Multi-Port Bi-Directional Resonant Solid State Transformer (GR-16-06)

 

 

Principal Investigator: Dr. Adel Nasiri

There is a shift in the decades-old paradigm of energy generation and distribution. The emerging concept includes new elements such as Distributed Generations (DG), energy storage, DC systems, and power electronics-based systems. The conventional 60Hz transformers cannot meet the flexibility and controllability demanded by this new paradigm. The goal of this project is to develop the concept for an efficient medium voltage Solid State Transformer (SST) to enable smart and reliable Distribution Systems (DS) for grid power. Many researchers have worked on the SST concept. However, this enabling technology did not make a significant penetration into the utility grid due to several drawbacks: low efficiency, low voltage/power capabilities, cost and resilient packaging of enabling high band gap devices, and concerns regarding fault protection.

The objective of this project is to use Medium Voltage (MV) Wide Band Gap (WBG) devices (i.e. SiC switches and diodes) to increase both SST voltage and power so it can be applied at the DS level. In addition, a novel resonance feature has been added to the SST concept to significantly increase its conversion efficiency. This resonant operation along with proper controls enables usage of low cost no-load disconnects or breakers for system fault protection. Detailed analyses of the proposed system will be performed both for the power electronics system design as well as application and integration in a DS.

There is an impending need in future electrical distribution systems for flexible, controllable, compact, and efficient medium voltage transformers. There are many opportunities for commercialization for the proposed system if the efficiency can be increased to 98%-99%. Potential applications include all of the utility distribution systems, microgrids, AC/DC networks, DC data centers, etc.

Presentation Materials

Fault Protection and Coordination in a DC Community Microgrid (GR-16-05)

Principal Investigator: Dr. Robert Cuzner

Community microgrids have emerged as an alternative to address the rising societal demands for electric infrastructures that are able to provide premium reliability and power quality levels while at the same time being economically and environmentally friendly.  The focus of this project is a community microgrid that supplies electricity to a group of houses within a neighborhood or several connected neighborhoods in close proximity. Such a system provides a unique opportunity for every day consumers to take advantage of renewable energy resources, such as solar through shared use.

Further benefit comes through inter-connection of DC enabled smart homes which have the best chance of driving towards net zero energy usage.  The benefit of DC interconnection of homes through a microgrid is lower cost and less complex integration of multiple shared energy sources and integration with energy storage.  However, the most significant roadblock to such systems is the availability of safe and reliable protective distribution equipment. In conventional AC distribution, fault current is limited by the source impedance of the upstream distribution feed and the closer a fault is to that feed, the higher the fault current will be.  Radial distribution of circuit breaker protected branches from the transformer feed to a house and then to the individual loads provides is a time-proven method for isolating a fault closest to its location.  A DC fed home has very different characteristics when fault behavior is considered, especially if the DC distribution includes multiple sources of power such as Solar PV, Battery back-up and DC converted utility feed.

If a near zero-ohm fault is suddenly applied, the fault characteristic is dominated by energy storage on the bus and inter-connecting cables. So effective DC protective circuits must be able to discern faults and isolate them from the rest of the system on the order of microseconds. The purpose of this project is develop and test solid state circuit breaker based radial distribution systems that can act to isolate faults with minimal need for sensing circuitry and without inter-device communications.  A unique approach is proposed which utilizes normally-on Wide Band Gap (WBG) Silicon Carbide (SiC) JFET or Gallium Nitride (GaN) HEMT devices as the fault interrupting solid state switch and a fast-starting isolated DC/DC converter as the protection driver.

The new SSCB detects short circuit faults by sensing its drain-source voltage rise, and draws power from the fault condition to turn and hold off the SiC JFET. This new circuit breaker technology offers a reaction time of 1-2μs, about 10X faster than any previously reported solid state circuit breakers and 10,000X faster than any mechanical circuit breakers.

Presentation Materials

A High Power Real-time Photovoltaic Source Simulator (GR-16-04)

Principal Investigator: Dr. Roy McCann

High power, e.g., 1 MW, photovoltaic (PV) source simulators can be utilized to evaluate the performance and study the grid integration issues of the utility scale PV inverters in the laboratories. However, due to the high cost of commercial PV simulators at MW level, which are usually programmable DC power supplies, this testing capability is not common in public testing facilities. In this project, a hybrid PV simulator is proposed to emulate PV arrays up to MW scale.

