Seung-Ki Sul

Seoul National University, Sŏul, Seoul, South Korea

Are you Seung-Ki Sul?

Claim your profile

Publications (314)357.96 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a novel electric propulsion system for naval ships, which consists of Active Front End (AFE) converters directly connected to battery Energy Storage Modules (ESMs). Employing the proposed AFE converters with ESMs in the power systems of naval ships can enhance the reliability and quality of the electric power. Furthermore, the fuel-efficiency of the generator can be improved by a higher loading factor of the generator and its prime movers. The proposed AFE configuration does not require an additional dedicated DC/AC converter for the ESMs. Instead of that, the AFE converter itself can control the DC link voltage and the discharging and/or charging of the ESMs. A control scheme to achieve these control objectives is also presented in this paper. The overall power system, including the generators and electrical loads of a naval ship, is implemented by a small scaled Power Hardware-In-the-Loop (PHIL) simulator. Through this experimental setup, the proposed system configuration and the power control strategies are verified. It is shown that the fuel-efficiency and transient dynamics can be improved in the normal and contingency operation modes.
    Journal of power electronics 01/2014; 14(2). · 0.78 Impact Factor
  • Yongsoon Park, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: The rotor angle can be estimated from the stator flux in permanent magnet synchronous motor (PMSM). Although integrations are essential to estimate the stator flux from the voltages and currents in the stationary reference frame, disturbances can arise in the process of integrations due to practical reasons. In this paper, a frequency-adaptive disturbance observer has been proposed to remove the disturbances in estimating the stator flux and to enhance the accuracy of the rotor angle estimation. The design and utilization of the proposed observer are detailed under the consideration of its application to the practical system driving PMSM. The performance of the proposed sensorless method has been mainly assessed through experiments at low speed operations, where the sensorless drive of PMSM is regarded as being extremely difficult without the signal injection.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency. In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible. The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions.
    IEEE Transactions on Power Electronics 01/2013; 28(6):2760-2769. · 5.73 Impact Factor
  • S. Choe, Eunsoo Jung, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a new sensorless method for a Synchronous Machine with an Inverter Integrated Rotor (SMIIR). The SMIIR is a newly developed machine based on the wound rotor synchronous machine (WRSM) but has no brushes and slip-rings. And conventional high-frequency signal injection sensorless methods are based on physical magnetic saliency. Therefore, conventional methods cannot be applied to the SMIIR which has no sufficient magnetic saliency. The proposed sensorless method suggests virtual resistance saliency created by the rotor-side inverter, whose axes can be placed arbitrarily. Based on this virtual saliency the rotor position information is included and excluded in the relationship between the high-frequency stator voltage and stator current. Because the SMIIR already injects high-frequency voltage for the power transfer, there is no need to inject additional voltage for the proposed high-frequency sensorless method. And initial +d axis detection algorithm using the rotor-side inverter without using magnetic saturation is also proposed. The feasibility of the proposed sensorless method was verified by experimental results with the prototype SMIIR.
    Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE; 01/2013
  • Myoungho Kim, Seung-Ki Sul, Anno Yoo
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper conducts modeling and controller design for SEries-connected Output Universal Link(SEOUL) converter. The SEOUL converter was proposed to interface multiple distributed power sources to the grid with reduced number of reactive components. It employs high-frequency transformer instead of bulky line-frequency transformer as Solid State Transformers(SSTs). Besides, it does not use large DC-link capacitor at the input-side and reduce the size of the input filter. This is inherently possible due to its original operating characteristic. The H-bridges connected to the grid does not perform PWM operation to make the input phase current sinusoidal. Instead, their switches operate synchronized to the grid frequency and the input phase currents are synthesized sinusoidally by the high-frequency power transfer part of the SEOUL converter. This paper focuses on the power transfer of SEOUl converter and develops the analytic model of it. Based on the developed model, a DC-link voltage control strategy is proposed with the decoupling control method. The developed model and proposed control method was verified by experiments. The resultant input phase current is kept as sinusoidal at various operating conditions.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Source
    Byung-Geuk Cho, Jung-Ik Ha, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: To obtain phase currents information in AC drives, shunt sensing technology is known to show great performance in cost-effectiveness and therefore it is widely used in low cost applications. However, shunt sensing methods are unable to acquire phase currents in certain operation conditions. This paper deals with the derivation of the boundary conditions for phase current reconstruction in three-shunt sensing inverters and proposes a voltage injection method to expand the measurable areas. As the boundary conditions are deeply dependent on the switching patterns, they are typically analyzed on the voltage vector plane for space vector pulse width modulation (SVPWM) and discontinuous pulse width modulation (DPWM). In the proposed method, the voltage injection and its compensation are conducted within one sampling period. This guarantees fast current reconstruction and the injected voltage is decided so as to minimize the current ripple. In addition to the voltage injection method, a sampling point shifting method is also introduced to improve the boundary conditions. Simulation and experimental results are presented to verify the boundary condition derivation and the effectiveness of the proposed voltage injection method.
