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The focus of this dissertation is to provide an in-depth understanding of the Model predictive control (MPC) technique of a three-phase voltage source converter for use in a fuel cell power system and a battery energy storage system (BESS) in grid-connected applications. The work presented here will help the researchers to further explore the flexibility of the MPC controller for design, analysis, and implementation in a power conversion system. With the growing demand for electricity, renewable sources of energy have garnered a lot of support from all quarters. The problem with these renewable sources is that the output from them is independent of the demand. The storage of electricity gives us an opportunity to effectively manage and balance the supply and demand of electricity. The second part of the dissertation studies the model predictive control technique to integrate a BESS with the grid. As an energy source, fuel cell power systems offer clean and efficient energy production and are currently under intensive development by several manufacturers. The viability, efficiency, and robustness of this technology depend on understanding, predicting and controlling the unique transient behavior of the fuel cell system. In the third part of the dissertation, the mathematical model of a fuel cell power system is designed and the system’s dynamic behavior at a grid-connected mode is discussed. The model predictive control technique is used to integrate the fuel cell power system with the grid. Consequently, this thesis focuses on a novel controller approach in order to obtain a more reliable and flexible three-phase inverter to integrate distributed energy sources with the grid.

Direct dynamics simulations are a very useful and general approach for studying the atomistic properties of complex chemical systems because they make it possible to construct a system’s potential energy surface under an electronic structure theory without the need for fitting an analytic potential energy function. Classical trajectories, an application category of direct dynamics simulations,which obey Newton’s laws, have been proven useful for researching atomic system of motion. Classical trajectories can be computed directly from electronic structure calculations without computing a global potential-energy surface. The potential energy and its derivatives are directly calculated by electronic structure methods during the integration of the classical equations of motion. Because the wave function is converged rather than propagated to generate a more accurate potential-energy surface in direct dynamics simulations, steps of moderate size can be taken by integrating the equations of motion into a local quadratic approximation of the surface (a second-order algorithm) if the analytic second derivatives (Hessians) can be computed. The following discusses our contributions: (I) We describe an accurate integration method that uses a second-order predictor step on a local quadratic surface, followed by a corrector step on a local surface fitted to the energies, gradients, and Hessians computed at the beginning and end points of the predictor step. In the predictor stage, this method utilizes the information (Location, Velocity, Gradient, and Hessian ) of the current time step to predict the location of the next time step. In the corrector stage, this method hires a fifth-order polynomial or a rational polynomial to fit the energy surface. Next, different from previous methods, we propose a new algorithm, which uses those information (Location, Velocity, Gradient, and Hessian) of the current time step and the previous time steps to predict the location of the next time step in the predictor step. Similarly, it uses a second-order predictor step on a local quadratic surface and a corrector step on a local surface fitted to the energies, gradients, and Hessians computed at the beginning and end points of the predictor step. Finally, we show a family of Hessian-based Predictor-Corrector integrates. These integrates make use of some information (Location, Velocity, Gradient and Hessian) about the previous time step and all information about the current time step. The corrector step exploits the fifth-order polynomial fit or the rational polynomial fit. The approach involves four Fourth-order predictors, six Fifth-order predictors, and four Sixth-order predictors. As in the previous methods, the second-order predictor steps on a local quadratic surface and the corrector steps on a better local surface are fitted to the energies, gradients, and Hessians computed at the beginning and end points of the predictor step. (II) We propose a tool for evaluating the accuracy of integrators for the trajectory calculation by employing monodromy matrix. We choose a general approach, the Velocity Verlet integrator, as a referent object. In here, we simulate a molecular without hydrogen ( CO2) and a molecular with hydrogen (H2O) motions. Many simulations show the family of Hessian-based Predictor-Corrector integrators perform well for Hessian update and non Hessian update by comparison of the eigenvalues of monodromy matrix. Compared to traditional methods, the new tool are more intuitive and clear.

Grid integration of renewable energy sources has proven to be a challenging problem that has been widely studied and continues to be of interest. Most modern wind energy conversion systems utilize power electronics converters/inverters to maintain voltage phase, frequency and magnitude at the grid-dictated values. While power electronics is an expanding area of interest, currently available solutions report high failure rates and elevated maintenance costs. In this work we investigate the performance of a continuously variable speed wind turbine using the dynamics published by Yves Rothenbuller of EPFL to model the dynamics of the CVT. Using real data sets of wind conditions in the South plains region of Texas, and performing simulations combined with a Simulink model of our experimental drivetrain, we incorporate the CVT model into a wind turbine model coupled to an induction generator. By controlling the driver axial forces of the CVT we control low- and high- speed shaft speeds to obtain maximum wind energy capture before the wind cut-out speed. The intent is to show how control inputs of the CVT affect power through the entire drivetrain to meet the objective of improving energy capture. The results for the overall integrated powertrain are presented and discussed integrating the CVT and the induction generator. The simulations were all performed utilizing real wind data taken from a met tower in the South plains area. The correct control of a gearless wind turbine yields encouraging results: • Improved energy capture. • Reduced power electronics needed for grid integration.

