A 6.78MHz Adaptive-ZVS Class-D PA with Dynamic Dead-Time for Wireless Power Transfer system

Department of Electrical EngineeringIn this thesis, a class-D power amplifier (PA) with adaptive zero-voltage switching (A-ZVS) technique for Low power 6.78 MHz resonant wireless power transfer (R-WPT) system is proposed. In R-WPT operation, the loading impedance of a PA can be varied by the process tolerance of the LC resonant components and WPT environments, such as the resonant topology, coupling coefficient and loading condition of the receiver. The proposed A-ZVS feedback loop of PA calibrates the equivalent resonant capacitance using PWM-controlled switched capacitor in real-time to achieve ZVS by adjusting the loading impedance to be slightly inductive. Furthermore, the proposed PA adjust the dead-time according to variation of WPT environments. The proposed PA was fully integrated except for one switched capacitor used as the tuning element and fabricated in a TSMC 0.18um BCD process. The measurement results demonstrated robust ZVS operation with a peak system efficiency of 52.7% and an enhanced maximum transmitting power of 107%.ope

Modeling and Control of a 7-Level Switched Capacitor Rectifier for Wireless Power Transfer Systems

Wireless power continues to increase in popularity for consumer device charging. Rectifier characteristics like efficiency, compactness, impedance tunability, and harmonic content make the multi-level switched capacitor rectifier (MSC) an exceptional candidate for modern WPT systems. The MSC shares the voltage conversion characteristics of a post-rectification buck-boost topology, reduces waveform distortion via its multi-level modulation scheme, demonstrates tank tunability via the phase control inherent to actively switched rectifiers, and accomplishes all this without a bulky filter inductor. In this work, the MSC WPT system operation is explained, and a loss model is constructed. A prototype system is used to validate the models, showing exceptional agreement with the predicted efficiencies. The modeled MSC efficiencies are between 96.1% and 98.0% over the experimental power range up to 20.0 W. Two significant control loops are required for the MSC to be implemented in a real system. First, the output power is regulated using the modulation of the rectifier\u27s input voltage. Second, the switching frequency of the rectifier must exactly match the WPT carrier frequency set by the inverter on the primary side. Here, a small signal discrete time model is used to construct four transfer functions relating to the output voltage. Then, four novel time-to-time transfer functions are built on top of the discrete time model to inform the frequency synchronization feedback loop. Both loops are tested and validated in isolation. Finally, the dual-loop control problem is defined, closed form equations that include loop interactions are derived, and stable wide-range dual-loop operation is demonstrated experimentally

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology