Abstract
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 units. This CC flow becomes out of control when the 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 units. In this paper, the model for CC flow is derived by the switching dynamics study of the units. It is found that the selection of design parameters plays an important role in the amount of CC flow. Detailed 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.
Highlights
The power quality, at all time, is a matter of concern where a number of nonlinear, harmonics producing, and sophisticated loads are connected in an electrical distribution network
In the case of a 3-phase system, shown in Figure 1(b), this circulating current flow exists as a zerosequence harmonics in the zero-sequence current flow when a circulating loop is created within the APFsh units and it is termed zero-sequence circulating current (ZSCC) flow
ZSCC flow is the same even though for case D, APFsh units are compensating higher current than that of C. These results indicate that the ZSCC flow does not depend on the amount of compensating current
Summary
The power quality, at all time, is a matter of concern where a number of nonlinear, harmonics producing, and sophisticated loads are connected in an electrical distribution network. A detailed technical review on parallel operation of APFsh for current and voltage harmonic compensation in a distributed generation (DG) network has been done in [1, 2] where the pros and cons of the different control methods have been discussed. For these cases, there is no physical/electrical link between the APFsh units. An attempt has been made here to discuss the issues related to hysteresis control
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