In the wake of past various blackouts, management and control of power system is going through essential transitions. To transform the modern grid into smart grid, various actions related to data acquisition and processing, security monitoring and control and energy/economy decisions have to be advanced to next level. Including of Phasor Measurement Units (PMUs) along with current SCADA (Supervisory Control and Data Acquisition) system is an essential step towards realization of smart grids. PMUs can give synchronized measurements of voltage and current phasors from the grid, however their placement and maintenance could be daunting task based on their cost and the size of the grid. Hence various optimization techniques have been used to solve Optimal PMU placement (OPP) problem that provides complete observability of the grid. It was assumed that a PMU used in power system will have a very large number of channels facilitating current measurements of all the incident branches possible when placed on a node. This thesis solves a more practical problem when number of channels in the PMUs is comparatively smaller and provides a generalized formulation of OPP problem. The formulated problem is extended to various cases of OPP problem based on requirement of observability, cost ratio, presence of zero injection buses, requirement of measurement redundancy, presence of SCADA, combination of different types of PMUs etc. For the power system network, matrices to define nodal connectivity and branch selectivity have been introduced. These matrices are used to formulate the generalized OPP problem for limited channel capacity PMUs. The problem has been tested on various standard IEEE test bus systems. Furthermore, application of PMU measurements for utilities must be addressed. This thesis develops a new model of state and parameter estimation of power systems using PMU measurements. The approach elaborates on bilinear model of power systems based on PMU measurements. Various correlations between states, parameters and PMU measurements have been included to make the solution more applicable to utility companies. A formula for parallel Kalman filter has been developed and implemented to do the state and parameter estimation of power systems. Parallel Kalman filter (PKF) is a special type of dynamic state estimation technique where a nonlinear model can be partitioned into two dependent linear models. Derivation of PKF is based on game theory where each opponent makes their move dependent on the outcome of the move played by the other opponent. Because of the knowledge of dynamics of the system and correlation between various errors along with errors due to approximation in parameters of the system, the developed dynamic state estimation technique tends to be more accurate than a dynamic state estimation technique using Kalman Filter, which in turn is more accurate than current static state estimation techniques.

A microgrid is a combination of Distributed Energy Resources (DERs), Energy Storage, and Controllable Loads. It is connected to the main grid through the Point of Common Coupling (PCC). The main objective of this research is to optimize energy flow within a microgrid with regards to economic dispatch, reliability and availability in both grid connected and islanded modes. A microgrid with Combined Heat and Power (CHP), Natural Gas Generator, Diesel Generator, Solar energy, Wind energy, and Battery Energy storage with power ratings 1.5MW, 1MW, 1MW, 500kW, 500kW and 500kW respectively is considered. A critical load of 2.5MW and non-critical load of 500kW are considered in this research. The critical load is always supplied with power in both modes of connection of the microgrid. In the grid connected mode, the main grid supplies power to the non-critical load. Reduced Gradient Algorithm method is implemented to find the economic dispatch of a microgrid. The total cost of microgrid in the islanded and grid connected modes is optimized using MATLAB code. The total cost includes the operation and maintenance cost, investment cost, fuel cost, replacement costs, etc. The optimization of generation cost is obtained by minimizing the cost function of the system while meeting the load demand. The minimum total cost of the system is obtained by comparing different scenarios of the micro sources along with the change in the wind profile of the microgrid. An event oriented analytical method called Fault Trees Analysis (FTA) is implemented for reliability optimization using PTC Windchill Solutions software in a microgrid. The reliability of each component in each micro source of the microgrid is calculated using Fault Tree Analysis. The reliability of critical and non-critical loads is evaluated. The quantitative and qualitative results of Fault Tree Analysis are evaluated in order to interpret the results of fault tree. The sensitivity and uncertainty of the fault tree results for both critical and non-critical loads are deduced by calculating the importance measures such as Risk Achievement Worth, Risk Reduction Worth, Criticality Importance and Fussel – Vesely Importance. Then from the results the components that are sensitive and at high risk are deduced. This illustrates that they must be maintained well to increase the reliability. Then Economic Dispatch using Reduced Gradient Method is implemented for the optimization of energy in the islanded mode of microgrid using MATLAB. The optimization of operation and maintenance cost of microgrid is obtained by minimizing the cost function of the system while meeting the load demand. The Operation & Maintenance cost (O&M) of each micro source is considered in its cost function. The minimum O&M cost of the system is obtained by comparing different scenarios of the micro sources along with the change in the wind and battery profiles in the microgrid. Lastly, the availability of microgrid is optimized by considering the total cost and Operating and Maintenance cost of microgrid in both islanded and grid connected modes. Then, the availability and generation cost of each micro source is compared and optimized in islanded as well as grid connected mode of microgrid. In the total cost and availability optimization, the optimized availability and minimal cost are obtained in both grid connected and islanded modes of a microgrid by considering the change in the wind profile. While in the O&M cost and availability optimization, the profiles with change in the wind forecast and battery energy storage are considered to obtain the optimized availability and minimal cost in both grid connected and islanded modes of a microgrid.

