Radial Force Sum Research Articles

COMPUTATIONAL AND EXPERIMENTAL ANALYSIS OF A DIFFUSER THAT CONSTITUTES A CONCEPTUAL AND UNPRECEDENTED DAWT FOR URBAN APPLICATIONS

This article presents numerical analyses of diffusers formed by different curved aerodynamic profiles and high lift-to-drag ratio airfoils, with and without the use of a ring flap (flanged diffuser) applied externally at the diffuser exit. The objective is to identify the optimal geometry for the fabrication of a full-scale prototype of a DAWT (Diffuser-Augmented Wind Turbine), which is a conceptual and innovative design developed for urban and rural use. The diffuser aims to increase the mass flow rate through the turbine, allowing for greater power extraction at low wind speeds caused by surrounding buildings. The mass flow increment factor is used as a performance parameter for the diffuser and it is found to have an approximately linear growth with the sum of radial forces, which is related to the lift coefficient of the employed aerodynamic profile. Both the application of the ring flap and the axial length of the diffuser generate higher radial forces and increase the mass flow rate through the diffuser. The diffuser with the NACA 2421 airfoil profile demonstrated a mass flow increment of 1.42 in a configuration with a flap and a configuration without a flap but with a longer axial length. The flap causes higher drag force and higher standard deviation. Therefore, for the fabrication of the turbine prototype, a flanged diffuser with the NACA2421 airfoil profile is chosen. By comparing the numerical and experimental results of diffusers with the NACA2421 airfoil profile, it is concluded that the experimentally obtained velocity increment is 7% lower than the increment indicated by numerical simulations.

Investigation of Effective Cases of Radial Force Sum Flattening for Acoustic Noise Reduction in Four Three-Phase Switched Reluctance Motors With Different Pole Configuration

Investigation of Effective Cases of Radial Force Sum Flattening for Acoustic Noise Reduction in Four Three-Phase Switched Reluctance Motors With Different Pole Configuration

Improved Current Profile Selection for Noise Reduction of Switched Reluctance Motor at Middle Speed Considering Back EMF

An improved current profile selection for noise reduction of a switched reluctance motor (SRM) during middle-speed operation is presented with the principle of flattening the three-phase radial force sum. The improved current is selected from the proposed algorithm, which considers the limited input voltage and back electromotive force influence at middle-speed operation. The improved current profile is compared with the single pulse current, which is the typical current for SRMs at middle-speed operation. The analysis results show that the variation of the radial force sum by the improved current profile is less than that of the single pulse current, although the influence of the back electromotive force is high. The effectiveness of radial force sum flattening is verified by the experimental results. The experiments were carried out with the downscaled operating point of a SRM owing to the limited range of the operating speed. The experiment results show a significant reduction in the highest and second-highest peak noises at 5.4 and 1.8 kHz by 11.04 and 17.51 dB, respectively, with the improved current profile. The other noises were also reduced.

Experimental Verification of Acoustic Noise and Radial Force Sum Variation in Switched Reluctance Motor

Acoustic noise reduction is one of the main topics of switched reluctance motor (SRM) developments. One of the effective methods is flattening three-phase radial force sum. This method is verified in experiments by optimizing the current profile. Novel current waveforms have been proposed recently for acoustic noise reduction without sacrificing the efficiency in the 18/12 SRM, which has competitive power density, torque density, peak efficiency, and outer dimensions compared with the permanent magnet motor employed in hybrid electric vehicles. In this article, electro-mechanical analysis and acoustic analysis are carried out to verify acoustic noise reduction in the 18/12 SRM. The relationship between radial force sum F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rsum</sub> , torque ripple T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rip</sub> , and acoustic noise is investigated. Experimental confirmation is also included.

Vibration Reduction Control of Switched Reluctance Machine

In this paper, a new vibration reduction control of the switched reluctance machine (SRM) is proposed, which takes into consideration the undesirable effects of the torque ripple. The control approach aims to reduce the variation of the sum of radial forces while optimizing the control parameters of the machine to achieve the torque ripple minimization. Thus, a reference current adapter is used in order to handle the tradeoff between the vibration reduction and the torque ripple reduction. It produces an auto-tuning reference current that limits the variation of the torque and of the total radial force. The effectiveness of the proposed control strategy is proved by simulation and experimental results. Comparisons with conventional control methods investigating vibrations, noise, and torque ripple are provided, which show the advantages of the control approach based on an auto-tuning reference current.