    Journal of power electronics 01/2013; 13(2). · 0.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to develop a new method to operate an interior permanent magnet synchronous machine (IPMSM) on the maximum torque per ampere (MTPA) condition. The characteristics of the MTPA condition were analyzed and the MTPA condition was derived based on the input electric power. The proposed method injects a small current signal used for tracking the MTPA operating point along with the fundamental current for torque generation. This method does not require any machine parameters or premade lookup table. The frequency of the injected signal is several hundred hertz, and the performance of the MTPA tracking is almost free from load torque disturbance. The feasibility of the proposed method was verified under various operating conditions with computer simulation and testing with an 11 kW IPMSM drive system.
    IEEE Transactions on Power Electronics 01/2013; 28(1):488-497. · 5.73 Impact Factor
  • Byung-Geuk Cho, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a reactive power sharing method is proposed for the operation of multiple distributed generation units. When the line impedance is unbalanced, accurate reactive power sharing is challenging with conventional current sharing or droop control strategies. This paper describes the effect of the unequal line impedances on the reactive power sharing accuracy, especially for mainly inductive line impedance. The proposed method compensates the impedance effect by modifying the droop slope and is shown to be effective through two parallel 1MVA units. The accuracy of the reactive power sharing is improved by 26.7% and 42.5% for each DG unit in the grid-connected mode and 11.9% in the islanding mode.
    ECCE Asia Downunder (ECCE Asia), 2013 IEEE; 01/2013
  • Jae-Jung Jung, Hak-Jun Lee, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a control scheme for the Modular Multilevel Converter (MMC) to drive a variable-speed AC machine, especially focusing on improving dynamic performance. Theoretically, the energy balance in the cell capacitors is prone to be unstable at startup and low frequency operation. Therefore, the MMC topology essentially requires advanced strategies for energy balancing so as to suppress the voltage pulsation of each cell capacitor. The pulsation is getting larger as the output frequency of MMC is getting lower. This paper proposes a strategy for robust dynamic response even at zero output frequency of MMC employing leg offset voltage injection. With this proposed strategy, an AC machine has been driven from standstill to rated speed without excessive cell capacitor voltage ripples. The experimental results verify that stable operation is guaranteed for both a 15r/min operation with 40% step load torque and the entire frequency operation with varying load torque.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Myoungho Kim, Seung-Ki Sul, Junggi Lee
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a turn-fault detection method for inverter-fed Interior Permanent Magnet Synchronous Machines(IPMSMs) using high-frequency current injection when the motor is at standstill. When the motor is stopped, the fault current which flows in the faulty turns and the phase currents can be expressed with the injected phase current and the mutual inductance between each phase winding and the faulty turns. Because of the turn-fault, the injected high frequency currents cause different losses according to the direction of the injection. The proposed detection method exploits the difference of the losses of each case to diagnose the turn-fault. Experimental results are provided to verify the proposed detection method. The resultant loss pattern agrees well with that of the electrical model and shows reasonable sensitivity to the turn-fault. Two-turn fault among 27 turns of a phase winding of the motor under test has been detected easily with existing hardware of the drive system.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • So-Yeon Kim, Byung-Geuk Cho, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a control strategy of an active front end (AFE) rectifier to cope with voltage deviation at the shipboard AC-power system. The voltage sags in naval ships may occur when the step load such as a large pulse power weapon is applied or when faults happen in the grid or generators themselves. In this paper, the capability of AFEs to support voltage is presented for the voltage sags. In the proposed control scheme, reactive power is utilized to achieve voltage compensation. For the verification of the effectiveness, simulation using MATLAB/Simulink and PLECS has been conducted.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a design and control method of Interior Permanent Magnet Synchronous Machines (IPMSMs), which is controlled in position sensorless mode based on high frequency signal injection, for absolute position detection and control capability has been addressed. Although conventional motor designs with symmetric structure work well in sensorless speed and torque control modes, their actual mechanical rotor position is unidentifiable since their inductance profile is repeated for every electrical revolution. In order to realize the mechanical rotor position detection capability, from a given template 6-pole/9-slot IPMSM with symmetric structure, an IPMSM design with asymmetric winding and asymmetric rotor geometry is proposed and constructed as a prototype. Based on the proposed design, the mechanical rotor position can be identified at the cost of slight degradation of basic motor characteristics such as torque ripples, harmonics in back EMF, and etc. The overall performances of the proposed IPMSM have been evaluated by rigorous FEM and experimental test.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Byung-Geuk Cho, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper deals with an LCL filter for the grid-connected converter. Active and passive damping methods are compared in a resonance suppression point of view and necessity of the passive damping is claimed, especially for high power systems in which switching frequency is limited lower than 2.5 kHz. Based on the analysis, LCL filter design procedure with passive damping for a two level voltage source converter is introduced. The filter components are optimally selected by investigating stored total energy in the filter and capacity of the converter. Then the resistors are inserted at several locations and comparisons are made to determine the most proper way of passive damping by examining the losses. The effectiveness of the study is supported by simulation and laboratory scale experiment.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
