A High-Power Medium-Voltage Open-Loop Induction Motor Drive for Industry Applications: Stability Analysis and Implementation

Due to their several advantages, induction motors are widely used for industrial applications today. The present study focuses on developing a robust high-power induction motor variable frequency drive. In order to test the algorithms of the motor control on an actual induction motor, it is important to first carry out simulation tests to verify and troubleshoot the control strategy. One of the most common software used for such a need is MATLAB/Simulink. To run such experiments requires a significant simulation time and at the same time must satisfy a certain level of accuracy. Therefore, one of the objectives of the thesis is to carry out a study on some of the ODE solvers of MATLAB/Simulink to choose the most efficient solver for the simulation tests of the motor control strategy. The fixed step solvers ode1, ode2 and ode4 and the variable step solvers ode45, ode113 and ode23 are studied in terms of the actual time taken to complete the simulations and the relative tolerance of each solver. Comparing the performance of the fixed step and variable step solvers it is evident that the variable step solvers outperformed the fixed step solvers in terms of both speed and accuracy. One of the most famous speed control strategies is the open loop V/Hz control. In this control method two modulation techniques were studied. This was the asynchronous modulation technique and the synchronous modulation technique. With the use of the asynchronous modulation technique subharmonics are introduced. To avoid the introduction of such harmful subharmonics the synchronous modulation technique is proposed. The synchronous modulation technique is implemented with the open loop V/Hz control strategy and simulation tests were carried out to verify the problem of subharmonics being removed. Another problem encountered with the open loop V/Hz control strategy is the presence of large current and torque oscillations of the motor at low to medium frequencies. This is due to the nonlinear interactions between the electrical and mechanical subsystems. To mitigate these unwanted oscillations a stability analysis of the open loop V/Hz control is carried out and a region of instability is determined. Two mitigation techniques are proposed in this thesis namely varying slope V/Hz control strategy and the active damping control strategy. The proposed techniques are verified and validated through simulation tests on a 7 MW medium voltage (MV) induction motor in MATLAB/Simulink and on a low voltage (LV) induction motor in laboratory without a mechanical load. Moreover, in this thesis it has been examined that with the consideration of the magnetic saturation of the motor, more stable operations are achieved. This is firstly verified in simulation where considering the magnetic saturation allowed the use of higher flux values providing more stable machine operations while at the same time allowing for a larger torque. With the experimental test on a 10-kW induction motor it was proved that the results obtained through simulations where more stable operations were seen as the value of the flux were increased were correct. In the power applications such as the ac-dc conversion for the above mentioned 7 MW medium voltage induction motor, a high total harmonic distortion (THD) can be seen in the primary currents with the use of the conventional diode-based ac-dc conversion. In addition, such a conversion does not permit the control of the dc link voltage and has not power factor correction. To overcome these shortcomings the Active Front End rectifier which uses IGBTs that can be electronically controlled is used. In the AFE, the waveform of the input current is monitored and is shaped to be sinusoidal as a result decreasing the THD. Another significant advantage of the AFE rectifier is its capability to handle regenerative power. In this thesis, two configurations of the AFE rectifier are studied. These two configurations include firstly the development of the AFE rectifier using a two-level three-phase inverter and secondly the development of the AFE rectifier with single phase H-bridge cells. From the comparison of the performance of the two configurations of the AFE it is seen that the AFE realised with the H Bridge cells and phase shifted secondary was the best in terms of the THD and the dc link voltage ripple. From these results the AFE realised with H Bridge circuits and phase shifted secondary is chosen for the operation of a real high-power induction motor controlled with the open loop V/Hz control strategy and equipped with the active damping technique for mitigating the current and torque oscillations

Rebar corrosion due to chlorides in synergy with sodium, potassium, and magnesium

The ability of steel reinforced concrete to withstand long service life is ensured by the strong binding between the concrete and the rebar. Although rebar corrosion deterioration in the presence of chlorides is well known, it is important to note that these anions are never present in isolation, i.e., other cations are also present within the exposed environment. Consequently, a study was conducted to investigate the rebar deterioration due to chlorides in the presence of different cations. A well-controlled laboratory experiment for assessing the corrosivity of sodium chloride, potassium chloride and magnesium chloride was conducted. The galvanostatic pulse technique was used to investigate the concrete-steel interfacial structure, which was modelled after a modified Randles circuit. Analysis revealed influences of the associated cations during the rebar corrosion process. A normalisation approach was used to compare chloride attacks on the rebar due to different salt solutions. Results suggest that chloride attacks in the presence of sodium cations are relatively corrosive

