J. Curtiss Fox

Introduction to the Clemson University 15 MW Hardware-In-the-Loop Grid Simulator

This paper is an introduction to the implementation of the 15 MW Hardware-In-the-Loop (HIL) Grid Simulator that serves as the corner stone of the Duke Energy Electric Grid Research, Innovation and Development (eGRID) Center. The eGRID Center is collocated with the Wind Turbine Drivetrain Testing Facility (WTDTF) within the SCE&G Energy Innovation Center at Clemson Universitys Restoration Institute in North Charleston, SC, USA. It will be demonstrated how the 15 MW Grid Simulator is able to be utilized in conjunction with either the 7.5 MW or the 15 MW wind turbine dynamometers within the WTDTF, or as a stand-alone test facility. The 15 MW Grid Simulator topology and technical details will be discussed as they relate to grid integration and performance evaluations of medium voltage, multi-megawatt equipment destined for the power system. The system topology consists of a unique combination of state-of-the-art power conversion equipment with passive reactive impedance divider circuits in order to provide a robust solution for fault ride-through evaluations while also having the accuracy and bandwidth to perform power quality evaluations and power hardware-in-the-loop experiments.

A survey on global PV interconnection standards

Photovoltaic energy (PV) is one of the cleanest forms of renewable energy. The popularity of this technology has been widely recognized with the incentives provided by the governments of various countries across the globe. Day by day, the growth rate of PV is steadily increasing. Renewable energy resources like PV are interfaced with power electronic inverters to enable its interconnection to the power system network. The conventional power system becomes more complex with increasing renewable energy interconnections to constitute a smarter grid. As the decentralized generation achieved by PV solar plants becomes more prevalent, the grid reliability becomes an important facet. The ramifications associated with the PV interconnection needs an adherence to reliable operation of the grid without any violations. Interconnection standards are clearly critical. Several organizations and technical committees are constantly involved in research to update and revise such standards on a frequent basis throughout the world. The focus of this paper is to present a consolidated compilation of PV interconnection standards across the globe.

Design, Development, and Commissioning of a Multimegawatt Test Facility for Renewable Energy Research

This paper documents the design, development, and commissioning effort for a multimegawatt mechanical and electrical test facility for renewable energy research. The mechanical test platforms are specifically designed to explore the machine dynamics of wind turbine nacelles. The electrical test areas can be interconnected with the mechanical platforms to facilitate complete mechanical and electrical evaluation of wind turbine performance related to grid code requirements or can be operated independently as multimegawatt test bays for testing and model verification of other devices.

Harmonic resonance repercussions of PV and associated distributed generators on distribution systems

The problems associated with the harmonics needs more attention as more number of distributed generators like PV and wind are integrated into a distribution system. Although the integration presents a lot of benefits, satisfying the needs of local load requirements by reducing the line losses and facilitating congestion management, the problems of power quality that impact the distribution system become a priority. IEEE 519 describes network resonance as a major contributor impacting harmonic levels. LC and LCL filters on the AC side of PV Solar (PV) inverters that are designed to mitigate higher order harmonics tend to interact with the impedance of the entire network by exciting the harmonic resonance modes. Apart from that, wind based induction generators and induction motors are associated with terminal capacitors for voltage support. The interaction of such capacitive elements of distributed generators with the entire system impedance also impact resonance modes. To witness the impact of DGs, a control scheme for a 1.25 MW PV inverter based on hysteresis control with a simple LC filter is designed. This paper will serve as a reference for planning engineers and researchers working towards power quality by addressing the impacts of PV with distribution systems.

Design and validation of a communication and control system for a 20MVA hardware-in-the-loop renewable energy test facility

As the electric grid evolves into the smart grid, the ability to adequately model and test components going on the grid becomes more critical. As such, the role of large scale testbeds capable of testing utility-scale equipment will play an ever increasing role in the development of smart grid technologies. A flexible and robust communication and control system is of paramount importance in the successful operation of such testbeds. This paper describes one approach to control of a large-scale hardware-in-the-loop power system testbed. Clemson Universitys Duke Energy eGRID is a multi-megawatt electric power laboratory combining real time grid simulation capabilities with a highly configurable, medium voltage three phase experimental grid. Control of this laboratory is achieved through the use of real-time hardware, a custom serial communication protocol, and FPGA-based data acquisition.

Real-time modeling of multi-level megawatt class power converters for Hardware-In-the-Loop testing

Hardware-In-the-Loop (HIL) testing using real-time simulation allows system designers to lower risks associated with system integration of new technology. Controller HIL (CHIL) is used here to verify the controller platform of a 15 MW amplifier that will be used as a grid simulator in Power HIL (PHIL) configuration. This allows elements of a smart electrical distribution system to be tested in an anticipated power system in a controlled laboratory environment. Details include a description of CHIL testing with simulation results and experimental results of the hardware implementation with open circuit measurements at the 24 kV experimental bus.

Controller Hardware-In-the-Loop validation of a magnetic core saturation algorithm for fault ride-through evaluations

In conjunction with the development of a wind turbine drivetrain testing facility, a fully configurable 15 MVA Hardware-In-the-Loop medium-voltage electric grid system capable of four-quadrant operation is being designed and installed. To successfully operate this system when performing fault ride-through evaluations, a control algorithm has been developed to prevent saturation of the interface transformers magnetic core. Prior to full implementation of this grid system, the high power components of the system are being evaluated using a real-time digital simulation (RTDS®) environment in order to identify any potential control or interface issues. In this paper, the various modeled components are discussed, the implementation of the feed-forward control algorithm to prevent interface transformer saturation is presented, and finally, the results of a test scenario are shown with and without the saturation control algorithm in place.

Heat generation and failure in padmount transformers due to zero sequence saturation

After a transformer failed following a double phase fault, there was an interest in understanding how the fault mechanism led to the failure. This paper investigate this fault condition in detail and demonstrate the underlying challenges in correcting the failure. The system electrical and thermal models were developed and simulated to analyze the transformer response under double phase fault conditions. Experimental measurements validated the simulation results on a real three phase distribution transformer. This paper presents the results from simulated and experimental analysis from double phase fault on a Yg-Yg distribution transformer.

High speed MW-rated induction motor drive system

Multi-physics design, simulation and analysis studies on an induction motor drive system rated 1 MW 15,000 RPM 4160 V are presented. Component level manufacturability and materials selection have been performed for the high speed application. Litz wire stator coils have been designed to reduce high frequency proximity losses. Prototype stator coils have been manufactured and tested. The various components of the system have been verified experimentally by bench tests. A novel power electronic drive using high power silicon carbide devices for the high speed application is developed. The complete motor and drive are now being manufactured for full load testing with the new dynamometer system at the eGrid Center of Clemson University.

Design and commissioning of 2.5 MW DC supply for evaluating megawatt scale smart solar inverters

Utility scale photovoltaic plants often use megawatt scale central inverters with high efficiency and power density. Inverter manufacturers now offer solutions over 2 MW for 1000 V DC class PV arrays. Certifying inverters at this power level can present test equipment design and procurement challenges. This paper describes a retrofit of an existing medium voltage, 9-level TECO Westinghouse VersaBridge series connected H-bridge (SCHB) inverter to supply DC power up to 2500 A at 1000 V for central inverter testing. Simulations in PLECS and controller hardware-in-the-loop experiments with RTDS were used for initial controller design. The SCHB pulse-width modulation scheme led to an interleaved output stage topology in a six parallel module configuration without requiring modification to the existing VersaBridge controller. Commissioning results are shown along with experimental results for the first inverter test article at 2500 A, 900 V.