Virginia Manzolini

Performance achievable in sensorless control of electrical drives strictly depends on the adopted synchronous machine. The combination of cross-saturation and saliency, both dependent by the current load and the rotor position, makes always the position estimation afflicted by an estimation error. When the machine is highly saturated, the sensorless control can even diverge resulting in a useless drive. Thus, it is of primary importance to know in advance the convergence region of the sensorless drive, i.e., the operating points, where the motor can be successfully controlled without a position sensor. The aim of this article is to show how to compute the estimation error, the saliency, and the convergence region (hereafter called self-sensing capabilities) starting from the flux linkages maps or, more generally, from the incremental inductances. The dependence on the rotor position is also considered. Finite element simulations and experimental measurements validate the proposed model. The code used to compute the self-sensing capabilities is available as an open source package.

Iron saturation affects the low-speed and standstill rotor position estimation of synchronous motors based on high frequency voltage injection, leading to an estimation error. In the case of a heavily saturated machine, the estimation algorithm could even fail, due to the absence of convergence points, making the sensorless drive impractical. This paper examines in depth the mentioned problem of convergence in salient rotor machines; a synchronous reluctance motor is assumed as case study since this kind of machine is considerably affected by iron saturation. At first, the paper models and describes in detail the high frequency voltage injection estimation mechanism. Then it analyses the convergence conditions and investigates the dependence of the estimation convergence range on the amplitude and phase of the reference current vector of the drive. Moreover, it proposes different methods to enhance the estimation convergence range, improving the accuracy as well. A comparison between the different approaches is given as well as hints for their design. At last the impact of airgap space harmonics is pointed out. The results are validated by simulations and experimental tests.

This paper deals with the design and evaluation of a short-circuit rotor-ring for enhanced self-sensing capability in a 2-pole slotless permanent-magnet motor. High-frequency rotor anisotropy is enabled by adding a short-circuited rotor-ring. Optimal ring-dimensions are determined by parametric numerical studies. An effective high-frequency saliency of up to 1.8 is demonstrated. The steady-state estimation error is within 2%, practically unaffected by load (current) level due to the large effective air-gap. The proposed observer performs properly also during dynamic load changes. Fall-times from 3000 to 0 rpm in less than 50 ms with negligible overshoot are demonstrated. In contrast to slotted self-sensing electrical machinery, the examined slotless machine exhibits negliglible impair of angular estimation error with load. Also parasitic effects such as power losses, heating and torque ripple are analyzed.

A synchronous reluctance motor drive exhibits an inherent unlimited speed range capability, in fact the maximum speed of this kind of machine is bounded only by mechanical limits. In order to exploit this peculiar characteristic of the drive while assuring the lowest power losses, a proper control algorithm has to be used. In particular, while the working speed is increasing, the control must be able to command the reluctance motor under the maximum torque per ampere condition at first, into the flux weakening region, and then on the maximum torque per voltage trajectory. To this purpose, a novel voltage control loop is presented in this work. It is combined with a field oriented current control and profitably exploits a polar coordinate representation of the current reference to operate the reluctance machine in compliance with current and voltage rating constraints in all the dierent operating conditions. Additional merits of the proposed scheme are the ease of implementation and the simple design. The stability of the proposed control algorithm is proved through a small signal analysis and simulations and experimental tests confirm its effectiveness.

Sensorless control schemes are object of great interest in the synchronous motor drives field. They permit to avoid the use of position sensors in the system, allowing several benefits. In this paper a sensorless control scheme is proposed for low speed or standstill operation of a synchronous motor drive, characterized by a rotor anisotropy. The method is based on a high frequency voltage injection in the stator motor windings. High frequency current response to this injection is obtained from the measured currents thanks to a high pass filter. These filtered currents describe an ellipse trajectory, that is deeply analysed considering all its components. In particular, ellipse major semi-axis tilt is related to the rotor position. A recursive least squares estimator is proposed for the ellipse equation coefficients identification. After some manipulations, the rotor position is extrapolated from these information.