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Prof. Yeongsu Bak
Keimyung University

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Research Keywords & Expertise

0 Power Electronics
0 Power Electronics and AC Machine Drive System
0 Matrix Converters
0 Power electronics converters, Topologies and control
0 power electronics for renewable energy

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Journal article
Published: 09 February 2021 in IEEE Transactions on Industrial Electronics
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This paper proposes a dynamic characteristic improvement of phase-shift full-bridge center-tapped (PSFB-CT) converter using a model predictive control (MPC) method. The PSFB-CT converter is widely used for low voltage DC/DC converters (LDC) in electric vehicles (EVs). In general, its output voltage is a control object which is usually controlled using a proportional-integral (PI) control-based output voltage controller and current controller. However, it has a disadvantage such as undesirable dynamic characteristic of the PSFB-CT converter and the necessity of gain tuning. Especially, if the gain of the PI controller is increased to improve the dynamic characteristic of the PSFB-CT converter, an overshoot of the output voltage can occur. In this paper, the advanced voltage control using the MPC method is proposed to improve the dynamic characteristic of the PSFB-CT converter without overshoot of the output voltage. As a result, not only fast dynamic characteristic but also robustness from a sudden change of load impedance. The effectiveness of the proposed MPC method was proved by the simulation and experimental results

ACS Style

Yeongsu Bak; Young Jae Lee; Kyo-Beum Lee. Dynamic Characteristic Improvement of Phase-Shift Full-Bridge Center-Tapped Converters Using a Model Predictive Control. IEEE Transactions on Industrial Electronics 2021, PP, 1 -1.

AMA Style

Yeongsu Bak, Young Jae Lee, Kyo-Beum Lee. Dynamic Characteristic Improvement of Phase-Shift Full-Bridge Center-Tapped Converters Using a Model Predictive Control. IEEE Transactions on Industrial Electronics. 2021; PP (99):1-1.

Chicago/Turabian Style

Yeongsu Bak; Young Jae Lee; Kyo-Beum Lee. 2021. "Dynamic Characteristic Improvement of Phase-Shift Full-Bridge Center-Tapped Converters Using a Model Predictive Control." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 13 December 2020 in Electronics
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This study presents finite set-predictive torque control (FS-PTC) with discrete space vector modulation (DSVM) for indirect matrix converter (IMC)-fed permanent magnet synchronous motors (PMSMs). The implementation of FS-PTC with DSVM in an IMC requires high computation time due to the large number of synthesized voltage vectors (VVs). To reduce computation time caused by considering all VVs, a new preselection strategy is proposed to reduce the computational numerations from 37 to 6 VVs. The proposed algorithm can reduce torque and flux ripples and achieve robust characteristics against parameter variations. Additionally, the increased degree of VVs can improve the correlation between the rectifier and inverter sides of the IMC. The effectiveness of the proposed method is verified by simulation and experimental results.

ACS Style

Ibrahim Mohd Alsofyani; Yeongsu Bak; Kyo-Beum Lee. Improved Finite Set-Predictive Torque Control of PMSM Fed by Indirect Matrix Converter with Discrete Space Vector Modulation. Electronics 2020, 9, 2133 .

AMA Style

Ibrahim Mohd Alsofyani, Yeongsu Bak, Kyo-Beum Lee. Improved Finite Set-Predictive Torque Control of PMSM Fed by Indirect Matrix Converter with Discrete Space Vector Modulation. Electronics. 2020; 9 (12):2133.

Chicago/Turabian Style

Ibrahim Mohd Alsofyani; Yeongsu Bak; Kyo-Beum Lee. 2020. "Improved Finite Set-Predictive Torque Control of PMSM Fed by Indirect Matrix Converter with Discrete Space Vector Modulation." Electronics 9, no. 12: 2133.

