Won-Cheol Lee

A new hybrid sensorless method using a back EMF estimator and a current model of permanent magnet synchronous motor

This paper presents a sensorless method which combined a back-EMF estimator and a current model of PMSM. Sensorless method using the back-EMF estimator, because of its position estimation method, the lowest controllable speed is limited despite of the correct back-EMF estimation. On the other hands, the current model based sensorless method has the benefit that robust control for large load torque. However, the correctness of the estimated back-EMF is determined by a back-EMF coefficient which is varied by load torque and speed. For these problems, this paper proposes the hybrid sensorless method that the back-EMF estimator for precise back-EMF estimating, and the current model of PMSM for robust control and extend the controllable speed region. This method offers not only non-necessary back-EMF coefficient which should be varied, but also wide speed operating region in no specific transition method.

Analysis of a new PWM method for conducted EMI reduction in a field oriented controlled induction motor

The prevalence of EMI noise problems has been considered many times over the past few years, in inverter fed motor control systems. The advent of high speed power devices, and the high dv/dt of switching devices, has resulted in EMI problems and leakage current. This paper describes the application of the newly developed EMI reduction technique of SVPWM in induction motor drives. This newly developed common mode voltage reduction SVPWM technique does not use any zero-voltage vector states for inverter control, hence can restrict the common mode voltage more efficiently than the conventional PWM technique. The validity of the proposed technique is verified through simulation and experimental results. In this paper, by applying the vector control system, the proposed technique is presented as superior in reducing EMI and equal control performance, compared to the conventional space-vector PWM technique.

Optimal washing time control algorithm for the drum washing machine using an inertia estimator

Generally, operating efficiency of drum washing machine is mostly affected by the washing time. The washing time is determined by the quantity and the type of the laundry. Although the type of the laundry is easily inputted by the user, however the quantity of the laundry can net be easily. Therefore, this paper suggests that the washing time is adjusted by the inertia estimator which can estimate the quantity of the laundry. The proposed algorithm is implemented on the PMSM drive using the low cost position sensor for practical washing machine application. And the experiment is performed by the motor of drum washing machine for the practical load condition.

A four-switch and half-bridge boost converter based BLDCM drive system for the DC-link voltage unbalancing compensation

This paper proposes a controller to compensate the DC-link voltage unbalance in the BLDC motor drive system based on the four-switch and half-bridge boost converter. In this paper, we can see that the proposed feedforward controller is useful for control of the neutral point voltage unbalance. The comparative experimental results show that the system became more robust by the feed-forward control of the neutral point voltage.

Comparison of work-related musculoskeletal symptoms between male cameramen and male office workers

BackgroundPrevious studies have classified cameramen’s job as physiologically heavy work and identified the risk factors of work-related musculoskeletal disorders (WRMDs) in cameramen. However, those studies limited their research subjects to cameramen. In this study, we compared the frequency and severity of WRMDs between cameramen and office workers.MethodsA total of 293 subjects working in four broadcasting companies in Korea were recruited. A questionnaire survey was conducted for a month, starting in October 2016. The subjects were divided into cameramen and office workers according to their occupation. We compared the frequency and severity of WRMDs and ergonomic risk assessment results between the two groups.ResultsThe high-risk WRMD group had a higher proportion of cameramen than office workers. Moreover, the high ergonomic risk group also had a higher proportion of cameramen than office workers for WRMDs in the upper extremities and waist+lower extremities. In the multivariable-adjusted model comparing cameramen and office workers, the odds ratio (OR) with 95% confidence interval (95% CI) for high-risk WRMDs was 3.50 (95% CI: 1.92–7.72) for the upper extremities and 3.18 (95% CI: 1.62–6.21) for the waist and the lower extremities. The ORs by body parts were 3.11 (95% CI: 1.28–7.57) for the neck, 3.90 (95% CI: 1.79–8.47) for the shoulders, and 4.23 (95% CI: 1.04–17.18) for the legs and feet.ConclusionsOur study suggests that cameramen are at high risk of WRMDs. Workplace improvements and management of the neck, shoulders, and lower extremities, which are susceptible to WRMDs, are necessary to prevent musculoskeletal disorders among cameramen.

A novel flicker mitigation method of auxiliary power unit for electric locomotive

There are many increasing demands for efficient high power density of auxiliary power unit(APU) for high speed traction application. Many techniques have been proposed to measure the voltage flicker on the traditional pulse width modulation(PWM) inverter. This paper proposes a novel functionality of the static inverter on the APU to mitigate the voltage flicker and regulate the output voltage. A new control algorithm for the inverter based on the Hilbert transform(HT) is presented. The HT is employed as an effective technique for tracking the voltage flicker levels in APU systems. Simulation results are provided to verify the tracking capabilities of the HT and to evaluate the performance of the proposed DG interface for multi-function operation.

Control of IPMSM drive system for drum washing machine

The drum washing machine needs high torque than the other types of washing machine because of the large load torque variation. Therefore, in this paper, we applied a interior permanent magnet synchronous motor (IPMSM) to the drum washing machine system. However, IPMSM operate at lower output torque than the other permanent magnet synchronous motor (PMSM) when the motor control is performed by the conventional control method. This paper suggests adaptive control method for IPMSM to obtain better torque performance and apply the control method in actual experiments of the drum washing machine system.

Simulation model for a seven-phase BLDCM drive system

BLDC motors have many advantages over brushed DC motors and induction motors. So, BLDC motors extend their application to many industrial fields. In this paper, the digital simulation and modeling of a 7-phase brushless DC motor have been presented. The 14-switch inverter and a 7-phase brushless DC motor drive system are simulated using hysteresis current controller and logic of switching pattern with the Boolean¡s function. Through some simulations, we found that our modeling and analysis of a 7-phase BLDCM with PWM inverter would be helpful for the further studies of the multi-phase BLDCM drive systems.