Feedback linearizing model predictive excitation controller design for multimachine power systems

In this paper, a nonlinear excitation controller is designed for multimachine power systems in order to enhance the transient stability under different operating conditions. The two-axis models of synchronous generators in multimachine power systems along with the dynamics of IEEE Type & #x2013;II excitation systems, are considered to design the proposed controller. The partial feedback linearization scheme is used to simplify the multimachine power system as it allows to decouple a multimachine power system based on the excitation control inputs of synchronous generators. A receding horizon-based continuous-time model predictive control scheme is used for partially linearized power systems to obtain linear control inputs. Finally, the nonlinear control laws, which also include receding horizon-based control inputs, are implemented on an IEEE 10-machine, 39-bus New England power system. The superiority of the proposed scheme is evaluated by providing comparisons with a similar existing nonlinear excitation controller where the control input for the feedback linearized model is obtained using the linear quadratic regulator (LQR) approach. The simulation results demonstrate that the proposed scheme performs better as compared to the LQR-based partial feedback linearizing excitation controller in terms of enhancing the stability margin

Feedback Linearization Based Power System Stabilizer Design with Control Limits

In power system controls, simplified analytical models are used to represent the dynamics of power system and controller designs are not rigorous with no stability analysis. One reason is because the power systems are complex nonlinear systems which pose difficulty for analysis. This paper presents a feedback linearization based power system stabilizer design for a single machine infinite bus power system. Since practical operating conditions require the magnitude of control signal to be within certain limits, the stability of the control system under control limits is also analyzed. Simulation results under different kinds of operating conditions show that the controller design not only can damp the power system oscillations very well but can also minimize the impact on the terminal voltage. In addition, the Brunovsky Canonical form of the power system model presented in this paper can be used for other forms of controller design

Robust decentralized control of power systems through excitation systems and thyristor controlled series capacitors

The objective of this work is robust decentralized control of power systems through excitation systems and Thyristor Controlled Series Capacitors (TCSC). Hence the dissertation consists of two parts. In the first part an algorithm for the design of nonlinear decentralized excitation control is developed based on a feedback linearization technique. Feedback linearization technique is applied in excitation control of each generator to obtain an interconnected system where subsystems have linear system matrices and interconnections are represented by nonlinear terms. Different ways of achieving decentralization are investigated: (1) linear robust control combined with observer decoupled state space; (2) disturbance accommodation control. While linear robust control guarantees the subsystem\u27s stability when the interconnection terms are bounded within certain values, disturbance accommodation control is based on linear models of the interconnection terms. Nonlinear simulations are performed on a three-machine nine-bus power system. The simulation results demonstrate the effectiveness of the proposed methodologies.;In the second part, indices for control signal selection and mode effectiveness and interaction are developed. They are applied in Thyristor Controlled Series Capacitor damping control, which is to improve inter-area oscillation damping over a range of operating conditions, for evaluating local signals.;Two case studies are performed to explain and demonstrate the effectiveness of the proposed methodologies. The first power system is the two-area four-machine inter-area oscillation benchmark system. The second is the western U.S. power system (WSCC).;The uncertainty shown in the case studies in this dissertation are variations of load conditions. It can also be variations of topologies. The damping controller proposed in this dissertation is to use local measurement as input signals. Local measurements can be obtained by phasor measurement units (PMU). The feasibility of these control schemes using PMU should be investigated using discrete control techniques. Meanwhile, the measurement errors, control signal delays are not considered in this dissertation. Further work can take above factors into consideration. (Abstract shortened by UMI.)

