This letter proposes a comprehensive zero-voltage switching analysis (ZVSA) to illustrate the commutation mechanism of full-bridge (FB) mosfets in resonant converters. Inherent contradiction between ...two conventional ZVSA techniques is discussed with specific consideration of a full-bridge LLC (FBLLC) resonant converter. An analytical approach is proposed to determine the accurate zero-voltage switching (ZVS) criterion for both zero- and finite-phase overlap operations of an FB network. Impact of the proposed ZVSA on power losses of FBLLC is explained analytically. Experimental results are presented not only to validate the proposed ZVSA, but also to validate its effect on FBLLC. Low load efficiency is improved by 6% with the proposed approach.
This paper presents a unified control scheme for automatic resonant frequency tracking (ARFT) in unregulated LLC series resonant dc-dc converters. The proposed strategy detects frequency drift by ...monitoring either phase or gain relationship of an exclusive variable pair in an LLC tank. Considering both phase angle and amplitude ratio of the state variables, the plant is modeled for a realistic ramp variation in resonant frequency. A two-step approach is proposed to choose the most suitable variable pair for ARFT. First, the best candidates for phase and gain comparison are selected individually based on the sensitivity criteria. Then, the final choice of variable pair is made by analytically deriving the frequency tracking error due to realistic variation in tank parameters and nonidealities. The proposed controller is implemented using analog electronics and the practical limit for circuit delays during low cost realization is clarified. Performance evaluation of the proposed control scheme is carried out on a lab prototype of the LLC converter.
This paper presents an optimal design approach for a dual-active-bridge series resonant converter (DABSRC) based on frequency domain analysis. The proposed design technique ensures efficient ...performance of DABSRC over a wide range of voltage gain and load variations. The operating principle of the converter is detailed to illustrate both zero voltage switching (ZVS) and zero current switching operations during bidirectional power transfer. Modeling the current-dependent power loss components as an equivalent series resistance, the converter is analyzed in frequency domain to derive amplitude and phase of the state variables accurately. Performing the power loss analysis in a normalized form, the characteristic equations for bidirectional power transfer, tank current, converter efficiency, and ZVS criteria are derived. Using these characteristics, the design of DABSRC is formulated as an efficiency optimization problem. Particle swarm optimization technique is adopted to determine the optimal tank parameters and transformer turns-ratio. Converter performance is evaluated on a 120-W lab-prototype, and peak efficiency of 95.2% and California energy commission efficiency of 92.1% are achieved. Close agreement among analytical predictions, numerical simulation, and experimental results validate the proposed design technique.
This paper proposes an automatic resonant frequency tracking scheme for resonant converters. A plant modeling approach is presented based on realistic ramp variation of resonant frequency due to ...slowly varying environmental conditions. The drift in resonant frequency is detected by observing the phase relationship of an electrical variable pair. A rigorous analysis is carried out to select the most suitable variable pair for phase comparison. The effects of circuit nonidealities on the proposed phase detection technique have been detailed. The proposed control technique has been implemented using low cost analog circuitry and is applied to a parallel LLC tank-based resonant boost dc-dc converter. Experimental results are presented on a 160-W prototype to validate the analytical predictions.
This letter proposes a structured approach for accurate estimation of diode reverse-recovery characteristics using datasheet specifications. Considering a conductance model of a diode, the entire ...reverse-recovery process is divided into four operating modes. The state equations for each mode are derived taking the circuit nonidealities, viz., device capacitance and parasitic inductances, into account. Analytical expressions for reverse-recovery charge, reverse-recovery time, and diode current are derived and numerically solved to estimate the diode conductance directly from manufacturer's data. An empirical model is proposed to characterize the effects of temperature variation on the diode conductance. Numerical simulation and experimental results are presented for antiparallel diodes of three MOSFETs having different current and voltage ratings and also for a discrete p-n diode at different junction temperatures. The maximum estimation error with the proposed approach is 5.1% for peak reverse-recovery current and less than 8% for reverse-recovery time, peak voltage, and energy loss.
