Potential applications of adaptive control theory to electrical power systems control are explored. In the first part of the paper, the status of adaptive control theory is reviewed. Current mechanisms and methods of electrical power systems control are then examined. The two areas in adaptive power system control that have received the most attention are adaptive generator exciter control and adaptive load-frequency control. Nine recent papers on adaptive exciter control are described, as also are three papers on adaptive load-frequency control. Potential applications of adaptive control to other power system control problems are noted.

A Perspective on Adaptive Control of Power Systems

The small time constants of power electronics devices lead to dynamic couplings with the electromagnetic transients of power networks, and thus complicate the modeling and stability analysis of power-electronics-based power systems. This paper presents a computationally efficient approach to assess the small-signal stability of inverter-fed power systems. The power system is partitioned into individual components, including the power inverters, network impedances, and power loads. The state-space model of individual inverter is first built, where the frequency response and eigenvalue analysis collectively characterize the contributions of different controller parameters to the terminal behavior in a wide frequency range. These component models, together with the network equations, are then algebraically assembled based on the interconnection relations at their terminals. As a consequence, the state matrix of the whole system, which is essential to the system stability analysis, can be reformulated in a computationally efficient way. The experimental results are finally given to validate the effectiveness of the modeling method and system stability analysis.

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Small-Signal Stability Analysis of Inverter-Fed Power Systems Using Component Connection Method

This paper presents an effective control scheme using a line-commutated high-voltage direct-current (HVDC) link with a designed rectifier current regulator (RCR) to simultaneously perform both power-fluctuation mitigation and damping improvement of four parallel-operated 80-MW offshore wind farms delivering generated power to a large utility grid. The proposed RCR of the HVDC link is designed by using modal control theory to contribute adequate damping to the studied four offshore wind farms under various wind speeds. A systematic analysis using a frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear model simulations is performed to demonstrate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed HVDC link combined with the designed RCR can not only render adequate damping characteristics to the studied offshore wind farms under various wind speeds but also effectively mitigate power fluctuations of the offshore wind farms under wind-speed disturbance conditions.

Power-Flow Control and Stability Enhancement of Four Parallel-Operated Offshore Wind Farms Using a Line-Commutated HVDC Link

A scheme for improving the dynamic stability of a parallel AC-DC power system is presented It uses a proportional-integral-derivative (PID) power-system stabilizer and a PID rectifier current regulator to enhance the damping for the electromechanical mode of the system The parameters of the proposed PID controllers are determined using a unified approach based on modal control theory Eigenvalue analyses are performed for the system under various operating conditions in order to compare the damping effects provided by the two different control schemes The effectiveness of the proposed damping schemes under disturbance conditions is demonstrated by computer-simulated dynamic-response tests based on a nonlinear system model >

Damping of a parallel AC-DC power system using PID power system stabilizers and rectifier current regulators

This paper presents a modified optimal controller for an interconnected power system. The design method does not need the specification of weighting matrices. The eigenvalues of electromechanical and exciter modes would be shifted to a prespecified vertical strip. For practical implementation, the design method only uses partial output feedback. For demonstrating the effectiveness of damping enhancement, eigenvalue analysis and nonlinear simulation results are used to show that the proposed controller gives significant improvement in the dynamic performance of the interconnected power system. >

Damping of power system oscillations with output feedback and strip eigenvalue assignment

This paper develops an optimal control strategy for improved dynamic performance of integrated ac/dc systems, based on power modulation techniques. The basic feature of the method is the minimization of the adverse reactive power interactions between the controls and voltage sensitive loads, which tend to reduce the effectiveness of the modulation process. A method for stability analysis, based on linearization techniques and eigenvalue sensitivities, is developed and applied to a typical ac/dc system with non-linearly voltage dependent load. The dynamic performance of the system, both with dc power modulation and power system stabilizer, is evaluated for various operating conditions, different load characteristics and different excitation systems. Finally, a dynamic simulation program is developed and used to obtain the exact transient response of the ac/dc system in the time domain. The simulation results presented in the paper verify the responses predicted from the linear eigenvalue sensitivity analysis.

Stability Analysis of a Modulated AC/DC System Using the Eigenvalue Sensitivity Approach

This paper develops a new technique for the design of optimal modulation controllers for multi-area ac/dc systems. The technique is based on optimal pole assignment using eigenvalue sensitivities. The basic feature of the proposed method is that both the diagonal and the off-diagonal elements of the weighting matrices are used for the eigenvalue assignment which results in increased design flexibility. The method is applied to the design of a modulation controller for a strongly interconnected three area ac/dc system. Dynamic simulation results presented in the paper show that the proposed modulation controller results in significant improvement of dynamic performance of the interconnected system.

Design of Optimal Modulation Controllers for Multiarea AC/DC Systems Using Eigenvalue Sensitivities

The authors present a novel approach to the design of decentralized optimal controls for integrated power systems. The approach involves the decomposition of the integrated system into interconnected subsystems and the independent control of each subsystem, considering the interactions at the interconnection points as unknown disturbances. The design of a reduced-order observer, capable of reconstructing the inaccessible states of the system and the unknown disturbances, and the integration of this observer into the overall control loop are presented. As an example, an optimal current regulator for HVDC system is presented to demonstrate the effectiveness of the proposed approach. >

Design of a reduced order observer for optimal decentralized control of HVDC systems

A general and efficient method is presented for transient simulation of HVDC converters. The method utilizes a novel algorithm that is based on network topological concepts and provides an efficient solution to the problem of modeling the inherently nonlinear characteristics and time-varying topology of static power converters caused by the switching action of the thyristor valves. The application of the algorithm to a six-pulse converter unit results in an extremely flexible and efficient model that can be easily interfaced to both the AC and DC sides of an integrated AC/DC system. >

Transient simulation of integrated AC/DC systems. I. Converter modeling and simulation

The development of a general algorithm, which constructs the state equations of switching systems as a function of the state of their switching elements, is presented. Although the algorithm is developed primarily for transient simulation of power electronics systems, it can be applied to any system that can be modeled by an equivalent circuit consisting of linear ERLC elements and ideal switches.

https://ieeexplore.ieee.org/iel5/31/23595/01086221.pdf

G. D. Galanos

Papers

Stability Analysis of a Modulated AC/DC System Using the Eigenvalue Sensitivity Approach

Design of Optimal Modulation Controllers for Multiarea AC/DC Systems Using Eigenvalue Sensitivities

Design of a reduced order observer for optimal decentralized control of HVDC systems

Transient simulation of integrated AC/DC systems. I. Converter modeling and simulation

An algorithm for transient simulation of power electronics systems