Nonlinear decentralized disturbance attenuation excitation control via new recursive design for multi-machine power systems

In this paper, a new nonlinear decentralized disturbance attenuation excitation control for multi-machine power systems is proposed based on recursive design without linearization treatment. The proposed controller improves system robustness to dynamic uncertainties and also attenuates bounded exogenous disturbances on the system in the sense of L 2-gain [1]. Computer test results on a 6-machine system show clearly that the proposed excitation control strategy can enhance transient stability of power systems more effectively than other excitation controllers.published_or_final_versio

A non‐linear adaptive excitation control scheme for feedback linearized synchronous generations in multimachine power systems

A new adaptive scheme is proposed in this paper to design excitation controllers for feedback linearized models of synchronous generators in multimachine power systems in order to ensure the stability during large disturbances. The proposed scheme uses speed deviations of synchronous generators, readily available measured physical properties of multimachine power systems, to make all generators within a power network as partially linearized as well as to provide more damping. An adaptive scheme is then used to estimate all unknown parameters which appear in the partial feedback linearizing excitation controllers in order to avoid parameter sensitivities of existing feedback linearization techniques. The overall stability of multimachine power systems is ensured through the excitation control and parameter adaptation laws. The Lyapunov stability theory is used to theoretically analyse the stability of multimachine power systems with the proposed scheme. Simulation studies are presented to evaluate the performance of the proposed excitation control scheme for two different test systems by different operating conditions including short-circuit faults on key locations along with variations in parameters for a large duration. Furthermore, comparative results are presented to highlight the superiority of the proposed adaptive partial feedback linearizing excitation control scheme over an existing partial feedback linearizing excitation controllers

Robust indirect field oriented control of induction generator

The paper presents a novel robust field oriented vector control for induction generators. The proposed controller exploits the concept of indirect field orientation and guarantees asymptotic DC-link voltage regulations when DC-load is constant or slowly varying. An output-feedback linearizing Lyapunov’s based technique is employed for the voltage controller design. Flux subsystem design provides robustness with respect to rotor resistance variations. Decomposition of the voltage and current-flux subsystems, based on the two-time scale separation, allows to use a simple controllers tuning procedure. Results of comparative experimental study with standard indirect field oriented control are presented. It is shown that in contrast to existing solutions designed controller provides system performances stabilization when speed and flux are varying. Experimentally shown that robust field oriented controller ensures robust flux regulation and robust stabilization of the torque current dynamics leading to improved energy efficiency of the electromechanical conversion process. Proposed controller is suitable for energy generation systems with variable speed operation

Maximum torque-per-Amp control for traction IM drives: theory and experimental results

A novel maximum torque per Ampere (MTPA) controller for induction motor (IM) drives is presented. It is shown to be highly suited to applications that do not demand an extremely fast dynamic response, for example electric vehicle drives. The proposed MTPA field oriented controller guarantees asymptotic torque (speed) tracking of smooth reference trajectories and maximises the torque per Ampere ratio when the developed torque is constant or slow varying. An output-feedback linearizing concept is employed for the design of torque and flux subsystems to compensate for the torque-dependent flux variations required to satisfy the MTPA condition. As a first step, a linear approximation of the IM magnetic system is considered. Then, based on a standard saturated IM model, the nonlinear static MTPA relationships for the rotor flux are derived as a function of the desired torque, and a modified torque-flux controller for the saturated machine is developed. The flux reference calculation method to achieve simultaneously an asymptotic field orientation, torque-flux decoupling and MTPA optimization in steady state is proposed. The method guarantees singularity-free operation and can be used as means to improve stator current transients. Experimental tests prove the accuracy of the control over a full torque range and show successful compensation of the magnetizing inductance variations caused by saturation. The proposed MTPA control algorithm also demonstrates a decoupling of the torque (speed) and flux dynamics to ensure asymptotic torque tracking. In addition, a higher torque per Ampere ratio is achieved together with an improved efficiency of electromechanical energy conversion

A Suboptimal Control Law To Improve The Transient Stability Of Power Systems

The application of optimal control theory to damp the electromechanical oscillations associated with the transient conditions in power systems has been given little attention. A suboptimal control law which minimizes the sum of the performance indices of the two linear systems given by a piecewise linear model of a power system improves the transient stability better than the usual optimal control law obtained from a linearized model. Further, the suboptimal control law presented in this paper assures stability of the system for all disturbances resulting in rotor oscillations of magnitudes less than a preselected limit. Copyright © 1976 by The Institute of Electrical and Electronics Engineers, Inc