Dong-Choon Lee

Yeungnam University, Onyang, South Chungcheong, South Korea

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Publications (85)96.45 Total impact

  • Thanh Hai Nguyen, Dong-Choon Lee, Chan-Ki Kim
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    ABSTRACT: In this letter, a novel converter topology of high-voltage direct current (HVDC) transmission for integrating the offshore wind farm (WF) with the grid is proposed, which consists of a series connection of the 12-pulse diode rectifiers and a voltage-source converter (VSC). For this topology, the PCC (point of common coupling) voltage of the offshore WF side is regulated at a constant magnitude and constant frequency by the WFVSC. Also, the current at the PCC becomes almost sinusoidal since the WFVSC functions as an active power filter for the 11th- and 13th-order harmonic current components. By virtue of the diode rectifier, the cost and power loss of HVDC converters is reduced compared with the case of the conventional fully rated VSC, whereas the performance is kept almost the same. The PSCAD/EMTDC simulation results for a 500-MW HVDC transmission system have been shown to verify the validity of the proposed scheme.
    IEEE Transactions on Power Electronics 01/2014; 29(4):1579-1584. · 5.73 Impact Factor
  • Source
    Thanh Hai Nguyen, Dong-Choon Lee, Jong-Ho Kang
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    ABSTRACT: This paper proposes a novel strategy for attenuating the output power fluctuation of the wind farm (WF) in a range of tens of seconds delivered to the grid, where the kinetic energy caused by the large inertia of the wind turbine systems is utilized. A control scheme of the two-level structure is applied to control the wind farm, which consists of a supervisory control of the wind farm and individual wind turbine controls. The supervisory control generates the output power reference of the wind farm, which is filtered out from the available power extracted from the wind by a low-pass filter (LPF). A lead-lag compensator is used for compensating for the phase delay of the output power reference compared with the available power. By this control strategy, when the reference power is lower than the maximum available power, some of individual wind turbines are operated in the storing mode of the kinetic energy by increasing the turbine speeds. Then, these individual wind turbines release the kinetic power by reducing the turbine speed, when the power command is higher than the available power. In addition, the pitch angle control systems of the wind turbines are also employed to limit the turbine speed not higher than the limitation value during the storing mode of kinetic energy. For coordinating the de-rated operation of the WT and the storing or releasing modes of the kinetic energy, the output power fluctuations are reduced by about 20%. The PSCAD/EMTDC simulations have been carried out for a 10-MW wind farm equipped with the permanent-magnet synchronous generator (PMSG) to verify the validity of the proposed method.
    Journal of Electrical Engineering and Technology 01/2014; 9(3). · 0.73 Impact Factor
  • Source
    Jin-Sang Park, Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: This paper proposes a frequency-locked loop (FLL) scheme for a single-phase grid-connected converter. A second-order generalized integrator (SOGI) based on fuzzy logic (FL) is applied to this converter to achieve precise phase angle detection. The use of this method enables the compensation of the nonlinear characteristic of the frequency error, which is defined in the SOGI scheme as the variation of the central frequency through the self-tuning gain. With the proposed scheme, the performance of the SOGI-FLL is further improved at the grid disturbances, which results in the stable operation of the grid converter under grid voltage sags or frequency variation. The PSIM simulation and experimental results are shown to verify the effectiveness of the proposed method.
    Journal of power electronics 01/2014; 14(3). · 0.78 Impact Factor
  • Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: In this paper, a hybrid control scheme for energy storage systems (ESS) and braking choppers for fault ride-through capability and a suppression of the output power fluctuation is proposed for permanent-magnet synchronous generator (PMSG) wind turbine systems. During grid faults, the dc-link voltage is controlled by the ESS instead of the line-side converter (LSC), whereas the LSC is exploited as a STATCOM to inject reactive current into the grid for assisting in the grid voltage recovery. The validity of the proposed system is verified by experimental results for a reduced-scale wind turbine simulator as well as simulation results for a 2-MW PMSG wind turbine system.
    IEEE Transactions on Industrial Electronics 01/2013; 60(7):2842-2850. · 6.50 Impact Factor
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    ABSTRACT: This paper proposes a new maximum power point tracking (MPPT) algorithm for variable-speed wind turbine systems, which takes advantage of the rotor inertia power. In this method, a proportional controller is added to the power control to effectively reduce the moment of inertia of the wind turbines, which can improve the fast performance of the MPPT control. The PSIM simulation and experimental results for a doubly-fed induction generator wind turbine system have proved the validity of the proposed algorithm.
    IEEE Transactions on Industrial Electronics 01/2013; 60(8):3207-3217. · 6.50 Impact Factor
