Reduced Torque Ripple And Switching Frequency Using Optimal DTC Switching Strategy For Open-End Winding Induction Machines

Direct Torque Control (DTC) of induction machine has received wide acceptance in many Variable Speed Drive (VSD) applications due to its simple control structure and excellent torque dynamic control performances. However, the DTC which employs a two-level inverter and hysteresis controllers produces two major drawbacks, namely, larger torque ripple and variable switching frequency, which might produce a very high switching frequency (or power loss), particularly at a very low speed operation. The root causes of the problems can be identified as follows; 1) delay actions in controlling the torque (which is commonly resulted in digital implementation of hysteresis controller) causes the torque cannot be exactly restricted within the hysteresis band, and hence produces a larger torque ripple 2) inappropriate selection of voltage vector (among a limited number of voltage vectors available in a two-level inverter) cannot restrict the increase of switching frequency in the hysteresis controller, as the torque slopes regulated in hysteresis bandwidth vary during operating conditions. This thesis proposes an optimal DTC switching strategy to reduce torque ripple and switching frequency for open-end winding induction machines. The open-end winding induction machine is supplied by a dual-inverter which can offer a greater number of voltage vectors and hence, gives more options to select the most optimal voltage vectors to minimize the problems. The most optimal voltage vectors for every speed range are identified as the vectors that can produce the minimum torque slopes. By minimizing the torque slopes, the torque ripple and switching frequency can be reduced. The identification is made by investigating the torque slope behaviours and torque control capabilities for every speed range. The selection of the most optimal voltage vectors is accomplished by using a modification of torque error status and a look-up table. To obtain a constant switching frequency, a Constant Switching Frequency Torque Controller (CSFTC) is proposed without the use of a PI controller and a knowledge of machine parameters. Some improvements obtained in the proposed strategy were verified via simulations and experimentations, as well as comparison with the conventional DTC. The improvements obtained are as follows; 1) reduction of torque ripple and switching frequency with the proposed optimal DTC switching strategy, 2) a constant switching frequency with the proposed CSFTC. The main benefit of the proposed strategy is its simplicity, where the DTC improvements can be obtained without the common approach, i.e. the use of Space Vector Modulation (SVM) which involves complex control algorithms. It also shown that the average improvement about 39% and 43% can be achieved toward reduction of torque ripple and switching frequency

Heading drift mitigation for low-cost inertial pedestrian navigation

The concept of autonomous pedestrian navigation is often adopted for indoor pedestrian navigation. For outdoors, a Global Positioning System (GPS) is often used for navigation by utilizing GPS signals for position computation but indoors, its signals are often unavailable. Therefore, autonomous pedestrian navigation for indoors can be realized with the use of independent sensors, such as low-cost inertial sensors, and these sensors are often known as Inertial Measurement Unit (IMU) where they do not rely on the reception of external information such as GPS signals. Using these sensors, a relative positioning concept from initialized position and attitude is used for navigation. The sensors sense the change in velocity and after integration, it is added to the previous position to obtain the current position. Such low-cost systems, however, are prone to errors that can result in a large position drift. This problem can be minimized by mounting the sensors on the pedestrian’s foot. During walking, the foot is briefly stationary while it is on the ground, sometimes called the zero-velocity period. If a non-zero velocity is then measured by the inertial sensors during this period, it is considered as an error and thus can be corrected. These repeated corrections to the inertial sensor’s velocity measurements can, therefore, be used to control the error growth and minimize the position drift. Nonetheless, it is still inadequate, mainly due to the remaining errors on the inertial sensor’s heading when the velocity corrections are used alone. Apart from the initialization issue, therefore, the heading drift problem still remains in such low-cost systems. In this research, two novel methods are developed and investigated to mitigate the heading drift problem when used with the velocity updates. The first method is termed Cardinal Heading Aided Inertial Navigation (CHAIN), where an algorithm is developed to use building ‘heading’ to aid the heading measurement in the Kalman Filter. The second method is termed the Rotated IMU (RIMU), where the foot-mounted inertial sensor is rotated about a single axis to increase the observability of the sensor’s heading. For the CHAIN, the method proposed has been investigated with real field trials using the low-cost Microstrain 3DM-GX3-25 inertial sensor. It shows a clear improvement in mitigating the heading drift error. It offers significant improvement in navigation accuracy for a long period, allowing autonomous pedestrian navigation for as long as 40 minutes with below 5 meters position error between start and end position. It does not require any extra heading sensors, such as a magnetometer or visual sensors such as a camera nor an extensive position or map database, and thus offers a cost-effective solution. Furthermore, its simplicity makes it feasible for it to be implemented in real-time, as very little computing capability is needed. For the RIMU, the method was tested with Nottingham Geospatial Institute (NGI) inertial data simulation software. Field trials were also undertaken using the same low-cost inertial sensor, mounted on a rotated platform prototype. This method improves the observability of the inertial sensor’s errors, resulting also in a decrease in the heading drift error at the expense of requiring extra components

