Abusaleh M. Imtiaz

“Time Shared Flyback Converter” Based Regenerative Cell Balancing Technique for Series Connected Li-Ion Battery Strings

A cell voltage equalizer circuit for future plug-in hybrid electric vehicles (PHEV) or renewable energy storage is proposed in this paper. This topology has fewer passive components compared to the conventional topologies found in the literature, and therefore, it could reduce implementation complexity. This circuit is based on a time shared flyback converter, and any number of series connected cells in a string could be used without any apparent issues ensuring good modular architecture. Each cell in a module shares a single converter during its allocated time slot allocated by a low-power microcontroller. In addition, dynamic allocation of time slots is possible to achieve a faster cell balancing, and the circuit dynamically distributes depleted charge among the cells in a regenerative fashion. The operating principles and design procedures of the proposed topology have been presented in the paper. The prototype of a four-cell lithium-ion battery balancer circuit with the proposed topology has been constructed, and the test results have been included.

A low-cost time shared cell balancing technique for future lithium-ion battery storage system featuring regenerative energy distribution

A new cell voltage equalizer topology for future plug-in hybrid electric vehicles (PHEV) or renewable energy storage has been proposed in this paper. This topology has fewer components compared to the conventional topologies found in the literatures, and therefore, it could reduce cost and fabrication complexity. This new circuit is based on a time shared fly-back converter, and any number of series connected cells could be used in a string without any apparent issues. Each cell in a string shares this converter during its allocated time slot provided by the microcontroller. In addition, dynamic allocations of the time slots are possible to achieve faster cell balancing, and the circuit dynamically distributes depleted charge among cells in a regenerative fashion — ensuring a very high efficiency. The prototype of a four-cell lithium-ion battery balancer circuit was designed and implemented. Simulation and experimental results are presented to verify the operation of the new topology.

Optimization of Subcell Interconnection for Multijunction Solar Cells Using Switching Power Converters

A multijunction solar cell can extract higher solar energy compared to a single junction cell by splitting the solar spectrum. Although extensive research on solar cell efficiency enhancement is in place, limited research materials are available to identify the optimum interconnection of multijunction solar subcells using power electronic circuits. Multijunction solar cells could be grouped into two main categories: vertical multijunction (VMJ) solar cells and lateral multijunction (LMJ) solar cells. In this paper, a detailed study to identify the optimum interconnection method for various multijunction solar cells has been conducted. The authors believe that the conducted research in this area is very limited, and an effective power electronic circuit could substantially improve the efficiency and utilization of a photovoltaic (PV) power system constructed from multijunction solar cells. A multiple input dc-to-dc boost converter has been used to demonstrate the advantage of the proposed interconnection technique. In order to ensure maximum power point (MPP) operation, a particle swarm optimization (PSO) algorithm has been applied needing only one MPP control for multiple solar modules resulting in cost and complexity reduction. The PSO algorithm has the potential to track the global maxima of the system even under complex illumination situations. A complete functional system with the implementation of the proposed algorithm has been presented in this paper with relevant experimental results.

Steady state analytical model of a “time shared li-ion cell blancing circuit” for Plug-in hybrid vehicles and utility energy storage

A steady-state analytical model of the recently proposed “Time shared li-ion cell balancing circuit” is presented in this paper. This paper provides the necessary analytical proof of the cell balancer circuit to be used in future Plug-in Hybrid vehicles (PHEV) or utility energy storage applications. The model presented here bridges the simulation and experimental results obtained previously. In addition, the prototype of a four-cell lithium-ion battery balancer circuit with reduced component count has been constructed, and the test results have been verified with the analytical model. Although the “proof of concept” circuit was built to balance only four cells, the analytical model suggests that any number of series connected cells could be used in a string and balanced. Moreover, the analytical model can be extended to characterize the circuit parameters for any number of cells without any apparent issues. This model was also being verified using the simulation and experime ntal results with only 2% error margin.

