Acquisition of rotor anisotropy signals in sensorless position control systems

Sensorless position control of induction motors relies on the detection of rotor anisotropies. The repetitive transient excitation through the switched voltages of the PWM inverter provides the test signals to identify the spatial orientation of the anisotropies that indicate the rotor position. The position information is contained in the inverter output voltages. These are measured against the neutral point of the star connected stator winding. The signals are heavily corrupted by disturbances. These originate from the propagation of travelling waves on a long motor cable and from the influence of high-frequency common mode currents. The paper describes how a clean position signal is extracted in the presence of such noise.