Dynamic Synchronized Phasor Estimator For Power Systems And Its Applications

Synchrophasor measurement has provided a novel method to monitor the power grid widely and the design of synchrophasor measurement technique is one of the most important essential elements. The accuracy of measurement has direct bear on the efficiency of other applications of Wide Area Measurement System (WAMS), such as state estimation, adaptive protection and fault location, etc. Although the accuracy of phasor measurement of the commercial Phasor Measurement Units (PMUs) can meet the most of the requirement of real-time applications in the steady state, the error of phasor measurement arises when a power system is under dynamic condition such as power oscillation and frequency deviation due to the impact of the dynamic characteristic of supplied signals. Therefore, it is necessary to develop a new synchrophasor measurement algorithm and a new frequency estimation algorithm, which can have accurate estimation under both steady state and dynamic condition. it is very important that can offer accurate phasor and frequency information across the whole power grid to help the high-level applications predict the develop direction of power system and make a rapid decision to protect the power system correctly.A great deal of effort has been put to the research on frequency tracking algorithm and synchrophasor measurement algorithm in presence of decaying dc components and dynamic characteristitcs. After a new dynamic frequency tracking estimator and a dynamic phasore estimator have been proposed, a dynamic fault-location estimator considering power systems'dynamic chariteristics expressed by the phasor measurement from PMUs is presented.Three-phase voltage signals are employed to estimated the density of the noise and the dynamic characteristic online, and then the real-time state of power system can be measured by introducing two variables, noise density variance and dynamic characteristic variance. Therefore, the new frequency-tracking algorithm can have fast tracking characteristic under dynamic condition and good anti-noise characteristic under high noise density condition by changing the forgetting factor in the Infinite Impulse Response (IIR) filters according to the estimation of noise density variance and dynamic characteristic variance. Besides, the algorithm proposed can be employed with ease when limited Digital Signal Processor (DSP) bandwidth is available as the the computation burden has been sharply reduced by applying a recursive algorithm. A few simulations under different conditions including phase shift, frequency step change and PSCAD/EMTDC simulation allows us to make a conclusion that the performace of proposed algorithm is much better than that of traditional one under both high-density noise condition and dynamic conditions.With the aspect of synchrophasor estimation, by considering the dynamic characteristic of supplied signals, the time-varying phasor of supplied signals are modeled by Taylor expansion and the Taylor derivatives are described by the adjoining phasor estimations of different data windows. The synchrophasor estimation from Discrete Fourier Transform(DFT) can be reassigned by using the derivatives in order to improve the accuracy of phasor estimation. Computer-generated signals tests and simulations by Real Time Digital System draw a conclusion that the proposed algorithm can dramatically improve the performance under variety of dynamic conditions with the cost of minus computational burden increase. Besides, the derivative of Taylor expansion can also be applied to detect the fault under power oscillation condition.It is necessary to consider dynamic characteristic and decaying DC component simultaneously and reduce their affect on phasor estimation. First, a dynamic signal model considering the decaying DC component is applied to model the fault current. Two filters, fundament component filter and DC component filter, estimate the fundamental phasor and decaying DC component. Finally, better fundamental phasor estimation is obtained by using a recursive algorithm. Ideal signal test, including decaying dc component, dynamic characteristics and both of them, and PSCAD/EMTDC based simulations allows us to draw a conclusion that the proposed algorithm can improve the accuracy of phasor measurement under power oscillation condition when a earth fault happens.A new algorithm extended from traditional fault location algorithms is proposed. This approach not only can express the space characteristic of supplied signals but also considers the supplied signals as time-variable signals whose magnitude and frequency are changing against time so that it has the ability of describing space property and time property of signals. Then, after using the adjoining phasor measurement to express the dynamic characteristic in term of derivatives, the accurate fault location can be attained via a Newton iteration method. PSCAD/EMTDC simulation based on a typical 230kV transmission line under different conditions, such as different fault location, fault resistance and fault type is performed. The simulation results show that the proposed algorithm not only have the merit of trandition two-terminal fault-location algorithm, but also can have a precise estimate of fault location under power oscillation condition.Overall, a theoretical system based on dynamic characteristics of power systems is achieved. This system includes a frequency-tracking algorithm that improves the performance of data acquisition system, a dynamic phasor estimator and a dynamic fault-location estimator.