Sung-Soo Hong

Dynamics and control of DC-to-DC converters driving other converters downstream

This paper reveals that the dynamics of a converter loaded with other converters downstream are markedly different from those of a standalone converter and conventional design techniques developed for converters with a resistive load could destabilize the control loop of converters combined with other converters. Based on comprehensive small-signal analyses, this paper presents the proper way of designing the control loop of converters driving other converters downstream. The analysis and design results are verified by both time- and frequency-domain simulations.

Modeling and small-signal analysis of controlled on-time boost power-factor-correction circuit

A large-signal average model for the controlled on-time boost power-factor-correction (PFC) circuit is developed and subsequently linearized, resulting in a small-signal model for the PFC circuit. AC analyses are performed using the small-signal model, revealing new results on the small-signal dynamics of the PFC circuit. The analysis results and model predictions are confirmed with experimental measurements on a 200-W prototype PFC circuit.

A New Cost-Effective Current-Balancing Multi-Channel LED Driver for a Large Screen LCD Backlight Units

A new current-balancing multi-channel LED driver is proposed in this paper. The conventional LED driver system consists of three cascaded power conversion stages and its driver stage has the same number of expensive boost converters as those of the LED channels. On the other hand, the proposed LED driver system consists of two cascaded power stages and its driver stage requires only passive devices instead of expensive boost converters. Nevertheless, all of the currents through multi-channel LEDs can be well balanced. Therefore, it features a smaller system size, improved efficiency, and lower cost. To confirm the validity of the proposed driver, its operation and performance are verified on a prototype for a 46” LCD TV.

Dual-coupled inductor-fed DC/DC converter for battery drive applications

A new isolated boost DC/DC converter suitable for a low-input-voltage application is introduced. The proposed converter features low switch current stresses, wide range of input voltage, and inherent inrush current protection, essential for the design of a low-to-high-voltage conversion circuit. A comparative analysis and experimental results are presented to show the validity of the proposed converter.

High-efficiency and low-cost tightly-regulated dual-output LLC resonant converter

A new high-efficiency and cost-effective dualoutput LLC resonant converter is proposed in this paper. The proposed converter can get tightly regulated dual-output voltages by adding only one auxiliary switch and PWM IC to conventional LLC resonant converter. Therefore, it features a simpler structure, less mass, and lower cost of production. Furthermore, since all power switches are turned on or off under zero-voltage switching (ZVS) or zero-current switching (ZCS), it has several favorable advantages such as high-efficiency, low switching loss, improved electromagnetic interference (EMI), and reduced burden on the cooling system. This paper presents a dual-output LLC resonant converter applicable to the PDP TV power supply. The proposed converter achieves maximum power conversion efficiency of 96.5% at full load condition. The operational principle, theoretical analysis, and design considerations are presented. Also, to confirm the operation, validity and features of the proposed converter, experimental results from a 420W, 200V dc /50V dc prototype are presented.

Analog Control Algorithm for Maximum Power Trackers Employed in Photovoltaic Applications

Tracking the Maximum Power Point(MPP) of a photovoltaic(PV) array is usually an essential part of a PV system. The problem considered by Maximum Power Point Tracking(MPPT) techniques is to find the voltage VMPP or current IMPP at which a PV array should operate to generate the maximum power output PMPP under a given temperature and irradiance. The MPPT control methods such as the perturb and observe method and the incremental conductance method require microprocessor or DSP to determine if the duty cycle should be increased or not. This paper proposes a simple and fast analog MPPT method. The proposed control scheme will track the MPP very fast and its hardware implementation is so simple, compared with the conventional techniques. The new algorithm can successfully track the MPP even in case of rapidly changing atmospheric conditions and has higher efficiency than ordinary algorithms.

Analysis and Design of a High Voltage Flyback Converter with Resonant Elements

This paper presents the operational characteristics of a high voltage flyback converter with resonant elements. In high voltage low power applications, the effect of a transformer’s stray capacitance might be the most important factor that influences the overall performance of the circuit. A detailed mode analysis and the design procedure are presented in designing the high voltage flyback converter. To verify and confirm the validities of the presented analysis and design procedure, a computer simulation and experiments have been performed.

Precise Analytical Solution for the Peak Gain of LLC Resonant Converters

Although LLC resonant converters have the advantages of a wide operation range and high efficiency, the lack of an analytical solution for the peak gain makes it difficult to optimize the resonant tank design, when considering not only the normal condition but also the holdup time requirement. In this paper, based on a mathematical analysis of a LLC resonant converter at the peak gain point, an analytical solution for the peak gain has been developed. By using the developed analytical solution, the peak gain with given resonant tank parameters can be obtained. To confirm the validity of the developed analytical solution, simulations and experimental results are compared.

Hardware-in-the-loop simulation of DC microgrid with Multi-Agent System for emergency demand response

This paper presents the real-time hardware-in-the-loop simulation (HILS) of DC microgrids containing multiple distributed resources (DRs) such as a battery energy storage system, a small distributed generator and a smart DC load. The power grid and the DRs are developed in the real-time simulation software, specifically Opal-RT RT-LAB software. The controllers of the DRs are developed as hardware devices using AVR microcontroller named as ATMega-128. The simulation model and hardware devices are integrated in the HILS framework. Each controller of the DRs acts as an intelligent agent that can communicate and cooperate with the coordinator and other agents. Emergency demand response problems are applied to the HILS setup for the performance verification.

Average current mode control to improve current distributions in multi-module esonant dc-to-dc converters

Multi-module interleaved resonant converters have been widely adapted to low-profile power supplies for flat-panel display electronics. In this multi-module approach of resonant converter, individual modules tend to have different circuit characteristics due to unavoidable resonant component mismatch, resulting in noticeable imbalance in the module currents and considerable ripple component in the output current. Many researchers have been studied on methodologies for an effective load current sharing for multi-module dc-to-dc converters. But, most of their results were confined to the treatments of passive components. This paper proposes a new average current mode control which actively controls the individual modules to share equal current at the presence of mismatches in their circuit components. The validity and performance of the proposed average current mode control is demonstrated using a 150 W two-module interleaved LLC series resonant dc-to-dc converter designed for LCD TV sets.