Akihiko Iwata

Investigation of gate voltage oscillations in an IGBT module under short circuit conditions

The gate voltage oscillations in IGBT modules under short circuit conditions were investigated. In IGBT modules containing two chips in parallel, the amplitudes of the gate voltage oscillations were considerably larger than those in modules with single chip configurations. To investigate the gate voltage oscillations, a small signal analysis was performed on parallel circuits containing two IGBT chips. The gate voltage oscillations in parallel chips configurations could be described by a feedback amplifier model. The results of this analysis showed that a high resistive impedance between the gates of the two chips in parallel and a low inductance between their emitters were effective in suppressing the gate voltage oscillations. These effects were confirmed by experiments.

Novel low loss active voltage clamp circuit for series connection of GCT thyristors

This paper describes novel low loss active voltage clamp circuits for the series connection of GCT thyristors. For high-voltage converters the series connection of power semiconductor devices is an essential technique for direct switching of high voltages. Several protection circuits have been applied to the series connection of GCT thyristors such as CRD snubber circuits which suppress overvoltages across GCT thyristors, and voltage balancing resistors to equalize voltage sharing in steady states. However, significant losses in these protection circuits lower the converters efficiency. The authors propose a novel low-loss protection circuits, which have active voltage clamp snubber circuits and static voltage balancing circuits. The clamp capacitor voltage of the active voltage clamp snubber circuits are designed to be higher than the equally divided DC-link voltage. This method can reduce the loss of the clamp circuit to no more than 1/10 of that of the conventional CRD snubber. Also the static voltage balancing circuits compensate for the voltage imbalance generated by the difference in the leakage current between the series connection GCT thyristors.

A new voltage sag compensator with a gradationally controlled voltage inverter

A newvoltage sagcompensator withagradationally controlled voltage inverter whichexceeds SEMI F47standard hasbeendeveloped. Itconsists ofagradationally controlled voltage inverter inwhich inverters areconnected inseries andarecharged atdifferent voltages toeachother, andwhichoutputs thesumofeachoutput voltage. Thissystem issmall andwith anextremely lowloss.

Development of current by-pass circuit of series connection current drive device

This paper has proposed a self-turn-on type current by-pass circuit which is a new circuit method. The main circuit current can continuously flow in this circuit, even if several of the current drive devices connected in series are open due to breakdowns. The composition, operation, and the circuit design method of the proposed circuit have been described in detail. Moreover, the method of constructing a simulation model of the fuse, which is an element of the circuit, was described. Moreover, the proposed circuit was simulated using that fuse model, the circuit constant was set, and the circuit operation was confirmed. As a result, a circuit that operated without increasing the MOSFET loss was achieved. Moreover, the proposed circuit was constructed for trial purposes, and a current by-pass examination when the diode was opened was executed. As a result, it was proven to be able to pass a current of 60 A continuously even when the diode was open.