풍력발전 시스템용 회전자 계통연계형 이중여자 권선형 유도발전기

Abstract

본 논문은 풍력발전 시스템용 회전자 계통연계형 이중여자 권선형 유도발전기 (grid-connected to rotor type doubly-fed induction generator, 이하 “회전자 계통연계형 DFIG”)에 관한 연구이다. 종래와 달리 고정자 권선 대신 회전자 권선이 계통에 연계된 회전자 계통연계형 DFIG 모델을 제안하며, 설계와 해석에 대한 연구를 수행하였다. 종래의 고정자 계통연계형 DFIG의 경우 1차측인 고정자부터 설계되어 고정자 내경이 결정된 후에 2차측인 회전자가 설계되므로 회전자의 효과적인 설계가 어렵고 회전자 내측 코어의 자속밀도가 낮은 단점이 있다. 따라서 고정자 계통연계형 DFIG에서 비효율적으로 사용되던 회전자를 효과적으로 설계함으로써, 소형경량화 및 단위중량당 토크의 증가가 가능한 회전자 계통연계형 DFIG 및 이를 설계하기 위한 장하분배법을 제안하였다. 제안된 회전자 계통계형 DFIG의 효과 및 설계방법의 타당성을 검증하기 위해 종래 모델과 제안 모델을 각각의 설계방법을 이용하여 설계 후 그 결과를 비교하였다. 슬립에 따른 전 속도영역에서의 DFIG의 발전 특성을 용이하게 살펴보고 설계결과를 검증하기 위하여 등가회로해석을 수행하였으며, 종래의 고정자 계통연계형 DFIG와 제안하는 회전자 계통연계형 DFIG의 속도에 따른 발전 및 효율 특성을 해석 후 이를 비교하였다. 또한 DFIG는 발전기로서 뿐만 아니라 전동기로서 동작이 가능하므로, 전동기 동작 시와 발전기 동작 시의 특성 해석을 각각 수행하였다. 전동기 동작 시 정밀한 특성 해석을 위해 유한요소해석을 수행하였으며, 종래 모델과 제안 모델의 효율과 토크 특성 등을 비교하였다. 또한 발전기 동작 특성 해석 시에는 발전 특성 해석을 위한 회로가 필요하므로 유한요소해석 및 전력전자 해석 툴을 이용한 연동해석을 수행하였으며, 제안하는 회전자 계통연계형의 발전 효율 및 단위 중량당 토크 특성 등을 살펴보았다. 다음 단계로서, 풍력발전기의 중요한 특성인 발전효율을 유지시키면서 단위중량당 토크를 최대화하기 위한 회전자 계통연계형 DFIG의 최적설계를 수행하였다. 최적설계를 위한 설계변수는 고정자 슬롯의 깊이와 폭 그리고 회전자 슬롯의 깊이와 폭으로 결정하였다. 실험계획을 위한 샘플링 기법으로서 LHS (latin hypercube sampling)을 적용하였으며, 연동해석을 이용하여 실험계획을 수행하였다. 또한 Kriging 기법을 이용하여 근사화 모델링을 수행하였으며, 유전 알고리즘 (genetic algorithm : GA)을 이용하여 목적함수와 제약조건을 만족하는 설계변수의 최적 값을 도출하였다. 최종적으로 초기 모델과 최적 모델의 시작품 제작 후 전동기 특성 및 발전기 특성의 성능평가를 통해 회전자 계통연계형 DFIG의 우수성을 입증하였으며, 설계, 해석 및 최적설계 결과의 타당성을 검증하였다.|This paper is the study on novel grid-connected to rotor type doubly fed induction generator (DFIG) for wind turbine system. A grid-connected to rotor type DFIG is proposed, in which the rotor winding is connected to the grid instead of the stator winding, and its design and analysis are performed. The main drawback of the conventional grid-connected to stator type is difficulty of effective design and low flux density in the inner rotor core because the stator is designed in advance, and then the rotor is designed. To reduce the size and weight, and to increase the torque per weight, novel grid-connected to rotor type DFIG and its design process using loading distribution method are proposed through its effective rotor design. To verify the effect of the proposed DFIG and the validity of its design process, the conventional type and proposed type are designed using respective design method, and then its design results are compared. To observe the generation characteristics according to slip variation in the whole speed range and to verify the design results, the equivalent circuit analysis is performed. The power generation and efficiency characteristics of the conventional type DFIG and the proposed type DFIG are analyzed and compared. Characteristic analysis of DFIG is performed considering motor operation and generator operation, because it can be operated as a motor as well as a generator. In the motor operation, FEA (finite element analysis) is performed to get accurate result, and the efficiency, torque, and another characteristics are compared. In the generator operation, a coupled analysis is performed which is combined FEA and power electronics simulation software, and the generation efficiency and torque per weight are calculated. In the next step, a shape optimization for the proposed grid-connected to rotor type DFIG is performed to maximize the torque per weight as well as to maintain the efficiency, which are significant parameters for wind turbine application. The optimal design variables are established which are the slot depth and slot width of the stator core, and the slot depth and slot width of the rotor core. LHS (latin hypercube sampling) is applied as a sampling method, and DOE (design of experiment) is performed using coupled analysis. The Kriging model is used to the approximate modeling and GA (genetic algorithm) is also employed to find optimal value, which satisfy the objective function and constraints. Finally, the excellence of the proposed grid-connected to rotor type DFIG and the validity of its design, analysis, and optimal design results were verified through experimental results of the initial model and optimal model.; This paper is the study on novel grid-connected to rotor type doubly fed induction generator (DFIG) for wind turbine system. A grid-connected to rotor type DFIG is proposed, in which the rotor winding is connected to the grid instead of the stator winding, and its design and analysis are performed. The main drawback of the conventional grid-connected to stator type is difficulty of effective design and low flux density in the inner rotor core because the stator is designed in advance, and then the rotor is designed. To reduce the size and weight, and to increase the torque per weight, novel grid-connected to rotor type DFIG and its design process using loading distribution method are proposed through its effective rotor design. To verify the effect of the proposed DFIG and the validity of its design process, the conventional type and proposed type are designed using respective design method, and then its design results are compared. To observe the generation characteristics according to slip variation in the whole speed range and to verify the design results, the equivalent circuit analysis is performed. The power generation and efficiency characteristics of the conventional type DFIG and the proposed type DFIG are analyzed and compared. Characteristic analysis of DFIG is performed considering motor operation and generator operation, because it can be operated as a motor as well as a generator. In the motor operation, FEA (finite element analysis) is performed to get accurate result, and the efficiency, torque, and another characteristics are compared. In the generator operation, a coupled analysis is performed which is combined FEA and power electronics simulation software, and the generation efficiency and torque per weight are calculated. In the next step, a shape optimization for the proposed grid-connected to rotor type DFIG is performed to maximize the torque per weight as well as to maintain the efficiency, which are significant parameters for wind turbine application. The optimal design variables are established which are the slot depth and slot width of the stator core, and the slot depth and slot width of the rotor core. LHS (latin hypercube sampling) is applied as a sampling method, and DOE (design of experiment) is performed using coupled analysis. The Kriging model is used to the approximate modeling and GA (genetic algorithm) is also employed to find optimal value, which satisfy the objective function and constraints. Finally, the excellence of the proposed grid-connected to rotor type DFIG and the validity of its design, analysis, and optimal design results were verified through experimental results of the initial model and optimal model.