Sakda Somkun

Magnetostriction Anisotropy and Rotational Magnetostriction of a Nonoriented Electrical Steel

Magnetostriction in nonoriented (NO) electrical steel is a possible source of vibration and acoustic noise in electrical machines. The anisotropy of the magnetostriction of NO steel can be far greater than that of its specific power loss which is often quoted. Also magnetostriction under rotational magnetization can be much higher than under alternating magnetization. This paper shows the relevance of magnetostrictive anisotropy to the rotational magnetostriction of a NO steel. An investigation of the effect of anisotropy in magnetostriction was carried out, followed by rotational magnetostriction measurements. A model based on an analogy of mechanical elasticity was used to describe the effect of magnetostrictive anisotropy on the rotational magnetostriction. Results show that a high value in rotational magnetostriction is mainly driven by its high magnetostriction in the transverse direction. The phenomenon is shown to be a source of asymmetrical deformation in the back iron of electrical machine cores where rotational flux predominates.

Novel control technique of single-phase PWM rectifier by compensating output ripple voltage

Novel control technique of single-phase PWM rectifier by compensating output ripple voltage is presented. Output ripple voltage is cancelled before feeding to voltage controller in order to increase system bandwidth while supply current is still nearly sinusoidal and maintains unity power factor. Output ripple voltage estimator is calculated by the information of peak value of supply voltage and current. Peak value estimator of sinusoidal signal is introduced with the help of a simple trigonometric rule. Additionally, feed forward current controller is also presented so as to improve tracking performance of supply current. The proposed scheme is simulated in order to compare with conventional scheme. The simulation results show that the proposed scheme is working effectively both in rectifying mode and regenerating mode

Measurement and Modeling of 2-D Magnetostriction of Nonoriented Electrical Steel

Magnetostriction of nonoriented electrical steel was measured under rotating flux magnetization conditions which occur in AC electrical machine stator cores, and compared with the magnetostriction calculated from a model based on a mechanical elasticity analogy. Shear magnetostriction and magnetostriction perpendicular to the magnetization direction are accounted for in the model which leads to an accurate representation of magnetostriction throughout the electrical steel lamination plane. This has the potential for improving the accuracy of stator core deformation and vibration calculations.

Effect of Magnetostriction Anisotropy in Nonoriented Electrical Steels on Deformation of Induction Motor Stator Cores

Magnetostriction in nonoriented (NO) electrical steels is a harmful source of vibration and acoustic noise in electrical machines. It is far more anisotropic than specific power loss, which results in more complexity in prediction of the vibration and acoustic noise. An investigation of the anisotropy in magnetostriction and mechanical elastic properties of a NO steel is presented in this paper. Measurements of deformation in the stator teeth of an induction motor model core were conducted in order to study the effect of the magnetostriction anisotropy. Strain due to Maxwell forces in the air gap was calculated and compared with the measured deformation. Measurement results indicate that anisotropic magnetostriction has a great impact on unsymmetrical deformation of the stator teeth of induction motor cores.

Modeling 2-D Magnetostriction in Nonoriented Electrical Steels Using a Simple Magnetic Domain Model

Magnetostriction in electrical steel is a source of acoustic noise and vibration of rotating electrical machine cores. Magnetostriction of nonoriented (NO) steel under 2-D magnetization is much greater than that under unidirectional, alternating magnetization. An analytical interpretation of the relevance of 2-D magnetostriction and magnetostrictive anisotropy of NO steel based on a simple magnetic domain model is presented. The analysis helps explain the effect of anisotropy on 2-D magnetostriction measurements made on commercial NO steels with different anisotropy factors. The magnitude of the 2-D magnetostriction is shown to depend on the magnetostrictive anisotropy and magnetic Poissons ratio.