The reference curves can be either generated by using an actual PV cell to ensure the high fidelity, or obtained by using model based methods, such that repeatable results can be produced. The power stage will consist of a grid-connected active front end and an interleaved dc-dc converter. A novel sliding mode controller will be developed to ensure the reference tracking performance and the bandwidth of the PV simulator. Both hardware-in-the-loop simulation and experimental studies will be performed to validate the effectiveness of the proposed PV simulator.

Presentation Materials

Distributed Power Quality Improvement using Power Electronics and Digital Signal Processing (GR-16-03)

 

Principal Investigator: Dr. Herbert Ginn

This project addresses power quality improvement for compensation of non-periodic load currents using sharing among distributed power electronic converters. A new technique is under development for load power quality improvement using three co-located power quality conditioners. Using simulation based on real-world data, compensator control methods have been developed for compensation and power quality improvement of highly distorting loads, such as those found in steel mills.

The compensator consists of three co-located devices with different calculation windows, called fast compensator, reactive compensator, and slow compensator. Each one of them is responsible for the compensation of one phenomenon in the non-periodic current: sharp edges, reactive current, and low frequency modulation, In order to improve the flexibility of the technique, a fuzzy based adaptive window is used for the slow compensator to find the optimum window for different load characteristics. In the current stage of this project a prototype demonstrator is under construction for experimental validation of the proposed method.

Presentation Materials

High Step-Up/Down Transformerless Modular-Multilevel DC-DC Converter (GR-16-02)

Principal Investigator: Dr. Roy McCann

This project develops and builds a high step-up/down transformerless dc-dc modular multilevel converter (MMC) that would be applicable to MV distribution-level power systems. The design achieves high voltage ratios for interfacing renewable energy sources such as photovoltaic, wind turbine and line interactive UPS systems. The converter uses an MMC approach operating in resonant mode in order to improve overall efficiency. This topology operates to step-up the input voltage with 1:10 or larger conversion ratio.

As a bidirectional converter, it also provides step-down capability at the same voltage ratio (10:1 or greater). By eliminating the presence of a magnetic core transformer as used in conventional designs, this project provides a small, low-cost, direct, and simple solution for high step-up/down converters while meeting the safety and isolation requirements given by IEC and UL standards.

Presentation Materials

PMU Role in Evaluating PV Generation Impact on Transmission Grid (GR-15-05)

 

Principal Investigator: Dr. Roy McCann

The increasing adoption of MW utility scale solar photovoltaic (PV) arrays presents challenges to existing electrical distribution systems. Large scale solar PV arrays may be located in areas where the feeder design was based on unidirectional power flows. With distributed PV generation, there may be disruptions to systems protection and compensation equipment.

This project investigates the use of distribution-level phasor measurement units to monitor and control distribution systems that include large PV sources in order to develop methods of mitigating voltage disruptions. The result is an understanding and recommendation for the use of real-time PMU information to control the local distribution and transmission system using FACTS and D-FACTS equipment to compensate for the effects of solar PV generation.

Presentation Materials

Mobile Power Substations (GR-15-03)

 

Principal Investigator: Dr. Juan Balda

Developing power grids that are resilient under disruptive events is one of the main objectives of electric utilities. A light-weight mobile power substation connecting two distribution feeders having different voltage levels would be a useful piece equipment to be deployed under emergency conditions. To this end, the main goal of this project is to evaluate potential designs for a mobile power substation characterized by its light weight so it can be transported in a single truck to interface two medium-voltage distribution systems operating under emergency conditions. The research team would evaluate arrangements providing electric isolation or not. Electric isolation will be implemented through the use of a medium-frequency transformer. Initial research will be centered on the modular multilevel converter (MMC) used in HVdc terminals since it may lead to a design with the highest power density.

