This paper presents a power transfer matrix model and multivariable control method for a doubly-fed induction generator (DFIG) wind energy system. The power transfer matrix model uses instantaneous real/reactive power components as the system state variables. It is shown that using the power transfer matrix model improves the robustness of controllers as the power waveforms are independent of a frame of reference. The sequential loop closing technique is used to design the controllers based on the linearized model of the wind energy system. The designed controller includes six compensators for capturing the maximum wind power and supplying the required reactive power to the DFIG. A power/current limiting scheme is also presented to protect power converters during a fault. The validity and performance of the proposed modeling and control approaches are investigated using a study system consisting of a grid-connected DFIG wind energy conversion system. This investigation uses the time-domain simulation of the study system to: 1) validate the presented model and its assumptions, 2) show the tracking and disturbance rejection capabilities of the designed control system, and 3) test the robustness of the designed controller to the uncertainties of the model parameters.Index Terms-Doubly fed induction generator (DFIG), dynamics modeling, instantaneous power, multivariable control, wind energy systems, wind power control, wind turbine generator.

Different methods for detecting broken bars in induction motors can be found in literature. Many of these methods are based on evaluating special frequency magnitudes in machine signals spectrums. Current, power, flux, etc are among these signals. Frequencies related to broken rotor fault are dependent to slip; therefore, correct diagnosis of fault depends on accurate determination of motor velocity and slip. The traditional methods typically require several sensors that should be pre-installed in some cases. A practical diagnosis method should be easily performed in site and does not take too much time. This paper presents a diagnosing method based on only a vibration sensor. Motor velocity oscillation due to broken rotor causes frequency components at twice slip frequency difference around speed frequency in vibration spectrum. Speed frequency and its harmonics as well as twice supply frequency, can easily and accurately be found in vibration spectrum, therefore the motor slip can be computed. Now components related to rotor fault can be found. According to this method, an apparatus consisting necessary hardware and software has been designed. Experimental tests have confirmed the efficiency of the method.

Please cite this article as: Esmaeil Rezaei A new model for the optimization of periodic inspection intervals with failure interaction: a case study for a turbine rotor (2015), http://dx. AbstractInspection is one of the important activities to detect and fix failures in repairable system. Optimization of inspection intervals has critical role in maintenance cost and operating system. When a component fails, it is renewed or repaired. A great deal of periodic inspection research is for hidden failure and considered one of the perfect (renew) and minimal repair policies. In literature, the lack of simultaneous consideration of both perfect and minimal repair in reliability model has been observed. This study presents new reliability model by synchronous consideration of both minimal and perfect repair. As well as, the expected total maintenance cost is presented and modeled to figure out the optimal inspection interval. The proposed model is more comprehensive model in reliability evaluation and can be applied in different pertinent problems. The model is applied to steam turbine system which the rotor considered as soft component and filter as hard component. The result revealed that the system should be inspected every 12 month.

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