This paper discusses the effect of Constant Power Loads (CPLs) on the stability of a Smart Transformer (ST). The main characteristic of a CPL is that its current decreases when its voltage increases and vice versa. Therefore, in small signal analysis a CPL behaves as a negative impedance, and as a consequence it can impact the system stability. The aim of this work is to establish how it is possible to stabilize the system by acting on the filter parameters and the control strategy. A distributed power generating systems supplied by a ST has been considered as case study. The analysis and the simulation results show that it is not possible to stabilize the system by using standard controllers without an appropriate selection of the output filter components.
This paper discusses models and methods for the analysis of PV systems with Distributed Maximum Power Point Tracking (DMPPT). An Energy Productivity Analysis Algorithm (EPAA) is discussed, integrating models and algorithms from component level to system level, allowing the analysis of PV systems operating in partial shading and electrical mismatched conditions. The EPAA provides realistic assessment of the energy productivity including the effects of PV panels characteristics, of shadows and of the MPPT converters. A comparative evaluation of boost-based vs buck-boost-based DMPPT solutions is presented in the paper, highlighting how the energy productivity of DMPPT PV systems is influenced by the parameters of real components.
This paper discusses an adaptive Maximum Power Point Tracking (MPPT) control involving minimum computing effort, suitable for implementation with low cost microcontrollers. The runtime multiple optimal setup of the Perturb&Observe MPPT algorithm, is achieved by exploiting the correlation existing among the MPPT efficiency and the onset of a permanent 3 level quantized oscillation around the MPP. As no operations on measured voltage, current and power are required, the adaptive MPPT control is achievable with very cheap digital devices. Experimental test results are presented in the paper, regarding a 70W LED lighting system fed by a photovoltaic source, including a energy storage device
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