Wind gust estimation for precise quasi - hovering control of quadrotor aircraft

This paper focuses on the control of quadrotor vehicles without wind sensors that are required to accurately track low-speed trajectories in the presence of moderate yet unknown wind gusts. By modeling the wind disturbance as exogenous inputs, and assuming that compensation of its effects can be achieved through quasistatic vehicle motions, this paper proposes an innovative estimation and control scheme comprising a linear dynamic filter for the estimation of such unknown inputs and requiring only position and attitude information. The filter is built upon results from Unknown Input Observer theory and allows estimation of wind and vehicle state without measurement of the wind itself. A simple feedback control law can be used to compensate for the offset position error induced by the disturbance. The proposed filter is independent of the recovery control scheme used to nullify the tracking error, as long as the corresponding applied rotor speeds are available. The solution is first checked in simulation environment by using the Robot Operating System middleware and the Gazebo simulator and then experimentally validated with a quadcopter system flying with real wind sources

Maze solving robot with automated obstacle avoidance

A quick development of innovation moves us to plan the best choice for an accurate mission. Numerous independent automated innovations are intimated in the lives of individuals making their work much easier. It has been seen that automated vehicles are presented so far, with shrewd abilities after enormous measures of cash spent yearly on the examination. Here in this paper, autonomous maze solving robot is developed with independent mapping and localization skill. Firstly, the maze solving vehicle is designed with three infrared sensors of which two is used for wall detection to avoid collision and the third is for obstacle detection for picking and placing the objects to clear its pathway with the help of robotic arm. Also, it desires to use robot where an environment unreachable for human. In addition, there are also places where use of robots is the only way to achieve a goal. For this, appropriate placement of sensory devices is very critical. We have successfully implemented a maze solving ability onto the robot so called MazeBot. It has been tested that the robot can solve the maze successfully without any interruption with the walls and the objects. In this design, the accuracy of measurements and the real-time processing allied with minimum processing power are the key components in overall embedded design

Erle-copter Simulation using ROS and Gazebo

The recent decrease in the price as well as size of semi-conductor logic and due to significant advancements in technologies such as microcontrollers, motors and sensors, the application of quadcopters in several fields has been achieved. However, testing of quadcopter prototypes still has a risk of damage due to faults and unexpected behavior. Hence, a method of testing of quadcopters in simulation mimicking the actual conditions of the real environment in an actual hardware test has been proposed. For this purpose, Gazebo simulator integrated with ROS has been chosen for the simulation of the path of the quadcopter. Moreover, the software Matlab/Simulink has been interfaced with Gazebo in order for the simulation of the quadcopter to be achieved

Surface Permanent Magnet Synchronous Motors’ Passive Sensorless Control: A Review

Sensorless control of permanent magnet synchronous motors is nowadays used in many industrial, home and traction applications, as it allows the presence of a position sensor to be avoided with benefits for the cost and reliability of the drive. An estimation of the rotor position is required to perform the field-oriented control (FOC), which is the most common control scheme used for this type of motor. Many algorithms have been developed for this purpose, which use different techniques to derive the rotor angle from the stator voltages and currents. Among them, the so-called passive methods have gained increasing interest as they do not introduce additional losses and current distortion associated instead with algorithms based on the injection of high-frequency signals. The aim of this paper is to present a review of the main passive sensorless methods proposed in the technical literature over the last few years, analyzing their main features and principles of operation. An experimental comparison among the most promising passive sensorless algorithms is then reported, focusing on their performance in the low-speed operating region

Novel ICT Applications for Pacific Agri-Food and Nutritious Systems: Best Practices, Gaps and Opportunities in Fiji

