Hong-Hee Lee

University of Ulsan, Urusan, Ulsan, South Korea

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Publications (103)70.4 Total impact

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    ABSTRACT: This paper introduces a simple grid-voltage-sensorless control scheme for single-phase power factor correction (PFC) boost converters. The grid voltage waveform is obtained based on the dc output voltage, the switching duty ratio, and a phase-lead compensator. In addition, the duty ratio feedback is utilized to obtain the unity input power factor and the zero harmonic current. The proposed control scheme is designed and mathematically analyzed based on a small-signal model of PFC boost converters. To verify the effectiveness of the proposed control scheme, several simulations and experiments are carried out in two applications: an industrial power system with a 60 Hz grid frequency and a commercial aircraft application with a 400 Hz grid frequency.
    Journal of power electronics 07/2014; 14(4):712-721. · 0.78 Impact Factor
  • Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: This paper introduces a low cost high performance three-phase unified power quality conditioner (UPQC) by using four-switch three-phase inverters. In the proposed UPQC, both shunt and series active power filters (APFs) are developed by using four-switch three-phase inverters so that the number of switching devices in the proposed topology is reduced from twelve in the traditional UPQC down 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 lessened. As a consequence, by using a smaller number of power switches with lower rating voltage in the proposed UPQC system, we can greatly reduce the system cost of the UPQC without degrading the harmonic compensation performance. Design of passive components for the proposed UPQC to achieve a good performance is discussed in detail in this paper. Simulation studies are performed to verify the effectiveness of the proposed topology.
    2014 IEEE 23rd International Symposium on Industrial Electronics (ISIE); 06/2014
  • Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: The presence of grid voltage distortion and nonlinear local load are badly impact on the performance of grid-connected distributed generation (DG). This paper introduces an enhanced current control strategy to improve the grid current performance of grid-connected DG under such scenario. The proposed current controller is designed in the synchronous reference frame and composed of a proportional-integral (PI) controller and three resonant controllers tuned at 6n (n = 1, 2, 3) of fundamental frequency. The proposed controller is operated without demand of local load current measurement, which means that no extra hardware is required to achieve good performance of the grid current. The DG with the proposed current controller can transfer a sinusoidal current into the utility grid despite the presence of distorted grid voltage and/or nonlinear local load. Various test cases are considered and experimental results are given to verify the effectiveness of the proposed current controller.
    2014 IEEE 23rd International Symposium on Industrial Electronics (ISIE); 06/2014
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    Cong-Long Nguyen, Hong-Hee Lee
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    ABSTRACT: By combining a wind turbine with an energy storage system (ESS), we are able to attenuate the intermittent wind power characteristic making the power derived from a wind farm dispatchable. This paper evaluates the influence of the phase delay of the low-pass filter in the conventional smoothing power control on the ESS capacity; longer phase delays require a larger ESS capacity. In order to eliminate the effect of the phase delay, we optimize the power dispatch using a zero-phase low-pass filter that results in a non-delayed response in the power dispatch. The proposed power dispatching method significantly minimizes the ESS capacity. In addition, the zero-phase lowpass filter, which is a symmetrical forward-reverse finite impulse response type, is designed simply with a small number of coefficients. Therefore, the proposed dispatching method is not only optimal, but can also be feasibly applied to real wind farms. The efficacy of the proposed dispatching method is verified by integrating a 3 MW wind turbine into the grid using wind data measured on Jeju Island.
    Journal of Electrical Engineering and Technology 05/2014; 9(3):1080-1088. · 0.73 Impact Factor
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    ABSTRACT: This paper develops the brushless dc (BLDC) motor sensorless control system for an automotive fuel pump. The sensorless techniques that are based on a hysteresis comparator and a potential start-up method with a high starting torque are suggested. The hysteresis comparator is used to compensate for the phase delay of the back EMFs due to a low-pass filter (LPF) and also prevent multiple output transitions from noise or ripple in the terminal voltages. The rotor position is aligned at standstill for maximum starting torque without an additional sensor and any information of motor parameters. Also, the stator current can be easily adjusted by modulating the pulse width of the switching devices during alignment. Some experiments are implemented on a single chip DSP controller to demonstrate the feasibility of the suggested sensorless and start-up techniques.