In order for pulsed power systems to improve as a whole, the individual components they are composed of must continue to improve. One of the key components of pulsed power systems are switching devices. Traditionally, switching devices utilized were of spark/gas-type. These types of devices boast high voltage and high current operation, making them quite desirable for pulsed power applications. Gas/spark-type switching devices do have several intrinsic deficiencies; specifically high conduction losses which must be dealt with via exhaustive cooling systems, large physical size and high maintenance. Solid state switching devices are an alluring solution to these issues with gas/spark-type devices. This thesis details experimental evaluation and simulation of a 4 kV n-type gate turn-off thyristor (GTO) designed for pulsed power applications. The primary criteria of evaluation are rate of current change (dI/dt), turn-on delay time (TD), and resistance of the device during turn-on events (Ron(t)). The device is an n-type, asymmetric-blocking GTO manufactured by Silicon Power (Part No. 14N40A10) with a DC blocking voltage of 4 kV. A test circuit was specifically designed to minimize stray inductance in order to capitalize on the dI/dt capabilities of the device under test (DUT). Experimental data collected from resistance measurements was used to develop a one-switch approximate model for use in simulation. Results of dI/dt experiments provide a profile of DUT operation at gate currents greater than initial test conditions (IG > ITG); specifically dI/dt > 70 kA/μs is achieved at IG ~3ITG. Turn-on delay time of the DUT is also characterized.

Renewable energy is opening a new window to solve the energy crisis of the world. Several countries along with USA are introducing a lot of wind energy to the grid. Wind energy is a relatively new technology and needs a lot of research to ensure proper operation and stability of the grid. The research needs to be carried out to better understand the wind energy characteristics, identify grid integration requirements of the wind energy and stable operation during energy production. During this study, different issues were addressed from each of these three aspects. The study initially works to identify an optical iteration process to conduct power quality analysis of a wind turbine. Proper power quality analysis of the wind turbine ensures better understanding of the turbine characteristics and provides better system planning. In this research a new method is proposed to carry out the power quality analysis process in a faster way with less computational burden. The method is validated by using real time data available from one of the wind turbine of ALSTOM. Next, the study focuses on grid Short Circuit Ratio (SCR) estimation procedure for wind energy. The grid SCR is critical to determine the performance of the grid connected wind turbine. During this study, a novel method is proposed to estimate the grid parameters and thus the SCR. The new method is validated using simulation data available from PSCAD/EMTDC software and real time data available from a commercial wind farm. The method is also compared with already available solutions to ensure better performance. Finally, a new method is shown to provide frequency response from Doubly Fed Induction Generator (DFIG) based wind turbine during frequency deviation. The method integrates an energy storage device with the grid through the DC capacitor and uses the already available AC/DC/AC converter for power conversion. The energy storage provides the required frequency response during power imbalance. The method is validated using simulation results available from MatLab/Simulink software.

Half-Bridge modules are essential to the design of power electronic systems such as dc-to-ac converters, synchronous dc-to-dc converters, and motor drivers. Silicon carbide (SiC) modules are a state-of-the-art solution for the development of high power and high temperature systems; this is due the material having several inherent superior electrical and thermal characteristics. Although SiC devices are state-of-the-art, they have not been fully evaluated and therefore have not become a widespread solution. In addition to the superior electrical characteristics of SiC, the thermal conductivity is also increased and therefore higher temperature operation can be achieved. It is crucial to develop an understanding of these devices by empirical measurement to fully understand the device and how it operates. In this thesis, the work required to develop a system for characterization of these modules is outlined. After a system has been developed, the DC characteristics of the modules will be tested vs. temperature and gate-to-source voltage when applicable. After the DC characteristics are measured for the modules, the switching characteristics will be measured vs. temperature, external gate resistance, and drain-to-source current in a classic clamped inductive double pulse test. This test is used to collect the required measurement data needed for analyzing the switching loss, reverse recovery of the body diode, and voltage overshoot of three different SiC half-bridge modules.

