Jason C. Neely

MPC of Switching in a Boost Converter Using a Hybrid State Model With a Sliding Mode Observer

In this paper, a model of a DC-DC (boost) converter is first expressed as a hybrid/switched/variable-structure system state model for the purpose of applying recently developed hybrid optimal control theory to control switching in a boost converter. Switching control is achieved by forming the embedded form of the hybrid state model, which enables the derivation of a control that solves for the switching function that minimizes a user-defined performance index. This approach eliminates the need to form average-value models and provides flexibility to balance competing objectives through appropriate weighting of individual terms in the performance index. Since, in practical situations, both the source voltage and the load resistance vary with time in unknown and unmeasurable ways, we introduce a sliding mode observer based on an enlarged state model which allows implicit estimation of the unknown variables. The combined optimal switching control and sliding mode observer are applied to a boost converter in which several nonidealities and losses are represented. The results of time-domain simulation and hardware experiments are used to validate and compare the response of the hybrid optimal control-sliding mode observer to that of a traditional current-mode control strategy.

Jumping-droplet electronics hot-spot cooling

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm × 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobic surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22–25 °C air temperature, 20%–45% relative humidity) to determine the effect of gap spacing (2–4 mm), electric field (50–250 V/cm) and app...

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.

Damping of inter-area oscillations using energy storage

Low frequency inter-area oscillations have been identified as a significant problem in utility systems due to the potential for system damage and the resulting restrictions on power transmission over select lines. Previous research has identified real power injection by energy storage based damping control nodes as a promising approach to mitigate inter-area oscillations. In this paper, a candidate energy storage system based on UltraCapacitor technology is evaluated for damping control applications in the Western Electric Coordinating Council (WECC), and an analytical method for ensuring proper stability margins is also presented for inclusion in a future supervisory control algorithm. Dynamic simulations of the WECC were performed to validate the expected system performance. Finally, the Nyquist stability criteria was employed to derive safe operating regions in the gain, time delay space for a simple two-area system to provide guaranteed margins of stability.

An economical diesel engine emulator for micro-grid research

The electric power grid is evolving into a state that has yet to be defined. Renewable and other distributed energy sources cannot be economically and reliably integrated into the existing grid because it has been optimized over decades to support large centralized generation sources. Thus, the problem of achieving greater penetration of renewable energy has sparked fervor in research to improve reliability and reduce cost. Herein, we consider the problem of accomplishing hardware verification on Micro-Grids with dispatchable (diesel-engine or other combustible) generators. A significant hurdle to evaluating newly developed control and optimization schema can be the experimental validation in hardware. Given the hazards, expense, and space requirements of operating a combustion engine, this paper provides a simple and reliable alternative that is suitable for university and other space-constrained laboratories that wish to extend and validate their ideas for renewable energy integration.

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.

Wind generation controls for damping of inter-area oscillations

Inter-area oscillations are one of the factors that limit transmission capacity in large interconnected systems. In this paper we investigate the effects of increasing wind generation on inter-area modes and propose the use of additional control schemes for wind plants for mitigation of inter-area oscillations. Control schemes include droop control and inertial emulation, which are originally aimed at improving transient stability. The sensitivities of inter-area modes to droop control and inertial emulation gains are identified. Implementation of suggested controls schemes via collocated energy storage devices is also explored.

Generation-After-Next Power Electronics: Ultrawide-bandgap devices, high-temperature packaging, and magnetic nanocomposite materials

A new generation of power electronic conversion systems is being enabled by wide-bandgap (WBG) devices. Applications in both the civilian and defense sectors are already beginning to benefit from the improved size, weight, and power (SWaP) now being demonstrated in power converters utilizing silicon carbide (SiC) and/or gallium nitride (GaN) switches, and numerous manufacturers are offering various types of switching devices fabricated from these two WBG semiconductors.

Small signal stability of the western North American power grid with high penetrations of renewable generation

The goal of this effort was to assess the effect of high penetration solar deployment on the small signal stability of the western North American power system (wNAPS). Small signal stability is concerned with the system response to small disturbances, where the system is operating in a linear region. The study area consisted of the region governed by the Western Electricity Coordinating Council (WECC). General Electrics Positive Sequence Load Flow software (PSLF®) was employed to simulate the power system. A resistive brake insertion was employed to stimulate the system. The data was then analyzed in MATLAB1® using subspace methods (Eigensystem Realization Algorithm). Two different WECC base cases were analyzed: 2022 light spring and 2016 heavy summer. Each base case was also modified to increase the percentage of wind and solar. In order to keep power flows the same, the modified cases replaced conventional generation with renewable generation. The replacements were performed on a regional basis so that solar and wind were placed in suitable locations. The main finding was that increased renewable penetration increases the frequency of inter-area modes, with minimal impact on damping. The slight increase in mode frequency was consistent with the loss of inertia as conventional generation is replaced with wind and solar. Then, distributed control of renewable generation was assessed as a potential mitigation, along with an analysis of the impact of communications latency on the distributed control algorithms.