Fault tolerant control for wind turbine pitch actuators

This paper develops a fault detection and isolation (FDI) and active fault tolerant control (FTC) of pitch actuators in wind turbines (WTs). This is accomplished combining a disturbance compensator with a controller, both of which are formulated in the discrete-time domain. The disturbance compensator has a dual purpose: to reconstruct the actuator fault (which is used by the FDI technique) and to design the discrete-time controller to obtain an active FTC. That is, the actuator faults are reconstructed and then the control inputs are modified with the reconstructed fault signal to achieve a FTC in the presence of actuator faults with a comparable behavior to the fault-free case. The proposed techniques are validated using the aeroelastic wind turbine simulator FAST. This software is designed by the U.S. National Renewable Energy Laboratory and is widely used for studying wind turbine control systems.Peer ReviewedPostprint (published version

Global Gain Outer Loop Method for Discrete-time Sliding Mode Control

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 조동일.본 논문에서는 이산 시간 슬라이딩 모드 제어 방법(discrete-time sliding mode control, DSMC) 및 외란 보상기(decoupled disturbance compensator, DDC)에 적용할 수 있는 전역 이득 외부 루프 방법(global gain outer loop method)을 분석하였다. 기존 DSMC 방법은 위치추종 성능이 좋고 외란에 대해 강인하며, 구현이 쉬워 다양한 제어환경에 널리 적용되고 있다. 또한 DSMC와 DDC를 함께 사용하여 느리게 변화하는 외란에 대해 강인함을 부여하는 연구가 진행되었다. 하지만 산업용 서보 시스템에서 위치 제어를 수행할 때, 램프 함수 형태의 외란이 인가될 경우 위치 오차가 0으로 수렴하지 못하는 문제가 발생한다. 본 논문에서는 램프 함수 형태의 외란이 있는 시스템에서 레퍼런스 입력을 재생성하여 정상상태 위치 에러를 0으로 수렴시키는 전역 이득 외부 루프 방법을 제안한다. 또한 제안한 방법은 제어 입력 포화(control input saturation)를 억제하는 효과를 갖는 보조상태변수(auxiliary state)기법과 함께 사용될 수 있음을 보인다. 특히 보조상태변수의 게인을 1로 설정할 경우, 목표 위치에서 추가적인 진동 없이 잘 제어가 됨을 보인다. 전역 이득 외부 루프 방법을 DSMC+DDC 방법에 적용할 때 최종값 정리를 이용하여 램프 함수 외란과 제어 입력 포화 이후에 위치 에러가 0이 되는 것을 보인다. 실제 산업용 서보 시스템에 제어기를 구현하여 제안하는 방법이 목표 위치에서 오버슈트를 줄이고 제어 성능을 향상시킴을 보였다.This paper presents a global gain outer loop method for discrete-time sliding mode control (DSMC) with a decoupled disturbance compensator (DDC). The original DSMC method is widely used in theoretical areas and industrial applications attributed to its excellent properties of trajectory tracking, robustness to disturbances and easy implementation. DSMC with DDC was developed to maintain closed-loop stability subject to slowly-varying disturbances. However, when the system suffers from ramp-type disturbance in position control application, overshoot arises at the end of motion. In this paper, a global gain outer loop method is proposed which regenerates the reference input and guarantees asymptotic convergence of the error state in the presence of ramp-type disturbance. Moreover, the developed method can be utilized with an auxiliary state method which is effective to maintain stability under control input saturation. Especially, we can set the gain of auxiliary state to 1 to suppress additional vibration at the end of motion. Final-value theorem is utilized to demonstrate the effectiveness of the proposed method. Experiments are performed on a servo system to demonstrate the improved overshoot performance.제 1 장 서 론 1 제 1.1 절 연구의 배경 1 제 1.2 절 연구의 구성 7 제 2 장 산업용 서보 시스템의 분석 8 제 2.1 절 플랜트 8 제 2.2 절 제어기 및 필터 10 제 3 장 전역 이득 외부 루프 방법 12 제 3.1 절 기존 DSMC+DDC 제어기 12 제 3.2 절 외부 루프를 추가한 DSMC+DDC 제어기 18 제 3.3 절 실험 결과 23 제 4 장 제어 입력 포화 상에서의 분석 30 제 4.1 절 기존 보조상태변수 방법 30 제 4.2 절 보조상태변수와 전역 이득 외부 루프 방법 34 제 4.3 절 실험 결과 37 제 5 장 결 론 41 참고문헌 42 Abstract 47 감사의 글 49Maste

