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Capacity enhancement and operational flexibility are two of the important limitations of the centralized shunt APF unit. These limitations can be conquered by the operation of multiple APF units in parallel and connected back to back by a common DC link capacitor. In that case, a circulating current (CC) flows within the APF units. This CC flow becomes out of control when the APF units operate in hysteresis based current controlled mode. One of the difficulties of this CC flow control or reduction is the variable switching frequency of the APF units. In this paper the model for CC flow is derived by the switching dynamics study of the APF units. It is found that the selection of design parameters plays an important role in the amount of CC flow. Details simulation, analysis, and real time performance show how the selection of design parameters affects the CC flow and the reduction of CC flow can also be achieved at an acceptable level by the proper selection of design parameters.
Khadem, S., Basu, M. & Conlon, M. (2013). Selection of Design Parameters to Reduce the Zero-Sequence Circulating Current Flow in Parallel Operation of DC Linked Multiple Shunt APF Units. Advances in Power Electronics, vol. 2013, pp.1-13. http://dx.doi.org/10.1155/2013/381581