Abstract: An inverter apparatus for driving a three-phase AC motor, having first and second arms each comprising plural parallel-connected transistors and plural parallel-connected diodes, is protected against overheating by detecting the composite current of the transistors and the composite current of the diodes in one of the first and second arms and determining the larger of the currents. The larger current, offering greater accuracy, is used to control the inverter. The apparatus is operative in either the regenerative or driving mode. Alternatively, a single detector can be used but the signal waves are clamped below a reference wave value.

Abstract: An inverter unit for driving a motor with multi-phased currents, each of the phases being derived from a.c. input voltages that are applied to respective input terminals, rectified and smoothed by capacitors before being applied to parallel-connected switching elements to develop each of the phased a.c. outputs. The capacitors may be connected in series and/or in parallel together with the switching elements. In order to reduce the effect of the distributed inductance contributed by the conductors used to connect the capacitances and switches, and thus the need for large snubber capacitances to compensate for the distributed inductances, the connectors are given a geometry and an orientation that causes the inductances to be minimized. Specifically, the conductors are of a bus-plate form, having a large area for improving heat dissipation, and an orientation so that the magnitude and direction of currents flowing through the bus-plates tend to minimize the effect of the distributed inductances.

Abstract: A sewing machine controller in which initially a rotation transfer ratio is calculated from the number of rotations of a motor and the detected number of rotations of the sewing machine shaft. Thereafter, the number of motor rotations is calculated as the product of the rotation transfer ratio and the desired number of rotations of the sewing machine.