Jul-Ki Seok

Yeungnam University, Onyang, South Chungcheong, South Korea

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Publications (69)84.55 Total impact

  • SeHwan Kim, Jul-Ki Seok
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    ABSTRACT: A hybrid position sensorless motor control strategy is developed to meet the challenges of electrically assisted turbo-charger (EATC) systems integrated into an automotive engine plant. The proposed controller has a straightforward structure with properties that combines the conventional current vector controller (CVC) and the proposed hexagon voltage modulation controller (HVMC). The proposed HVMC accomplishes the maximum available voltage utilization, allowing a larger motor torque generation per ampere than that of current control alone in the 2nd flux weakening region. This feature leads to a higher PM flux linkage of the motor design, which lets us capture the reliable back-EMF information at the starting speed. In addition, setting a lower bound of the base speed can be achieved to avoid non-ideal current regulation problems at higher speeds. The proposed structure can offer further flexibilities in motor design and drive control, beyond a conventional turbo-charger.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • YoungSun Lee, SeYoung Park, Jul-Ki Seok
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    ABSTRACT: This paper evaluates the comprehensive optimization process of associated passive components of three-phase front-end interleaved boost converters (IBCs) to enhance the power density. It was found that the circulating zero-sequence current between rectifiers gives a negative impact on the low-order harmonics of the input current. The effect of circulating current was first analyzed in detail and the average input current model was developed in the presence of the circulating current. The model is subsequently incorporated into the development of the physics-based average current controller to compensate for harmonic distortions without sacrificing the system power density. The proposed method can be an attractive solution for enhancing the power density of low-power consumer electronic applications that need to meet the harmonic regulations.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
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    Amir Parastar, Jul-Ki Seok
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    ABSTRACT: Offshore wind farms are rapidly growing owing to their comparatively more stable wind conditions than onshore and land-based wind farms. The power capacity of offshore wind turbines has been increased to 5MW in order to capture a larger amount of wind energy, which results in an increase of each component's size. Furthermore, the weight of the marine turbine components installed in the nacelle directly influences the total mechanical design, as well as the operation and maintenance (O&M) costs. A reduction in the weight of the nacelle allows for cost-effective tower and foundation structures. On the other hand, longer transmission distances from an offshore wind turbine to the load leads to higher energy losses. In this regard, DC transmission is more useful than AC transmission in terms of efficiency because no reactive power is generated/consumed by DC transmission cables. This paper describes some of the challenges and difficulties faced in designing high-power-density power conversion systems (HPDPCSs) for offshore wind turbines. A new approach for high gain/high voltage systems is introduced using transformerless power conversion technologies. Finally, the proposed converter is evaluated in terms of step-up conversion ratio, device number, modulation, and costs.
    Journal of power electronics 01/2013; 13(5). · 0.78 Impact Factor
  • SeHwan Kim, Jul-Ki Seok
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    ABSTRACT: A hybrid maximum voltage utilization controller is developed for interior permanent-magnet synchronous motors over a wide operating range. The structure of the controller combines the current vector control (CVC)-type maximum torque per ampere controller and the modulating voltage-scaled controller (MVSC). The hybrid structure provides a smooth transition from the CVC to the proposed MVSC mode by deactivating the current regulator in the flux weakening region. A seamless transition to a full six-step modulation can be realized by adjusting the scaling gain, which is a significant merit in terms of power utilization for wide flux weakening applications. This paper also examines the torque control accuracy under motor parameter drifts to determine how to decouple its effect using a voltage disturbance state-filter design.
    IEEE Transactions on Power Electronics 01/2013; 28(12):5639-5646. · 5.73 Impact Factor
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    ABSTRACT: This paper presents a new solid-state step-up resonant Marx modulator (S3RM2) with a continuous output current for offshore wind energy applications. The developed topology is based on the Marx generator concept, where magnetic switches are replaced by solid-state switching devices. The proposed converter is characterized by resonant switching transitions to achieve minimal switching losses and maximum system efficiency. Therefore, a higher switching frequency is conceivable to attain a higher power density. A double module consists of the 4-active switches operating at the output voltage up to seven times as high as the input voltage. An appropriate output capacitor size is considered to eliminate output voltage ripples and work as charge storage. The series-modular and cascade configurations of the S3RM2 have the advantage of being readily applicable to multilevel power switching converters with an arbitrary number of levels. The developed topology has been implemented on a 5-kW prototype converter to verify its feasibility.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • SeHwan Kim, Jul-Ki Seok
