A Novel Multicell DC-AC Converter for Applications in Renewable Energy Systems

Abstract-This paper presents a novel dc-ac converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage. The proposed converter is realized using an isolated multicell topology where the total ac output of the system is formed by series connection of several full-bridge converter stages. The dc links of the full bridges are supplied by individual dc-dc isolation stages which are arranged in parallel concerning the dc input of the total system. Therefore, all switching cells of the proposed converter can be equipped with modern low-voltage high-current power MOSFETs, which results in an improved efficiency as compared to conventional isolated dc-ac converters. Furthermore, the cells are operated in an interleaved pulsewidth-modulation mode which, in connection with the low voltage level of each cell, significantly reduces the filtering effort on the ac output of the overall system. The paper describes the operating principle, analyzes the fundamental relationships which are relevant for component selection, and presents a specific circuit design. Finally, measurements taken from a 2-kW laboratory model are presented

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Modeling and Control of a Modular Battery Management System for Lithium-ion Battery Packs

High voltage (HV) traction battery packs in electric-drive vehicles (HEV, PHEV, BEV) consist of a large number of battery cells connected in series. As individual cells exhibit mismatches in characteristics such as capacity, inner resistance, and run-time state-of-charge (SOC), cell balancing must be incorporated into the battery management system (BMS). Conventional passive cell balancing does not fully address the mismatch issues, which leads to shorter battery lifetime, and the need to over-size the battery pack. To overcome the problems associated with the conventional architecture, a modular battery management system incorporating both active cell balancing and high voltage (HV) to low-voltage (LV) dc-dc conversion has been developed. The HV-to-LV converter is a series-input, parallel-output dc-dc system with inputs connected across the battery cells or cell modules, while paralleled outputs supply loads on the LV bus. This thesis is focused on modeling, control and design of the modular battery management system. Several critical issues are addressed: (1) stability of the converter system with distributed control in energy storage application is analyzed and simulated; (2) the steady-state model of the dual-active-bridge (DAB) isolated converter with phase-shift modulation is refined and applied to the modular converter system with cell balancing; (3) practical methods for estimation of the lithium-ion battery state-of-charge (SOC) and state-of-health (SOH) are developed in forms suitable for implementation on low-cost microcontrollers. Finally, a modular hybrid balancing system with module-level active balancing and cell-level passive balancing is developed and experimentally validated. The techniques developed in this thesis can be applied to designs of large automotive battery packs with improved performance, reduced size, reduced cost, and longer lifetime