The concept of multilevel voltage source inverters and their modulation topologies are described. The concept of the Optimized Harmonic Stepped-Waveform (OHSW) technique for a multilevel inverter is presented. By applying this concept, specific harmonics can be eliminated, and the output voltage THD can be improved. A procedure to achieve the appropriate switching angles of the OHSW is proposed. Experimental results are presented to verify the concept. The proposed OHSW technique is implemented on a multilevel inverter using cascaded-inverter with separated dc sources. Comparison between the Selective Harmonic Eliminated PWM and the OHSW is also presented. / Master of Science

No description available.

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

With worldwide growing demand for electric energy, there has been a great interest in exploring photovoltaic (PV) sources. For the PV generation system, the power converter is the most essential part for the efficiency and function performance. In recent years, there have been quite a few new transformerless PV inverters topologies, which eliminate the traditional line frequency transformers to achieve lower cost and higher efficiency, and maintain lower leakage current as well. With an overview of the state-of-the-art transformerless PV inverters, a new inverter technology is summarized in the Chapter 2, which is named V-NPC inverter technology. Based this V-NPC technology, a family of high efficiency transformerless inverters are proposed and detailly analyzed. The experimental results demonstrate the validity of V-NPC technology and high performance of the transformerless inverters. For the lower power level transformerless inverters, most of the innovative topologies try to use super junction metal oxide semiconductor field effect transistor(MOSFET) to boost efficiency, but these MOSFET based inverter topologies suffer from one or more of these drawbacks: MOSFET failure risk from body diode reverse recovery, increased conduction losses due to more devices, or low magnetics utilization. By splitting the conventional MOSFET based phase leg with an optimized inductor, Chapter 3 proposes a novel MOSFET based phase leg configuration to minimize these drawbacks. Based on the proposed phase leg configuration, a high efficiency single-phase MOSFET transformerless inverter is presented for the PV micro-inverter applications. The PWM modulation and circuit operation principle are then described. The common mode and differential mode voltage model is then presented and analyzed for circuit design. Experimental results of a 250 W hardware prototype are shown to demonstrate the merits of the proposed MOSFET based phase-le and the proposed transformerless inverter. New codes require PV inverters to provide system regulation and service to improve the distribution system stabilization. One obvious impact on PV inverters is that they now need to have reactive power generation capability. The Chapter 4 improves the MOFET based transformerless inverter in the Chapter 3 and proposed a novel pulse width modulation (PWM) method for reactive power generation. The ground loop voltage of this inverter under the proposed PWM method is also derived with common mode and differential mode circuit analyses, which indicate that high-frequency voltage component can be minimized with symmetrical design of inductors. A 250-W inverter hardware prototype has been designed and fabricated. Steady state and transient operating conditions are tested to demonstrate the validity of improved inverter and proposed PWM method for reactive power generation, high efficiency of the inverter circuit, and the high-frequency-free ground loop voltage. Besides the high efficiency inverter circuit, the grid connection function is also the essential part of the PV system. The Chapter 5 present the overall function blocks for a grid-connected PV inverter system. The current control and voltage control loop is then analyzed, modeled, and designed. The dynamic reactive power generation is also realized in the control system. The new PLL method for the grid frequency/voltage disturbance is also realized and demonstrate the validity of the detection and protection capability for the voltage/frequency disturbance. At last, a brief conclusion is given in the Chapter 6 about each work. After that, future works on device packaging, system integration, innovation on inverter circuit, and standard compliance are discussed. / Ph. D.

No description available.

A full electro-thermal simulation of a three-phase space-vector-modulated (SVM) inverter is performed and validated with measurements. Electrical parameters are extracted over temperature for the insulated gate bipolar transistor (IGBT) and diode electro-thermal models. A thermal network methodology that includes thermal coupling between devices is applied to a six-pack module package containing multiple IGBT and diode chips. The electro-thermal device models and six-pack module thermal model are used to simulate SVM inverter operation at several power levels. Good agreement between model and measurement is obtained for steady state operation of the three-phase inverter. In addition, transient heating of a single IGBT in the six-pack module is modeled and validated, yielding good agreement. / Master of Science

