Steven F. Glover

Fiber-Optically Controlled Pulsed Power Switches

The development and testing of fiber-optically controlled trigger generators (TGs) based on high gain photoconductive semiconductor switches (PCSSs), constructed from high resistivity GaAs, are described in this paper. The TGs are optimized to trigger the high voltage switches (HVSs) in pulsed power systems, where they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total system output. Future pulsed power systems are even more dependent on triggering, as they consist of many more HVS and, in some cases, produce shaped pulses by independent timing of the HVS. The goal of the PCSS TG is to improve timing precision and replace high voltage trigger cables or line-of-sight optics with fiber-optic trigger control. The PCSS trigger has independent EMP-free timing control via 200-mum-diameter optical fibers. This design is simpler than other TG because optical isolation allows PCSS triggers to be remotely located near the HVS at any voltage. PCSS can improve the performance of prime power HVS, diverters, and diagnostics by supplying trigger pulses with subnanosecond jitter and rise time that are more precise and easily adjusted than the conventional TG. For pulse-charged HVS, the PCSS TG can generally derive their trigger energy from the stray fields of the HVS. High gain PCSS capabilities for producing pulsed power TG have been demonstrated previously (not all simultaneously): 220 kV, 8 kA, 350-ps rise time, 100-ns pulsewidth, 50-ps rms jitter, and 10-kHz repetition rate. Furthermore, PCSS has previously triggered a 300-kV trigatron with 100-ps rms jitter.

The advanced microgrid. Integration and interoperability

This white paper focuses on “advanced microgrids,” but sections do, out of necessity, reference today’s commercially available systems and installations in order to clearly distinguish the differences and advances. Advanced microgrids have been identified as being a necessary part of the modern electrical grid through a two DOE microgrid workshops, 1 ’ 2 the National Institute of Standards and Technology, 3 Smart Grid Interoperability Panel and other related sources. With their grid-interconnectivity advantages, advanced microgrids will improve system 4 energy efficiency and reliability and provide enabling technologies for grid-independence to end-user sites. One popular definition that has been evolved and is used in multiple references is that a microgrid is a group of interconnected loads and distributed-energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode. Further, an advanced microgrid can then be loosely defined as a dynamic microgrid. The value of microgrids to protect the nation’s electrical grid from power outages is becoming increasingly important in the face of the increased frequency and intensity of events caused by severe weather. Advanced microgrids will serve to mitigate power 1 “DOE Microgrid Workshop Report,” Office of Electricity Delivery and Energy Reliability Smart Grid R&D Program, http://energy.gov/oe/downloads/microgrid-workshop-report-august-2011, Aug 2011. 2 “DOE Microgrid Workshop Report,” Office of Electricity Delivery and Energy Reliability Smart Grid R&D Program, http://energy.gov/oe/downloads/2012-doe-microgrid-workshop-summary-report-september-2012, Sep 2012. 3 SGIP webpage for applicable Smart Grid Interconnections, http://www.sgip.org/#sthash.6Gcyft6W.dpbs. 4 “DOE Microgrid Workshop Report,” Office of Electricity Delivery and Energy Reliability Smart Grid R&D Program, http://energy.gov/oe/downloads/2012-doe-microgrid-workshop-summary-report-september-2012, Sep 2012. disruption economic impacts. 5 Advanced microgrids will contain all the essential elements of a large-scale grid, such as the ability to (a) balance electrical demand with sources, (b) schedule the dispatch of resources, and (c) preserve grid reliability (both adequacy and security). In addition to these basic features, an advanced microgrid will also be able to interact with, connect to, and disconnect from another grid. An advanced microgrid is aptly named “micro” in the sense that a power rating of 1 MW (plus or minus one order of magnitude) is approximately a million times smaller than the U.S. power grid’s peak load of 1 TW. Some of the complexities required for a large grid such as complicated market operation systems, state estimation systems, complex resource commitment, and dispatch algorithms will be simplified. New advanced microgrids will enable the user the flexibility to securely manage the reliability and resiliency of the system and connected loads. By shifting resources and partitioning the systems in different configurations, a system-survival resiliency essentially is created. System owners can then optimally use system resources to address threats and potential consequences, and even respond to short-time-frame priority changes that may occur. Whether the primary driver for establishing a microgrid is cost saving, surety, or reliability, benefits will accrue to the system owner.

