Auto-Tuning of DC Microgrid Power Converters Based on a Constant Frequency Injection

Abstract

In a DC microgrid environment, usually, many power electronic converters, each involving multiple con-trolloops, are connected to the common DC bus. In such a scenario, the performance of some loops can be different from their designed behavior for an individual converter, due to the possible interactions. Thus, in order to maintain the desired dynamic performance of different loops, and to avoid stability issues, it is important to perform on-line tuning of the power converters regulators. This paper presents the application of a closed-loop autotuning technique to the DC microgrid power converters. The technique consists of injecting a small-signal sinusoidal perturbation, at a constant frequency, i.e., the desired crossover frequency, into a generic control loop of the digitally controlled switched-mode power supplies (SMPS). Subsequently, the signals before and after perturbation point are phase-shifted by a certain phase, i.e., half of the desired phase margin, and then subtracted, to define an error signal. Finally, the regulator parameters are tuned to make the error signal converge to zero, allowing, thus, to reach the desired phase margin and crossover frequency. In addition, this paper takes account for the situation in which, a generic loop can not achieve the desired phase margin at a given reference crossover frequency. The proposed technique requires low signal processing effort, and it is robust to noise and perturbations coming from the other converters connected to the common DC bus. So, it allows multiple converters to auto-tune their regulators, simultaneously. The experimental validation of the technique in a laboratory prototype of DC microgrid, confirms the successful achievement of the desired crossover frequency and phase margin.