Current measurement in power electronic and motor drive applications - a comprehensive study

Current measurement has many applications in power electronics and motor drives. Current measurement is used for control, protection, monitoring, and power management purposes. Parameters such as low cost, accuracy, high current measurement, isolation needs, broad frequency bandwidth, linearity and stability with temperature variations, high immunity to dv/dt, low realization effort, fast response time, and compatibility with integration process are required to ensure high performance of current sensors. Various current sensing techniques based on different physical effects such as Faraday\u27s induction law, Ohm\u27s law, Lorentz force law, magneto-resistance effect, and magnetic saturation are studied in this thesis. Review and examination of these current measurement methods are presented. The most common current sensing method is to insert a sensing resistor in the path of an unknown current. This method incurs significant power loss in a sense resistor at high output currents. Alternatives for accurate and lossless current measurement are presented in this thesis. Various current sensing techniques with self-tuning and self-calibration for accurate and continuous current measurement are also discussed. Isolation and large bandwidth from dc to several kilo-hertz or mega-hertz are the most difficult, but also most crucial characteristics of current measurement. Electromagnetic-based current sensing techniques, which are used to achieve these characteristics, are analyzed. Many applications require average current information for control purposes. Different average current sensing methods of measuring average current are also reviewed. --Abstract, page iii

Advances in Sensors and Sensing for Technical Condition Assessment and NDT

The adequate assessment of key apparatus conditions is a hot topic in all branches of industry. Various online and offline diagnostic methods are widely applied to provide early detections of any abnormality in exploitation. Furthermore, different sensors may also be applied to capture selected physical quantities that may be used to indicate the type of potential fault. The essential steps of the signal analysis regarding the technical condition assessment process may be listed as: signal measurement (using relevant sensors), processing, modelling, and classification. In the Special Issue entitled “Advances in Sensors and Sensing for Technical Condition Assessment and NDT”, we present the latest research in various areas of technology

Micro-manufactured Rogowski coils for fault detection of aircraft electrical wiring and interconnection systems (EWIS)

Aircraft wiring failures have increased over the last few years resulting in arc faults and high-energy flashover on the wiring bundle, which can propagate down through aircraft Electrical Wiring and Interconnect Systems (EWIS). It is considered cost prohibitive to completely rewire a plane in terms of man hours and operational time lost to do this, and most faults are only detectable whilst the aircraft is in flight. Temperature, humidity and vibration all accelerate ageing and failure effects on EWIS. This research investigates methods of in-situ non-invasive testing of aircraft wiring during fight. Failure Mode Effects and Analysis (FMEA) was performed on legacy aircraft EWIS using data obtained from RAF Brize Norton. Micro-Electro-mechanical- Systems (MEMS) were evaluated for use in a wire monitoring system that measures the environmental parameters responsible for ageing and failure of EWIS. Such MEMS can be developed into a Health and Usage Monitoring MicroSystem (HUMMS) by incorporating advanced signal processing and prognostic software. Current and humidity sensors were chosen for further investigation in this thesis. These sensors can be positioned inside and outside cable connectors of EWIS so that arc faults can be reliably detected and located. This thesis presents the design, manufacture and test of micro-manufactured Rogowski sensors. The manufactured sensors were benchmarked against commercial high frequency current transformers (HFCT), as these devices can also detect high frequency current signature due to wire insulation failure. Results indicate that these sensors possess superior voltage output compared to the HFCT. The design, manufacture and test of a polymer capacitive humidity sensor is also presented. Two different types of polymer were reviewed as part of the evaluation. A feature of the sensor design is recovery from exposure to chemicals found on wiring bundles. Current and humidity sensors were demonstrated to be suitable for integrating onto a common substrate with accelerometers, temperature sensors and pressure sensors for health monitoring and prognostics of aircraft EWIS.Engineering and Physical Sciences Research Council (EPSRC

Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Micro-manufactured Rogowski coils for fault detection of aircraft electrical wiring and interconnect systems (EWIS)