Journal article
Published: 21 February 2020 in Electronics
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This paper presents not only a hardware-simulator development for hydraulic turbine generation systems (HTGS) in a district heating system (DHS) but also its control strategies and sequence. Generally, a DHS uses a differential pressure control valve (DPCV) to supply high-pressure–high-temperature fluids for customers depending on distance. However, long-term exposure of the DPCV to fluids increases the probability of cavitation and leads to heat loss in an event of cavitation. Therefore, a HTGS was introduced to solve this problem. It performs differential pressure control of the fluids, replaces the DPCV, and converts excess energy wasted by the DPCV to electrical energy. In this paper, the development of a hardware-simulator for HTGSs with a back-to-back converter, which uses two-level topologies, is proposed; moreover, control strategies and sequence used in this design are presented. The performance and validity of the proposed hardware-simulator and its control strategies are demonstrated by experimental results.

ACS Style

Sung-Soo Jeon; Young Jae Lee; Yeongsu Bak; Kyo-Beum Lee. Hardware-Simulator Development and Implementation for Hydraulic Turbine Generation Systems in a District Heating System. Electronics 2020, 9, 368 .

AMA Style

Sung-Soo Jeon, Young Jae Lee, Yeongsu Bak, Kyo-Beum Lee. Hardware-Simulator Development and Implementation for Hydraulic Turbine Generation Systems in a District Heating System. Electronics. 2020; 9 (2):368.

Chicago/Turabian Style

Sung-Soo Jeon; Young Jae Lee; Yeongsu Bak; Kyo-Beum Lee. 2020. "Hardware-Simulator Development and Implementation for Hydraulic Turbine Generation Systems in a District Heating System." Electronics 9, no. 2: 368.

Journal article
Published: 10 September 2019 in IFAC-PapersOnLine
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This paper proposes a controller design for a stability improvement of an integrated charging system in hybrid electric vehicle (HEV). Conventional HEVs include a starter generator system, which consists of generator and its drive inverter. Contrary to them, the proposed integrated charging system operates as a generator drive system and bi-directional battery charging system by installing some power relays and additional circuit in general HEVs. Therefore, the integrated charging system results in reduced system components in HEV by eliminating on-board charger (OBC), also the weight and system volume can be decreased. In addition, a feed-forward compensation method is proposed to improve the transient states characteristics of the battery charging system in this paper. The effectiveness and validity of proposed design and control method for the integrated charging system is verified by simulation results.

ACS Style

Ho-Sung Kang; Seok-Min Kim; Yeongsu Bak; Kyo-Beum Lee. A Controller Design for a Stability Improvement of an Integrated Charging System in Hybrid Electric Vehicle. IFAC-PapersOnLine 2019, 52, 141 -146.

AMA Style

Ho-Sung Kang, Seok-Min Kim, Yeongsu Bak, Kyo-Beum Lee. A Controller Design for a Stability Improvement of an Integrated Charging System in Hybrid Electric Vehicle. IFAC-PapersOnLine. 2019; 52 (4):141-146.

Chicago/Turabian Style

Ho-Sung Kang; Seok-Min Kim; Yeongsu Bak; Kyo-Beum Lee. 2019. "A Controller Design for a Stability Improvement of an Integrated Charging System in Hybrid Electric Vehicle." IFAC-PapersOnLine 52, no. 4: 141-146.

Journal article
Published: 22 June 2019 in Electronics
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This paper presents a control method for phase-shift full-bridge center-tapped (PSFB-CT) converters using hybrid fuzzy sliding mode controllers (SMCs). Conventionally, the output voltage of a PSFB-CT converter is controlled by using a proportional-integral (PI) controller. However, the dynamic characteristic of the converter is undesirable, and the converter is not robust to disturbances. In order to overcome these disadvantages, the SMC based on PI control has been applied for the PSFB-CT converter. However, there is a chattering problem when the SMC gain is increased to improve the dynamic characteristic. In this paper, a control method for the PSFB-CT converter using fuzzy logic control is proposed. By varying the gain of the SMC through the fuzzy logic control, not only can the dynamic characteristic of the PSFB-CT converter be improved, but the chattering problem can also be relieved. The effectiveness of the proposed control method for the PSFB-CT converter was verified by the simulation and experimental results.

ACS Style

Young Jae Lee; Yeongsu Bak; Kyo-Beum Lee. Control Method for Phase-Shift Full-Bridge Center-Tapped Converters Using a Hybrid Fuzzy Sliding Mode Controller. Electronics 2019, 8, 705 .