    IEEE Transactions on Power Electronics 01/2014; 29(3):1382-1391. · 5.73 Impact Factor
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    ABSTRACT: Integrating energy storage system (ESS) with a large wind farm can smooth out the intermittent power characteristic of the renewable source so as to make the wind farm dispatchable. This paper evaluates the fact that the phase delay of the low-pass filter in the dispatching power control influences the ESS capacity and the longer phase delay requires the bigger ESS capacity. In order to avoid the effect of the phase delay, we introduce an effective low-pass filter that has a zero phase delay in the pass-band region to control optimally the dispatching power of wind farm. The effective low-pass filter, which is a finite impulse response (FIR) type, is designed based on the Kaiser Window function and its phase delay in the pass-band is eliminated totally by adding a phase-compensator. Thanks to the developed filter, the required ESS capacity rating is reduced significantly. The efficacy of the proposed dispatching method is verified by integrating 3MW wind turbine to grid with a real wind data measured in Jeju Island.
    International Smart Grid Conference & Exhibition 2013, Jeju; 07/2013
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    ABSTRACT: Due to the cost, it is a crucial requirement to utilize an economical battery capacity for the wind energy conversion system. In this paper, the optimal BESS capacity is determined for the wind farm whose dispatched power is assigned by the min-max dispatching method. Based on a lifetime cost function that indicates the BESS cost spent to dispatch 1kWh wind energy to grid, the battery capacity can be optimized so as to obtain the minimum system operation cost. Moreover, the battery state of charge (SOC) is also managed to be in a safe range to ensure the system undamaged. In order to clarify the proposed optimizing method, a 3MW permanent magnet synchronous generator (PMSG) wind turbine model and real wind speed data measured each minute are investigated.
    2013 Power Electronics Annual Conference; 07/2013
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    ABSTRACT: This paper proposes the control method for reducing a total harmonic distortion (THD) of the grid current at the three-phase grid-connected inverter systems when the grid voltages are distorted. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and attenuation due to a hardware low-pass filter. Both the gain and angle of a compensation voltage for suppressing the harmonic currents at the minimum point of THD of the grid current are derived. The simulation and experimental results show the validity of the proposed control method.
    Power Engineering, Energy and Electrical Drives (POWERENG), 2013 Fourth International Conference on; 01/2013
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    Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: This paper presents an enhanced control strategy which consists of a proportional-integral controller and a repetitive controller (RC) for improving the voltage performance of distributed generation (DG) under nonlinear load conditions. The proposed voltage controller is able to maintain a sinusoidal voltage at the point of common coupling (PCC) of the DG regardless of the harmonic voltage drop in the system impedance due to nonlinear load currents. In addition, by employing the delay time of the RC at one-sixth of the fundamental period, the proposed RC can overcome the slow response drawback of the traditional PI-RC. The proposed control strategy is analyzed and the design of the RC is presented in detail. The feasibility of the proposed control strategy is verified through simulation and experimental results.
    Journal of power electronics 01/2013; 13(3). · 0.78 Impact Factor
  • Hong-Hee Lee, H.M. Nguyen
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    ABSTRACT: This paper focuses on the common-mode voltage reduction and the power quality of matrix converters for a low-voltage transfer ratio of less than 0.5 by the direct space vector modulation (DSVM) method. The principles of selecting suitable switching configurations based on new space vector sectors are described, and an entire switching table for the new control strategy is developed. The matrix converter with the proposed method reduces peak-to-peak common-mode voltage remarkably. The new DSVM method has advantages over the conventional DSVM method, such as lower total harmonic distortion of line-to-line output voltage and a reduction in switching loss by a minimum number of switching commutations. The proposed DSVM method can be easily implemented in software. Simulation and experimental results are shown to verify the effectiveness of the proposed DSVM method.
