40 research outputs found
Indirect Rotor Field Oriented Control of Induction Motor With Rotor Time Constant Estimation
Full text linkThis thesis presents an estimation technique of the inverse rotor time constant for
Indirect Rotor Field Oriented Control (IRFOC) induction motor application. In this
estimation technique two different equations are used to estimate the rotor flux in the
stator reference frame. One of the equations is a function of the rotor time constant,
rotor angular velocity and the stator currents, and the other equation is a function of
measured stator currents and voltages. The equation that uses the voltage and the
current signals of the stator serves as reference model, while the other equation
works as an adjustable model with respect to the variation of the rotor time constant.
Measurements of two phases of the current, and speed using an optical encoder are
required in this estimation technique. The stator phase voltages are estimated from
the DC bus voltage and the switching commands signals with compensation of the
dead time effect.
Field oriented control of induction motor is gaining wides acceptance in high
performance AC motor drive applications. Field oriented control, in its both forms as a direct or indirect, gives the AC motor dynamics that are equivalent to that of a
DC motor. However, direct and indirect field oriented control suffer from specific
theoretical and practical problems. The approach of direct field oriented control with
Hall sensors for flux sensing has limitations governed by the physical structure of the
machine itself. On the other hand, the approach of indirect field oriented control of
induction machines is highly dependent on the rotor parameters, which are not easily
accessible for measurements except for the rotor speed.
In a DC motor, spatial relationship of the torque and flux is maintained by the
physical construction of the motor armature and field circuits. However, in an
induction motor such spatial relationship does not maintain as such machine has
usually a single terminal where electric power is supplied. Therefore, such
relationship is maintained by external control methods. In a basic IRFOC of an
induction motor, speed and phase currents are sensed in order to control the stator
current vector such a way so it can be resolved into two components, one is to
control the rotor flux and the other to control the motor torque. Successful
decomposition of stator current vector into these two components requires the
knowledge of the instantaneous position, of the rotor flux vector. Since the position of
the rotor flux vector is estimated in an IRFOC scheme, and is dependent on the
motor model (more specifically the rotor parameters), these parameters must be
obtained accurately and match the motor parameters at all times. Unfortunately, rotor
parameters vary and are not easily accessible for measurements. Therefore, this
uncertainty about the rotor flux vector position degrades the dynamic operation of
the drive.Enormous efforts have been made to improve IRFOC
complicated hardware and software in order to coixpensate for such imperfection.
Hence, this work focuses on the Indirect Rotor Field Oriented Control of induction
motors with estimation of the rotor time constant. A simple yet effective rotor time
constant identification method is presented and used for updating the slip calculator
used by the IRFOC algorithms.
A complete simulation model of an induction motor and IRFOC scheme is presented
and tested using SIMULINWMATLAB, and experimentally implemented on a DSP
Board (MCK243j without any need for voltage phase sensors. Simulation and
experimental results were presented and compared to verify the validity of the
proposed estimator for different operating conditions
Design and Construction of a DC-to-DC Converter for Electric Vehicle Application
Full text linkA DC-to-DC converter has been designed to control the speed of a DC
motor for electric vehicle application. The power circuit of the converter
consists of transistorised power switches (IGBTs) to step-down the voltage to
the level required by the speed and load demand. The series shunt resistor
method is used to control the current and keep it below the maximum rate of the
power transistors and the motor especially at the starting point. The transistor
gate drive circuit was designed to provide the maximum isolation between the
power and the control circuits.
A controller chip originally used to control a three phase brushless DC
motor is programmed and modified to control a brushed DC motor. This controller chip provides the pulse width modulation (PWM) control signal in
order to drive the power switches at fixed frequency and variable duty cycle.
More over using this chip a control over the current flow through the power
circuit could be achieved, this will protect the circuit from any faulty conditions
taking the benefit of Cycle-by-Cycle current detection
Fitness function X-means for prolonging wireless sensor networks lifetime
Get PDFX-means and k-means are clustering algorithms proposed as a solution for prolonging wireless sensor networks (WSN) lifetime. In general, X-means overcomes k-means limitations such as predetermined number of clusters. The main concept of X-means is to create a network with basic clusters called parents and then generate (j) number of children clusters by parents splitting. X-means did not provide any criteria for splitting parent’s clusters, nor does it provide a method to determine the acceptable number of children. This article proposes fitness function X-means (FFX-means) as an enhancement of X-means; FFX-means has a new method that determines if the parent clusters are worth splitting or not based on predefined network criteria, and later on it determines the number of children. Furthermore, FFX-means proposes a new cluster-heads selection method, where the cluster-head is selected based on the remaining energy of the node and the intra-cluster distance. The simulation results show that FFX-means extend network lifetime by 11.5% over X-means and 75.34% over k-means. Furthermore, the results show that FFX-means balance the node’s energy consumption, and nearly all nodes depleted their energy within an acceptable range of simulation rounds.
