• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.4
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• pp.299-306
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• 2003

The rotor flux position is needed to perform vector control of induction motor. But rotor speed information is needed to get accurate the rotor flux position. It is difficult to implement the open loop method without speed information or the motor equation only because of noise or the motor parameter error. This paper presents the speed estimator can use the arbitrary rotor flux observer by separating the flux observer and speed estimator and apply the three flux observers proposed by Ohtani, Lorenz and full order flux observer. The validity of speed estimator presented is verified and the performance using the three rotor flux observers is analyzed by the simulation and experiment.

• Progress in Superconductivity
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• v.3 no.2
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• pp.151-158
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• 2002

We developed a useful SQUID magnetometer for biomagnetic applications, magnetoencepha-logram(MEG) and magnetocardiogram(MCG), etc. The SQUIDs are based on Double Relaxation Oscillation SQUID(DROS). DROS consists of two SQUIDs(signal SQUID and reference SQUID) in series, and a relaxation circuit of an inductor and a resistor. Specially we used single reference junction instead of the reference SQUID. The SQUIDs are based on hysteretic $Nb/AlO_{x}$Nb junctions, fabricated by using a simple four level process. Because DROS magnetometer has large flux-to-voltage transfer coefficient, we can use simple flux-locked loop electronics fur SQUID operation. When the DROS magnetometer was operated inside a magnetically shielded room, its average magnetic field noise was about 3 (equation omitted) at 100 Hz. This noise level is low enough to measure biomagnetic fields. In this paper, we describe noise characteristics of DROS magnetometer, depending on the operation condition . .

• Progress in Superconductivity
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• v.7 no.1
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• pp.46-51
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• 2005

We have developed control electronics to operate flux-locked loop (FLL), and analog signal filters to process FLL outputs for 64-channel Double Relaxation Oscillation SQUID (DROS) magnetocardiography (MCG) system. Control electronics consisting of a preamplifier, an integrator, and a feedback, is compact and low-cost due to larger swing voltage and flux-to-voltage transfer coefficients of DROS than those of dc SQUIDs. Analog signal filter (ASF) serially chained with a high-pass filter having a cut-off frequency of 0.1 Hz, an amplifier having a gain of 100, a low-pass filter of 100 Hz, and a notch filter of 60 Hz makes FLL output suitable for MCG. The noise of a preamplifier in FLL control electronics is $7\;nV/{\surd}\;Hz$ at 1 Hz, $1.5\;nV/{\surd}\;Hz$ at 100 Hz that contributes $6\;fT/{\surd}\;Hz$ at 1 Hz, $1.3\;fT/{\surd}\;Hz$ at 100 Hz in readout electronics, and the noise of ASF electronics is $150\;{\mu}V/{\surd}\;Hz$ equivalent to $0.13\;fT/{\surd}\;Hz$ within the range of $1{\sim}100\;Hz$. When DROSs are connected to readout electronics inside a magnetically shielded room, the noise of 64-channel DROS system is $10\;fT/{\surd}\;Hz$ at 1 Hz, $5\;fT/{\surd}\;Hz$ at 100 Hz on the average, low enough to measure human MCG.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.9
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• pp.1217-1222
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• 2013

It is very important to diminish noise source of electric motor systems that are used for home appliance area. We have studied on the noise reduction of BLDC motor, mainly focusing on reducing noise source from cogging torque. This noise source causes resonance of fan & motor systems. This study showed that the higher harmonic component of the cogging torque was the main factor for noise generation. Therefor, to reduce noise of bldc motor for refrigerator, this study suggested peanut shaped magnet which surface flux has similar sinusoidal wave form.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.278-282
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• 2011

We discuss two possible optical noise sources in an electro-optic camera loaded on a low earth orbit satellite. The first noise source was a reflection at the window for signal rays incident upon the window which is placed before the FPA plane. The second noise source came from a reflection at the surface of the FPA cell when the signal flux is not entirely absorbed. We investigate the noise generation processes for two optical noise sources, and a parametric solution is used to estimate the optical noise effects.