This thesis proposes novel methods and comprehensive analysis for power loss calculation, DC-link current and voltage ripple estimation, and bus bar design in two-level three-phase voltage source inverters (VSIs). A novel method of MOSFET voltage rise- and fall-time estimations for the switching power loss calculation is developed. The estimation accuracy is significantly improved by the proposed method. In order to provide a reference for thermal management design, inverter power loss analysis is presented. Using the parameters obtained from the semiconductor device datasheets and inverter operating conditions, power loss calculations of three types of devices, namely IGBT, MOSFET, and diode, are discussed. The conduction power loss calculations for these three devices are straightforward; and, the switching power loss of IGBTs and diodes can be obtained from the energy losses given by datasheets. However, many MOSFET datasheets do not provide the switching energy losses directly. Therefore, to acquire MOSFET switching energy losses, switching transient times must be estimated as accurately as possible. The impacts of inverter anti-parallel diode reverse recovery on the DC-link current and voltage ripples are investigated. According to the analysis, the impact of diode reverse recovery on the voltage ripple is negligible, while the RMS value of current ripple is influenced by both diode reverse recovery and inverter switching frequency. A novel method is developed to calculate the ripple current RMS value and the estimation accuracy is significantly improved. Depending on the calculated current and voltage ripples, DC-link capacitor selection is introduced. Generally speaking, failures in the DC-link capacitors take place more frequently than the failures in other parts of the inverter system, and plenty of research has been focusing on minimizing the required DC-link capacitance. As a result, the accurate estimations of DC-link current and voltage ripples are vital in the optimization methods. In addition, with the accurate estimations, the over-design in the DC-link capacitance could be reduced. Finally, the design of a practical bus bar is presented. The DC current distribution is aff ected by the numbers and locations of the DC input tabs, while the AC current distribution is influenced by the numbers and locations of the installation holes for DC-link capacitors and semiconductor devices. Furthermore, parasitic parameters of the bus bar, especially the stray inductance and voltage spikes caused by this inductance during switching turn-o transients, are also discussed from the angle of the design rules and correlation between the parameters and bus bar geometry structure. In the end, a bus bar is designed with balanced current distribution and low stray inductance. / Thesis / Doctor of Philosophy (PhD)

Die vorliegende Arbeit befasst sich mit der Entwicklung, Herstellung und Untersuchung von ZnO-basierten Feldeffekttransistoren (FET). Dabei werden im ersten Teil Eigenschaften von ein- und mehrschichtigen Isolatoren mit hohen Dielektrizitätskonstanten betrachtet, die mittels gepulster Laserabscheidung (PLD) dargestellt wurden. Die elektrischen und kapazitiven Eigenschaften dieser Isolatoren innerhalb von Metall-Isolator-Metall (MIM) bzw. Metall-Isolator-Halbleiter (MIS) Übergängen wurden untersucht. Letzterer wurde schließlich als Gate-Struktur in Metall-Isolator-Halbleiter-FET (MISFET) mit unten (backgate) bzw. oben liegendem Gate (topgate) genutzt. Der zweite Teil konzentriert sich auf Metal-Halbleiter-FET (MESFET), die einen Schottky-Kontakt alsGate nutzen. Dieser wurde mittels reaktiver Kathodenzerstäubung (Sputtern) von Ag, Pt, Pd oder Au unter Einflußvon Sauerstoff hergestellt. ZnO-MESFET stellen eine vielversprechende Alternative zu den bisher in der Oxid-basierten Elektronik verwendeten MISFET dar. Durch die Variation des verwendeten Gate-Metalls, Dotierung, Dicke und Struktur des Kanals und Kontakstruktur, wurde ein Herstellungsstandard gefunden, der zu weiteren Untersuchungen herangezogen wurde. So wurde die Degradation der MESFET unter Belastung durch dauerhaft angelegte Spannung, Einfluss von Licht und erhöhten Temperaturen sowie lange Lagerung getestet. Weiterhin wurden ZnO-MESFET auf industriell genutztem Glasssubstrat hergestellt und untersucht, um die Möglichkeit einer großflächigen Anwendung in Anzeigeelementen aufzuzeigen. Einfache integrierte Schaltungen, wie Inverter und ein NOR-Gatter, wurden realisiert. Dazu wurden Inverter mit sogenannten Pegelschiebern verwendet, welche die Ausgangsspannung des Inverters so verschieben, dass eine logische Aneinanderreihungvon Invertern möglich wird. Schließlich wurden volltransparente MESFET und Inverter, basierend auf neuartigen transparenten gleichrichtenden Kontakten demonstriert.