Heading drift mitigation for low-cost inertial pedestrian navigation

The concept of autonomous pedestrian navigation is often adopted for indoor pedestrian navigation. For outdoors, a Global Positioning System (GPS) is often used for navigation by utilizing GPS signals for position computation but indoors, its signals are often unavailable. Therefore, autonomous pedestrian navigation for indoors can be realized with the use of independent sensors, such as low-cost inertial sensors, and these sensors are often known as Inertial Measurement Unit (IMU) where they do not rely on the reception of external information such as GPS signals. Using these sensors, a relative positioning concept from initialized position and attitude is used for navigation. The sensors sense the change in velocity and after integration, it is added to the previous position to obtain the current position. Such low-cost systems, however, are prone to errors that can result in a large position drift. This problem can be minimized by mounting the sensors on the pedestrian’s foot. During walking, the foot is briefly stationary while it is on the ground, sometimes called the zero-velocity period. If a non-zero velocity is then measured by the inertial sensors during this period, it is considered as an error and thus can be corrected. These repeated corrections to the inertial sensor’s velocity measurements can, therefore, be used to control the error growth and minimize the position drift. Nonetheless, it is still inadequate, mainly due to the remaining errors on the inertial sensor’s heading when the velocity corrections are used alone. Apart from the initialization issue, therefore, the heading drift problem still remains in such low-cost systems. In this research, two novel methods are developed and investigated to mitigate the heading drift problem when used with the velocity updates. The first method is termed Cardinal Heading Aided Inertial Navigation (CHAIN), where an algorithm is developed to use building ‘heading’ to aid the heading measurement in the Kalman Filter. The second method is termed the Rotated IMU (RIMU), where the foot-mounted inertial sensor is rotated about a single axis to increase the observability of the sensor’s heading. For the CHAIN, the method proposed has been investigated with real field trials using the low-cost Microstrain 3DM-GX3-25 inertial sensor. It shows a clear improvement in mitigating the heading drift error. It offers significant improvement in navigation accuracy for a long period, allowing autonomous pedestrian navigation for as long as 40 minutes with below 5 meters position error between start and end position. It does not require any extra heading sensors, such as a magnetometer or visual sensors such as a camera nor an extensive position or map database, and thus offers a cost-effective solution. Furthermore, its simplicity makes it feasible for it to be implemented in real-time, as very little computing capability is needed. For the RIMU, the method was tested with Nottingham Geospatial Institute (NGI) inertial data simulation software. Field trials were also undertaken using the same low-cost inertial sensor, mounted on a rotated platform prototype. This method improves the observability of the inertial sensor’s errors, resulting also in a decrease in the heading drift error at the expense of requiring extra components

Three-Phase Virtual Instrument Measurement System

Electrical engineering laboratory often involves measurement of current and voltage signals. Conventionally, it is accomplished by using various types of hardwired measurement equipments. If further signals information is required the oscilloscope becomes the preference. However, for measurement of voltage that is connected to the mains, prior knowledge to isolation is a must. Conventional oscilloscopes neither have the isolation function nor the data logging capabilities for further analysis. This paper presents the hardware and software development of a custom-built three-phase measurement system, equipped with isolation and data logging features. It also includes a description of the application of virtual instrumentation, written in LabVIEW that uses the developed hardware. A case study will also be presented

Silicon carbide schottky diodes forward and reverse current properties upon fast electron radiation

This paper investigates on the reaction of 10 and 15MGy, 3MeV electron irradiation upon off-the-shelves (commercial) Silicon Carbide Schottky diodes from Infineon Technologies (model: IDH08SG60C) and STMicroelectronics (model: STPSC806). Such irradiation reduces the forward-bias current. The reduction is mainly due to the significant increase of the series resistance (i.e. Infineon: 1.45Ω at before irradiation → 121×103 Ω at 15MGy); STMicroelectronics: 1.44Ω at before irradiation → 2.1×109 Ω at 15MGy). This increase in series resistance gives 4.6 and 8.2 orders of magnitude reduction for the forward-bias current density of Infineon and STMicroelectronics respectively. It is also observed that the ideality factor and the saturation current of the diodes increases with increasing dose (i.e. ideality factor- Infineon: 1.01 at before irradiation → 1.05 at 15MGy; STMicroelectronics: 1.02 at before irradiation → 1.3 at 15MGy | saturation current- Infineon: 1.6×10-17A at before irradiation → 2.5×10-17A at 15MGy; STMicroelectronics: 2.4×10-15A at before irradiation → 8×10-15A at 15MGy). Reverse-bias leakage current density in model by Infineon increases by one order of magnitude after 15MGy irradiation, however, in model by STMicroelectronics decreases by one order of magnitude. Overall, for these particular samples studied, Infineon devices have shown to be better in quality and more radiation resistance toward electron irradiation in forward-bias operation while STMicroelectronics exhibit better characteristics in reverse-bias operation