Fault detection and fault tolerant control in wind turbines

Renewable energy is an important sustainable energy in the world. Up to now, as an essential part of low emissions energy in a lot of countries, renewable energy has been important to the national energy security, and played a significant role in reducing carbon emissions. It comes from natural resources, such as wind, solar, rain, tides, biomass, and geothermal heat. Among them, wind energy is rapidly emerging as a low carbon, resource efficient, cost effective sustainable technology in the world. Due to the demand of higher power production installations with less environmental impacts, the continuous increase in size of wind turbines and the recently developed offshore (floating) technologies have led to new challenges in the wind turbine systems.Wind turbines (WTs) are complex systems with large flexible structures that work under very turbulent and unpredictable environmental conditions for a variable electrical grid. The maximization of wind energy conversion systems, load reduction strategies, mechanical fatigue minimization problems, costs per kilowatt hour reduction strategies, reliability matters, stability problems, and availability (sustainability) aspects demand the use of advanced (multivariable and multiobjective) cooperative control systems to regulate variables such as pitch, torque, power, rotor speed, power factors of every wind turbine, etc. Meanwhile, with increasing demands for efficiency and product quality and progressing integration of automatic control systems in high-cost and safety-critical processes, the fields of fault detection and isolation (FDI) and fault tolerant control (FTC) play an important role. This thesis covers the theoretical development and also the implementation of different FDI and FTC techniques in WTs. The purpose of wind turbine FDI systems is to detect and locate degradations and failures in the operation of WT components as early as possible, so that maintenance operations can be performed in due time (e.g., during time periods with low wind speed). Therefore, the number of costly corrective maintenance actions can be reduced and consequently the loss of wind power production due to maintenance operations is minimized. The objective of FTC is to design appropriate controllers such that the resulting closed-loop system can tolerate abnormal operations of specific control components and retain overall system stability with acceptable system performance. Different FDI and FTC contributions are presented in this thesis and published in different JCR-indexed journals and international conference proceedings. These contributions embrace a wide range of realistic WTs faults as well as different WTs types (onshore, fixed offshore, and floating). In the first main contribution, the normalized gradient method is used to estimate the pitch actuator parameters to be able to detect faults in it. In this case, an onshore WT is used for the simulations. Second contribution involves not only to detect faults but also to isolate them in the pitch actuator system. To achieve this, a discrete-time domain disturbance compensator with a controller to detect and isolate pitch actuator faults is designed. Third main contribution designs a super-twisting controller by using feedback of the fore-aft and side-to-side acceleration signals of the WT tower to provide fault tolerance capabilities to the WT and improve the overall performance of the system. In this instance, a fixed-jacket offshore WT is used. Throughout the aforementioned research, it was observed that some faults induce to saturation of the control signal leading to system instability. To preclude that problem, the fourth contribution of this thesis designs a dynamic reference trajectory based on hysteresis. Finally, the fifth and last contribution is related to floating-barge WTs and the challenges that this WTs face. The performance of the proposed contributions are tested in simulations with the aero-elastic code FAST.La energía renovable es una energía sustentable importante en el mundo. Hasta ahora, como parte esencial de la energía de bajas emisiones en muchos países, la energía renovable ha sido importante para la seguridad energética nacional, y jugó un papel importante en la reducción de las emisiones de carbono. Proviene de recursos naturales, como el viento, la energía solar, la lluvia, las mareas, la biomasa y el calor geotérmico. Entre ellos, la energía eólica está emergiendo rápidamente como una tecnología sostenible de bajo carbono, eficiente en el uso de los recursos y rentable en el mundo. Debido a la demanda de instalaciones de producción de mayor potencia con menos impactos ambientales, el aumento continuo en el tamaño de las turbinas eólicas y las tecnologías offshore (flotantes) recientemente desarrolladas han llevado a nuevos desafíos en los sistemas de turbinas eólicas. Las turbinas eólicas son sistemas complejos con grandes estructuras flexibles que funcionan en condiciones ambientales muy turbulentas e impredecibles para una red eléctrica variable. La maximización de los sistemas de conversión de energía eólica, los problemas de minimización de la fatiga mecánica, los costos por kilovatios-hora de estrategias de reducción, cuestiones de confiabilidad, problemas de estabilidad y disponibilidad (sostenibilidad) exigen el uso de sistemas avanzados de control cooperativo (multivariable y multiobjetivo) para regular variables tales como paso, par, potencia, velocidad del rotor, factores de potencia de cada aerogenerador, etc. Mientras tanto, con las crecientes demandas de eficiencia y calidad del producto y la progresiva integración de los sistemas de control automático en los procesos de alto costo y de seguridad crítica, los campos de detección y aislamiento de fallos (FDI) y control tolerante a fallos (FTC) juegan un papel importante. Esta tesis cubre el desarrollo teórico y también la implementación de diferentes técnicas de FDI y FTC en turbinas eólicas. El propósito de los sistemas FDI es detectar y ubicar las degradaciones y fallos en la operación de los componentes tan pronto como sea posible, de modo que las operaciones de mantenimiento puedan realizarse a su debido tiempo (por ejemplo, durante periodos con baja velocidad del viento). Por lo tanto, se puede reducir el número de costosas acciones de mantenimiento correctivo y, en consecuencia, se reduce al mínimo la pérdida de producción de energía eólica debido a las operaciones de mantenimiento. El objetivo de la FTC es diseñar controladores apropiados de modo que el sistema de bucle cerrado resultante pueda tolerar operaciones anormales de componentes de control específicos y retener la estabilidad general del sistema con un rendimiento aceptable del sistema. Diferentes contribuciones de FDI y FTC se presentan en esta tesis y se publican en diferentes revistas indexadas a JCR y en congresos internacionales. Estas contribuciones abarcan una amplia gama de fallos WTs realistas, así como diferentes tipos de turbinas (en tierra, en alta mar ancladas al fondo del mar y flotantes). El rendimiento de las contribuciones propuestas se prueba en simulaciones con el código aeroelástico FAST.Postprint (published version