  • Myoungho Kim, Seung-Ki Sul, Junggi Lee
    [Show abstract] [Hide abstract]
    ABSTRACT: Accurate measurement of phase current is crucial in a current-controlled PMSM drive system. Current measurement error directly deteriorates torque control performance. This paper analyzes effects of the current measurement error on the phase current and the output voltage of the current controller. Based on the analysis, a compensation method is proposed. It compensates the offset error and the scaling error separately without any additional hardware but using the output voltage reference of the current controller. The proposed method can be applied to general current-controlled PMSM drives in whole operation range. Experimental results verify the effectiveness of the proposed compensation method.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
  • Sungho Jung, Hak-Jun Lee, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a layout of Insulated Gate Bipolar Transistor(IGBT)-based Current Source Converter (CSC) to reduce stray inductance is proposed. Due to the rapid evolution of IGBT, it has become a competitive switching device in comparison with other high power switching devices even in MW power conversion system. The higher switching frequency of IGBT might reduce the size of other passive component of CSC significantly, and the demerits of CSC can be diminished remarkably, while the merits of CSC can be retained. However, since the switching speed of IGBT is high, the overshoot of the voltage across IGBT due to the stray inductance increases. And, the switching loss and voltage stress would be prohibitive. To decrease the stray inductance, a layout of power circuit exploiting magnetic coupling between bus bar connecting switching devices is devised in this paper. The stray inductances of two different layouts of IGBT-based CSC are compared to verify the effectiveness of the proposed strategy, experimentally.
    01/2012;
  • Myoungho Kim, Anno Yoo, Seung-Ki Sul
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes an isolated universal-link ac–ac power converter suitable for grid connection. The proposed power converter can have multiple ports to connect various loads or electric energy sources, and the configuration can be arranged according to the situation. The proposed power converter does not need to employ the large interface inductor at input side and the huge electrolytic capacitor at dc link. Moreover, it utilizes high-frequency transformers for the galvanic isolation instead of bulky line-frequency transformers. These characteristics of the proposed power converter result in the reduction of the system volume and weight remarkably. The proposed power converter is the modular structure, and an H-bridge works as a basic module of the converter. By stacking the modules, the power converter can be adapted to the high-voltage grid and the various types of loads and/or sources. This paper addresses the structure of the proposed power converter and the fundamental principle of power flow. The operation of the proposed converter is verified by both computer simulations and experimental results with a laboratory-level prototype system.
    IEEE Transactions on Industry Applications 01/2012; 48(2):685-696. · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a synchronous motor with an inverter integrated rotor (SMIIR) is introduced, and its control scheme is proposed. This presents a new breed of synchronous motor in that it integrates an inverter inside the rotor. The basic operational principle and control strategies are discussed. Given these new strategies, the SMIIR can be considered as a synchronous motor which changes its field according to the harmonic voltage of the stator inverter. The feasibility of the proposed structure of the drive system and its operation principle are evaluated through experimental results.
    IEEE Transactions on Industry Applications 01/2012; 48(6):1993-2001. · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an active anti-islanding detection method using negative sequence voltage injection to the grid through a three-phase photovoltaic inverters. Because islanding operation mode can cause a variety of problems, the islanding detection of grid-connected photovoltaic inverter is the mandatory feature. The islanding mode is detected by measuring the magnitude of negative sequence impedance calculated by the negative sequence voltage and current at the point of common coupling. Simulation and experimental test are performed to verify the effectiveness of the proposed method which can detect the islanding mode in the specified time. The test has been done in accordance with the condition on IEEE Std 929-2000.
    The Transactions of the Korean Institute of Power Electronics. 01/2012; 17(6).
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a nine-phase permanent-magnet synchronous motor (PMSM) drive system based on multiple three-phase voltage source inverters. The nine-phase PMSM was developed as a traction motor for an ultrahigh-speed elevator. The mathematical model of the motor was simplified through symmetry of the system. Using the simplified model, the drive system can be controlled by the well-known $d{-}q$ control theory. The feasibility and validity of the drive system were experimentally demonstrated at the world's tallest elevator test tower. Moreover, an additional experiment was performed to ensure the fault-tolerance capability of the system.
    IEEE Transactions on Industry Applications 01/2012; 48(3):987-995. · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In Permanent Magnet Synchronous Machine (PMSM) drives, linear region, which is inside the inscribed circle of the voltage hexagon in the voltage plane, is mainly used for the stable operation. To enhance torque capability under the limited input DC link voltage, the region outside the inscribed circle of the voltage hexagon, known as overmodulation region, can be exploited in the flux-weakening operation. However, the operation of drive system in the overmodulation region cannot be free from the degradation of speed control performance. This paper presents investigations on control issues in the overmodulation region and proposes an algorithm for improving the speed control performance in the overmodulation region. The effectiveness of the proposed method is verified by computer simulations and experiments.
    01/2012;

