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Centralized control, which can overcome the ill interactional effects among decentralized controllers, impels a real need for fast and reliable computational algorithms to improve the accuracy of phasor and power measurements. This paper deals with discrete Fourier transform (DFT)-based measurement techniques. Based on the practical frequency tracking method proposed by the same authors in another paper, this paper develops practical compensation method to improve the phasor and power measurement accuracy of the DFT algorithm. The method proposed by this paper takes full advantage of the DFT algorithm. It simply modifies the DFT results. With notable accuracy improvement, the calculation burden of the proposed method is little more than the DFT algorithm. The method can be used for on-line purposes. Though the analog signal studied in this paper is sinusoidal signal, the method proposed by this paper has good performance in the presence of harmonics. Some examples are given to demonstrate the feasibility, simpleness and robustness of the proposed method. Index Terms--Amplitude estimation, discrete Fourier transforms (DFTs), frequency measurement, phase measurement, power measurement.

In this paper, we provide a solution to the long-standing problem of transient stabilization of multimachine power systems with nonnegligible transfer conductances. More specifically, we consider the full 3n-dimensional model of the n-generator system with lossy transmission lines and loads and prove the existence of a nonlinear static state feedback law for the generator excitation field that ensures asymptotic stability of the operating point with a well-defined estimate of the domain of attraction provided by a bona fide Lyapunov function. To design the control law we apply the recently introduced interconnection and damping assignment passivity-based control methodology that endows the closed-loop system with a port-controlled Hamiltonian structure with desired total energy function. The latter consists of terms akin to kinetic and potential energies, thus has a clear physical interpretation. Our derivations underscore the deleterious effects of resistive elements which, as is well known, hamper the assignment of simple "gradient" energy functions and compel us to include nonstandard cross terms. A key step in the construction is the modification of the energy transfer between the electrical and the mechanical parts of the system which is obtained via the introduction of state-modulated interconnections that play the role of multipliers in classical passivity theory. Index Terms--Nonlinear systems, passivity-based control, power systems, stability.

Comprehensive analysis of discrete Fourier transform (DFT) error is given in this paper, including why it is accurate when used in the case of synchronous sampling and how error rises when sampling frequency does not synchronized to signal frequency. Simple but precise expressions of phase angle error and amplitude error are given. Practical formulas to calculate the true phase angle and amplitude are presented. The formulas are very simple and precise. Based on the formula to calculate true phase angle, a new frequency tracking method is developed. The proposed method can be calculated recursively. And, with notable accuracy improvement, the calculation burden is little more than the traditional DFT method. Also, an adaptive method to suppress the effect of harmonics is presented, which adds very little calculation burden with satisfying performance. The most distinguished feature of the proposed method is that it is not only precise, but also simple. Some examples are given to demonstrate the feasibility, precision, simpleness and robustness of the proposed method. Index Terms--Asynchronons sampling, discrete Fourier transform (DFT), frequency measurement, phase measurement.

Byline: Xiaohong Jiao, Yuanzhang Sun To enhance the transient stability of a synchronous generator, non-linear adaptive control of the governor is investigated based on modern non-linear adaptive techniques. A non-linear adaptive feedback governor controller is designed to play the role not only in damping the rotor angle oscillations but also in reaching the desired performance during post-temporary-fault or post-permanent-fault. The proposed controller can render the resulting closed-loop system to converge quickly to a stable equilibrium point, irrespective of the operating equilibrium point of the system and the fault sequence in transmission line. Some comparison results with the governor controllers obtained by existing design methods are given in simulation to demonstrate the effectiveness of the proposed control schemes.