Hong-Hee Lee

University of Ulsan, Ulsan, Ulsan, South Korea

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Publications (156)143.05 Total impact

  • Amirhossein Ghods · Hong-Hee Lee
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    ABSTRACT: Due to the importance of induction motors’ continuous operation, early detection of faults has become a major trend. As reported in an IEEE study, bearing failures include more than half of mechanical faults. To detect existence of this fault, methods such as (short-time) Fourier, (continuous–discrete) wavelet, and Park transforms introduced. Static modeling of fault behavior is determined to be the major deficiency of above-mentioned methods. In other words, using conventional detection techniques, fault is assumed to have deterministic behavior, in which the fault frequencies are constant. As a matter of fact, fault characteristics can be affected under loading or environmental conditions, which makes conventional standing invalid. Authors of this paper have developed their previously introduced technique, frequency-domain discrete wavelet transform (FD-DWT) into a stochastic model. This makes the detection process valid for more variety of fault conditions and leads to earlier detection of fault and less damage to motor compared to other strategies.
    No preview · Article · Dec 2015 · Neurocomputing
  • Nho-Van Nguyen · Tam-Khanh Tu Nguyen · Hong-Hee Lee
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    ABSTRACT: This paper introduces a novel pulse width modulation (PWM) technique to eliminate common-mode voltage in odd-multilevel inverters using the three zero common-mode vectors principles. Similarly, as in conventional PWM for multilevel inverters, this PWM can be properly depicted in an active two-level voltage inverter. With the help of two standardized PWM patterns, the characteristics of the PWM process can be fully explored in that active inverter as a switching time diagram and switching state sequence. Due to an unequal number of commutations of three phases in each sampling period, the switching loss is optimized by a proposed current-based mapping algorithm. The switching loss reduction can be up to 25% compared to the same PWM technique with nonoptimized algorithms. The PWM method has been then generalized as an equipotential PWM control, which is valid to both odd- and even-multilevel inverters . The theoretical analysis is verified by simulation and experimental results.
    No preview · Article · Oct 2015 · IEEE Transactions on Power Electronics
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    Quoc Nam Trinh · Hong-Hee Lee
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    ABSTRACT: A standard repetitive controller (RC) is theoretically able to replace a bank of resonant controllers in harmonic signals tracking applications. However, the traditional RC has some drawbacks such as a poor dynamic response and a complex structure to compensate grid frequency deviations for an effective unified power quality conditioner (UPQC) control scheme. In order to solve these problems, an improved RC with an outstanding dynamic response and a simplified grid frequency adaptive scheme is proposed for UPQC control systems in this paper. The control strategy developed for the UPQC has delay time, i.e., one-sixth of a fundamental period (Tp/6), repetitive controllers. As a result, the UPQC system can provide a fast dynamic response along with good compensation performance under both nonlinear and unbalanced loads. Furthermore, to guarantee the excellent performance of the UPQC under grid frequency deviations, a grid frequency adaptive scheme was developed for the RC using a simple first order Padé’s approximation. When compared with other approaches, the proposed control method is simpler in structure and requires little computing time. Moreover, the entire control strategy can be easily implemented with a low-cost DSP. The effectiveness of the proposed control method is verified through various experimental tests.
    Full-text · Article · Jul 2015 · Journal of power electronics
  • Anh-Vu Ho · Tae-Won Chun · Hong-Hee Lee · Heung-Geun Kim

    No preview · Conference Paper · Jun 2015
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    Cong-Long Nguyen · hong-hee lee
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    ABSTRACT: This paper focuses on determining the power dispatch capability of wind-battery hybrid power system (WBHPS). To cooperate with the transmission system operator (TSO) in the modern electric power market, the power dispatch capability of the WBHPS must be defined primarily at beginning of each dispatching time interval. Based on the wind power available and the battery capacity status, the power dispatch capability which means the power level of the WBHPS can dispatch to grid is determined. The proposed determination method aims to satisfy two crucial constraints while the wind power is being integrated into grid. The first constraint associated with the battery capacity is to guarantee the battery power lower than its rating. And, the second one is to keep the state of charge (SOC) of the battery within a safe range. In order to determine the maximum and minimum range of the power dispatch, the availability level of the wind power in each dispatching time interval is estimated based on the wind speed forecast. To evaluate the proposed determination method, we perform a numerical study using a 3-MW wind turbine generator with a real wind speed data measured on Jeju Island. Index Terms—Wind-battery hybrid power system (WBHPS), transmission system operator (TSO), power dispatch control, state of charge (SOC) control, wind power forecast.
    Full-text · Conference Paper · Jun 2015
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    Cong-Long Nguyen · Hong-Hee Lee