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    ABSTRACT: This paper proposes an enhanced direct torque and flux control method using the discrete-time version of the physical constraints to complete the finite-settling-step direct torque and flux control (FSS-DTFC) algorithm with a constant switching frequency. Successful application of the control approach has been corroborated by a graphical and analytical analysis that naturally leads to a single voltage selection policy for the discrete-time current limit (DTCL)-based FSS-DTFC. The algorithm has the advantage of providing adequate results over the number of potential secondary upsets found in the steady-state current limit (SSCL)-based DTFC. The proposed voltage selection rule enables the motor to track the fast changes in torque and stator flux linkage, which improves dynamic responses significantly over a wide constant-power operating region. The control strategy has been evaluated on a 900W IPMSM in both simulation and experiment.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
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    ABSTRACT: Recent power electronics and variable-frequency motor drive technologies have been applied to air conditioners to improve efficiency and power density. However, the mechanical vibrations and acoustic noise resulting from the compressor still remain as a serious problem. This paper presents the development and implementation of an online disturbance state-filter for the suppression of multiple unknown and time-varying vibrations of air conditioning systems. The proposed design has a form of the state-filter based on a Luenburger-style closed-loop speed observer. An active vibration decoupling strategy with an estimated disturbance is provided, which manipulates a motor torque command. Since the proposed estimation does not require any additional transducers or hardware for obtaining real-time information upon disturbances, it is suitable for retrofitting industrial air conditioners.
    Journal of power electronics 01/2012; 12(6). · 0.78 Impact Factor
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    ABSTRACT: This paper proposes the development and implementation of a hybrid maximum voltage utilization controller for interior permanent magnet synchronous motors (IPMSMs) over a wide operating region. It has a structure that combines the current vector control (CVC)-type Maximum Torque Per Ampere (MTPA) controller and the modulating voltage scaled controller (MVSC). Particularly, the current regulator is deactivated for achieving the true maximum voltage utilization in the MVSC region. The hybrid structure provides a smooth transition from the CVC to the proposed MVSC mode by deactivating the current regulator in the flux weakening region. A seamless transition to the full six-step modulation can be easily realized by adjusting a scaling gain, which can be considered a very significant merit in terms of power utilization for wide flux weakening applications. This paper also attempts to investigate the torque control accuracy under motor parameter drifts and provide how to decouple its influence using a voltage disturbance state-filter design.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
  • Sehwan Kim, Jul-Ki Seok
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    ABSTRACT: This paper proposes a voltage-limited finite-settling-step direct torque and flux control (FSS-DTFC) method with a constant switching frequency for torque-controlled interior permanent-magnet synchronous motors (IPMSMs). The proposed control law dynamically scales voltage vectors on the hexagonal voltage boundary to ensure maximum torque capabilities at given operating conditions, while simultaneously regulating the stator flux linkage magnitude under flux-weakening operation. Instead of evaluating control performance based on intuitive voltage selection rule, this paper focuses on developing a discrete time function of the rate of change of an air-gap torque for facilitating optimal voltage vector choices. Then, this analytical solution leads to optimal voltage modification at each time step with respect to the available inverter voltage. The voltage-limited FSS-DTFC approach has potential advantages of achieving fastest transient torque trajectories and direct manipulation of the stator flux linkage while exploiting maximum voltage excitation.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
  • Source
    SeHwan Kim, Chan-Hee Choi, Jul-Ki Seok
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    ABSTRACT: This paper presents the development and implementation of an online voltage disturbance estimator to achieve the precise torque control of interior permanent magnet synchronous motors (IPMSMs) over a wide operating region. Different design methodologies for disturbance extraction are analyzed using a complex vector frequency-response function (FRF) and evaluated in terms of estimation accuracy. The proposed design has a form of the state-filter based on a Luenburger-style closed-loop stator current vector observer. We provide an accurate torque control strategy with the estimated disturbance, which is based on a torque command manipulation. In addition, the developed estimator is proven to work with any torque control schemes incorporating even with numerous lookup tables. The proposed disturbance estimation scheme has the advantage of being general and readily applicable to a wide range of other systems, such as PWM converters and symmetric machines.