Genetic Optimization for Pulsed Power System Configuration

Pulsed power systems traditionally have been designed to provide a pulse that is nonprogrammable or requires hardware modifications to adjust the output shape. Advancements in pulsed power technologies are enabling system designs that allow for greater flexibility such as programmable current shaping. Material science, which uses current pulse shaping to obtain data for Equation of State (EOS) analysis, is driving much of this work. Programming of pulsed power systems through the use of a simulation and a manual curve fitting approach can work well for systems that only have a few controllable parameters and simple spectral content. Complex systems with many controllable parameters become unmanageable from a manual trial-and-error perspective. This paper discusses an approach to the optimization of a current adder output using genetic algorithms. The approach to system programmability presented herein will allow for a more simplified user interface and system control as the requirements for flexibility and complexity in future systems increase.

Hamiltonian control design for DC microgrids with stochastic sources and loads with applications

To achieve high performance operation of micro-grids that contain stochastic sources and loads is a challenge that will impact cost and complexity. Developing alternative methods for controlling and analyzing these systems will provide insight into tradeoffs that can be made during the design phase. This paper presents a design methodology, based on Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) [1] for a hierarchical control scheme that regulates renewable energy sources and energy storage in a DC micro-grid. Recent literature has indicated that there exists a trade-off in information and power flow and that intelligent, coordinated control of power flow in a microgrid system can modify energy storage hardware requirements. Two scenarios are considered; i) simple two stochastic source with variable load renewable DC Microgrid example and ii) a three zone electric ship with DC Microgrid and varying pulse load profiles.

Pulsed- and DC-Charged PCSS-Based Trigger Generators

Prior to this research, we have developed high-gain, GaAs, photoconductive semiconductor switches (PCSSs) to trigger 50–300 kV high voltage switches (HVSs). We have demonstrated that PCSSs can trigger a variety of pulsed power switches operating at 50–300kV by locating the trigger generator directly at the HVS. This was demonstrated for two types of DC-charged trigatrons and two types of field distortion mid-plane switches, including a ±100 kVDC switch produced by the High Current Electronics Institute (HCEI) used in the linear transformer driver. The lowest rms jitter obtained from triggering a HVS with a PCSS was 100 ps from a 300 kV pulse-charged trigatron. PCSSs are the key component in these independently timed, fiber-optically controlled, low jitter trigger generators (TGs) for HVSs. TGs are critical sub-systems for reliable, efficient pulsed power facilities because they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total system output. Future facility scale pulsed power systems are even more dependent on triggering, as they consist of many more triggered HVSs and produce shaped-pulses by independent timing of the HVSs. As pulsed power systems become more complex, the complexity of the associated trigger systems also increases. One means to reduce this complexity is to allow the trigger system to be charged directly from the voltage appearing across the HVS. However, for slow or DC charged pulsed power systems this can be particularly challenging as the DC hold off of the PCSS dramatically declines. This paper presents results seeking to address HVS performance requirements over large operating ranges by triggering using a pulsed charged PCSS based TG. Switch operating conditions as low as 45% of self break were achieved. A DC charged PCSS based TG is also introduced and demonstrated over a 39 kV – 61 kV operating range. DC charged PCSS allow the TG to be directly charged from slow or DC charged pulsed power systems. GaAs PCSSs and neutron irradiated GaAs (n-GaAs) PCSSs were used to investigate the DC charged operation.

