Dynamic Response of FOC Induction Motors Using MTPA Considering Voltage Constraints

Maximum torque per ampere (MTPA) strategies are aimed to improve the efficiency of induction motor (IM) which regularly operate at low load levels. However, these strategies penalize the dynamic response due to the need to remagnetize the machine when torque must be increased. Dynamics of torque during remagnetization are strongly conditioned by current constraints, as well as by voltage constraints when the machine operates at high speeds. Once torque dynamics must be limited, torque during remagnetization process can be profiled to follow a ramp to reduce jerk. It is needed in this case to determine the minimum settling time (maximum slope of the torque ramp) achievable by fully exploiting the current limits of machine and inverter. Furthermore, when remagnetization occurs at high speeds, current regulator will be subjected to voltage constraints. This paper deals with the selection of overmodulation strategies during the remagnetization process, with the aim of guaranteeing proper operation of the current regulator under severe voltage constraints.