Reliability study of silicon carbide Schottky Diode with fast electron irradiation

The impact of fast electron exposure upon the performance of commercial silicon carbide Schottky diodes has been studied. Under 3 MeV electrons, absorbed dose of 10 and 15 MGy at room temperature, the forward current density-voltage characteristic of INFINEON and STMICROELECTRONICS devices have been decreased by 4.6 and 8.2 orders of magnitude respectively. The reduction is associated with the significant rise in the series resistance (INFINEON: 1.45 Ω to 121×103 Ω; STMICROELECTRONICS: 1.44 Ω to 2.1 × 109 Ω) due to the irradiation-induced defects. Besides that, the reverse leakage current density in INFINEON increased by one order of magnitude while reverse leakage current density in STMICROELECTRONICS decreased by about one order of magnitude. We have also observed an increase in ideality factor (INFINEON: 1.01 to 1.05; STMICROELECTRONICS: 1.02 to 1.3) and saturation current (INFINEON: 1.6×10-17 A to 2.5×10-17 A; STMICROELECTRONICS: 2.4×10-15 A to 8 × 10-15 A) as a result of electron irradiation. Overall, for particular devices studied, INFINEON have better quality devices and more radiation resistance compared to STMICROELECTRONICS

Direct Torque Control of BLDC Motor with Constant Switching Frequency

Direct torque control (DTC) has become a popular technique for brushless motor control because it provides fast dynamic torque response. Hysteresis band control is the most popular techniques used in the DTC BLDC motor drive caused the simplest technique. However the conventional DTC have problems as switching frequency that varies with operating conditions and high torque ripple. This paper presents direct torque control (DTC) of BLDC motor with constant switching frequency torque controller. The torque ripple will get reduced by this method constant switching frequency operation. The feasibility of this method in minimizing the torque ripple is verified through some simulation results

Mind-mapping strategy in process writing approach: Idea extension evidence for introductory paragraph

Extending ideas in essay writing is challenging for many ESL students, let alone the low ones. The students need help writing ideas, even in the introductory paragraph. Mind mapping strategy could help students develop ideas by forming wh-questions using identified keywords. Hence, this research is conducted to determine the evidence of a mind-mapping strategy in extending ideas for writing introductory paragraphs in the Malaysian University English Test (MUET) Writing Task 2 (Extended Essay). Also, it intends to explore the students’ steps in the mind-mapping strategy to extend ideas in the introductory paragraph writing process. The research design is a sequential explanatory mixed-method approach where data were gathered through a needs assessment survey, diagnostic tests, and semi-structured interviews. Process writing activities were designed as a treatment after the survey, and pre-test scores supported the necessity to employ the mind-mapping strategy to the experimental group. Conversely, a control group was formed to contrast the strategy with free writing activities. Test scores of the two groups after eight weeks of the treatment were compared using Klimova’s (2014) writing components. The diagnostic pre and post-test scores on ideas extension showed evidence of the strategy. The qualitative findings also augmented the strategy’s usefulness in five aspects: 1) as an idea generation strategy; 2) using keywords and wh-questions; 3) clear step-by-step processes; 4) improved idea development; and 5) the importance of a good beginning. Further study could expand the strategy’s advantages in idea extension and content paragraph organisation for the MUET writing tasks and other essay writing processes

Teachers’ techniques in developing of akhlaq and values in the students

Akhlaq and moral values among students who want to be born by the national education system can be achieved through the implementation of the inculcation of noble values in the teachings. Therefore, this article presents the findings related to the the students’ perception of the techniques of the inculcation of noble values during classroom instructions.This descriptive survey study approach was conducted in one of the schools in the district of Kuala Muda/Yan in Kedah.A total number of Forms 4 and 2 students were selected as the respondents to complete the questionnaire.The study findings found that based on students’ perception, there were five techniques that gained overall moderately high mean value, namely modelling, lecture, discussion, positive reinforcement and negative reinforcement. Meanwhile, other techniques were at medium low level. In summary, this study has shown that certain application techniques in instilling values should be practiced by teachers towards to increase students’ moral understanding and development towards realizing the National Education Philosophy and the Malaysian Education Blueprint 2013-2025 in the context of producing human capital that are stable and harmon