Grid Resiliency Lab

Former Graduate Students

Former PhD Students

Parthkumar Bhuvela

  • PhD Graduate, Electrical Engineering, from University of South Carolina, August 2024
  • MS , Electrical Engineering, from Michigan Technological University, 2016
  • B.S., Electronics & Communications Engineering, from National Institute of Technology Surat, 2013
  • Dissertation: DESIGN AND DEVELOPMENT OF DIRECT MEDIUM VOLTAGE SOLAR PV RESONANT INVERTER
Abstract

Title: DESIGN AND DEVELOPMENT OF DIRECT MEDIUM VOLTAGE SOLAR PV RESONANT INVERTER

An inverter is generally employed with MV LFT to connect to the grid in a grid tied PV system. However, in some single-stage topologies, the LFTs are replaced by HFT combined with an unfolder inverter. Generally, these topologies have limited use at high power MV grids due to high switching losses on the primary side. In this study, a direct medium voltage (MV) grid connected solar PV inverter topology is proposed based on LLC resonant converter and high frequency transformer (HFT). Rectified sinusoidal AC output voltage is formed at the converter stage and a line frequency unfolder inverter is utilized to connect to the MV grid. Line frequency MV Unfolder avoids high-speed

switching at MV stage and reduces switching losses are minimized. A combination of phase shift and switching frequency modulation is employed to follow the reference current at the output of the grid. Optimal trajectory based on loss analysis is determined for minimizing losses in the system. Hence, the losses are minimized in three stages compared to existing technology: (1) Compact transformer size resulting into reduced core losses, (2) Reduced switching losses in LLC stage with optimal trajectory using controls, (3) No switching losses in unfolder inverter stage operating at line frequency.

A simple design procedure is proposed for resonant tank components, magnetizing inductance, and output filter components as well. 1/3MW single phase system is designed and the method is verified through line regulation, load regulation and THD simulations in MATLAB/Simulink, A MV HFT is designed, simulated, developed, and verified through experimental results, achieving maximum efficiency of about 98%. A 150kW rated inverter is analyzed with mathematical calculations and compared with existing control methods. The system is successfully tested with peak efficiency of 97.5% and ZVS conditions analyzed at low voltage grid connection. The topology is simulated with MV grid connection in MATLAB/Simulink and a prototype is built for 4.16kV single phase output. Experimental results for ZVS conditions at MV have been carried out.

Ahmad El Shafei

  • PhD Graduate, from University of Wisconsin Milwaukee
  • Dissertation: HIGH POWER, MEDIUM FREQUENCY, AND MEDIUM VOLTAGE TRANSFORMER DESIGN AND IMPLEMENTATION
Abstract

Many industrial applications that require high-power and high-voltage DC-DC conversion are emerging. Space-borne and off-shore wind farms, fleet fast electric vehicle charging stations, large data centers, and smart distribution systems are among the applications. Solid State Transformer (SST) is a promising concept for addressing these emerging applications. It replaces the traditional Low Frequency Transformer (LFT) while offering many advanced features such as VAR compensation, voltage regulation, fault isolation, and DC connectivity.

Many technical challenges related to high voltage stress, efficiency, reliability, protection, and insulation must be addressed before the technology is ready for commercial deployment. Among the major challenges in the construction of SSTs are the strategies for connecting to Medium Voltage (MV) level. This issue has primarily been addressed by synthesizing multicellular SST concepts based on modules rated for a fraction of the total MV side voltage and connecting these modules in series at the input side. Silicon Carbide (SiC) semiconductor development enables the fabrication of power semiconductor devices with high blocking voltage capabilities while achieving superior switching and conduction performances. When compared to modular lower voltage converters, these higher voltage semiconductors enable the construction of single-cell SSTs by avoiding the series connection of several modules, resulting in simple, reliable, lighter mass, more power dense, higher efficiency, and cost effective converter

structures.

This dissertation proposes a solution to this major issue. The proposed work focuses on the development of a dual active bridge with high power, medium voltage, and medium frequency control. This architecture addresses the shortcomings of existing modular systems by providing a more power dense, cost-effective, and efficient solution. For the first time, this topology is investigated on a 700kW system connected to a 13kVdc input to generate 7.2kVdc at the

output. The use of 10kV SiC modules and gate drivers in an active neutral point clamped to two level dual active bridge converter is investigated. A special emphasis will be placed on a comprehensive transformer design that employs a multi-physics approach that addresses all magnetic, electrical, insulation, and thermal aspects. The transformer is designed and tested to ensure the system’s viability.

Garry Jean-Pierre

  • PhD Graduate, Electrical Engineering, from University of Wisconsin Milwaukee
  • MS , Electrical Engineering, from University of Wisconsin-Milwaukee, Milwaukee, WI, 2017.
  • B.S., Electrical Engineering, from University of Wisconsin-Milwaukee, Milwaukee, WI, 2016.
  • Dissertation: DESIGN, CONTROL, AND DEVELOPMENT OF A MULTILEVEL CONVERTER MEDIUM VOLTAGE AC TO LOW VOLTAGE DC FOR FLEET ELECTRIC VEHICLE CHARGE STATION
Abstract

 There is a shift in the technology of vehicles from gas and diesel engines to electric vehicles (EVs). Approximately ten million EVs were available globally in 2020 and it is projected that number will reach 145 million by 2030. To power the increasing number of EVs, the number of EV charging stations is growing at a significant rate. In order to provide flexibility and longer driving ranges to customers, the trend is to install DC fast charging stations. These chargers demand high power at low voltage, which our existing electrical distribution system cannot accommodate without major upgrades. Currently, bulky transformers are used to step down to a lower voltage level in order to directly connect to the medium voltage (MV) utility grid. This results in lowered efficiency and increased cost and size of the charging system.

