• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.355-356
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• 2015

This paper proposes a control strategy of total output power ripple cancellation for both of Machine-Side Converter (MSC) and Grid-Side Converter (GSC) in a DFIG under unbalanced grid conditions. The proposed control strategy for the MSC is the zero torque ripple control algorithm with an enhanced LVRT capability. The control algorithm for the MSC exhibits reduced torque pulsation in steady-state unbalanced grid conditions. In addition, this control algorithm also minimizes a peak value of rotor current in transient unbalanced grid conditions. The total output power ripple cancellation control algorithm is adopted in the GSC. The total output power ripple cancellation is achieved by nullifying the oscillating component of the total output active and reactive power at the summing point of stator and rotor of DFIG. The proposed control strategy for the GSC reduces the output power oscillation leading to the improved quality of wind farms output.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.54-60
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• 2010

This paper presents a new algorithm for determining generator operation point for maintaining stability considering generator faults in Jeju-Haenam HVDC system. As the HVDC system consumes reactive power for the transmission of active power substantially, compensation of reactive power is essential. And the HVDC system is operated on frequency control mode. That is to say, the HVDC system almost manages system frequency. Therefore, we recognized that the Jeju system could be unstable if the reactive power consumed by the HVDC is insufficient when out-of-step occurs with large generators. When the solution of power flow analysis does not converge due to the unstable system phenomenon, we have difficulty in establishing countermeasures as the post-fault information is not available. In this paper, for the purpose of overcoming this difficulty in establishing countermeasures, we introduce the CPF(Continuation Power Flow) algorithm. This paper suggests an algorithm for calculating the output limitation of the generator to maintain the stability in case of generator fault in the Jeju system.

• Proceedings of the KIEE Conference
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• 1979.08a
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• pp.136-137
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• 1979

• Journal of Power Electronics
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• v.7 no.1
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• pp.72-80
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• 2007

Voltage sags are one of the most frequently occurring power quality problems challenging power systems today. The Unified Power Quality Conditioner (UPQC) is one of the major custom power solutions that are capable of mitigating the effect of supply voltage sags at the load or Point of Common Coupling (PCC). A UPQC-Q employs a control method in which the series compensator injects a voltage that leads the supply current by $90^{\circ}C$ so that the series compensator at steady state consumes no active power. However, the UPQC-Q has the disadvantage that its series compensator needs to be overrated. Thus it cannot offer effective compensation. This paper proposes a new control scheme for the UPQC-Q that offers minimum power injection. The proposed minimum power injection method takes into consideration the limits on the rated voltage capacity of the series compensator and its control scheme. The validity of the proposed control scheme is investigated through simulation and experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.7
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• pp.97-104
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• 2011

This paper presents modeling and control for the emerging IGBT converter-based high-voltage direct-current system (IGBT-HVDC). This paper adds to the representation of the IGBT-HVDC system in the dq-synchronous reference frame and its decoupled control scheme. Additionally, since the IGBT-HVDC is able to actively support the grid due to its capacity to control independently active and reactive power production, a reactive power control scheme is presented in order to regulate/contribute to the voltage at a remote location by taking into account its operational state and limits. The ability of the control scheme is assessed and discussed by means of simulations using ahybrid power system, which consists of a permanent magnetic synchronous-generator (PMSG) based wind turbine, an IGBT-HVDC, and a local load.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.116-128
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• 2010

Modeling of the three phase electric arc furnace and its voltage flicker mitigation are the purposes of this paper. For modeling of the electric arc furnace, at first, the arc is modeled by using current-voltage characteristic of a real arc. Then, the arc random characteristic has been taken into account by modulating the ac voltage via a band limited white noise. The electric arc furnace compensation with static VAr compensator, Thyristor Controlled Reactor combined with a Fixed Capacitor bank (TCR/FC), is discussed for closed loop control of the compensator. Instantaneous flicker sensation curves, before and after accomplishing compensation, are measured based on IEC standard. A new method for controlling TCR/FC compensator is proposed. This method is based on applying a predictive approach with closed loop control of the TCR/FC. In this method, by using the previous samples of the load reactive power, the future values of the load reactive power are predicted in order to consider the time delay in the compensator control. Also, in closed loop control, two different approaches are considered. The former is based on voltage regulation at the point of common coupling (PCC) and the later is based on enhancement of power factor at PCC. Finally, in order to show the effectiveness of the proposed methodology, the simulation results are provided.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.8
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• pp.757-764
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• 1991

This paper proposes a novel control method of voltage type current-controlled reactive/harmonic compensator. The proposed method does not rely on the explicit computation of load power, but indirectly controls the compensation current by regulating dc link voltage of the converter. It is shown that the system can be modeled as a simple linear system that facilitates an analytical approach to the system characteristics. With the model, the effects of the controller gains on the dynamic and steady state response of the system are investigated. Experimental results show that the proposed control method works well in spite of the simplicity of control circuitry.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.934-935
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• 2015

This paper presents the sensorless control method that employs the adaptive back-EMF(Electromotive Force) and current model observer of interior permanent magnet synchronous motor(IPMSM). The estimated back EMF considering a saliency is obtained by using the adaptive control method. The estimated EMF is inputted to the current model observer which is connected in series with adaptive back EMF estimator and is used to estimate the position and speed of the rotor. In order to improve the shortcomings of conventional method using the current error components multiplied in the compensation constant, the modified instantaneous reactive power compensator is applied. The validity of the control system presented is verified by the simulation.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1438-1449
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• 2018

The importance of power system stability has been emphasized with an increase of wind energy penetration in the power system. Accordingly, the guarantee on various control capabilities, including active and reactive power control of wind farms, was regarded as the most important aspect for the connection to the grid. To control the wind farm active power, the wind farm controller was introduced. The wind farm controller decides the power set points for each wind turbine generating unit and each wind turbine generating unit controls its power according to the set points from the wind farm controller. Therefore, co-relationship between wind farm controller and wind turbine controllers are significantly important. This paper proposes some control methods of wind farm active power control based on modified wind turbine control for power system stability and structures to connect wind turbine controllers to wind farm controller. Besides, this paper contributes to development of control algorithm considering not only electrical components but also mechanical components. The proposed contributions were verified by full simulation including power electronics and turbulent wind speed. The scenario refers to the active power control regulations of the Eltra and Elkraft system in Denmark.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.4
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• pp.474-483
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• 1996

In this paper, as a part of the method improving stability, the load-flow calculation in D.C. power system and the models for stability analysis are studied with A.C-D.C. interconnected power systems transmission performed. Moreover, the theory is established in relation to each control method of D.C. power systems. Then the stability of A.C-D.C.interconnected power systems is compared and considered by the way of dividing the operating control method of the rectifier inverter converter into ACR-AVR, APR-A.gamma.R, A.alpha.R-ACR. The dynamics characteristic of terminal voltage, frequency, active-reactive power and rotor angle of the generator with disturbances and load fluctuations is considered. In addition, the characteristic of direct voltage, direct current, power and control systems. From this the comparative analysis of the direct current control method, the possibility of the stability analysis of A.C.-D.C. interconnected power system is considered. (author). refs., figs., tabs.