Sharif Digital Repository

Functional quality in the mechanical products is governed mainly by the degree of satisfaction of the design requirements, which itself depends on the variations in the effective variables. The functional parameters cannot be easily measured in mass production, and thus, are not usually considered as a direct inspection objective. Process capability indices are useful tools for evaluating the ability of a process to produce the dependent variables of a product that meet certain specifications. In this paper, the conventional process capability concept is extended to develop a computational tool for analysis of the functional quality of a mechanical product. Through defining new proper... 

Using elastic couplings in servo motor drives may lead to torsional oscillations which are usually extinguished by reducing the bandwidth of the control system as a countermeasure. A high performance servo drive however needs fast dynamic characteristics. The conventional controllers, such as PI controllers, may not be able to improve the dynamic response while keeping the system stable. Fractional order modeling offers a good framework for flexible structures such as two mass servo drives. In this paper, the dynamic response and stability of two-mass servo drive is improved using a fractional order controller. The fractional order controller allows increasing the phase margin of the system... 

Two major structures for rotor core of superconducting synchronous machine are air-cored and magnetic-cored structures. Magnetic-cored structure can be divided into two categories including salient and non-salient magnetic core. In this paper, three different structures of superconducting synchronous machine comprising air-cored, non-salient magnetic-cored and salient magnetic-cored, have been studied and compared considering required superconducting wire and machine weight. Required superconducting wire determines the capital cost and the weight of the machine determines the running cost in the case of portable applications such as ships and aircrafts  

Fast fault detection and reconfiguration of power converters is necessary in electrical drives to prevent further damage and to make the continuity of service possible. On the other hand, component minimized converters may provide the benefits of higher reliability and less volume and cost. In this paper, a new fault-tolerant converter topology is studied. This converter has five legs before the fault occurrence, and after fault detection the converter continues to function with four legs. A very fast fault detection and reconfiguration scheme is presented and studied. Simulations and experimental tests are performed to evaluate the structure requirements, the digital reconfigurable... 

Brushless doubly fed induction machine has recently attracted attention in variable speed generators and motor drives. In order to have a high performance control, a precise dynamic model is required. This paper aims at introducing a model of brushless doubly fed induction machine taking core loss into account. The details of model derivation are outlined and the torque relation is expressed in the general reference frame. The model is then used for simulation of the dynamic performance of the machine. The error introduced by neglecting core loss effect is also shown  

In this paper, different switching tables proposed for the Direct Torque Controlled (DTC) of a six-phase induction machine are simulated and implemented. A six-phase induction motor has 64 space voltage vectors which result in increased complexity in the selecting of inverters switching. The unsuitable selection of a switching table leads to large harmonics especially at low speed and it also reduces drive efficiency. A six-phase induction machine has large zero sequence harmonic currents of the order 6k ±1. These harmonic currents are varied in various techniques. Decreasing this loss is essential in a six-phase induction machine. The main purpose of this paper is to improve the ST-DTC of... 

FPGAs are interesting choices for control of power electronics converters and electrical drives. In this paper, implementation of the control method of a reduced switch- count five-leg converter is carried out. Two PWM methods are studied. For verification of the implemented controller in a practical manner, without risking the damaging of the real system, "FPGA in the loop" experiments are performed. It is shown that using the proposed methodology, FPGA implementation and verification is fast and effective. The provided results show the high performance of the implemented controller on the FPGA, therefore the feasibility and suitability of the FPGA for this application is approved  

This paper presents a mathematical model for Brushless Doubly-Fed Machine (BDFM) based on Stator Flux Orientation (SFO) in positive and negative reference frames under unbalanced grid voltage conditions. A negative controller is designed to eliminate the effects of unbalanced conditions on electrical torque. The model and controller performance during unbalanced conditions is validated by time domain simulation in MATLAB/Simulink  

This paper presents a high performance Direct Torque Control (DTC) theme for the induction motor using Indirect Matrix Converter (IMC). To improve the dynamic behavior of motor, Active Learning Method (ALM) is implemented on the DTC. The ALM uses its own modeling technique called the ink drop spread (IDS) method. Functionally the IMC is very similar to the Direct Matrix Converter (DMC) but it has separate line and load bridges. In the inverter stage, the classical DTC method is employed. In the rectifier stage, in order to reduce losses caused by snubber circuit the rectifier four-step commutation method is employed. By suitably selecting switching pattern and using Active Learning Method... 

