Modular converter system for low-cost off-grid energy storage using second life Li-ion batteries

Lithium ion batteries are promising for small off- grid energy storage applications in developing countries because of their high energy density and long life. However, costs are prohibitive. Instead, we consider 'used' Li-ion batteries for this application, finding experimentally that many discarded laptop cells, for example, still have good capacity and cycle life. In order to make safe and optimal use of such cells, we present a modular power management system using a separate power converter for every cell. This novel approach allows individual batteries to be used to their full capacity. The power converters operate in voltage droop control mode to provide easy charge balancing and implement a battery management system to estimate the capacity of each cell, as we demonstrate experimentally.Comment: Presented at IEEE GHTC Oct 10-14, 2014, Silicon Valle

Modeling and simulation enabled UAV electrical power system design

With the diversity of mission capability and the associated requirement for more advanced technologies, designing modern unmanned aerial vehicle (UAV) systems is an especially challenging task. In particular, the increasing reliance on the electrical power system for delivering key aircraft functions, both electrical and mechanical, requires that a systems-approach be employed in their development. A key factor in this process is the use of modeling and simulation to inform upon critical design choices made. However, effective systems-level simulation of complex UAV power systems presents many challenges, which must be addressed to maximize the value of such methods. This paper presents the initial stages of a power system design process for a medium altitude long endurance (MALE) UAV focusing particularly on the development of three full candidate architecture models and associated technologies. The unique challenges faced in developing such a suite of models and their ultimate role in the design process is explored, with case studies presented to reinforce key points. The role of the developed models in supporting the design process is then discussed

Modeling a Grid-Connected PV/Battery Microgrid System with MPPT Controller

This paper focuses on performance analyzing and dynamic modeling of the current grid-tied fixed array 6.84kW solar photovoltaic system located at Florida Atlantic University (FAU). A battery energy storage system is designed and applied to improve the systems stability and reliability. An overview of the entire system and its PV module are presented. In sequel, the corresponding I-V and P-V curves are obtained using MATLAB-Simulink package. Actual data was collected and utilized for the modeling and simulation of the system. In addition, a grid- connected PV/Battery system with Maximum Power Point Tracking (MPPT) controller is modeled to analyze the system performance that has been evaluated under two different test conditions: (1) PV power production is higher than the load demand (2) PV generated power is less than required load. A battery system has also been sized to provide smoothing services to this array. The simulation results show the effective of the proposed method. This system can be implemented in developing countries with similar weather conditions to Florida.Comment: 6 pages, 14 figures, PVSC 201

Electrochemical energy storage device for securing future renewable energy

An electrochemical cell comprising molten sodium and molten sulphur as the anode and cathode, respectively, with beta alumina electrolyte has never found extensive use. An approach to develop large energy storage device based on aqueous sodium electrolyte at low temperature is described. An electrochemical cell with low cost, safe and utilizing sustainable manganese dioxide (MnO2) cathode coupled with zinc (Zn) anode in aqueous sodium hydroxide (NaOH) electrolyte is reported. The cyclic voltammetric (CV) profiles are found to be quite different in terms of peak position and current response depending on concentration of NaOH electrolyte. Among the concentrations of NaOH studied (2, 5, 7 and 10 M) the best performance was found to be between 5 and 7 M. The CV curves exhibits a pair of reversible redox peaks (within 1e- region) corresponding to sodium ion insertion and extraction but while extending the potential window to second electron reduction resulted in irreversible nature. This is explained to the formation of inhomogeneous reduction reaction due to slow electron diffusion. CV experiments at various scan rates revealed that the MnO2 material may not be suitable enough for higher scan rates indicating a sluggish kinetics occurring in the bulk material. Our study highlights the MnO2 cathode in NaOH electrolyte features a flat discharge voltage of 1.3 V vs. Zn with discharge capacity of 220 mAh/g