In order to determine the safe operating limits of SiC 9 kV SGTOs a test system was designed and built to stress the devices with high current density pulses (over 10X the rated densities) for greater than 10,000 high current discharges. A total of 7 SiC SGTOs were pulsed on the test system for over 250,000 pulses total. The data from these pulses is then used to calculate the device performance. The DC characteristics were monitored as part of the automated test system as well as on an Agilent B1505A high power device analyzer. Using a combination of the switching characteristic information as well as the DC characteristic curves it was determined that for 100 µs square pulses the devices could operate without failure up to 2.0 kA for an extended amount of time (>> 10,000 shots). Above 2.0 kA the device characteristics degrade rapidly. The cause of this degradation is explored in order to identify the primary failure modes associated with operating these devices at such high current densities. The cause of the observed failures are partially due to packaging breakdown at high currents as well as a permanent reduction in high level lifetime and mobility of minority carriers. Based off the current body of knowledge it is postulated that the observed reduction is due to the formation of stacking faults in the device which serve as deep level traps for the minority carriers.

In this study the current state of 12 kV, N-channel, 4H-Silicon carbide Insulated-Gate Bipolar transistors (IGBTs) was investigated for use in high voltage and high power applications. These next-generation switches offer many potential benefits to the Army including cost, weight, and space reductions in power electronics as well as an increase in mission capabilities. Silicon carbide provides superior electrical, thermal, and mechanical properties at high voltages, but its fabrication process is relatively new in comparison to silicon. For this work, two methods were used to understand the IGBT’s internal operation, to identify failure mechanisms, and to quantify the device’s performance. The first method involved the creation of a calibrated, physics-based model for device and circuit simulations. The second method involved the development of high voltage infrastructure to enable the collection of laboratory parametric measurements. The impact of this study will be advantageous to the development of robust devices, the creation of new applications, and the improvement of current processes and circuit designs.

This paper explores the implementation of functional relationship variables in Discrete Event Simulation (DES) programming through the integration of outside programs such as MATLAB and Excel, along with innovative Arena programming in Arena simulation programs. Discrete event programming depends on and is most easily used when variables in a system are represented by common probability density functions such as exponential or Poisson. However, real world systems many times have variables that can not be accurately represented by these probability density functions but are functionally related to factors inside the simulation, such as queue length; and outside the simulation, such as temperature or tides. Using outside programs to model these functional variables greatly eases programming time in relation to attempting the same variable implementation in Arena alone and results in much greater simulation accuracy and usefulness in decision making.

The VPX based data acquisition and processing system is a 3U OpenVPX based embedded computer that has been specifically designed for instrumentation and signal processing applications. It has features that make it ideal for use in high speed data acquisition, data streaming and real time data processing applications. The development of this project involved step by step modular debugging. The debugging process helped in identifying and isolating the problems in the VPX system. The thesis explains stepwise procedure of the design, development and debugging of the project, VPX based data acquisition and processing system, which was assigned to author during his internship tenure at Innovative Integration.

With the interest in RF (radio frequency) and HPM (high power microwave) directed energy applications growing, rapid capacitor charger technology has advanced to meet the input power management parameters to these systems. Current mode control is seen as a desirable control method for the power inverter to quickly charge the capacitor bank. An analog current mode control platform has been demonstrated at the P3E (pulsed power and power electronics) Laboratory. Engineering design advancements have resulted in optimization for power density. Further developments in current mode control have yielded: 1) a current mode control approach that allows multiple inverters to be stacked for high power (100 kW capability) applications 2) a digital peak current mode control approach that allows for adaptive slope compensation with a reduction of analog peripheral circuitry. The method to handle slope compensation for the peak current mode control has also progressed along with the hardware developments. To artificially adjust the current upslope into the CS pin of the analog IC, the initial use of a BJT emitter follower matured into an op-amp circuit for a more eloquent solution. . The digital peak current mode control was then implemented with a dsPIC controller and demonstrated specifically with a pulse forming network charging application. The digital control method continuously monitors the peak output current and adjusts the current limit with relation to the PWM duty cycle. The continued development of these control methods has led to a digital control platform that shows improvements over the analog method while still providing peak current mode control with stable operation at duty cycles greater than 50%.

