Back-to-back Converter Control of Grid-connected Wind Turbine to Mitigate Voltage Drop Caused by Faults

Power electronic converters enable wind turbines, operating at variable speed, to generate electricity more efficiently. Among variable speed operating turbine generators, permanent magnetic synchronous generator (PMSG) has got more attentions due to low cost and maintenance requirements. In addition, the converter in a wind turbine with PMSG decouples the turbine from the power grid, which favors them for grid codes. In this paper, the performance of back-to-back (B2B) converter control of a wind turbine system with PMSG is investigated on a faulty grid. The switching strategy of the grid side converter is designed to improve voltage drop caused by the fault in the grid while the maximum available active power of wind turbine system is injected to the grid and the DC link voltage in the converter is regulated. The methodology of the converter control is elaborated in details and its performance on a sample faulty grid is assessed through simulation

Continuous distraction osteogenesis device with MAAC controller for mandibular reconstruction applications

Abstract Background Distraction osteogenesis (DO) is a novel technique widely used in human body reconstruction. DO has got a significant role in maxillofacial reconstruction applications (MRA); through this method, bone defects and skeletal deformities in various cranio-maxillofacial areas could be reconstructed with superior results in comparison to conventional methods. Recent studies revealed in a DO solution, using an automatic continuous distractor could significantly improve the results while decreasing the existing issues. This study is aimed at designing and developing a novel automatic continuous distraction osteogenesis (ACDO) device to be used in the MRA. Methods The design is comprised of a lead screw translation mechanism and a stepper motor, placed outside of the mouth to generate the desired continuous linear force. This externally generated and controlled distraction force (DF) is transferred into the moving bone segment via a flexible miniature transition system. The system is also equipped with an extra-oral ACDO controller, to generate an accurate, reliable, and stable continuous DF. Results Simulation and experimental results have justified the controller outputs and the desired accuracy of the device. Experiments have been conducted on a sheep jaw bone and results have showed that the developed device could offer a continuous DF of 38 N with distraction accuracy of 7.6 nm on the bone segment, while reducing the distraction time span. Conclusion Continuous DF with high resolution positioning control, along with the smaller size of the distractor placed in the oral cavity will help in improving the result of the reconstruction operation and leading to a successful DO procedure in a shorter time period. The developed ACDO device has less than 1% positioning error while generating sufficient DF. These features make this device a suitable distractor for an enhanced DO treatment in MRA

Cerebellar repetitive transcranial magnetic stimulation (rTMS) for essential tremor: A double-blind, sham-controlled, crossover, add-on clinical trial

BACKGROUND:There is controversial evidence about the effect of cerebellar low-frequency stimulation in patients with essential tremor (ET). OBJECTIVES:In this study we assessed safety and effectiveness of 1 Hz (low-frequency) cerebellar repetitive transcranial magnetic stimulation (rTMS) on tremor severity in patients with essential tremor in a sham-controlled crossover trial. METHODS:A total of 23 patients assigned into two groups to receive either sham (n = 10) or rTMS (n = 13) treatment, with crossing over after a two-month washout period. Intervention consisted of 900 pulses of 1 Hz rTMS at 90% resting motor threshold or the same protocol of sham stimulation over each cerebellar hemisphere for 5 consecutive days. Tremor severity was assessed by Fahn-Tolosa-Marin (FTM) scale at baseline and at days 5, 12 and 30 after intervention. The FTM consists of 3 subscales including tremor severity rating, performance of motor tasks, and functional disability. Carry-over and treatment effects were analyzed using independent samples t-test. RESULTS:There was no significant improvement in the total FTM scores in rTMS compared to the sham stimulation on day 5 (p = 0.132), day 12 (p = 0.574), or day 30 (p = 0.382). Similarly, FTM subscales, including tremor severity rating, motor tasks, and functional disability did not improve significantly after rTMS treatment. Mild headache and local pain were the most frequent adverse events. CONCLUSION:Although cerebellar rTMS seems to have acceptable safety when used in ET patients, this study could not prove any efficacy for it in reduction of tremor in these patients. Larger studies are needed to evaluate efficacy of this therapeutic intervention and to provide evidence about the optimal stimulation parameters