335 research outputs found
Experimental and analytical performance evaluation of SiC power devices in the matrix converter
With the commercial availability of SiC power devices, their acceptance is expected grows in consideration to the excellent low switching loss, high temperature operation and high voltage rating capabilities of these devices. This paper presents the comparative performance evaluation of different SiC power devices in matrix converter at various temperatures and switching frequencies. To this end, firstly, gate or base drive circuits for Normally-off SiC JFET, SiC MOSFET and SiC BJT which taking into account the special demands for these devices are presented. Then, three 2-phase to 1-phase matrix converters are built with different SiC power devices to measure the switching waveforms and power losses for them at different temperatures and switching frequencies. Based on the measured data, three different SiC power devices are compared in terms of switching times, conduction and switching losses and efficiency at different temperatures and switching frequencies. Furthermore, a theoretical investigation of the power losses of three phase matrix converter with Normally-off SiC JFET, SiC MOSFET, SiC BJT and Si IGBT is described. The power losses estimation indicates that a 7 KW matrix converter would potentially have an efficiency of approximately 96% in high switching frequency if equipped with SiC devices
Modeling of Sic Power Semiconductor Devices For Switching Converter Applications
Thanks to recent progress in SiC technology, SiC JFETs, MOSFETs and Schottky diodes are now commercially available from several manufactories such as Cree, GeneSiC and Infineon. SiC devices hold the promise of faster switching speed compared to Si devices, which can lead to superior converter performance, because the converter can operate at higher switching frequencies with acceptable switching losses, so that passive filter size is reduced. However, the ultimate achievable switching speed is determined not only by internal semiconductor device physics, but also by circuit parasitic elements. Therefore, in order to accurately predict switching losses and actual switching waveforms, including overshoot and ringing, accurate models are needed not only for the semiconductor devices, but also for the circuit parasitics.
In this dissertation, a new physics-based model accounting for non-uniform current distribution in JFET region for the power SiC DMOSFET is presented. Finite element simulation shows that current saturation for typical device geometry is due to two-dimensional (2-D) carrier distribution effects in JFET region caused by current spreading from the channel to the JFET region. Based on this phenomenon, a new model is proposed that represents the non-uniform current distribution in the JFET region using a non-linear voltage source and a resistance network. Advantages of the proposed model are that a single set of equations describes operation in both the linear and saturation regions, and that it provides a more physical description of MOSFET operation. The model represents an original contribution in the area of physics-based power semiconductor device modeling. This model is validated both statically and under resistive conditions for SiC DMOSFET showing overall good matching with experimental results and finite element simulations.
This dissertation also presents a simple physics-based power Schottky diode model which is comprised of a voltage controlled current source, a temperature dependent drift region resistance and a nonlinear capacitance. A detailed parameter extraction procedure for this model is also discussed in this work. The developed procedure includes the extraction of doping concentration, active area and thickness of drift region, which are needed in the power Schottky diode model. The main advantage is that the developed procedure does not require any knowledge of device fabrication, which is usually not available to circuit designers. The only measurements required for the parameter extraction are a simple static I-V characterization and C-V measurements. Furthermore, the physics-based SiC Schottky diode model is also temperature dependent and is generally applicable to SiC Schottky diodes. This procedure is demonstrated for four different Schottky diodes from two different manufacturers. The parameter extraction procedure represents an original contribution in the area of characterization of power semiconductor devices.
In order to capture the parasitic ringing in the very fast switching transients, a procedure to accurately model circuit parasitics is also presented. A double pulse test-bench was built to characterize the resistive and inductive switching behavior of the SiC devices. The parasitic inductances for resistive and inductive switching of SiC devices in this switching test circuit were modeled and analyzed using a three-dimensional (3-D) inductance extraction program. The gate-to-source switching loop and drain-to-source switching loop parasitic inductances of the PCB layout are extracted and simulated together with previously developed power SiC device models in Pspice. Simulation results show good agreement with experimental results under both resistive and inductive switching conditions
Wide Band Gap Devices and Their Application in Power Electronics
Power electronic systems have a great impact on modern society. Their applications target a more sustainable future by minimizing the negative impacts of industrialization on the environment, such as global warming effects and greenhouse gas emission. Power devices based on wide band gap (WBG) material have the potential to deliver a paradigm shift in regard to energy efficiency and working with respect to the devices based on mature silicon (Si). Gallium nitride (GaN) and silicon carbide (SiC) have been treated as one of the most promising WBG materials that allow the performance limits of matured Si switching devices to be significantly exceeded. WBG-based power devices enable fast switching with lower power losses at higher switching frequency and hence, allow the development of high power density and high efficiency power converters. This paper reviews popular SiC and GaN power devices, discusses the associated merits and challenges, and finally their applications in power electronics
Silicon carbide technology for extreme environments
PhD ThesisWith mankind’s ever increasing curiosity to explore the unknown, including a variety of
hostile environments where we cannot tread, there exists a need for machines to do
work on our behalf. For applications in the most extreme environments and applications
silicon based electronics cannot function, and there is a requirement for circuits and
sensors to be built from wide band gap materials capable of operation in these domains.
