Sheldon S. Williamson

Topological overview of hybrid electric and fuel cell vehicular power system architectures and configurations

This paper discusses the operational characteristics of the topologies for hybrid electric vehicles (HEV), fuel cell vehicles (FCV), and more electric vehicles (MEV). A brief description of series hybrid, parallel hybrid, and fuel cell-based propulsion systems are presented. The paper also presents fuel cell propulsion applications, more specific to light-duty passenger cars as well as heavy-duty buses. Finally, some of the major fundamental issues that currently face these advanced vehicular technologies including the challenges for market penetration are highlighted.

Power electronics intensive solutions for advanced electric, hybrid electric, and fuel cell vehicular power systems

There is a clear trend in the automotive industry to use more electrical systems in order to satisfy the ever-growing vehicular load demands. Thus, it is imperative that automotive electrical power systems will obviously undergo a drastic change in the next 10-20 years. Currently, the situation in the automotive industry is such that the demands for higher fuel economy and more electric power are driving advanced vehicular power system voltages to higher levels. For example, the projected increase in total power demand is estimated to be about three to four times that of the current value. This means that the total future power demand of a typical advanced vehicle could roughly reach a value as high as 10 kW. In order to satisfy this huge vehicular load, the approach is to integrate power electronics intensive solutions within advanced vehicular power systems. In view of this fact, this paper aims at reviewing the present situation as well as projected future research and development work of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (EVs, HEVs, and FCVs). The paper will first introduce the proposed power system architectures for HEVs and FCVs and will then go on to exhaustively discuss the specific applications of dc/dc and dc/ac power electronic converters in advanced automotive power systems

Comprehensive drive train efficiency analysis of hybrid electric and fuel cell vehicles based on motor-controller efficiency modeling

From the point of view of overall hybrid electric vehicle (HEV) and fuel cell vehicle (FCV) drive train efficiency, the research focus is mainly on the efficiency analysis of the power train components, which prove to be an integral part of modern HEV and FCV drive trains. The critical portion of any HEV electrical system consists of a power electronic converter (inverter) and a suitable traction motor. Thus, the efficiency analysis of the inverter/motor is of prime importance for the calculation of the overall efficiency of the drive trains. This paper aims at modeling the efficiencies of the traction motor/controller through efficiency maps. Efficiency maps are a convenient way to represent motor drive systems of large and complex systems, like that of a HEV. The paper uses the advanced vehicle simulator (ADVISOR) software for the simulations of a large-sized car, similar to a Chevy Lumina, over the urban dynamometer-driving schedule and highway fuel economy test drive cycles. Furthermore, the paper investigates the traction motor efficiency maps and consequent overall drive train efficiencies of commercially available Honda Insight and Toyota Prius HEVs. In all the case studies, the aim is to analyze the overall drive train efficiency over the city and highway drive cycles based on the inverter/motor efficiency maps

Comparative assessment of hybrid electric and fuel cell vehicles based on comprehensive well-to-wheels efficiency analysis

One of the major issues surrounding the research and development work involving hybrid electric and fuel cell vehicles (HEVs and FCVs) is their overall efficiency of converting the input fuel into actual work at the wheels of the vehicle. The main idea behind efficiency comparisons between HEVs and FCVs is the analysis of their respective well-to-tank (WTT) and tank-to-wheels (TTW) efficiencies, the product of which reveals the well-to-wheels (WTW) efficiency, which is one of the deciding factors for technology acceptance. This paper primarily aims at presenting critical comparative issues with regards to the overall efficiencies of the most popularly proposed HEV and FCV topologies. Finally, the overall efficiency analysis performed in this paper will lay down the foundation for a concrete conclusive comparison between advanced vehicular topologies of the future.

Fuel cell vehicles: opportunities and challenges

One of the major goals of the automotive industry is to improve vehicular fuel efficiency and performance with much lesser percentages of harmful tailpipe emissions. One of the major technologies includes fuel cell vehicles (FCV). Various advantages of fuel cells including reliability, simplicity, quietness of operation, and low pollution have made them an attractive potential candidate for providing automotive power. This work aims at discussing the basic possible topologies of fuel cell vehicles and the major issues that need to be overcome in order to make them practically viable. In addition, critical comparative factors between the FCV option and its closest competitor, the hybrid electric vehicles (HEV) option, are presented. Finally, This work provides a summary of various fuel cell demonstration vehicles wherein various social and cost related issues are addressed.