Presentation Materials

Future Hybrid Microgrids (GR-14-08)

Principal Investigator:Dr.  Alan Mantooth and Dr. Juan Balda 

This project includes the design and construction of a hybrid microgrid prototype. A number of voltage source converters will be built to emulate the components of the hybrid microgrid: DC sub-transmission converter, distributed resources, local generators (combined heat and power) and various loads. The small-scale microgrid prototype will be able to test the algorithm for different operating modes: normal AC grid parallel connected mode, transition-to-island mode, island mode, and AC grid reconnection mode. Future projects based on this work could include a full-scale hybrid microgrid test bed being built at the University of Arkansas. Because the hybrid microgrid has a DC sub-transmission port, it is able to connect to future DC grids. The DC line has the ability of bidirectional power flow so that power from distributed resources in different DC microgrids can be distributed and stored in an optimized way. The proposed hybrid microgrid increases the power reliability by adding the DC line without increasing short-circuit current capability.

Presentation Materials

PV Inverter Control to Sustain High Quality of Service (GR-14-05)

 

Principal Investigator: Andrea Benigni 

High penetration levels of PV power generation can produce significant undesirable effects on distribution networks. The focus of this project is to define strategies for the planning, control, and coordination of PV plants that take into consideration quality of service requirements. Changes in feeder voltage profiles, including voltage rise and unbalance; change in feeder loading, including potential equipment overloading; frequent operation of voltage-control and regulation devices, line voltage regulators, and capacitor banks; reactive-power flow fluctuation due to operation of switched capacitor banks; overcurrent and overvoltage protection misoperation and change in electric losses and power factors are some of the main consequences that can arise due to high levels of PV power production. This project focuses on aspects that affect voltage quality and the related equipment. For example, one of the expected foci of the project will be on mitigating the negative effect on voltage quality and tap changer transformer of fast ramp rates due to cloud fields.

Presentation Materials

Compensation Methods for Non-Periodic Currents

Principal Investigators: Herb Ginn and Charles Brice 

Time-variance of load parameters causes load currents to lose their periodicity with respect to the supply voltage. Switching operations in power systems, arc furnaces and spot welders are examples of loads that draw non-periodic currents. Non-periodicity contributes to a decline in the energy transmission effectiveness and creates negative effects similar to harmonic distortion. However, compensation of non-periodic currents is much more difficult than for harmonic compensation due to the time varying spectra. This project is a pilot study that will investigate properties of non-periodic currents and compensation approaches using the arc-furnace and cycloconverter as test cases. Based on the non-periodic current properties we will investigate the cost effectiveness of non-periodic current compensators for use in power systems considering recent advances in power electronics in conjunction with powerful digital control platforms. The objective of the compensator is to provide a means to remove or reduce the negative impact of non-periodic currents in a three-phase system on the source side of the compensator. Successful completion of this scoping project will lead to understanding of compensation methods and their impact/benefits for non-periodic currents in distribution systems.

Reliability of Grid-Connected Power Electronics - A Case Study

Principal Investigator: Enrico Santi 

The goal of this project is to study the reliability of grid-connected power electronic systems. In recent times there has a been a convergence of power systems and power electronics, with switching converters of ever increasing power levels connected to the grid to perform various tasks such as power conversion (e.g., alternative energy interface to the grid), power quality improvement (e.g., STATCOMs and static VAR compensators), power flow control (e.g., thyristor-controlled series compensators and gate controlled series capacitors), and so on. Reliability is a significant concern for grid-connected power electronics, because traditional grid elements such as transmission lines and power transformers tend to be extremely rugged and have a very long lifetime, so there is a concern that the introduction of power electronics may negatively affect overall grid reliability.

A power electronic system is a complex electro-thermo-mechanical system and therefore many failure mechanisms are possible. The goal of this preliminary investigation is to perform a case study on a commercial product to evaluate power electronics reliability. The case study examines a specific product but the ultimate goal is to generalize the results and develop general guidelines and methodologies to study reliability of grid-connected power electronics systems.

Transmission Planning Improvements with Probabilistic Convex PCH Models

Principal Investigator: Roy McCann 

This project develops a method for analyzing electric transmission and generation systems that incorporates aspects of long-term planning models with operational (real-time market and security/thermal constrained) system constraints. Recognizing that optimal power flow problems are generally non-convex, the research considers non-parametric probabilistic (Bayesian) techniques for optimizing planning scenarios with consideration of variable wind generation. In the case of market-based (LIP/LMP) operational cost constraints, a convex optimization method will be investigated. The topic of probabilistic convex optimization methods have been previously developed in the context of machine learning algorithms (e.g., speech recognition, automated VLSI design, etc.) but not for electric power system planning and operations. However, the challenges of optimizing complex systems with uncertain operating conditions under cost constraints have many similarities.

