Network-Based Analysis of Small-Disturbance Angle Stability of Power Systems

This paper investigates small-disturbance angle stability of power systems with emphasis on the role of power network topology, which sheds new light on the instability mechanism. We introduce the concepts of active power flow graph and critical lines. It is shown that the inertia of the Laplacian matrix of this graph provides information on the stability and type of an equilibrium point. Then, the instability mechanism is elaborated from the impact of critical lines on the inertia of the Laplacian matrix. A stability criterion in terms of a critical line-based matrix is established. This criterion is a necessary and sufficient condition to judge the stability and type of an equilibrium point. It includes the existing results in the literature and applies to the unsolved cases where the critical lines exist but do not form cutsets. Moreover, we introduce the concept of equivalent weight between a pair of buses. Another stability criterion in terms of the equivalent weight is developed, from which the small-disturbance instability can be interpreted as the “electrical antagonism” between some buses in the power network resulting from the critical lines. The equivalent weight can also be used as a stability index and provides guidance for system operation. The obtained results are illustrated by numerical simulations.postprin

Self-Organized Synchronization and Voltage Stability in Networks of Synchronous Machines

The integration of renewable energy sources in the course of the energy transition is accompanied by grid decentralization and fluctuating power feed-in characteristics. This raises new challenges for power system stability and design. We intend to investigate power system stability from the viewpoint of self-organized synchronization aspects. In this approach, the power grid is represented by a network of synchronous machines. We supplement the classical Kuramoto-like network model, which assumes constant voltages, with dynamical voltage equations, and thus obtain an extended version, that incorporates the coupled categories voltage stability and rotor angle synchronization. We compare disturbance scenarios in small systems simulated on the basis of both classical and extended model and we discuss resultant implications and possible applications to complex modern power grids.Comment: 9 pages, 9 figure

The Price of Synchrony: Resistive Losses due to Phase Synchronization in Power Networks

We investigate the total resistive losses incurred in returning a power network of identical generators to a synchronous state following a transient stability event or in maintaining this state in the presence of persistent stochastic disturbances. We formulate this cost as the input-output $H^2$ norm of a linear dynamical system with distributed disturbances. We derive an expression for the total resistive losses that scales with the size of the network as well as properties of the generators and power lines, but is independent of the network topology. This topologically invariant scaling of what we term the price of synchrony is in contrast to typical power system stability notions like rate of convergence or the region of attraction for rotor-angle stability. Our result indicates that highly connected power networks, whilst desirable for higher phase synchrony, do not offer an advantage in terms of the total resistive power losses needed to achieve this synchrony. Furthermore, if power flow is the mechanism used to achieve synchrony in highly-distributed-generation networks, the cost increases unboundedly with the number of generators.Comment: 7 pages; 2 figure

Doktrin pengasingan kuasa : falsafah, praktis dan kerelatifan di Malaysia

Penulisan ini membincangkan tentang doktrin pengasingan kuasa berdasarkan kerangka teori institusionalisme. Doktrin ini dipraktiskan dalam trias politica atau politik tiga serangkai iaitu badan legislatif, eksekutif dan kehakiman. Falsafah dan praktis doktrin pengasingan kuasa ini adalah ditekankan bagi sesebuah negara bercorak demokrasi untuk mempamerkan wujudnya pengasingan kuasa serta autonomi bidangan di antara ketigatiga badan kerajaan. Hal ini penting untuk disoroti kerana Malaysia tidak terkecuali daripada mengamalkan sistem demokrasi dan pada masa yang sama mempraktiskan doktrin pengasingan kuasa dalam kerajaan federalisme berlapisnya sebagai satu pegangan fundamental. Akauntabiliti untuk menzahirkan doktrin pengasingan kuasa ini merupakan perkara yang penting memandangkan ia telah dimaktubkan dalam Perlembagaan Persekutuan