Overview of Bearingless Induction Motors

Table 1

Comparison of control strategies.

	Advantages	Disadvantages	Techniques
VC	Realizing easily; no special requirements for hardware and software	Causing coupling between two sets of the windings	Generating the current control signals using the feedback and coordinate transformation
IC	Achieving IC of radial suspension force, and hence improving the flexibility of torque control scheme	Requiring additional magnetic flux observer	Obtaining the torque winding flux linage dependently
DTC	Fast torque response; less parameter dependence; no need for current control	Causing errors due to variation of stator resistance and drift in flux linkage estimation	Generating the voltage vectors using independent torque and flux computations
NDC	Flexible control algorithms; adapting nonlinear theories and parameter variations	Requiring sophisticated hardware and intensive computation or experiential knowledge	Taking advantage of neural network or other nonlinear theory
SC	Removing the mechanical sensors, and hence reducing the system cost and size; readily merging into other controls	Requiring sophisticated hardware and intensive computation	Estimating the position and displacement based on the motor mutual inductance