Analysis of Unbalanced Dual Induction Motor Drive Configuration Supplied by Single Inverter for Parameter Estimation

Parallel supply of two induction motors by a single inverter is nowadays a mature technology that has several industrial applications, such as railway. Under ideally symmetrical FOC at equal mechanical speed, both motors draw the same current and produce the same torque and flux. However, parameter deviations, in particular stator resistance, can arise due to several factors, such as temperature variations or inappropriate cable contacts. This leads to a complex distribution of the current vectors, flux vectors and torque distribution between both motors, which strongly depends on the actual torque and speeds. In this work, the resulting asymmetrical flux and current sharing under non-identical dual motors will be analysed and further investigated for the purpose of parameter estimation. It will be proved that the stator current vector as well as the rotor flux vector, in both magnitude and angle, provide relevant information about the stator resistance in the proximity to zero speed operation. Simulations are presented to demonstrate the effect of stator resistance variations on current and flux sharing for non-equal parameter dual motors under average FOC. An experimental test bench with two unequal motors is presented. Experimental results prove the meaningful information that current vector and flux vector contain about the different stator resistance of the two machines.