Matteo Felice Iacchetti

Axial Flux PM Machines With Concentrated Armature Windings: Design Analysis and Test Validation of Wind Energy Generators

Some design and operation aspects of axial flux permanent magnet synchronous machines, wound with concentrated coils, are presented. Due to their high number of poles, compactness, and excellent waveform quality and efficiency, these machines show satisfactory operation at low speeds, both as direct drive generators and as motors. In this paper, after a general analysis of the model and design features of this kind of machine, the attention is focused on wind power generation: The main sizing equations are defined, and the most relevant figures of merit are examined by means of a suitable parametric analysis. Some experimental results obtained by testing a three-phase, 50-kW, and 70-rpm prototype are presented and discussed, validating the modeling theory and the design procedure.

Analysis and Test of Diode Rectifier Solutions in Grid-Connected Wind Energy Conversion Systems Employing Modular Permanent-Magnet Synchronous Generators

This paper deals with the ac-dc interface conversion in grid-connected wind energy conversion systems based on modular permanent-magnet synchronous generators. In particular, some solutions based on diode rectifiers are extensively analyzed as for the waveforms, the efficiency, and the torque ripple, by considering several connections, which are allowed by the inherent modularity of the considered generators. Rectifier schemes with a high number of pulses can be easily realized without using special shifter transformers so that these solutions can be attractive for low- and medium-power applications.

An MRAS Observer for Sensorless DFIM Drives With Direct Estimation of the Torque and Flux Rotor Current Components

This paper proposes a model reference adjustable system observer for the sensorless control of doubly fed induction machines. The formulation is based on the direct calculation of the torque and flux rotor current components in the stator-flux-oriented coordinates by using the stator currents and voltages and the norm of the rotor current space vector. The tuning of the observer is discussed, and a theoretical sensitivity and stability analysis is performed in order to investigate the behavior of the observer under mismatched parameters. The paper is completed by the experimental validation of the observer performances.

Effects of Mismatched Parameters in MRAS Sensorless Doubly Fed Induction Machine Drives

This paper deals with a performance analysis of sensorless drives based on doubly fed induction machines. A simplified model of the whole system equipped with a generic model reference adaptive system (MRAS) observer is introduced, by taking also into account a mismatch in the parameters. Three MRAS known in literature are analyzed in detail and meaningful analytic relations between the mismatched parameters and the error in the estimated rotor position during a steady-state operation are deduced. Then, a stability analysis is performed and the stability regions of each drive are found. Finally, the theoretical results are experimentally validated.

Adaptive Tuning of the Stator Inductance in a Rotor-Current-Based MRAS Observer for Sensorless Doubly Fed Induction-Machine Drives

This paper deals with the adaptive tuning of the stator inductance in a rotor-current-based Model Reference Adaptive System observer for the sensorless control of doubly fed induction machines. At first, the effect of mismatched parameters in this observer is discussed in order to show the considerable influence of the stator inductance on the accuracy of the estimated rotor position. Then, an adaptive tuning of the stator inductance is proposed and a small signal model is deduced in order to design the tuning loop. Moreover, a theoretical sensitivity and stability analysis is performed. Finally, the performances of the proposed scheme are experimentally investigated and validated.

Evaluation of Manufacturing Dissymmetry Effects in Axial Flux Permanent-Magnet Machines: Analysis Method Based on Field Functions

An analytical method is presented to evaluate the field and global quantities for the operation and design analysis of axial flux permanent-magnet (PM) machines. The method, of general applicability, is based on the definition and superposition of suited field functions, able to accurately model the different singularities of the studied device: PM field distribution, effects of slotting, and radial end effects. Selected explorative FEM analyses are used in order to investigate the field functions shape and to help in identifying their structure and parameters. Then, the flux density distribution is obtained, as a function of the rotor position, taking into account some manufacture dissymmetry effects, such as air-gap offsets and PM rotor disk inclinations. This approach allows to analyze the effect of dissymmetry on the circulation of current among winding parallel paths in no-load operation. Moreover, by using the Maxwell stress tensor, the stress distribution is evaluated, as well as the resultant axial forces and the bending torques on the shaft due to the rotor disk tilts. Several FEM simulations show the soundness of the proposed method, which exhibits high accuracy and great evaluation speed.

Stator Inductance Self-Tuning in an Air-Gap-Power-Vector-Based Observer for the Sensorless Control of Doubly Fed Induction Machines

This paper focuses on the improvement of an air-gap-power-vector-based observer for sensorless doubly fed induction generators. After showing how a mismatch in the machine inductances can worsen the performance of the basic observer scheme, an adaptive tuning of the stator inductance is proposed. The adaptation is achieved by minimizing the error between the squared modulus of two suitable air-gap complex power space vectors. A criterion to settle the dynamics of the adaptation mechanism is provided, and a sensitivity analysis in the steady-state operation is performed. Some experimental results are reported and discussed in order to validate the soundness of the proposed adaptive tuning algorithm.

An Observer for Sensorless DFIM Drives Based on the Natural Fifth Harmonic of the Line Voltage, Without Stator Current Measurement

This paper proposes an observer for the sensorless control of doubly fed induction machines which is based on the effect of a natural signal injection in the stator windings due to the fifth harmonic of the line voltage. A method to extract the rotor position and speed only from the rotor current and stator voltage measurements is developed: As a novelty, the stator current measurement and the anisotropies in the machine design are not required. A phase-locked loop is used in order to track the harmonic current component which is induced in the rotor by the fifth line voltage harmonic and whose speed and position are directly related to the rotor speed and position. The tuning of the observer parameters is discussed together with the effect of the other line voltage harmonics. This paper is completed by the experimental validation of the observer performances.

An Open-Loop Sensorless Slip Position Estimator of a DFIM Based on Air-gap Active Power Calculations—Sensitivity Study

This paper presents a sensitivity study for a new sensorless method for the direct estimation of the slip position of the wound-rotor induction machine. The method estimates directly the slip position as the difference between two angles: the rotor current position measured in the rotor reference frame and the same variable computed in the reference frame synchronous with the stator electromotive force. This is obtained using the active power that crosses the airgap as an auxiliary variable. Since the slip position is directly obtained, it is not necessary to know the stator flux in order to implement the field orientation. The method is not dependent on the stator selfinductance, being robust to parameter variations. Accuracy mainly depends on the mismatch of the ratio between the stator and mutual inductances. The estimation error is low in a large region of the dq rotor current plane except near the d-axis. Simulation and experimental results show that the method is appropriate for vector control of the doubly fed induction machine (DFIM) in a wide variety of applications.

Numerical Integration of ODEs in Real-Time Systems Like State Observers: Stability Aspects

This paper deals with the performance of some numerical integration methods for Ordinary Differential Equations in real time applications involving stiffness. After summarising the main results about accuracy and stability of some well known schemes, the point of view of the control is emphasized, by showing the impact of the numerical integration on the dynamics of the discretized model. Moreover some peculiarities of the numerical integration in hybrid systems are touched by introducing a simple hybrid model for testing the performances of some numerical integration schemes. Finally some experimental tests are shown, dealing with a control of a sensorless drive whose model is characterised by stiffness.