Indraneel Sen

Power System Stabilizers Design for Interconnected Power Systems

This paper proposes a method of designing fixed parameter decentralized power system stabilizers (PSS) for interconnected multi-machine power systems. Conventional design technique using a single machine infinite bus approximation involves the frequency response estimation called the GEP(s) between the AVR input and the resultant electrical torque. This requires the knowledge of equivalent external reactance and infinite bus voltage or their estimated values at each machine. Other design techniques using P-Vr characteristics or residues are based on complete system information. In the proposed method, information available at the high voltage bus of the step-up transformer is used to set up a modified Heffron-Phillips model. With this model it is possible to decide the structure of the PSS compensator and tune its parameters at each machine in the multi-machine environment, using only those signals that are available at the generating station. The efficacy of the proposed design technique has been evaluated on three of the most widely used test systems. The simulation results have shown that the performance of the proposed stabilizer is comparable to that which could be obtained by conventional design but without the need for the estimation and computation of external system parameters.

Tuning of PID controller based AGC system using genetic algorithms

This paper deals with the tuning of AGC of an interconnected power system using genetic algorithms (GA). A two-area AGC system is considered for study and both the areas are considered to be equipped with PID controllers. Parameters of these PID controllers are obtained using a novel genetic algorithm based optimization technique. For comparison, the same parameters are also tuned using the Ziegler-Nichols method. The performance of the proposed controller has been compared with the performance of the conventional integral controller in order to demonstrate the superiority of the proposed GA based PID controller.

A Nonlinear Voltage Regulator With One Tunable Parameter for Multimachine Power Systems

This paper proposes a nonlinear voltage regulator with one tunable parameter for multimachine power systems. Based on output feedback linearization, this regulator can achieve simultaneous voltage regulation and small-signal performance objectives. Conventionally output feedback linearization has been used for voltage regulator design by taking infinite bus voltage as reference. Unfortunately, this controller has poor small-signal performance and cannot be applied to multimachine systems without the estimation of the equivalent external reactance seen from the generator. This paper proposes a voltage regulator design by redefining the rotor angle at each generator with respect to the secondary voltage of the step-up transformer as reference instead of a common synchronously rotating reference frame. Using synchronizing and damping torques analysis, we show that the proposed voltage regulator achieves simultaneous voltage regulation and damping performance over a range of system and operating conditions by controlling the relative angle between the generator internal voltage angle δ and the secondary voltage of the step up transformer. The performance of the proposed voltage regulator is evaluated on a single machine infinite bus system and two widely used multimachine test systems.

Synchronizing and Damping Torques Analysis of Nonlinear Voltage Regulators

This paper makes an attempt to assess the benefits of replacing a conventional generator excitation system (AVR+PSS) with a nonlinear voltage regulator using the concepts of synchronizing and damping torque components in a single machine infinite bus (SMIB) system. In recent years, there has been considerable interest in designing nonlinear excitation controllers, which are expected to give better dynamic performance over a wider range of system and operating conditions. The performance of these controllers is often justified by simulation studies on few test cases which may not adequately represent the diverse operating conditions of a typical power system. The performance of two such nonlinear controllers which are designed based on feedback linearization and include automatic voltage regulation with good dynamic performance have been analyzed using an SMIB model. Linearizing the nonlinear control laws along with the SMIB system equations, a Heffron Phillips type of a model has been derived. Concepts of synchronizing and damping torque components have been used to show that such controllers can impair the small signal stability under certain operating conditions. This paper shows the possibility of negative damping contribution due to nonlinear voltage regulators and gives a new insight on understanding the physical impact of complex nonlinear control laws on power system dynamics.

A novel fuzzy logic based power system stabilizer for a multimachine system

This paper describes the design of a fuzzy logic based controller to counter the small signal oscillatory instability in power systems. The stabilizing signal is computed in real time using suitable fuzzy membership functions depending upon the state of the generator on the speed-acceleration phase plane. The use of output membership function permits further fine tuning of the controller parameters for varied system configurations specially in multimachine environment. The efficacy of the proposed stabilizing technique has been demonstrated using multi-machine computer simulation model of power system under a wide range of system and test conditions.

Low frequency oscillations in power systems: A physical account and adaptive stabilizers

This paper presents a physical explanation of the phenomenon of low frequency oscillations experienced in power systems. A brief account of the present practice of providing fixed gain power system stabilizers (PSS) is followed by a summary of some of the recent design proposals for adaptive PSS. A novel PSS based on the effort of cancelling the negative damping torque produced by the automatic voltage regulator (AVR) is presented along with some recent studies on a multimachine system using a frequency identification technique.

New approach for the design of pole placement power system stabilizers

Pole placement power system stabilizers (PSS) are well known for their superior performance when compared to the conventional lead-lag stabilizers. They require feedback of all the state variables which are generally not measurable. In multi machine systems pole placement designs require feedback of other machine states as well. This paper proposes a new approach for the pole placement based PSS. In this paper, recently proposed modified Heffron Phillips model is used for the PSS design. It is derived by taking the secondary bus voltage of the step-up transformer as reference instead of infinite bus. State variables of this model are locally measurable, which makes the pole placement design decentralized. The performance of the proposed controller is evaluated on a single machine infinite bus system over a wide range of operating conditions. The proposed PSS performance is found to be better than the conventional PSS.

A Nomogram for Estimating the Three Parameters of the Weibull Distribution

A nomogram based on the method of moments is given for estimating the three parameters of the Weibull distribution. Iterative procedures for parameter estimation using digital computers require initial estimates of the parameters. An empirical procedure..

Power system stability enhancement using a STATCOM with ESS

This paper describes the use of a STATCOM with Energy Storage System (ESS) to improve the small signal stability of power systems. The ESS considered is a wind farm based Permanent Magnet Synchronous Generator (PMSG) along with an AC/DC converter that is connected to a standard STATCOM. With this configuration of STATCOM/ESS extremely effective control strategies for modulation of reactive and active powers can be devised to improve transient and dynamic stability limits of the system. In this paper this is demonstrated by computer simulation studies on a SMIB model equipped with a STATCOM-ESS combination.

Power System Stability enhancement by Single Network Adaptive Critic Stabilizers

This paper proposes a Single Network Adaptive Critic (SNAC) based Power System Stabilizer (PSS) for enhancing the small-signal stability of power systems over a wide range of operating conditions. SNAC uses only a single critic neural network instead of the action-critic dual network architecture of typical adaptive critic designs. SNAC eliminates the iterative training loops between the action and critic networks and greatly simplifies the training procedure. The performance of the proposed PSS has been tested on a Single Machine Infinite Bus test system for various system and loading conditions. The proposed stabilizer, which is relatively easier to synthesize, consistently outperformed stabilizers based on conventional lead-lag and linear quadratic regulator designs.