This dissertation presents the design insights towards the realization of a fully monolithic ratio frequency (RF) cascode silicon (Si) BiCMOS power amplifier (PA) using the integrated envelope tracking (ET) technique (i.e., an “ET-PA” system). The dissertation begins with the introduction of ET as an efficiency-linearity enhancement technique by demonstrate its operating principle with the RF/analog/digital system co-simulations in SPICE and analytic analysis. The bandwidth and timing mismatch sensitivities are compared between the ET and the envelope-elimination-and-restoration (EER) techniques. A discrete linear-assisted switching envelope modulator is designed to investigate the overall ET-PA system performances using a monolithic SiGe common-emitter PA for broadband 3G/4G cellular signals with high peak-to-average ratio (PAR). The design trade-off of the switching frequency and the bandwidth of the envelope modulator on the ET-PA will be studied carefully to improve the linearity without degrading the overall efficiency. After the design insights for the circuits and the ET-PA system are well-understood, a fully monolithic SiGe BiCMOS cascode ET-PA will be implemented and presented. The proper circuitry topology and envelope shaping method will be investigated to successfully apply the differential cascode SiGe/BiCMOS PA into the ET-PA system. The integrated CMOS envelope modulator is optimized specific to this cascode PA, where its finite bandwidth and switching frequency are considered for achieving a high efficiency with minimal distortion and low spurious noise. Such optimization of the monolithic envelope modulator design for a fully-integrated ET-PA system is novel and different from almost all the works previously published in the literature. Further improvements of the fully monolithic BiCMOS ET-PA will also be carried out by: (1) the combination of ET and transistor resizing techniques for additional efficiency enhancement at the low output power regions for power saving; (2) the integration of the ET technique with the power-combined SiGe PA with an on-chip transformer for higher linear output power; and (3) the design of the monolithic Bipolar-CMOS-DMOS (BCD) envelope modulator for higher voltage and higher power applications. Based on the literature surveys, all the above monolithic ET-PA designs achieved state-of-the-art world record efficiencies for Si-based RF PAs for broadband high PAR signals without needing any predisotortion technique. More work is underway to increase the maximum output linear power to enable this revolutionary silicon-based ET-PA technology into real products space for various handsets and wireless applications.

I am grateful to Dr.Stephen Bayne for taking me as a graduate student early in my Masters. He has been a guide in every sense. His thoughts and insights to Electrical Engineering have only broadened my horizon in Electrical Engineering. His ideas and guidance have been instrumental in publishing three IEEE conference papers during my time here. His belief in my abilities and constant encouragement has made me work harder to achieve my goals. I would like to thank Dr.Michael Giesselmann for accepting to be the co-chair on my committee for my thesis defense. I thank Mr. Jerry Lopez for being a great mentor. He has been an inspiration throughout my Masters. His work ethics and commitment has been a great influence on me. He has set a high benchmark which has left me chasing constantly. Interacting with him has only made me a better person. I thank my friends Chaitanya S.K, Purvi Patni and Sanjar Hussain for encouraging me throughout my Masters. I thank Mr. Sandeep Nimmagadda for helping me with my research and internship. I thank Srividya for being my pillar of strength throughout my Masters. Without her it wouldn’t have been possible to survive the day to day hardships of life in USA. Lastly I would like to thank my parents and Almighty from the bottom of my heart for giving me the opportunity to study in the United States. Without their blessings none of this would have been possible.

High power electronics are approaching their limit with Silicon (Si) semiconductor devices, and a new material will soon be needed to take over in high stress and high temperature environments. Silicon Carbide (SiC) is a newly introduced material that may be the next step for a high power semiconductor material. Testing of this material has been done previously and this is a slightly different approach/continuation of that work. The work done concluded that SiC is a durable material that will be a good solution for high power semiconductor devices. This testing has been done to help further characterize and determine the viability of SiC JFET devices at room temperature and 150°C. The series of tests included are designed to highly stress the device and try to find out if any other properties of SiC are different from Si. The tests performed on these devices are millions of high current discharges through the devices at room temperature and 150°C. These conditions push the material to its limit and are far beyond what Silicon devices could handle. The results from all the testing is documented and analyzed to better understand how this new material reacts under high stress. The tests concluded that SiC is a very durable material and should be tested further to continue the advancement of the understanding and use of this material.