Calculation of parameter ranges for robust gain tuning of power system controllers

This work proposes a computational tool to assist power system engineers in the field tuning of power system stabilizers (PSSs) and Automatic Voltage Regulators (AVRs). The outcome of this tool is a range of gain values for theses controllers within which there is a theoretical guarantee of stability for the closed-loop system. This range is given as a set of limit values for the static gains of the controllers of interest, in such a way that the engineer responsible for the field tuning of PSSs and/or AVRs can be confident with respect to system stability when adjusting the corresponding static gains within this range. This feature of the proposed tool is highly desirable from a practical viewpoint, since the PSS and AVR commissioning stage always involve some readjustment of the controller gains to account for the differences between the nominal model and the actual behavior of the system. By capturing these differences as uncertainties in the model, this computational tool is able to guarantee stability for the whole uncertain model using an approach based on linear matrix inequalities. It is also important to remark that the tool proposed in this paper can also be applied to other types of parameters of either PSSs or Power Oscillation Dampers, as well as other types of controllers (such as speed governors, for example). To show its effectiveness, applications of the proposed tool to two benchmarks for small signal stability studies are presented at the end of this paper.

O poder da caneta: a Medida Provisória no processo legislativo estadual

A Medida Provisória (MP) brasileira é um dos instrumentos legislativos mais poderosos nas mãos do Presidente da República para alterar unilateralmente o status quo. Apesar de o judiciário ter reconhecido a competência dos governadores para instituir e adotar a MP, esta existe apenas em seis estados. O artigo procura explicar a não adoção deste instrumento legislativo pela maioria dos estados. Enfatiza-se a escassa ou marginal relevância que é dada à MP pelo governador nos seis casos que a adotaram. Defende-se, aqui, que os governadores, diferentemente dos presidentes, não necessitam de mais um instrumento legislativo ou da ampliação da delegação de prerrogativas legislativas para garantir sua agenda frente a seus respectivos legislativos, já que com ou sem poder de decreto estadual os governadores controlariam a já limitada agenda decisória nos estados.