Bong-Gyoo Cho

Design of half-bridge piezo-transformer converters in the AC adapter applications

As a viable alternative to magnetic transformers in the power supply for portable electronics, this paper presents a miniaturized off-line travel adapter or charger for cellular phones using the piezoelectric transformer. Various design considerations in the design of ac PT adapters are investigated before coming up with the proposed pseudo-resonant topology. A prototype hardware design is also presented and verified by simulations and experiments

New Control Strategy for 2-stage Utility-Connected Photovoltaic Power Conditioning System with a low cost digital processor

In this paper, a simple control method for two-stage utility grid-connected photovoltaic power conditioning systems (PCS) is proposed. This approach enables maximum power point tracking control with post-stage inverter current information instead of calculating solar array power, which significantly simplifies the controller and the sensing part. Furthermore, there is no feedback loop in the pre-stage converter to control solar array voltage because the MPP tracker drives the converter switch duty-cycle. This simple PCS control strategy can reduce the cost and size, and can be utilized with a low cost digital processor. For verification of the proposed control strategy, the 2.5 kW two-stage photovoltaic grid-connected PCS hardware that consists of boost converter cascaded with a single-phase inverter has been built and tested

Small-signal modeling of the tapped-inductor converter under variable frequency control

In this paper, a small-signal averaged model for the tapped-inductor (TI) converter under variable frequency control, which operates at the critical conduction mode (CRM) (the boundary between continuous conduction mode (CCM) and discontinuous conduction mode (DCM)) is presented. Based on the state-space averaging approach the state variable derivatives and the constraints that account for variable frequency control lead to full-order small-signal model. And the special behavior of the inductor current in the CRM reduces the order of the basic state-space averaged model by one. The full-order model and reduced-order model predictions are verified with experiment measurements on a prototype TI buck converter.

Design of Peak and Charge Current-mode Control for Parallel Module Solar Array Regulator System

In general, the current mode controller is used to share the current in the parallel operation of a power stage. However, the parallel operation of the solar array regulator system (SAR) should be carefully designed because of the nonlinear characteristic solar array (SA), such as a negative dynamic resistance (r s ) and a SA V-I curve. In the post works, the detailed analysis of stability and dynamics of the SAR system employing current mode control has been not carried out. For these works, the SAR system employing current mode control was analyzed and compared using both large and small signal approaches. From the results of analysis, the stability problems and design issues of the SAR using current mode control for parallel operation were investigated. Finally, the considered problems and issues were tested for the verification through experiments.

Digital Control of the Parallel Interleaved Solar Array Regulator Using the Digital Signal Processor

In this paper, a digital control approach for the parallel interleaved solar array regulator (SAR) is proposed. The proposed control scheme achieves stable operation in the entire region of the solar array (SA). Additionally, by making the effective load characteristic of the SAR seen by the SA as a resistive load sink, the current sharing among the converter modules is possible. Also, this method can be applied to conventional parallel buck and boost converters. The small signal analysis with the digital sampling effect is performed. A SAR system that consists of two 100W parallel module buck converters with a TMS320F2812 DSP has been experimented using a real 200W solar array to validate the proposed digital control scheme.

Design and analysis of high-voltage transformer for HID lamp igniter

In this paper, requirements for the HID lamp igniter transformer capable of hot strike are described. A small size high voltage (HV) transformer composed of a ferrite core and an outer wall is designed. The characteristics such as flux linkage, current density and inductance are simulated with finite element methodology. The design guideline of the HV transformer that produces an output voltage with a peak value of 25 kV and a pulse width of larger than 100 nS for a 35 W automotive HID ballast prototype is discussed as an illustrative example

Modeling and Characterization of Radial-mode Disk-type Piezoelectric Transformer for AC/DC Adapter

For characterization of the newly developed radial-mode disk-type piezoelectric transformer (PT) for ac/dc adapter applications, the closed-form solution of the wave equation, including a loss model for the PT design, was obtained without FEM tools and used to build the electrical equivalent circuit model. The constructed model can be used with the circuit analysis program to predict the operating characteristics of the piezoelectric transformer in the target system. The optimal design procedure of the PT to meet the circuit operation requirements is also presented. The design procedure and the model was verified by experimental data using the prototype PT sample

Power system structure and control strategy for Fuel Cell Hybrid Vehicle

Various power system structures are simulated and analyzed in order to improve the power and energy performance of the Fuel Cell Hybrid Electric Vehicle (FCHEV) using a supercapacitor. In this paper, an optimization of the existing Type E structure, hereafter called buck-boost Type E, and its control strategy are proposed to control the power system of the FCHEV and to operate the fuel cell in the efficient range. The performances of the buck-boost Type E are compared with those of the conventional system structures by simulating acceleration, the Japan 10-15 driving cycle, and the FTP 75 driving cycle tests. The results are verified through scaled down experimental equipment.

Adaptive Phase Control Method for Load Variation of Resonant Converter with Piezoelectric Transformer

this paper proposes a new method eliminating external effect from (load, temperature) variation on a Piezoelectric Transformer (PT) converter by utilizing the phase-locked loop (PLL) modulation technique. The PLL control scheme involves detecting phase difference between injected sinusoidal signal and demodulated terminal voltage of PT. Generally, frequency control method decreases the efficiency of PT in wide input range. And, duty cycle control method has a problem of insufficient operating range for the load variation. In other to overcome these problems, this paper introduces a two loop control (PWM and PLL) with PT which provides wide ZVS condition nearly independent of the load variation, and excellent line regulation for the universal input voltage and load range. The performance of the proposed control method is verified by experimental result with 40 [W] DC/DC converter hardware prototypes.

PWM-switch Model of Tapped Inductor Converters under Hysteretic Current-mode Control

In this paper, a small signal analysis for tapped inductor converter under the critical conduction mode control (CRM) is presented. Critical conduction mode control is one of the hysteretic current mode controls in variable switching frequency operation. In first, a mathematically-described variable-frequency control modeling method for tapped inductor converters is introduced through extending the state-space averaging approach. Based on the results of the method, a newly-developed PWM-switch small-signal model for CRM control method is derived, which provides a physically-intuitive circuit model. The model greatly reduces the efforts in analyzing complex converters such as the tapped inductor converters. In order to verify those models, experimental results of a tapped inductor converter are presented. The general converter model parameters are summarized in the conclusion as well