Abusaleh M. Imtiaz

Bio: Abusaleh M. Imtiaz is an academic researcher from University of Utah. The author has contributed to research in topics: Maximum power point tracking & Photovoltaic system. The author has an hindex of 8, co-authored 17 publications receiving 323 citations.

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

Abstract: 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

Abstract: 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

Abstract: 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.

All-in-One Photovoltaic Power System: Features and Challenges Involved in Cell-Level Power Conversion in ac Solar Cells

Abstract: Power converters constructed from discrete components are difficult to mass produce, and their installation requires a significant labor cost for the proper interconnection among the panel, inverter, and grid. Several critical applications, such as portable power stations (for use on a battlefield or scientific expedition), will require key attributes from a photovoltaic (PV)-based power system, such as modularity, high reliability, and quick set-up time. Therefore, a paradigm shift in the design of the entire PV power system is needed to mitigate this need. To increase the converter reliability and portability, the active and passive elements of a power converter [especially capacitors and active switches such as metal-oxide-semiconductor field-effect transistors (MOSFETs), junction gate field-effect transistors (JFETs), or insulated-gate bipolar transistors (IGBTs)] could be embedded on the same substrate material used for fabricating the p-n junctions in the PV panel. To the authors' knowledge, there is no prior work in cell-level power conversion with embedded converters, and therefore this project idea could be considered "outside the box." A novel fabrication process along with experimental results are presented in this article, 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. In addition, the effect of light exposure on converter switches has been analyzed to understand the converter behavior at various illumination levels. Simulation and experimental results have been provided to support this analysis. In addition to process-related challenges and issues, the justification of this integration is explained by achieving higher reliability, portability and complete modular construction for PV-based energy harvesting units.

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

Abstract: 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.

A 20 mV Input Boost Converter With Efficient Digital Control for Thermoelectric Energy Harvesting

Abstract: This paper presents a low power boost converter for thermoelectric energy harvesting that demonstrates an efficiency that is 15% higher than the state-of-the-art for voltage conversion ratios above 20. This is achieved by utilizing a technique allowing synchronous rectification in the discontinuous conduction mode. A low-power method for input voltage monitoring is presented. The low input voltage requirements allow operation from a thermoelectric generator powered by body heat. The converter, fabricated in a 0.13 μm CMOS process, operates from input voltages ranging from 20 mV to 250 mV while supplying a regulated 1 V output. The converter consumes 1.6 (1.1) μW of quiescent power, delivers up to 25 (175) μW of output power, and is 46 (75)% efficient for a 20 mV and 100 mV input, respectively.

Passive and active battery balancing comparison based on MATLAB simulation

Abstract: Battery systems are affected by many factors, the most important one is the cells unbalancing. Without the balancing system, the individual cell voltages will differ over time, battery pack capacity will decrease quickly. That will result in the fail of the total battery system. Thus cell balancing acts an important role on the battery life preserving. Different cell balancing methodologies have been proposed for battery pack. This paper presents a review and comparisons between the different proposed balancing topologies for battery string based on MATLAB/Simulink® simulation. The comparison carried out according to circuit design, balancing simulation, practical implementations, application, balancing speed, complexity, cost, size, balancing system efficiency, voltage/current stress … etc.

A Chain Structure of Switched Capacitor for Improved Cell Balancing Speed of Lithium-Ion Batteries

Abstract: Among various active cell balancing circuits, a switched capacitor circuit is promising because it can be implemented with low cost and small size. However, when the switched capacitor is applied in the lithium-ion battery, cell balancing speed is generally slow when the number of batteries is high. Therefore, this paper proposes the chain structure of the switched capacitor to increase balancing speed, particularly among outer cells. In this paper, the cell balancing principle of the conventional switched capacitor is explained, and the reason why slow cell balancing of the switched capacitor is shown in the lithium-ion battery is analyzed. To improve cell balancing speed, two circuits with chain structure are proposed. The balancing performance of the proposed circuits is confirmed by computer simulation, and a comparison between conventional and proposed circuits is presented. The theoretical analysis on the cell balancing speed of conventional structures and the proposed chain structure is also shown in this paper. Experimental tests were carried out to verify the validity of the proposed structures, and the experimental results show an improved balancing performance of the proposed circuit.

Energy Sharing Control Scheme for State-of-Charge Balancing of Distributed Battery Energy Storage System

Abstract: This paper presents an energy sharing state-of-charge (SOC) balancing control scheme based on a distributed battery energy storage system architecture where the cell balancing system and the dc bus voltage regulation system are combined into a single system. The battery cells are decoupled from one another by connecting each cell with a small lower power dc–dc power converter. The small power converters are utilized to achieve both SOC balancing between the battery cells and dc bus voltage regulation at the same time. The battery cells' SOC imbalance issue is addressed from the root by using the energy sharing concept to automatically adjust the discharge/charge rate of each cell while maintaining a regulated dc bus voltage. Consequently, there is no need to transfer the excess energy between the cells for SOC balancing. The theoretical basis and experimental prototype results are provided to illustrate and validate the proposed energy sharing controller.