Silva Hiti

IPM synchronous machine drive response to a single-phase open circuit fault

This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical dq-transformation techniques. This paper presents a new dq synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of q axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated: (1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter DC link via the antiparallel diodes; and (2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.

Output selection for tuning of field oriented controllers: steady state analysis

This paper presents the use of local sensitivity analysis techniques to study which output signal of several proposed in the literature can lead to better performance of on-line tuning for rotor time constant variations using model reference adaptive control (MRAC) in indirect field oriented control (IFOC) of induction motors. The expectation is that the output with the highest sensitivity to rotor time constant should be the more suitable for IFOC controller MRAC tuning. We derive the output relative sensitivity functions for steady state operation for active power, reactive power, electromagnetic torque, and the ratio of reactive power and torque to rotor time constant and study their variability as a function of slip frequency. The relative sensitivity functions are used to study their usefulness for rotor time constant tuning. No signal can give uniform satisfactory sensitivity properties over the full range of machine operation. Suggestions are given on how to tackle this issue.

Optimum Current Control in the Field-Weakened Region for Permanent Magnet AC Machines

This paper presents current regulation algorithm for permanent magnet AC machines that provides smooth transition in the entire field-weakened region. The algorithm offers robust and simple current regulation with maximum torque capability for permanent magnet AC machines despite significant changes in the voltage source and machine parameters. The algorithm identifies when the machine enters field-weakened region and determines the optimum d-axis and q-axis current command for the machine. In addition, the algorithm identifies when the machine reached the maximum torque per flux and it regulates current accordingly. Simulation and experimental results are presented, which prove the algorithm functionality.