AMA Style

Young Jae Lee, Yeongsu Bak, Kyo-Beum Lee. Control Method for Phase-Shift Full-Bridge Center-Tapped Converters Using a Hybrid Fuzzy Sliding Mode Controller. Electronics. 2019; 8 (6):705.

Chicago/Turabian Style

Young Jae Lee; Yeongsu Bak; Kyo-Beum Lee. 2019. "Control Method for Phase-Shift Full-Bridge Center-Tapped Converters Using a Hybrid Fuzzy Sliding Mode Controller." Electronics 8, no. 6: 705.

Journal article
Published: 08 May 2019 in IEEE Transactions on Industrial Electronics
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This paper presents an improved rotating restart method for a sensorless permanent-magnet synchronous motor (PMSM) drive system using repetitive zero voltage vectors. To restart the sensorless PMSM drive system, a method for estimating initial rotor position and speed is required due to the absence of sensors such as encoders and resolvers. The rotor position and speed can be estimated using the short-circuit current vectors generated by applying zero voltage vectors. However, the estimated rotor position and speed can be inaccurate. The inaccurate rotor position causes the current is distorted by the back electromotive force (EMF) of the PMSM and it is impossible to precisely control the system. Therefore, an improved rotating restart method for the sensorless PMSM drive system using repetitive zero voltage vectors is proposed. The effectiveness of the proposed method is verified through simulation and experimental results using a 5-kW PMSM drive system.

ACS Style

Dong-Woo Seo; Yeongsu Bak; Kyo-Beum Lee. An Improved Rotating Restart Method for a Sensorless Permanent Magnet Synchronous Motor Drive System Using Repetitive Zero Voltage Vectors. IEEE Transactions on Industrial Electronics 2019, 67, 3496 -3504.

AMA Style

Dong-Woo Seo, Yeongsu Bak, Kyo-Beum Lee. An Improved Rotating Restart Method for a Sensorless Permanent Magnet Synchronous Motor Drive System Using Repetitive Zero Voltage Vectors. IEEE Transactions on Industrial Electronics. 2019; 67 (5):3496-3504.

Chicago/Turabian Style

Dong-Woo Seo; Yeongsu Bak; Kyo-Beum Lee. 2019. "An Improved Rotating Restart Method for a Sensorless Permanent Magnet Synchronous Motor Drive System Using Repetitive Zero Voltage Vectors." IEEE Transactions on Industrial Electronics 67, no. 5: 3496-3504.

Journal article
Published: 01 April 2019 in IEEE Transactions on Power Electronics
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In this paper, two simple control methods are proposed for improving direct torque control with a constant frequency torque controller (CFTC-DTC) in induction machines. The CFTC-DTC was initially introduced to reduce torque ripple and achieve constant switching frequency in inverters. However, when compared to the original direct torque control, the CFTC-DTC algorithm suffers from slow torque dynamic response owing to the selection of zero-voltage vectors during torque transient. In addition, when the motor operates at low speed, flux droop occurs at sector transitions, which leads to undesirable current distortions. The problem of flux droop occurs because of short-duty voltage cycles and small radial voltage components at low speeds. This paper has two main contributions: to eliminate zero-voltage vectors during torque dynamics in order to establish a fast torque response in the transient state, and to minimize the flux droop at the sector transitions by applying another triangular carrier and modifying the torque output in order to increase the duty voltage cycles at low motor speeds. A detailed analysis of the problems and proposed methods is presented. Experimental results are provided to validate the effectiveness of both proposed methods.

ACS Style

Ibrahim Mohd Alsofyani; Yeongsu Bak; Kyo-Beum Lee. Fast Torque Control and Minimized Sector-Flux Droop for Constant Frequency Torque Controller Based DTC of Induction Machines. IEEE Transactions on Power Electronics 2019, 34, 12141 -12153.

AMA Style

Ibrahim Mohd Alsofyani, Yeongsu Bak, Kyo-Beum Lee. Fast Torque Control and Minimized Sector-Flux Droop for Constant Frequency Torque Controller Based DTC of Induction Machines. IEEE Transactions on Power Electronics. 2019; 34 (12):12141-12153.

