Fast and Reliable Primary Frequency Reserves From Refrigerators with Decentralized Stochastic Control

Due to increasing shares of renewable energy sources, more frequency reserves are required to maintain power system stability. In this paper, we present a decentralized control scheme that allows a large aggregation of refrigerators to provide Primary Frequency Control (PFC) reserves to the grid based on local frequency measurements and without communication. The control is based on stochastic switching of refrigerators depending on the frequency deviation. We develop methods to account for typical lockout constraints of compressors and increased power consumption during the startup phase. In addition, we propose a procedure to dynamically reset the thermostat temperature limits in order to provide reliable PFC reserves, as well as a corrective temperature feedback loop to build robustness to biased frequency deviations. Furthermore, we introduce an additional randomization layer in the controller to account for thermostat resolution limitations, and finally, we modify the control design to account for refrigerator door openings. Extensive simulations with actual frequency signal data and with different aggregation sizes, load characteristics, and control parameters, demonstrate that the proposed controller outperforms a relevant state-of-the-art controller.Comment: 44 pages, 17 figures, 9 Tables, submitted to IEEE Transactions on Power System

Feasibility study of a novel robotic system for transperitoneal partial nephrectomy: An in vivo experimental animal study

Purpose: To evaluate the safety and feasibility of partial nephrectomy with the use of the novel robotic system in an in vivo animal model. Methods: Right partial nephrectomy was performed in female pigs by a surgical team consisting of one surgeon and one bedside assistant. Both were experienced in laparoscopic surgery and trained in the use of the novel robotic system. The partial nephrectomies were performed using four trocars (three trocars for the robotic arms and one as an assistant trocar). The completion of the operations, set-up time, operation time, warm ischemia time (WIT) and complication events were recorded. The decrease in all variables between the first and last operation was calculated. Results: In total, eight partial nephrectomies were performed in eight female pigs. All operations were successfully completed. The median set-up time was 19.5 (range, 15-30) minutes, while the estimated median operative time was 80.5 minutes (range, 59-114). The median WIT was 23.5 minutes (range, 17-32) and intra- or postoperative complications were not observed. All variables decreased in consecutive operations. More precisely, the decrease in the set-up time was calculated to 15 minutes between the first and third attempts. The operative time was reduced by 55 minutes between the first and last operation, while the WIT was decreased by 15 minutes during the consecutive attempts. No complications were noticed in any operation. Conclusions: Using the newly introduced robotic system, all the advantages of robotic surgery are optimized and incorporated, and partial nephrectomies can be performed in a safe and effective manner