Análise de estabilidade e desempenho de técnicas de paralelismo semcomunicação aplicadas a sistemas UPS não idênticas

Abstract

The increase on the demand for high quality electrical energy supplies and the increasing use of alternative energy sources has motivated several works on the parallel operation of UPS (Uninterruptible Power Supply) systems. In this context, some techniques have been developed for the stability analysis of parallel operation, without communication, of UPS systems. In this specific case there is no explicit exchange ofinformation among the UPS units to achieve the synchronization condition in the whole system. In the theoretical analysis of such systems, in most of these techniques, it is usual to consider that the UPS units are identical, which is a very restrictive condition in real applications. In this dissertation the stability analysis of the synchronization condition is presented taking into consideration small parametric mismatches among the UPS units, while they are connected to a common power bus supplying energy to the same load, and assuming that each unit behaves as a nonlinear oscillator. After a brief review of the UPS parallel operation techniques without communication, which are based on the so-called Droop Method that depends on estimates of the active and reactive powers delivered by each UPS unit, some metrics are proposed to compare, by means of MonteCarlo analysis basedon simulation results, the performance robustness to parametric mismatch and presence of noise on the measurements. Finally, it is shown that the tested techniques, for the levels of parametric uncertainty and measurementadditive noise considered, seems to be robust. The method of stability analysis using Floquet multipliers, adapted for the non identical UPS units case, is also presented in this work. The main limitations of this stability analysis technique is the necessity of prior knowledge on the synchronous trajectory of the system, and the assumption of periodic synchronization error. Although the synchronous behavior corresponding to small changes in the parameters is different from the target behavior, such fact seems to not affect the qualitative analysis based on this technique, and therefore synchronous stabilityregions in the UPS units parameter space could be obtained for the non identical case.