A study was conducted by a team led by Dr Bibhya Sharma of The University of the South Pacific on ICT tools used by the agricultural sector in Fiji. The seminal aim of the assignment, commissioned under the CTA-led project on Promoting Nutritious Food Systems in the Pacific Islands, is not only to create awareness in the Pacific but also to help farmers and consumers leverage on current and new ICT tools, such as mobile apps, 3D printers and blockchain technology for best results. At the initial stage, a Fiji wide survey was carried out in various institutions including research institutions, academic organisations, private institutions, mobile service providers, development agencies and the government ministries. Agriculture still remains one of the major contributors of Fiji’s Gross Domestic Product (GDP) and heralds a stronghold of its economy. Moreover, agriculture in Fiji continues to grow rapidly with a lot of investments from the Fijian Government and help from outside donors. However, there have been issues such as late harvests, irregular weather pattern, failing yields, reduction in agricultural land areas, poor and late deliveries, and by-product wastage seen as reasons causing a decline in the agricultural sector. These reasons are not new to Fiji, rather they have been in existence for a long period of time now. The decline of the sector which is still contributing so much to the country’s GDP makes a serious case for changes and innovations

Improving Overall Equipment Effectiveness by Enabling Autonomous Maintenance Pillar for Integrated Work Systems

Integrated Work System (IWS) and Overall Equipment Effectiveness (OEE) are two popular approaches used by production firms to identify and eliminate production losses. In a highly competitive business environment, companies must increase their efficiency in the manufacturing process to support resilient business continuity. While OEE is widely used as a quantitative tool for measuring the performance of total productive maintenance (TPM), the IWS approach integrates equipment, processes, and involvement of people into a unified approach to reduce costs, improve quality, and increase productivity. Principally, there is an alignment between the two concepts. The IWS has the potential to maximize OEE to eliminate equipment failure and defects, minimize downtime, and maximize productivity with less time, effort, and waste. The purpose of this work is to compare the performance of the OEE with the implementation of the IWS pillar, i.e., autonomous maintenance (AM). The rollout of the AM pillar was carried out on the two identical packaging machines (HLP1) with a speed of 120 packets per minute. The data which is shown in this paper is for both machines during the operational hours. Finally, the analysis showed positive results for both machines within a five-month period, with an increase of 27% and 15% in OEE, respectively. Later in the discussion, the root cause and SWOT analysis were perused for OEE and TPM, respectively, in this paper

Optimized Tongue Driven System Using Artificial Intelligence

This paper presents a cost effective design of a wearable wireless tongue drive system (TDS) for disabled individuals, particularly with spinal cord injuries (SCIs). We propose a basic TDS whose language is specifically designed for issuing movement based commands, be it a gadget or a self-governing transport chair. While the overall industrial penetration of TDS is low, we offer a cheap and straightforward design for a TDS that consists of items which amount to as low as US$30. A data-driven based approach has been used to classify the tongue-gestures with a response time of less than 0.25 seconds. Compared with other machine learning algorithms, the proposed TDS is equipped with shallow neural networks that govern all the decisions when it comes to classifying the tongue gesture. This has been achieved after a thorough data analysis and rigorous comparison with other classification techniques along with hardware deployment. With its open architecture, the newly designed TDS can be an ideal tool to control other movement based peripherals. The final test accuracy amounts to 93.4% when the TDS is tested on human subjects

Rebar corrosion due to chlorides in the presence of different cations

Recent attention on effects of climate change in the Pacific island countries (PIC’s) have focused on a multitude of areas which are at risk in the Pacific region. These include food security, flora and fauna, land accessibility, groundwater contamination and so on. These aspects are essential for sustainable development of the small island states in the Pacific region. One issue, which appears synonymous with climate change in the Pacific is sea-level rise. The rising sea level can have detrimental effects on civil infrastructure since its intrusion further inland can lead to deterioration of nearby civil metallic infrastructure due to corrosion. Since metropolisation of major PIC’s are mainly near the sea or along coast line, this presents a significant problem within the overall paradigm of sustainable development. In this regards, a study was undertaken to investigate the influences of different chloride salts (i.e. NaCl, KCl, MgCl2) on the corrosion of steel re-inforcing bars (rebar’s) in concrete mortars. This study is important to understand structural health conditions, especially for foundations in ground, and to understand the corrosion intensities in the presence of different cations, which can be significantly controlled by groundwater migration. The galvanostatic pulse technique was used to evaluate the effect of varying chloride contents of different salts on rebar corrosion. Results from this study are presented in an attempt to provide a conceptual model for understanding the interaction of aforementioned salts with metallic infrastructure. A holistic discussion is presented which are important for sustainable development in the PIC’s