Abstract
While the integration of base-load fuel cells into the built environment is expected to provide numerous benefits to the user, the steady-state and dynamic behavior of these stationary fuel cell systems can produce an undesirable impact on the grid distribution circuit at the point of connection. In the present paper, a load-following active power filter (LFAPF) is proposed to mitigate the grid impact of such systems and instead improve overall local power quality. To evaluate the strategy, the LFAPF is integrated into a SOFC system inverter with one-cycle control (OCC) to provide the fundamental benefits of a traditional active power filter (APF) while also damping out short-term line current transients. The LFAPF benefit is illustrated through simulation of an SOFC interconnected with the utility electric distribution system and a building electricity demand that is modeled as a dynamic non-linear load. Three installation cases are examined: (1) a load-following SOFC, (2) a base-loaded SOFC, and (3) an offline SOFC. Without LFAPF, the load-following SOFC causes load transients due to the finite SOFC response time, and the base-loaded SOFC case has transients that appear more severe because they represent a larger overall percentage of the grid-provided load. The integration of an LFAPF improves the steady-state behavior over the base case and mitigates voltage sags and step changes. Thus integrating an LFAPF can, by providing useful services to both the utility and the end-user, facilitate the integration of an SOFC into the distribution system.
Highlights
The commercial deployment of large fuel cells (>200 kW) is accelerating to provide base-load power for a variety of applications including hotels, universities, food processing and industrial facilities, and waste water treatment plants
The voltage for the solid oxide fuel cell (SOFC)-only case does increase as a result of this transient due to the power quality of the load, but as the load-following active power filter (LFAPF) compensates reactive power and harmonics, the SOFC/LFAPF voltage is uniformly constant throughout the evening transient
A design for an one-cycle control (OCC) load-following active power filter is described and the functionality is demonstrated through implementation in an SOFC system interconnection model
Summary
The commercial deployment of large fuel cells (>200 kW) is accelerating to provide base-load power for a variety of applications including hotels, universities, food processing and industrial facilities, and waste water treatment plants. While much research and development has been occurring on alternative energy technologies, a key aspect of the successful widespread deployment of distributed generation (DG) is a robust grid interconnection This grid interconnection should ideally be designed to maximize overall DG benefits, increase power reliability for the customer, and improve grid functionality for the utility. A voltage sag can accompany a sudden surge of inrush current, which may disrupt functionality or cause failure in delicate equipment on a neighboring circuit This voltage sag can be greatly reduced or eliminated by supplying this current at the site of the load instead, since the voltage drop occurs locally and cannot be addressed by the grid due to the line impedance of the electric power distribution system. A sensitivity analysis in Section 5 illustrates the dependence of the LFAPF overall effectiveness on the design parameters, and Section 6 presents the conclusions
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