MULTI-SITE MANAGEMENT AND CONTROL OF DISPERSED MICRO-COGENERATION UNITS BASED ON FUEL CELLS

摘要

The increasing environmental concerns about energy activities move power systems towards a newscenario, where dispersed generation and conventional one coexist: the former close to theconsumption, possibly in microgrids, the latter in bulk installations far from the consumption.Future systems will be characterized by better performing grids, able to compensate forgeographical and temporal fluctuation of generation and loads by interconnecting local power systemsand wheeling large generation. Load side too will contribute to the change, thanks to emergingpossibilities offered to consumers (next prosumers) to participate into the electricity markets with anincreased flexibility of their demand.In the new scenario, power systems are faced with many challenges, in terms of both technical andnon-technical issues. At the same time, new business opportunities will arise, together with improvedenergy efficiency and better usage of primary sources. Investments in new local generating facilitiesembedded in microgrids may offer good chances of profitable economic returns as well as a moreenvironment-friendly energy usage. In this scope, small and micro cogeneration systems based on fuelcells may be convenient.Fuel cells are electrochemical devices that convert chemical energy into electricity and heat,through reactions between a fuel and an oxidant triggered in the presence of an electrolyte. Fuel cellsystems are available to meet the requirements of applications ranging from portable electronics topower plants. In addition to the fuel cell stack itself, a fuel cell system includes a fuel processor andsubsystems to manage air, water, heat and electricity. The overall system is efficient at full and partload,widely scalable, environmentally friendly, and potentially competitive with conventionaltechnologies.Recently, in a RTD project at our University a micro-cogeneration unit based on fuel cells has beenstudied, developed and prototyped for dispersed applications, where the fuel is obtained by reformingnatural gas. The size is such that it may be used in residential units and small commercial installationsto supply both heat and electricity. If electrical distribution supply is available, electric surplus/deficitof energy is sold/bought; otherwise, as during network outages, micro-cogeneration system can workin islanded mode, with the duty of satisfying its own loads. Multiple micro-cogeneration units can beconnected on the electrical side to work together (assumed it is allowed by local grid code), thusgaining in flexibility of operation; in this case a central control is needed to manage the couplings andthe opportunities of the resulting multi-site system.The paper illustrates the control system functions and actions needed to guarantee the correct andeconomic operation of a multi-site micro-cogeneration installation based on fuel-cells. Both cases ofsynchronous and islanded operation are discussed. A mathematical model of the optimal operation insynchronous mode is presented. The results obtained on the test system show the characteristics of theproposed solution.