STABLE OPERATION OF INDUCTION-TYPE BEARINGLESS MOTORS UNDER LOADED CONDITIONS

A control method, which realizes stable operation in induction-type be aringless motors under loaded conditions, is proposed. Without a propo sed control method, both the amplitude and the direction of radial for ce vary in accordance with loads. These variations result in interfere nces of radial force commands in two perpendicular axes. The interfere nces become a serious problem as a load increases. A shaft finally tou ches down without proper compensations. It is found that a decoupling of the radial force commands can be realized with compensations of bot h amplitude and phase angle of four-pole motor current. A decoupling c ontroller is proposed with the principle of a field-oriented controlle r of conventional induction motors. The results of experiments show th e validity of compensations. It is shown that induction-type bearingle ss motors can be operated stably under loaded conditions, as well as t ransient conditions.