Chicago/Turabian Style

Ibrahim Mohd Alsofyani; Yeongsu Bak; Kyo-Beum Lee. 2019. "Fast Torque Control and Minimized Sector-Flux Droop for Constant Frequency Torque Controller Based DTC of Induction Machines." IEEE Transactions on Power Electronics 34, no. 12: 12141-12153.

Journal article
Published: 31 January 2019 in IEEE Transactions on Power Electronics
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This paper proposes a new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and ten power switches. This novel boost switched-capacitor 7-level inverter (BSC7LI) possesses voltage boosting capability with an achievable maximum voltage level 1.5 times the input direct current (dc) voltage. The generation of higher output voltage does not incur high-voltage stress on any power switch in this topology, as the peak inverse voltages of all power switches do not exceed the input source voltage. In addition, capacitor voltage balancing is not essential since the floating capacitors are effectively balanced during the charging and discharging processes. Furthermore, the proposed topology eliminates the need for multiple isolated dc sources, and a single dc source is sufficient in both its single-phase and three-phase topologies. The operating principle and steady-state analysis of the proposed topology are elaborated. Experimental results from a single-phase prototype are then presented to verify the validity of the proposed topology.

ACS Style

Sze Sing Lee; Yeongsu Bak; Seok-Min Kim; Anto Joseph; Kyo-Beum Lee. New Family of Boost Switched-Capacitor Seven-Level Inverters (BSC7LI). IEEE Transactions on Power Electronics 2019, 34, 10471 -10479.

AMA Style

Sze Sing Lee, Yeongsu Bak, Seok-Min Kim, Anto Joseph, Kyo-Beum Lee. New Family of Boost Switched-Capacitor Seven-Level Inverters (BSC7LI). IEEE Transactions on Power Electronics. 2019; 34 (11):10471-10479.

Chicago/Turabian Style

Sze Sing Lee; Yeongsu Bak; Seok-Min Kim; Anto Joseph; Kyo-Beum Lee. 2019. "New Family of Boost Switched-Capacitor Seven-Level Inverters (BSC7LI)." IEEE Transactions on Power Electronics 34, no. 11: 10471-10479.

Journal article
Published: 17 January 2019 in IEEE Transactions on Industry Applications
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The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies.

ACS Style

Sze Sing Lee; Kyo-Beum Lee; Ibrahim Mohd Alsofyani; Yeongsu Bak; Jing Fang Wong. Improved Switched-Capacitor Integrated Multilevel Inverter With a DC Source String. IEEE Transactions on Industry Applications 2019, 55, 7368 -7376.

AMA Style

Sze Sing Lee, Kyo-Beum Lee, Ibrahim Mohd Alsofyani, Yeongsu Bak, Jing Fang Wong. Improved Switched-Capacitor Integrated Multilevel Inverter With a DC Source String. IEEE Transactions on Industry Applications. 2019; 55 (6):7368-7376.

Chicago/Turabian Style

Sze Sing Lee; Kyo-Beum Lee; Ibrahim Mohd Alsofyani; Yeongsu Bak; Jing Fang Wong. 2019. "Improved Switched-Capacitor Integrated Multilevel Inverter With a DC Source String." IEEE Transactions on Industry Applications 55, no. 6: 7368-7376.

Journal article
Published: 02 January 2018 in Applied Sciences
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This paper presents a low-voltage ride-through (LVRT) control strategy for grid-connected energy storage systems (ESSs). In the past, researchers have investigated the LVRT control strategies to apply them to wind power generation (WPG) and solar energy generation (SEG) systems. Regardless of the energy source, the main purpose of the LVRT control strategies is to inject reactive power into the grid depending on the grid-code regulations using the grid-side inverter; the proposed LVRT control strategy for grid-connected ESSs also has the same purpose. However, unlike the WPG and SEG systems having unidirectional power flow, grid-connected ESSs have a bidirectional power flow. Therefore, the charging condition of the grid-connected ESSs should be considered for the LVRT control strategy. The proposed LVRT control strategy for grid-connected ESSs determines the injection quantity of the active and reactive currents, and the strategy depends on the voltage drop ratio of the three-phase grid. Additionally, in this paper, we analyzed the variations of the point of common coupling (PCC) voltage depending on the phase of the reactive current during the charging and discharging conditions. The validity of the proposed LVRT control strategy is verified and the variations of the PCC voltage of the grid-connected ESS are analyzed by simulation and experimental results.

