• 전력전자학회논문지
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• 제16권1호
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• pp.11-19
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• 2011

본 연구에서는 풍력발전시스템의 다양한 특성들을 고려한 DFIG풍력발전시스템 하드웨어 시뮬레이터를 개발하였다. 개발한 하드웨어 시뮬레이터는 유도전동기를 이용한 풍력터빈 모델과 이중여자 유도발전기 그리고 컨버터와 인버터로 구성된 Back-to-Back컨버터로 구성되었다. 특히 풍력터빈 시뮬레이터는 풍속계를 이용하여 실시간으로 풍속을 측정하고 측정된 바람으로 블레이드의 특성을 모의하였다. DFIG풍력발전 시뮬레이터에서 생산되는 전력은 MPPT제어를 수행하는 MSC(Machine Side Converter)와 DC link전압을 일정하게 제어하는 GSC(Grid Side Converter)에 의해 계통에 연계되어 운전한다. 제안하는 시스템은 PSCAD/EMTDC 프로그램을 이용하여 시뮬레이션 하였으며, 축소모형실험을 통해서 성능을 검증하였다.

• Journal of Electrical Engineering and Technology
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• 제5권2호
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• pp.299-306
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• 2010

This paper proposes a new doubly-fed induction generator (DFIG) system using a matrix converter controlled by direct duty ratio pulse-width modulation (DDPWM) scheme. DDPWM is a recently proposed carrier based modulation strategy for matrix converters which employs a triangular carrier and voltage references in a voltage source inverter. By using DDPWM, the matrix converter can directly and effectively generate rotor voltages following the voltage references within the closed control loop. The operation of the proposed DFIG system was verified through computer simulation and experimental works with a hardware simulator of a wind power turbine, which was built using a motor-generator set with vector drive. The simulation and experimental results confirm that a matrix converter with a DDPWM modulation scheme can be effectively applied for a DFIG wind power system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.23-24
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• 2007

Most of modern wind turbines employs a doubly-fed induction generator (DFIG) system because it has many advantages due to variable-speed operation, relatively high efficiency and it small converter size. The DFIG system uses a wound rotor induction machine so that the magnetizing current of the generator can be fed from both the stator and the rotor. This paper presents a protection relaying algorism for DFIG using the DQ equivalent circuits. The induced voltages calculated from the stator and rotor sides are nearly the same in the steady state. They become different in the DQ equivalent circuits during an internal fault. The proposed algorithm compares the inducted voltages estimated from the stator and the rotor circuit converted into the stationary reference frame. If the difference between the induced voltages exceeds the threshold, the proposed algorithm detects an turn-to-turn fault.

• 전력전자학회논문지
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• 제13권2호
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• pp.152-162
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• 2008

본 논문은 이중여자 유도형(DFIG) 풍력발전시스템에서 유효전력과 무효전력을 직접적으로 제어하기 위한 슬라이딩 모드 기반의 직접전력제어기법을 제시한다. 제안하는 제어기법은 슬라이딩 모드 기반의 전력제어기부와 전력회로부의 스위칭 지령값을 위한 공간전압벡터변조방식(SVM)으로 구성된다. 본 논문에서 제안하고 있는 공간전압벡터 변조방식을 이용한 슬라이딩 모드 기반의 전력제어기법은 고정된 스위칭 주파수에서 기기상수의 변화에 강인한 전력제어가 가능하고, 기존의 자속기준제어기법(FOC)에서 사용되었던 전류제어기와 축변환 없이 직접적으로 전력을 제어함으로써 제어구조가 간단하다. 시뮬레이션과 실험 결과를 통해 제안하는 제어기법의 타당성을 확인한다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(2)
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• pp.639-643
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• 2003

We are interested in this paper on the control of an electromechanical system consisting of a doubly-fed induction generator(DFIG), driven by a prime mover that can supply or extract mechanical power, e.g., a flywheel inertia, and an induction motor(IM). The stator of the Induction machine is connected to the stator of the generator whose rotor voltage is regulated by a bidirectional converter. The main interest of this configuration is that it permits a bidirectional power flow between the motor, which may operate in regenerative mode, and the generator We propose a passivity-based controller to regulate the motor mechanical speed. Since this kind of controllers achieve stabilization via energy balancing, regulation of the power flow in the system is naturally incorporated. Simulation results are presented to illustrate the main points of our paper.

• Journal of Electrical Engineering and Technology
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• 제10권6호
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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 Electrical Engineering and Technology
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• 제10권2호
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• pp.487-495
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• 2015

This paper proposes a new robust decentralized power oscillation dampers (POD) design of doubly-fed induction generator (DFIG) wind turbine for damping of low frequency electromechanical oscillations in an interconnected power system. The POD structure is based on the practical $2^{nd}$-order lead/lag compensator with single input. Without exact mathematical model, the inverse output multiplicative perturbation is applied to represent system uncertainties such as system parameters variation, various loading conditions etc. The parameters optimization of decentralized PODs is carried out so that the stabilizing performance and robust stability margin against system uncertainties are guaranteed. The improved firefly algorithm is applied to tune the optimal POD parameters automatically. Simulation study in two-area four-machine interconnected system shows that the proposed robust POD is much superior to the conventional POD in terms of stabilizing effect and robustness.

• Journal of Electrical Engineering and Technology
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• 제5권3호
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• pp.443-450
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• 2010

An enhanced control strategy for variable-speed unbalanced stand-alone doubly-fed induction generator-based wind energy conversion systems is proposed in this paper. The control scheme is applied to the rotor-side converter to eliminate stator voltage imbalance. The proposed current controller is developed based on the proportional-resonant regulator, which is implemented in the stator stationary reference frame. The resonant controller is tuned at the stator synchronous frequency to achieve zero steady-state errors in rotor currents without decomposing the positive and negative sequence components. The computational complexity of the proposed control algorithm is greatly simplified, and control performance is significantly improved. Finally, simulations and experimental results are presented to verify the feasibility and the robustness of the proposed control scheme.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2010년도 하계학술대회 논문집
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• pp.194-195
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• 2010

This paper investigates control algorithms for a doubly fed induction generator (DFIG) with back-to-back converter in medium-voltage wind power system under unbalanced grid conditions. Operation of DFIG under unbalanced grid conditions causes several problems such as overcurrent, unbalanced currents, active power pulsation and torque pulsation. Three different control algorithms to compensate for the unbalanced conditions have been investigated with respect to four performance factors; fault ride-through capability, efficiency, harmonic distortions and torque pulsation. The control algorithm having zero amplitude of negative sequence current shows the most cost-effective performance concerning fault ride-through capability and efficiency. The control algorithm for nullifying the oscillating component of the instantaneous active power generates least harmonic distortions. Combination of these two control algorithms depending on the operating requirements presents most optimized performance factors under the generalized unbalanced operating conditions.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권3호
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• pp.306-312
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• 2013

Doubly fed induction generator (DFIG) systems widely used globally are highly sensitive to the grid disturbance due to the structure that the stator is connected to the grid. In the past, when a grid fault occurs in order to prevent a system, generators are separated from the grid regardless of the fault duration time. Recently, however, the grid connection standards(Grid Code)says that for the failures removed within a certain time, the generator remains operation without separating from the grid. This paper proposes a new flux tracking LVRT(Low-Voltage Ride Through) control based on system modeling equations. The validity of the proposed strategy has been demonstrated by computer simulations.