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Jafar Siahbalaee,Sadegh Vaez-Zadeh,Farzad Tahami 전력전자학회 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.6
The main objective of this a paper is to improve the efficiency of permanent magnet synchronous motors (PMSMs) by using an improved direct torque control (DTC) strategy. The basic idea behind the proposed strategy is to predict the impact of a small change in the stator flux amplitude at each sampling period to decrease electrical loss before the change is applied. Accordingly, at every sampling time, a voltage vector is predicted and applied to the machine to fulfill the flux change. The motor drive simulations confirm a significant improvement in efficiency as well as a very fast and smooth response under the proposed strategy.
Jafar Ahmadia,Elham Basiri,S.M.T.K. MirMostafaee 한국통계학회 2016 Journal of the Korean Statistical Society Vol.45 No.2
Choosing the sample size is a problem faced by anyone doing a survey of any type. ‘‘What sample size do we need?’’ is one of the most frequently asked questions of statisticians. The answer always starts with ‘‘It depends on...’’. In this paper, we respond to this question by considering two criteria, total cost of experiment and mean squared prediction error in prediction problem. Towards this end, we discuss the problem of Bayesian predicting future observations from an exponential distribution based on an observed sample, when the information sample size is fixed as well as a random variable. Some distributions for the information sample size are considered and then for each case we find the parameter of distribution of the information sample size, such that the point predictor of a future order statistic has minimum mean squared prediction error when the total cost of experiment is bounded. To show the usefulness of our results, we present a simulation study. Finally, we apply our results to some real data sets in life testing.
Distribution-free prediction intervals for order statistics based on record coverage
Jafar Ahmadia,N. Balakrishnan 한국통계학회 2011 Journal of the Korean Statistical Society Vol.40 No.2
In this paper, based on the largest and smallest observations at the times when a new record of either kind (upper or lower) occurs, we discuss the prediction of future order statistics. The proposed prediction intervals are distribution-free in that the corresponding coverage probabilities are known exactly without any assumption about the parent distribution other than that it being continuous. An exact expression for the prediction coefficient of these intervals is derived. Similarly, prediction intervals for future records based on observed order statistics are also obtained. Finally, two real-life data, one involving the average July temperatures in Neurenburg, Switzerland, and the other involving the amount of annual rainfall at the Los Angeles Civic Center, are used to illustrate the procedures developed here.
Jafar Rasi,Behzad Mozaffari Tazehkand,Javad Musevi Niya 한국전자통신연구원 2015 ETRI Journal Vol.37 No.1
In this paper, a selective coefficient updating (SCU) approach at each branch of the per-tone equalization (PTEQ) structure has been applied for insufficient cyclic prefix (CP) length. Because of the high number of adaptive filters and their complex adaption process in the PTEQ structure, SCU has been proposed. Using this method leads to a reduction in the computational complexity, while the performance remains almost unchanged. Moreover, the use of set-membership filtering with variable step size is proposed for a sufficient CP case to increase convergence speed and decrease the average number of calculations. Simulation results show that despite the aforementioned algorithms having similar performance in comparison with conventional algorithms, they are able to reduce the number of calculations necessary. In addition, compensation of both the channel effect and the transmitter/receiver in-phase/quadrature-phase imbalances are achievable by these algorithms.