This paper describes a new configuration and control method for an uninterruptible power supply (UPS) with a bidirectional cycloconverter. When commercial AC power is operating normally, the load is supplied by commercial AC power and the bidirectional cycloconverter operates as a battery charger. During interruptions of commercial AC power, the bidirectional cycloconverter operates as an inverter and supplies AC power to the load. Unlike a conventional UPS, this new configuration does not require a battery charger, so it can be small, light-weight, cost-effective, and highly efficient. The output voltage characteristics and the transient voltage drop in the output when commercial AC power fails are also discussed by numerical analysis and experiments.

This paper describes power feed techniques for telephone subscribers in a metallic two-wire digital subscriber loop system and optical fiber subscriber loop systems. In a metallic two-wire digital subscriber loop system, Digital Service Unit (DSU) and Digital Telephone (DTEL) are installed on the subscriber premises. The power consumption of the equipment increases compared with that of the conventional analog telephone. Therefore, it is difficult to feed sufficient power to the equipment using a conventional 48 V constant-voltage power supply. A constant current power feeding method from the central office is suitable because constant power can be obtained with little energy loss. A small-size and low-cost constant current converter has been developed. In optical fiber subscriber loop systems, it is difficult to feed the customer's equipment with power from the central office. Therefore, an uniterruptible DC power unit has to be installed on the subscriber's premises. The power unit is composed of sealed lead-acid batteries and a multi-input converter which has rectifier and DC-DC converter functions. This converter is very small and low-cost. The life of a sealed lead-acid battery can be prolonged by coating the outside of the battery container with aluminum or fluoric-resin film, and by optimizing the calcium content in the electrode grid alloy.

A distributed power supply system with highly efficient characteristics has been developed to replace conventional centralized power systems in telecommunications offices. In this system as in conventional centralized power systems, a stand-by energy system composed of batteries and engine-generator sets is used as a back-up system for the commericial power lines. However, the distributed power system, except for the engine-generator set, is installed in the telecommunications room. Thus, the floor load limitation is an important design factor. This paper describes a stand-by energy system design that considers floor load conditions and is based on reliability analyses. These analyses show that the distributed power system should be designed as follows: (1) Using a fully duplicated engine-generator set. (2) With battery reserve time reduced to one sixth that of conventional centralized power systems. (3) With transfer switch unavailability designed to be less than one half of the existence switch unavailability.