Simultaneous Identification of Multiple Control Loops in DC Microgrid Power Converters

Abstract

Power electronic converters used in a dc microgrid environment are usually equipped with several control loops. When many converters are connected to a common dc bus, the performance of some loops can be different from the behavior designed for the stand-alone converter, depending on the number, topology, and control of the interconnected converters. In order to establish the performance of each loop in real-time, it is important to continuously monitor the loop gains. This article presents the application of an online identification technique in rapid and simultaneous measurement of several control loops in dc microgrid power converters. To this end, multiple orthogonal pseudorandom binary sequences (PRBSs) are simultaneously injected into different loops of power converters. Since the frequency components excited by each PRBS are unique and different from any other, multiple PRBSs can be injected at the same time. This will allow to measure all the loop gains in only one measurement cycle. Hence, the operating condition of the system is kept unchanged during the measurement, which is an important factor to achieve accurate monitoring. The online identification method is applied to an experimental dc microgrid prototype, composed of three droop-controlled converters. After identifying different control loops, an adaptive tuning algorithm is implemented to adjust the digital compensator of each loop, in order to reach the desired dynamic performance. The reported experimental results confirm the accuracy and the applicability of this technique.