Sensorless field oriented control of multiple-motors fed by multiple-converters systems

On Multiple-Motor systems fed by Multiple-Converter systems a set of electric motor drives share the load through a common mechanical coupling. Such a coupling is exploited in this paper to realize a sensorless field oriented control, based on a quite common back-emf technique to estimate the rotor flux angular position and an original approach to correct the estimation errors. The technique is based on the injection of very low frequency, sinusoidal signals on the current references of one of the motor drives. If the estimated rotor flux position is correct, the drive output torque does not show variations. Differently, if the estimation is incorrect, a torque ripple is generated at the frequency of the injected signal, whose effects on the system speed are easily compensated by the main speed controller. However, due to the mechanical coupling, an additional component of the reference torque current at the frequency of the injected signals is generated on all the other drives. By minimizing this component, the rotor flux position estimation can be effectively corrected, as well as errors in estimating the stator and rotor resistances.