• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.1
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• pp.33-39
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• 1988

In this paper, a stand-alone wound rotor induction generator system is proposed and its steady state characteristics are analyzed. It is shown that the self-excitation of the system can be acheined by exciting the rotor through the PWM inverter. The analysis is based upon the eguivalent circuit and the steady state dq model of the mahine. The results show that the proposed system can be made to generate constant voltage constant frequency power for various speed and load conditions.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.503-504
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• 2015

This paper deals with the analysis of characteristics of position and speed estimator of an adaptive sensorless control algorithm for PMSM drives. The analysis shows that the back emf constant variation results in the position estimation error, but does not the speed estimation error. The simulation and experimental results are shown to verify the analysis result and the usefulness of the back emf constant estimator.

• Journal of Power Electronics
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• v.14 no.1
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• pp.175-182
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• 2014

Tracking harmonic current quickly and precisely is one of the keys to designing active power filters (APF). In the past, the current state feedback decoupling PI control was an effective means for three-phase systems in the current control of constant voltage constant frequency inverters and high frequency PWM reversible rectifiers. This paper analyzes in detail the limitation of the conventional PI conditioner in the APF application field and presents a novel PI control method. Canceling the delay of one sampling period and the misadjustment for tracking the harmonic current is the key problem of this PI control. In this PI control, the predictive output current value is obtained by a state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by a repetitive predictor synchronously. The repetitive predictor can achieve better predictions of the harmonic current. By this means, the misadjustment of the conventional PI control for tracking the harmonic current is cancelled. The experiment results with a three-level NPC APF indicate that the steady-state accuracy and dynamic response of this method are satisfying when the proposed control scheme is implemented.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.86-92
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• 2016

Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doubly-fed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.

• Journal of Electrical Engineering and Technology
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• v.10 no.6
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• pp.2221-2227
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• 2015

To arrest a frequency nadir, a stepwise inertial control (SIC) scheme generates a constant active power reference signal of a wind turbine generator (WTG) immediately after a disturbance and maintains it for the predetermined time. From that point, however, the reference of a WTG abruptly decreases to restore the rotor speed for the predefined period. The abrupt decrease of WTG output power will inevitably cause a second frequency dip. In this paper, we propose a modified SIC scheme of a doubly-fed induction generator (DFIG) that can prevent a second frequency dip. A reference value of the modified SIC scheme consists of a reference for the maximum power point tracking control and a constant value. The former is set to be proportional to the cube of the rotor speed; the latter is determined so that the rotor speed does not reach the minimum operating limit by considering the mechanical power curve of a DFIG. The performance of the modified SIC was investigated for a 100 MW aggregated DFIG-based wind power plant under various wind conditions using an EMTP-RV simulator. The results show that the proposed SIC scheme significantly increases the frequency nadir without causing a second frequency dip.

• Journal of Integrative Natural Science
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• v.15 no.3
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• pp.99-110
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• 2022

Solar photovoltaic (PV) system shows a non-linear current (I) -voltage (V) characteristics, which depends on the surrounding environment factors, such as irradiance, temperature, and the wind. Solar PV system, with current (I) - voltage (V) and power (P) - Voltage (V) characteristics, specifies a unique operating point at where the possible maximum power point (MPP) is delivered. At the MPP, the PV array operates at maximum power efficiency. In order to continuously harvest maximum power at any point of time from solar PV modules, a good MPPT algorithms need to be employed. Currently, due to its simplicity and easy implementation, Perturb and Observe (P&O) algorithms are the most commonly used MPPT control method in the PV systems but it has a drawback at suddenly varying environment situations, due to constant step size. In this paper, to overcome the difficulties of the fast changing environment and suddenly changing the power of PV array due to constant step size in the P&O algorithm, least mean Square (LMS) methods is proposed together with P&O MPPT algorithm which is superior to traditional P&O MPPT. PV output power is predicted using LMS method to improve the tracking speed and deduce the possibility of misjudgment of increasing and decreasing the PV output. Simulation results shows that the proposed MPPT technique can track the MPP accurately as well as its dynamic response is very fast in response to the change of environmental parameters in comparison with the conventional P&O MPPT algorithm, and improves system performance.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1473-1479
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• 2011

In this paper, speed control of IPMSM drives for the next generation domestic high speed railway system using multilevel inverter is presented. Multilevel inverter is suitable for the high-voltage high-capacity motor drive system because noise and switching frequency of power semiconductor devices is reduced. For the speed control of IPMSM using multilevel inverter, maximum torque control is applied in a constant torque region, and field weakening control is applied in a constant power region. Simulation programs based on Matlab/Simulink are developed. Finally the designed system is verified by simulation and their characteristics are analyzed by the simulation results.

• Journal of Power Electronics
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• v.12 no.1
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• pp.113-119
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• 2012

This paper describes the design and control of a phase shift full bridge converter with a current doubler, which can be used for the on-board charger for the lead-acid battery of electric forklifts. Unlike the common resistance load, the battery has a large capacitance element and it absorbs the entire converter output ripple current, thereby shortening the battery life and degrading the system efficiency. In this paper a phase shift full bridge converter with a current doubler has been adopted to decrease the output ripple current and the transformer rating of the charger. The charge controller is designed by using the small signal model of the converter, taking into consideration the internal impedance of the battery. The stability and performance of the battery charger is then verified by constant current (CC) and constant voltage (CV) charge experiments using a lead-acid battery bank for an electric forklift.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.69-72
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• 2012

In this study, deposition of low-dielectric constant SiOC(H) films by conventional plasma-enhanced chemical vapor deposition (PECVD) were investigated through various characterization techniques. The results show that, with an increase in the plasma power density, the relative dielectric constant (k) of the deposited films decreases whereas the refractive index increases. This is mainly due to the incorporation of organic molecules with $CH_3$ group into the Si-O-Si cage structure. It is as confirmed by FT-IR measurements in which the absorption peak at 1,129 $cm^{-1}$ corresponding to Si-O-Si cage structure increases with power plasma density. Electrical characterization reveals that even after fast thermal annealing process, the leakage current density of the deposited films is in the order of $10^{-11}$ A/cm at 1.5 MV/cm. The reliability of the SiOC(H) film is also further characterized by using BTS test.

• International Journal of Control, Automation, and Systems
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• v.5 no.6
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• pp.652-662
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• 2007

This paper presents a new and simple method for sensorless operation of matrix converter drives using a constant air-gap flux and the imaginary power flowing to the motor. To improve low-speed sensorless performance, the non-linearities of a matrix converter drive such as commutation delays, turn-on and turn-off times of switching devices, and on-state switching device voltage drop are modeled using PQR transformation and compensated using a reference current control scheme. The proposed compensation method is applied for high performance induction motor drives using a 3 kW matrix converter system. Experimental results are shown to illustrate the feasibility of the proposed strategy.