Correction to: Metabolic reprogramming of T regulatory cells in the hypoxic tumor microenvironment (Cancer Immunology, Immunotherapy, (2021), 70, 8, (2103-2121), 10.1007/s00262-020-02842-y)
No full textin the hypoxic tumor microenvironment, written by Varun Sasidharan Nair, Reem Saleh, Salman M. Toor, Farhan S. Cyprian and Eyad Elkord, was originally published electronically on the publisher’s internet portal on 03 February 2021 without open access. With the author(s)’ decision to opt for Open Choice the copyright of the article changed on 25 May 2021 to © The Author(s) 2021 and this article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. The original article has been corrected
Improvements on the High Frequency Signal Injection Method for Permanent Magnet Synchronous Motors and its Application in the Hybrid Drive Position Control
No full textThis paper presents a hybrid rotor position estimation for permanent magnet synchronous motor (PMSM) over wide speed range. At zero and low speeds, a rotor position error compensation scheme is proposed to improve the performance of high frequency signal injection method. This includes the incorporation of system modeling and Kalman filtering to improve the estimation performance during transient. At medium and high speeds, a novel yet simple approach called direct scaling is presented to estimate the rotor position. The two methods are combined in a hybrid scheme and implemented for position control of PMSM drive. Simulation results demonstrate the improvements in the high frequency signal injection method during steady state and transient conditions. The performance of the hybrid sensorless motor drive for wide speed range is also tested via simulations. The obtained results show the effectiveness of the proposed methods over the entire speed rang
Robust sliding mode controller for buck DC converter in off-grid applications
Full text linkThis paper presents a robust sliding mode controller of DC-DC buck converter for renewable energy applications, such as photovoltaic systems in off-grid configurations. Photovoltaic systems in off-grid configuration are exposed to significant variations in input voltage and power loads. The proposed sliding mode controller presents a simple and efficient method of continuously updating the duty cycle of a pulse width modulation unit (PWM) of a buck converter. The PWM unit is operated at constant switching frequency of 10 kHz carrier signal and varying duty cycle. The differences in input voltage and power load are treated as two bounded uncertainties, thus eliminating the need for input voltage sensor and output current sensors leaving the system with a single sensor required to measure the converter output voltage. That is, measured output voltage is compared with the reference voltage to continuously update the average duty cycle value of PWM unit. Adjustment of PWM duty cycle is performed while maintaining the sliding condition always fulfilled. The simulation results of the proposed controller showed robustness and accuracy against power load fluctuation, changes in desired output voltage, and variations in the input supply voltage that may result from the varying level of irradiance and temperature.</p
Ageing effect on the relaxation properties of bitumen
No full textThe ageing of bitumen has a significant impact on the mechanical behavior of asphalt concrete. In this study, Dynamic Shear Rheometer (DSR) tests were utilized to investigate the effect of ageing on the relaxation properties of bituminous materials. PEN 70/100 bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the bitumen films. Three evaluation indices, explicitly the shear stress at 0 s and 100 s, the ratio of shear stress at 0 s and 100 s and the time that shear stress reduces to 50% and 25% of the initial value, were used to determine the evolution of the relaxation properties of bitumen. The results show that, in comparison to fresh bitumen, aged samples show higher residual shear stresses after relaxation and are more susceptible to stress accumulation thus cracking. In addition, temperature, followed by pressure and ageing time, was found to have the stronger impact on bitumen ageing.Pavement Engineerin
Framework for replacing steel with aluminum fibers in bituminous mixes
No full textThis research explores the incentives for replacing steel fibers with aluminum fibers in fiber modified bituminous mixes. In this work the focus is on fiber modified bituminous mixes especially designed for induction heating. Inductive fibers are heated up because eddy currents are generated - according to Joule’s law - when alternating magnetic field is applied by electro-magnetic induction coil. Aluminum fiber-type particles are proposed as an alternative solution for developing corrosion resistant and lightweight bituminous mixes capable to be induced by electro-magnetic fields. In another publication (Pavlatos et al., Inductive bituminous mortar with steel and aluminum fibers, Advances in Materials and Pavement Performance Prediction, Submitted, 2018), a finite element three-dimensional model is developed in order to determine the effective electrical conductivity of steel and aluminum fiber modified bituminous mortar, as well as to show the potential utilization of alternative particles for developing multi-functional paving materials with improved properties.Pavement Engineerin
Modified phase locked loop for grid connected single phase inverter
Get PDFConnecting a single-phase or three-phase inverter to the grid in distributed generation applications requires synchronization with the grid. Synchronization of an inverter-connected distributed generation units in its basic form necessitates accurate information about the frequency and phase angle of the utility grid. Phase Locked Loop (PLL) circuit is usually used for the purpose of synchronization. However, deviation in the grid frequency from nominal value will cause errors in the PLL estimated outputs, and that’s a major drawback. Moreover, if the grid is heavily distorted with low order harmonics the estimation of the grid phase angle deteriorates resulting in higher oscillations (errors) appearing in the synchronization voltage signals. This paper proposes a modified time delay PLL (MTDPLL) technique that continuously updates a variable time delay unit to keep track of the variation in the grid frequency. The MTDPLL is implemented along a Multi-Harmonic Decoupling Cell (MHDC) to overcome the effects of distortion caused by gird lower order harmonics. The performance of the proposed MTDPLL is verified by simulation and compared in terms of performance and accuracy with recent PLL techniques
Fuzzy Logic Control for Low-Voltage Ride-Through Single-Phase Grid-Connected PV Inverter
Full text linkThis paper presents a control scheme for a photovoltaic (PV) system that uses a single-phase grid-connected inverter with low-voltage ride-through (LVRT) capability. In this scheme, two PI regulators are used to adjust the power angle and voltage modulation index of the inverter; therefore, controlling the inverter’s active and reactive output power, respectively. A fuzzy logic controller (FLC) is also implemented to manage the inverter’s operation during the LVRT operation. The FLC adjusts (or de-rates) the inverter’s reference active and reactive power commands based on the grid voltage sag and the power available from the PV system. Therefore, the inverter operation has been divided into two modes: (i) Maximum power point tracking (MPPT) during the normal operating conditions of the grid, and (ii) LVRT support when the grid is operating under faulty conditions. In the LVRT mode, the de-rating of the inverter active output power allows for injection of some reactive power, hence providing voltage support to the grid and enhancing the utilization factor of the inverter’s capacity. The proposed system was modelled and simulated using MATLAB Simulink. The simulation results showed good system performance in response to changes in reference power command, and in adjusting the amount of active and reactive power injected into the grid