This dissertation formulates a solution to this significant problem. The proposed work addresses the development of a control scheme and multilevel converter for MV AC to low voltage DC intended for fleet EV charging stations. This architecture removes the shortcomings of the existing systems and offers modular structure, scalability, galvanic isolation, and high efficiency. This topology is investigated for a 1 MW system connected to the 13.8 kV AC grid to create 1 kV DC for EV charging. A robust control structure is proposed for voltage balancing and current sharing among various stages of the converter. The converter and high frequency transformer (HFT) are also investigated for the DC/DC conversion. In order to mitigate power losses, root mean squared (RMS) current minimization and power loss minimization controls are evaluated and the power loss minimization method is found to be superior. A three module single-phase prototype using hardware in the loop (HIL) is developed and tested to verify the viability of the system.

Hadi Akbarihaghighat

  • PhD Graduate, Electrical Engineering, from University of Wisconsin Milwaukee
  • MS , Electrical Engineering, from Sharif University of Technology, Tehran, Iran, 2003
  • B.S., Electrical Engineering, from Amikabir University of Technology, Tehran, Iran, 2001.
  • Dissertation: A DISTRIBUTED CONTROL SYSTEM FOR MICROGRIDS WITH WIDE DYNAMIC RESPONSE COMPONENTS
Abstract

Inverters play a vital part in microgrid operations and control, boosting system flexibility and efficiency. However, their limited physical inertia makes them vulnerable to network-induced oscillations. Research is primarily focused on addressing this by adding inertia to the inverter side. Earlier analysis of stand-alone microgrids utilized pure inverter-based systems with droop control for power sharing among units, and generators were responsible for voltage and frequency control. Inverter-based systems without communication latency have been studied. However, these studies don’t provide a complete dynamic model of microgrids, especially for hybrid microgrids. In this study, a systematic approach is presented to model a hybrid microgrid consisting of one synchronous generator and two inverters operating in two modes. The master inverter is responsible for voltage and frequency control during islanded mode, and setting power values for the generator and slave inverter. It also supports the grid as a voltage source in grid-connected mode. The proposed MG differs from previous studies in its control approach, dynamics, and role of the master inverter for supporting pulse load and communication delay compensation. Power sharing is done via communication, not by droop control, so there’s no need to add inertia to the inverter side. The synchronous generator will use an outer droop loop to adjust power based on valuesiii from the master inverter, while the slave inverter contributes power based on values received from the master inverter. The dissertation presents a state-space model for analyzing hybrid microgrids (MG) with various dynamic components, including a detailed model of generator, two inverters. The model captures the details of the control loops of the generator and inverters, but not the switching action. The energy storage-based inverter controls voltage and frequency, while the generator and slave inverter receive active and reactive power commands from the master inverter. The model also takes into account the effect of communication delay on the control of the hybrid MG. Each sub model is linearized around an operating point and the resulting system matrix is used to derive the eigenvalues. This dissertation focuses on the study of the transient response of a hybrid MG using eigenvalues to indicate the frequency and damping of oscillatory components in both islanded and grid-connected modes Electrical vehicle charger can serve as an example of a hybrid system based on the mentioned topology. This study can generate a platform to analyze such applications and increase the stability and resilience of the system.

Bora  Novakovic

  • Research Focus: RENEWABLE ENERGY
  • Ph.D. Graduate, 2017 from University of Wisconsin Milwaukee
  • B.S., from University of Belgrade, Belgrade, Serbia, 2007.
  • Electrical Engineer
    Rockwell Automation

Mohammad Rashidi

  • PhD Graduate, December 2017, from University of Wisconsin Milwaukee
  • MS, Electrical engineer, from Amirkabir University of Technology (Tehran Polytechnic),Tehran, Iran, 2012.
  • BS, Electrical engineer, from Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran,2010.
  • Dissertation: “DESIGN AND IMPLEMENTATION OF A MULTI-PORT SOLID STATE TRANSFORMER FOR FLEXIBLE DISTRIBUTED ENERGY RESOURCES (DER) INTEGRATION”
Abstract:

Conventional power system includes four major sections, bulk generation, transmission network, distribution network, and loads. The main converter in the conventional electric grid is the low frequency passive transformer providing galvanic isolation and voltage regulation for various voltage zones. In this configuration, small-scale renewable energy resources are connected to the power system at low voltage zones or inside microgrids.

Recent developments in the design of power electronic elements with higher voltage and power ratings and medium/high frequency enable making use of solid state transformer at different voltage levels in the distribution system and microgrid design. In this work, the concept of a MultiPort Solid State Transformer (MPSST) for distribution network application is introduced. MPSST provides a compact, integrated and galvanically isolated multi-port node for microgrid and distribution applications and reduces the number and size of the converters in the concept of efficient smart distribution systems. A new architecture for distribution systems integrating distributed generation (DG) at different voltage zones using MPSST is proposed, studied and simulated. The developed concept interconnects different voltage types and levels using one compact converter with a centralized control logic. Also, a general method is developed and mathematically analyzed to provide active and reactive power support using the local alternative power sources through MPSST.

MPSST is a combination of high-frequency power electronic converters and a multiwinding high-frequency transformer. The total size of the MPSST is dramatically smaller than the conventional transformers with the same voltage and power rating. MPSST also enables online measurement and data collection and active control of the parameters at all connected ports. A two-layer control technique, which is a combination of duty cycle control and a modified phase shift control is used to regulate the voltage and power flow of the different ports. Since the converter has several independent and dependent variables, a transfer matrix between variables of the converter is calculated and used in system control.