This project benefits member companies whose operations include the real-time electricity markets (LIM/LMP, day-ahead, hour-ahead, 5-minute intervals) by providing planning models that more closely align with actual operating conditions. This will also include the effects of large-scale wind farm generation in optimizing future asset utilization. That is, the intent is to provide improved power flows over transmission lines within their respective thermal/stability/security constraints in order to best support electricity market transactions.

Correcting Current Imbalances in Three-Phase Feeders

Principal Investigator: Juan Carlos Balda (UA)

Important adverse effects of unbalanced loading in three-phase distribution feeders are additional system losses, overheating of feeders and motor loads, and unequal voltage drops. The main goal of this project is to develop an unbalanced-current static compensator (UCSC) for correcting current imbalances in three-phase distribution systems, and thus, overcoming the above adverse effects. The UCSC compensates for both active and reactive components of each phase current. The initial topology will consist of fundamental-frequency (distribution) transformers, H-bridges for AC-DC conversion, and electrolytic capacitors. The research team will explore different topologies in order to determine the most cost-effective option. The development of the control algorithm is one of the most important activities. Each phase of the UCSC injects a compensating current into the distribution feeder independently of the currents injected into the other two phases. The research team will analyze the operation of the USCS as stand-alone equipment or coordinated with the substation power transformer. The first year of the research project will consider the UCSC design for a selected application including simulations to demonstrate the feasibility of the proposed ideas. The second year of the project will seek to develop a prototype.

Solid State Transformers

Principal Investigator: Juan Carlos Balda (UA)

The traditional fundamental-frequency power transformer is a key component in many applications where it is necessary to step up or step down the voltage from one level to another. This operation is done efficiently at the expense of needing a large size/volume. In several new applications, where size or volume is critical, a solid-state transformer may be the key to change the voltage from one level to another at the expense of lower efficiencies and greater system complexity. The main goal of this project is to develop a modular solid-state transformer (SST) for applications demanding space limitations, interconnecting solar or wind farms with the power grid, and improving power quality issues such as high fault currents. Modules are connected in series on the high-voltage (HV) side and in parallel or in series on the low-voltage (LV) side, depending on the selected application. The HV DC side of the SST module consists of a three-level full bridge topology switching under zero-current and zero-voltage switching. The LV DC side could be a two- or three-level full bridge topology depending on the applications. It is envisioned that the high-frequency link operates at about 20 kHz and a high-frequency transformer provides the required voltage ration for the selected application. Initially, the research team will consider SiC 1.2 kV MOSFETs for the HV side that will be packaged by UA. The LV side of the SST could use the same devices but their voltage rating will depend on the selected application. Applications for this prototype are not limited to distribution systems, others like electric train traction will be considered also.

Transient Stability Improvements in Wind Farms Using Filters and PE Devices

Principal Investigator: Enrico Santi (USC)

The goal of this project is to investigate transient stability issues related to wind farms and how these issues can be mitigated through control. Different types of wind farms (type C and type D) will be simulated. Two cases will be considered: without and with FACTS-based series compensation. In the case of no series compensation, modal analysis and time-frequency methods will be used to find the optimal location of damping filters, of the active, passive, or hybrid type. The second case of series transmission line compensation using FACTS devices (TCSCs and GCSCs) will then be examined. Series compensation increases line loadability but introduces resonant modes that cause sub-synchronous resonance (SSR) problems. The project will investigate the design of coordinated controllers for FACTS devices and for the power electronic converters used for wind farm interface to the grid (type C and D) to damp SSR oscillations. The Time-Frequency Technique (TFT) of analysis will be used together with modal analysis to gain additional insight into system dynamics.