Impact of energy storage device selection on the overall drive train efficiency and performance of heavy-duty hybrid vehicles

One of the key components of a hybrid electric vehicle (HEV) drive train is its secondary energy storage device. The automotive industry is still in the process of debating on the fact, as to which device provides the best option in HEVs, for the purpose of load leveling. This paper aims at providing a fair idea with regards to the selection of secondary energy sources, based on vehicle performance characteristics and overall drive train efficiency. The performances of lead-acid (PBA), lithium-ion (Li-Ion), nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), and nickel-zinc (Ni-Zn) batteries, as well as ultra-capacitors (UC) are investigated over city and highway driving schedules for a heavy-duty diesel-parallel hybrid transit bus application. Based on the simulation studies for the above-mentioned storage devices, the Ni-MH, PBA, and the ultra-capacitor technologies demonstrate best results in terms of fuel economy and percentage drive train efficiency. On the other hand, the Ni-Zn and Li-Ion batteries show much promise, but still demand a great deal of research and development work, before they become a viable option for HEV applications. Finally, the paper compares and summarizes critical performance characteristics for the energy storage devices under investigation.

Comparative Investigation of Series and Parallel Hybrid Electric Drive Trains for Heavy-Duty Transit Bus Applications

In recent times, diesel powered hybrid electric vehicles have attracted their fair share of attention from automakers worldwide. It is a well-known fact that diesel hybrid technology is being used increasingly to improve the performance of a number of city transit buses. The exclusive combination of advanced diesel engines and sophisticated hybrid electric vehicle (HEV) technologies holds much promise for dramatic reductions in both emissions as well as fuel consumption. Currently, transit bus manufacturers incorporate the popularly accepted series or parallel hybrid electric drive train architectures for hybridization depending on specific performance demands. From the point of view of heavy-duty vehicular drive train hybridization, a major debate in the auto industry involves analyzing and comparing both the series as well as parallel HEV systems. Keeping this issue in mind, this paper aims to comprehensively investigate and evaluate series and parallel hybrid electric drive train topologies for heavy-duty diesel transit buses from the point of view of overall efficiency and parametric performance studies. In general, the vital proposal of this paper involves the depiction of suitability of parallel hybrid drive trains over series hybrid drive trains, more specific to city transit bus applications

Distributed fuel cell generation in restructured power systems

This paper emphasizes the role of fuel cells as one of the popular options for distributed generation (DG) applications in restructured power systems. Typical topologies of fuel cell-based distributed generation systems are introduced, and major issues concerning interconnection with the utility grid are highlighted. Also presented in the paper are some of the issues related to marketing and standardization of fuel cell DG technology. Finally, a few working examples of fuel cell-based DG systems in the US and around the world are reviewed and their operation and performance characteristics are discussed

Control and Stabilization of DC/DC Buck-Boost Converters Loaded by Constant Power Loads in Vehicular Systems using a Novel Digital Scheme

Power electronics based power systems are being increasingly considered for transportation systems such as land, sea/undersea, air, and space vehicles due to their advantages in efficiency, performance, flexibility, and power density. In order to have superior performance, these multi-converter systems need to be rigorously regulated. Dynamic response of tightly regulated power electronic converters in distributed power electronic systems is similar to the dynamic response of a constant power load (CPL), which acts as negative impedance and destabilizes the DC bus and the system. In order to mitigate the instability problem in multi-converter systems, in this paper, we present a novel digital technique to control DC/DC converters driving CPLs in vehicular systems. The proposed method achieves the output voltage regulation based on generating high and low power pulses instead of conventional pulse width modulation (PWM) techniques. It is simple, straight forward, and easy to implement in specifically designed integrated circuits (IC), digital signal processors (DSP), or field programmable gate arrays (FPGA). Moreover, its dynamic response is fast and robust. Simulation results of applying the proposed method to a DC/DC buck-boost converter confirm the analytical results.

Modern Automotive Power Systems: Advancements into the Future

The recent trend in the automotive industry is to create a new fleet of advanced vehicular technologies. The most popularly targeted automotive technology is the hybrid electric vehicle (HEV) powered by the existing internal combustion engine (ICE) technology as well as a suitable electric traction motor system. In addition, the auto industry has shown an increased interest in fuel cell vehicles (FCV) as well as battery electric vehicles (BEV), which probably might become the solutions to the inevitable oil shortage scenario that will face the world in about 50 years time. This paper aims at providing a detailed technological overview of proposed HEV, FCV, and BEV automotive technologies. Furthermore, this paper will present a brief comparative analysis of the above-mentioned advanced vehicular systems from the point of view of the overall cost, fuel economy, and well-to-wheels (WTW) efficiency. A brief summary of commercially available HEVs and developed FCV prototypes will be presented as well.