Fault diagnosis and sustainable control of wind turbines: Robust data-driven and model-based strategies

Fault Diagnosis and Sustainable Control of Wind Turbines: Robust Data-Driven and Model-Based Strategies discusses the development of reliable and robust fault diagnosis and fault-tolerant (‘sustainable’) control schemes by means of data-driven and model-based approaches. These strategies are able to cope with unknown nonlinear systems and noisy measurements. The book also discusses simpler solutions relying on data-driven and model-based methodologies, which are key when on-line implementations are considered for the proposed schemes. The book targets both professional engineers working in industry and researchers in academic and scientific institutions. In order to improve the safety, reliability and efficiency of wind turbine systems, thus avoiding expensive unplanned maintenance, the accommodation of faults in their early occurrence is fundamental. To highlight the potential of the proposed methods in real applications, hardware-in-the-loop test facilities (representing realistic wind turbine systems) are considered to analyze the digital implementation of the designed solutions. The achieved results show that the developed schemes are able to maintain the desired performances, thus validating their reliability and viability in real-time implementations. Different groups of readers-ranging from industrial engineers wishing to gain insight into the applications’ potential of new fault diagnosis and sustainable control methods, to the academic control community looking for new problems to tackle-will find much to learn from this work

Adaptive Signal Processing Strategy for a Wind Farm System Fault Accommodation

In order to improve the availability of offshore wind farms, thus avoiding unplanned operation and maintenance costs, which can be high for offshore installations, the accommodation of faults in their earlier occurrence is fundamental. This paper addresses the design of an active fault tolerant control scheme that is applied to a wind park benchmark of nine wind turbines, based on their nonlinear models, as well as the wind and interactions between the wind turbines in the wind farm. Note that, due to the structure of the system and its control strategy, it can be considered as a fault tolerant cooperative control problem of an autonomous plant. The controller accommodation scheme provides the on-line estimate of the fault signals generated by nonlinear filters exploiting the nonlinear geometric approach to obtain estimates decoupled from both model uncertainty and the interactions among the turbines. This paper proposes also a data-driven approach to provide these disturbance terms in analytical forms, which are subsequently used for designing the nonlinear filters for fault estimation. This feature of the work, followed by the simpler solution relying on a data-driven approach, can represent the key point when on-line implementations are considered for a viable application of the proposed scheme

Active actuator fault-tolerant control of a wind turbine benchmark model

This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating unit of a grid is considered as a benchmark to show the design procedure, including the aspects of the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive simulations of the benchmark process are practical tools for assessing experimentally the features of the developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors. Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the proposed methodology

Fault diagnosis and process monitoring through model-based case based reasoning

In this paper, we present a method for the fault detection and isolation based on the residual generation coupled with a case based reasoning approach. The main idea is to reconstruct the outputs of the system from the measurement using the extended Kalman filter. The estimations completed with qualitative information are included in a Case Based Reasoning system in order to discriminate the possible faults and to have a reliable diagnosis. The reference model is simulated by the dynamic hybrid simulator, PrODHyS. The use of this method is illustrated through an application in the field of chemical proces

Fault Detection, Supervision and Safety for Energy Conversion Systems: Wind Turbines and Hydroelectric Plants

The motivation for this article comes from a real need to have an open discussion about the challenges of fault detection and supervision for very demanding systems, such as energy conversion systems. These features represent the key characteristic to identify possible malfunctions affecting the system (i.e. the so-called faults) and, at the same time, the capability to continue working while maintaining power conversion efficiency, if proper countermeasures are adopted. Moreover, the safety issue has begun to stimulate research and development in a wide range of industrial communities particularly for those systems demanding a high degree of reliability and availability, such as wind turbines and hydroelectric plants. In fact, once the faults are promptly detected and compensated, the system will be able to maintain specified operable and committable conditions, and at the same time should avoid expensive maintenance works. For very large installations a clear conflict exists between ensuring a high degree of availability and reducing costly maintenance, thus justifying the solutions addressed in the proposed contribution

Analysis and Application of Advanced Control Strategies to a Heating Element Nonlinear Model