Abedalsalam (Salam) Bani-Ahmed

  • PhD Graduate,from University of Wisconsin Milwaukee, December 2017
  • MS, Computer Engineering from Jordan University of Science & Technology, Irbid, Jordan, 2011.
  • BS, Computer Engineering from Yarmouk University, Irbid, Jordan, 2007.
  • Dissertation: “DESIGN AND IMPLEMENTATION OF A TRUE DECENTRALIZED AUTONOMOUS CONTROL ARCHITECTURE FOR MICROGRIDS.”
Abstract:

Microgrids can serve as an integral part of the future power distribution systems. Most microgrids are currently managed by centralized controllers. There are two major concerns associated with the centralized controllers. One is that the single controller can become performance and reliability bottleneck for the entire system and its failure can bring the entire system down. The second concern is the communication delays that can degrade the system performance. As a solution, a true decentralized control architecture for microgrids is developed and presented. Distributing the control functions to local agents decreases the possibility of network congestion, and leads to the mitigation of long distance transmission of critical commands. Decentralization will also enhance the reliability of the system since the single point of failure is eliminated. In the proposed architecture, primary and secondary microgrid controls layers are combined into one physical layer. Tertiary control is performed by the controller located at the grid point of connection. Each decentralized controller is responsible of multicasting its status and local measurements, creating a general awareness of the microgrid status among all decentralized controllers. The proof-of concept implementation provides a practical evidence of the successful mitigation of the drawback of control command transmission over the network. A Failure Management Unit comprises failure detection mechanisms and a recovery algorithm is proposed and applied to a microgrid case study. Coordination between controllers during the recovery period requires low-bandwidth communications, which has no significant overhead on the communication infrastructure. The proof-of-concept of the true decentralization of microgrid control architecture is implemented using Hardware-in-the-Loop platform. The test results show a robust detection and recovery outcome during a system failure. System test results show the robustness of the proposed architecture for microgrid energy management and control scenarios.

Seyed Ahmad Hamidi

  • PhD Graduate, December 2017, from University of Wisconsin Milwaukee
  • MS from K. N. Toosi University of Technology, Tehran, Iran, 2009.
  • BS from Shiraz University, Shiraz, Iran, 2006.
  • Dissertation: DC LINE-INTERACTIVE UNINTERRUPTIVLE POWER SUPPLE (UPS) WITH LEVELING FOR CONSTANT POWER AND PULSE LOADS
Abstract

Uninterruptible Power Supply (UPS) systems are usually considered as a backup power for electrical systems, providing emergency power when the main power source fails. UPS systems ensure an uninterruptible, reliable and high quality electrical power for systems with critical loads in which a continuous and reliable power supply is a vital requirement.  A novel UPS system topology, DC line-interactive UPS, has been introduced. The new proposed UPS system is based on the DC concept where the power flow in the system has DC characteristic. The new DC UPS system has several advantageous with respect to the on-line 3-phase UPS which is extensively used in industry, such as lower size, cost and weight due to replacing the three-phase dual converter in the on-line UPS system with a single stage single phase DC/DC converter and thus higher efficiency is expected.

The proposed system will also provide load leveling feature for the main AC/DC rectifier which has not been offered by conventional AC UPS systems. It applies load power smoothing to reduce the rating of the incoming AC line and consequently reduce the installation cost and time. Moreover, the new UPS technology improves the medical imaging system up-time, reliability, efficiency, and cost, and is applicable to several imaging modalities such as CT, MR and X-ray as well.

Luke Weber

  • PhD Graduate, August 2016, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 2009
  • BS, Electrical Engineering, Marquette University, Milwaukee, Wisconsin, 1985
  • Dissertation:TRANSIENT CONTROL OF SYNCHRONOUS MACHINE ACTIVE AND REACTIVE POWER IN MICRO-GRID POWER SYSTEMS
Abstract

There are two main topics associated with this dissertation. The first is to investigate phase–to–neutral fault current magnitude occurring in generators with multiple zero–sequence current sources. The second is to design, model, and tune a linear control system for operating a micro–grid in the event of a separation from the electric power system. In the former case, detailed generator, AC8B excitation system, and four–wire electric power system models are constructed. Where available, manufacturers data is used to validate the generator and exciter models. A gain–delay with frequency droop control is used to model an internal combustion engine and governor. The four wire system is connected through a transformer impedance to an infinite bus. Phase–to–neutral faults are imposed on the system, and fault magnitudes analyzed against three–phase faults to gauge their severity. In the latter case, a balanced three–phase system is assumed. The model structure from the former case – but using data for a different generator – is incorporated with a model for an energy storage device and a net load model to form a micro–grid. The primary control model for the energy storage device has a high level of detail, as does the energy storage device plant model in describing the LC filter and transformer. A gain–delay battery and inverter model is used at the front end. The net load model is intended to be the difference between renewable energy sources and load within a micro–grid system that has separated from the grid. Given the variability of both renewable generation and load, frequency and voltage stability are not guaranteed. This work is an attempt to model components of a proposed micro–grid system at the University of Wisconsin Milwaukee, and design, model, and tune a linear control system for operation in the event of a separation from the electric power system.

Ashishkumar Solanki

  • PhD Graduate, January 2015, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Gannon University, Erie, PA,2008.
  • BS, Electrical Engineering, from S.P. University, Gujarat, India,2007.
  • Dissertation:VIRTUAL DROOP CONTROL FRAMEWORK AND STABILITY ANALYSES FOR MICROGRIDS WITH HIGH PENETRATION OF RENEWABLES
Abstract

Microgrids can provide the most promising means of integrating large amounts of distributed sources into the power grid and can supply reliable power to critical loads. However, managing distributed sources and loads within a microgrid during island and grid-tie modes and during transitions is a challenge. Stable operation of a microgrid is a concern specifically during the starting of motor loads, switching of large loads, and in presence of high penetration of renewable resources. Hence, a generalized control framework is required to regulate microgrid voltage and frequency, maintain power quality, manage Distributed Generations (DG) and ensure microgrid stability. Several control methods have been developed for microgrid control. Majority of these techniques are based on natural droop control or modified natural droop control, which rely on voltage and frequency variations as inputs to control algorithms. At present, there are no methods available for sizing the capacities needed to ensure reliable operation and stability. A new microgrid control framework, Virtual Droop Control (VDC), for power management as well as for voltage and frequency regulation is proposed in this thesis. The proposed control method analyzes the effect of intermittent resources and dispatches the power commands to individual generation assets ensuring stable operation of the microgrid.

