Junichi Yamamoto

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..

PFM and PWM Hybrid controlled LLC converter

This paper proposes the new LLC converter with unique control method. Generally, LLC resonant converter, which is controlled by PFM, has the drawback of (1) difficulty of PWM controllability, (2) difficulty of constant current limitation, and (3) narrow input voltage range limitation. These difficulties come from the resonant operation. In order to overcome those drawbacks, a hybrid control of PFM and PWM is employed for LLC. The resonant frequency is set to lower frequency to generate triangle current waveform, and the output voltage can be controlled by PWM and PFM through adjustment of resonant inductor energy. The experimental results for 48Vin, 16Vo, 80W board achieves 90% efficiency and validated this method is useful practically.

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 strategy for bi-directional LLC resonant converter with seamless operation

This paper proposes the simple and seamless operation technique for bi-directional LLC resonant converter. Generally, bi-directional operation of LLC resonant converter is complicated and difficult to control. Because, the switching frequency has to be changed across fsr (series resonant frequency) and the switching sequences (the switching timing between high voltage side and low voltage side) has to be changed due to resonant characteristics as well. In order to simplify the switching scheme between forward and reverse direction, the switching frequency has been moved to higher frequency than series resonant frequency where ZVS condition is maintained. As a result, the simple switching sequence has been achieved for both forward and reverse direction. The experimental results for 400Vin, 48Vo, 300W board achieves 93% efficiency and validated this method is useful practically.

Seamless operation of bi-directional LLC resonant converter for PV system

This paper proposes the simple and seamless operation technique for bi-directional LLC converter. Generally, bi-directional operation of LLC converter is complicated and difficult to control. Because, the switching frequency has to be changed across fsr (series resonant frequency) and the switching sequences has to be also changed due to resonant characteristics. In order to simplify the switching scheme, the switching frequency is moved to higher frequency than fsr where ZVS condition is maintained and simple switching sequence is achieved for both direction. The experimental results for 400Vin, 48Vo, 300W board achieves 93% efficiency and validated this method is useful practically.

Principle of overall AC equivalent model for bidirectional series resonant DC-DC converter

Recently, the series resonant converter is widely used for various applications. Moreover, the synchronous rectifier technique has been investigated in low voltage application achieving higher efficiency. The bi-directional series resonant converter can be realized by establishing the synchronous rectifier technique. This paper investigates the ac equivalent model and operating characteristics of bi-directional series resonant converter.

AC analysis of symmetry and asymmetry Bi-directional current resonant converter

So far, the operating characteristics of asymmetry type current resonant converter as LLC converter are discussed in detail. However, the detail operating characteristics discussions of symmetry type resonant converter have not been carried out. This paper investigates the AC characteristics of symmetry type bi-directional current resonant converter, and their soft-switching regions are also investigated.

Detail operating characteristics of Bi-directional LLC resonant converter

In renewable energy systems such as the PV system, the batteries are connected to ensure a stable supply of energy. Therefore, the bi-directional power conditioners have a key role in renewable power systems. In this paper, bi-directional LLC resonant converter as the power conditioner is proposed. The ac analysis and operating characteristics of bi-directional LLC resonant converter are investigated.

Hybrid controlled soft-switching half-bridge converter in DCM operation with voltage doubler rectifier for battery charge application

This paper proposes a PFM+PWM hybrid controlled soft-switching half-bridge converter which has both benefit of conventional half-bridge converter and LLC converter. Generally, conventional half-bridge converter has good constant current characteristic due to PWM control, however it has some drawbacks of (1) primary side switches and secondary side diodes operate under hard switching, (2) two magnetic components. Meanwhile, the LLC resonant converter has the benefit of achieving ZVS and ZCS, however it cant realize a constant current (CC) characteristic because of resonant fashion. In order to achieve soft-switching and CC characteristic using half-bridge converter, a DCM operation are employed, which can be controlled by PWM+PFM Hybrid Control. In this paper the operating characteristics of the proposed half-bridge converter are experimentally verified. The experimental results for 48Vin, 16Vo, 80W board achieves 90% efficiency and validated this method is useful practically.

Consideration of current resonant converter topology for bi-directional applications

This paper investigates the topology selection of the current resonant converter for bidirectional applications. The current resonant converter has several topologies which categorized switch network construction and resonant network construction. It is important that the topology is selected suitable for each application from several circuit topologies. In this paper, the operating characteristics are discussed in detailed in order to evaluate the appropriateness for each application. Moreover, the applicable topology is selected from detail operating characteristics.