Stable positioning of bearingless induction machine under temperature variation

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In recent years, developments of bearingless drives are undergoing several parts of the world. The bearingless drives are the electric motors or generators with self-magnetic suspensions. Thus, there is increasing expectation of wide range of applications such as vacuum, low or high temperature conditions, harsh environments, long life and highly reliable machines. In fact, extensive developments can be seen in artificial heart blood pumps, canned pumps in chemical plants, semiconductor processes, bio reactors in bio engineering, telescope positioning in space satellitesThe investigators have been done notable research in induction type bearingless motors. A control method to suspend a rotation shaft at rated load torque has been made obvious. However, there exist a possible problem of touch down of the shaft under temperature variations of a rotor resistanceIn this research, magnetic suspension is found to be unstable is flux vectors have phase differences when rotor resistance reference value has discrepancy with respect to the actual rotor resistance. To avoid this problem, on-line estimation method of the rotor resistance is proposed. In the proposed method, a unique bearingless magnetic suspension feedback signal is used. In order to suspend a shaft weight, a static radial force is required, thus, radial force commands automatically generated in feedback loops to cancel the static force. Information of radial force command is employed to find the rotor resistance value. In addition, temperature drift in gap sensors are extensively compensated to realize practical system setup