Stability and voltage regulation enhancement using an optimal gain vector

Abstract

Abstract--This paper addresses a control methodology to enhance stability and voltage regulation for the existing power systems with conventional PSS and AVR equipments. The control design problem is reduced to find a new control loop including a simple fixed gain vector. In order to optimal tuning of gain elements, the problem is formulated via an ∞ H static output feedback ( ∞ H -SOF) control technique, and the solution is easily carried out using a developed iterative linear matrix inequalities (ILMI) algorithm. A singlemachine infinite-bus system example is given to illustrate the developed approach. The results of the proposed control strategy are compared with conventional PSS design. The robust controller is shown to maintain the robust performance and minimize the effect of disturbance properly. I. INTRODUCTIONower systems continuously experience changes in operating conditions due to variations in generation/load and a wide range of disturbances [1]. Power system stability and voltage regulation have been considered as an important problem for secure system operation over the years. Currently, because of expanding physical setups, functionality and complexity of power systems, the mentioned problem becomes a more significant than the past. That is why in recent years a great deal of attention has been paid to application of advanced control techniques in power system as one of the more promising application areas.On the other hand, the real-world power systems still use the simple controllers that their parameters are usually tuned based on classical, experiences and trial-and-error approaches. Although these controllers are incapable to obtain good dynamical performance for a wide range of operating conditions and disturbances, however, the real electric industry because of some probable risks, bugs and/or having a The performance of these schemes essentially depends upon the selection of switching time. Moreover, using different control surfaces through a highly nonlinear structure increases the complexity of designed controllers.This paper presents a methodology to enhance the stability and voltage regulation of existing power system without opening their conventional PSS and AVR devices. The methodology provides a simple vector gain in parallel with the conventional control devices. The design objectives are formulated via an H∞ static output feedback (H∞-SOF) control problem and the optimal static gains are obtained using a developed iterative linear matrix inequalities (ILMI) algorithm.The resulting control framework is not only robust but it also allows direct and effective trade-off between voltage regulation and damping performance. The proposed controller uses the well available measure signals and has merely proportional gains; so gives considerable promise for implementation, especially in a multi-machine system. In fact the proposed control strategy attempts to make a bridge between the simplicity of control structure and robustness of stability and performance to satisfy the simultaneous ...

A Wide Range Robust PSS Design Based on Power System Pole-Placement Using Linear Matrix Inequality

“…From the previous discussion, this is equivalent to satisfy (19), (20). While this problem is not jointly convex in the variables (X D , X ∞ , Y, K), convexity can be enforced by finding a common solution…”

“…These nonlinear equations can be linearized around each operating point, such that small signal model of the power system can be determined. The Hefferon-Philips model is one of these power system linear models [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The studies on linear system show that the system response has not enough damping ratio and it might be unstable in some operating points [1][2][3][4][5][6][7][8].…”

“…In order to increase the damping of the power system response, classical controllers can be used which are usually designed for an operating point. If a phase lead transfer function is used in control mechanism, a conventional PSS is achieved [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Since the PSS is designed for one operational point, it has good performance only in the designed operating condition and it should be redesigned to achieve good performance in the other operational points.…”

“…Therefore, H ∞ method can be combined with other methods to improve performance of the PSS [5][6][7][8]. Some of these desirable methods are combination of H ∞ and H 2 [5,19] or combination of H ∞ and Pole-Placement methods [6][7]. In these combined methods, the design problem can be converted to a LMI problem, whose solving determines the stabilizer parameters [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…In order to achieve desirable power system response, closed loop poles should be placed in specific zone. Although in references [5,19] combined H ∞ and H 2 methods are used, but this zonal constraint is not considered. Therefore, an important goal of this paper is to consider the above mentioned characteristics simultaneously.…”