Viability in hybrid systems

AbstractHybrid systems are interacting systems of digital automata and continuous plants subject to disturbances. The digital automata are used to force the state trajectory of the continuous plant to obey a performance specification. For the basic concepts and notation for hybrid systems, see Kohn and Nerode (1993), and other papers in the same volume. Here we introduce tools for analyzing enforcing viability of all possible plant state trajectories of a hybrid system by suitable choices of finite state control automata. Thus, the performance specification considered here is that the state of the plant remain in a prescribed viability set of states at all times (Aubin, 1991). The tools introduced are local viability graphs and viability graphs for hybrid systems. We construct control automata which guarantee viability as the fixpoints of certain operators on graphs. When control and state spaces are compact, the viability set is closed, and a non-empty closed subset of a viability graph is given with a sturdiness property, one can extract finite state automata guaranteeing viable trajectories. This paper is a sequel to Kohn and Nerode (1993), especially Appendix II

Comparative Analysis of Parallel vs Series Hybrid Electric Powertrains

In the United States, more than a quarter of greenhouse gas (GHGs) emissions (27%) are attributed to the transportation sector which comprises mainly of vehicles powered by internal combustion engines (ICE). To reduce the dependence on fossil fuels and the resulting GHG emissions associated with conventional ICE vehicles, plug-in hybrid vehicles are being promoted as a viable near-term vehicle technology. This paper is a comparative experimental study of two types of hybrid systems: parallel (also known as plug-in hybrid) and series (also known as extended-range electric) hybrid systems. The two hybrid systems are modelled on an electric bicycle platform and field tested to analyze their performance. The fuel economy was measured and compared in L/100km and the electric powertrain efficiency of the system was measured and compared in watt-hours per kilometer (Wh/km). A sensitivity analysis is carried out in terms of different transmission gear ratios and the variable setpoints in the hybrid control logic to access the impact these factors have on the performance of the hybrid system. This paper focuses only on the technological aspect of the hybrid system and any social and policy aspects associated are not considered. The constructive modeling of the hybrid system, the limitations faced during the process and the results of the field tests are presented

Development of ERAU VOLTRON Hybrid-Electric Powerplant

The energy density of today’s batteries is not high enough for electric powered aircraft to achieve an operationally viable range plus FAA stipulated reserve flight times. Hybrid-electric power generation systems may be able to bridge the gap, providing a way for these aircraft to fly distances not possible with batteries alone. There is a recognition that gasoline-electric hybrid systems can deliver specific energy and specific power that are higher than any currently available battery system. Embry-Riddle Aeronautical University’s (ERAU’s) Eagle Flight Research Center (EFRC) is building a 70+ kW hybrid-electric power generation system using a rotary engine and Permanent Magnet Synchronous Machine (PMSM) & Inverter. The rotary engine will be directly coupled to the PMSM which will generate electrical energy to power multi-rotor eVTOL vehicles. These results will be achieved by utilizing advanced control systems implemented on a National Instruments Compact RIO. Past research conducted at the EFRC demonstrated the ability to design and operate a hybrid-electric powerplant. The VOLTRON project will attempt to create a system with an even higher specific energy but with the compact size and high power characteristics of a rotary engine and eventually alternative fuel flexibility

Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits

Resolving quantum many-body problems represents one of the greatest challenges in physics and physical chemistry, due to the prohibitively large computational resources that would be required by using classical computers. A solution has been foreseen by directly simulating the time evolution through sequences of quantum gates applied to arrays of qubits, i.e. by implementing a digital quantum simulator. Superconducting circuits and resonators are emerging as an extremely-promising platform for quantum computation architectures, but a digital quantum simulator proposal that is straightforwardly scalable, universal, and realizable with state-of-the-art technology is presently lacking. Here we propose a viable scheme to implement a universal quantum simulator with hybrid spin-photon qubits in an array of superconducting resonators, which is intrinsically scalable and allows for local control. As representative examples we consider the transverse-field Ising model, a spin-1 Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically simulate the scheme by including the main sources of decoherence. In addition, we show how to circumvent the potentially harmful effects of inhomogeneous broadening of the spin systems

Influence of Architecture Design on the Performance and Fuel Efficiency of Hydraulic Hybrid Transmissions

Hydraulic hybrids are a proven and effective alternative to electric hybrids for increasing the fuel efficiency of on-road vehicles. To further the state-of-the-art this work investigates how architecture design influences the performance, fuel efficiency, and controllability of hydraulic hybrid transmissions. To that end a novel neural network based power management controller was proposed and investigated for conventional hydraulic hybrids. This control scheme trained a neural network to generalize the globally optimal, though non-implementable, state trajectories generated by dynamic programming. Once trained the neural network was used for online prediction of a transmission’s optimal state trajectory during untrained cycles forming the basis of an implementable controller. During hardware-in-the-loop (HIL) testing the proposed control strategy improved fuel efficiency by up to 25.5% when compared with baseline approaches. To further improve performance and fuel efficiency a novel transmission architecture termed a Blended Hydraulic Hybrid was proposed and investigated. This novel architecture improves on existing hydraulic hybrids by partially decoupling power transmission from energy storage while simultaneously providing means to recouple the systems when advantageous. Optimal control studies showed the proposed architecture improved fuel efficiency over both baseline mechanical and conventional hydraulic hybrid transmissions. Effective system level and supervisory control schemes were also proposed for the blended hybrid. In order to investigate the concept’s feasibility a blended hybrid transmission was constructed and successfully tested on a HIL transmission dynamometer. Finally to investigate controllability and driver perception an SUV was retrofitted with a blended hybrid transmission. Successful on-road vehicle testing showcased the potential of this novel hybrid architecture as a viable alternative to more conventional electric hybrids in the transportation sector

