A universal-phase rectifier architecture for rural telecom exchanges in developing countries

This paper describes a complete power plant architecture for rural telecom exchanges where grid power is unreliable. Telecom power plants are three phase rectifiers with isolated DC outputs which convert the grid AC input to a 48 V DC supply. In developing countries, significant power outages are experienced in rural and semi-urban areas. In these places, the power from the grid can be available in form of one, two or three phases during a day. The currently used power plants are not designed to handle this variation in input phases. Significant design effort is required to restructure the architecture of this power plant to solve this problem. In this paper, a simple approach is proposed to handle this situation. Currently used power plants have a rectifier followed by an isolated DC-DC converter. It is proposed that, a four leg diode bridge can be used instead of a three phase rectifier. The use of a four-leg bridge leads to automatic selection of active input phases without the need of any extra phase selection circuitry. The technique is easy to adapt in the currently used topologies. In order to reduce the voltage swing to subsequent isolated DC-DC stage, a clamped boost or buck stage is proposed. The resulting architecture has an operational input voltage between 90 V (rms) during single phase to 480 V (rms) during three phases. Passive power factor improvement techniques in form of, Ziogas filter, are used to improve the power factor. The complete topology of the power plant and its operation are explained in detail. The proposed system is verified using a 1 kW prototype.