Emad Manla

  • PhD Graduate, August 2015, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from University of Wisconsin-Milwaukee, WI. 2009
  • BS, Electrical Engineering, from the American University of Sharjah, United Arab Emirates. 2006
  • Dissertation:INTEGRATED LI-ION ULTRACAPACITOR WITH LEAD ACID BATTERY FOR VEHICULAR START-STOP
Abstract

Advancements in automobile manufacturing aim at improving the driving experience at every level possible. One improvement aspect is increasing gas efficiency via hybridization, which can be achieved by introducing a feature called start-stop. This feature automatically switches the internal combustion engine off when it idles and switches it back on when it is time to resume driving. This application has been proven to reduce the amount of gas consumption and emission of greenhouse effect gases in the atmosphere. However, the repeated cranking of the engine puts a large amount of stress on the lead acid battery required to perform the cranking, which effectively reduces its life span. This dissertation presents a hybrid energy storage system assembled from a lead acid battery and an ultracapacitor module connected in parallel. The Li-ion ultracapacitor was tested and modeled to predict its behavior when connected in a system requiring pulsed power such as the one proposed. Both test and simulation results show that the proposed hybrid design significantly reduces the cranking loading and stress on the battery. The ultracapacitor module can take the majority of the cranking current, effectively reducing the stress on the battery. The amount of cranking current provided by the ultracapacitor can be easily controlled via controlling the resistance of the cable connected directly between the ultracapacitor module and the car circuitry.

Yogesh Patel

  • PhD Graduate, December 2012, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Illinois Institute of Technology, Chicago. 2003
  • BS, Electrical Engineering, from Maharaja Sayajirao University of Baroda, India. 2000
  • Dissertation: MULTI-LEVEL MEDIUM VOLTAGE INVERTER FOR DC DISTRIBUTED WIND FARM TO ESTABLISH GRID INTERFACE AND PROVIDE ANCILLARY SUPPORT
Abstract

Wind energy has gained in popularity in recent years due to cost, security and environmental concerns associated with conventional energy sources like fossil fuels. However, the utilization of wind energy in power systems creates many technical and non-technical challenges that need to be addressed for successful integrations. The main technical issues related to wind energy are its uncertainty and variability and their impacts on stability, reliability and quality of the electric power. In systems with high wind energy penetrations, unlike conventional generations, sudden changes in active and/or reactive power demand cannot be supported by wind energy. This lack of demand support may create unwanted voltage and frequency variations in the grid. On the hand, the existing AC distributed wind farms have several drawbacks including complexity, higher cost, and lower efficiency.

In this dissertation, a medium voltage direct current (MVDC) distribution system for wind farms is investigated. The proposed system offers higher reliability, lower cost, higher efficiency and more importantly grid support. It also allows for easier integration of energy storage systems at DC level. Design, control, implementation, and testing of a three-level medium voltage inverter are presented. The inverter can provide active and reactive power support to the grid in case of frequency and voltage droops. Simulation and experimental results are presented to verify the viability of the proposed system and control techniques.

Goran Mandic

  • PhD Graduate, July 2012, from University of Wisconsin Milwaukee
  • BS, Electrical Engineering, University of Belgrade, Belgrade, Serbia, 2004.
  • Dissertation: LITHIUM-ION ULTRACAPACITOR ENERGY STORAGE INTEGRATED WITH A VARIABLE SPEED WIND TURBINE FOR IMPROVED POWER CONVERSION CONTROL
Abstract

The energy of wind has been increasingly used for electric power generation worldwide due to its availability and ecologically sustainability. Utilization of wind energy in modern power systems creates many technical and economical challenges that need to be addressed for successful large scale wind energy integration. Variations in wind velocity result in variations of output power produced by wind turbines. Variable power output becomes a challenge as a number of wind turbines integrated into power systems increase. Power variations cause voltage and frequency disturbances that may lead to activation of relay protective equipment, that sense these disturbances, which may result in power outages. While a majority of power produced in modern power systems comes from synchronous generators that have large inertias and whose control systems can compensate for slow power variations in the system, faster power variations at the scale of fraction of a second to the tens of seconds can seriously reduce reliability of power system operation. Energy storage integrated with wind turbines can address this challenge. In this dissertation, lithium-ion ultracapacitors are investigated as a potential solution for filtering power variations at the scale of tens of seconds. Another class of issues related to utilization of wind energy is related to economical operation of wind energy conversion systems. Wind speed variations create large mechanical loads on wind turbine components, which lead to their early failures. One of the most critical components of a wind turbine is a gearbox that mechanically couples turbine rotor and generator. Gearboxes are exposed to large mechanical load variations which lead to their early failures and increased cost of wind turbine operation. This dissertation proposes a new critical load reduction strategy that removes mechanical load components that are the most dangerous in terms of harmful effect they have on a gearbox, resulting in more reliably operation of a wind turbine.