ACS Style

Yeongsu Bak; June-Seok Lee; Kyo-Beum Lee. Low-Voltage Ride-Through Control Strategy for a Grid-Connected Energy Storage System. Applied Sciences 2018, 8, 57 .

AMA Style

Yeongsu Bak, June-Seok Lee, Kyo-Beum Lee. Low-Voltage Ride-Through Control Strategy for a Grid-Connected Energy Storage System. Applied Sciences. 2018; 8 (1):57.

Chicago/Turabian Style

Yeongsu Bak; June-Seok Lee; Kyo-Beum Lee. 2018. "Low-Voltage Ride-Through Control Strategy for a Grid-Connected Energy Storage System." Applied Sciences 8, no. 1: 57.

Journal article
Published: 27 December 2016 in Energies
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This paper proposes a balanced current control strategy for the current source rectifier (CSR) stage of an indirect matrix converter (IMC) under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI) of the IMC has unbalanced voltage conditions, it affects the currents of the CSR stage and VSI stage, and the currents are distorted. Above all, the distorted currents of the CSR stage cause instability in the overall system, which can affect the life span of the system. Therefore, in this paper, a control strategy for balanced currents in the CSR stage is proposed. To achieve balanced currents in the CSR stage, the VSI stage should receive DC power without ripple components from the CSR stage. This is implemented by controlling the currents in the VSI stage. Therefore, the proposed control strategy decouples the positive and negative phase-sequence components existing in the unbalanced voltages and currents of the VSI stage. Using the proposed control strategy under unbalanced grid voltage conditions, the stability and life span of the overall system can be improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results.

ACS Style

Yeongsu Bak; June-Seok Lee; Kyo-Beum Lee. Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions. Energies 2016, 10, 27 .

AMA Style

Yeongsu Bak, June-Seok Lee, Kyo-Beum Lee. Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions. Energies. 2016; 10 (1):27.

Chicago/Turabian Style

Yeongsu Bak; June-Seok Lee; Kyo-Beum Lee. 2016. "Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions." Energies 10, no. 1: 27.

Journal article
Published: 30 April 2015 in Energies
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This paper presents an indirect matrix converter (IMC) topology for hybrid electric vehicle (HEV) application with three-phase and single-phase outputs. The HEV includes mechanical, electrical, control, and electrochemical systems among others. In the mechanical system, a traction motor and a compressor motor are used to drive the HEV. The traction motor and the compressor motor are usually operated as three-phase and single-phase motors, respectively. In this respect, a dual AC-drive system can operate the traction and the compressor motor simultaneously. Furthermore, compared to a conventional dual matrix converter system, the proposed topology can reduce the number of switches that the dual outputs share with a DC-link. The application of this system for HEV has advantages, like long lifetime and reduced volume due to the lack of a DC-link. The proposed control strategy and modulation schemes ensure the sinusoidal input and output waveforms and bidirectional power transmission. The proposed system for the HEV application is verified by simulation and experiments.

ACS Style

Yeongsu Bak; Eunsil Lee; Kyo-Beum Lee. Indirect Matrix Converter for Hybrid Electric Vehicle Application with Three-Phase and Single-Phase Outputs. Energies 2015, 8, 3849 -3866.

AMA Style

Yeongsu Bak, Eunsil Lee, Kyo-Beum Lee. Indirect Matrix Converter for Hybrid Electric Vehicle Application with Three-Phase and Single-Phase Outputs. Energies. 2015; 8 (5):3849-3866.

Chicago/Turabian Style

Yeongsu Bak; Eunsil Lee; Kyo-Beum Lee. 2015. "Indirect Matrix Converter for Hybrid Electric Vehicle Application with Three-Phase and Single-Phase Outputs." Energies 8, no. 5: 3849-3866.