With the rise in demand for renewable energy sources, photovoltaics have become increasingly popular as a means of reducing household dependence on the utility grid for power. But solar panels generate dc electricity, a dc to ac inverter is required to allow the energy to be used by the existing ac electrical distribution. Traditional full bridge inverters are able to accomplish this, but they suffer from many problems such as low efficiency, large size, high cost, and generation of electrical noise, especially common mode noise. Efforts to solve these issues have resulted in improved solutions, but they do not eliminate all of the problems and even exaggerate some of them. Soft switching inverters are able to achieve high efficiency by eliminating the switching losses of the power stage switches. Since this action requires additional components that are large and have additional losses associated with them, these topologies have traditionally been limited to higher power levels. The resonant snubber inverter is a soft switching topology that eliminates many of these problems by taking advantage of the bipolar switching action of the power stage switches. This allows for a significant size reduction in the additional parts and elimination of common mode noise, making it an ideal candidate for lower power levels. Previous attempts to implement the resonant snubber inverter have been hampered by low efficiency due to parasitics of the silicon devices used, but, with recent developments in new semiconductor technologies such as silicon carbide and gallium nitride, these problems can be minimized and possibly eliminated. The goal of this thesis is to design and experimentally verify a design of a resonant snubber inverter that takes advantage of new semiconductor materials to improve efficiency while maintaining minimal additional, parts, simple control, and elimination of common mode noise. A 600 W prototype is built. The performance improvements over previous designs are verified and compared to alternative high efficiency solutions along with a novel control technique for the auxiliary resonant snubber. A standalone and grid tie controller are developed to verify that the auxiliary resonant snubber and new auxiliary control technique does not complicate the closed loop control. / Master of Science

The goal of this thesis project was to design and build a three-phase inverter controlled by the TMS320F2812 DSP by Texas Instruments. The TMS320F2812 is controlled in order to make inverters generate output waveforms which mimic the main reference signal coming from a computer. The project included building three different inverters on two platforms including auxiliary circuits and designing five pulse width modulation (PWM) switching algorithms for the inverters. The motivation was that a newly designed inverter was required as an intermediary device between a computer and a laboratory-scaled model of a wind turbine. This type of wind turbine is used to educate students and engineers and to extract experimental wind power data. However, since commercial inverters don’t follow the main reference signal which is sent from the computer in order to operate the laboratory-scaled wind turbine, a controllable and variable inverter needed to be designed to receive that signal. The results are as follows. The voltage source inverter (VSI) and the current-controlled voltage source inverter (CC-VSI) were built on the VSI platform, and the current source inverter (CSI) was built on the CSI platform. Furthermore, the TMS320F2812’s analog digital converter (ADC) driver circuit and the output LC filter were also designed as auxiliary circuits. Five PWM switching programs were written; three switching algorithms for the VSI, and one algorithm each for the CC-VSI and the CSI. The output waveforms from the combination of hardware and software mentioned above were captured, and they follow the main reference signal very well. Although each of the inverters performed well, the VSI in combination with the Space Vector PWM switching algorithm produced the cleanest output voltage waveforms with the least amount of noise. The inverters built in this thesis project can be applied to the laboratory-scaled wind turbine, the maximum power tracking in solar panels, and equipment for analyzing digital signal processing. However, before using the inverters in those applications, much work remains to be done to solve the problems related to the signal distortion caused by the dead band time, harmonic signals caused by the fixed switching frequency, and the reliability issues caused by mounting on the bread board. In conclusion, although this thesis does not illustrate the entire process of or explain every requirement for building the three inverters, enough information about the topology of the inverters, the hardware design, and the PWM switching algorithms is provided in this thesis to enable one to remake all three of the three-phase inverters. / text