Impact of Distributed Generation on the Stability of Electrical Power Systems

the performance of a power system with significant penetration of distributed resources is described to assess different types of stability of the bulk network. For this purpose, a hypothetical network is simulated, assuming a large number of fuel cells and micro-turbines as dispersed units in the low-voltage area. The investigation is carried out at constant load demands but with different contributions from fuel cells and micro-turbines. Thus, the rated and supplied powers of the conventional synchronous generators are adjusted to achieve the power balance in the network. With each penetration level of the distributed generation, the performance of the network is studied and different stability classes are analysed. The results are compared with the performance of the network without any distributed generation, as a reference case, to highlight the influence of penetration levels of such units on the stability of the entire network. THE concept of integrating small and medium size generating units into distribution networks as alternative generating sources is becoming a reality worldwide [1, 2]. Social and political considerations, which encourage the utilization of renewable sources, resulted in large scale deployment of Distributed Generation “DG” in power systems [3, 4]. This paradigm is motivated by the increasing concern over greenhouse gas emissions and the need for eliminating the unnecessary transmission and distribution costs . Thus, it is expected that DG will have a significant contribution in electrical power systems in the near future, where small generating sources located close to load centres are dispersed in the distribution networks.
The utilization of DG sources inherently offers a number of technical, environmental and economical benefits for utilities and consumers due to their location close to the customer . Modularity, power loss reduction, improving the voltage profiles, deferring the transmission and distribution investments and offsetting the pollutant emissions represent some of these advantages. Many types of these new technologies are based on power electronic converters for grid coupling unlike conventional synchronous generators . In addition, some DG units, like photovoltaic and fuel cells, are not characterized by the electromechanical energy conversion concept. The special characteristics of the DG units and their low inertia can produce many technical and operating challenges regarding the stability of power systems. Generally, a small number of quite small-size DG units, compared to the large centralized power stations, will not influence the operation of the power network and hence their impact can be neglected. However, when networks begin to contain large numbers of DG units with higher capacities, the overall dynamics of power systems are significantly impacted . Therefore, power system analysis including DG units becomes an emerging problem especially with the wide range of technologies associated with DG units and the configuration uniqueness of each distribution network . The most favourable types of DG technologies installed at consumer sites are those providing combined heat and power generation. Therefore, conventional fossil-fuel generators are candidates as DG units to be utilized in large scales in the near future, which would achieve the prospective reduction in the investment costs . Two different DG technologies, namely fuel cells and micro turbines, can be considered as promising sources either as individual units or in the hybrid configuration . Hence, the performance and characteristic of modern power systems comprising large numbers of such DG units have to be analyzed.

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