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 a single-phase, single-stage buck-boost inverter for photovoltaic (PV) systems. The presented topology has one common terminal in input and output ports which eliminates common ...mode leakage current problem in the grid-connected PV applications. Although it uses four switches, its operation is bimodal and only two switches receive high-frequency pulse width modulation signals in each mode. Its principle of operation is described in detail with the help of equivalent circuits. Its dynamic model is presented, based on which a bimodal controller is designed. Experimental results, in stand-alone and grid-connected mode, obtained with a 300-W laboratory prototype are presented to validate its performance.
This paper presents three nonisolated high voltage gain dc-dc converters with ripple-free input current. The proposed converters combine coupled inductors and voltage-doubler structure (VDS) to ...achieve high step-up of input voltage. An active clamp circuit is used to suppress voltage spike of the switch caused by of the leakage inductor of the coupled inductor. VDS is placed in the secondary winding of the coupled inductor that clamps the diodes voltage stress. Working principle and design methodology of the proposed converters are presented in detail. Experimental results for a 300 W laboratory prototype, 48 V input voltage, and regulated output voltage of 400 V, are shown to validate the operation of proposed converters.
This article proposes a digital peak current program mode control scheme for switched reluctance machine (SRM) drives. To control phase currents, in general, a hysteresis controller (HC) is widely ...used due to its simplicity and robustness. However, realizing HC on a digital platform requires a significantly high ratio of sampling to switching frequency. To obviate such steep demands on data sampling, the proposed scheme uses the precepts of the digital current program mode control, widely used for dc-dc converters. For amenability with the SRM drive, this article proposes a transformation that represents an SRM by its dc-equivalent circuit. This transformation also simplifies the mathematical modeling of the drive. Then, to consider variations in phase-inductance and back-emf, parameter adaption through real-time estimations is incorporated in the proposed scheme. A stability criterion is derived from the robustness analysis by probing the effect of estimation errors on reference tracking performance. Finally, the proposed scheme is experimentally validated using a 1 kW, 3000 r/min 6/4 SRM-based laboratory prototype. Also, the proposed scheme is bench-marked against the conventional HC and model predictive control scheme, realized on the same digital platform.
Generally, single-stage buck-boost inverters consist of distinct circuits operating individually in buck/boost or positive/negative modes, the latter definitely leading to crossover distortion in the ...output current. This paper proposes a switching strategy that changes the bimodal operation of a single-stage buck-boost topology to a single-mode inverter. This is due to the consequent voltage gain that ensures that the output voltage polarity, apart from its magnitude, is an exclusive function of the duty ratio. Operational principle and salient hardware design are explained with the help of equivalent circuits. Details about the dynamic model are presented, based on which controller design is carried out for both stand-alone and grid-connected operation. Experimental results obtained from a 300-W, 110-V laboratory prototype are presented to validate the performance of the proposed switching strategy.
This article proposes an improved analytical method for accurate evaluation of flux-linkage characteristics for a given switched reluctance machine (SRM). Initially, air-gap inductance is calculated ...using an approximated analytical method, which incorporates the effect of fringing fluxes. Then, precepts of a conventional method are used to compute these characteristics under saturation, with a proposed new analytical model for nonuniform flux distribution in stator and rotor poles. Finally, for error quantification, these characteristics are benchmarked against those from a standard finite element analysis (FEA) based software. Both mean and standard deviation of the estimation errors are presented to quantify estimation accuracy. To establish its general validity, these characteristics are evaluated using the proposed method for six SRMs of different geometries and compared with those obtained from FEA. For further benchmarking, speed-torque characteristics obtained from the proposed method and FEA are presented and compared. Finally, both flux-linkage and torque-speed data are experimentally obtained from a 5 kW, 270 V, 12 000 r/min, 6/4 SRM and presented for validating the accuracy of the proposed method.
The instantaneous average current sharing (IACS) control strategy ensures accurate transient and steady-state current sharing among uninterruptible power supply (UPS) modules connected in parallel, ...but is dependent on a communication backbone. This paper proposes a new IACS scheme that is more reliable and economically efficient. In the process of deriving this control scheme, two existing IACS schemes are examined in detail. It is shown that both the schemes offer distinct structural and performance related advantages and disadvantages. The proposed scheme is shown to provide more reliable operation without sacrificing the system performance and incurring extra control cost. Performance of the proposed approach is analytically predicted and validated through experimental results with a 22.5-kW system supported by three parallel-connected three-phase UPS modules.
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.
