Análise do desempenho de geradores síncronos distribuídos com controladores dotados de modos de operação comutáveis

Abstract

Synchronous generators from industrial plants with co-generation, which operate in parallel with the power system, are normally equipped with an excitation and speed controller. The excitation controller functions in the constant power factor regulator mode,while the speed controller operates in droop mode. Although these strategies are adequate under steady state, in other ways, they impede the function of these synchronous machines in response to eventual disturbances, which implies the risk of stability loss of these electric systems, those being the electric energy system and industrial electric system. This risk is divided into possible loss of voltage stability which is reflected through voltage sag on the bars and in presumed loss of rotor stability, associated with the electromechanical oscillations that may result in asynchrony and the shutdown of the generators. In this manner, in those situations where voltage sag is present on the system bus, the excitation controllers of the generators should operate in the voltage regulation mode, under the intent of allowing the synchronous machines to contribute to voltage recuperation. When faced with the situation of plant isolation in relation to the main network, besides the supply of reactive energy for adjusting the voltage on its terminals, which is the excitation controllers, operating in regulator voltage mode, the machines should supply the maximum feasible active power in order to continue operating synchronously, and supply the highest possible quantity of load. This demands that the turbine speed controller operates in isochronous mode. In line with this perspective, this question was investigated as part of this work, by computer simulations using the ATP (Alternative Transients Program) with the aim of analysing the behaviour of the generators when submitted to these disturbances. In the simulated cases, the speed controller automatically switches to the isochronous mode, should the industrial system lose its connection with the distribution network from the power utility. In addition, the excitation controllers automatically change to the voltage regulator mode, for this type of occurrence as well as in those situations, due to overvoltage, where the power system suffers voltage sag. The obtained results show that the desired performance of the synchronous generators, in terms of stability is assured through this operation strategy expansion for the controller modes. This means that the industrial systems can contribute to the voltage stability of the power system; on the other hand, the machines maintain synchronism when they lose their connection with the distribution network, while changing the operational modes of the controllers. The conclusion reached, points out that speed controllers with the capacity to automatically change from droop mode to isochronous mode and excitation control systems, also with the ability to change automatically from power factor regulators to voltage regulators, should be standardized to equip any distributed generator. This being due to the flexibility offered by this actuated hybrid strategy, which is very useful for conducting these controllers when faced with inherent disturbances that occur on electrical systems.