On-Line Controller Tuning for DC Microgrid Power Converters with the Ability to Track Maximum Allowable Bandwidth

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 auto-tuning for the controller parameters. In general, the existing auto-tuning 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 un-modelled dynamics in the feedback loop. This paper addresses the infeasibility issue by adding an external control loop on top of the auto-tuning 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.