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This article presents a 6.78-MHz wireless power transfer (WPT) system, which is configured to automatically cancel the reactance in primary and secondary. In the WPT system, the detuning caused by the parameter variation, the implementation of the frequency control, and components tolerance will decrease a lot the system performance, especially in very low coupling (k = 0.06) and low power applications. The delivered power is sensitive to the reactance under low coupling and high-frequency conditions, accordingly, a novel self-adaptive WPT system to automatically retune the resonance is proposed. The proposed concept uses a synchronous series compensator (SSC) instead of a capacitor in series with the secondary to tune it, which can automatically cancel the reactance caused by the inductor, nonresistive load or frequency variation, hence increases the system performance in terms of delivered power and efficiency. A prototype has been built and tested experimentally to validate the feasibility of the proposed concept. A constant power of 1.8 W can be transmitted with 50% overall efficiency at a coil separation distance of 1.5 cm between the printed-circuit-board transmitter (3 × 3 cm2) and receiver (1 × 2 cm2) under wide detuning conditions, being 0.95 the ratio between distance and the equivalent diameter of receiver. [ABSTRACT FROM AUTHOR]

The nonlinear and linear controls proposed by Alou and Soto provide very fast transient response (voltage step from 1 to 1.5 V in 2 \mu\s). This nonlinear control is based on hysteretic control of Cout current. This system is very sensitive to effects, like aging, temperature, input and output voltage variation, etc., that modify the switching frequency. This paper proposes a frequency loop to avoid the frequency variation and to adjust the switching frequency to the nominal value by changing the hysteretic band. A 5-MHz buck converter is developed, and experimental results validate the loop design, obtaining the same fast transient response (from 1.5 to 2.5 V in 2 \mu\s) while keeping switching frequency constant in steady state. [ABSTRACT FROM AUTHOR]

This article presents a control linearization technique for a single-phase single-stage inverter with multiple modulation strategies. The power topology is based on an flying capacitor multi-level (FCML) inverter, and the control is based on the plant inversion. The proposed technique allows decoupling the control of the input current and the output voltage, which simplifies the control in two ways: first, the control of both variables is independent and second, the controllers are independent of the modulation applied, thanks to the plant inversion. This control is implemented in an field-programmable gate array. Since the converter operates at variable frequency, two different data acquisition alternatives are explored: sampling at variable frequency (once per switching cycle) or sampling at constant frequency (higher than the switching frequency).The proposed control is validated by simulation and experimental results with a 1-kVA prototype. [ABSTRACT FROM AUTHOR]

V2Ic control provides very fast dynamic performance to the Buck converter both under load steps and under voltage reference steps. However, the design of this control is complex since it is prone to subharmonic oscillations and several parameters affect the stability of the system. This paper derives and validates a very accurate modeling and stability analysis of a closed-loop V2Ic control using the Floquet theory. This allows the derivation of sensitivity analysis to design a robust converter. The proposed methodology is validated on a 5-MHz Buck converter. The work is also extended to V2 control using the same methodology, showing high accuracy and robustness. The paper also demonstrates, on the V2 control, that even a low bandwidth-linear controller can affect the stability of a ripple-based control. [ABSTRACT FROM AUTHOR]

Over the past few years, RF power amplifiers are taking advantage of the switched dc–dc converters to use them in several architectures that may improve the efficiency of the amplifier, keeping a good linearity. The use of linearization techniques such as envelope elimination and restoration and envelope tracking requires a very fast dc–dc power converter to provide variable voltage supply to the power amplifier, but theoretically, the efficiency can be much higher than using the classical amplifiers belonging to classes A, B, or AB. The purpose of this paper is to analyze the state of the art of the power converters used as envelope amplifiers in this application where a fast output voltage variation is required. The power topologies are explored and several important parameters such as efficiency, bandwidth, and output voltage range are discussed. Some of these topologies are compared in terms of efficiency for a particular set of specifications. [ABSTRACT FROM AUTHOR]

Envelope tracking (ET) and envelope elimination and restoration (EER) are techniques that have gained in importance in the last decade in order to obtain highly efficient radio frequency power amplifier that transmits signals with high peak-to-average power ratio. In this study, a multilevel multiphase buck converter is presented as a solution for the envelope amplifier used in ET and EER. The presented multiphase buck converter generates multilevel voltage using “node” duty cycles and nonlinear control. In this way, the multilevel is implemented using only one simple power stage. However, the complexity of the multilevel converter implementation has been shifted from complicated power topologies to complicated digital control. Detailed discussion regarding the influence of the design parameters (switching frequency, output filter, and time resolution of the digital control) on the performance of the proposed envelope amplifier is presented. The design of the output filter is conducted fulfilling the constraints of the envelope slew rate and minimum driver pulse that can be reproduced. In the cases when these two constraints cannot be fulfilled, they may be relieved by the modified control that is presented and experimentally validated. Finally, in order to validate the concept, a prototype has been designed and integrated with a nonlinear class F amplifier. Efficiency measurements showed that by employing EER, it is possible to save up to 15% of power losses, comparing to the case when it is supplied by a constant voltage. Additionally, adjacent channel power ratio has been measured. The obtained results showed the value higher than 30 dB for signals up to 5 MHz of bandwidth, without using a predistortion technique. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage converter for a high-bandwidth and high-efficiency envelope amplifier. In the proposed application, due to the high peak-to-average-power ratio, high bandwidth, and the power level requirements, the envelope amplifier has low efficiency. Therefore, many efforts have been made to increase the efficiency of the envelope amplifier. To achieve this improvement, the current ripple cancellation technique is applied in this paper to a synchronous buck converter to cancel the output current ripple and to decrease the switching frequency without a reduction in the large signal bandwidth, for open-loop operation and for the envelope elimination and restoration technique. The advantages of the proposed design are presented and validated experimentally. The transfer function of the output filter of the buck converter with a ripple cancellation circuit has been modeled and compared to measurements, showing a good correspondence. Experimental validation is provided at 4 MHz of switching frequency, for dc and for variable output voltage, applying a sinusoidal reference and a 64-QAM signal. Experimental validation of the efficiency improvement is provided, compared to the equivalent design of the conventional buck converter in terms of the output voltage ripple rejection ratio and large signal bandwidth. [ABSTRACT FROM AUTHOR]