Kazuo Kuroki

Direct linked type frequency changer based on DC-clamped bilateral switching circuit topology

This paper describes a direct linked type frequency changer (hereafter called DLT-FC) proposed by the authors. The DLT-FC is a converter circuit with a new configuration for direct frequency change. The DLT-FC does not require a DC link circuit, nor bilateral switches. In addition, DC snubber circuits can be applied without the need for a regenerative circuit of snubber energy. Therefore, the DLT-FC can be designed to be compact and lightweight, and have a long life. The authors made a prototype of the DLT-FC and experimentally checked its operation. The results indicate that the performance of the DLT-FC makes it suitable for industrial use.

Power Transistorized Uninterruptible Power Supply

Rotary-type uninterruptible power supply (UPS) units, which were in extensive use in the past, have been superseded by static-type units using thyristor inverters. Application of power transistors in an UPS unit has been under study in an effort to attain higher performance and compactness. The output capacity of a transistorized UPS unit has been increased from 20 to 100 kVA by the development of a new power transistor, a new protective method, and a new control method. A reduction of outline dimensions has been achieved (the volume reduction rate claimed is 1-3.5), and an improvement of conversion efficiency (approximately five percent), etc.

Analysis and reduction of radiated EMI noise from converter systems

It is well known that high dv/dt rates on switching devices are the source of EMI noise. This paper describes a mechanism and reduction methods of radiated EMI noise on IGBTs. The radiated EMI noise is generated by oscillating current flowing through the IGBTs output capacity and the snubber circuit, which we call equivalent circuit of radiated EMI noise. The oscillating current of the equivalent circuit is forced to flow by high dv/dt rates of IGBT switching operation. Radiated EMI noise can be analyzed by frequency evolution of oscillating current. The results of this analysis show the relationship of high-frequency impedance of the equivalent circuit to radiated EMI noise, as well as the behavior of the IGBTs switching voltage waveform. In addition, it is indicated that using a di/dt control gate drive circuit is effective as a means for reducing radiated EMI noise. It is clarified that the standard for industrial equipment of CISPR can be satisfied by using the proposed gate drive circuit. The effects of the method have been verified by experimental and simulational results.

A novel gate drive circuit for low-loss system using IGBT saturation voltage characteristics

This paper proposes the new gate drive circuit for IGBTs to reduce the turn-off loss. The feature of the circuit is to drive an IGBT with plural gate resistors which were settled by the turn-off current levels. From the experiment and simulation results, the turn-off loss was cut to more than 50% in comparison with the conventional drive system.