Unified Unbalanced Synchronous Reference Frame Current Control for Single-Phase Grid-Connected Voltage-Source Converters

This paper presents a unified structure of the unbalanced synchronous reference current control strategies for single-phase grid-tied voltage-source converters to obtain a zero steady-state error in the line current. An arbitrary waveform is used as the orthogonal current for the stationary to rotating frame axis transformation of the reference and measured grid currents. Various choices of such orthogonal signals lead to different control structures with the same performance characteristics. This causes a temporary unbalanced system, in which double-line frequency components appear in the control loops during the transient state. The proposed method with cross-axis decoupling, tuned at the control loop bandwidth by greater than eight times the grid frequency, has better performance than the existing virtual balanced synchronous reference frame scheme. Absence of the orthogonal signal generation guarantees the stability criterion of the control scheme. A zero steady-state error is still achieved under conditions of uncertainty in the converter parameters. Simulation and experimental results of a 1.5-kVA pulse width modulation rectifier validate the proposed methodology.

Design and Implementation of an Interleaved Boost DC-DC Converter for PEM Fuel Cells

This paper elaborates a design and implementation of a 2-phase interleaved boost DC-DC converter as the power conditioning circuit for PEM fuel cells. The converter ripple current is analyzed so as to determine the inductance value, which would draw the fuel cell ripple current less than 4 % of its nominal value for a longer lifetime and efficient operation. Compact design is benefited from reduced inductor core volume due to paralleled connection as well as microprocessor-based control. Practical implementation is also discussed. Selection of simulation and experimental results is presented to validate the design methodology. The converter has the maximum output power of 1 kW at the output voltage of 120 V with the efficiency better than 92 %.

Mechanical Resonance in Nonoriented Electrical Steels Induced by Magnetostriction Under PWM Voltage Excitation

Acoustic noise in inverter-fed motors can increase if resonance induced by magnetostriction occurs. This paper presents results of measurements of magnetostriction-induced mechanical resonance in nonoriented (NO) steels, commonly used in motor cores, under pulse width modulation (PWM) excitation. The resonant frequency of a strip of NO steels was determined and it was magnetized by PWM voltage waveforms. The PWM switching frequency was chosen to be the same as the sample resonant frequency. The peak-to-peak magnetostriction under PWM excitation was up to 28% higher than that under sinusoidal excitation when an integer multiple of the switching frequency matched the resonant frequency of the sample.

Single-phase grid-connected voltage source converter for LCL filter with grid-current feedback

LCL filters are extensively integrated with single-phase grid-tied voltage source converters due to their higher ripple attenuation capability. LCL filters lead to system instability due to the resonance of the filter. Limited range of resonance frequency and bandwidth ensures the stability of the system by proper design of the current controller and filter. This paper presents the modeling, design and control of a single-phase grid-connected VSC, including an LCL filter, with reactive power injecting capability. A simple PI controller in the unbalanced synchronous reference frame is designed with the Extended Symmetrical Optimum method for the grid current feedback control loop. The q-axis current control is used to inject the reactive power. The system is modeled and simulated in MATLAB/Simulink® and results are verified with an experimental setup of 1.5 kVA VSC.

Fast DC bus voltage control of single-phase PWM rectifiers using a ripple voltage estimator

The double line frequency ripple on the DC bus voltage of single-phase PWM rectifiers causes distortion in the line current and sluggish control dynamic. This paper presents an estimating scheme for the DC bus ripple voltage, which is used to cancel the ripple component in the measured bus voltage. This results in no oscillating component circulating in the bus voltage control loop. With this, the loop bandwidth can be increased to enhance the control dynamic. The proposed ripple voltage estimator uses the line current magnitude from the virtual synchronous reference frame current control loop, and the line voltage amplitude and frequency from the Park-based PLL as the input variables. Simulation and experiment of a 1-kW single PWM rectifier validate the proposed methodology. Experimental results show that under a load change of 960 W the proposed ripple cancellation scheme reduced the bus fluctuation by 50% of the conventional scheme and the settling time decreased from 3 line voltage cycles to one cycle with the line current THD of 2.5%.