    Energy Conversion Congress and Exposition (ECCE), 2011 IEEE; 10/2011
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    Chan-Hee Choi, Jul-Ki Seok, R.D. Lorenz
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    ABSTRACT: This paper proposes a wide-speed deadbeat-direct torque and flux control (DB-DTFC) method associated with inverter voltage and current constraints of interior permanent-magnet synchronous motors (IPMSMs). The proposed approach has potential advantages controlling torque and flux linkage at voltage and current limits since integrators are not involved for torque control or flux weakening. An automatic transition between non-limited operation and six-step modulation can be achieved without modifying the control law. To support this, we provide a graphical and analytic analysis that naturally leads to a unique stator voltage vector selection on the hexagon. The proposed controller can maximize the available inverter voltage and generate higher output torque than conventional current vector controllers at high speeds. The method developed in this paper also maintains beneficial DTC features, such as fast dynamics and direct manipulation of the stator flux linkage for flux weakening.
    Energy Conversion Congress and Exposition (ECCE), 2011 IEEE; 10/2011
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    Sung-Kuk Kim, Jul-Ki Seok
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    ABSTRACT: This paper presents a nonparametric approach to failure detection of broken rotor bars in inverter-fed induction motors (IMs). We lay the mathematical foundation for a diagnostic model of a rotor bar fault that captures the rotor bar high-frequency (HF) characteristics. The model shows that the HF equivalent motor resistance can be used as a direct indicator of broken rotor bars. It should be emphasized that the proposed detection methodology is applicable to any shape of rotor slot design by incorporating the idea of synchronous reference frame based injection and by taking the HF resistance as the fault detector. The proposed detection technique is also insensitive to other motor parameters and is effective under arbitrary load conditions. The full time-domain-based signature process provides efficient detection and enhances fault isolation. The identification scheme was implemented and tested on an inverter-fed 1.5-kW IM.
    IEEE Transactions on Industry Applications 09/2011; · 1.67 Impact Factor
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    ABSTRACT: In this paper, a controller design of a voice coil motor (VCM) with enhanced disturbance input decoupling performance, especially for precise automated manufacturing processes, is proposed. To enhance the force control accuracy, a disturbance state filter for force control is applied to estimate and compensate for the varying dynamics of VCM systems, such as nonlinearly variable loads and other uncertainties. The state filter estimation accuracy in the presence of system parameter errors is fully analyzed. In addition, the proposed disturbance decoupling method is computationally efficient and robust to other parameter errors. The proposed algorithm is implemented in a developed VCM actuator and verified to be appropriate for a VCM drive system with unknown disturbances.
    Power Electronics and ECCE Asia (ICPE & ECCE), 2011 IEEE 8th International Conference on; 07/2011
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    ABSTRACT: In this paper, the feasibility of applying a position sensorless control technique to hybrid electric vehicles (HEVs) is practically evaluated. The proposed position estimator has a straightforward structure with properties that combines the model and the saliency tracking-based rotor position estimation for interior permanent magnet synchronous motors (IPMSMs). The proposed method can be used in the event of sensor loss or sensor recovery to sustain continuity of operations. The developed system takes into account the estimated position transition between two distinct sensorless methods. The transition is enhanced by introducing a synchronized transition algorithm based on a single tracking observer. Extensive experimental results are presented to verify the principles and show a reliable estimation performance over the entire speed range including standstill under 150% load conditions.
    Journal of power electronics 01/2011; 11(4). · 0.78 Impact Factor
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    Sung-Kuk Kim, Jul-Ki Seok
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    ABSTRACT: This paper presents a non-parametric approach to failure detection of a broken rotor bar for an inverter-fed induction motors (IM). We lay the mathematical foundation for the concept of a diagnostic model of a rotor bar fault. The diagnostic model captures rotor bar high frequency (HF) characteristics which leads us to a conclusion that the HF equivalent motor resistance can be used as a direct indicator of broken rotor bars. The proposed detection technique is insensitive to other motor parameters and is effective under arbitrary load conditions. The time domain-based signature analysis enables the efficient detection and enhances fault isolation property. The identification scheme was implemented and tested on an inverter-fed 1.5 kW induction motor.
    Energy Conversion Congress and Exposition (ECCE), 2010 IEEE; 10/2010
