A technique for stator-resistance-based thermal protection suitable for a low-cost vector controlled induction machine drive is suggested in this paper. In order to provide accurate stator resistance monitoring at medium and high speeds the dc-signal-injection based method is selected. The main property of the scheme is that small regulated DC current is periodically injected in the stator windings without interrupting the flux and torque control loops. In the proposed scheme inverter nonlinearities are properly compensated and accurate resistance estimation is achieved with minimal level of injected DC current. This results in consistent and controllable torque ripple, which is minimal and constant for any actual stator resistance value. Estimated stator resistance can be also used for control algorithm tuning. The method is implemented in fixed point microprocessor and tested on low cost shaft-sensorless induction machine drive under various operation modes.
This paper presents a novel algorithm for the induction motor torque control in field weakening region. Proposed method insures maximum DC bus utilization and extends the torque-speed curve up to the system limits. Controller is based on the stator voltage angle control. It provides full DC link disturbance rejection and offers the torque response time sufficient for most applications. The algorithm is simple, without the outer flux loop nor the inner current loop. Dynamic response is preserved over wide speed range by means of gain-scheduling. Simulations and experiments prove an ease of implementation and the robustness of the proposed solution. The paper comprises analytical considerations, simulation results, a detailed description of implementation steps and extensive experimental results.
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