This paper describes the dead angle and transfer characteristics of the feedback control circuit in a magnetic-amplifier-controlled DC-DC converter. The dead angle occurs depending on the inductance in the saturable core after saturation and the recovery time in the rectifier diode. It is necessary to select a suitable combination of core and diode because recovery time in the diode varies according to the inductance in the core after saturation. An amorphous core and a Schottky diode is the most suitable for obtaining a small dead angle. When the saturable reactor cores are varied, the converter DC gain shows different values. This is because the DC gain is in proportion to the flux changing rate in the saturable core and the current gain in the control transistor. Combining a control transistor with a large current gain and an amorphous core with a large flux changing rate effectively increases the DC gain. A core of large cross-sectional area and small magnetic path length effectively increases the control gain. The results will be very useful in designing converter control circuits.

This paper describes configuration and operation of a high-frequency link resonant inverter using cycloconverter techniques. In this inverter, a resonant link high-frequency voltage generated in a primary resonant inverter is isolated by a high-frequency transformer, then directly converted into a resonant link low-frequency voltage in a cycloconverter. The switching losses and surge voltage levels can be reduced by making all switches in the primary inverter and the cycloconverter operate at zero voltage. The relationship between characteristic impedance of the resonant circuit and the conversion efficiency, and the distortion factor characteristics of the output voltage waveforms are discussed by comparing of analytical and experimental results.

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.

Heat recovery methods and the amount of heat that can be recovered from fuel cell exhaust gas is described. The cooling performance of an absorption refrigerator that uses fuel cell waste heat is also described. Two heat recovery methods from the exhaust gas are considered: one uses heat recovery from mixed exhaust gas from the cathode side of the cells and the reformer (mixed type); the other uses separate heat recovery from these sites (separate type). Simulation shows that the amount of heat recovered between 60 and 75 with the separate type of heat recovery is greater than with the mixed type of heat recovery. The cooling capacity of the refrigerator using the separate type heat recovery and recovering heat between 65 and 85 is about 2.5 times that of one using a generator (heat source) with a constant 85 temperature.