Ravi Nanayakkara

  • PhD Graduate, December 2012, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Marquette University, Milwaukee, WI, 2001.
  • BS, Electrical Engineering, from University of Wisconsin-Milwaukee, Milwaukee, WI, 1997.
  • Dissertation: SCR-BASED WIND ENERGY CONVERSION CIRCUITRY AND CONTROLS FOR DC DISTRIBUTED WIND FARMS
Abstract

The current state of art for electrical power generated by wind generators are in alternating current (AC). The wind farms distribute this power as 3-phase AC. There are inherent stability issues with AC power distribution. The grid power transfer capacity is limited by the distance and characteristic impedance of the lines. Furthermore, wind generators have to implement complicated, costly, and inefficient back-to-back converters to implement AC generation. AC distribution does not offer an easy integration of energy storage. To mitigate these drawbacks with AC generation and distribution, direct current (DC) generation and high voltage direct current (HVDC) distribution for the wind farms is proposed. DC power distribution is inherently stable. The generators convert AC power to DC without the use of a back-to-back converter. DC grid offers an easy integration of energy storage.

The proposed configuration for the generator is connected to a HVDC bus using a 12 pulse thyristor network, which can apply Maximum Power Point Tracking (MPPT). To properly control the system, several estimators are designed and applied. This includes a firing angle, generator output voltage, and DC current estimators to reduce the noise effects. A DSP-based controller is designed and implemented to control the system and provide gate pulses. Performance of the proposed system under faults and drivetrain torque pulsation have been analyzed as well. Converter paralleling when turbines operate at different electrical power levels are also studied. The proposed new Wind Energy Conversion System (WECS) is described in details and is verified using MATLAB®/ Simulink® simulation and experimental test setup. The proposed solution offers higher reliability, lower conversion power loss, and lower cost. The following is proposed as future work. Study different control methods for controlling the SCR’s. Investigate reducing torque pulsations of the PMSG as well as using the proposed power conversion method for DFIG turbines. Explore options for communication/control between PMSG, circuit protection and grid-tied inverters. Investigate the best possible configuration for DC storage/connection to the HVDC/MVDC bus. Study the filtering needed to improve the DC bus voltage at the generator.

Ali Esmaili

  • PhD Graduate,May  2012, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Sharif University of Technology, Tehran, Iran, 2005.
  • BS, Electrical Engineering, from Shiraz (Pahlavi) University , Shiraz, Iran, 2003.
  • Dissertation: ENERGY STORAGE FOR SHORT-TERM AND LONG-TERM WIND ENERGY SUPPORT
Abstract

Wind farm output power fluctuations create adverse effects on the voltage, frequency, and transient stability of the utility grid. Short term wind farm power variations and steep ramp rates cause voltage instability, especially if the farm is located in weak grid areas. In this diisertation, integration of wind energy with energy storage devices to support the short-term shortcomings of wind energy is discussed. A turbine level hybrid configuration of an energy storage system is used to limit the power ramp rate and apply power smoothing. The utilized energy storages devices are zinc bromide flow battery and Lithium-Ion Capacitors (LIC). The actual models of the battery and capacitor, which are derived from testing, are used in this study. The wind farm power is also modeled using measured wind speed data. FCP and ACP as two new concepts have been introduced to evaluate the effect of energy storage system for wind energy support. The analyses show that significant improvements can be made to shape the output power of the farm using practical and turbine level energy storage systems.

Moreover, the dissertation studies a wind farm integrated with a storage device in order to shift the wind power generation to the peak demand periods. A model of system including practical utility level battery integrated with wind farm at wind turbine level is developed and presented. In order to measure the effect of this integration, actual profiles of load, wind energy, and other power sources is studied and the Effective Load Carrying Capability (ELCC) for wind energy, after and before adding the battery, is calculated. Results show that the battery can make some improvements in the ELCC of wind energy.

A wind turbine emulator is built in the lab, and was connected to a storage device, which is tied to the grid. Different tests were conducted at various situations. The wind emulator power data indicates the need for a mechanism to reduce the uncertainty of the wind power. The analysis and figures show that wind power variations and fluctuations can be mitigated using a storage system with a proper control algorithm.

Omar Abdel-baqi

  • PhD Graduate, July 2010, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, in Signal and System, University of Detroit Mercy, Detroit, USA, 2005.
  • BS, in Industrial Automation, Palestine Polytechnic University, Palestine.
  • Dissertation: SERIES VOLTAGE COMPENSATION FOR DOUBLY-FED INDUCTION GENERATOR WIND TURBINE LOW VOLTAGE RIDE-THROUGH SOLUTION
Abstract

Wind is clean and unlimited free source of energy. But in order for the wind energy to be effectively and efficiently harvest without interruption, the wind generators required to ride-through grid disturbances and support the grid during voltage sag events. The Doubly-Fed Induction Generator (DFIG) is known for its poor response to the voltage sags. This work develops an approach to provide a robust ride through technique for the DFIG during different types of voltage sags.
In this work, a mathematical model for the DFIG is developed and used to analyze the voltage sags effects. The DFIG stator flux is the main state that affects the system during the voltage sags. A component of the stator flux declines with the slow time constant of the generator during sudden voltage sag and forces a large rise of current in the rotor windings. This current rise damages double conversion power electronics converter connected to the rotor winding.

The existing techniques for Low Voltage Ride Through (LVRT) solutions have many drawbacks. In brief, they introduce undesirable spikes in generator torque and currents. In addition, they do not provide support to the grid during low voltage conditions.

In order to mitigate the effect of the slow declining component of the stator flux during voltage sags, the system is augmented with a series converter on stator circuitry. The converter injects a voltage on the stator to correct the air gap flux and to ultimately prevent the rotor current rise. A dead-beat control technique is developed to adjust the converter. In addition to the extensive computer simulation, a laboratory scale prototype is developed to validate the proposed solution. The size of the energy storage system required for the converter is also discussed in this thesis.
Future work directions are proposed including more robust control technique, minimizing number of additional parts and bigger laboratory scale prototype.

