Sharif Digital Repository

The flux and torque hysteresis bands are the only gains to be adjusted in direct torque control (DTC). The torque ripple and harmonic loss of motor and switching loss of inverter are greatly influenced by them. In this paper the effects of flux and torque hysteresis bands on inverter switching loss, harmonic loss and torque ripple of induction motor are investigated through a cost function. Minimizing this cost function leads to the optimum value of the hysteresis bands of torque and flux controllers. The effect of motor speed on cost function is also investigated. © 2003 International Academic Publishers/World Publishing Corporation  

The torque ripple and harmonic loss of motor and switching loss of inverter are greatly influenced by sampling time in the direct torque control method. Hence these variables must be observed in the control process to maximize performance of the system. In this paper the effects of sampling time on inverter switching loss, harmonic loss and torque ripple of induction motor are investigated. To find their optimum values a cost function consisting of motor harmonic losses, torque ripples and inverter switching losses are defined. Minimizing this cost function leads to the optimum value of the sampling time. © 2003 IEEE  

In this paper, LQG/LTR controller is designed for attitude control of the geostationary satellite at nominal mode. Usage actuator is the reaction wheel and control torque is determined by the LQR regulator. LQR controller signal has good performance, if all states are considered in feedback, but does not include model and sensors noises. Usage sensors are sun and earth sensors and EKF is used for estimation of noisy states. Then, LQG and LQG/LTR controllers are designed based on the estimated states, and are compared with LQR controller. The results show that robustness and performance of LQG/LTR are better than LQG and its control overshoot is smaller than LQR. The term that is provided in... 

Spin-Transfer Torque RAM (STT-RAM) is a promising alternative to SRAM for implementing on-chip L2 and L3 caches. One of the most critical challenges in STT-RAM is reliability due to limited write endurance, which results in insufficient lifetime, as well as various types of errors. Previous studies have focused on either presenting various cache architectures/management techniques to improve the lifetime of STT-RAM caches or utilizing different Error Correcting Codes (ECCs) to protect against the permanent and transient errors. However, there is no quantitative analysis in the literature to determine the impact of ECCs on the lifetime of the STT-RAM caches. This paper formulates this impact... 

As technology process node scales down, on-chip SRAM caches lose their efficiency because of their low scalability, high leakage power, and increasing rate of soft errors. Among emerging memory technologies, Spin-Transfer Torque Magnetic RAM (STT-MRAM) is known as the most promising replacement for SRAM-based cache memories. The main advantages of STT-MRAM are its non-volatility, near-zero leakage power, higher density, soft-error immunity, and higher scalability. Despite these advantages, high error rate in STT-MRAM cells due to retention failure, write failure, and read disturbance threatens the reliability of cache memories built upon STT-MRAM technology. The error rate is significantly... 

As technology process node scales down, on-chip SRAM caches lose their efficiency because of their low scalability, high leakage power, and increasing rate of soft errors. Among emerging memory technologies, Spin-Transfer Torque Magnetic RAM (STT-MRAM) is known as the most promising replacement for SRAM-based cache memories. The main advantages of STT-MRAM are its non-volatility, near-zero leakage power, higher density, soft-error immunity, and higher scalability. Despite these advantages, high error rate in STT-MRAM cells due to retention failure, write failure, and read disturbance threatens the reliability of cache memories built upon STT-MRAM technology. The error rate is significantly... 

As technology process node scales down, on-chip SRAM caches lose their efficiency because of their low scalability, high leakage power, and increasing rate of soft errors. Among emerging memory technologies, Spin-Transfer Torque Magnetic RAM (STT-MRAM) is known as the most promising replacement for SRAM-based cache memories. The main advantages of STT-MRAM are its non-volatility, near-zero leakage power, higher density, soft-error immunity, and higher scalability. Despite these advantages, high error rate in STT-MRAM cells due to retention failure, write failure, and read disturbance threatens the reliability of cache memories built upon STT-MRAM technology. The error rate is significantly... 

In this paper, a new and simple control method based on Direct Torque Control (DTC) of induction motors is proposed for a multi-machine system. Similar to a conventional DTC, the proposed method has two separate control loops. In the torque control loop, before selection of optimum voltage from the DTC look-up table, the system overall requirement is determined based on requirements of motors torque. Also, Switchable Master-Slave control is used in the flux control loop. The method, which is simulated for a two-parallel induction machine system, can be extended to a multi-machine system. Simulation results are also provided to investigate the performance of the proposed technique. © 2008... 

Recent development in memory technologies has introduced Spin-Transfer Torque Magnetic RAM (STT-MRAM) as the most promising replacement for SRAMs in on-chip cache memories. Besides its lower leakage power, higher density, immunity to radiation-induced particles, and non-volatility, an unintentional bit flip during read operation, referred to as read disturbance error, is a severe reliability challenge in STT-MRAM caches. One major source of read disturbance error in STT-MRAM caches is simultaneous accesses to all tags for parallel comparison operation in a cache set, which has not been addressed in previous work. This paper first demonstrates that high read accesses to tag arrays extremely... 

Employing a small Non-Volatile Memory (NVM) as the Persistent Journal Area (PJA) along with a DRAM-based buffer is an efficient approach to overcome DRAM vulnerability, named NVB-Buffer. Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is one of the most promising PJA candidates thanks to providing high endurance, non-volatility, and DRAM-like latency. Despite these advantages, STT-MRAM faces major reliability challenges, i.e. Retention Failure, Read Disturbance, and Write Failure, which have not been addressed in previously suggested NVB-Buffers. In this paper, we first demonstrate that the retention failure is the dominant source of errors in NVB-Buffers as it suffers from... 

