29 research outputs found
Comparison of AC/DC converters and the principles of a new control strategy in small-scale wind turbine systems
No full textThis paper provides a detailed comparison of AC/DC converters commonly used in small-scale wind turbine systems. The paper reviews the main AC/DC converter topologies first including rectifier, switch-mode rectifier and inverter, and provides their operational features and characteristics. Then based on the previous analytical and comparison studies, it describes a novel multi-mode control strategy, which aims to improve the performance of small-scale wind turbines over a wide operating speed range while considering trade-off between performance and control complexity in such converters.Lujie Chen, Wen. L. Soong, Mehanathan Pathmanathan and Nesimi Ertugrulhttp://aupec2012.org
Maximum torque per ampere control of phase advance modulation of a SPM wind generator
No full textSurface permanent magnet (PM) machines are normally operated by controlling the d-axis and q-axis currents. This paper examines the control of surface PM generators based on controlling the terminal voltage magnitude V and power-factor angle θ. This is well-suited for generator operation when using a switched-mode rectifier and avoids the need for a rotor position sensor. The parameters required for generating a given value of torque with minimum phase current in order to minimize copper losses are derived in this paper. This will be achieved by controlling V and θ to keep the d-axis current equal to zero at low speed, before switching to field-weakening control at higher speeds. Simulated and experimental results will be used to verify the control strategy, and the efficiency achieved.Mehanathan Pathmanathan, Wen Soong and Nesimi Ertugru
V-theta control of inverters used in SPM wind turbine generators
No full textThis paper examines a position sensorless modulation strategy, called V-θ control, for six-switch fully-controlled rectifiers (inverters) for surface permanent magnet (SPM) generators in small-scale wind turbines. In this strategy, the SPM generator torque is commanded by controlling the magnitude of the phase voltage and its phase shift with respect to the current waveform. Simulated results obtained using simplified and PWM inclusive simulation models were used to validate the analytical findings presented. Experimental results are shown comparing the proposed V-θ control method with both phase advance and conventional switched-mode rectifier (SMR) modulated AC/DC converters. The V-θ control was found to produce up to 22% more power at a given speed compared to phase advance modulation.Mehanathan Pathmanathan, Wen L. Soong, Nesimi Ertugru
Phase advance modulation of low-cost power electronic converters for SPM wind turbine generators.
No full textThis research investigates the control of low-cost power electronic converters for small-scale wind turbines under standalone applications. The system utilizes a surface permanent magnet (SPM) generator operating with a semi-bridge switched-mode rectifier (SMR) into a DC voltage load. Conventional control of a semi-bridge SMR results in lower output power than an inverter (i.e. fully-controlled voltage source rectifier) due to the SMR’s inability to control its input power factor. Phase-advance modulation was introduced by Rivas et al. as a method of generating increased output power from a semi-bridge SMR by modulating the leg voltage of each phase at three different levels during the phase current positive half cycle. This method produced a controllable leading phase shift on the phase current waveform with respect to the phase voltage. Previous studies focussed on using phase advance modulation to extract maximum power from Lundell alternator and interior permanent magnet (IPM) generators at a fixed speed (1,800 rpm). No research had been conducted on the performance of SPM generators under phase advance modulation techniques. This study examines how the voltage and power factor angle of a SPM generator can be controlled to ensure that the generator produces maximum output power at a given speed. A simplified version of phase advance modulation, called zero-epsilon modulation, is used to implement voltage-power factor angle control and hence extract the maximum value of power at a given SPM generator speed. Wind turbine generators are required to have controllable values of torque in order to perform maximum power point tracking. It is desirable therefore to be able to control a SPM generator used in wind turbines to a commanded value of torque while maintaining a high value of efficiency. This study will present the techniques required to use zero-epsilon modulation to control a SPM generator under maximum torque per ampere conditions, thereby minimizing generator copper losses. The voltage and power factor required by an inverter operating under maximum torque per ampere control for a given generator speed and commanded torque is used to calculate the required zero-epsilon control parameters. A closed-loop current controller was used to minimize the error between the commanded and actual values of generator torque. Simulation and experimental results are used to validate the proposed approach. The above research has demonstrated the feasibility of phase advance modulation as a low-cost alternative to inverter modulation for controlling a SPM generator to produce maximum output power at a given speed. In addition, phase advance modulation has been shown to be capable of controlling a SPM generator to produce a commanded value of torque under maximum torque per ampere conditions at a given speed. These results make a significant contribution towards the development of low-cost, high performance small-scale wind turbine generators.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201
Dynamic wind turbine output power reduction under varying wind speed conditions due to inertia
No full textABSTRACTThe inertia of wind turbines causes a reduction in their output power due to their inability to operate at the turbine maximum co‐efficient of performance point under dynamic wind conditions. In this paper, this dynamic power reduction is studied analytically and using simulations, assuming that a steady‐state optimal torque control strategy is used.The concepts of the natural and actual turbine time‐constant are introduced, and typical values for these parameters are examined. It is shown that for the typical turbine co‐efficient of performance curve used, the average turbine speed can be assumed to be determined by the average wind speed. With this assumption, analytical expressions for the power reduction with infinite and then finite turbine inertia are determined for sine‐wave wind speed variations. The results are then generalized for arbitrary wind speed profiles.A numerical wind turbine system simulation model is used to validate the analytical results for step and sine‐wave wind speed variations. Finally, it is used with real wind speed data to compare with the analytical predictions. Copyright © 2012 John Wiley & Sons, Ltd.Chun Tang, Wen L. Soong, Peter Freere, Mehanathan Pathmanathan and Nesimi Ertugru
Notice of Withdrawal Real-time signal frequency analysis in variable speed drives using the sparse fast Fourier transform (sFFT)
No full textReal-time signal frequency analysis in variable speed drives using the sparse fast Fourier transform (sFFT)
No full textThis paper investigates the implementation and the use of the sparse fast Fourier transform algorithm in the converter control of a variable speed drive. The algorithm is proposed due to the reduction in computational complexity compared to the conventional fast Fourier transform for the special case of sparse signals. After discussing the theory and a simulation model, experimental results obtained using a field programmable gate array (FPGA) implementation are presented, showing the effectiveness of the proposed solution.QC 20181001</p
Quasi - two-level converter operation strategy for overvoltage mitigation in long cable applications
No full text
The Sri Lankan Debt Crisis: Is there a way out?
No full textThis thesis deals with the current debt crisis is Sri Lanka, which was brought about by rapid development following the end of the civil war, and how best to prevent future debt crises by providing recommendations to policy makers. This thesis makes use of two models, the Balance-of-Payments (BOP) Constrained growth model, and the Flying Goose Model (FGM) of development which was observed in East Asian countries during their fast-paced growth period. The BOP model is used to identify industries within Sri Lanka’s economy which have a high income elasticity of demand by the rest of the world. The results of the data analysis find that Sri Lanka has a high income elasticity of demand in the machinery and chemical sectors with in the manufacturing industry. The Sri Lankan economy is also diagnosed in the context of the FGM to understand in what stage of the FGM Sri Lanka is in, by means of carrying out non-parametric analysis on the FDI per capita, the trade dependence ratio, the revealed comparative advantage index and other economic parameters. From the evidence presented by the two models, policy recommendations go in the direction of promoting selective industrial policy, in order to enhance the growth of these targeted industries identified by the BOP model through means of accelerating the Flying Goose Model of development