This work addresses the initial development of silicon carbide circuits to monitor
conditions and transmit information from such hostile environments. The
characterisation, simulation and implementation of silicon carbide based circuits
utilising proprietary high temperature passives is explored.
Silicon carbide is a wide band gap semiconductor material with highly suitable
properties for high-power, high frequency and high temperature applications. The
bandgap varies depending on polytype, but the most commonly used polytype 4H, has a
value of 3.265 eV at room temperature, which reduces as the thermal ionization of
electrons from the valence band to the conduction band increases, allowing operation in
ambient up to 600°C.
Whilst silicon carbide allows for the growth of a native oxide, the quality has limitations
and therefore junction field effect transistors (JFETs) have been utilised as the switch in
this work. The characteristics of JFET devices are similar to those of early thermionic
valve technology and their use in circuits is well known. In conjunction with JFETs,
Schottky barrier diodes (SBDs) have been used as both varactors and rectifiers.
Simulation models for high temperature components have been created through their
characterisation of their electrical parameters at elevated temperatures.
The JFETs were characterised at temperatures up to 573K, and values for TO V , β , λ ,
IS , RS and junction capacitances were extracted and then used to mathematically
describe the operation of circuits using SPICE. The transconductance of SiC JFETs at
high temperatures has been shown to decrease quadratically indicating a strong
dependence upon carrier mobility in the channel. The channel resistance also decreased
quadratically as a direct result of both electric field and temperature enhanced trap
emission. The JFETs were tested to be operational up to 775K, where they failed due to
delamination of an external passivation layer.
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Schottky diodes were characterised up to 573K, across the temperature range and values
for ideality factor, capacitance, series resistance and forward voltage drop were
extracted to mathematically model the devices. The series resistance of a SiC SBD
exhibited a quadratic relationship with temperature indicating that it is dominated by
optical phonon scattering of charge carriers. The observed deviation from a temperature
independent ideality factor is due to the recombination of carriers in the depletion
region affected by both traps and the formation of an interfacial layer at the SiC/metal
interface.
To compliment the silicon carbide active devices utilised in this work, high temperature
passive devices and packaging/circuit boards were developed. Both HfO2 and AlN
materials were investigated for use as potential high temperature capacitor dielectrics in
metal-insulator-metal (MIM) capacitor structures. The different thicknesses of HfO2
(60nm and 90nm) and 300nm for AlN and the relevance to fabrication techniques are
examined and their effective capacitor behaviour at high temperature explored. The
HfO2 based capacitor structures exhibited high levels of leakage current at temperatures
above 100°C. Along with elevated leakage when subjected to higher electric fields. This
current leakage is due to the thin dielectric and high defect density and essentially turns
the capacitors into high value resistors in the order of MΩ. This renders the devices
unsuitable as capacitors in hostile environments at the scales tested. To address this
issue AlN capacitors with a greater dielectric film thickness were fabricated with
reduced leakage currents in comparison even at an electric field of 50MV/cm at 600K.
The work demonstrated the world’s first high temperature wireless sensor node powered
using energy harvesting technology, capable of operation at 573K. The module
demonstrated the world’s first amplitude modulation (AM) and frequency modulation
(FM) communication techniques at high temperature. It also demonstrated a novel high
temperature self oscillating boost converter cable of boosting voltages from a
thermoelectric generator also operating at this temperature.
The AM oscillator operated at a maximum temperature of 553K and at a frequency of
19.4MHz with a signal amplitude 65dB above background noise. Realised from JFETs
and HfO2 capacitors, modulation of the output signal was achieved by varying the load
resistance by use of a second SiC JFET. By applying a negative signal voltage of
between -2.5 and -3V, a 50% reduction in the signal amplitude and therefore Amplitude
Modulation was achieved by modulating the power within the oscillator through the use
of this secondary JFET. Temperature drift in the characteristics were also observed,
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with a decrease in oscillation frequency of almost 200 kHz when the temperature
changed from 300K to 573K. This decrease is due to the increase in capacitance density
of the HfO2 MIM capacitors and increasing junction capacitances of the JFET used as
the amplifier within the oscillator circuit.
Direct frequency modulation of a SiC Voltage Controlled Oscillator was demonstrated
at a temperature of 573K with a oscillation frequency of 17MHz. Realised from an SiC
JFET, AlN capacitors and a SiC SBD used as a varactor. It was possible to vary the
frequency of oscillations by 100 kHz with an input signal no greater than 1.5V being
applied to the SiC SBD. The effects of temperature drift were more dramatic in
comparison to the AM circuit at 400 kHz over the entire temperature range, a result of
the properties of the AlN film which causes the capacitors to increase in capacitance
density by 10%.
