Effects of machine asymmetry on a two-machine direct torque controlled induction motor drive

This paper is concerned with the controller-driven interactions between the induction motors of a single-inverter, two-machine direct torque controlled drive system. The main control strategies used for such a drive system are the Master-slave (MS) control and the Mean control. The performance of these control methods can get affected by the inherent asymmetries in the induction machines. A commonly occurring example of asymmetry is a stator winding turns short circuit fault. In a two-machine system, since both machines are connected to a common inverter, a fault in one machine affects the performance of the other machine through the drive control system. A detailed comparison of the machine interactions which take place in two-machine drive systems controlled by the MS and Mean control methods is done considering a situation where there is a stator inter-turn fault in one of the machines. An experimentally validated dynamic model of an induction machine with stator faults is used to analyse these interactions. The machine interactions are also studied for the case in which the load on the two machines is different. The paper presents a detailed analysis and experimental results of these machine interactions, in the steady state.