Structure Preserving Power System Research Articles

Voltage Frequency Control Using SVC Devices Coupled With Voltage Dependent Loads

This paper proposes a decentralized control based on static var compensator (SVC) devices to improve the frequency control of high voltage transmission systems. For a realistic structure preserving power system with voltage dependent loads, we propose a sufficient condition based on a strict Lyapunov energy function, which is utilized to design a nonlinear adaptive SVC controller. This controller only requires local bus measures and parameters. Furthermore, we also present an SVC with a conventional frequency droop controller. The performance of the two considered SVC control systems are evaluated on the well known IEEE New England 39-bus 10-machine power system and compared with conventional SVC controllers.

Decentralized Nonlinear Robust Coordinated Control of UPFC and Generators in Multi‐ Machine Power System Via Pseudo‐Generalized Hamiltonian Theory

AbstractIn this paper, based on a structure preserving power system with a unified power flow controller (UPFC), using pseudo‐generalized Hamiltonian function method and boundary‐function method, a nonlinear robust coordinated control law is constructed for multi‐machine power system oscillation damping. The 4‐machine 2‐area power system is used to demonstrate the performance of the proposed controller. Simulation results indicate that the proposed coordinated control scheme can effectively improve both transient stability and voltage regulation performance of the power system. ©2014 Chinese Automatic Control Society and Wiley Publishing Asia Pty Ltd

A sliding mode controller for SSSC to delay Hopf bifurcation in a differential-algebraic power system model

A novel sliding mode controller (SMC) is proposed for static synchronous series capacitors (SSSCs) to delay Hopf bifurcation (HBF) in a differential-algebraic power system model. The proposed controller consists of an equivalent control term and a switching term. The major drawback of SMC approach, viz., the undesired chattering is eliminated by introducing a continuously changing switching term instead of the conventional switching function. The effectiveness of the controller is demonstrated in a bifurcation perspective. Steady state bifurcation diagrams are constructed by the application of an algorithm based on continuation method for the entire Jacobian matrix of structure preserving power system model. From the bifurcation diagram, existence of HBF is identified with the help of eigen value analysis. Occurrence of HBF is confirmed through computation of HBF index. The effectiveness of the proposed SMC over the conventional PI controller for SSSC in delaying HBF and maintaining load voltage constant for higher reactive power loading is illustrated for a 3 machine, 9-bus system.

An Explicit Solution of the Power Balance Equations of Structure Preserving Power System Models

In this paper, we consider the widely popular structure-preserving models used to describe the dynamic behavior of multimachine power systems. These models consist of differential-algebraic equations, where the algebraic constraints stem from the power flow balance between generators, loads, and lines. Our main contribution is the explicit computation of a solution for these algebraic equations under the assumption that the loads are constant impedances. This result is of interest for transient stabilization problems where, to estimate the domain of attraction of a given control law, it is sometimes necessary to explicitly solve the algebraic constraints. Besides this application, we believe this result may be of interest in other problems of power systems analysis.

Nonlinear Decentralized Disturbance Attenuation Excitation Control for Power Systems With Nonlinear Loads Based on the Hamiltonian Theory

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel nonlinear control scheme for disturbance attenuation of structure preserving multimachine power systems based on Hamiltonian theory is proposed in this paper. The proposed control scheme includes two steps: first, the dissipative Hamiltonian realization of structure preserving power system is completed using the singular perturbation approach in which the algebraic equations are considered as a limit of fast dynamics; second, a nonlinear decentralized disturbance attenuation excitation controller is designed without linearization to improve transient stability of power system as well as the robustness with respect to unknown exogenous disturbance in the sense of <formula formulatype="inline"><tex>$L_2$</tex></formula>-gain. Simulation on a two-area system demonstrates that the proposed scheme can enhance transient stability of the system regardless of the exogenous disturbance. </para>

The sparse formulation of ISPS and its application to voltage stability margin sensitivity and estimation

The sparse formulation of the invariant sub-space parametric sensitivity (ISPS) of the structure preserving power system model is derived. The ISPS is the projection of parametric sensitivity onto a particular critical eigensubspace of interest. In this paper, major modifications are proposed to extend the applicability of the ISPS. ISPS is computed while tracing simultaneously the trajectory of both dynamic and algebraic state variables. By doing so, the sparsity of total Jacobian (the Jacobian that corresponds to both dynamic and algebraic variables) is fully exploited. The authors also derived a new voltage stability margin estimation from the measure of ISPS. It is shown here that the derived margin sensitivity vector can be calculated with essentially no further cost once the measure of ISPS is available. The voltage stability margin for any other parameter variations can be easily estimated without re-computing the P-V curves. With this methodology, effective controls can be easily coordinated by quantifying the relative importance of a wide range of control parameters. Numerical studies with the IEEE New England 39-bus system shows the potential applications of the method.

Lyapunov functions for multimachine power systems with dynamic loads

This paper develops Lyapunov functions for power systems which have dynamic reactive power loads. These functions are extensions of earlier Lyapunov functions derived for structure preserving power system models having static loads. In order to obtain strict Lyapunov functions, the transient response of the dynamic load must have a logarithmic dependence on voltage. A Lyapunov function is initially generated using a first integral analysis. A Popov criterion analysis is then undertaken for comparison. The developed Lyapunov functions enable the investigation of the interaction between generator (angle) and load dynamics in multimachine power systems.

Invariant subspace parametric sensitivity (ISPS) of structure-preserving power system models

In this paper, the parametric sensitivities of a structure-preserving power system model are derived. The parametric sensitivities give the sensitivities of an equilibrium point with respect to a particular parameter of interest. A new invariant subspace parametric sensitivity (ISPS) is derived by projecting the total parametric sensitivity onto a particular eigenspace of interest. The ISPS provides the sensitivity of system stability. At a particular eigensubspace, ISPS of all the parameters under consideration are represented by a right eigenvector multiplied by a scalar /spl sigma/. Then the parameter which has the most influence on the subspace can be determined by selecting the largest value of /spl sigma/. The methodology is applied to a New England 39-bus system to identify components and parameters that are responsible fora possible system instability.

A piecewise global small-disturbance voltage-stability analysis of structure-preserving power system models

This paper provides a tutorial introduction to the small-disturbance voltage-stability analysis as applied to the structure-preserving power system model. Salient features of this approach are: (1) both dynamic and static models that are relevant to voltage stability are included-in particular, the effect of load dynamics and generator current limits are considered; (2) realistic load increases and a generation sharing scheme with relevant limits are included; and (3) for a given load increase and generation sharing scenario, all possible critical points that may lead to voltage instability are systematically traced and identified.

The parallel implementation of the waveform relaxation method for transient stability simulations

The WR (waveform relaxation) algorithm is extended to a structure-preserving power system model in which the loads are retained. This results in a system of differential/algebraic equations (DAEs). Power system exhibit several unique dynamic properties which may be exploited in an advantageous manner by the WR algorithm. These physical properties include the coherency properties of the power system which lead to the partitions for the textured model approach, the near diagonal dominance which leads to longer windows for uniform convergence, and the localized response from which the multirate capabilities of the WR method can be used. These characteristics enable power systems to obtain more favorable results than were obtained in VLSI simulations. The authors present several theoretical results as well as computational results on parallel implementation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>