A novel self oscillating boost converter was commissioned using a counter wound
transformer on high temperature ferrite, a SiC JFET and a SiC SBD. Based upon the
operation of a free running blocking oscillator, oscillatory behaviour is a result of the
electric and magnetic variations in the winding of the transformer and the amplification
characteristics of a JFET. It demonstrated the ability to boost an input voltage of 1.3
volts to 3.9 volts at 573K and exhibited an efficiency of 30% at room temperature. The
frequency of operation was highly dependent upon the input voltage due to the
increased current flow through the primary coil portion of the transformer and the
ambient temperature causing an increase in permeability of the ferrite, thus altering the
inductance of both primary and secondary windings. However due its simplicity and its
ability to boost the input voltage by 250% meant it was capable of powering the
transmitters and in conjunction with a Themoelectric Generator so formed the basis for
a self powered high temperature silicon carbide sensor node.
The demonstration of these high temperature circuits provide the initial stages of being
able to produce a high temperature wireless sensor node capable of operation in hostile
environments. Utilising the self oscillating boost converter and a high temperature
Thermoelectric Generator these prototype circuits were showed the ability to harvest
energy from the high temperature ambient and power the silicon carbide circuitry.
Along with appropriate sensor technology it demonstrated the feasibility of being able
to monitor and transmit information from hazardous locations which is currently
unachievable
Survey of applications of WBG devices in power electronics
Master of ScienceDepartment of Electrical and Computer EngineeringBehrooz MirafzalWide bandgap devices have gained increasing attention in the market of power electronics for their ability to perform even in harsh environments. The high voltage blocking and high temperature withstanding capabilities make them outperform existing Silicon devices. They are expected to find places in future traction systems, electric vehicles, LED lightning and renewable energy engineering systems. In spite of several other advantages later mentioned in this paper, WBG devices also face a few challenges which need to be addressed before they can be applied in large scale in industries. Electromagnetic interference and new requirements in packaging methods are some of the challenges being faced by WBG devices. After the commercialization of these devices, many experiments are being carried out to understand and validate their abilities and drawbacks. This paper summarizes the experimental results of various applications of mainly Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices and also includes a section explaining the current challenges for their employment and improvements being made to overcome them
Silicon carbide based DC-DC converters for deployment in hostile environments
PhD ThesisThe development of power modules for deployment in hostile environments,
where the elevated ambient temperatures demand high temperature capability of the
entire converter system, requires innovative power electronic circuits to meet stringent
requirements in terms of efficiency, power-density and reliability. To simultaneously
meet these conflicting requirements in extreme environment applications is quite
challenging. To realise these power modules, the relevant control circuitry also needs to
operate at elevated temperatures. The recent advances in silicon carbide devices has
allowed the realisation of not just high frequency, high efficiency power converters, but
also the power electronic converters that can operate at elevated temperatures, beyond
those possible using conventional silicon-based technology.
High power-density power converters are key components for power supply
systems in applications where space and weight are critical parameters. The demand for
higher power density requires the use of high-frequency DC-DC converters to overcome
the increase in size and power losses due to the use of transformers. The increase in
converter switching frequency reduces the size of passive components whilst increasing
the electromagnetic interference (EMI) emissions.
A performance comparison of SiC MOSFETs and JFETs in a high-power
DC-DC converter to form part of a single phase PV inverter system is presented. The
drive design requirements for optimum performance in the energy conversion system
are also detailed. The converter was tested under continuous conduction mode at
frequencies up to 250 kHz. The converter power efficiency, switch power loss and
temperature measurements are then compared with the ultra-high speed CoolMOS
switches and SiC diodes. The high voltage, high frequency and high temperature
operation capability of the SiC DUTs are also demonstrated. The all SiC converters
showed more stable efficiencies of 95.5% and 96% for the switching frequency range
for the SiC MOSFET and JFET, respectively. A comparison of radiated noise showed
the highest noise signature for the SiC JFET and lowest for the SiC MOSFET. The
negative gate voltage requirement of the SiC MOSFET introduces up to 6 dBÎĽV
increase in radiated noise, due to the induced current in the high frequency resonant
stray loop in the gate drive negative power plane.
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A gate driver is an essential part of any power electronic circuitry to control the
switching of the power semiconductor devices. The desire to place the gate driver
physically close to the power switches in the converter, leads to the necessity of a
temperature resilient PWM generator to control the power electronics module. At
elevated temperatures, the ability to control electrical systems will be a key enabler for
future technology enhancements.