Aircraft wiring failures have increased over the last few years resulting in arc faults and high-energy flashover on the wiring bundle, which can propagate down through aircraft Electrical Wiring and Interconnect Systems (EWIS). It is considered cost prohibitive to completely rewire a plane in terms of man hours and operational time lost to do this, and most faults are only detectable whilst the aircraft is in flight. Temperature, humidity and vibration all accelerate ageing and failure effects on EWIS. This research investigates methods of in-situ non-invasive testing of aircraft wiring during fight. Failure Mode Effects and Analysis (FMEA) was performed on legacy aircraft EWIS using data obtained from RAF Brize Norton. Micro-Electro-mechanical- Systems (MEMS) were evaluated for use in a wire monitoring system that measures the environmental parameters responsible for ageing and failure of EWIS. Such MEMS can be developed into a Health and Usage Monitoring MicroSystem (HUMMS) by incorporating advanced signal processing and prognostic software. Current and humidity sensors were chosen for further investigation in this thesis. These sensors can be positioned inside and outside cable connectors of EWIS so that arc faults can be reliably detected and located. This thesis presents the design, manufacture and test of micro-manufactured Rogowski sensors. The manufactured sensors were benchmarked against commercial high frequency current transformers (HFCT), as these devices can also detect high frequency current signature due to wire insulation failure. Results indicate that these sensors possess superior voltage output compared to the HFCT. The design, manufacture and test of a polymer capacitive humidity sensor is also presented. Two different types of polymer were reviewed as part of the evaluation. A feature of the sensor design is recovery from exposure to chemicals found on wiring bundles. Current and humidity sensors were demonstrated to be suitable for integrating onto a common substrate with accelerometers, temperature sensors and pressure sensors for health monitoring and prognostics of aircraft EWIS

Design and operation of a harmonic gyrotron based on a cusp electron gun

Strathclyde theses - ask staff. Thesis no. : T13121This thesis presents the results of successful operation of a 2nd harmonic gyrotron based on a cusp electron gun. The numerical and experimental results agreed well with the gyrotron design parameters. Two gyrotrons based on a cusp electron gun were designed: the first gyrotron operated at the 2nd harmonic and the second gyrotron was studied to look at the scaling of this concept for operation at the 7th harmonic at a frequency of 390 GHz. The cusp electron gun was used to produce the electron beam in the gyrotron which was annular in shape. The electron beam had a voltage of 40 kV, a current of 1.5A and a velocity ratio (perpendicular component to horizontal component) of 1.5. The experimental results from the first cusp electron gun and measurements of the high quality electron beam with ~8% velocity spread and ~10% alpha spread are presented. Analytical, numerical and experimental results of a DC harmonic gyrotron are presented. The 3D PIC code MAGIC was used to simulate the interaction of the harmonic gyrotron such as the TE71 mode at the 7th cyclotron harmonic with the large orbit electron beam with the beam thickness and beam spread introduced into the simulation. The interaction cavity of both gyrotrons was in the form of a smooth cylindrical waveguide. The relationship between the cavity dimensions and cavity Q values has been studied for optimized output at the design mode with the aim of suppressing other competing modes. A linear output taper was designed with low mode conversion at the gyrotron output. A Vector Network Analyzer with high frequency millmetre wave heads was used to measure the millimeter wave properties of the gyrotron cavity. Experiments were conducted using the electron gun for the harmonic gyrotron. The gyrotron and electron gun were built as well as the interlock and safety system, pulsed power supply and magnet, the cooling and vacuum system. Millimetre wave radiation was measured for the 2.6 mm diameter cavity gyrotron operating at the 2nd harmonic at a magnetic field of 2.08 T. Experiments demonstrated that the harmonic gyrotron was sensitive to the magnetic field and electron beam parameters. Millimetre wave radiation from 108GHz to 110GHz was measured with the use of a W-band rectifying crystal detector and high pass cut off filters. The frequency of the measured millimeter wave radiation agreed very well with the design and predictions of theory.This thesis presents the results of successful operation of a 2nd harmonic gyrotron based on a cusp electron gun. The numerical and experimental results agreed well with the gyrotron design parameters. Two gyrotrons based on a cusp electron gun were designed: the first gyrotron operated at the 2nd harmonic and the second gyrotron was studied to look at the scaling of this concept for operation at the 7th harmonic at a frequency of 390 GHz. The cusp electron gun was used to produce the electron beam in the gyrotron which was annular in shape. The electron beam had a voltage of 40 kV, a current of 1.5A and a velocity ratio (perpendicular component to horizontal component) of 1.5. The experimental results from the first cusp electron gun and measurements of the high quality electron beam with ~8% velocity spread and ~10% alpha spread are presented. Analytical, numerical and experimental results of a DC harmonic gyrotron are presented. The 3D PIC code MAGIC was used to simulate the interaction of the harmonic gyrotron such as the TE71 mode at the 7th cyclotron harmonic with the large orbit electron beam with the beam thickness and beam spread introduced into the simulation. The interaction cavity of both gyrotrons was in the form of a smooth cylindrical waveguide. The relationship between the cavity dimensions and cavity Q values has been studied for optimized output at the design mode with the aim of suppressing other competing modes. A linear output taper was designed with low mode conversion at the gyrotron output. A Vector Network Analyzer with high frequency millmetre wave heads was used to measure the millimeter wave properties of the gyrotron cavity. Experiments were conducted using the electron gun for the harmonic gyrotron. The gyrotron and electron gun were built as well as the interlock and safety system, pulsed power supply and magnet, the cooling and vacuum system. Millimetre wave radiation was measured for the 2.6 mm diameter cavity gyrotron operating at the 2nd harmonic at a magnetic field of 2.08 T. Experiments demonstrated that the harmonic gyrotron was sensitive to the magnetic field and electron beam parameters. Millimetre wave radiation from 108GHz to 110GHz was measured with the use of a W-band rectifying crystal detector and high pass cut off filters. The frequency of the measured millimeter wave radiation agreed very well with the design and predictions of theory

