Simultaneous Identification of Multiple Control Loops in DC Microgrid Power Converters

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

Deadtime Impact on the small-signal output impedance of Single-Phase Power Electronic Converters

The deadtime is an important factor in the design of power-electronic converters in order to prevent shoot-through faults. The deadtime may also cause a voltage error and an undesired damping effect which, in turn, affect the converter stability. As most effects caused by the deadtime are highly nonlinear, conventional modeling techniques to analyze these effects cannot be straightforwardly applied. This paper proposes a novel frequency-domain approach to model the damping effect caused by the deadtime in single-phase half-bridge inverters. Hardware-in-the-loop (HIL) simulations and laboratory measurements are presented and used to demonstrate the effectiveness of the proposed method.acceptedVersionPeer reviewe

PRBS-based loop gain identification and output impedance shaping in DC microgrid power converters

Due to potential dynamic interactions among dc microgrid power converters, the performance of some of their control loops can vary from the designed behavior. Thus, online monitoring of different control loops within a dc microgrid power converter is highly desirable. This paper proposes the simultaneous identification of several control loops within dc microgrid power converters, by injecting orthogonal pseudo-random binary sequences (PRBSs), and measuring all the loop gains in one measurement cycle. The identification results can be used for different purposes such as controller autotuning, impedance shaping, etc. Herein, an example of output impedance estimation and shaping based on locally-measured loop gains is presented. The proposed identification technique and its application in output impedance shaping are validated on an experimental dc microgrid prototype, composed of three droop-controlled power converters

Shape and volume of craniofacial cavities in intentional skull deformations

Intentional cranial deformations (ICD) have been observed worldwide but are especially prevalent in preColombian cultures. The purpose of this study was to assess the consequences of ICD on three cranial cavities (intracranial cavity, orbits, and maxillary sinuses) and on cranial vault thickness, in order to screen for morphological changes due to the external constraints exerted by the deformation device. We acquired CT-scans for 39 deformed and 19 control skulls. We studied the thickness of the skull vault using qualitative and quantitative methods. We computed the volumes of the orbits, of the maxillary sinuses, and of the intracranial cavity using haptic-aided semi-automatic segmentation. We finally defined 3D distances and angles within orbits and maxillary sinuses based on 27 anatomical landmarks and measured these features on the 58 skulls. Our results show specific bone thickness patterns in some types of ICD, with localized thinning in regions subjected to increased pressure and thickening in other regions. Our findings confirm that volumes of the cranial cavities are not affected by ICDs but that the shapes of the orbits and of the maxillary sinuses are modified in circumferential deformations. We conclude that ICDs can modify the shape of the cranial cavities and the thickness of their walls but conserve their volumes. These results provide new insights into the morphological effects associated with ICDs and call for similar investigations in subjects with deformational plagiocephalies and craniosynostoses. Am J Phys Anthropol 151:110-119, 2013. © 2013 Wiley Periodicals, Inc