Koosuke Harada

Bio: Koosuke Harada is an academic researcher from Kyushu University. The author has contributed to research in topics: Ćuk converter & Switched-mode power supply. The author has an hindex of 21, co-authored 160 publications receiving 1956 citations.

A noncontact charger using a resonant converter with parallel capacitor of the secondary coil

Abstract: A noncontact charging system using a resonant converter is presented in this paper, where the power transfer ability of a detachable transformer is improved by using a parallel capacitor connected to the secondary coil. A method to get the optimum value of the capacitance which would maximize the charging current is described. A method of application to the practical circuit such as a voltage resonant converter is also described.

A new method to regulate resonant converters

Abstract: A resonant frequency-modulation method is presented as an alternative to the switching frequency-modulation method to regulate resonant converters. A switch-controlled inductor and switch-controlled capacitor, in which switching losses are found to be very low due to zero-current or zero-voltage switching, are developed to do so. A new family of resonant converters that are regulated at a fixed switching frequency is proposed. A steady-state analysis of the Class E resonant converter regulated by a switch-controlled capacitor is presented. Theoretical and experimental results verify the validity of the proposed method. The efficiency measured from a breadboard of 1 MHz, 5 V, 25 W Class E regulated resonant DC-DC converter is up to 83%. >

The Cascade Connection of Switching Regulators

Abstract: A method for the cascade connection of switching regulators is introduced which is useful for low-voltage power supplies. It is common to use a reactor with a secondary winding in order to obtain a sufficiently small step-down ratio (E out /E in ). In this method, how-ever, a switching surge occurs because of the leakage inductance of the two-winding reactor. On the other hand, by the method presented here, we will be able to have a sufficiently small step-down ratio and a sufficiently large regulation range with no occurrence of the switching surge. Furthermore, a new method is proposed for isolating the supply and the load circuit.

Phase-controlled DC-AC converter with high-frequency switching

Abstract: An analysis of the phase-controlled DC-AC converter is presented. This converter has a pair of switches in each side of the primary and the secondary of the isolation transformer. The voltage conversion ratio is controlled by the phase difference between the two pairs of switches. The averaged equivalent circuit for low frequency operation is derived. The switching surge during commutation is much reduced by dividing the reactor into two parts. As a result, the transformer is miniaturized by increasing the switching frequency and the reactive energy can be easily recovered to the DC source. This DC-AC converter is especially suitable for small uninterruptible power supply systems. >

Analysis and optimization of a nondissipative LC turn-off snubber

Abstract: A nondissipative LC turn-off snubber is used to reduce the voltage stress on a switching transistor, which is caused by the energy stored in the transformer leakage inductance. A detailed analysis of the fundamental characteristics of a buck-boost converter with an LC snubber is given, clarifying the effect of the snubber capacitance. In particular, it is found that the transformer current increases with the snubber capacitance, the transistor surge voltage and power loss are evaluated, and the optimum value of the snubber capacitance is derived. The most effective value of the snubber inductance is also discussed. >

Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques

Abstract: The many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in PV power generation.

Wireless Power Transfer for Electric Vehicle Applications

Abstract: Wireless power transfer (WPT) using magnetic resonance is the technology which could set human free from the annoying wires. In fact, the WPT adopts the same basic theory which has already been developed for at least 30 years with the term inductive power transfer. WPT technology is developing rapidly in recent years. At kilowatts power level, the transfer distance increases from several millimeters to several hundred millimeters with a grid to load efficiency above 90%. The advances make the WPT very attractive to the electric vehicle (EV) charging applications in both stationary and dynamic charging scenarios. This paper reviewed the technologies in the WPT area applicable to EV wireless charging. By introducing WPT in EVs, the obstacles of charging time, range, and cost can be easily mitigated. Battery technology is no longer relevant in the mass market penetration of EVs. It is hoped that researchers could be encouraged by the state-of-the-art achievements, and push forward the further development of WPT as well as the expansion of EV.

Design considerations for a contactless electric vehicle battery charger

Abstract: This paper overviews theoretical and practical design issues related to inductive power transfer systems and verifies the developed theory using a practical electric vehicle battery charger. The design focuses on the necessary approaches to ensure power transfer over the complete operating range of the system. As such, a new approach to the design of the primary resonant circuit is proposed, whereby deviations from design expectations due to phase or frequency shift are minimized. Of particular interest are systems that are neither loosely nor tightly coupled. The developed solution depends on the selected primary and secondary resonant topologies, the magnetic coupling coefficient, and the secondary quality factor.

System and method for inductive charging of portable devices

Abstract: A system and method for variable power transfer in an inductive charging or power system. In accordance with an embodiment the system comprises a pad or similar base unit that contains a primary, which creates an alternating magnetic field. A receiver comprises a means for receiving the energy from the alternating magnetic field from the pad and transferring it to a mobile device, battery, or other device. In accordance with various embodiments, additional features can be incorporated into the system to provide greater power transfer efficiency, and to allow the system to be easily modified for applications that have different power requirements. These include variations in the material used to manufacture the primary and/or the receiver coils; modified circuit designs to be used on the primary and/or receiver side; and additional circuits and components that perform specialized tasks, such as mobile device or battery identification, and automatic voltage or power-setting for different devices or batteries.

Development of a microcontroller-based, photovoltaic maximum power point tracking control system

Abstract: Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.