Design and Modeling of Fiber Optical Current Sensor Based on Magnetostriction

A novel fiber optical current sensor (FOCS) which is based on a giant magnetostrictive material, Terfenol-D (T-D) is modeled and prototyped. Several experiments have been conducted to validate the expected results. Magnetostriction is defined as the change in dimensions of a material under the influence of an external magnetic field. The cause of the change in length is due to the rotation and re-orientation of the small magnetic domains in the magnetostrictive material. The magnetostriction of Terfenol-D is modeled and investigated using several software packages. Here, a magnetostriction-based FOCS using a Terfenol-D/epoxy composite is investigated. Particularly, the FOCS is based on applying magnetostrictive composite material to transform an external magnetic field into a corresponding mechanical strain caused by the magnetostriction of the composite. The composite is incorporated in the FOCS for increased durability, flexibility in shape, extended frequency response, and tensile strength compared to monolithic materials. Coupling Terfenol-D with a fiber Bragg grating (FBG) is an excellent method of magnetic field sensing. It consists of an FBG embedded in the composite that converts magnetostrictive strain into frequency chirp of the optical signal in proportion to a magnetic field. This will form a sensor that is compact, lightweight, and immune from electromagnetic interference. For electromagnetic interference mitigation and optimal signal condition, an FBG, which can be easily integrated with an optical fiber network and reflect a narrow band of wavelengths based on grating periods, is used to encode strain information onto an optical signal. This FOCS has potential in detecting power systems faults due to its advantages over the conventional current transformers. Experiments have been performed to investigate the effect of direct current (DC) and alternate current (AC) on the response of the FOCS. Consistent results that indicate its reliability have been obtained. The experiment results matched the predicted response. The effect of the temperature on the response of the FOCS also has been investigated. Finally, future research directions are presented for the enhancement of the FOCS technology

Virtual Prototyping Methodology for Power Automation Cyber-Physical-Systems

In this thesis, the author proposes a circular system development model which considers all the stages in a typical development process for industrial systems. In particular, the present work shows that the use of virtual prototyping at early stages of the system development may reduce the overall design and verification effort by allowing the exploration of the complete system architecture, and uncovering integration issues early on. The modeling techniques of this research are based on VHDL-AMS, yet supporting other modeling languages such as C/C++, SPICE, and Verilog-AMS, together with integrated simulation tools. Contrasting with conventional approaches, it is shown that the proposed methodology is adapted for small-scale Cyber-Physical Systems (CPS) design and verification thanks to the modularity and scalability of the modeling approach. The proposed modeling techniques enable seamlessly the CPS design together with the implementation of their subsystems. In particular, the contribution of this work improves the virtual prototyping approach that has been successfully used during the development of smart electrical sensors and monitoring equipment for high and medium voltage applications. The design of the measurement and self-calibration circuits of a medium voltage current sensor based on the Rogowski coil transducer is presented as an example. The proposed small-scale CPS design methodology based on virtual prototyping, namely VP-based design methodology, uses important theoretical concepts from layered design, component-based design, and platform-based design. These foundations are the basis to build a modeling methodology that provides a vehicle that can be used to improve system verification towards correct-by-design systems. The main contributions of this research are: the re-definition of the system development lifecycle by using a virtual prototyping methodology; the design and implementation of a model library that maximizes the reuse of computational models and their related IP; and a set of VHDL-AMS modeling guidelines established with the purpose of improving the modularity and scalability of virtual prototypes. These elements are key for supporting the introduction of virtual prototyping into industrial companies that can thoroughly profit from this approach, but cannot commit a specific team to the creation, support, and maintenance of computational models and its dedicated infrastructure. Thanks to the progressive nature of the proposed methodology, virtual prototypes can indeed be introduced with relatively low initial effort and enhanced over time. The presented methodology and its infrastructure may grow into a bidirectional communication medium between non-expert system designers (i.e. system architects and virtual integrators) and domain specialists such as mechanical designers, power electrical designers, embedded-electronics designers, and software designers. The proposed design methodology advocates the reduction of the CPS design complexity by the implementation of a meet-in-the-middle approach for system-level modeling. In this direction, the modeling techniques introduced in this work facilitate the architectural design space exploration, critical cross-domain variable analysis (especially important in the component interfaces), and system-level optimization and verification

