Stability and Control of Power Systems using Vector Lyapunov Functions and Sum-of-Squares Methods

Recently sum-of-squares (SOS) based methods have been used for the stability analysis and control synthesis of polynomial dynamical systems. This analysis framework was also extended to non-polynomial dynamical systems, including power systems, using an algebraic reformulation technique that recasts the system's dynamics into a set of polynomial differential algebraic equations. Nevertheless, for large scale dynamical systems this method becomes inapplicable due to its computational complexity. For this reason we develop a subsystem based stability analysis approach using vector Lyapunov functions and introduce a parallel and scalable algorithm to infer the stability of the interconnected system with the help of the subsystem Lyapunov functions. Furthermore, we design adaptive and distributed control laws that guarantee asymptotic stability under a given external disturbance. Finally, we apply this algorithm for the stability analysis and control synthesis of a network preserving power system.Comment: to appear at the 14th annual European Control Conferenc

Stochastic Model for Power Grid Dynamics

We introduce a stochastic model that describes the quasi-static dynamics of an electric transmission network under perturbations introduced by random load fluctuations, random removing of system components from service, random repair times for the failed components, and random response times to implement optimal system corrections for removing line overloads in a damaged or stressed transmission network. We use a linear approximation to the network flow equations and apply linear programming techniques that optimize the dispatching of generators and loads in order to eliminate the network overloads associated with a damaged system. We also provide a simple model for the operator's response to various contingency events that is not always optimal due to either failure of the state estimation system or due to the incorrect subjective assessment of the severity associated with these events. This further allows us to use a game theoretic framework for casting the optimization of the operator's response into the choice of the optimal strategy which minimizes the operating cost. We use a simple strategy space which is the degree of tolerance to line overloads and which is an automatic control (optimization) parameter that can be adjusted to trade off automatic load shed without propagating cascades versus reduced load shed and an increased risk of propagating cascades. The tolerance parameter is chosen to describes a smooth transition from a risk averse to a risk taken strategy...Comment: framework for a system-level analysis of the power grid from the viewpoint of complex network

BUILDING THE NEW DIMENSION OF STRATEGIC CORPORATE SOCIAL RESPONSIBILITY: ENVIRONMENTAL LEADERSHIP

The paper aims to emphasize the role of environmental leadership as main option for combining the Corporate Social Responsibility (CSR) policy with the business goals and targets in order to satisfy both shareholders’ interests and social interests, in terms of profit, productivity and social awareness. Under these circumstances, the paper describes the way environmental leadership is being built and introduced in the organizational culture of a company, regardless of its size, becoming a very efficient and effective philosophy of managing people and achieving performance targets. Nowadays.environmental leadership, corporate social responsibility, strategy, business performance

Study of population by domicile and residence. Natural movement and imbalances

The evolution of the Romanian population is one that has to attract interest, especially from the point of view of the decrease in the birth rate, which will further determine the reduction from year to year of the population, both resident and domicile in Romania. Against the background of the increase of the death-birth rate, i.e. the ratio of deceased to newborn in favor of the deceased, the age pyramid will be changed in the sense that, at the base, the younger generations will be reduced to the middle and especially towards the peak of the pyramid being net contingents over previous periods. In this context, we can speak with certainty about a phenomenon of aging of the population, i.e., of increasing the number of older people on the background of the decrease of the birth rate. In this article, the authors study the evolution of the population over time, presenting tables and graphs that highlight this aging phenomenon. In summary, we can say that birth rates are decreasing, mortality increases, marriage decreases, divorcement increases, and emigration of a part of the population, especially from younger generations and with more special training. Birthplaces are highlighted, in the context of the couples breaking up or not, in order to have an image that the generation of young children does not have an immediate or long-lasting perspective. There are many births outside marriages, especially in rural areas and less in urban areas. The age at which the marriages are made is advanced, and on this complex background we come to the conclusion of a certain aging process of the Romanian population. At the same time, we also appreciate that the population resident or domiciled in Romania will also gradually decrease. There are predictions that, in 2050, the population of Romania, if this trend of the main demographic indicators is maintained, will reach about 17 million inhabitants