Experimental Verification of a Model-Based Zero and Low-Speed Angle Observer for Bearingless Permanent Magnet Machines

Bearingless machines are used for a variety of applications with demand for low mechanical loss, low wear and low contamination. These machines use contact-free magnetic suspension to levitate the rotor. The control of the machine requires precise radial and angular position information in order to ensure stable levitation. This informa- tion is usually obtained with two types of sensors: radial displacement sensors and angle sensors. Alternatively, an angle-sensorless control scheme can be used, reducing the complexity and the cost of the machine. While such a control is well known for conventional machines it is challenging to adapt it for bearingless machines. The reason is that most methods fail to provide the angle information at zero- and low-speed but bearingless machines require knowledge about the rotor angle at all speeds in order to function. The theoretical mode of operation of a model-based angle observer for zero- and low-speed operation of a bear- ingless machine was shown in previous publications. The observer obtains the rotor angle estimation error by analyzing the performance of the radial bearing and comparing it to the performance of a model with zero angle error. This observer can be used at zero- and at low-speeds. This paper provides a more detailed description of the non-idealities of the zero- and low-speed observer and presents new results of machine operation without angle sensors. The generation of torque and force inside the machineisanalyzedinmoredetail. Theexperimentallyverifiedresultsofthispaperindicatethatthenovelobserver can be used up to speeds at which back-electromotive force estimation is possible.