This paper examines an inductive power transfer (IPT) system with a rotary transformer as an alternative solution to slip ring systems for a contactless energy transfer to rotating equipment. A prototype system is set up, consisting of a rotating ball bearing shaft and an exemplary sensor circuit mounted on the shaft. Three possible transformer configurations are analyzed theoretically and experimentally regarding the self-inductance, the coupling factor and the losses in the litz wire. To utilize the intrinsic stray inductances of the rotary transformer, a series compensated resonant converter is implemented for the prototype system
In this paper, the operating modes of the bidirectional CLLLC resonant converter are analyzed in time domain to determine the steady-state operating point. The operating mode boundaries, mode transitions and mode distribution are discussed and the dependencies of modes on voltage transfer ratio, inductor ratio and switching frequency are illustrated. Based on the mode analysis results, normalized equations and characteristics for the resonant tank currents and voltages are presented, which support the designer selecting the optimal operating point. A prototype system is built and it is shown that the calculations predict the resonant current, voltage behavior, and output power characteristic very well
Multi-resonant converters like the CLLLC topology are known for their outstanding efficiency and high power density. Little information has however been published about the influences of secondary side diode junction capacitances on the output characteristics of the resonant converter. This paper presents a detailed analysis of these influences in the inductive working range and reviews practical design considerations of the converter. Therefore, experimental results of an inductive power transfer system, using a CLLLC resonant topology, are compared to theoretical time domain solution, showing significant effects of different semiconductor materials and devices on output power. These effects will be discussed and explained in detail by using measured key waveforms
Inductive power transfer (IPT) systems significantly depend on magnetic coupling and coil characteristics. To achieve maximum coupling in case of an air gap and misalignments, different coil shapes were investigated. Based on this research a special orthogonal coil system and arrangement was designed. The magnetic design is presented along with FEM-simulations and measurements. With its mechanical structure the presented IPT system is positioning tolerant and interoperable with a huge variaty of car models. It requires a minimum of space while maintaining high flexibility and efficiency. Corresponding illustrations and analysis are provided to clearly show the design of a bidirectional resonant converter. Measurements of the entire system at full load (3kW) are made
This paper proposes a portable 11 kW off-board charger for electric vehicles. In the ac/dc stage, a three-phase power factor correction (PFC) in Vienna topology is chosen. The loss and volume of the PFC inductance are calculated over a wide range of parameters and optimized with regard to design, winding, and core material. A three-phase LLC resonant converter operating at 1 MHz is chosen for the galvanically isolated dc/dc stage. A parametrizable loss model of the high-frequency transformer and the resonance inductor is developed to minimize volume, weight, and losses. With the help of an automated algorithm using these loss models, the inductive components are optimized in terms of winding specification, magnetic material, and core geometry, verified by finite element analysis and measurements. For the ac/dc stage, 900 V SiC devices are adopted, and 1200 V SiC devices are used in the primary and secondary sides of the dc/dc stage. A variable dc-link voltage is utilized to adjust the charging profile and to operate the LLC resonant converter at the most efficient point near the series resonance frequency. A mechatronically integrated portable air-cooled off-board charger prototype with 11 kW, three-phase 400 VAC input, and 620–850 VDC output is realized and tested. The prototype demonstrates a power density of 2.3 kW/liter (37.7 W/in³), a peak efficiency of 96%, and 95.8% efficiency over the defined battery voltage range.
In this work, a resonant push-pull dc-dc converter suitable for switching frequencies in the MHz-range is investigated. Despite a simple design procedure with no need of multiresonant tuning, the converter topology is capable of providing a constant output current over a wide output voltage range in unregulated operation. Based on an analytical solution of steady-state operation, normalized dependencies of converter behavior are determined and used to formulate generalized design considerations. In order to verify the theoretical analysis, the design procedure of a 300 W prototype operating at a switching frequency of 6.78 MHz is described considering the impact of circuit parasitics on converter operation. The prototype provides a stable operation within the full output voltage range of 0-150 V and reaches a peak efficiency of 93% at the nominal output voltage. A rapid transient response of the converter is demonstrated by applying a closed-loop on/off-control to the prototype.
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