The method is based on the single-machine-infinite-bus models derived from the multi-machine power system by coherency-based reduction technique. Dynamic simulations using a 10-machine power system model are presented in order to show the effectiveness of the PSS designed according to the proposed method.

A polytopic representation of uncertainties in the operating conditions is introduced for a sequential design of decentralized Flexible AC Transmission Systems (FACTS) controllers for a multi-machine power system. An H ∞ -output feedback design procedure using Linear Matrix Inequality (LMI) is applied. Two different types of uncertainties are considered in the design. One uncertainty is due to the interaction from the undesigned loop when evaluating performance, which is bounded in the design of controller using mixed-sensitivity. Another source of uncertainty is considered in the design due to changing in operating point, which is treated by Polytopic Linear Differential Inclusion (PLDI) where various operating conditions are used in the model. The performance of the controllers is verified through non-linear simulations under large disturbances.

This paper focuses on studying the structure of ANN α-th order inverse and its application as a TCSC controller in a real power system to increase its transient stability. The inverse consisting of two integrators and a static ANN which has 5 inputs, including two additional inputs relevant to initial power and operating mode, can guarantee large-scale linearization of the power system. With almost the same structure, the controller is firstly used to control a single-machine infinite-bus system and then the real multi-machine system. Simulation results show that the TCSC controller is very effective.

In this paper, an effectiveness function of a FACTS damping controller is proposed for the selection of its installing location and feedback signal by taking account of not only its effectiveness, but also its robustness and non-negative interactions with other controllers in a multi-machine power system. An example three-machine power system is presented in the paper.

Power system stabilizer design for multi-machine power systems is studied in this paper. The difficulties of applying some existing design methods to stabilizers for day to day commercial operation are first discussed from the practical application point of view. Then, it is shown that whereas the design problem can be conveniently formulated as a large-scale system decentralized stabilization problem, it can also be translated into an equivalent one of feedback controller design for a multi-input multi-output system. The frequency response based sequential loop closure method is suggested for the design and it is applied to a model of 10 machine 54-th order power system. The results from computer analysis and simulation and the nature of the proposed method have showed that, the new design method may have some advantages in avoiding the difficulties discussed

Effective utilization of the thyristorly controlled shunt elements to power system transient stability enhancement requires a strategy of the optimal simultaneous active and reactive power control. A strategy of such optimal control is derived in the paper from direct Lyapunov method as the strategy which forces the fastest dissipation of the total system energy in the transient state. This theoretical control strategy uses two control signals based on the state variables locally not available at the shunt element bus. It is proved in the paper that both theoretical signals can be replaced by the time derivative of two electric quantities derived from local measurements. Control algorithm based on these quantities gives smooth and very effective regulation. Tests done for two and multi-machine systems have confirmed validity and robustness of the proposed new control trategy and control signals.

Most of the investigations into direct methods for power system stability analysis have been limited to lower order simplified models as Lyapunov functions are readily constructed for conservative systems. This paper presents recent results on extending direct methods to more realistic multi-machine models. The results are based on the general concept of constant total system energy. It can be shown that the post-disturbance Newton’s second law equation for each rotating machine multiplied by its transient speed, and integrated over time, results in energy terms that added with kinetic energy terms must equal an arbitrary constant when evaluated along a trajectory that satisfies the post-disturbance equations. This constant energy or Hamiltonian formulation is then used in conjunction with the potential energy boundary surface method to estimate power system stability. The method is illustrated on a simple system with a high order machine model and associated voltage control.

Power system stabilizers are used to improve the dynamic stability of large interconnected systems. They utilize signals derived from rotor speed deviation, accelerating power or a combination of these signals and provide a corrective input to the excitation system. The conventional design of the PSS (Power System Stabilizer) is based on classical control techniques. This paper presents a general approach of designing power system stabilizers based on modal control theory and applicable to multi-machine power systems. The objective of the design is to shift the closed loop poles to preassigned locations. Two specific methods are discussed. In the first method a least squares approach is used to select the feedback gains corresponding to the desired inputs to the PSS. In the second method, the dynamic compensator of a given order is designed using a nonlinear optimization technique. A comparison of the two methods is presented utilizing the example of a single machine system. The extensions to multimachine system are suggested.

Since the latter half of 1960s, several supplementary control schemes - PID control, phase compensator, output feedback control etc. - have been studied to damp out the sustained low frequency oscillations in steady state and it is an important problem to select the proper values of the parameters of power system stabilizers (PSS). This paper presents a unified approach to select the optimal parameters of PSSs in multi-machine power system. The performance measure is chosen as a typical quadratic form in time domain and the sensitivity of performance with respect to the PSS parameters is derived using the gradient matrix. To get the sensitivity of performance, it is required to solve two Lyapunov equations whose solutions exist even if the system is unstable. Thus, to get the feasible solution, it must be preceded to check the stability. In this algorithm, it takes a long time to solve Lyapunov equations. To deal with this problem, a new method is also presented and this method contributes to saving of computation time. By considering the actual constraints of parameters, the entire problem is converted to the static minimization problem with some linear constraints and the gradient projection algorithm is applied to solve it. Application to a sample system showed a satisfactory result.

This paper describes field-test results where direct feedback of tie-line power from a tie-line was used in order to control electric power transients on the tie-line. The electric power was fed back into the automatic voltage regulator of a synchronous generator and damping was improved by phase shifting the tie-line power signal with an appropriately tuned digital controller operating in the feedback loop. The test results shown in this paper are a small portion of a comprehensive set of test results that were obtained in recent tests conducted on the Alberta system in Canada to assess the effects of dynamic loads on the tie-line power oscillations and to evaluate the digital tie-line stabilizer that was developed by Professor K. Bollinger of the Power Systems Research Group at the University of Saskatchewan. The paper contains a description of the digital controller, a general description of the tuning procedure for damping oscillations on the large multi-machine network on which the controller was tested, and a brief description of identification techniques that were used to obtain a model of the power system.

Eigenvalue method based on state space matrix and other conventional methods used for dynamic stability analysis are not suited for a multi-machine system consisting of hundreds of machines with automatic voltage regulators and speed governors. This paper shows that the frequency response method is very useful for such a large scale system. The stabillity analysis is based on operational transfer matrix from internal angles to input mechanical torques. The critical stability condition obtained by the proposed method is compared with that obtained from field tests and it is shown that the proposed method is sufficiently accurate and efficient. Eigenvalues and mode shapes of the power system are also calculated by using the operational transfer matrix. Two algorithms are presented; topological method and iteration method. The analysis methods are used for planning, design and operation of power systems.

A technique, based on singular perturbation theory for constructing the equivalents of power systems for dynamic stability studies is presented. Response of the equivalent is improved by the addition of a correction term. The technique yields computational advantages since the slow and fast sub-systems are analysed separately and in two different time scales. Examples of a single machine infinite bus system and a multi-machine system are presented to illustrate the method.

A method is described for generating Lyapunov functions for multi machine power systems. It is based on recent work on stability tests for interconnected dissipative control systems.