open4siSustainable control has begun to stimulate research and development in a wide range of industrial communities particularly for systems that demand a high degree of reliability and availability (sustainability) and at the same time characterised by expensive and/or safety critical maintenance work. For heating systems such as HVAC plants, clear conflict exists between ensuring a high degree of availability and reducing costly maintenance times. HVAC systems have highly non-linear dynamics and a stochastic and uncontrollable driving force as input in the form of intake air speed, presenting an interesting challenge for modern control methods. Suitable control methods can provide sustainable maximisation of energy conversion efficiency over wider than normally expected air speeds and temperatures, whilst also giving a degree of “tolerance” to certain faults, providing an important impact on maintenance scheduling, e.g. by capturing the effects of some system faults before they become serious.This paper presents the design of different control strategies applied to a heating element nonlinear model. The description of this heating element was obtained exploiting a data driven and physically meaningful nonlinear continuous time model, which represents a test bed used in passive air conditioning for sustainable housing applications. This model has low complexity while achieving high simulation performance. The physical meaningfulness of the model provides an enhanced insight into the performance and functionality of the system. In return, this information can be used during the system simulation and improved model based and data driven control designs for tight temperature regulation. The main purpose of this study is thus to give several examples of viable and practical designs of control schemes with application to this heating element model. Moreover, extensive simulations and Monte Carlo analysis are the tools for assessing experimentally the main features of the proposed control schemes, in the presence of modelling and measurement errors. These developed control methods are also compared in order to evaluate advantages and drawbacks of the considered solutions. Finally, the exploited simulation tools can serve to highlight the potential application of the proposed control strategies to real air conditioning systems.openTurhan, T.; Simani, S.; Zajic, I.; Gokcen Akkurt, G.Turhan, T.; Simani, Silvio; Zajic, I.; Gokcen Akkurt, G

Application of a data-driven fuzzy control design to a wind turbine benchmark model

In general, the modelling of wind turbines is a challenging task, since they are complex dynamic systems, whose aerodynamics are nonlinear and unsteady. Accurate models should contain many degrees of freedom, and their control algorithm design must account for these complexities. However, these algorithms must capture the most important turbine dynamics without being too complex and unwieldy, mainly when they have to be implemented in real-time applications. The first contribution of this work consists of providing an application example of the design and testing through simulations, of a data-driven fuzzy wind turbine control. In particular, the strategy is based on fuzzy modelling and identification approaches to model-based control design. Fuzzy modelling and identification can represent an alternative for developing experimental models of complex systems, directly derived directly from measured input-output data without detailed system assumptions. Regarding the controller design, this paper suggests again a fuzzy control approach for the adjustment of both the wind turbine blade pitch angle and the generator torque. The effectiveness of the proposed strategies is assessed on the data sequences acquired from the considered wind turbine benchmark. Several experiments provide the evidence of the advantages of the proposed regulator with respect to different control methods

Advanced Issues of Wind Turbine Modelling and Control

The motivation for this paper comes from a real need to have an overview about the challenges of modelling and control for very demanding systems, such as wind turbine systems, which require reliability, availability, maintainability, and safety over power conversion efficiency. These issues have begun to stimulate research and development in the wide control community particularly for these installations that need a high degree of “sustainability”. Note that this topic represents a key point mainly for offshore wind turbines with very large rotors, since they are characterised by challenging modelling and control problems, as well as expensive and safety critical maintenance works. In this case, a clear conflict exists between ensuring a high degree of availability and reducing maintenance times, which affect the final energy cost. On the other hand, wind turbines have highly nonlinear dynamics, with a stochastic and uncontrollable driving force as input in the form of wind speed, thus representing an interesting challenge also from the modelling point of view. Suitable control methods can provide a sustainable optimisation of the energy conversion efficiency over wider than normally expected working conditions. Moreover, a proper mathematical description of the wind turbine system should be able to capture the complete behaviour of the process under monitoring, thus providing an important impact on the control design itself. In this way, the control scheme could guarantee prescribed performance, whilst also giving a degree of “tolerance” to possible deviation of characteristic properties or system parameters from standard conditions, if properly included in the wind turbine model itself. The most important developments in advanced controllers for wind turbines are addressed, and open problems in the areas of modelling of wind turbines are also outlined

Advanced issues of wind turbine modelling and control

The motivation for this paper comes from a real need to have an overview about the challenges of modelling and control for very demanding systems, such as wind turbine systems, which require reliability, availability, maintainability, and safety over power conversion efficiency. These issues have begun to stimulate research and development in the wide control community particularly for these installations that need a high degree of "sustainability". Note that this topic represents a key point mainly for offshore wind turbines with very large rotors, since they are characterised by challenging modelling and control problems, as well as expensive and safety critical maintenance works. In this case, a clear conflict exists between ensuring a high degree of availability and reducing maintenance times, which affect the final energy cost. On the other hand, wind turbines have highly nonlinear dynamics, with a stochastic and uncontrollable driving force as input in the form of wind speed, thus representing an interesting challenge also from the modelling point of view. Suitable control methods can provide a sustainable optimisation of the energy conversion efficiency over wider than normally expected working conditions. Moreover, a proper mathematical description of the wind turbine system should be able to capture the complete behaviour of the process under monitoring, thus providing an important impact on the control design itself. In this way, the control scheme could guarantee prescribed performance, whilst also giving a degree of "tolerance" to possible deviation of characteristic properties or system parameters from standard conditions, if properly included in the wind turbine model itself. The most important developments in advanced controllers for wind turbines are addressed, and open problems in the areas of modelling of wind turbines are also outlined

Effects of human immunodeficiency virus infection and treatment with antiretroviral therapy on immunological responses to childhood vaccines