Tin T. Luu

  • PhD Graduate, December 2010, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, University of Wisconsin-Milwaukee, WI, 2005
  • BS, Electrical Engineering , University of Wisconsin-Milwaukee, WI, 2003
  • Dissertation: TRANSIENT STABILITY IMPROVEMENT FOR DFIG WIND TURBINES USING ULTRACAPACITOR
Abstract

Wind energy source is characterized as variable and unpredictable. A random wind speed and blade rotational turbulence can produce fluctuations on the voltage and power supplied into the system. This fluctuated power makes the wind power undispatchable, causing frequency deviations and power outage when wind power penetration is significant. The fluctuating power will impact on power balance and voltage at the point of common coupling. Output power of wind turbine is cubic function of the wind speed. Since wind speed is a nearly random parameter, the output power of the wind turbine is also random process. Even a small variation of wind speed could cause a large variation in the output power. As a result, a large voltage fluctuation may cause voltage variations outside the regulation limit at connection point.

Energy storage devices such as batteries, ultra capacitors, super inductors, and flywheels can be utilized in a hybrid system to solve this problem. A selective control method to mitigate the power fluctuations using the rotor inertia is introduced in the literature. This method is also modified to obtain better energy capturing efficiency. The energy extracting capability using this method is comparable with other methods such as Maximum Power Extraction (MPE) algorithm. In this thesis, a new integrated topology of DFIG wind turbine and Ultracapcitor is introduced. The Ultracapcitor is directly placed on the DC bus of the power conversion device on the rotor. A control technique is developed to adjust the active and reactive power of the turbine, apply power smoothing, and keep the DC bus voltage within an acceptable range.

Matlab Simulink simulation results for various cases are performed on a doubly fed induction generator that verifies the theoretical analysis.

YounHee Lee

  • PhD Graduate, Aug 2008, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Kookmin University, Seoul, Korea, 198
  • BS, Electrical Engineering , from Polytechnic University, NY, 1994
  • Dissertation: Modeling and Simulation of Conducted EMI Noise Generated in the Electric Power Converters of the Electric and Hybrid Electric Vehicles
Abstract

In developing a complex power electronic system, proper modeling at prototype sample level can save the time and cost to develop final product. Hybrid Electric Vehicle (HEV) is equipped with several high-powered electric devices such as DC/DC converters and DC/AC inverters. Considering that there are many restrictions in mounting and wiring the electric power system in engine room, analysis and modeling of Electromagnetic Interference (EMI) coupling path is crucial in designing optimal electric power system satisfying various EMC regulations. In this thesis, conductive common mode (CM) and differential mode (DM) equivalent models for those electric power converters used in Hybrid Electric Vehicles (HEV) were developed and evaluated through the simulation both in time domain and frequency domain. The simulation results were compared to those of real experimental tests performed in EMC testing Laboratory. It is confirmed that the suggested noise equivalent models followed the actual power electric systems in the point of conducted CM and DM EMI view.

Asghar Abedini

  • PhD Graduate, December 2008, from University of Wisconsin Milwaukee
  • MS, Electrical Engineering, from Sharif University of Technology, Tehran, Iran, 2003.
  • BS, Electrical Engineering , rom Isfahan University of Technology, Isfahan, Iran, 2001.
  • Dissertation: Integration of Permanent Magnet Synchronous Generator Wind Turbines into Power Grid.

Zeljko Jankovic

  • Research Focus: Modeling and implementation of a Microgrid-tie power inventor
  • Ph.D. Graduate 2020, from University of Wisconsin Milwaukee
  • B.S., BS from University of Belgrade, Belgrade, Serbia, 2009.
  • Project Engineer
    Rockwell Automation

Former MS Students

Sidharth Ashok

MS Graduate, May 2014, University of Wisconsin Milwaukee

Thesis: Modeling Ans Protection Scheme for IEEE 34 Radial Distribution Feeder with and without Dirstributed Generation

Abstract

The existing power system was not designed with distribution generation (DG) in mind. As DG penetration is being considered by many distribution utilities, there is a rising need to address many incompatibility issues which puts a big emphasis on the need to review and implement suitable protection scheme. The usual practice for existing distribution feeders is the Overcurrent scheme which includes coordination between fuses and reclosers. But when DG is added to the distribution feeder, the configuration is no more radial as there is contribution of fault currents from the DG’s and if the existing protection scheme is applied then this could lead to various issues like fuse misoperation or nuisance tripping considering temporary and permanent fault conditions.

This thesis presents a study on the modeling of existing IEEE 34 radial distribution feeder and scaling of the system from 24.9kV to 12.47kV keeping in mind the existing conditions and also proposes a protection scheme with and without the addition of DG’s to the feeder nodes. The protection scheme involves providing appropriate relaying with suitable fuse selection and Current transformer settings. Considerations for proper transformer grounding and capacitor bank fusing protection is also simulated and reviewed. When DG’s added, the results show increase in fault contribution and hence causing misoperations which needs to avoided. Relaying considerations are also provided when an islanded mode occurs. The entire analysis has been simulated by a combination of various tools like Aspen One liner, CYMDist and Wavewin with occasional simulations and calculations performed in MATLAB environment.

BS EEE, SASTRA University, India, 2012

Ali Yousef

MS Graduate, June 2011, University of Wisconsin Milwaukee

Thesis: WIND TURBINE ENERGY STORAGE LEVEL FOR LOW VOLTAGE RIDE THROUGH (LVRT)

Abstract

Renewable energy is a green source of energy that is clean, available and sustainable. Wind energy generation has been experiencing the largest growth among renewable sources due to lower cost and advanced technologies. Wind energy power plants or farms need low maintenance and last for long time. The increasing higher penetration of wind energy in the grid has transformed wind energy into major player in grid operation and economics. Wind energy systems now have to participate in grid support and provide ancillary services.

