Sihun Yang

Dynamic characteristics model of bi-directional DC-DC converter using state-space averaging method

In the fields of using green energy such as EV power system and the PV system, the bi-directional DC-DC converter, which is used to control the charge and discharge of batteries, is now attracting more and more attention. In the bi-directional DC-DC converter for the battery charger, the response characteristics and stability of one are key points for the performance of the whole system. However, it is complex to analyze the dynamic characteristics and control design, because both of forward direction mode and reverse direction mode of the converter have to be considered. In this paper, the simplified dynamic model of the bi-directional DC-DC converter is presented. Transfer functions of the converter are derived by using the state-space averaging method. And, the frequency characteristics of the converter for both of buck mode and boost mode are discussed. Finally, experimental results are shown to confirm the validity of the proposed dynamic model of the converter.

Design consideration of flat transformer in LLC resonant converter for low core loss

Low-profile, high efficiency power supply is todays industry trend for Plasma Display Panel (PDP) application system. Transformer is the major challenge and bottleneck for achieving low-profile, high power density converter. Generally, it is necessary for low-profile converter to operate it at high switching frequency. However, it is very difficult to design converter using flat magnetic component because flat transformer temperature becomes high at high switching frequency. In this paper, the design and analysis of flat transformer in LLC resonant converter for the PDP TV is proposed to reduce temperature of the transformer. In this proposed converter, flat transformer is integrated into advanced power conversion application systems. Low-profile power module of profile of about 14mm is achieved. Temperature inside of transformer repressed to 71ºC and an overall efficiency of about 96.6% was obtained.

Adaptive driving of synchronous rectifier for LLC converter without signal sensing

This paper presents the novel driving technique of synchronous rectifier (SR) for the LLC converter. The unique characteristic of “Vo*D=constant” of LLC converter is utilized to predict optimal duty ratio D, where D is the conduction period of secondary diode. This technique does not need the sensing of SR current neither SR voltage. Additionally, the auto tuning technique is implemented to adjust the duty ratio precisely as well by digital control using TIs DSP of Piccolo TMS320F28027. The technique is confirmed by experimentally..

Seamless dynamic model for bi-directional DC-DC converter

In this paper, bi-directional DC-DC converter is analyzed using a seamless dynamic model with an independent voltage source and an independent current source, which polarity depends on the direction of the power flow. In the seamless dynamic model, the independent voltage source represents a battery and an independent current source represents the load or energy source. A small signal model is derived using a state space averaging method, and simulated results about the transient response characteristics are presented.

Sensing-less drive of synchronous rectifier for LLC resonant converter

This paper presents the novel driving technique of synchronous rectifier (SR) for the LLC converter. The unique characteristic of “Vo*D=constant” of LLC converter is utilized to predict optimal duty ratio D, where D is the conduction period of secondary diode. This technique does not need the sensing of SR current neither SR voltage. The technique is confirmed by experimentally.

Operating mechanism of SiC-SIT DC circuit breaker in 400V-DC power supply system for data center — In case of grounding fault

In DC power supply system, a fast response circuit breaker is required. Semiconductor DC circuit breaker is an important key technology in DC power supply system. This paper considers the operating characteristics of Silicon Carbide-Static Induction Transistor (SiC-SIT) based DC circuit breaker in DC power supply system when grounding fault occurs. The operating mechanism of grounding fault case is explained compared with short fault case.

A new stability assessment criterion for dc power systems using multi-level virtual conductors

This paper presents a new stability criterion for bidirectional DC-DC converters in a dc power system. Factually, it is so sophisticated to use conventional stability criteria to assess the stability of a dc power system consists of huge number of nodes. The proposed criterion gives an overall indicator for the stability at each node in the dc power system. It based on perturbing the system at a certain node by injecting a small ac current at this node, and accordingly monitoring the variation of the voltage at this node. Then, the node impedance can be calculated. This node impedance implies the stability status of the system at that node. The concept of the node impedance stability criterion is introduced, and the application of this criterion to a dc power system is investigated, as well.

Seamless dynamic model for DC-DC converters applicable to bi-directional power transfer

In this paper, seamless model of bi-directional DC-DC converter which is applicable to bi-directional power transfer is proposed. Conventional modeling method of bi-directional DC-DC converter is complex, because different models are needed for different directions of power flow. On the other hand, seamless model can be applied for both directions of power flow. Seamless circuit model is expressed by voltage source and bi-polar current source, and polarity of current source shows direction of power flow. In this model, control loop need to be switched by direction of power flow. Therefore analyzing and controlling bi-directional DC-DC converter is much easier than conventional way. Seamless dynamic model are derived by state-space averaging method. Analytical, simulated, experimental results are investigated, and availability of seamless model is suggested.

Design of low-profile LLC resonant converter for low transformer loss

This paper presents the design of two flat transformers in low-profile LLC resonant converter for low transformer loss. The trend toward high power density, high efficiency, and low profile in power supplies has exposed a number of limitations in the use of magnetic component structures. Therefore, LLC resonant converter can be operated at high switching frequency with high efficiency, because the switching loss is reduced by soft-switching. However, flat transformer loss becomes problems at high switching frequency. As a result, flat transformers temperature becomes high. Therefore, it is necessary to reduce the transformer temperature by analyzing the loss. In this paper, design for low transformer loss is presented.

Design of LLC resonant converter using planar magnetic component

This paper presents the design and implementation of LLC resonant converter using planar magnetic component. In the LLC resonant converter, ZVS turn-on and ZCS turn-off of MOSFETs and diode rectifiers can be achieved over the entire operating range, respectively. Therefore, the switching loss is reduced and we can operate the converter at higher switching frequency. At that frequency, planar magnetic component is a viable option. In this proposed converter, the magnetic component is integrated into advanced power conversion technique to implement a low-profile power supply for PDP application systems. An efficiency of about 96.7% was obtained.