    IEEE Transactions on Power Electronics 01/2013; 28(2):920-929. · 5.73 Impact Factor
  • Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: This paper proposes an enhanced current controller for three-phase shunt active power filters (SAPFs). The proposed current controller is composed of a proportional-integral (PI) controller and two repetitive controllers (RCs) where the RCs are designed with a delay time of one sixth of the fundamental period (T/6). With the combination of these RCs, the SAPF can offer a good harmonic compensation performance under various types of nonlinear loads (three-phase or single-phase nonlinear loads). As consequence, the supply current is effectively compensated to be sinusoidal despite the nonlinear load current. In addition, the proposed SAPF also can provide a fast dynamic response under load variations to maintain the supply current sinusoidal. The effectiveness of the proposed controller is verified through simulation results.
    Electrical Machines and Systems (ICEMS), 2013 International Conference on; 01/2013
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    Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: This paper proposes a novel control strategy for a unified power quality conditioner (UPQC) including a series and a shunt active power filter (APF) to compensate the harmonics in both the distorted supply voltage and the nonlinear load current. In the series APF control scheme, a proportional-integral (PI) controller and a resonant controller tuned at six multiples of the fundamental frequency of the network () are performed to compensate the harmonics in the distorted source. Meanwhile, a PI controller and three resonant controllers tuned at (n=1, 2, 3) are designed in the shunt APF control scheme to mitigate the harmonic currents produced by nonlinear loads. The performance of the proposed UPQC is significantly improved when compared to that of the conventional control strategy thanks to the effective design of the resonant controllers. The feasibility of the proposed UPQC control scheme is validated through simulation and experimental results.
    Journal of power electronics 01/2013; 13(1). · 0.78 Impact Factor
  • Quoc-Nam Trinh, Hong-Hee Lee
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    ABSTRACT: This paper proposes an advanced control strategy to enhance performance of shunt active power filter (APF). The proposed control scheme requires only two current sensors at the supply side and does not need a harmonic detector. In order to make the supply currents sinusoidal, an effective harmonic compensation method is developed with the aid of a conventional proportional-integral (PI) and vector PI controllers. The absence of the harmonic detector not only simplifies the control scheme but also significantly improves the accuracy of the APF, since the control performance is no longer affected by the performance of the harmonic tracking process. Furthermore, the total cost to implement the proposed APF becomes lower, owing to the minimized current sensors and the use of a four-switch three-phase inverter. Despite the simplified hardware, the performance of the APF is improved significantly compared to the traditional control scheme, thanks to the effectiveness of the proposed compensation scheme. The proposed control scheme is theoretically analyzed, and a 1.5-kVA APF is built in the laboratory to validate the feasibility of the proposed control strategy.
    IEEE Transactions on Industrial Electronics 01/2013; 60(12):5400-5410. · 6.50 Impact Factor
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    ABSTRACT: Use of the battery energy storage system (BESS) as a power buffer becomes a feasible solution to mitigate the intermittent wind power characteristic. Due to the cost, utilizing an economical battery capacity is a crucial requirement of the system design. In this paper, dispatch power strategies are overviewed and the min-max method is selected as the most suitable one for integrating the wind power to grid. A lifetime cost function, which indicates the BESS cost spent to dispatch 1kWh, is defined with the dispatch principle so that the battery capacity can be optimized. With using the optimal capacity, the minimum system operation cost is achieved and the dispatched power is able to satisfy its scheduled reference in any dispatching time period. Moreover, the battery state of charge (SOC) is also managed to be in a safe range so as to guarantee the system undamaged. In order to clarify the proposed determination method, a case study with a 3MW permanent magnet synchronous generator (PMSG) wind turbine model is investigated.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Quoc-Hoan Tran, Tae-Won Chun, Hong-Hee Lee
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    ABSTRACT: This paper proposes an open circuit fault tolerant strategy with a fault detector for the inverter stage in indirect matrix converter (IMC). When an open switch fault occurs in IMC, the location of faulty switches in the inverter stage can be exactly identified by the fault detector which compares the output voltages of the analytical model with the measured output voltages. In order to keep the continuous operation without output voltage fluctuation, the fault tolerant strategy is developed to control indirect matrix converter based on the concept of four-leg matrix converter. The proposed fault tolerant strategy can maintain the same output performance during the faulty condition as the healthy condition. Simulation results are given to verify the effectiveness of the proposed method.