Light-Generated Effects on Power Switches Used in a Planar PV Power System With Monolithically Embedded Power Converters

The reliability, efficiency, and controllability of photovoltaic (PV) power systems can be increased by embedding the components of a typical power converter on the same Si substrate of a PV cell. In order to achieve more insight into the macro or surface electronics, a novel fabrication process along with experimental results have been presented in this paper, demonstrating the integration of PV cells and major components needed to build a power converter on the same substrate/wafer. Because of the cell level power conversion, PV panels constructed from these cells are likely to be immune to partial shading and hot-spot effects. Several critical applications such as a portable power station in a battlefield or scientific expedition can greatly benefit from an “all in one” PV system featuring several key attributes such as modularity, high reliability, and quick setup time. In this paper, the effect of light exposure on converter switches embedded on the PV substrate has been analyzed to understand the converter behavior at various illumination conditions. Simulation and experimental results have been provided to support the concept presented in this paper. To the knowledge of the authors, surface or macro electronics have not been implemented to PV power systems yet, and therefore, the effect of light on the surface switches needs to be studied greater depth.

AC solar cells: An embedded “all in one” PV power system

Power converters constructed from discrete components are difficult to mass produce, and the installation involves a significant labor cost to have the proper interconnection among the panel, inverter and the grid. These facts indicate that the present PV technology may not be able to address the challenges involved in reaching the DOE target of

Film bulk acoustic resonator (FBAR) based power converters: A new trend featuring EMI reduction and high power density

1/W. Therefore, a paradigm shift in the design of the entire PV power system is needed to reach this goal. In order to increase the converter reliability and watts/

Contour-Mode Ring-Shaped AlN Microresonator on Si and Feasibility of Its Application in Series-Resonant Converter

, the active and passive elements of a power converter (especially capacitors and active switches such as MOSFETs, JFETs or IGBTs) could be embedded on the same substrate material used for fabricating the p-n junctions in the photovoltaic panel. To the knowledge of the author, there is no prior work in cell level power conversion, and therefore, this project idea could be considered as an “Out of the box” kind. A novel fabrication process is proposed in this paper demonstrating the integration of PV cells and two major components needed to build a power converter. Because of the cell level power conversion, PV panels constructed from these cells are likely to be immune to partial shading and hot-spot effects. The end goal of this research is to produce 120V/240V ac output directly from the panel. An extremely accurate device simulator (*Silvaco Athena/Atlas) was used to generate reasonably accurate characteristics of the proposed PV system.

Interconnection and optimization issues of multijunction solar cells — A new mitigation approach using switching power converters

In this paper, a series resonant converter and a LED driver have been implemented by using a film bulk acoustic resonators (FBAR) in place of the inductor. This MEMS device can offer very high inductance density with excellent Q factor and can be conveniently fabricated in a CMOS compatible process. FBARs are smaller in size and weight compared to an inductor offering the same inductance per volume and quality factor, and therefore,, FBAR based power converters can offer higher power density. Simulation and experimental results with zero voltage switching (ZVS) and zero current switching (ZCS) have been provided to validate the use of FBARs in power converter circuits. The EMI of a discrete inductor based converter has been compared to that of an FBAR based converter, and the FBAR based converter showed better EMI performance. To the knowledge of the authors, the use of FBAR in power converter circuits has not been reported in the literature yet.

Contour mode piezoelectric ring micro-resonators on Si for series resonant converters

Microelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. The main intention of this paper is to present a ring-shaped aluminum nitride (AlN) piezoelectric microresonator that can be used as an energy-transferring device to replace inductors/capacitors in low-power resonant converters for biomedical applications. Finite-element simulation results have been provided, showing the mode of vibration at resonant frequency. The zero-voltage switching (ZVS) condition for a series-resonant converter incorporating the proposed MEMS resonator has been presented analytically and verified through experiment. This ZVS condition can be found in terms of the equivalent circuit parameters of the resonator. To the knowledge of the authors, ZVS analysis based on the equivalent electrical circuit model of the thin piezoelectric film resonators has not yet been reported in the literature. A CMOS-compatible fabrication process has been proposed and implemented. In addition, the fabricated devices have been characterized and experimental results are included in this paper. The first contour-mode AlN MEMS resonator with moderately low resonant frequency and motional resistance is reported in this paper with measured resonant frequency and motional resistance of 87.28 MHz and 36.728 Ω, respectively.