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    ABSTRACT: In this paper, a novel scheme for the estimation of the equivalent series resistance (ESR) of the dc-link electrolytic capacitor in three-phase ac/dc pulsewidth-modulation converters is proposed for condition monitoring. First, a controlled ac current component is injected into the input. Then, it induces ac voltage ripples on the dc output. By manipulating these ac voltage and current components with digital filters, the value of the ESR can be calculated, where the recursive least squares algorithm is used for reliable estimation results. In addition, the value of the ESR is corrected by considering the temperature effect, for which a simple temperature-sensing circuit has been designed. The simulation and experimental results show that the estimation error of the ESR is within a reasonable range, thereby enabling the determination of the appropriate time for the replacement of the capacitor.
    IEEE Transactions on Industrial Electronics 01/2013; 60(9):4118-4127. · 6.50 Impact Factor
  • Thanh Hai Nguyen, Dong-Choon Lee, Chan-Ki Kim
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    ABSTRACT: This paper proposes a cost-effective configuration of high-voltage direct current (HVDC) links for integrating the offshore wind farms with the grid, which consists of a hybrid of a twelve-pulse diode rectifier (12P-Rec) and a modular multilevel converter (MMC) for the sending-end converter on the offshore side and a fully-rated MMC for the receiving-end converter on the onshore side. For this scheme, the receiving-end MMC (REMMC) controls the DC voltage of the HVDC link, whereas the sending-end MMC (SEMMC) regulates the offshore AC voltage at a constant magnitude and frequency. Also, the SEMMC operates as if it is an active power filter to compensate for the high order harmonic currents such as 11th-, 13th-, 23rd-, and 25th-ones produced by the 12P-Rec. By utilizing the diode rectifier, the cost and power loss of the HVDC converter are lower than those of the fully-rated voltage-source converter (VSC), whereas the performance is kept almost the same. The validity of the proposed scheme is verified by the PSCAD/EMTDC simulation results for a 600-MW HVDC transmission system integrated with an offshore wind farm.
    Industrial Electronics Society, IECON 2013 - 39th Annual Conference of the IEEE; 01/2013
  • Jin-Sang Park, Dong-Choon Lee, Tan Luong Van
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    ABSTRACT: In this paper, a frequency-locked loop (FLL) algorithm using the self-tuning gain is proposed for a precise phase angle detection from a second-order generalized integrator (SOGI) in a single-phase AC system. The integrator gain in the FLL is tuned by the fuzzy logic controller in which the frequency error and its variation are adopted as control input variables. In this method, the nonlinear characteristic of the frequency error to the variation of the central frequency is compensated by the self-tuning gain. With the proposed algorithm, the performance of the SOGI-FLL is much improved at the grid faults. The simulation and experimental results have verified the validity of the proposed method.
    ECCE Asia Downunder (ECCE Asia), 2013 IEEE; 01/2013
  • Source
    Nguyen Qui Tu Vo, Dong-Choon Lee
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    ABSTRACT: In this paper, a feedback linearization control is proposed to regulate the output voltages of a three-phase four-wire inverter under the unbalanced and nonlinear load conditions. First, the nonlinear model of system including the output LC filters is derived in the d-q-0 synchronous reference frame. Then, the system is linearized by the multi-input multi-output feedback linearization. The tracking controllers for d-q-0-components of three-phase line-to-neutral load voltages are designed by linear control theory. The experimental results have shown that the proposed control method gives the good performance in response to the load conditions.
    The Transactions of the Korean Institute of Power Electronics. 01/2013; 18(4).
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    Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: This paper proposes a novel scheme for the current controller for the grid-side converter (GSC) of permanent-magnet synchronous generator (PMSG) wind turbines to eliminate the high-order harmonics in the grid currents under grid voltage disturbances. The voltage unbalance and harmonics in three-phase systems cause grid current distortions. In order to mitigate the input current distortions, multi-loop current controllers are applied, where the positive-sequence component is regulated by proportional-integral (PI) controllers, and the negative-sequence and high-order harmonic components are regulated by proportional-resonance (PR) controllers. For extracting the positive/negative-sequence and harmonic components of the grid voltages and currents without a phase delay or magnitude reduction, composite observers are applied, which give faster and more precise estimation results. In addition, an active damping method using PR controllers to damp the grid current component of the resonant frequency is employed to improve the operating stability of VSCs with inductor-capacitor-inductor (LCL) filters. The validity of the proposed method is verified by simulation and experimental results.
    Journal of power electronics 01/2013; 13(3). · 0.78 Impact Factor
  • Source
