Faisal H. Khan

“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 Comprehensive Review of Catastrophic Faults in PV Arrays: Types, Detection, and Mitigation Techniques

Three major catastrophic failures in photovoltaic (PV) arrays are ground faults, line-to-line faults, and arc faults. Although there have not been many such failures, recent fire events on April 5, 2009, in Bakersfield, CA, USA, and on April 16, 2011, in Mount Holly, NC, USA, suggest the need for improvements in present fault detection and mitigation techniques, as well as amendments to existing codes and standards to avoid such accidents. This review investigates the effect of faults on the operation of PV arrays and identifies limitations to existing detection and mitigation methods. A survey of state-of-the-art fault detection and mitigation technologies and commercially available products is also presented.

Start-Up and Dynamic Modeling of the Multilevel Modular Capacitor-Clamped Converter

This paper will present the analytical proof of concept of the multilevel modular capacitor-clamped converter (MMCCC). The quantitative analysis of the charge transfer mechanism among the capacitors of the MMCCC explains the start-up and steady-state voltage balancing. Once these capacitor voltages are found for different time intervals, the start-up and steady-state voltages at various nodes of the MMCCC can be obtained. This analysis provides the necessary proof that explains the stable operation of the converter when a load is connected to the low-voltage side of the circuit. In addition, the analysis also shows how the LV side of the converter is (1/N)th of the HV side excitation when the conversion ratio of the circuit is N. In addition to the analytical and simulation results, experimental results are included to support the analytical proof of concept.

Multiple Load-Source Integration in a Multilevel Modular Capacitor Clamped DC-DC Converter Featuring Fault Tolerant Capability

A multilevel modular capacitor-clamped DC-DC converter (MMCCC) will be presented in this paper with some of its advantageous features. By virtue of the modular nature of the converter, it is possible to integrate multiple loads and sources with the converter at the same time. The modular construction of the MMCCC topology provides autotransformer-like taps in the circuit, and depending on the conversion ratio of the converter, it becomes possible to connect several dc sources and loads at these taps. The modularity of the new converter is not limited to only this dc transformer (auto) like operation, but also provides redundancy and fault bypass capability in the circuit. Using the modularity feature, some redundant modules can be operated in bypass state, and during some faults, these redundant modules can be used to replace a faulty module to maintain an uninterrupted operation. Moreover, by obtaining a flexible conversion ratio, the MMCCC converter can transfer power in both directions. Thus, this MMCCC topology could be a solution to establish a power management system among multiple sources and loads having different operating voltages.

5 kW Multilevel DC-DC Converter for Hybrid Electric and Fuel Cell Automotive Applications

A 5 kW multilevel modular capacitor clamped dc-dc converter (MMCCC) for future hybrid electric vehicle and fuel cell automotive applications will be presented in this paper. The modular structure of the MMCCC topology was utilized to build this 5 kW converter with high reliability and fault bypassing capability. Moreover, the circuit has flexible conversion ratio that leads to establish bi-directional power management for automotive applications. In addition, the MMCCC exhibits better component utilization compared to the well known flying capacitor dc-dc converter. Thus, the MMCCC circuit can be made more compact and reliable compared to many other capacitor clamped dc-dc converters for high power applications.

Switching cells and their implications for power electronic circuits

This paper will introduce two basic switching cells, P-cell and N-cell, along with their implications and applications in power electronic circuits. The concept of switching cells in power electronic circuits started in the late 1970s. The basic cells presented in this paper have one switching element (transistor) and one diode. The P-cell is the mirror circuit of the N-cell and vice-versa, and this paper suggests that (1) most power electronic circuits can be analyzed and re-constructed using these basic switching cells, (2) single, dual, and 6-pack switching modules should be configured and laid-out according to the basic switching cells and not necessarily the conventional way used by industry, and (3) many benefits such as minimal parasitic inductance and dead-time elimination or minimization may come about. The present paper will describe the construction and operation of these basic switching cells, and it will also show a sequential method to reconstruct several classical dc-dc converters, a voltage source inverter (VSI), and a current source inverter (CSI) using these basic switching cells. In addition, the use of basic switching cells introduces some new topologies of dc-dc converters that originate from the buck, boost, and Ćuk converter for negative input voltages. This paper will also illustrate the experimental results of the new and existing topologies constructed from basic switching cells.

Deriving New Topologies of DC-DC Converters Featuring Basic Switching Cells

This paper will introduce the two basic switching cells, P-cell and N-cell, and their applications in different power electronic circuits. These basic cells have one switching element and one diode. The P-cell is the mirror circuit of the N-cell and vice-versa, and this paper suggests that any power electronic circuit can be analyzed and re-constructed using these basic switching cells. The present paper will describe the construction and operation of the basic switching cells, and it will also show a sequential method to construct several DC-DC converters from these basic switching cells. Moreover, considering the potential of combining these cells in multiple fashions, new kinds of power electronic circuits can be designed

Efficiency Characterization and Impedance Modeling of a Multilevel Switched-Capacitor Converter Using Pulse Dropping Switching Scheme

A pulse dropping switching technique (PDT) has been presented in this paper to accomplish variable conversion ratio (CR) in a multilevel modular capacitor-clamped dc-dc converter in the step-up conversion mode. The switching pattern is generated by comparing a triangular wave with a rectangular wave, and a proper output voltage regulation can be obtained by controlling the relative frequency and amplitude of these two waveforms. A state-space modeling technique has been applied here to estimate the variation in equivalent output resistance (EOR) for different operating conditions of the PDT. The EOR can be varied in a wide range without changing the operating frequency of the converter, and thereby the PDT enhances the degrees of freedom to accomplish voltage regulation in a two-phase switched-capacitor converter. Slow-switching limit of the converter has been derived to define the boundary of the EOR. Different challenges and limitations of the proposed modulation scheme has been discussed in detail, and the proposed analysis has been verified by comparing the analytical expressions with the simulation and experimental results for different switching frequencies, modulation indices, and number of active modules. In addition, variations in the CR, efficiency and ripple voltage for different number of active modules and switching conditions have been described in detail.

Power electronics' circuit topology - the basic switching cells

Abstract—In this paper, two basic switching cells, P-cell and Ncell, are presented to investigate the topological nature of power electronics circuits. Both cells consist of a switching device and a diode and are the basic building blocks for almost all power electronics circuits. The mirror relationship of the P-cell and Ncell will be revealed. This paper describes the two basic switching cells and shows how all dc-dc converters, voltage source inverters, current source inverters, and multilevel converters are constituted from the two basic cells. Through these two basic cells, great insights about the topology of all power electronics circuits can be obtained for the construction and decomposition of existing power electronic circuits. New power conversion circuits can now be easily derived and invented.

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.