1,721,006 research outputs found
Adaptive tuning of the stator inductance in a rotor - current - based MRAS observer for sensorless doubly fed induction machine drives
No full textThis 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
On line tuning of the stator inductance in a MRAS observer for sensorless DFIM drives
No full textThis paper proposes a scheme for the self tuning of the stator inductance in a Rotor Current MRAS Observer for the sensorless control of Doubly Fed Induction Machines. The effect of mismatched parameters in this observer is briefly discussed and the strong dependence of the estimated rotor position on the stator inductance is highlighted. A self tuning scheme is formulated by using only quantities which are already exploited by the observer, so that only a marginally additional computational effort is required in the implementation. Some guidelines to design the tuning loop are given. Finally the performances of the proposed scheme are experimentally tested and discussed
Enhanced torque control in a DFIG connected to a DC grid by a diode rectifier
No full textThis paper considers the control of a doubly fed induction machine (DFIG) connected to a dc-bus or dc-grid by using a diode rectifier placed on the stator-side and a single PWM converter on the rotor. In this system, the torque and the frequency have to be regulated simultaneously, in order to make the prime mover operating at the maximum power point and to guarantee at the same time a flux level near the rated value. Since this system is based on a unique reduced-power controlled converter and a diode rectifier, a noticeable reduction of the costs of the power electronics can be achieved. However, the diode bridge causes stator current and voltage harmonics which produce a noticeable torque ripple. A regulation scheme able to reduce the torque ripple is proposed in this paper: resonant current controllers are implemented to track the sixth harmonic components in the reference rotor current commands, in such a way to kill the corresponding harmonic in the electromagnetic torque
Stator Frequency Regulation in a Field-Oriented Controlled DFIG Connected to a DC Link
No full textDispersed generation systems need several elements that should work together. One possible way to connect these elements is through a common dc link. This paper discusses a new control method for the doubly fed induction generator when connected to a dc link. Considerable benefits are obtained in this configuration, because a simple diode bridge can be used on the stator and only an ac/dc power electronic inverter is needed to control the rotor currents. As the ac mains do not impose the stator frequency, this should be regulated to get an appropriate operation of the induction machine. This paper proposes a method to regulate the stator frequency and control the torque based on adjustments of the d - q rotor reference currents by using the field-oriented control. The analysis and synthesis of the control system based on a simplified model is discussed. Simulations and experimental results show that the proposed control exhibits good dynamics in the torque control and in frequency regulation
Sensorless Torque Control of a DFIG connected to a DC Link
No full textThis paper presents a frequency regulation system and a sensorless method for the direct estimation of
the slip position of the wound-rotor induction machine connected to a DC link, performing a torque control. Since the stator is connected to the DC link through a diode bridge, it is also necessary to implement the stator
frequency regulation. Connecting the DFIG to a DC link using a diode bridge on the stator brings considerable
benefits, because only a dc/ac power electronic inverter is required. In this system the magnetizing current is
necessarily fed by the rotor: this makes the considered sensorless method particularly appropriate, because,
under mismatched parameters, it gives small estimation errors. Simulation and experimental results are presented matching and showing good performances
An Observer for Sensorless DFIM Drives Based on the Natural Fifth Harmonic of the Line Voltage, without Stator Current Measurement
No full textThis 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. The paper is completed by the experimental validation of the observer performances
A scheme for the power control in a DFIG connected to a DC bus via a diode rectifier
Full text linkThis paper deals with a new conversion topology for doubly-fed induction generators (DFIGs) suitable for wind energy conversion systems integrated in microgrids. It consists of a DFIG which is fed by a pulse width modulation converter on the rotor and with the stator connected to a dc grid through a diode rectifier. In this configuration, the stator diode rectifier and the rotor-side inverter share the same dc bus, so that the conventional grid-side inverter is avoided. Since only a diode rectifier designed for the full power and a reduced power inverter are required, this layout allows a cheap and effective integration of the DFIG with other generating and storage systems connected to the same dc bus. A simple control technique suitable to regulate the power delivered to the dc grid is proposed. The scheme is based on the regulation of the amplitude of a suited fraction of the rotor flux linkage: the optimal value of this fraction is theoretically deduced in order to minimize the DFIG derating due to the current harmonics. The effectiveness of the proposed control is proven by simulations and experimental tests
Operation and design issues of a doubly fed induction generator stator connected to a dc net by a diode rectifier
Full text linkThe operation of a doubly fed induction generator (DFIG) connected to a dc net is considered in this study. The dc net is connected to the stator of the DFIG by a diode rectifier and simultaneously feeds the rotor-side inverter, which is used to control the machine. When the dc net operates at constant voltage, this solution preserves the possibility to work with a low flux at low speed, and, at the same time, reduces the cost of the power electronics. In fact, the only needed electronic converter is the rotor inverter designed for a fraction of the machine power. After introducing a simple control technique, the study proposes an analytic model for the steady-state operation and discusses the design specifications of the DFIG for given values of the dc voltage and of the power of the wind turbine. The most appropriate stator and rotor rated powers, rated stator voltage and turns ratio of the DFIG are deduced. Simulations and experimental results are presented in order to support the theory
FEM2D Based Analytical Model of the Air Gap Magnetic Field in Surface PM Synchronous Machines
No full textThe paper presents an analytical model of the
air gap field in a surface mounted PM Synchronous Machine.
The method is FEM2D based, because it starts from the FEM
identification of suited “field functions”: each field function
describes the air gap flux density behavior, related to one field
perturbation cause, acting alone (stator slotting, rotor
anisotropy, field excitation source, armature reaction m.m.f.s).
The soundness of the method is proved by the good agreement
of the field behavior obtained by FEM and by the proposed
methodology. The field analytical expressions are suited to be
used to evaluate the waveforms of e.m.f.s and torques
Design guidelines for wound Inter-Phase Reactors in high-power rectifier systems
No full textThis paper reviews the design procedure of wound-type Inter-Phase Reactors used in high power rectifier systems, and gives some guidelines for an optimized sizing aimed at minimizing costs and active mass. In particular, the paper proposes a design algorithm to identify the optimal number of coils and turns and clarifies the role of the air-gap in minimizing the magneto-motive force unbalance and affecting the column peak flux density
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