Genesis: A 5-MA Programmable Pulsed-Power Driver for Isentropic Compression Experiments

Enabling technologies are being developed at Sandia National Laboratories to improve the performance and flexibility of compact pulsed power drivers for magnetically driven dynamic materials properties research. We have designed a modular system capable of precision current pulse shaping through the selective triggering of pulse forming components into a disk transmission line feeding a strip line load. The system is comprised of two hundred and forty 200 kV, 60 kA modules in a low inductance configuration capable of producing 250–350 kbar of magnetic pressure in a 1.75 nH, 20 mm wide strip line load. The system, called Genesis, measures approximately 5 meters in diameter and is capable of producing shaped currents greater than 5 MA. This performance is enabled through the use of a serviceable solid dielectric insulator system which minimizes the system inductance and reduces the stored energy and operating voltage requirements. Genesis can be programmed by the user to generate precision pulse shapes with rise times of 220–500 ns, allowing characterization of a range of materials from tungsten to polypropylene. This paper provides an overview of the Genesis design including the use of genetic optimization to shape currents through selective module triggering.

Genetic Optimization for Pulsed-Power System Configuration

Pulsed-power systems traditionally have been designed to provide a pulse that is non programmable or requires hardware modifications to adjust the output waveform shape. Advancements in pulsed-power technologies are enabling system designs that allow for greater flexibility such as programmable current shaping. Material science, which uses current pulse shaping to obtain data for the equation of state analysis, is driving much of this work. The programming of pulsed-power systems through the use of simulations and manual curve fitting techniques can work well for systems that only have a few controllable parameters and are generating waveforms with simple spectral content. Complex systems with many controllable parameters become unmanageable for manual trial and error to be effective. This paper discusses the characterization and modeling of a scaled down programmable current adder directed at investigating technical issues that will be encountered in full-scale drivers. A discussion of the procedure used to optimize the adder current output, using genetic algorithms, is presented. The approach to system programmability presented in this paper will allow for a more simplified user interface and system control, as the requirements for flexibility and complexity in future systems increase.

Wind turbine emulation for intelligent microgrid development

Wind is being aggressively pursued as a potential source of renewable electric power. However, the principal difficulty when integrating wind power into the utility is one of controls. Regulating a power system to provide balance between source and load is challenging when a significant amount of generation is produced by variable sources. This has sparked a wave of research into the development of controls for microgrids with high renewable penetration levels. However, generating repeatable experiments for a system that includes wind power is not straightforward. In this paper, a simple methodology for implementing an 11-kW wind turbine emulator without a torque sensor is presented for supporting microgrid research. In particular, the direct-torque-control feature of a commercial induction motor drive with brake resistor is used, and the torque reference is generated using an industrial computer. Simulation results are presented.

Secure Scalable Microgrid Test Bed at Sandia National Laboratories

High penetration levels of stochastic renewable sources introduce variability into power systems that result in voltage and frequency regulation difficulties. As the cost of fossil fuels increase and governments mandate large renewable-energy portfolios, new engineering approaches will be necessary to compensate for this variable generation. Today renewable energy penetration levels are often limited by using curtailment, by installing additional fossil-fuel-based generation, or by installing expensive energy storage. Recent research focused on mitigating regulation challenges include: advanced sensing, storage, and controls. This paper introduces a new research facility at Sandia National Laboratories dedicated to the development of tools for designing and implementing adaptive, secure, scalable, microgrids with high penetration levels of stochastic renewables.

Genesis: A 5 MA programmable pulsed power driver for Isentropic Compression Experiments

Enabling technologies are being developed at Sandia National Laboratories to improve the performance and flexibility of compact pulsed-power drivers for magnetically driven dynamic materials properties research. We have designed a modular system that is capable of precision current pulse shaping through the selective triggering of pulse-forming components into a disk transmission line feeding a strip line load. The system is composed of 240 200-kV 60-kA modules in a low-inductance configuration that is capable of producing 250-350 kbar of magnetic pressure in a 1.75-nH 20-mm-wide strip line load. The system, called Genesis , measures approximately 5 m in diameter and is capable of producing shaped currents that are greater than 5 MA. This performance is enabled through the use of a serviceable solid-dielectric insulator system which minimizes the system inductance and reduces the stored energy and operating voltage requirements. Genesis can be programmed by the user to generate precision pulse shapes with rise times of 220-500 ns, allowing characterization of a range of materials from tungsten to polypropylene. This paper provides an overview of the Genesis design, including the use of genetic optimization to shape currents through selective module triggering.