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    ABSTRACT: We propose a current injection-based estimator to identify accurately standstill induction motor (IM) parameters necessary for vector control. A mathematical model that faithfully represents the general deep bar effect is introduced. Then, two exciting signals with a different frequency are sequentially injected to track the parameters based on the frequency function of the rotor bar. The proposed methodology employs closed-loop control of an injected current due to little knowledge of the unknown motor, rather than the open-loop voltage injection approaches commonly used in sensorless control schemes. Subsequently, this control scheme proactively prevents electrical accidents resulting from inadequate open-loop voltage injection. Our developed specialized offline commissioning test compensates for the phase delay resulting from the drive, which significantly affects estimation precision. The effectiveness of the identification technique is validated by means of experiments performed on three different IMs.
    IEEE Transactions on Industry Applications 11/2009; · 1.67 Impact Factor
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    ABSTRACT: This paper presents a discrete time deadbeat-direct torque and flux controller (DB-DTFC) for interior permanent magnet synchronous machines (IPMSMs). A Gopinath-style discrete time flux linkage observer is developed which contains two different flux estimation methods based on current and voltage models for flux linkage. This observer produces correctly estimated flux linkages needed for accurate DB-DTFC implementation. In order to eliminate the sampling delay due to a characteristic of digital control computation, a complex vector model-based rotor reference frame current observer is also developed. Combining the discrete time current and flux linkage observers, the correct single time step (deadbeat) air-gap torque and stator flux linkage control at the (constant) switching frequency is achieved and experimentally evaluated.
    Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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    Kyung-Rae Cho, Jul-Ki Seok
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    ABSTRACT: We have developed a pure-integration-based flux acquisition method for ac adjustable-speed drives. Based on the current-measurement-error analysis, a simple resonant-type observer is utilized to eliminate the drift or dc offset that originated in the current acquisition process. All the processes in correcting the problem do not rely on motor parameters and do not interfere with other higher frequency contents such as inverter nonlinearity and motor cogging effects. The proposed technique further contains a residual error compensator to completely correct the initial value error and to eliminate miscellaneous dc offset errors of the integrator. The acquisition accuracy of the flux is significantly improved through pure integration by restraining the error of the flux magnitude and phase angle at a low stator frequency. Since the proposed scheme is based on a two-phase current measurement system, it is suitable for retrofitting ac drives, where two current sensors are commonly used.
    IEEE Transactions on Industry Applications 09/2009; · 1.67 Impact Factor
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    Kyung-Rae Cho, Jul-Ki Seok
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    ABSTRACT: This paper analyzes a high-frequency (HF) voltage-injection-based rotor winding temperature estimation method for current-regulated squirrel-cage induction motors (IMs). We develop a theoretical HF model of the rotor bar and then first provide an analysis of relevant HF model-based estimation aspects, such as the dependence of the rotor leakage inductance on the temperature and the relationship between the rotor resistance and rotor leakage inductance. We also include an analysis of magnetic saturation to improve the estimation accuracy, as well as an analysis of the phase delay effect resulting from the drive that significantly affects the HF signal precision. Then, a specialized offline commissioning scheme is proposed to compensate for the effect of the phase delay and magnetic saturation. The estimation technique and sensitivity analysis are verified by means of experiments performed on an inverter-fed 1.5-kW IM.
    IEEE Transactions on Industry Applications 09/2009; · 1.67 Impact Factor
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    Chan-Hee Choi, Jul-Ki Seok
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    ABSTRACT: In this paper, we propose an injection-based axis switching (IAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize position detection error and velocity estimation ripple resulting from the zero-current-clamping (ZCC) effect for surface-mounted permanent-magnet motors. When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitude-modulated pattern. Using this information, the IAS technique allows one to avoid multiple zero crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load condition, the pulsating voltage is injected only on the d -axis, while the d -axis current is controlled to a certain nonzero value. Under a load condition, the injection voltage is switched to the q -axis, while the d -axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance in a region of ZCC without a predefined offline commissioning test than the standard pulsating injection scheme. Experiments illustrate the effectiveness of the proposed method in suppressing the estimation error caused by the ZCC disturbance and in extending the system bandwidth.
    IEEE Transactions on Industry Applications 01/2009; · 1.67 Impact Factor

Publication Stats

488 Citations
84.55 Total Impact Points

Institutions

  • 2001–2010
    • Yeungnam University
      • Department of Electrical Engineering
      Onyang, South Chungcheong, South Korea
  • 1995–1997
    • Seoul National University
      • Department of Electrical and Computer Engineering
      Seoul, Seoul, South Korea