    Full-text · Dataset · May 2015
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    Quoc Nam Trinh · Hong-Hee Lee
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    ABSTRACT: This paper introduces a novel topology and an effective control strategy for a shunt hybrid power filter (SHPF) to simultaneously compensate harmonic currents and reactive power. The proposed SHPF topology is composed of an LC passive filter tuned to the 7th harmonic frequency and a small-rated active filter connected in parallel with the inductor L-pf of the LC passive filter. Together with the SHPF topology, we also propose a control strategy, which consists of a proportional-integral (PI) controller for DC-link voltage regulation and a PI plus repetitive current controller, in order to compensate both the harmonic current and the reactive power without the need for additional hardware. Thanks to the effectiveness of the proposed control scheme, the supply current is sufficiently compensated to be sinusoidal and in-phase with the supply voltage, regardless of the distorted and phase lagging of the load current. The effectiveness of the proposed SHPF topology and control strategy is verified by simulated and experimental results.
    Full-text · Article · May 2015 · Journal of Electrical Engineering and Technology
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    Quoc Nam Trinh · Hong-Hee Lee
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    ABSTRACT: This paper introduces a low cost, high efficiency, high performance three-phase unified power quality conditioner (UPQC) by using four-switch three-phase inverters (FSTPIs) and an extra capacitor in the shunt active power filter (APF) side of the UPQC. In the proposed UPQC, both shunt and series APFs are developed by using FSTPIs so that the number of switching devices is reduced from twelve to eight devices. In addition, by inserting an additional capacitor in series with the shunt APF, the DC-link voltage in the proposed UPQC can also be greatly reduced. As a result, the system cost and power loss of the proposed UPQC is significantly minimized thanks to the use of a smaller number of power switches with a lower rating voltage without degrading the compensation performance of the UPQC. Design of passive components for the proposed UPQC to achieve a good performance is presented in detail. In addition, comparisons on power loss, overall system efficiency, compensation performance between the proposed UPQC and the traditional one are also determined in this paper. Simulation and experimental studies are performed to verify the validity of the proposed topology.
    Full-text · Article · May 2015 · Journal of Electrical Engineering and Technology
  • Huu-Nhan Nguyen · Hong-Hee Lee
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    ABSTRACT: This paper presents an enhanced space vector modulation (SVM) method to drive matrix converters (MCs) with zero common-mode voltage by using the rotating vectors, which are not used in the traditional SVM for MCs. The reference output voltage vector is generated by a combination of the closer rotating vectors in order to minimize the output distortion. Explicit equations are used to develop the switching patterns so that the proposed SVM method can achieve full control of the output voltage vector and input current phase angle with good performance of the input/output current waveforms. Together with the theoretical analysis, the experimental results are provided to validate the feasibility of the proposed method.
    No preview · Article · Apr 2015 · IEEE Transactions on Power Electronics
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    Cong-Long Nguyen · Hong-Hee Lee
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    ABSTRACT: This paper develops a digital control scheme with power factor correction for a front-end converter in an electric vehicle battery charger. The front-end converter, which is the boost-type switching-mode rectifier, takes both two roles of the battery charger including the power factor control and the robust charging performance. The proposed control scheme consisting of a charging control algorithm and a grid current control algorithm aims to obtain the unity input power factor and robust performance. Based on the linear averaged model of the converter, the constant-current constant-voltage (CC-CV) charging control algorithm is proposed through only one proportional-integral (PI) controller and a current feed-forward path. In the current control algorithm, we utilize a second band pass filter, a single-phase phase-locked loop (PLL) technique, and a duty-ratio feed-forward term to control the grid current not only to be in phase with the grid voltage but also to be a pure sinusoidal waveform. In order to verify the effectiveness of the proposed control scheme, both simulations and experiments are carried out.
    Full-text · Article · Apr 2015
  • Nho-Van Nguyen · Tam-Khanh Tu Nguyen · Hong-Hee Lee
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    ABSTRACT: This paper presents a novel switching voltage model and an offset-based pulse width modulation (PWM) scheme for multilevel inverters with unbalanced DC sources. The switching voltage model under a DC voltage imbalance will be formulated in general form for multilevel neutral-point-clamped topologies. Analysis of the reference switching voltages from active and non-active switching voltage components in abc coordinates can enable voltage implementation for an unbalanced DC-source condition. Offset voltage is introduced as an indispensable variable in the switching voltage model for multilevel voltage-source inverters. The PWM performance is controlled through the design of two offset components in a subsequence. One main offset may refer to the common mode voltage, and the other offset restricts its effect on the quality of PWM control in related DC levels. The PWM quality can be improved as the switching loss is reduced in a discontinuous PWM mode by setting the local offset, which is related to the load currents. The validity of the proposed algorithm is verified by experimental results.
    No preview · Article · Mar 2015 · Journal of power electronics
  • Huu-Nhan Nguyen · Hong-Hee Lee

