Abstract: A transfer of power between an energy storage device and a load is controlled by obtaining a DC voltage from the energy storage device, and controlling a phase angle of AC power delivered to the load to keep the DC voltage substantially constant. The phase angle of the AC power is controlled by controlling a current component of the AC power.

Abstract: This device for converting a very-low-amplitude steady voltage signal into an alternating voltage signal, of the type comprising a centre-tapped transformer (1) associated with a transistor (3,4) chopper (2), is characterised in that the transformer (1) and the transistors (3,4) are arranged in a housing (15) held at very low temperature and in which is arranged a material (20) for thermal insulation of the transistors (3,4) with respect to the rest of the housing so as to reduce temperature fluctuations and allow operation of these transistors by self-heating due to their drive current.

Abstract: The disclosed substance has a general chemical formula of La.sub.2 -Cu.sub.1 -O.sub.z, z being 3.84 to 4.00. The disclosed substance shows, at a temperature below 20.degree. K., superconductivity, either potential or real, and the substance also shows, at a temperature below 30.degree. K., superconductive photoconductivity in response to incident exciting light in a wavelength range of 420 to 640 nm. The substance is produced by heating a mixture of starting material therefor at 900.degree.-1,050.degree. C. for 5-10 hours to cause solid state reaction, cooling gradually, shaping under pressure, re-sintering at 700.degree.-1,200.degree. C., and cooling either quickly at a rate of 2,000.degree.-900.degree. C./sec or slowly at a rate of 150.degree.-200.degree. C./hour.