Control for high momentary torque from vector-controlled induction machines

This paper assesses short-term induction motor torque capabilities and investigates field-weakening strategies to provide high momentary torque via vector controllers. Scalar controllers reduce voltage below the base speed to avoid magnetic saturation and do not completely utilize the available dc bus voltage. Vector controllers achieve decoupled control of torque and flux, and can use available dc bus voltage below the base speed without saturating the machine. Compared to maximum torque-per-ampere control, the study aimed to maximize momentary torque limited only by the dc bus voltage. Results for vector controllers show that field-oriented-controlled induction motor drives provide the highest peak torque capability at low speeds, whereas direct torque-controlled drives provide higher peak torque at high speeds. For the test machine, these controllers are shown to support up to 2.5 times the breakdown torque below a critical speed.