• Progress in Superconductivity
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• v.5 no.1
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• pp.55-60
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• 2003

We designed and constructed integrated 3-channel flux-locked-loop (FLL) electronic system for the control and readout of high-T$_{c}$ SQUIDs. This system consists of low noise preamplifiers, integrators, interface circuits, and software. FLL operation was carried out with biased signals of 19 KHz modulated current and 150 KHz modulated flux, which are reconstructed as detected signals by preamplifier and demodulator. Computer controlled interface circuits regulate FLL circuit and adjust SQUID parameters to the optimum operating condition. The software regulates interface circuits to make an auto-tuning for the control of SQUIDs, and displays readout data from FLL circuit. 3-channel SQUID electronic system was assembled with 3 FLL-interface circuit boards and a power supply board in the aluminum case of 56 mm ${\times}$ 53 mm${\times}$ 150 mm. Overall noise of the system was around 150 fT/(equation omitted)Hz when measured in the shielded room, 200 fT/(equation omitted)Hz in a weakly shielded room, respectively.y.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.4
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• pp.693-698
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• 2007

In general the distributed winding method is applied for induction motor in order to have the sinusoidal flux distribution. Recently the concentrated winding method is the interested technique so as to lower the material cost portion of copper coil. In the concentrated winding induction motor the harmonic flux and the torque deterioration by it would be occurred. To restrain ill effect of harmonic flux distribution by concentrated winding, the skew of rotor conduction bar is very important design variable. This study is focused on the optimal design of rotor bar's skew and winding turns for concentrated winding induction motor. In this study, the control method of harmonic parasitic torque in concentrated winding induction motor is proposed and validated its practicality through the experiment. As a result of this study, large skew angle which was not conventional in distributed winding was favorable in the concentrated winding induction motor. The concentrated winding induction motor which is designed per the proposed method of this study can be manufactured more cost effectively than conventional distributed winding.

• Communications of the Korean Mathematical Society
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• v.33 no.3
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• pp.1025-1037
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• 2018

We consider an ill-posed problem for the heat equation $u_{xx}=u_t$ in the quarter plane {x > 0, t > 0}. We propose a new method to compute the heat flux $h(t)=u_x(1,t)$ from the boundary temperature g(t) = u(1, t). The operator $g{\mapsto}h=Hg$ is unbounded in $L^2({\mathbb{R}})$, so we approximate h(t) by $h_{\delta}(t)=u_x(1+{\delta},\;t)$, ${\delta}{\rightarrow}0$. When noise is present, the data is $g_{\epsilon}$ leading to a corresponding heat $h_{{\delta},{\epsilon}}$. We obtain an estimate of the error ${\parallel}h-h_{{\delta},{\epsilon}}{\parallel}$, as well as the error when $h_{{\delta},{\epsilon}}$ is approximated by the trapezoidal rule. With an a priori choice rule ${\delta}={\delta}({\epsilon})$ and ${\tau}={\tau}({\epsilon})$, the step size of the trapezoidal rule, the main theorem gives the error of the heat flux as a function of noise level ${\epsilon}$. Numerical examples show that the proposed method is effective and stable.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.33-40
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• 2007

Rotatory two-phase transverse flux machine(TFM) is a relatively new type of motor with high power density, high torque, and low speed in comparison to conventional electrical motors. However, it has some shortcomings,.i.e. complex construction and high possibility of the magnetically induced nitration due to its inherent structure. This Paper investigates the characteristics of the magnetic force and the torque in the rotatory two-phase TFM by using the 3-D finite element method and the spectral analysis. This research shows that the average torque decreases and that the torque ripple increases as the phase delay increases. It also shows that the unbalanced magnetic force is one of the dominant excitation forces in this machine. And it proposes a new topology of rotatory two-phase TFM to eliminate the unbalanced magnetic force.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.4
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• pp.201-207
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• 2005

This paper has investigated the sensorless vector control method of induction motor based on the stator flux oriented voltage equation and the digital low pass filter (LPF) with compensator of phase/gain. The Proposed vector control method is easy to decide the stator reference voltages and control of motor, since it is based on stator flux vector But this method has sensitive structure to excessive sensor noise and PWM pulsating components of stator currents because the measured stator currents are directly used to compensate the internal resistive voltage drop at the determination of stator reference voltages. To eliminate the noise sensitive of proposed vector drive, this paper propose the digital LPF with compensator of phase/gain base on orthogonal property of stator current vector in stationary $\alpha$, $\beta$ reference frame. The proposed methods have been simulated and implemented on a sensorless vector drive for 750W three-phase induction motor. The simulation and experimental results demonstrate effectiveness of the proposed methods.