Ludovico Ortombina

Model Sensitivity of Fundamental-Frequency-Based Position Estimators for Sensorless PM and Reluctance Synchronous Motor Drives

Sensorless drives for permanent magnet (PM) and reluctance synchronous motors are quite interesting options in modern ac drives. Fundamental-frequency observers provide a rotor position estimate, to be used instead of that measured by delicate sensors. The estimation algorithms are based on either the extended electromotive force or active flux concepts. They feature easy implementation, although their reliability may be undermined by both corrupted measurements and parameter variations, especially in the case of anisotropic rotor structures. Through an analytical sensitivity analysis, this article investigates the influence of model uncertainty on the observed position. The substantial relationships between cause (parameter uncertainty or measurement error) and effect (position error) are validated by experimental results, which also highlights the effects of the q-axis inductance and resistance values on the electric measurement sensitivities. The resulting functions and graphic plots are useful to draw interesting considerations about the motor selection and the control design of the sensorless drive.

Comprehensive magnetic modelling of internal PM synchronous motors through radial basis function networks

The paper proposes the novel application of Radial Basis Function (RBF) networks to the magnetic modelling of any PM synchronous motor, with special emphasis on internal PM rotors. The advantages are the use of already available measurements, the precision and completeness of the continuous 2D model, which inherently includes all the nonlinearity and cross-coupling effects and that does not use any interpolation algorithm. The paper includes the theory of operation and experimental results, obtained on a laboratory prototype.

Model sensitivity assessment for sensorless PM and reluctance motor drives

Sensorless drives for permanent magnet and reluctance synchronous motors are an interesting option in modern drives. Modified observers, such as the ones based on extended electromotive force or active flux, are used to get a unified model of the motor. The fundamental frequency based observer is of easy implementation, although the reliability of the model is undermined by parameter variations and corrupted measurements, especially when anisotropic motors are adopted. This study aims at analysing the influence of all motor model uncertainties, by means of an analytical sensitivity analysis. The resulting functions and graphic plots are useful to draw interesting considerations about the sensorless drive, in terms of motor selection and control design.

Advanced current control of synchronous reluctance motors

The presence of rare-earth materials in permanent magnet synchronous motors has shifted the attention of the research towards the rediscovery of the synchronous reluctance motors. However, they present a highly nonlinear magnetic structure that makes the current control design a troublesome task. Standard proportional-integral controllers may fail in assuring the desired dynamic performances in the whole operating region. However, their simplicity is still attractive, when compared to other more complex controllers, such as the predictive ones. This paper aims at proposing two modified proportional-integral controllers tailored on the synchronous reluctance motors magnetic characteristics. At the heart of the process stands the knowledge of an accurate model of the motor. The design process is thus accurately described and both simulation and experimental tests are reported.

Online stator resistance tracking for reluctance and interior permanent magnet synchronous motors

In the frame of the green economy, anisotropic synchronous motors are gaining considerable shares of market. There are already several interesting proposals about the accurate magnetic modelling of their complex magnetic structure, that generally require the a priori knowledge of the stator resistance. It is true that there are many papers even about the resistance estimation, but quite surprisingly most of them either require the knowledge of other parameters or do not meet the specifications on accuracy and online tracking. Above all, existing injection-based techniques are oriented to isotropic motors and the injection is given as reference to the current component that is not involved in the torque production. The simple transfer to anisotropic motors would cause non-negligible torque ripple. This paper focuses a new method for the online estimation and tracking of the stator resistance, specially suited for anisotropic motors. The usual injection procedure is reversed, i.e. there is a current injection followed by a voltage measurement. It will be demonstrated that the method features a resistance measurement with the best signal-to-noise ratio, for a given torque ripple. The technique does not require the knowledge of any other parameter. The paper includes both the mathematical foundations and experimental results on a laboratory prototype.