Standing-wave ultrasonic motors are a modern class of positioning systems, which are used to deliver a high precision linear or rotary motion with an unlimited stroke. The design process should be performed through an effective optimization algorithm in order to guaranty proper and efficient function of these motors. An optimization method of ultrasonic motors is proposed based on the combination of finite element method and factorial design as a design of experiments in this study. The results show the ability of this method in optimal design of ultrasonic motors especially those which have a complex structure and multi modes operation principle  

This paper describes a control scheme that allows an IPMS motor drive system to operate in the event of current and speed sensor faults. This task can be achieved by two control strategies: a nominal performance controller and a fault detection part. The nominal controller combines field oriented control and addresses fault tolerance scheme. Fault-tolerant strategy will operate in parallel with the system until a fault is detected. This approach is based on the adaptive backstepping observer. Stator resistance as possible source of system uncertainty is taken into account under different operating conditions. Sensors failure are detected and developed observer is used to estimate currents... 

Conventional back-to-back converters with input power factor correction are still the best solution for motor drive applications which are usually subjected to considerable load changes during their operation. Since converter components, especially input-side inductances are designed for nominal power rating, the rated input power factor and input current distortion aren't achievable in light loads. In this paper a control method is proposed to improve the input current distortion and input power factor in light loads. This is achieved by increasing the switching frequency according to the reduction in load. Since conduction and switching losses decrease in light loads, the overall losses by... 

Sub-harmonic stability issues due to the interaction between a load-commutated motor drive and a synchronous turbo-generator train in a Liquefied Natural Gas (LNG) station are studied in this paper. The sub-harmonic current injected by motor drives may excite the mechanical torsional modes of turbogenerator train. In this paper, the electro-mechanical interaction phenomenon is investigated and an active damper is proposed to absorb the sub-harmonic currents of motor drives and increase the damping of the electro-mechanical system. Simulations and experiments validate the instability problem and effectiveness of the proposed solution. © 2018 EPE Association  

A mechanical system inherently affected by the conditions, factors, and parameters of uncertainties. Without including the uncertainty effects in the design procedure, the designs may not be robust and reliable. Robust design optimization (RDO) method is a procedure to find the insensitive design with respect to the variations. On the other hand, reliability is measured by the probability of satisfying a specific design criterion. Therefore, a reliable design is a design that satisfies the specified criteria even with some uncertainties in variables and parameters. Reliability-based design optimization (RBDO) is an optimization procedure that incorporates reliability requirements to find the... 

In this paper a fast flux search controller based on the Neuro-fuzzy systems is proposed to achieve the best efficiency of a direct torque controlled induction motor at light load. In this method the reference flux value is determined through a minimization algorithm with stator current as objective function. This paper discusses and demonstrates the application of Neurofuzzy filtering to stator current estimation. Simulation and experimental results are presented to show the fast response of proposed controller. © 2009 IEEE  

Control of Synchronous Motors at low speed has been the topic of several studies for the last years. Due to the lower amplitude of Back-EMF voltage in lower speed, it is inappropriate to merely rely on induced voltages for position estimation. In this paper, a new double carrier PWM modulation is presented in which two carrier frequencies are utilized for two legs of the inverter. This proposed method rectify the need of powerful processors which decreases the cost of the electric drive system. Employing a non-linear control system and an automatic gain control, ensures the sensorless control of the motor for a wide range of speed. © 2019 IEEE  

In this paper, a new post-fault vector control of an induction motor, fed by a faulty Cascaded H-Bridge (CHB) inverter, is presented. Among fault tolerant control methods, waveform based methods are suitable for closed-loop control and provide higher output voltage. In order to control the speed of the motor, a rotor field oriented control (RFOC) is used. During the fault, the FOC is modified to decrease the fault impact on the motor as low as possible. The proposed method is validated by means of simulation results for different loads and faults. The results show an improvement in both the final operating point and the transient response of the motor  

In a motor-drive system, there are many factors which can be considered as a figure of merit in drive control algorithm. All of these factors should be evaluated simultaneously to achieve the reliable performance of drive. In this paper, an optimization problem is constructed on a direct torque controlled induction motor drive using a candidate from different parts of drive system: inverter loss from section of solid state converter, motor loss from section of electromechanical converter and torque ripple from mechanical section. Minimization of this cost function leads to the optimum values of drive control parameters. © 2008 IEEE  

This work considers the problem of designing a fault tolerant system for IPMS motor drive subject to current sensor fault. To achieve this goal, two control strategies are considered. The first is based on field oriented control and a developed adaptive backstepping observer which simultaneously are used in the case of fault-free. The second approach proposed is concerned with fault tolerant strategy based on observer for faulty conditions. Stator resistance as possible source of system uncertainty is taken into account under different operating conditions. Current sensors failures are detected and observer based on adaptive backstepping approach is used to estimate currents and stator... 

Vector control induction motor drives are particularly sensitive to the variation of motor parameters. As a consequence, the field orientation is missed, leading to substantial degradation of performance. The performance of traction motors can be even more degraded by the substantial core loss due to their high supply frequency. In this paper, a flux observer using combined voltage and current model is presented. The influence of the core loss resistance is considered in motor models. This control system is robust against simultaneous variations of the stator resistance, rotor resistances, as well as the mismatch of the equivalent stator core-loss resistance, yielding a globally stable...