­AC-DC Conversion

AC-DC conversion, as the name suggests, converts AC voltage to DC voltage, which is rectified and smoothed to generate DC voltage. Rectification can be classified into full-wave and half-wave rectification. Rectification can be classified into full-wave rectification and half-wave, in which full-wave rectification uses both positive and negative AC, and half-wave rectification uses either positive or negative AC. We develop the conversion to achieve a constant DC voltage without disturbance.

­DC-AC Conversion

DC-AC conversion converts a DC voltage into an AC voltage by using a semiconductor device and controlling its on/off to generate an AC voltage. In power conversion, PWM (Pulse Wide Modulation) signals with pulse widths corresponding to on/off times are often used as control signals.

The AC Drive/inverter converts AC voltage to DC voltage through a rectifier circuit and performs reverse conversion to convert the DC voltage to any AC voltage and frequency. During the reverse conversion, conversion losses, such as conduction losses due to the internal resistance of the semiconductor device and switching losses due to switching delays, result in lower conversion efficiency. We develop switching control technology and new device application technology to reduce this conversion loss, leading to higher efficiency and smaller AC Drives/inverters.

Cooling Technology

Since the conversion loss of power semiconductor devices causes heat generation and is a bottleneck in the miniaturization of AC Drives/inverters, it is necessary to have a cooling mechanism that takes heat generation into account. From the equipment’s thermal design stage, we analyze the temperature and airflow distribution of the casing and the substrate by simulation and develop technologies to optimize and miniaturize the cooling structure without making prototypes.

Noise-Resistant and Harmonicless Technology

Since power conversion involves a large amount of power to handle and noise to be generated, anti-noise measures are particularly important to reduce the impact on other electronic devices. EMC (Electro Magnetic Compatibility), which does not harm the electromagnetic environment caused by noise from electronic devices and does not affect the system, uses shielding and filters as countermeasures. Power conversion generates harmonics due to current distortion. As a countermeasure, it is a common practice to add reactors that block the current by coiling the wires. A matrix converter, a type of AC Drive/inverter incorporating our proprietary technology, does not convert to DC; hence, the current is almost the same sine wave as the commercial power supply and is harmonicless.

New Device Usage Technology

Power conversion started with the use of thyristors. Today, power MOS FETs (metal-oxide-semiconductor field-effect transistors) and IGBTs (insulated-gate bipolar transistors) are widely used. In recent years, wide bandgap semiconductor devices, such as SiC (silicon carbide) and GaN (gallium nitride), too, have attracted attention because of their faster performance, higher breakdown voltage, and high-temperature operation. Wide bandgap semiconductors require a large transition energy from the valence band to the conductor. We conduct R&D on the application of these devices because they can be made in smaller sizes and are more efficient than conventional silicon semiconductors.