Online Controller Tuning for DC Microgrid Power Converters With the Ability to Track Maximum Allowable Bandwidth

TLDR: In this paper , an external control loop is added to the autotuning unit to adjust the reference crossover frequency until the phase margin specification is fulfilled, which is capable of tracking the highest bandwidth at which the reference phase margin is achievable.

Abstract: Possible dynamic interactions among multiple dc microgrid power converters that are connected to a common dc bus can lead to performance degradation or even stability issues in some control loops. Thus, in order to maintain a desired dynamic behavior when operating conditions or system parameters are changing, an interesting approach is to adopt autotuning for the controller parameters. In general, existing autotuning methods are based on the evaluation of the stability specifications (e.g., the crossover frequency and the phase margin) and the adaptation of the controller to ensure the specified dynamic properties. However, the desired bandwidth and phase margin may not be achievable due to parameter changes, unexpected additional delays, or unmodeled dynamics in the feedback loop. This article addresses the infeasibility issue by adding an external control loop on top of the autotuning unit. This external loop adjusts the reference crossover frequency until the phase margin specification is fulfilled. As a result, the proposed scheme is capable of tracking the highest bandwidth at which the reference phase margin is achievable, i.e., the maximum allowable bandwidth. The proposed method is applied to a dc microgrid prototype, and the simulation and experimental results are discussed.