    No preview · Article · Jan 2015 · IEEE Transactions on Power Electronics
  • Huu-Nhan Nguyen · Hong-Hee Lee

    No preview · Article · Jan 2015 · IEEE Transactions on Power Electronics
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    Cong-Long Nguyen · Hong-Hee Lee · Tae-Won Chun
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    ABSTRACT: Utilizing the optimal capacity of a battery in wind-battery hybrid power systems is crucial to minimize costs. In this paper, we modify the min-max dispatch method to effectively integrate wind power into the grid. In line with the dispatch principle, we define a lifetime cost function, which indicates the battery energy storage system (BESS) cost of dispatching 1 kWh of wind energy, to determine the optimal battery capacity. By using the optimal battery capacity, the operation costs are minimized and the hybrid system is able to dispatch the scheduled power at any dispatching time. Moreover, the short-term power dispatch control is also considered; we smooth the transient power between two consecutive dispatching intervals and control the state of charge (SOC) of the battery by an online-control algorithm. To evaluate the performance of the proposed optimization method and the short-term power dispatch control, we perform several numerical studies with a 3MW wind turbine generator and real wind speed data.
    Full-text · Article · Jan 2015 · IEEE Transactions on Industry Applications
  • Quoc-Nam Trinh · Hong-Hee Lee
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    ABSTRACT: In the above-named article [ibid., IEEE Trans. Ind. Electron., vol. 60, no. 12, pp. 5400-5410, Dec. 2013], there were some errors in (7) and (8). In (7), there is a duplication of a "+" sign. In addition, the authors note that (8) also contains redundant terms and is incorrect. The correct versions of (7) and (8) are given here.
    No preview · Article · Dec 2014 · IEEE Transactions on Industrial Electronics
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    Quoc-Nam Trinh · Hong-Hee Lee
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    ABSTRACT: This study proposes an enhanced resonant control strategy for the unified power quality conditioner (UPQC) to simultaneously tackle voltage sags, unbalance and distortions on the supply side as well as current harmonics on the load side. The proposed control strategy is developed in both the series and shunt active power filters (APFs) of the UPQC. In the series APF, a proportional-resonant controller and a resonant controller are employed to mitigate voltage sags, unbalance and distortions, whereas a proportional-integral (PI) controller and three vector PI controllers are used in the shunt APF to compensate harmonic currents. The performance of the proposed UPQC control scheme is significantly improved compared with the conventional control strategy owing to the superiority of the resonant controllers. In addition, voltage sag/harmonic and current harmonic detectors are not required in the proposed control scheme, which helps to simplify the control strategy and to improve the control accuracy. The proposed control strategy is theoretically analysed and its feasibility is validated through experiments.
    Full-text · Article · Dec 2014 · IET Generation Transmission & Distribution
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    Quoc-Nam Trinh · Hong-Hee Lee
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    ABSTRACT: This paper introduces an advanced current control strategy for grid-connected operations of distributed generation (DG), which supports the DG to transfer a sinusoidal current into the utility grid despite the distorted grid voltage and nonlinear local load conditions. The proposed current controller is designed in the synchronous reference frame and composed of a proportional–integral (PI) controller and a repetitive controller (RC). An RC serves as a bank of resonant controllers, which can compensate a large number of harmonic components with a simple delay function. Hence, the control strategy can be greatly simplified. In addition, the proposed control method does not require the local load current measurement or harmonic analysis of the grid voltage. Therefore, the proposed control method can be easily adopted into the traditional DG control system without installation of extra hardware. Despite the reduced number of sensors, the grid current quality is significantly improved compared with the traditional methods with the PI controller. The operation principle of the proposed control method is analyzed in detail, and its effectiveness is validated through simulated and experimental results.
