1,721,063 research outputs found
Novel maximum power point tracking strategies for electronically tuned linear alternators
Full text linkLinear alternators (LAs) are widely applied in many energy conversion systems based on pressure waves, to avoid linear to rotary conversion mechanisms. The control of the LA is the key element to maximise the system's electric power and efficiency. However, the LA resonant frequency cannot be accurately controlled by mechanical design due to parameter tolerance. Furthermore, the operating frequency is generally not strictly constant in real-time, making maximum power point tracking (MPPT) hard to achieve. Two MPPT strategies are proposed here to adjust the electronic stiffness amount in real time. They are hereafter referred to as symmetrical signal injection method and electronic stiffness perturbation method. The latter one is selected and validated via simulation studies
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
Feasibility study of an induction motor rim drive for an aircraft boundary-layer-ingestion fan
Full text linkThis paper presents a feasibility study for an induction motorrim drive to power aircraft BLI fans. The design is developedfrom a BLI-fan specification for traditional aircraftarchitecture: the rotor is fastened to the rim of the bladeshroud, not to obstruct the fan duct and interfere with the airflow.The main objective of this study is the identification ofachievable power density and efficiency levels with aninduction motor rim drive configuration considering thestructural requirements for the integrity of the rotor operatingwith high tip speeds. The proposed 250 kW, 14,000 rpmdesign example achieves an efficiency in excess of 97% withan active mass around 20 kg.<br/
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
Parasitic Currents in Structural Paths of YASA Axial Flux PM Machines: Estimation and Tests
No full textThis paper evaluates the parasitic currents that can occur in the structural part of some types of yokeless and segmented armature axial flux permanent magnet machines, where the frame-supporting stator floating teeth can originate stray paths. In this paper, these paths are defined and modeled, and the consequent effects (induced electro motive forces and currents) are estimated. The amount of these effects depends on the machine geometry, the magnetic circuit structure, and the winding layout. In this paper, the analysis is performed on two different rating machines, comparing their results. The model is validated by measurements on the corresponding prototypes
A Sea-State-Dependent Control Strategy for Wave Energy Converters: Power Limiting in Large Wave Conditions and Energy Maximising in Moderate Wave Conditions
Full text linkConventional control strategies for wave energy converters (WECs) maximise power capture of the WEC by amplifying its responses, but this exacerbates hardware constraint violations not generally taken into account, causing undesirable shutdown of electrical systems in adverse wave conditions. When WECs operate close to power take-off (PTO) capacity, the primary control objective is to limit peak power for hardware protection purposes, enabling longer continuous electricity generation time. In this paper, we propose a sea-state-dependent control strategy based on model predictive control to maximise the annual energy production of a WEC with a realistic PTO: in small to moderate sea states it adopts a conventional energy-maximising objective function to increase output power, while in higher sea states a speed-limiting objective function may be utilised to enable longer generating time before shutdown becomes necessary. While this control strategy applies to a wide range of WECs, here we carry out the case study on an attenuator WEC called M4, with gearbox transmission and a permanent magnet synchronous generator (PMSG) as its PTO, which is being designed for a 1/4 scale ocean test in Albany, Australia. Simulation results show that compared with a benchmark passive damping controller, a 66% increase in annual energy production can be expected at the targeted site
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