An efficient and reliable Multi-Level Cell (MLC) Spin-Transfer Torque Random Access Memory (STT-RAM) is proposed based on a Drop-And-Rearrange Approach, called DARA. Since CNN models are rather robust, less important bits are dropped, allowing important bits to be written in safe and reliable Single-Level Cell mode. Also, bits are rearranged to make the representation better aligned with memory cell characteristics. Bits with higher impact on the features value are stored in safer bit positions reducing the chance of read/write circuits to malfunction. Experimental results show that our approach provides comparable to error-free scenario reliability level, while doubling the bandwidth and... 

Application of a flux search controller in direct torque control of induction motor drives produces divergence problem and steady state flux ripple, because of the disturbance in the control loop. In this paper, an investigation about the origin of this noise has been performed. It is shown that the variation of voltage harmonics is the main reason of disturbance in the flux control loop. The minimum allowable value of flux step has been determined based on this analysis to prevent the divergence problem. Feasibility of noise cancellation has been discussed. Experimental results are presented to justify the theoretical analysis. © 2005 IEEE  

Flux search controllers are proposed to improve the efficiency of electrical motors especially induction motors. In this paper, a flux search controller is proposed to increase the efficiency of a direct torque controlled induction motor with light load. The reference flux value is determined through a two stage minimization algorithm with the amplitude of the stator current as the objective function. In the transient state, a great flux step is used to speed up the convergence. In the steady state, a noise cancellation algorithm is used to let using small flux step and improves the steady state behavior of flux controller. Simulation and experimental confirm the fast dynamics of the... 

Performance and reliability are two prominent factors in the design of data storage systems. To achieve higher performance, recently storage system designers use DynamicDynamic RAMRAM (DRAM)-based buffers. The volatility of DRAM brings up the possibility of data loss and data inconsistency. Thus, a part of the main storage is conventionally used as the journal area to be able of recovering unflushed data pages in the case of power failure. Moreover, periodically flushing buffered data pages to the main storage is a common mechanism to preserve a high level of reliability. This scheme, however, leads to a considerable increase in storage write traffic, which adversely affects the performance.... 

Recent development in memory technologies has introduced Spin-Transfer Torque Magnetic RAM (STT-MRAM) as the most promising replacement for SRAMs in on-chip cache memories. Besides its lower leakage power, higher density, immunity to radiation-induced particles, and non-volatility, an unintentional bit flip during read operation, referred to as read disturbance error, is a severe reliability challenge in STT-MRAM caches. One major source of read disturbance error in STT-MRAM caches is simultaneous accesses to all tags for parallel comparison operation in a cache set, which has not been addressed in previous work. This article first demonstrates that high read accesses to tag array extremely... 

Purpose: The paper aims to address the combined attitude control and Sun tracking problem in a flexible spacecraft in the presence of external and internal disturbances. The attitude stabilization of a flexible satellite is generally a challenging control problem, because of the facts that satellite kinematic and dynamic equations are inherently nonlinear, the rigid–flexible coupling dynamical effect, as well as the uncertainty that arises from the effect of actuator anomalies. Design/methodology/approach: To deal with these issues in the combined attitude and Sun tracking system, a novel control scheme is proposed based on the adaptive fuzzy Jacobian approach. The augmented spacecraft model... 

The failure of mechanical components is a common phenomenon in satellites. This failure can happen in the satellite attitude control system, which causes that the control system of the satellite becomes underactuated. There have been many attempts to control the orientation of underactuated satellites. However, in most studies, the inertia matrix of the satellite is assumed to be diagonal with respect to the body coordinate system, and no limitations on the amount of torque applied by the reaction wheels have been considered. In this paper, at first, it is attempted to control the satellite using the motion planning method. The satellite control inputs are assumed to be cubic spline with... 

It has been suggested that the central nervous system simplifies muscle control through basic units, called synergies. In this study, we have developed a novel target-matching protocol and used non-negative matrix factorization (NMF) technique to extract trunk muscle synergies and corresponding torque synergies. Isometric torque data at the L5/S1 level and electromyographic patterns of twelve abdominal and back muscles from twelve healthy participants (five females) were simultaneously recorded. Each participant performed a total number of 24 isometric target-matching tasks using 12 different angular directions and 2 levels of uniaxial and biaxial exertions. Within- and between-subject... 

Abstract The torque exerted on the walls of a micro cylindrical Couette gas flow is studied using Direct Simulation Monte Carlo (DSMC) method and analytical solutions. An analytical solution for temperature filed under specified wall heat flux condition is proposed using a previously introduced power-law (PL) wall-scaling approach. The results of cylindrical Couette flow under specified wall heat flux condition are compared with those of isothermal flow. The effects of rarefaction, compressibility, tangential momentum accommodation coefficient (TMAC) and gas-surface heat exchange on the torque values are investigated for slip to free molecular flow regimes. The results indicate that the... 

In this paper, a less studied factor in the asymmetrical rolling process of sheets, namely the rolls horizontal displacement, is investigated using an analytical approach based on the slab method analysis. The presented method is capable of computing the force and torque of the process under different asymmetrical factors such as the rolls horizontal displacement, the interface friction inequality, and the rolls speed mismatch. A formula is presented to predict the outgoing sheet curvature induced by the rolls horizontal displacement. The results can be potentially used in producing curved sheets of various shapes by the asymmetrical rolling process. The analytical model is compared with a...