Current Reference Selection for Acoustic Noise Reduction in Two Switched Reluctance Motors by Flattening Radial Force Sum

In this paper, a selection of a few current references for acoustic noise reduction in the 36–24 and the 18–12 switched reluctance motors is presented. It is seen that the difference in radial force profile results in few optimal current references. It is found that the optimal current reference with extreme radial force sum flattening results in increased rms current and loss in a magnetically saturated region of the 18–12 SRM. Thus, proper selection of the current references is necessary. Analysis, simulation, and experimental results are presented with the conventional and optimal currents to verify the effectiveness of flattening radial force sum method in acoustic noise reduction. It is shown that effective acoustic noise reduction and efficiency improvement are confirmed with proposed current reference selection.

Acoustic Noise Reduction of a High-Efficiency Switched Reluctance Motor for Hybrid Electric Vehicles With Novel Current Waveform

One of the major topics of switched reluctance machines (SRMs) is how to reduce the acoustic noise and vibration without decreasing the efficiency. In this paper, a few novel current profiling methods are proposed to reduce the acoustic noise by flatting the radial force sum and to reduce optimal torque ripple with best efforts to enhance the efficiency. The proposed method is adopted to the 18/12 pole SRM, which has identical outer dimensions and competitive torque, output power, efficiency, and operating region of the permanent-magnet motor used in the hybrid vehicles. It is found that the proposed method can improve not only the radial force ripple characteristic but also the iron loss minimization. The efficiency enhancement is also found to be possible in a few cases depending on the demanding criteria; thanks to the phase shift of the fundamental component of the current waveform. The proposed method is verified in the experiments.

Current Waveform for Noise Reduction of a Switched Reluctance Motor Under Magnetically Saturated Condition

A novel method is proposed to derive the current waveform to reduce noise and vibration of a switched reluctance motor in a magnetically saturated region. Principle of noise and vibration reduction is based on reducing the variation of the radial force sum. To realize the minimum variation in the sum of the radial forces, radial force expression has been derived. In a magnetically saturated region, radial force expression is approximated with Fourier series with parameters as a function of current. With the proper approximation of radial force, the current waveform is derived to minimize the variation of the radial force sum. The proposed current waveform consists of dc, fundamental, second, and third harmonic components. Finite-element analysis and experiment result are included to show the validity of the proposed method.

Noise Reduction of Switched Reluctance Motor With High Number of Poles by Novel Simplified Current Waveform at Low Speed and Low Torque Region

In this paper, the theoretical strategy and experimental results for noise reduction of a switched reluctance motor with a high number of poles are presented using a novel simplified current profile at low speed and low torque region. The noise reduction is carried out by the principle of reducing the variation of the sum of radial forces. The variation of the sum of three-phase radial forces of the A-phase tooth, the B-phase tooth, and the C-phase tooth is a cause of vibration and acoustic noise. Thus, the variation of the sum of these forces is aimed to be minimized by current profiling. In this paper, a simple current waveform with reduced harmonic order is proposed. This has advantages of low rate of change of the current, easy current regulation, low root mean square (rms) and peak currents, low torque ripple, and higher efficiency. An improved current regulation method is also implemented. In experiment, it has been found that significant noise and vibration reductions can be achieved with the proposed current waveform.

Acoustic Noise and Vibration Reduction of SRM by Elimination of Third Harmonic Component in Sum of Radial Forces

A novel method to reduce an acoustic noise and the vibration of a switched reluctance motor has been proposed. In this method, driving current is a sum of dc, fundamental, the second- and the third-harmonic components. This driving current is determined to eliminate the third harmonic component in the sum of radial forces of the stator teeth. Consequently, an acoustic noise and a vibration are reduced. The effectiveness of the proposed method is confirmed by means of finite-element method and test machine experiments.