Takanari Sasaya

In-pipe Wireless Micro Robot

An in-pipe microrobot which moves at 10 mm/s in a pipe of 15 mm diameter without power supply wire is developed. The robot consists of a microwave energy supply device, a locomotive mechanism using a piezoelectric bimorph actuator, and a control circuit. The energy supply device consists of rectifying circuits and a compact receiving antenna. The required energy of 200 mW is supplied via microwave without wire. 14 GHz microwave is rectified into DC electric energy at a high converting efficiency of 52%. The locomotive device of multi-layered bimorph actuator is newly developed and consumes only 50 mW. The control circuit consists of a saw tooth generator and a programmable logic device, and controls the direction of the robot motion by outside light signal.

Novel dead time controlled gate driver using the current sensor of SiC-MOSFET

In comparison with Si-IGBT, Silicon Carbide (SiC)-MOSFET is expected to reduce switching loss and conduction loss of low-current region, as well as to remove external Free Wheeling Diode (FWD). However, because SiC-MOSFET bodydiode has high forward voltage, the diode conduction loss increases in the period of the dead time and, as a result, its loss reduction effect by using SiC-MOSFET decreases. This work proposes a novel dead time controlled gate driver using the current sense transistor integrated with SiC-MOSFET. Proposed gate driver has a high responsiveness and a high robustness against the switching noise, the dead time can be shortened within 0.1μs without external components. In addition, it can consist with both the dead time control and the detection short-circuit current, which is the radical function in one current sensor. In the experimental validation result of 10kW boost converter with SiC-MOSFET, the efficiency with the proposed gate driver was 1% higher than the efficiency without it.

A Dead-Time-Controlled Gate Driver Using Current-Sense FET Integrated in SiC MOSFET

In comparison with silicon IGBT, silicon carbide (SiC) MOSFET is expected to reduce the switching loss and the conduction loss and to remove external freewheeling diodes (FWDs). However, its body diode has comparatively high forward voltage; therefore, the diode conduction loss generated during dead time increases. As a result, the loss reduction by the use of the SiC MOSFET can be weakened. This paper proposes a simple dead-time controller integrated in an isolated gate driver in order to reduce the diode conduction loss during the dead time. The proposed method has high speed and high robustness against switching noise by using of a current-sense FET with small parasitic capacitance. As a result, the diode conduction time can be shortened within 0.1 μs. In addition, the proposed dead-time control method can be achieved by existing components, including the current-sense FET, which is currently used for short-circuit current detection in hybrid vehicle applications. The proposed method was applied to a 10 kW boost converter with SiC MOSFET. The experimental results showed 1% higher efficiency of the converter with the proposed dead-time-controlled gate driver compared to that without dead-time control circuit, and the efficiency was the similar level as when a SiC Schottky barrier diode (SBD) was used as FWDs.