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    ABSTRACT: This paper proposes a coordinated control of the reactive power between the STATCOMs (static synchronous compensators) and the grid-side converters (GSC) of wind farms equipped with PMSGs (permanent-magnet synchronous generators), by which the voltage fluctuations at the PCC (point of common coupling) are mitigated in the steady state. In addition, the level of voltage sags is reduced during grid faults. To do this, the GSC and the STATCOM supply reactive power to the grid coordinately, where the GSCs are fully utilized to provide the reactive power for the grid prior to the STATCOM operation. For this, the GSC capability of delivering active and reactive power under variable wind speed conditions is analyzed in detail. In addition, the PCC voltage regulation of the power systems integrated with large wind farms are analyzed for short-term and long-term operations. With this coordinated control scheme, the low power capacity of STATCOMs can be used to achieve the low-voltage ride-through (LVRT) capability of the wind farms during grid faults. The effectiveness of the proposed strategy has been verified by PSCAD/EMTDC simulation results.
    Journal of power electronics 01/2013; 13(5). · 0.78 Impact Factor
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    ABSTRACT: This paper proposes a fault diagnosis method of the line-to-line voltage sensors in grid-connected 3-phase voltage source converters. The line-to-line voltage sensors are an essential device to obtain the information of the grid side voltages for controlling the converters. If there are problems in the voltage sensors by some faults, the controller obtains wrong information of the grid voltage. It causes the unbalance 3 phase currents and the pulsation of the DC-link voltage even though the power grid is healthy. Therefore fault diagnosis methods are required to detect the failure and to avoid the abnormal operation. This proposed diagnosis method identifies whether the fault is at the voltage sensor or the power grid when the abnormal values are measured from the line-to-line voltage sensors. Then the fault tolerance control is possible in case of the voltage sensor fault. The proposed method can improve the system reliability by just adding some software algorithm without additional hardware circuits. The usefulness of this paper is verified through the computer simulation and experiment.
    Industrial Technology (ICIT), 2013 IEEE International Conference on; 01/2013
  • Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: This paper suggests an operation and control strategy of an offshore wind farm based on a high-voltage DC (HVDC) transmission, where the variable-speed permanent-magnet synchronous generator (PMSG) wind turbine system is adopted. The HVDC transmission system consists of a hybrid of a twelve-pulse diode rectifier and a voltage-source converter (VSC) on offshore side, whereas a VSC is employed on AC grid side (GSVSC). For this topology, the twelve-pulse diode rectifier is capable of delivering a part of wind farm power, the rest of which is absorbed naturally by the wind farm VSC (WFVSC) since the WFVSC is controlled and operated as a voltage source of a constant frequency. At grid sags, a low-voltage ride-through of HVDC transmission is achieved, in which the HVDC link voltage is controlled by the WFVSC, and the wind farm output power is reduced by increasing the generator speeds. By utilizing the uncontrolled rectifier, a cost of HVDC converter is reduced compared with a case of the fully rated VSC, while the performance is the same. PSCAD/EMTDC simulation results for a 500-MW offshore wind farm have been shown to verify the validity of the proposed scheme.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
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    Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: This paper proposes a novel current control scheme for vector-controlled induction machine (IM) drives in the overmodulation (OVM) range, with which the voltage utilization of the voltage-source inverter (VSI) can be maximized. In the OVM region, the original voltage reference is modified by changing its magnitude and angle, which causes the motor current to be distorted, resulting in a deterioration of the current control performance. To meet with this situation, the harmonic components in the feedback currents should be eliminated before being input to the PI current controllers. For this, a composite observer is applied to extract the fundamental and harmonic components from the distorted currents, which gives a good performance without a delay and the effect of a fundamental frequency variation. In addition, through a detailed analysis of the response of the PI current controllers in the OVM range, the effectiveness of using the composite observer is demonstrated. Simulation and experimental results for a 3-kW induction motor drive are shown to verify the validity of the proposed method.
    Journal of power electronics 01/2012; 12(3). · 0.78 Impact Factor
  • Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: This paper proposes a robust control scheme for the grid-connected single-phase converter of small permanent-magnet synchronous generator (PMSG) wind turbines under distorted grid voltages. The single-phase grid current is controlled to be sinusoidal by eliminating the high-order harmonic components. For this, the fundamental and high-order harmonic components of the grid voltage and current are extracted by the composite observer without a delay. Then, a phase-lock loop (PLL) scheme is employed for the fundamental component of the grid voltage to detect the phase angle of the grid voltage for the grid current controller. The multi-PR (proportional-resonant) controllers are used to regulate the grid current. In the system, the boost converter controls the DC-link voltage and the grid converter controls the generator output power. The validity of the proposed scheme is verified by the simulation and experimental results.
    Power Electronics and Machines in Wind Applications (PEMWA), 2012 IEEE; 01/2012