Original published work submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctorate of Philosophy in Virology. Johannesburg 2017.Introduction: HIV-infected and HIV-exposed-uninfected children have a heightened susceptibility to some vaccine preventable disease. There is a paucity of data on immunogenicity of vaccines in these children, including HIV-infected children who are initiated on early antiretroviral therapy (ART). We evaluated the effect of maternal HIV-exposure and timing of ART in HIV-infected children on antibody responses to combined diphtheria-toxoid (DT) -tetanus-toxoid (TT)-whole cell pertussis (wP) and Haemophilus influenzae type b conjugate vaccine (HibCV); monovalent hepatitis B vaccine (HepB) and live-attenuated measles vaccine (MV). Methods: Samples obtained from children aged 6–12 weeks who had been enrolled into the CIPRA-SA study were analysed. Briefly, HIV-uninfected children born to HIV-uninfected (HIV-unexposed) and HIV-infected mothers (HEU). Additionally, we enrolled perinatally HIV-infected children with CD4+%≥25% randomized to deferred-ART (i.e. initiated when clinically or immunologically indicated per the then WHO recommended treatment criteria; ART-Def) or immediate-ART initiation (i.e. initiated on ART immediately upon confirmation of HIV-infection status at 4-10 weeks of age; ART-Immed). Children enrolled in the ART-Immed arm were further randomized to interrupt ART at one-year (ART/12m) or two-years of age (ART/24m). Additionally, a convenience sample of HIV-infected children with CD4+<25% initiated on immediate-ART was enrolled (ART-CD4+<25%). Children received a primary series of DTwP-HibCV/HepB at 6, 10 and 14 weeks of age; and MV at 40 weeks of age. Booster dose of DTwP and MV was given at 15-18 months of age. Sampling time-points were: prior to the first dose of vaccine, four weeks after the third dose (18 weeks age), 24 weeks after the third dose (39.3 weeks of age), at the time of the booster dose (15- 18 months age), two to four weeks after the booster dose and at 24 months of age. Samples were analysed for antibodies for DT, TT, PT, FHA, HepB measured by Luminex microbead-immunoassay; and MV antibodies were quantified by an indirect enzyme immunoassay. Results: Antibody kinetics and response to primary series of DTwP-HibCV/HepB: Pre-vaccination GMCs were higher in HIV-unexposed than HEU children for TT, but lower for HepB, DT and FHA. Post-vaccination, sero-conversion, sero-protection and GMCs were similar in HEU and HIV-unexposed children for all vaccines. Furthermore, GMCs were higher in HIV-unexposed for TT, DT, HepB and FHA than in ART-Immed children; and for TT, HepB and PT than in ART-Def children. Nevertheless, there was no difference in proportion of HIV-unexposed and HIV-infected children who developed sero-protective vaccine-specific antibody levels post-vaccination. The timing of ART initiation generally did not affect immune responses to vaccines between HIV-infected groups. Antibody kinetics and booster responses to DTwP-HibCV/HepB vaccines: Pre-booster GMCs were generally higher in HIV-unexposed than HIV-infected children for all vaccine epitopes. Post-booster and at 24 months of age the ART-Def group had lower GMCs (except to FHA), and were less likely to have sero-protective antibody levels compared to HIV-unexposed group. Also, post-booster and at 24 months of age, GMC were generally higher in HIV-unexposed than ART-Immed children, and a higher percentage of HIV-unexposed than ART-Immed children maintained antibody levels ≥1IU/ml to TT and DT at 24 months of age. The GMCs and percentage of children with sero-protective thresholds were similar pre-booster and at 24 months of age between HIV-unexposed and HEU children. Antibody kinetics and response to measles virus vaccine: At 7.3 weeks of age, the proportion with sero-protective titers was higher in HIV-unexposed (65.2%) compared to any HIV-infected group (range: 16.7% to 41.8%); but dropped to <17% in all Groups at age 19.6 weeks. Twenty-eight weeks following the first measles-vaccine, ART/12m were less likely to have sero-protective titers (79.3%) compared to HIV-unexposed (94.8%; p<0.001), ART-Def (95.7%; p=0.003) or ART/24m (92.1%; p=0.02). Although the proportion with sero-protective levels were similar between groups immediately post-booster dose, this was lower in HEU (79.6%; p=0.002) and ART/12m (80.3%; p=0.01) compared to HIV-unexposed (94.3%) 41-weeks later. Conclusion: Primary vaccination with DTwP-HibCV/HBV of HIV-infected children initiated on early-ART confers similar immunity compared to HIV-unexposed children. HIV-infected children had poor anamnestic responses, if ART was not initiated prior to primary vaccination. In contrast, the memory response and persistence of antibody to most vaccine epitopes were similar between HIV-unexposed and HEU children. Increased waning of vaccine induced immunity over a 24 month period in ART-Def, ART/12m and HEU children following MV booster-dose; indicating the need for further booster doses after two-years of age in these children. I recommend close monitoring of HEU children, as this group makes up most children born to HIV-infected mothers and what facets of the immune system have been impacted by maternal exposure to HIV.MT201