Murilo E. C. Bento

Performance analysis of Wide-Area Damping Control Design methods

In this paper, three different Wide-Area Damping Control design methods are considered for a two-level control scheme. The important challenges involved in this control design are output-feedback, communication time-delays, loss of remote signals and multivariable control design. Three different control design methods, found in the literature, are analyzed: Riccati equation solution, Linear Matrix Inequalities and Genetic Algorithms. The performance of the three different controllers is discussed and compared using modal analysis and time-domain simulations of the multimachine Southern/Southeastern Brazilian equivalent power system.

Design of Power Systems Stabilizers for distributed synchronous generators using Linear Matrix Inequality solvers

The objective of this research is to evaluate the performance of a Power System Stabilizers (PSS), designed using a formulation based on Linear Matrix Inequalities (LMIs), in an Electric Power Distribution System (EPDS) with distributed synchronous generators operating under unbalanced three-phase. Under these conditions, the steady-state operation of the EPDS is not an equilibrium point, which introduces a new condition not covered by typical PSS design techniques. To overcome this problem, an EPDS modeling technique developed on a previous work by the authors research group was used. For the PSS design, a technique called V-K iteration was employed and the maximization of the minimum damping was set as the controller design objective. Furthermore, three LMI solvers were used (and compared) to assess design feasibility. A total of 880 operating points (for which the open loop minimum damping was smaller than 3%) were considered for the design. The results show that the proposed formulation is feasible and good controller performances can be achieved by the different PSSs designed using each of the tested LMI solvers.

Efficiency analysis of local and central controllers in an electric power system

This research presents an analysis of efficiency of local controllers and wide-area damping controllers (WADCs) in damping the electromechanical modes of an electric power system (EPS). A procedure to design WADCs using Relative Gain Array (RGA) is used. The RGA provides indicatives of which elements of the WADCs are recommended to design. These indicatives may improve the dynamic performance and reduce the WADC design time. The design method of WADC and of the local controller is based on genetic algorithms. Time-delays were considered in the design using Pade approximation. Modal analysis and nonlinear simulations in the time domain were carried out in the Simplified Australian Power System. The results achieved show the best performance in terms of damping of the designed WADC by RGA theory.

Design analysis of wide-area damping controllers using genetic algorithms

This research presents a procedure to design wide-area damping controllers (WADCs) using Relative Gain Array (RGA). The RGA provides indicatives of which elements of the controller are recommended to design. These indicatives may improve the dynamic performance and reduce the WADC design time. The objective of this research was to evaluate statistically the designed wide-area damping controllers using this theory and when do not use. The design method of WADC used is based on genetic algorithms. Time-delays were considered in the design using Pade approximation. Modal analysis and non-linear simulations in the time domain were carried out in the Simplified Australian Power System. The results achieved show the best performance in terms of damping of the designed WADC by RGA theory.

Wide-area measurements-based two-level control design considering power system operation uncertainties

In this paper, a procedure to design Wide-Area Damping Controller based on the solution of the Riccati equation considering uncertainties of the system operation is proposed. Originally, the method based on Riccati equation does not consider uncertainties, providing a satisfactory damping only for the nominal operating condition. In this paper, the resulting controller presents fixed order, communication time-delays and it is robust to load, topological variations and time-delays. Besides, the closed-loop system presents quadratic stability. The performance of the proposal procedure is evaluated through the modal analysis and non-linear time-domain simulations of the Brazilian 7 bus Equivalent Power System Model, an IEEE benchmark system for small-signal analysis.

Procedure to account for DG mandatory disconnection during voltage stability assessment

During static voltage stability analysis, as the load grows, bus voltages tend to drop. This voltage reduction may cause undervoltage trip of distributed generators which, in turn, may diminish the Voltage Stability Margin (VSM) of the bulk power system. The purpose of this paper is to evaluate the effect of Distributed Generation (DG) undervoltage mandatory disconnection in the VSM of transmission systems. To achieve this, a predictor/corrector scheme is proposed to successively find power flow solutions right before and after DG units trip. The proposed method was employed with the 107 bus Brazilian reduced interconnected system, showing that DG mandatory disconnection is responsible to reduce the VSM from 11.4% to about 9% for the three DG penetration levels considered (10%, 20% and 30%). The predictor/corrector scheme also identified the specific bus in which DG units are critical to the bulk power system stability, indicating that their undervoltage protection requirements should be adjusted.

A control scheme for mitigation of DFIG oscillatory behavior related to FIDVR problem

This paper proposes a control scheme for the grid-side converter (GSC) of the doubly fed induction generator (DFIG) in order to mitigate the oscillatory effect of the generator speed caused by the problem of Fault Induced Delayed Voltage Recovery (FIDVR). In this scheme, the mode of control changes the reference of the current of the GSC to the DFIG contribute with the injection of reactive power to the grid. The FIDVR problem is caused by the presence of induction motors in the system. The DFIG is connected to the distribution system operating under unbalanced conditions. Several conditions of load imbalance were used to evaluate the effect of the imbalance in the oscillations of the DFIG comparing the results between balanced and unbalanced conditions. It was observed that the presence of the negative sequence component of the electromagnetic torque of the motor, due to operation of unbalanced conditions, causes the net torque to be smaller (when compared to the balanced case) and consequently it takes longer for the motor to reach the steady-state. This effect has impact on the oscillatory behavior of the DFIG reducing the damping of the electromechanical oscillations. The damping and the frequency of the oscillations are obtained by the Prony method. The results showed that the increase in the percentage of load unbalance causes a change in the damping of the oscillations of the DFIG. The proposed control scheme was capable of reducing oscillatory behavior of the DFIG and increase the damping of the electromechanical oscillations of the generator.