    Industrial Electronics Society, IECON 2013 - 39th Annual Conference of the IEEE; 01/2013
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    Quoc-Nam Trinh, Hong-Hee Lee, Tae-Won Chun
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    ABSTRACT: This paper develops an enhanced harmonic voltage compensator which is implemented with the aid of two repetitive controllers (RCs) in order to improve the output voltage performance of stand-alone distributed generation (DG) systems. The proposed harmonic voltage compensator is able to maintain the DG output voltage sinusoidal regardless of the use of nonlinear and/or unbalanced loads in the load side. In addition, it can offer good steady-state performance under various types of loads and a very fast dynamic response under load variations to overcome the slow dynamic response issue of the traditional RC. The feasibility of the proposed control strategy is verified through simulations and experiments.
    Journal of power electronics 01/2013; 13(6). · 0.78 Impact Factor
  • Mojaharul Islam, Hong-Hee Lee
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    ABSTRACT: Communications for monitoring, control and management of microgrid are very important for smart operation. This paper analyzed the information of microgrid for monitoring, control and management purposes and maps them according to power system automation standard IEC61850. IEEE 802.11g and IEEE 802.16 standard based interoperable, cost-effective and reliable wireless communication network is proposed for real time monitoring, control and management of microgrid. Multi-agent technology is adopted to define the responsibilities of different intelligent devices. Performance analysis is carried out by modeling microgrid nodes and traffic according to IEC61850 with Optimized Network Engineering Tool (OPNET). Experimental results demonstrate the performance of the proposed network for reliable operation of microgrid in both islanded and grid connected modes.
    Proceedings of the 8th international conference on Intelligent Computing Theories and Applications; 07/2012
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    Cong-Long Nguyen, Hong-Hee Lee
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    ABSTRACT: This paper presents an effective control scheme for an electric vehicle battery charger where a symmetrical bridgeless power factor-corrected converter and a buck converter are cascaded. Both converters have been popular in industries because of their high efficiency, low cost, and compact size, hence combining these converters makes the overall battery charging system strongly efficient. Moreover, this charger topology can operate at universal input voltage and attain a desired battery current and voltage without ripple. In order to achieve a unity input power factor and zero input current harmonic distortion, the proposed control scheme adopts duty ratio feed-forward control technique in both current and voltage control loop. Additionally, in the current loop, its reference is created by a phase-locked loop (PLL) block, leading to a pure sinusoidal input current although the input voltage waveform is being distorted. The feasibility and practical value of the proposed approach are verified by simulation and experimental results with an 110V/60Hz ac line input and 1.5kW-72V dc output of the battery charging system.
    2012 Power Electronics Annual Conference; 07/2012
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    ABSTRACT: This paper describes a simple grid current control method for the grid-connected operation, and inverter voltage control method based on the phase locked loop (PLL) for the intentional islanding operation at the three-phase grid-connected inverter. The PLL controller based on the pq theory with a simple P-controller is used to synchronize the phase of inverter output voltage with a grid voltage at the grid-connected operation or generate a desired inverter output voltage at the islanding operation. The outputs of current controller are connected together to those of voltage controller, in order to prevent a sudden change of the outputs of both controllers during the transfer instant. The simulation and experimental results are carried out to verify the effectiveness of the proposed control strategies.
    Renewable Energy Research and Applications (ICRERA), 2012 International Conference on; 01/2012