Development and Analysis of a Hybrid Solid Oxide Fuel Cell Microturbine System

Hybrid solid oxide fuel cell microturbine (SOFC-MT) systems present opportunities for improvement over conventional systems, including high electric efficiency, cogeneration, and the potential for low carbon emissions. Hybrid systems require stringent control, however, and competing systems (including non-hybrid SOFC systems) currently generate power reliably and efficiently. In order to advance toward commercialization, hybrid systems need to adopt a control strategy that maintains safe and efficient operation, while also exhibiting favorable exergetic and economic performance. The present work investigates the SOFC stack's dynamic response to step changes in control variables, as well as the hybrid and non-hybrid systems' energetic, exergetic, economic, and environmental performances. The numerical, 1-D, SOFC stack model developed herein allows for simulations on multiple timescales. An equivalent circuit combines the fuel cell's irreversiblities with the charge double layer. The hybrid and non-hybrid models integrate the SOFC stack model with the balance-of-plant component models, evaluating the energy and exergy flows through each component. Finally, the techno-economic model calculates the hybrid and non-hybrid systems' levelized costs of electricity (LCOEs). Manipulating the current density is found to be the most effective way to control the fuel cell stack's power, giving rise to instantaneous power changes without restricting the fuel cell stack's fuel utilization. The charge double layer negligibly influences the fuel cell stack's behavior during normal operation, even during proportional-integral control. During baseload operation, the hybrid system model exhibits an LCOE of 8.7 cents/kWh, and the non-hybrid system exhibits an LCOE of 11.9 cents/kWh. The hybrid system also operates at higher electric and exergetic efficiencies (58% (HHV) and 64%, respectively) than the non-hybrid system (44% (HHV) and 51%, respectively). The non-hybrid system cogenerates greater thermal energy than the hybrid system, however, yielding a fuel cost that is on par with that of the hybrid system. Both systems meet the EPA's proposed carbon pollution standard for new combustion turbines of 0.50 kg CO2/kWh. Hybrid systems demonstrate the potential to save fuel and money. Continued development of these systems, particularly focused on improving the system's dynamic behavior and minimizing cost, is warranted. Investment in hybrid systems will likely become viable in the future

Improving the Availability of Organic Forage Seed in Wales

The EU regulation requiring organic farmers to use 100% organic herbage seed is looming closer. Currently they are ‘enjoying’ a derogation from this because suitable seed is not available. For 2004 seeds mixtures had to contain at least 50% organic seed. This breathing space before full 100% organic seed is required is giving the organic industry time to improve the availability of suitable species and varieties. Historically there was a viable herbage seed production industry in the lowland and southern areas of Wales. This area turned to livestock production during its more profitable periods, with specialist arable and herbage seed production switching largely to south east England. The agronomic potential remains in Wales but now needs to be developed to meet specific organic needs. A recent survey of organic farmers in Wales (see Gwlad issue 26) identifiedpersistence, total annual yield and early spring growth as the most important characters in a seeds mix. Sourcing organic seed of such forage varieties is essential for the continued development of the organic sector. Following a series of farmer discussion group meetings where these concerns were highlighted a feasibility project funded by Farming Connect, is looking at the potential of producing organic forage seed in Wales. Experimental plot work at IGER has been addressing some of the challenges in organic forage seed production. Four farmers from organic discussion groups, with a range of farm types and systems are involved in developing this work by hosting field scale demonstration plots. Field plots, designed with farmer involvement, have focused on the feasibility of different approaches to forage grass seed production (plans are in Appendix A). Initially the emphasis has been on weed control, crop nutrition and integration of forage seed production into the farming systems using seed crops of perennial ryegrass, hybrid ryegrass and timothy. Harvesting, drying and cleaning of seed have also been addressed. The first demonstration area of the hybrid ryegrass variety AberLinnet was successfully harvested in 2003, with further areas harvested in 2004. To involve all stakeholders, the project included Organic and Seed Certification bodies, as well as seed companies to progress organic forage seed production in Wales and to develop a better understanding of the challenges involved. Achievements to date: • Successful farmer participation and development of this as a route to developing organic herbage seed production agronomy and harvesting techniques. • Inclusion of other stakeholders in meetings • Herbage seed yields at potentially commercially viable levels on most sites • Identification of areas for further work • Publication of results and project progress at a range of levels from Gwlad and organic e- bulletin to scientific and farmer conferences in Wales, UK, Europe and Australia. (Details in Appendix B) • Dissemination of results obtained at farmer group meetings in England and Wales. • An overview factsheet is in progress Identification of the gaps: • Lack of farmer confidence to proceed to commercial enterprise. • A need to address further technical issues highlighted as a result of the initial work (eg clover variety, weed control). • Designing sound rotations that meet with certification standards (organic and seed) needs to be addressed. • Integration of seed production into a range of arable and or livestock systems is important to the viability and practicality of organic herbage seed production. • The expertise and confidence of the organic growers needs to be developed. • Developing farm scale harvesting, drying, distribution and marketing with farmers, and other stakeholders. • Lack of active organic seed processor and marketing presence in the area The next Phase This should be viewed in two parts; in the short term we need to ensure continuity of cropping on the farm sites and dissemination of information, building on the successes of the initial project; the longer term aims are the development of infrastructure, cooperation of interested stakeholders (eg seed companies, machinery rings, certification bodies) and scaling up to a commercially viable level from the farm