Control of dynamic capacitor

Industrial plants are faced with stringent requirements by the utility to maintain near unity power factor. These plants have traditionally utilized switched capacitor banks as a cost-effective means for power factor correction. However, if there is a significant level of harmonics present in the current that is disturbing neighboring loads, then a separate unit for harmonic filtering is required as well. By the time a realistic system is configured, significant cost and complexity is encountered. In a previous paper, the concept of a dynamic capacitor or D-CAP was introduced as a means by which to achieve dynamic VAR injection as well as active harmonic filtering in one single integrated unit. The topology consists of taking an existing asset like a PFC capacitor, adding couple AC switches and small LC components per phase and thereby realize an asset with augmented functionalities. Although the power stage is simple, the control becomes very complex. This paper discusses the intricacies of controlling such an architecture and provides keen insights into how one would go about designing a controller.