Module-type switching rectifier for cathodic protection of underground and maritime metallic structures

Cathodic protection is widely used to prevent corrosion of steel materials buried underground and in seawater. As a rectifier for cathodic protection, the conventional phase-controlled rectifiers with 50- or 60-Hz isolation transformers have been used so far in spite of such shortcomings as large volume, heavy weight, and poor power factor. In order to overcome such disadvantages, this paper proposes a new module-type switching rectifier for cathodic protection, which is composed of two parts, namely, ac/dc converter and module-type dc/dc converter. The ac/dc converter is a single-phase insulated gate bipolar transistor pulsewidth-modulation rectifier, thus resulting in almost unity power factor and controlled dc output voltage. The module-type dc/dc converter operates under zero-voltage switching/zero-current switching condition to permit high-frequency switching operation. It enables the use of a high-frequency transformer for electrical isolation, thus reducing volume and weight of the overall system and improving system efficiency. It is anticipated that the proposed rectifier techniques will apply to the similar technical areas such as multiple-module power supply systems and modular converter-fed dc motor drives.