Reduction of circulating current flow in parallel operation of APF based on hysteresis current control

Capacity enhancement and operation flexibility are two of the important limitations of the centralized Shunt Active Power Filter (APF_sh) unit. This can be overcome by multiple and parallel APF_sh units (in distributed mode) with a common DC link. In that case, a circulating current (CC) can flow. In the case of a hysteresis current controller based multiple APF_sh units in load sharing mode, this CC control is not yet achieved. One of the difficulties of this CC flow control or reduction is the variable switching frequency of the APF_sh units. In this paper, the model for CC flow is derived by the switching dynamics study of the APF_sh units. Detailed simulation and real time study show that the reduction of CC flow can be achieved at an acceptable level by proper selection of design parameters.