Stability Oriented Design Considerations in the Control of Cascaded Converters through their Impedance Models

Various power conversion applications require the power converters to be cascaded with one another, to meet the load requirements. However, generally the trend is to cater to the control system design of individual converters and then cascade them with the other converters. Such cascaded systems can give sub optimal performance with poor stability margins. This paper tries to address this issue by investigating the interaction of the individual converters along with their control systems on the other converter, at their point of coupling. An active front end three phase rectifier cascaded with a voltage controlled buck converter is considered here to demonstrate the stability oriented control system design. Detailed impedance modeling of these converters are presented and their mutual interaction is studied for understanding the system stability. Extensive simulation results are presented to validate the analysis.