Publication Stats

6k Citations
357.96 Total Impact Points

Institutions

  • 1992–2012
    • Seoul National University
      • • School of Electrical Engineering and Computer Sciences
      • • Department of Electrical and Computer Engineering
      • • School of Computer Science and Engineering
      • • Korea Electrical Engineering & Sciences Research Institute
      Sŏul, Seoul, South Korea
  • 2005–2009
    • Kongju National University
      • Division of Electrical, Electronic and Control Engineering
      Kongju, South Chungcheong, South Korea
  • 2008
    • Georgia Institute of Technology
      Atlanta, Georgia, United States
  • 2007–2008
    • University of Padova
      Padua, Veneto, Italy
    • Samsung
      Sŏul, Seoul, South Korea
  • 2000–2007
    • Hyundai Motor Company
      Sŏul, Seoul, South Korea
  • 2006
    • RWTH Aachen University
      • Institute for Power Electronics and Electrical Drives
      Aachen, North Rhine-Westphalia, Germany
    • Virginia Polytechnic Institute and State University
      • Department of Electrical and Computer Engineering
      Blacksburg, VA, United States
  • 2003
    • Oregon Center for Advanced Technology Education
      Torrance, California, United States
  • 1999
    • University of Wisconsin, Madison
      • Department of Electrical and Computer Engineering
      Madison, MS, United States
  • 1995–1999
    • Soonchunhyang University
      • Department of Electrical and Electronic Engineering
      Asan, South Chungcheong, South Korea
  • 1998
    • R&D Systems
      Minneapolis, Minnesota, United States
  • 1997
    • Kangwon National University
      • Department of Electronics Engineering
      Kang-neung, Gangwon, South Korea
  • 1996
    • Seoul Semiconductor Co.
      Sŏul, Seoul, South Korea