Smart Green Power Node Prototype Build

Principal Investigators: Alan Mantooth (UA), Roger Dougal (USC)

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GRAPES Students testing components of the Smart Green Power Node

A “Green Power Node” is a communicative power electronic system that manages the flow of power between (mostly DC) on-site power resources such as generation, storage, and loads, while it also provides a bidirectional interface to a 240 V single-phase residential grid connection that supports smart grid management. Example power sources that may connect to the system include photovoltaic cells or fuel cells. Example storage systems include batteries, either stationary or in a vehicle. Example loads include variable-speed drives in heat pumps, electric vehicles, kitchen appliances and consumer electronics. In the first phase of the project, GRAPES researchers worked to provide a general-purpose node to integrate DC and AC power and load resources in residential power systems and to provide standardized grid-side connection, with the objective of making the system dispatchable from the grid side and uninterruptable on the customer side. Universal and bidirectional power ports on the DC side connect to a variety of power resources. Network data interface for local and grid-area data access is included in the system. In the current phase of the project, researchers are constructing a 2-kW field-testable prototype of the Smart Green Power Node.

Power Packaging

Principal Investigator: Simon Ang (UA)

The first phase of the Power Module Packaging Project concentrated on achieving the high-voltage (10 kV or higher) breakdown requirements of the power electronic modules consisting of two power semiconductor devices. A new dielectric based on the polyamide imide embedded with nanoparticles was developed using a sol-gel method. It was demonstrated that this dielectric could increase the breakdown voltage of the power module. Several power module architectures were also developed; in particular, the concept for a double-sided high-voltage power module. For practical applications in grid-tied power electronic applications, the current-carrying capability of these power electronic modules should be increased. Due to the relatively small current-carrying capability of the wide-bandgap power semiconductor devices, it is necessary to parallel several of these devices in practical power electronic modules. As a continuation of the current SiC power module development effort, researchers will work to improve processing capability of high-voltage SiC power modules through optimized device paralleling.

Power System State Estimation Using Power Converter Front-Ends

Principal Investigators: Roy McCann (UA), Enrico Santi (USC)

This project was a collaborative UA/USC effort on power system state-estimation and power flow control. Development at USC used a power converter to make wideband three-phase impedance measurements at its interface to the power grid. This provided information about harmonic and high-frequency impedances in order to predict harmonic propagation and voltage distortion at various locations on the power network, allowing researchers to identify harmonic polluters and to predict resonances. UA researchers investigated localized power control acting at the distribution level through coordination of power electronic systems with the objective of influencing power flows across the transmission grid. Using impedance information developed at USC, optimization to thermal and stability limits of the existing transmission line and generation infrastructure is achieved through coordination of distribution-level power electronic equipment.

Impact of Grid-Connected Renewable Energy Sources on Power Quality

Principal Investigator: Yong-June Shin (USC)

The contribution of distributed generation to renewable energy sources has been significantly increasing for the past decade. Due to the uncertain nature of renewable energy sources, improper integration or coordination of these sources could be a threat to the power quality of the existing electric power grid. In particular, harmonic distortion will be a significant concern in large offshore wind farms, where the extensive cable system may cause unexpected harmonic resonances of voltage and current.

This project investigated the system-wide power quality management problem of grid-connected renewable energy sources. Among the variety of types of renewable energy sources, this project focused specifically on resolving power quality problems of the grid-connected wind turbine generators (WTGs), which could then be extended to other types of renewable energy sources. This research project included a survey of the existing and/or planned deployment of smart-grid demonstration sites with renewable resources; modeling of renewable energy sources with power electronics for energy conversion, energy storage devices, and harmonic filters; and simulation of grid-connected renewable energy sources.

GaN Optical Isolation for Wide Bandgap Power Electronic Systems

Principal Investigators: Alan Mantooth (UA), Enrico Santi (USC)

There is a need for switching power semiconductor devices that can operate at high voltages, at high temperatures, and at high switching frequencies with low losses. Switching power semiconductor devices fabricated from a wide bandgap material such as SiC or GaN can outperform conventional silicon devices, due to material property advantages. One common problem in grid-connected applications is the need to provide high-voltage isolation of gate drives, while still operating efficiently at the high switching frequencies and high temperatures enabled by wide bandgap devices. This includes optical supply of gate control energy, optical switching of gate potentials, and optical feedback of sensed quantities such as main switch current. Thus protection and current sensing capabilities are an integral part of the proposed interface. The optical coupling was realized using GaN devices that provide superior speed, efficiency and voltage-isolation capability. An additional advantage for GaN power devices is that the proposed drive can be technologically compatible with GaN processes used for power device fabrication, so that eventually a monolithically integrated GaN power device with an optically isolated drive can be realized. This project was funded jointly by GRAPES and an NSF Fundamental Research Grant.