    Full-text · Article · Dec 2014 · IEEE Transactions on Industrial Electronics
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    ABSTRACT: Common-mode voltage (CMV) causes overvoltage stress to winding insulation and damages AC motors. CMV with high dv/dt causes leakage currents, which create noise problems for equipment installed near the converter. This study proposes a new pulse-width modulation (PWM) strategy for three-level T-type NPC inverters. This strategy substantially eliminates CMV. The principle for selecting suitable triangle carrier signals for the three-level T-type NPC is described. The proposed method can mitigate the peak value of CMV by 50% compared with the phase disposition pulse-width modulation method. Furthermore, the proposed method exhibits better harmonic spectrum and lower root mean square value for the CMV than those of the reduced-CMV method on the basis of the phase opposition disposition PWM scheme with modulation index higher than 0.5. The proposed modulation can easily be implemented using software without any additional hardware modifications. Both simulation and experimental results demonstrate that the proposed carrier phase-shift PWM method has good output waveform performance and reduces CMV.
    No preview · Article · Nov 2014 · Journal of power electronics
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    ABSTRACT: This paper proposes a phase-locked loop (PLL)- based seamless transfer control method between grid-connected and islanding modes in a three-phase grid-connected inverter. The PLL is used to synchronize the phase of the load voltage to a grid voltage in grid-connected operation, and to generate an angle with the desired frequency in islanding operation. The stability of both the grid current loop for grid-connected operation and the load voltage control loop for islanding operation is analyzed. The phase and magnitude of the load voltage are successively matched to the grid voltage for a seamless transfer from islanding to grid-connected operation. When grid voltage sag occurs, an operating sequence including a PLL operation is suggested in order to transfer smoothly to islanding operation and to provide a stable and seamless voltage to a sensitive load under the voltage sag condition. The simulation and experimental results are carried out to verify the effectiveness of the proposed algorithm.
    No preview · Article · Oct 2014 · IEEE Transactions on Power Electronics
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    Cong-Long Nguyen · Hong-Hee Lee
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    ABSTRACT: Abstract—Use of a battery energy storage system (BESS) becomes a feasible solution to mitigate the intermittent characteristic of wind power resource. Due to the cost, the minimal battery capacity is the crucial requirement to obtain the economic wind-battery system operation. In this paper, an optimal power dispatch strategy is proposed to minimize the storage capacity while the fluctuation mitigation requirement (FMR) imposed by grid codes is satisfied. The power dispatch which is determined through a first-order low-pass filter (FLF) is optimized by adjusting the filter smoothing time constant (FSTC). In order to optimize the FSTC, we introduce two online-based optimization methods that include a linear search approach and a direct computation approach. In the first method, the search objective is the appropriate FSTC to minimize the BESS capacity with a constraint that the power dispatch satisfies the FMR in a time window. In the second method, we demonstrate a mathematical relationship between the FSTC and FMR in 1-sampling time scale; therefore, the optimal solution can be directly computed. As a result, the proposed power dispatch strategy significantly reduces the BESS capacity. In order to verify the effectiveness of the proposed power dispatch strategy, case studies using a 3-MW wind turbine with real wind speed data are shown.
    Full-text · Conference Paper · Sep 2014