The performance of polytopic models in smart DC microgrids

Abstract

The huge progress of power electronics technology along last decades opens extraordinary new possibilities for the electric grid. Some examples of what can be achieved with the incorporation of electronic power converters in the system are the penetration of RS (renewable sources) and storage, boosting reliability and power quality, and integrating consumers as part of the system. However, there are still some challenges ahead before the massive deployment of Smart Grids.Lately, a lot of research has been carried out on converters topologies and control strategies in order to get the most out of the microgrids. Therefore, there is a need for methodologies that allow designers to foresee the behavior of these systems comprised of several different power converters governed by the proposed control strategies. In this context, this paper studies the performance of the polytopic models for the analysis of commercial power converters working in dc microgrids. This is a nonlinear modeling technique which integrates small-signal models obtained in different operation points by means of suitable weighting functions. Furthermore, the linear local models can be obtained in a blackbox fashion using suitable two-port models as can be the G-parameters models. This work particularly focuses on the analysis of different power converters using the well-known dc bus signaling control strategy. Thus the modeling of the diverse possible states in which this control technique can operate, and more important the transitions among them, are investigated. In addition, the feasibility of applying system level control techniques to the polytopic models of the converters, such as current sharing or voltage restoration, is considered.

Blackbox Large-Signal Modeling of Grid-Connected DC-AC Electronic Power Converters

“…Furthermore, nonlinear structures like the Wiener-Hammerstein approach [14] or the polytopic approach [17] have been also proposed for DC-DC converters. More recently, some new strategies have been proposed: to consider the effect of system-level controllers [19,20,27,28], to improve the performance of the model in case strong nonlinearities are present in the system [29], or the first approach towards a blackbox large-signal stability analysis [30]. A review about blackbox modeling structures for DC-DC converters can be found in [31].…”

“…As mentioned in Section 2, this methodology is based on a weighted combination of small-signal models identified around different operating points. This approach has been successfully applied in DC systems [17,19,20,31], and extended to AC EPCs in [35] at simulation level. Therefore, the present work is the first evidence of a polytopic model applied to represent an actual three-phase DC-AC EPC.…”

“…The nonlinearities are included in a static block, often using look-up tables, whereas the dynamic behavior is represented by a linear dynamic block [12][13][14][15][16]. Finally, the dynamic nonlinear models are based on a polytopic approach, where local models around different equilibrium points are integrated in a nonlinear structure [17][18][19][20][21]. The focus of these models is on the small and large signal behavior of the converters under normal operation, short-circuit fault models [22][23][24] are out of the scope of this work.…”

Black-Box Behavioral Modeling of Voltage and Frequency Response Characteristic for Islanded Microgrid

“…Even for the identification modeling of the whole microgrid, the first step is to build non-linear models of the microgrid components, and then combine them into the microgrid model which is complex in model structure. For instance, Reference [14] described the relationships between the input and output voltage current of each DG by multi-segment nonlinear functions and then combined them together to build up the microgrid model. However, as the scale of the microgrid increases, the adaptability of this method is greatly limited.…”

Switched Polytopic Controller Applied on a Positive Reconfigurable Power Electronic Converter

“…A related analysis applied to smart grid was proposed in [62]; in this paper just simulation results for a PV, battery and grid converter was considered. A non-linear behavior modeling, based on a look-up table and a polytopic structure, was reported on [63]. In such paper, the cascade and parallel configuration connected to an electronic load was modeled in terms of their G-parameters; numerical and experimental results are presented for two commercial DC-DC converters.…”