• 산업기술연구
• /
• 제24권A호
• /
• pp.119-126
• /
• 2004

BLDC Motor is one of the widely utilizable motors in servo system. The accurate calculation of the power loss for the IGBT and Inverse diode with Bipolar and Unipolar switching modes the driving modes is important for the design of drives for their heat treatment. If it were not for temperature-sensors in devices, it is difficult to get direct power loss, so. Power losses may be modeled by computer modeling to obtain the Calculation of the Power loss for Inverter in BLDC Motor with switching modes which is presented in this paper. The computer modeling is carried out by Matlab simulation. The power loss consists of conduction losses Conduction losses are the source of occurrence due to The IGBT and Inverse diode currents. Switching losses are the source of occurrence due to switching on/off in the devices, and gives the dominant influence to the loss. As a result, the unipolar I mode is best in reducing the heat losses.

• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.480-489
• /
• 2016

A novel hybrid carrier-based pulse width modulation (CBPWM) scheme that combines unipolar and dipolar modulations is proposed for single-phase three-level rectifiers, which are widely applied in railway traction drive systems. The proposed CBPWM method can satisfy the volt-second balancing principle in the complete modulation index region through overmodulation compensation. The modulation scheme features two modulation modes: unipolar and dipolar. The operation range limits of these modulation modes can be modified by changing the separation coefficient. In comparison with the traditional unipolar CBPWM, the proposed hybrid CBPWM scheme can provide advantageous features, such as lower high-order harmonic distortion of the line current and better utilization of switching frequency. The separation coefficient value is optimized to achieve the maximum utilization of these advantages. The experimental results verify the feasibility and effectiveness of the proposed hybrid CBPWM scheme.

• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.490-497
• /
• 2016

The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.

• Journal of Power Electronics
• /
• 제11권5호
• /
• pp.726-733
• /
• 2011

BLDC Motors are widely used in various speed control applications due to their ease of control and low cost. Generally, the unipolar PWM method is used for speed control applications. However, the unipolar PWM method has a current spike problem in the braking operation which can be a problem in speed reversal which generally happens in position control applications. However, the current spike problem can be solved by the conventional bipolar PWM method. Although the current spike problem can be solved, the conventional bipolar PWM method has the problem of a large current ripple. In this paper, a novel bipolar PWM method is proposed to solve this problem. The current ripple and the current spike problems are analyzed in this paper for the unipolar and bipolar PWM methods. At last, the merits of the proposed bipolar PWM method are proven by experiment.

• 대한기계학회논문집B
• /
• 제27권1호
• /
• pp.46-53
• /
• 2003

Effects of electric force on the morphology and growth of aggregates were studied experimentally. Nano-sized NaCl particles were supplied to a flame to perform the unipolar charging state. This electric precursor did not modify a temperature profile of the flame. The morphology of aggregates was measured by TEM image processing technique and the light scattering technique. In the unipolar charged state, the fractal dimension of aggregates was smaller than that of' the electrically neutral state. This result was in good agreement with our previous numerical simulations.

• 한국대기환경학회지
• /
• 제17권3호
• /
• pp.259-268
• /
• 2001

In this study, we have developed a simulation method to predict the initial collection efficiency of a unipolar charged fiber in the electret filters. The particle sizes considered were in the submicron range and thus Brownian motion of particles was also taken into consideration along with electrostatic forces acting on the particles. The simulation results were compared with other investigators experimental data on single fiber efficiency as well as with the calculated results using the existing correlations on single fiber efficiency. It has been shown that simulation results are in good agreement both with the experimental data with those predicted by the correlations.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.231-233
• /
• 2001

Axial magnetic field(AMF) type electrodes can be increase the interrupting capability of vacuum interrupters. Depending on the design, the principle of the local axial magnetic field arrangement are different. In this paper, a new AMF contact design based on a unipolar field arrangement and its characteristics are introduced. The influence of the unipolar AMF on the arc behavior is described by high-speed video camera. In addition, three-dimensional AMF simulations have been peformed by means of a finite element analysis(FEM) program to analyze the influence of magnetic field distribution on the AMF performance. The high interrupting capability of the unipolar AMF type electrode has been confirmed by three-phase test.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
• /
• 제31권2호
• /
• pp.88-93
• /
• 2020

Objectives: Mood disorder is highly comorbid with attention deficit/hyperactivity disorder (ADHD), and comorbid ADHD symptoms are associated with suicide risk. The aim of this study was to examine the association between comorbid ADHD symptoms and the number of suicide attempts among patients with unipolar and bipolar depression. Methods: In this cross-sectional study, 100 patients with either unipolar or bipolar depression constituted the final sample. Pearson's correlation and multiple regression analyses were conducted to examine the association between comorbid ADHD symptoms and suicide risk. Results: Among patients with bipolar depression, the number of suicide attempts was significantly correlated with ADHD symptoms (r=0.324, p<0.01). ADHD symptoms significantly predicted the number of suicide attempts (β=0.249, p<0.05). Conclusion: Our findings underscore the importance of screening and assessing ADHD symptoms in male young adults with depressive disorders.

• 대한기계학회논문집B
• /
• 제25권1호
• /
• pp.9-17
• /
• 2001

A numerical study has been carried out on the evolution of the particle size distribution for unipolar charged particles that experience coagulation in an alternating electric field. The collision frequency function of charged particles was analytically derived. The log-normal size distribution function is utilized for representing a poly-disperse size distribution and the moments of the particle size distribution are used to solve the general dynamic equation considering only AC electric force effect. The results are compared with the effects of brownian coagulation.

• 한국의류학회지
• /
• 제27권11호
• /
• pp.1279-1290
• /
• 2003

The purpose of this study was to make a scale for measuring the subjective hand of fabrics. For this purpose subjective hand expressions which were published in the journals were reviewed. 11 pairs(9 biopolar-pairs, 2 unipolar-pairs) were selected after searching the definitions in a dictionary followed by focus group interview and survey. To find out if these terminological biopolar pairs are agreed with the biopolar pairs in human sensation, a survey of fabric hand was undertaken using a scale consisted of 20 words(18 words from biopolar-pairs, 2 words from unipolar pairs). Among 11 pairs, 10 pairs except [taktakhada-poksinhada] were accepted as biopolar pair of word terminologically and sensuously. [taktakhada-poksinhada] was recognized as a biopolar pair terminologically but not sensuously. These 20 words were classified as 5 factors-surface contour, density, flexibility, dampness, and extensibility