Design and Implementation of Partial Discharge Measurement Sensors for On-line Condition Assessment of Power Distribution System Components

Unplanned interruptions of power supply due to failure of critical components of the distribution network have considerable impact on the modern society. Efficient condition assessment can avoid the loss of critical components by early detection of incoming threats. One of the biggest shortcomings of today's progressing maintenance technology is the lack of low cost instrumentation solutions which are simple in implementation and easily applicable to the network. In this work partial discharge (PD) measurements have been considered for insulation condition assessment of distribution system components such as overhead covered conductors (CCs) and cables. A high frequency Rogowski coil induction sensor is designed for this purpose. An accurate electrical model of the sensor is necessary for efficient signal processing of the sensed signal and for reliable interpretation of the measured signal. A new method to determine the electrical parameters of Rogowski coil sensor is presented. In-depth analysis of the design stages of Rogowski coil is presented using experimental and simulated environment. Various geometrical designs of Rogowski coil are investigated to analyze the effects of geometrical parameters on high frequency performance of the coil. The guidelines presented regarding geometrical structure are useful when trading off the benefits for better mechanical and electrical design of such sensors. Location of the detected PD faults is an important task of the diagnostics system in power lines. The conventional techniques of locating PD faults have been known for a single section of a power line. However, these techniques are not suitable for power lines having multi-sections or for branched line networks. In this work, finding the location of PD fault on a power line is recognized as a two stage function; (i) identification of the faulty section, and (ii) location of fault point on the identified section. The direction of arrival (DOA) technique is introduced to identify faulty section whereas fault point location can be determined by conventional techniques. The technique is equally applicable for CC lines or cable networks. The DOA technique is integrated over a cable feeder and an on-line automated condition monitoring and diagnostic scheme is proposed. Low cost, non-intrusive installation and favorable operating features of Rogowski coil sensor make it suitable for development of an enhanced and automated diagnostic system which can easily be integrated into the distribution network

Direct current hybrid breakers : a design and its realization

The use of semiconductors for electric power circuit breakers instead of conventional breakers remains a utopia when designing fault current interrupters for high power networks. The major problems concerning power semiconductor circuit breakers are the excessive heat losses and their sensitivity to transients. However, conventional breakers are capable of dealing with such matters. A combination of the two methods, or so-called ‘hybrid breakers’, would appear to be a solution; however, hybrid breakers use separate parallel branches for conducting the main current and interrupting the short-circuit current. Such breakers are intended for protecting direct current (DC) traction systems. In this thesis hybrid switching techniques for current limitation and purely solidstate current interruption are investigated for DC breakers. This work analyzes the transient behavior of hybrid breakers and compares their operations with conventional breakers and similar solid-state devices in DC systems. Therefore a hybrid breaker was constructed and tested in a specially designed high power test circuit. A vacuum breaker was chosen as the main breaker in the main conducting path; then a commutation path was connected across the vacuum breaker where it provided current limitation and interruption. The commutation path operated only during any current interruption and the process required additional circuits. These included a certain energy storage, overvoltage suppressor and commutation switch. So that when discharging this energy, a controlled counter-current injection could be produced. That countercurrent opposed the main current in the breaker by superposition in order to create a forced currentzero. One-stage and two-stage commutation circuits have been treated extensively. This study project contains both theoretical and experimental investigations. A direct current shortcircuit source was constructed capable of delivering power equivalent to a fault. It supplied a direct voltage of 1kVDC which was rectified having been obtained from a 3-phase 10kV/380V supply. The source was successfully tested to deliver a fault current of 7kA with a time constant of 5ms. The hybrid breaker that was developed could provide protection for 750VDC traction systems. The breaker was equipped with a fault-recognizing circuit based on a current level triggering. An electronic circuit was built for this need and was included in the system. It monitored the system continuously and took action by generating trip signals when a fault was recognized. Interruption was followed by a suitable timing of the fast contact separation in the main breaker and the currentzero creation. An electrodynamically driven mechanism was successfully tested having a dead-time of 300:s to separate the main breaker contacts. Furthermore, a maximum peak current injection of kA at a frequency of 500Hz could be obtained in order to produce an artificial current-zero in the vacuum breaker. A successful current interruption with a prospective value of 5kA was achieved by the hybrid switching technique. In addition, measures were taken to prevent overvoltages. Experimentally, the concept of a hybrid breaker was compared with the functioning of all mechanical (air breaker) and all electronical (IGCT breaker) versions. Although a single stage interrupting method was verified experimentally, two two-stage interrupting methods were analyzed theoretically