Variable wind speed leads to variable wind power generation, voltage fluctuations, and frequency deviations, which are the main problems related to wind energy integration into grid. These problems become more evident in weak grids. In addition, wind farms have to take the grid problems into consideration and have to provide support during grid instability and transients.In this thesis, a PMSG wind turbine full energy conversion system design and modeling have been performed using Matlab Simulink. The system is a grid integrated and applies MPPT control to extract the maximum power from the wind and utilizes a full conversion circuitry to interface the unregulated generator AC power to the grid. Modules of Lithium-Ion Capacitors (LIC) have been placed on the DC bus in order to support the grid with wind energy power smoothing and LVRT. LICs offer high power density and reasonable energy density. During grid faults, wind energy can be stored in the LICs and discharged into grid as soon as the voltage restored. This feature will support the grid to stabilize the voltage. Detailed modeling of the architecture and controls have been performed to verify the viability of the proposed system.

BSEE from Birzait University, Palestine, 2009

Milad Pashapour

MS Graduate, June 2011, University of Wisconsin Milwaukee

Thesis: WIND TURBINE ENERGY STORAGE LEVEL FOR LOW VOLTAGE RIDE THROUGH (LVRT)

Abstract

With the rapidly growing energy demand and shrinking supply of expendable resources, recently, much attention has been paid to alternative energy sources and more efficient ways of harnessing energy. The Photovoltaic (PV) solar cells can directly convert sunlight to electricity. In this research work, design, simulation, and implementation for utilization of solar PV panels to power a golf cart have been performed. Three PV panels are installed on top of a golf cart and are designed to charge a 36-volt battery system. The maximum power rating of the three panels is 261 watts. This rating is the power output under Standard Test Conditions known as STC. We have also designed and utilized a Maximum Power Point Tracking (MPPT) intelligent controller which is able to vary the voltage of the panel to keep its operating point closer to its maximum output power at different sun irritations.

The actual power gain over a non-MPPT controller with the same panel will vary with conditions, but a 10-30% gain is typical. We are applying a multi-stage charging technique that allows for a fuller battery charge without reducing the battery life or “boiling off” the electrolyte. The battery is held at a higher voltage for a period of time while it gets the full charge, and then the voltage is reduced to provide maintenance charge without overcharging the battery. Temperature compensation avoids excessive electrolyte usage and thermal runaway at higher temperatures and helps compensate for increased internal resistance in the battery at lower temperatures. This results in a longer battery life due to not overcharging at higher temperatures while still preserving full charges at low temperatures.The proposed system has been designed, modeled, implemented and tested. The results are presented and discussed in this thesis. The test results indicate that the installed PV panels can provide enough power for modest usage of the cart.

MSEE University of Tarbiat Modaress, Tehran, Iran, 2005
BSEE University of Polytechnic, Tehran, Iran, 2002

Salaheddin Zabalawi

MS Graduate, December 2008, University of Wisconsin Milwaukee

Thesis: A LINEAR GENERATOR FOR POWERING IMPLANTED ELECTRONIC DEVICES

Abstract

Due to recent developments in power electronics devices and systems, permanent magnet machines are finding many applications in various fields, including automotive systems and renewable energy. These machines provide high efficiency, compact size, robustness, light weight, and low noise. These features qualify them as the best suitable machine for medical applications. The system proposed is a self-contained, small size, and reliable device that can continuously provide power. The proposed linear generator will have two layers of Permanent Magnets (PM) and one layer of coils. It generates power from multidirectional movement. The movement of the device will cause the middle coils layer to move. The relative movement of the coils versus PMs, on two sides, creates a varying flux in the windings. This change in flux produces voltage in the winding and can be converted into electrical power if a load is connected. In order to provide a continuous power source, the muscle used in this system must not stop working. The best option for such a system is to use a muscle that is linked to the respiratory system. Some of these muscles are accessible without having to tap into the windpipes themselves. There are many potential locations in the human body for implantation of the proposed device. The primary target location is the abdominal wall, due to continuous movement, sufficient travel distance and small surgical risks. The output voltage produced by the generator is a very small, alternating-current (AC) waveform, which must be appropriately transformed and rectified for a given load.

BSEE from American University of Sharjah, United Arab Emirates, 2006.

Thomas Laubenstein

MS Graduate, May 2010, University of Wisconsin Milwaukee

Thesis: SPEED AND TORQUE CONTROL OF PERMANENT MAGNET SYNCHRONOUS GENERATORS FOR WIND POWER APPLICATIONS

Abstract

The world is constantly increasing its need for electrical power. Electronic devices are gaining greater popularity throughout the world. Studies show that power consumption will increase over 40% in the next 20 years. As a result new technologies are being investigated to help supply the need for the increased electrical power.

Energy resources are separated into two major groups: Non-Renewable and Renewable. Power production from non-renewable resources has been around for many, many, decades. The most widely used source of non-renewable resources is the coal-fired power plant. Even though coal has been well established it does have some undesired effects on the environment. It tends to add pollution, in the form of “greenhouse gasses”, to the environment and the supply is limited. The concept of producing power from renewable resources has regained popularity in recent years. Hydroelectric power plants have been used all over the world for many years. It is non-pollution and as long as water in the river keeps flowing the source for power will keep replenishing itself. Other forms of renewable energy power production are from wind, solar, and geothermal energy sources. Even though the renewable energy sources are considered to be non-polluting they do have some drawbacks. For example, power production is not always consistent and there are some undesirable impacts to the environment.This thesis investigates one form of renewable energy power production. Wind energy has had an increasing amount of research to support it. This paper investigates maximum power production profile of a wind turbine containing a permanent magnet synchronous generator and implements both speed and torque controls during instances of higher wind speeds. Implementation is supported through simulation results.