Here an SiC/SOI-based PWM gate driver is proposed and designed using a
current source technique to accomplish variable duty-cycle PWM generation. The ring
oscillator and constant current source stages use low power normally-on, epitaxial
SiC-JFETs fabricated at Newcastle University. The amplification and control stages use
enhancement-mode signal SOI MOSFETs. Both SOI MOSFETs will be replaced by
future high current SiC-JFETs with only minor modification to the clamp-stage circuit
design. In the proposed design, the duty cycle can be varied from 10% to 90%. The
PWM generator is then evaluated in a 200 kHz step-up converter which results in a 91%
efficiency at 81% duty cycle.
High temperature environments are incompatible with standard battery
technologies, and so, energy harvesting is a suitable technology when remote
monitoring of these extreme environments is performed through the use of wireless
sensor nodes. Energy harvesting devices often produce voltages which are unusable
directly by electronic loads and so require power management circuits to convert the
electrical output to a level which is usable by monitoring electronics and sensors.
Therefore a DC-DC step-up converter that can handle low input voltages is required.
The first demonstration of a novel self-starting DC-DC converter is reported, to
supply power to a wireless sensor node for deployment in high temperature
environments. Utilising SiC devices a novel boost converter topology has been realised
which is suitable for boosting a low voltage to a level sufficient to power a sensor node
at temperatures up to 300 °C. The converter operates in the boundary between
continuous and discontinuous mode of operation and has a VCR of 3 at 300 °C. This
topology is able to self start and so requires no external control circuitry, making it ideal
for energy harvesting applications, where the energy supply may be intermittent.EPSRC and BAE
SYSTEMS through the Dorothy Hodgkin Postgraduate Awar
Experimental Investigation of Low-Voltage Silicon Carbide (SiC) Semiconductor Devices for Power Conversion Applications
Enhancing the performance and efficiency of power converter systems requires fast-switching power devices with considerably low switching and conduction losses. Silicon (Si) semiconductor devices are the essential components in electronic converter designs, and their behaviors and switching characteristics determine the system’s overall performance and efficiency. These conventional Si devices are nearing to hit their physical and operational limits in meeting power converter requirements with respect to high temperature and large voltage conditions. However, silicon carbide (SiC) power devices enable greater converter efficiency and better power density, particularly under hard switching frequencies and high output voltages due to their outstanding material properties, including lower on-state resistance, higher electric field, and wider energy bandgap. This research focuses on emerging SiC semiconductor devices in dc-dc electronic converters to maximize system efficiencies, improve power densities, and overcome the existing limitations of Si technology. The aim of this research is to examine switching behaviors of SiC-based semiconductors, especially at a 650 V blocking voltage range, and to demonstrate their impact on power converter performance. This experimental research investigates and compares the device behaviors of the SiC cascode JFET and SiC MOSFET with Si IGBT and Si MOSFET devices at a similar voltage and current ratings. The switching behaviors of each device technologies are demonstrated at different parameters, and the switching energy losses under various voltages and currents are experimentally evaluated in detail using a double-pulse test (DPT). The switching voltage and current derivatives for each transistor are illustrated as well. Finally, SiC-based converters are examined at different frequency levels, input voltages, and load conditions to fully test and explore the converter design with SiC diodes and transistors with respect to semiconductor loss, overall efficiency, and converter size and cost. Thus, this research will validate the superior switching performance of 650 V SiC power devices and show significantly improved overall efficiency in the SiC-based converters
The Development and Packaging of a High-Density, Three-Phase, Silicon Carbide (SiC) Motor Drive
Technology advances within the power electronics field are resulting in systems characterized by higher operating efficiencies, reduced footprint, minimal form factor, and decreasing mass. In particular, these attributes and characteristics are being inserted into numerous consumer applications, such as light-emitting diode lighting, compact fluorescent lighting, smart phones, and tablet PCs, to industrial applications that include hybrid, electric, and plug-in electric vehicles and more electric aircraft. To achieve the increase in energy efficiency and significant reduction in size and mass of these systems, power semiconductor device manufacturers are developing silicon carbide (SiC) semiconductor technology.
In this dissertation, the author discusses the design, development, packaging, and fabrication of the world\u27s first multichip power module (MCPM) that integrates SiC power transistors with silicon-on-insulator (SOI) integrated circuits. The fabricated MCPM prototype is a 4 kW, three-phase inverter that operates at temperatures in excess of 250 °C. The integration of high-temperature metal-oxide semiconductor (HTMOS) SOI bare die control components with SiC power JFET bare die into a single compact module are presented in this work. The high-temperature operation of SiC switches allows for increased power density over silicon electronics by an order of magnitude, leading to highly miniaturized power converters.
This dissertation is organized into a compilation of publications written by the author over the course of his Ph.D. work. The work presented throughout these publications covers the challenges associated with power electronics miniaturization and packaging including high-power density, high-temperature, and high-efficiency operation of the power electronic system under study
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