Jakob Stoustrup

Fault tolerant control of wind turbines: a benchmark model

Abstract The installed energy generation capacity of wind turbines is increasing dramatically on a global scale; this means that reliability of wind turbines is of higher importance. A part of this task is to improve fault detection and accommodation schemes of the wind turbine. This paper presents a benchmark model for simulation of fault detection and accommodation schemes. This benchmark model deals with the wind turbine on a system level containing sensors, actuators and systems faults in the pitch system, drive train, generator and converter system.

Fault-Tolerant Control of Wind Turbines: A Benchmark Model

This paper presents a test benchmark model for the evaluation of fault detection and accommodation schemes. This benchmark model deals with the wind turbine on a system level, and it includes sensor, actuator, and system faults, namely faults in the pitch system, the drive train, the generator, and the converter system. Since it is a system-level model, converter and pitch system models are simplified because these are controlled by internal controllers working at higher frequencies than the system model. The model represents a three-bladed pitch-controlled variable-speed wind turbine with a nominal power of 4.8 MW. The fault detection and isolation (FDI) problem was addressed by several teams, and five of the solutions are compared in the second part of this paper. This comparison relies on additional test data in which the faults occur in different operating conditions than in the test data used for the FDI design.

Estimation of effective wind speed

The wind speed has a huge impact on the dynamic response of wind turbine. Because of this, many control algorithms use a measure of the wind speed to increase performance, e.g. by gain scheduling and feed forward. Unfortunately, no accurate measurement of the effective wind speed is online available from direct measurements, which means that it must be estimated in order to make such control methods applicable in practice. In this paper a new method is presented for the estimation of the effective wind speed. First, the rotor speed and aerodynamic torque are estimated by a combined state and input observer. These two variables combined with the measured pitch angle is then used to calculate the effective wind speed by an inversion of a static aerodynamic model.

Passive fault tolerant control of a double inverted pendulum : a case study

(28/10/2019) Passive fault tolerant control of a double inverted pendulum a case study A passive fault tolerant control scheme is suggested, in which a nominal controller is augmented with an additional block, which guarantees stability and performance after the occurrence of a fault. The method is based on the YJBK parameterization, which requires the nominal controller to be implemented in observer based form. The proposed method is applied to a double inverted pendulum system, for which an H_inf controller has been designed and verified in a lab setup. In this case study, the fault is a degradation of the tacho loop.

Design of integrated systems for the control and detection of actuator/sensor faults

Considers control systems operating under potentially faulty conditions. Discusses the problem of designing a single unit which not only handles the required control action but also identifies faults occurring in actuators and sensors. In common practice, units for control and for diagnosis are designed separately. Attempts to identify situations in which this is a reasonable approach and cases in which the design of each unit should take the other into consideration. Presents a complete characterization for each case and gives systematic design procedures for both the integrated and non‐integrated design of control and diagnosis units. Shows how a combined module for control and diagnosis can be designed which is able to follow references and reject disturbances robustly, control the system so that undetected faults do not have disastrous effects, reduce the number of false alarms and identify which faults have occurred.

Fault tolerant control: a simultaneous stabilization result

This note discusses the problem of designing fault tolerant compensators that stabilize a given system both in the nominal situation, as well as in the situation where one of the sensors or one of the actuators has failed. It is shown that such compensators always exist, provided that the system is detectable from each output and that it is stabilizable. The proof of this result is constructive, and a worked example shows how to design a fault tolerant compensator for a simple, yet challenging system. A family of second order systems is described that requires fault tolerant compensators of arbitrarily high order.

Plug & Play Control: Control Technology towards new Challenges

Control engineering is in many ways a mature technology that has found its way into almost every industrial sector with an almost countless number of successful applications. Nevertheless, there still remains significant challenges to overcome that prevent the technology from further spread. One of these challenges is related to the fact that large industrial processes are always live systems in the sense that they are subject to constant change in terms of instrumentation (sensors and actuators) and in terms of subsystems that are added or removed. This means that an advanced control system might be based on a system model that is valid only for a rather short time span and might be turned off by the operator, when it seizes to operate satisfactorily for this reason. Moreover, most of the advanced design methodologies offered by our community are monolithic in nature, in the sense that the only way to modify the control system is to perform a completely new design of the whole system in response to what might be even tiny changes in instrumentation. Such a constant redesign of the whole control system is usually not feasible due to cost and commissioning issues. This paper is a position paper in the sense that it probably provides more questions than answers. The objective of the paper is to highlight some of the challenges that the control community is facing, if the advanced methods should be made applicable to a wider range of applications, in particular those that can be described as live systems for which sensors and actuators are added or removed, and likewise, for which subsystems are added or remove dfrom time to time. The challenge is defined as creating control systems that can automatically accommodate changes of this radical nature. A number of industrial case studies to exemplify the challenges are described.

Robust performance of systems with structured uncertainties in state space

Abstract This paper considers robust performance analysis and state feedback design for systems with time-varying parameter uncertainties. The notion of a strongly robust H ∞ performance criterion is introduced, and its applications in robust performance analysis and synthesis for nominally linear systems with time-varying uncertainties are discussed and compared with the constant scaled small gain criterion. It is shown that most robust performance analysis and synthesis problems under this strongly robust ∞ performance criterion can be transformed into linear matrix inequality problems, and can be solved through finite-dimensional convex programming. The results are in general less conservative than those using small gain type criteria.

Integration of Control and Fault Detection: Nominal and Robust Design 1

Abstract The integrated design of control and fault detection is studied. The result of the analysis is that it is possible to separate the design of the controller and the filter for fault detection in the case where the nominal model can be assumed to be fairly accurate. In the uncertain case, however, the design of the filter and the controller can not be separated when an optimal design is desired. For systems with Significant uncertainties, there turns out to be a fundamental trade-off between the performance in the control loop and the performance in the filter

Active and passive fault-tolerant LPV control of wind turbines

This paper addresses the design and comparison of active and passive fault-tolerant linear parameter-varying (LPV) controllers for wind turbines. The considered wind turbine plant model is characterized by parameter variations along the nominal operating trajectory and includes a model of an incipient fault in the pitch system. We propose the design of an active fault-tolerant controller (AFTC) based on an existing LPV controller design method and extend this method to apply for the design of a passive fault-tolerant controller (PFTC). Both controllers are based on output feedback and are scheduled on the varying parameter to manage the parameter-varying nature of the model. The PFTC only relies on measured system variables and an estimated wind speed, while the AFTC also relies on information from a fault diagnosis system. Consequently, the optimization problem involved in designing the PFTC is more difficult to solve, as it involves solving bilinear matrix inequalities (BMIs) instead of linear matrix inequalities (LMIs). Simulation results show the performance of the active fault-tolerant control system to be slightly superior to that of the passive fault-tolerant control system.