BSEE from University of Wisconsin-Milwaukee, 1998.

Eric Biehr

MS Graduate, 2010, University of Wisconsin Milwaukee

Thesis: X-RAY TUBE INDUCTION MOTOR DESIGN OPTIMIZATION TECHNIQUE

Abstract

High power CT X-ray tubes require the use of a rotating target to ensure the focal track is kept below the material’s temperature limit during x-ray generation. The target rotation is driven by a mono or poly-phase induction motor. Modern x-ray tubes vary in envelope size, bearing technology, moment of inertia, and have inherent motor design challenges such as large air gaps and wide temperature operating ranges leading to various motor sizes and performance requirements. An approach to design optimization utilizing Design Analysis of Computer Experiments with consideration for Design Analysis for Cost will be defined and demonstrated on a 3-phase induction motor for an x-ray tube. Multiple X’s (inputs) will be defined from envelope/size limitations, performance requirements, and standard induction motor design considerations. Four Y’s (outputs), including three performance requirements and one requirement to minimize cost, will be optimized through a total of 18,000 potential designs. This parameterized electro-mechanical design optimization achieves the simultaneous objectives of required performance in a small and lower cost package, achieving almost 50% estimated cost reduction.

This paper will present the approach and execution for an optimized induction motor design meeting all requirements, and practical application will be demonstrated experimentally on design prototypes with component level dynamometer bench tests, hence validating the software design tool.

BSEE University of Milwaukee-Wisconsin, 2004

Zoran Vrankovic

MS Graduate, 2006, University of Wisconsin Milwaukee

Thesis: A NOVEL BATTERY CHARGER FOR AUTOMOTIVE APPLICATIONS

Abstract

In this thesis, a new power electronics topology is introduced for battery pulse charging. The topology is based on a bidirectional isolated Cuk converter. The charging method provides positive and negative current and resting periods. This charging method results in less generated heat and longer battery life cycle. Different operating modes of the system and its small signal analysis are presented. The small signal system has been modeled using MATLAB. Simulation results are also provided to validate the mathematical analysis.

Sean Cunningham

MS Graduate,May 2017, University of Wisconsin Milwaukee

Thesis: THEORY, SIMULATION, AND IMPLEMENTATION OF GRID CONNECTED BACK TO BACK-CONVERTERS UTILIZING VOLTAGE ORIENTED CONTROL

Abstract

This work presents a back to back converter topology with the ability to connect two power systems of different voltages and frequencies for the exchange of power. By utilizing indirect AC/AC conversion decoupling is achieved between the power systems with one of the three-phase, two-level voltage source converters performing the AC/DC conversion that maintains the required DC bus voltage level at unity power factor while the other converter operates in all four quadrants supplying/consuming active and/or reactive power with the other power system. The prototype implementation resides at UW-Milwaukee’s USR Building microgrid test bed facility with an emphasis in the design to approach the requirements for harmonic control as recommended by IEEE 519-2014 without power filtering AC capacitors. The challenge in this project was to develop the model based firmware and control for the custom digital signal controller boards interfaced to Rockwell Automation’s PowerFlex 753-Series converters with only a high level knowledge of the proprietary power structure available.

BSEE from University of Minnesota-Twin Cities, 2004.

Md Abdul Gaffar

MS Graduate,May 2018, University of Wisconsin Milwaukee

Thesis: DESIGN OF A HIGH FREQUENCY FOUR PORT TRANSFORMER FOR DC/DC CONVERTERS

Abstract

Large scale integration of renewable energy systems (RES) and energy storage systems (ESS) demands a better connectivity between distributed sources and loads. Multi-port solid state transformer (MPSST) plays a critical role as a joint node to integrate RESs, ESSs, utility grid, and loads. MPSST offers several advantages including independent power flow control on each port, voltage or current regulations, compactness and portability, and galvanic isolation.

This thesis seeks to address some of the remaining challenges of using MPSST. Operation of the converter in closed-loop with phase shift modulation is analyzed for a dual active bridge as the control building block and a four-port DC/DC converter as the MPSST in Ansys Simplorer. The high frequency transformer part was designed and modeled in Ansys Maxwell. The model is validated with FEA simulation and various metrics like flux density (B), current density (J), magnetic field intensity (H), core loss, winding loss were investigated for different operating conditions to evaluate the transformer performance.

A co-simulation between the magnetic environment in Ansys Maxwell, and power electronics and control part in Ansys Simplorer, has been carried out to benefit from the utilization of the developed realistic high frequency transformer for the operation of the MPSST.

BSEE Bangladesh University of Engineering and Technology,2008

Azadeh Mazaheri

MS Graduate, 2015, University of Wisconsin Milwaukee

Thesis: ENERGY EFFICIENCY AND MODELING ENERGY STORAGE FOR BUILDINGS

Abstract

An advanced Energy Storage device modeling, namely, Zinc Bromide, is proposed to integrate a new software Smartbuilds, developed by Marquette University, based on an integrated building. Smartbuilds will provide the platform to integrate all the components of the proposed Building which incorporate with renewable energy and energy storage system. The zinc bromide modeling results show that the battery’s open-circuit voltage is a direct function of the state of charge (SOC) of the battery. Furthermore, resistance is also a function of sate of charge at constant temperature. A Coulomb Counting technique is used to adjust the estimated SOC according to battery current. Simulation studies are made with Matlab/Simulink. Proposed Zinc bromide battery model has been compared with Energyplus, building energy simulation program, battery model and it has been translated to Energyplus battery model to integrate in Energyplus. Example case studies are provided to show the results.

BSEE BS from Islamic Azad University of Najafabad, Najafabad, Iran 2003