Roger J. King

A Normalized Model for the Half-Bridge Series Resonant Converter

Closed-form steady-state equations are derived for the halfbridge series resonant converter with a rectified (dc) load. Normalized curves for various currents and voltages are then plotted as a function of the circuit parameters. Experimental results based on a 10-kHz converter are presented for comparison with the calculations.

Small-Signal Model for the Series Resonant Converter

The results of a previous discrete-time model of the series resonant dc-dc converter are reviewed and from these a small signal dynamic model is derived. This model is valid for low frequencies and is based on the modulation of the diode conduction angle for control. The basic converter is modeled separately from its output filter to facilitate the use of these results for design purposes. Experimental results are presented.

A Large-Signal Dynamic Simulation for the Series Resonant Converter

A simple nonlinear discrete-time dynamic model for the series resonant dc-dc converter is derived using approximations appropriate to most power converters. This model is useful for the dynamic simulation of a series resonant converter using only a desktop calculator. The model is compared with a laboratory converter for a large transient event.

Inherent Overload Protection for the Series Resonant Converter

The overload characteristics of the full bridge series resonant power converter are considered. This includes analyses of the two most common control methods presently in use. The first of these uses a current zero crossing detector to synchronize the control signals and is referred to as the ¿ controller. The second is driven by a voltage controlled oscillator and is referred to as the ¿ controller. It is shown that the ¿ controller has certain reliability advantages in that it can be designed with inherent short circuit protection. Experimental results are included for an 86 kHz converter using power metal-oxide-semiconductor field-effect transistors (MOSFETs).

Modeling the Full-Bridge Series-Resonant Power Converter

A steady state model is derived for the full-bridge series-resonant power converter. Normalized parametric curves for various currents and voltages are then plotted versus the triggering angle of the switching devices. The calculations are compared with experimental measurements made on a 50 kHz converter and a discussion of certain operating problems is presented.

Control method for multi-microgrid systems in smart grid environment—Stability, optimization and smart demand participation

This paper presents a control strategy for microgrids in smart grid environment. A hierarchical control strategy is developed to ensure stability and to optimize operation of microgrid. Communication, control and advanced metering infrastructure of smart grids are used to facilitate this control strategy. The control strategy incorporates storage device, electric car, various distributed energy resources and loads. Proposed control strategy considers microgrid operation in island and grid-connected mode. Island microgrid is stabilized by managing storage devices, dispatchable energy units and controllable loads. The control strategy is based on demand participation while stability of system has the highest priority. Theoretical discussion beyond presented algorithms reveal evidently the effectiveness of the proposed control method.

Analysis and design of an unusual unity-power-factor rectifier

A unity-power-factor rectifier that has a parallel-resonant tank tuned to the second harmonic of the line frequency is analyzed for two filter configurations. A unidirectional-power-flow version of the current-sourced rectifier can operate stably open loop or can be current limited down to zero output voltage. The large inductor normally required is an outstanding disadvantage which can be partially overcome using a resonant filter. The design-oriented analysis includes variable-frequency operation and key component ratings. A design procedure is suggested, and complete experimental verification is obtained using a 120 V, 500 W. 60 Hz rectifier switching at 50 kHz. >

Transformer Induced Instability of the Series Resonant Converter

It is shown that the common series resonant power converter is subject to a low frequency oscillation that can lead to the loss of cyclic stability. This oscillation is caused by a low frequency resonant circuit formed by the normal L and C components in series with the magnetizing inductance of the output transformer. Three methods for eliminating this oscillation are presented and analyzed. One of these methods requires a change in the circuit topology during the resonance cycle. This requires a new set of steady state equations which are derived and presented in a normalized form. Experimental results are included which demonstrate the nature of the low frequency oscillation before cyclic stability is lost.

A Fourier analysis for a fast simulation algorithm (for power convertors)

A powerful discrete modeling approach to the simulation of a switching converter that has appeared in power electronics literature over the last several years is briefly reviewed, and some desirable traits for its matrix exponential subroutine are discussed. The key result is a systematic and generic Fourier analysis that operates on the steady-state solution as provided by a discrete model. The Fourier analysis algorithm was tested on a phase-controlled parallel-loaded resonant converter which is useful as a fixed-frequency low-distortion AC source. Three verifications of the algorithm were made: a phasor analysis, an alternate closed-form analysis directed specifically to the problem at hand, and an analysis using experimental data. The performance of the algorithm was good for the case considered. >

Previously unobserved effects of delay on current-mode control

A new sampled-data model for the current-mode controlled buck converter includes for the first time the effects of delay in the current loop. Modified z-transforms are used in this new model for constant frequency trailing-edge modulation. Realistic amounts of delay are found to be particularly significant when the buck converter is operating in the continuous conduction mode near the discontinuous conduction mode boundary. The new model is used to predict the loop gain measurements obtained with the digital modulator and with conventional measurement techniques. It is shown that conventional loop gain measurement techniques are insufficient to measure the loop gain in this region of operation. It is also shown that the digital modulator can add a significant amount of delay, thereby altering the loop gain of the circuit being measured. However, if care is taken to minimize this delay, a good loop gain measurement can be achieved. The new model accurately predicts the boundary condition for subharmonic instability. In addition, it reduces to Ridleys current-mode control model for the case of zero delay.