Smart Green Power Node (SGPN) Electronics

Principal Investigators: Alan Mantooth (UA), Roger Dougal (USC)

This project began with the identification of the business case for a (notionally residential) Smart Green Power Node, the requirements for such a node, and the power electronic circuitry and control and communication methods for it. This project was cooperatively developed between USC and UA. A “Green Power Node” is a communicative power electronic system that manages the flow of power between (mostly DC) on-site power resources such as generation, storage, and loads, while it also provides bidirectional interface to a 240 V single-phase residential grid connection that supports smart grid management. Example power sources that may connect to this system include photovoltaic cells or fuel cells. Example storage systems include batteries (stationary or in a vehicle). Example loads include variable-speed drives in heat pumps, electric vehicles, kitchen appliances and consumer electronics.

Industrial Extension of Green Power Node

Principal Investigator: Roger Dougal (USC)

Like the residential SGPN, custom installations are currently needed for customer connections of energy resrouces such as PV, an energy storage system, the electric grid, and traditionally-fueled generation. This project worked to develop the tools needed to build a direct, off-the-shelf power solution that would simplify the deployment of an industrial-sized SGPN. Methods were developed to extend power management concepts developed in the SGPN project to the industrial and commercial scale, including a mix of utility-owned and customer-owned power resources. It developed a means for managing local smart grids and local distributed energy resources to maximize the value of both on-site and grid-supplied power. This work integrated with research in control of distributed energy resources to ensure that the necessary control functions and islanding mode algorithms are supported, with a particular emphasis placed on smooth transitions between modes.

Hybrid Microgrid

Principal Investigator: Juan Carlos Balda (UA)

The objective of this GRAPES project was to coordinate a tightly-coupled battery energy storage unit (BESU) with a diesel or natural-gas synchronous generator (SG) within a microgrid. The BESU and SG are owned by a medium-sized business on a weak (rural) feeder. The SG is used for emergency power but it can be also used for peak shaving. While the SG is running, the microgrid could be isolated from the utility grid, or drawing a small amount of power. This allows for both improvement in power quality and participation in demand response programs. The voltage on the microgrid can be regulated by coordinating the SG and BESU. Several methods that do not require modifying the SG controls were explored for coordination with the objective that any existing SG capable of running grid-paralleled can be used. These include proportional, state-feedback, and feed-forward methods. Models of the components were developed using MATLAB/Simulink™ and coordination methods were implemented to compare them. The feed-forward methods are shown to offer the best real-world performance.

The main conclusions of this research work are the following:
1. Integrating a BESU into a microgrid with primarily synchronous generation can significantly improve power quality when the microgrid is subjected to sudden load or generation changes. This allows the same power quality to be achieved without increasing the amount of synchronous generation operating, resulting in fuel savings.
2. The control scheme used for the BESU is a key factor in obtaining the most benefit from the system. Selecting a good control scheme does not necessarily mean a complex one, as simple feed-forward schemes are shown to have very good performance compared with more complicated alternatives.
In addition to the experimental conclusions, this work yielded benefits in the form of software models of both distributed synchronous generation and distributed inverter-based generation, available to GRAPES members. Ultimately, the project illustrated the benefits of how coordination between different distributed resources improves performance of the system as a whole.

Assessment of Rapid Voltage Collapse Induced by Power Electronics

Principal Investigators: Charles Brice (USC), Yong-June Shin (USC)

Transmission-level power system studies invariably include power-flow analysis for the purposes of ensuring that line and transformer ratings are adequate and to assess the probability of voltage collapse. These power-flow studies are used in transmission planning and in operation of the bulk power system (on-line power flow). Load models are essential, especially if the study concerns voltage collapse. Increasing power electronic front ends (e.g., motor drives) with high control bandwidths may make existing load models inadequate, decreasing situational awareness for operators. In particular, if the load is modeled too simplistically, the model may have drastically different response to a change in the voltage than does the actual load. This project proposes that time-synchronized data acquired by phasor measurement units (PMUs) in conjunction with advanced signal processing techniques ensures that accurate time-varying load models are available for use in voltage stability studies.

