Centralized Control of Dispersed Generators Providing Ancillary Services in Distribution Networks Part I: Theoretical Aspects

Recent improvements and advances in power electronic technology offer potential solutions to several technical and economical problems associated with distribution networks. In particular, dispersed generation (DG) units that use this technology can provide both energy and ancillary services. In this paper, a selected number of DG units (in particular, fuel cells and photovoltaic cell-based systems), interconnected with the distribution network through power electronic interfaces, are coordinated by a centralized control system to provide the usual energy service as well as some ancillary services, such as reactive power control and compensation for some continuous PQ disturbances, such as waveform distortions, unbalances, and voltage fluctuations. The centralized control system can operate with strategies aimed at either compensating for the disturbances in the busbars of the whole system or in some areas of the network where there are customers whose needs require enhanced power quality control. The selected DG units can also provide load following and backup services to a local, privileged load. This paper, which reports the modelling of the considered DG units and the theoretical aspects regarding the centralized control system, is a companion paper to a paper in which computer simulations on an actual distribution grid are reported, demonstrating the effectiveness of the compensation actions at various operating conditions.