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Reducing Switching Losses in Indirect Matrix Converter Drives
Yeongsu Bak,Kyo-Beum Lee 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5
This paper presents a discontinuous pulse width modulation (DPWM) method to reduce switching losses in an indirect matrix converter (IMC) drive. The IMC has a number of power semiconductor switches. In other words, it consists of a rectifier stage and an inverter stage for AC/AC power conversion, which are composed of 12 and 6 switching devices, respectively. Therefore, the switching devices of the IMC suffer from high switching losses in the IMC drives. Various topologies to reduce switching losses have been studied by eliminating a number of switches from the rectifier stage. In this study, in contrast to prior research, a DPWM method is presented to reduce the switching losses of the inverter stage. The effectiveness of the proposed method to reduce switching losses in IMC drives is verified by simulations and experimental results.
Heating and emission characteristics of briquettes developed from spent coffee grounds
Yeongsu Kim,Tusan Park,Donghyuck Hong 대한환경공학회 2022 Environmental Engineering Research Vol.27 No.4
The development of biomass fuels to replace fossil fuels is on the rise, with increased bioenergy research on spent coffee grounds (SCG). However, no biofuel can currently replace anthracite briquettes. Unlike ordinary solid fossil fuels, anthracite briquettes are heated for a long time and retain the same form after combustion, making them easier to transport. In this study, binders are used to develop a solid fuel that allows SCG to retain their shape after combustion. Specifically, bottom ash (BA) and kaolinite clay (KC) are mixed in different ratios then processed with a press machine and cured to produce briquettes that exhibit zero damage, even after combustion. The results show that the optimal composition for SGC briquette production according to fuel quality and ash shape retention is 20 wt.% SCG; 71 wt.% BA; 9 wt.% KC; and 15 wt.% solution with a 20:1 water/Ca(OH)₂ mixing ratio. This results in a low heating value of 15.8 MJ/kg, 86.82% durability before combustion, and 99.46% durability after combustion. In addition, combustion tests with SCG briquettes confirmed their potential as an environmentally friendly alternative fuel to anthracite briquettes.
Hardware‑simulator development and implementation of battery charger for personal mobility devices
Yeongsu Bak 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.2
Recently, research on personal mobility devices (PMDs) such as electric motorcycles, electric bikes, electric scooters, and electric wheelchairs has been globally proceeded. However, PMDs have a disadvantage since the required battery voltage is different depending on the type of PMD. Therefore, to charge the battery of a PMD, an individual battery charger should be used depending on type of PMD which reduces industrial usability and availability of PMDs. To solve this problem, a battery charger capable of responding to various battery voltages is required. In this paper, the hardware-simulator development of a battery charger that can respond to the various battery voltages of PMDs is proposed, and it consists of a boost converter, a half-bridge series resonant converter, and a buck converter. Additionally, this paper presents a control strategy for use in the proposed hardware simulator. The effectiveness of the proposed hardware simulator and its control strategy are verified by experimental results.
Yeongsu Bak,Yun Jang,이교범 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.6
This paper presents an improved torque predictive control (TPC) for permanent magnet synchronous motors (PMSMs) using an indirect matrix converter (IMC). The IMC has characteristics such as a high power density and sinusoidal waveforms of the input-output currents. Additionally, this configuration does not have any DC-link capacitors. Due to these advantages of the IMC, it is used in various application field such as electric vehicles and railway cars. Recently, research on various torque control methods for PMSM drives using an IMC is being actively pursued. In this paper, an improved TPC method for PMSM drives using an IMC is proposed. In the improved TPC method, the magnitudes of the voltage vectors applied to control the torque and flux of the PMSM are adjusted depending on the PMSM torque control such as the steady state and transient response. Therefore, it is able to reduce the ripples of the output current and torque in the low-speed and high-speed load ranges. Additionally, the improved TPC can improve the dynamic torque response when compared with the conventional TPC. The effectiveness of the improved TPC method is verified by experimental results.
Image Understanding for Visual Dialog
( Yeongsu Cho ),( Incheol Kim ) 한국정보처리학회 2019 Journal of information processing systems Vol.15 No.5
This study proposes a deep neural network model based on an encoder-decoder structure for visual dialogs. Ongoing linguistic understanding of the dialog history and context is important to generate correct answers to questions in visual dialogs followed by questions and answers regarding images. Nevertheless, in many cases, a visual understanding that can identify scenes or object attributes contained in images is beneficial. Hence, in the proposed model, by employing a separate person detector and an attribute recognizer in addition to visual features extracted from the entire input image at the encoding stage using a convolutional neural network, we emphasize attributes, such as gender, age, and dress concept of the people in the corresponding image and use them to generate answers. The results of the experiments conducted using VisDial v0.9, a large benchmark dataset, confirmed that the proposed model performed well.
Restarting Method for Hydraulic Turbine Generation Systems Applied PMSG Sensorless Control
Yeongsu Bak,Kyo-Beum Lee 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper presents a restarting method for hydraulic turbine generation systems applied permanent magnet synchronous generator (PMSG) sensorless control. The hydraulic turbine generation systems replace a differential pressure control valves (DPCVs) in order to utilize an unused differential pressure (DP) energy in the heat transmission network. The DP control of high-pressure fluids in the heat transmission network is performed through the sensorless control of the PMSG connected to the hydraulic turbine, which is consistently rotated by the high-pressure fluids flowing into the heat transmission network. In these systems, the rotor frequency and position of the PMSG are required for the restarting method. In this paper, the restarting method for the hydraulic turbine generation systems is proposed and it is performed by estimating the rotor frequency and position of the PMSG using the shortcircuit current vectors. The effectiveness of the proposed restarting method is verified by simulation results.
Bak, Yeongsu,Jang, Yun,Lee, Kyo-Beum The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.6
This paper presents an improved torque predictive control (TPC) for permanent magnet synchronous motors (PMSMs) using an indirect matrix converter (IMC). The IMC has characteristics such as a high power density and sinusoidal waveforms of the input-output currents. Additionally, this configuration does not have any DC-link capacitors. Due to these advantages of the IMC, it is used in various application field such as electric vehicles and railway cars. Recently, research on various torque control methods for PMSM drives using an IMC is being actively pursued. In this paper, an improved TPC method for PMSM drives using an IMC is proposed. In the improved TPC method, the magnitudes of the voltage vectors applied to control the torque and flux of the PMSM are adjusted depending on the PMSM torque control such as the steady state and transient response. Therefore, it is able to reduce the ripples of the output current and torque in the low-speed and high-speed load ranges. Additionally, the improved TPC can improve the dynamic torque response when compared with the conventional TPC. The effectiveness of the improved TPC method is verified by experimental results.