  • Source
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    ABSTRACT: 3-phase AC-DC PWM (Pulse Width Modulation) converter has a possibility of open-switch faults due to some trouble of the switching devices and gate drivers. In this case, the converter causes imbalance of the AC input currents and the pulsation of DC-link voltage. This paper proposes fault tolerant control strategy of 3-phase AC-DC PWM converter under multiple open-switch fault conditions. So a detection method of the open-switch faults and fault tolerance methods are suggested according to fault cases. In this paper, two or more switches fault cases are dealt with. Both computer simulation and experimental results verify the usefulness of the proposed fault-tolerant control algorithm.
    01/2012;
  • Tan Luong Van, Dong-Choon Lee
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    ABSTRACT: This paper proposes a new strategy of the output power smoothening for the variable speed wind turbine systems, which is based on the pitch angle control using the fuzzy logic controller. In this method, the turbine power and its reference are used as control input variables for the fuzzy logic controller (FLC), in which the turbine power reference is determined depending on the double exponential smoothening (DES) method. This method is effective to smoothen the generator output power without any need of the power compensation by the energy storage system. The effectiveness of the proposed method is verified by simulation results for a 2-MW PMSG wind turbine system.
    IPEC, 2012 Conference on Power & Energy; 01/2012
  • Thanh Hai Nguyen, Dong-Choon Lee
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    ABSTRACT: In this paper, a novel control scheme to mitigate the grid current distortion due to grid voltage disturbance is proposed for a grid-connected voltage-source converter (VSC) with inductor-capacitor-inductor (LCL) filters. Voltage unbalance and harmonics in three-phase systems cause the DC-link voltage ripples and the grid current distortion. In order to mitigate the input current distortion and the DC-link voltage ripples, the multi-loop harmonic current controllers are applied to regulate positive- and negative-sequence currents as well as high-order harmonic currents by proportional-integral (PI) and proportional-resonance (PR) regulators, respectively. In addition, a new active damping method which is the PR controllers regulating the grid current at a resonant frequency is employed to increase the control stability of the VSC with LCL filter. The resonant grid current component is extracted by the band-pass filters (BPF). Furthermore, the positive- and negative-sequence and harmonic components of grid voltages and currents are obtained by a composite observer. The simulation and experimental results have been illustrated to validate the effectiveness of the proposed method.
    01/2012;
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    ABSTRACT: In this paper, a novel scheme for the condition monitoring of lithium polymer batteries is proposed, based on the sigma-point Kalman filter (SPKF) theory. For this, a runtime-based battery model is derived, from which the state-of-charge (SOC) and the capacity of the battery are accurately predicted. By considering the variation of the serial ohmic resistance () in this model, the estimation performance is improved. Furthermore, with the SPKF, the effects of the sensing noise and disturbance can be compensated and the estimation error due to linearization of the nonlinear battery model is decreased. The effectiveness of the proposed method is verified by Matlab/Simulink simulation and experimental results. The results have shown that in the range of a SOC that is higher than 40%, the estimation error is about 1.2% in the simulation and 1.5% in the experiment. In addition, the convergence time in the SPKF algorithm can be as fast as 300 s.
    Journal of power electronics 01/2012; 12(5). · 0.78 Impact Factor
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    ABSTRACT: This paper proposes a low-voltage ride-through technique of a doubly fed induction generator (DFIG) wind turbine system using a dynamic voltage restorer (DVR). For effective control of the DVR, digital all-pass filters are used for extracting the positive-sequence component from the unbalanced grid voltage since they have the advantages of giving a desired phase shift and no magnitude reduction over conventional low- or high-pass filters. Using the positive-sequence component, the phase angles for the positive- and negative-sequence components of the grid voltage are derived. A control algorithm for the DVR that is dual voltage controllers only is implemented for the two sequence components in the dq synchronous reference frame. In order to achieve the power rating reduction of the DVR, the stator power reference for the DFIG is reduced during faults. In addition, a control scheme of pitch angle system is applied to stabilize the operation of the wind turbine system in the event of grid faults. PSCAD/EMTDC simulations show the effectiveness of the proposed technique and a feasibility of reducing the power rating of DVR for the fault ride-through capability of DFIG. The validity of the proposed control scheme for the DVR has also been verified by experimental results.
    IEEE Transactions on Energy Conversion 01/2011; 26(3):871-882. · 3.35 Impact Factor

Publication Stats

681 Citations
96.45 Total Impact Points

Institutions

  • 1997–2010
    • Yeungnam University
      • Department of Electrical Engineering
      Onyang, South Chungcheong, South Korea
  • 2008
    • Assiut University
      • Department of Electrical Engineering
      Asyūţ, Muhafazat Asyut, Egypt