Flexible Research Control Platform for Grid-connected Converters

Principal Investigator: Herb Ginn (USC)

This project developed a digital control system for power electronics that interfaces with Power Electronic Building Block (PEBB) type converter power stages in order to provide a flexible and reconfigurable platform for grid-connected converter control development. In addition, a hardware-in-the-loop interface was included in the digital controller in order to allow maximum flexibility for laboratory setups. For example, a set of converters in a back-to-back configuration could be utilized to mimic an energy source such as a PV array or wind turbine system. A control development kit is provided that generates code for the digital control system using a graphical user interface. Common blocks for controls used in grid-connected converter applications are provided.

Power Module Layout Synthesis Tool

Principal Investigator: Alan Mantooth (UA)

This was a multi-year project into the design and implementation of a CAD tool that is used to analyze and optimize the simultaneous electrical, mechanical and thermal issues involved in power module design. This project will focus on the development of algorithms for thermal model abstraction, constrained optimization at the lumped-element level of representation, and layout synthesis of power modules accounting for the electrical parasitic, thermal management issues and mechanical constraints imposed by common substrate materials. As power electronics become more ubiquitous, it is clear that one bottleneck to realization is the ability to design the module to handle parasitics, heat loads, and stresses. This tool will be useful in a huge variety of contexts in power module design and such a capability does not exist today! Design productivity will be enhanced by at least an order of magnitude.

GPS-Based "Smart" Electronic Recloser

Principal Investigators: Yong-June Shin (USC), Herb Ginn (USC)

This project has two primary goals aimed at the design of the next generation of reclosers with enhanced fault detection capabilities and semiconductor switches.

The first goal of this project is to design a detection technique for high impedance faults (HIFs) in distribution networks. HIFs are one of the most challenging types of faults in power system networks, since HIFS don’t produce any significant changes that could be detected using traditional power system protection techniques. In this project, our technical approach is time-frequency analysis (TFA), a well-known tool for investigating transient and stationary signals by simultaneous use of time and frequency. We will apply TFA techniques in order to extract signatures from HIFs. The extracted features will be classified using pattern recognition techniques in order to achieve detection of the HIF. The detection method will be evaluated by means of four criteria: dependability, security, speed and cost. Next we will pinpoint the faulted feeder and locate the HIF using provided time-synchronized voltage and current data in the distribution network.

The second goal of the project is the exploratory scoping of the feasibility, technical competitiveness, and system requirements for a hybrid circuit recloser having both power electronic and mechanical elements. The hybrid recloser could (1) enable controlled current testing of a circuit prior to reclosing, so as to avoid reclosing into a persistent hard fault, and (2) permit soft restart of the disconnected grid segment.

Modular Multilevel Converter for Transmission-Level Battery Storage

Principal Investigator: Roy McCann (UA)

This project investigates the design of a modular multilevel power converter (MMC) for interfacing battery energy storage to the transmission-level electric utility grid. An investigation of appropriate energy storage technologies will be conducted in order to set the parameters for the converter design. The converter will then be optimized in terms of a multi-stage output topology, switching device selection, and DC-DC battery interface. Overall, this provides a basis for developing MW capacity transmission-level modular multi-stage converters. Grid storage technologies will be mainly considered for the functions of frequency regulation, damping of sub-synchronous resonance, voltage support, and reserve capacity. Relative costs, power levels, and charge/discharge profiles will be tabulated and used to establish the range of parameters for a converter that will be suitable for grid-connected energy storage technologies. The project will include the development of an IEEE-style benchmark of a regional transmission system that would benefit from battery storage with an SSSC interface. A prototype SSSC z-source converter will be built and validated based on the analysis and simulations described above.

DC Circuit Protection

Principal Investigator: Roger Dougal (USC)

This project will develop a .5 kV-50 A-scale prototype of a system for protection of branch-circuits and loads in DC power distribution systems. The system was previously demonstrated at small-scale by a former USC researcher. The high-power prototype advances the technology towards an industry-relevant scale. The system protects the distribution wiring against short circuits and overloads and protects the load against power insufficiency or system instability during momentary power outages or voltage sags. This project is cooperatively supported by GRAPES and by USC via a Magellan Scholarship won by the student team performing the work.