This paper proposes a generic control scheme for automatic resonant frequency tracking (ARFT) in resonant converters. The plant is modeled based on realistic ramp variation of resonant frequency due ...to slowly varying environmental conditions. The proposed ARFT scheme monitors the gain relationship between an exclusive electrical variable pair to detect frequency drift. An analytical approach is presented to select the most suitable variable pair for gain comparison. The effects of tank parameter variation and circuit nonidealities on the gain relationship of the chosen variable pair have been analyzed. An online correction mechanism is proposed to nullify the influence of load variation on the proposed technique. Second-order generalized integrator-based low-cost analog realization of the proposed strategy is detailed. Analytical predictions are experimentally validated by applying the control scheme to a parallel LLC tank-based resonant dc-dc converter.
This article proposes a structured method for characterizing the capacitive couplers used in wireless electric vehicle (EV) charging systems. Most of the existing approaches rely on expensive ...finite-element analysis (FEA) tools for estimating the mutual capacitance between the coupler plates. An experimental technique is found in the literature that relies on a series <inline-formula><tex-math notation="LaTeX">LC</tex-math></inline-formula> resonant circuit but suffers from certain limitations. A parallel <inline-formula><tex-math notation="LaTeX">LC</tex-math></inline-formula> resonance-based approach is introduced in this article to address those issues. The suggested method requires an initial estimate of the mutual capacitance, which is achieved by deriving an empirical formula. Also, a comprehensive algorithm is presented to design an inductor with low interwinding capacitance, which aids the proposed characterization procedure. An experimental prototype of the capacitive coupler is fabricated and characterized for different vertical distances between the coupler plates under both aligned and misaligned conditions. The outcomes of the proposed method are compared with FEA simulation results, and close agreement between these data is noted.
Switching frequency is utilized as a degree of freedom in digital control strategies for power converters. In addition to carrier-based schemes, quadrature oscillators offer an alternative method for ...the generation of variable frequency switching pulses. In this article, amplitude instability in a computationally simple digital quadrature oscillator is analyzed. Algorithms for stabilizing the oscillator are developed based on this. Further implementation issues arising are addressed and a systematic comparison to carrier-based schemes is executed. It is shown that the proposed approach can be implemented with only four additions and four comparison steps without resorting to multiplication. The studies are validated in system simulation and experiments on a commercial field programmable gate array board.
The LCC resonant converter with a capacitive output filter is a popular topology for variable load applications, though the simultaneous design requirements of wide load range, soft switching, and ...low conduction loss are not clearly tackled in available design strategies. In this paper, the existing time-domain analysis of the converter is extended in a normalized design-oriented fashion. The proposed extension to boundary modes lends itself to the derivation of critical converter characteristics such as the soft switching range. A dimensionless converter and load characteristic-based design algorithm with parameter decoupling is developed to meet the load requirements. The design algorithm reduces converter rms current while meeting practical requirements of zero voltage switching and constraints on switching frequency across the load range. The proposed design method is validated using circuit simulations incorporating series dissipative non-idealities and the transformer magnetizing inductance, and also on a 160 W laboratory prototype with switching frequency within the designated limits and <inline-formula><tex-math notation="LaTeX">>96\%</tex-math></inline-formula> experimental efficiency.
This paper proposes a generic control scheme for automatic resonant frequency tracking (ARFT) in resonant converters. The plant is modeled based on realistic ramp variation of resonant frequency ...due to slowly varying environmental conditions. The proposed ARFT scheme monitors the gain relationship between an exclusive electrical variable pair to detect frequency drift. An analytical approach is presented to select the most suitable variable pair for gain comparison. The effects of tank parameter variation and circuit nonidealities on the gain relationship of the chosen variable pair have been analyzed. An online correction mechanism is proposed to nullify the influence of load variation on the proposed technique. Second-order generalized integrator-based low-cost analog realization of the proposed strategy is detailed. Analytical predictions are experimentally validated by applying the control scheme to a parallel Formula Omitted tank-based resonant dc-dc converter.
