Fabio Tinazzi

Energy-Efficient Autonomous Solar Water-Pumping System for Permanent-Magnet Synchronous Motors

This paper presents a novel stand-alone solar-powered water-pumping system, especially suited for usage in rural or remote areas. The system is primarily designed to reduce both cost and complexity, while simultaneously guaranteeing optimal utilization of the photovoltaic generator. The use of standard hardware and control architectures ensures ease of installation, service, and maintenance. The proposed solution consists of a water pump driven by a permanent-magnet synchronous motor, controlled by a conventional field oriented control scheme. The photovoltaic array is directly connected to the dc bus of the inverter, with no intermediate power conversion stages. A perturbation based extremum-seeking controller adjusts the motor speed reference to attain the maximum power point operation of the photovoltaic array. Both simulations and experimental results on a full-scale prototype support the effectiveness of the proposed system.

Benefits of Direct Phase Voltage Measurement in the Rotor Initial Position Detection for Permanent-Magnet Motor Drives

This paper shows how the problem of estimating the initial rotor position in permanent-magnet sensorless drives can benefit from the availability of a direct measurement of motor phase voltages. Two different estimation methods are presented for this purpose. The first is a readjustment of a classic procedure based on the detection, by means of the injection of voltage test pulses, of inductance variations due to motor saliencies, from which it is then possible to infer the position of the rotor. Since the application of irregular test pulses may increase the estimation uncertainties, the available voltage measurement is exploited to implement a closed-loop amplitude control of the test pulses. The second method is introduced both to overcome an issue related to the digital measurement approach adopted in this paper and to allow position estimation even in a motor with no relevant saliency, a case for which the first method is inappropriate. The effectiveness of the proposed solutions is validated by several experimental tests, which are carried out on two motors with different saliency properties.

Torque Estimation in High-Efficency IPM Synchronous Motor Drives

In modern electrical drives, the energy saving starts with the careful generation of the electromagnetic torque, which involves the electrical motor and its current control. A modern choice is represented by an anisotropic synchronous interior permanent magnet (IPM) motor combined with the maximum torque per ampere (MTPA) control technique. The MTPA locus brings along additional information that is worth deepening. In particular, this paper shows that a proper rearrangement of the torque expression in MTPA condition, merged with a simple least-square algorithm, returns an accurate online estimation of the electromagnetic torque. The effectiveness of the proposed method is proved by a worked out example, based on an IPM drive model fitted with finite-element analysis and experimental measurements, including motor saturation effects. The torque estimator extends its usability in the whole working region of the drive, even during transients outside the MTPA curve, and it comes almost for free. In this, the proposed method should be technically sound in many industrial applications.

Estimation of the direct-axis inductance in PM synchronous motor drives at standstill

The call for human mobility reduction pushes research in electrical drives towards the implementation of efficient self-commissioning procedures. As a preliminary and crucial step, an accurate estimation of motor parameters is necessary. As a part of a process of careful review of existing and often either rough-and-ready or bulky estimation methods, this work copes with the light and precise estimation of the direct flux linkage in permanent magnet motors at standstill. The estimation is based on multi-sinusoidal signal injection, and signal post-processing through Goertzel algorithm, for the sake of very low computational complexity. The procedure considers both iron losses and saturation effects. A set of experimental results show the feasibility of the method, while the comparison with finite element analysis confirms the accuracy of the estimation.

Energy efficiency measurements in IM: The non-trivial application of the norm IEC 60034-2-3:2013

Adjustable speed induction motors (IMs) drives based on voltage source inverters (VSIs) have become rather popular and widespread, owing to their capability of enabling a substantial improvement of energy utilisation, compared to fixed speed motors directly connected to the main supply. Since inverters produce additional losses in the drive, some concerns about the determination of the overall energy efficiency of the system obviously arise. Therefore, a proper method to assess the efficiency of VSI-fed IMs in a systematic and standardised way is becoming mandatory. To fulfil this task, the IEC 60034-2-3 Technical Specification has been recently issued. However, many details are still under definition, due to the manifold aspects of a standardised measurement procedure, such as the inverter topology, the DC bus input voltage level, the output voltage amplitude and frequency and the modulation technique. Therefore, in its current form, the specification cannot be considered a straightforward and ultimate answer to the efficiency measurement. In this paper, some problems regarding the application of the new IEC 60034-2-3:2013 are addressed and some possible solutions are proposed. As a tangible contribution, a proposal for the structure of an automated energy efficiency measurement procedure is provided as well.

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.

Enhanced low-speed operations of back EMF-based sensorless anisotropic PMSM drives

Under the thrust of the increasing demand of energy-efficiency and reliability, sensorless permanent magnet synchronous motor drives are showing compelling advances. The presence of a salient magnetic structure (anisotropic rotor) reduces the presence of magnets and it is fundamental for operations at zero and very low speed, obtained by injecting and processing high frequency signals. But the excitation signals cause unwanted torque ripple, noise and vibrations. This work deals with the lowering of the lower speed limit, above which the estimation techniques can work without any signal injection. Specifically, the proposed method mitigates the instability problems of back electromotive-based observers when the drive operates in generating mode. The speed and position estimates are based on a modified phase locked loop observer. It trusts on direct phase voltage measurements, even if it works also with standard compensated reference voltage signals. An accurate laboratory measurements campaign, focused on showing the injection-free speed range improvements, is included in the paper.

Advanced self-commissioning and feed-forward compensation of inverter non-linearities

Accurate compensation of inverter non-linearities is highly desirable especially in high performance drives where a perfect correspondence between reference voltages and real output voltages is required. In this paper a self-commissioning procedure able to determine each contribute to the overall output voltage distortion and save it to a Look-Up Table (LUT) is described along with a detailed theoretical analysis of the different causes and effects of each non-linearity. The procedure is based on Sine-Triangle Pulse Width Modulation (ST-PWM), requires two additional relays and can be carried out autonomously by an inverter controller. A feed-forward compensation approach based on the extracted data is proposed for ST-PWM and for Space Vector Modulation (SVM) techniques. The feasibility and effectiveness of the proposed solution are demonstrated by experimental results.

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.

A novel approach to torque estimation in IPM synchronous motor drives

Environmental-friendly technologies are growing up fast and they are getting more and more attention. In such a scenario, Interior Permanent Magnet (IPM) synchronous motors have all the peculiarities to satisfy the drive efficiency requests. So far, techniques like the Maximum Torque-per-Ampere (MTPA) were a stimulating field of research, because of the great results in term of energy savings. The MTPA locus brings along additional information that is still worth deepening. A proper rearrangement of the torque expression in MTPA condition, obtained by describing the q-axis flux linkage by a polynomial approximation, merged with a simple least-square algorithm, returns a fast and accurate on-line estimation of the electromagnetic torque. The effectiveness of the proposed method is proved by a worked out example, based on a IPM drive model fitted with finite-element analysis and experimental measurements, and including motor saturation effects.