Fault-tolerant Control of a Wind Turbine with a Squirrel-cage Induction Generator and Rotor Bar Defects

Abstract

Original scientific paperWind turbines are usually installed on remote locations and in order to increase their economic competence malfunctions should be reduced and prevented. Faults of wind turbine generator electromechanical parts are common and very expensive. This paper proposes a fault-tolerant control strategy for variable-speed variable-pitch wind turbines in case of identified and characterised squirrel-cage generator rotor bar defect. An upgrade of the torque control loop with flux-angle-based torque modulation is proposed. In order to avoid or to postpone generator cage defects, usage of pitch controller in the low wind speed region is introduced. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their life cycle and energy production. Practical implementation aspects such as estimation of variables used in control and estimate errors are considered and respected in operation, as well as fault-induced asymmetries. Simulation results for the case of a megawatt class wind turbine and the identified rotor bar fault are presented.Key words: Wind turbine control, Torque control, Generator fault-tolerant control, Nonlinear estimation, Asymmetric field-oriented controlUpravljanje vjetroagregatom otporno na oštećenja kaveza asinkronog generatora. Vjetroagregati se obično postavljaju na udaljene, nepristupačne lokacije te je potrebno spriječiti nastanak kvarova da bi se povećala njihova ekonomska konkurentnost. Kvarovi elektromehaničkih dijelova generatora vjetroagregatačesti su i vrlo skupi. U ovom radu predstavljen je koncept upravljanja vjetroagregatima s promjenjivom brzinom vrtnje i zakretom lopatica za slučaj identificiranog i okarakteriziranog oštećenja kaveza asinkronog generatora. Predložena je nadogradnja na postojeći algoritam upravljanja momentom zasnovana na njegovoj modulaciji s obzirom na položaj magnetskog toka generatora. Da bi se izbjeglo ili usporilo širenje napuknuća kaveza generatora, predložena je primjena regulacijskog kruga za zakret lopatica i u režimu rada vjetroagregata ispod nazivne brzine vrtnje. Predstavljena strategija upravljanja razvijena je uvažavajući mogućnost modularnog nadovezivanja na postojeće metode upravljanja već postavljenih vjetroagregata s ciljem produženja njihova životnog vijeka i povećanja proizvodnje energije. Razmatrani su i uvaženi aspekti vezani uz praktičnu izvedbu, kao što je estimacija varijabli korištenih u upravljackom algoritmu i pripadajuće pogreške estimata, kao i nesimetrije uzrokovane nastankom kvara. U radu su dani simulacijski rezultati za slučaj vjetroagregata iz megavatne klase s dijagnosticiranim napuknućem kaveza rotora.Ključne riječi: upravljanje vjetroagregatom, upravljanje momentom, upravljanje otporno na kvarove generatora, nelinearna estimacija, vektorsko upravljanje nesimetričnog stroja

Influence of Wind Turbine Generator Fault-tolerant Control on Power Production Quality

“…This is mainly referred to the field-oriented control (FOC) or direct torque control (DTC) and their derivatives, which are in charge of balancing between generator torque and wind turbine aerodynamical torque, and of ensuring the optimum power production trajectory tracking [4,5,7].…”

“…Different strategies are proposed, mostly based on redundancies of sensors and electronic components, and control algorithm is used to evaluate the trustworthiness of each [3]. In our past work we proposed a fault-tolerant control procedure for rotor-bar fault of a squirrel-cage induction generator (SCIG) [4] and for the stator inter-turn insulation fault that can be applied on both synchronous and asynchronous electrical machines [5]. Observed faults cover about 70% of electrical machine faults [6].…”

Fault-tolerant Control of a Wind Turbine with Generator Stator Inter-turn Faults

“…Relations (12) and (13) show that d and q coordinates are not fully decoupled and changing the voltage value in one axis affects also the other. By introducing correction voltages ∆u sd and ∆u sq , fully decoupled relations are derived:…”

“…This paper applies the proposed method for the case of stator inter-turn isolation fault and achieves smooth generator operation in the faulty conditions. A similar work related to the asymmetries caused by SCIG rotor-bar faults is [13]. This paper is organized as follows.…”

“…In our recent papers [4] and [5] we proposed a general idea of fault-tolerant control algorithm for generator electromechanical faults and its application in suppressing the rotor-bar defect in SCIGs. Algorithm is based on proper extension of widely adopted control strategies used in wind turbines, mainly on torque control loop with field-oriented control (FOC).…”