The automotive industry is waking up to the fact that hybrid electric vehicles could provide an answer to the ever-increasing need for lower-polluting and more fuel-efficient forms of personal transport. This is the first book to give comprehensive coverage of all aspects of the hybrid vehicle design, from its power plant and energy storage systems, to supporting chassis subsystems necessary for realising hybrid modes of operation. Key topics covered include hybrid propulsion system architectures, propulsion system sizing, electric traction system sizing and design, loss mechanisms, system simulation and vehicle certification.
Inspec keywords: energy storage; electric drives; electric propulsion; hybrid power systems; hybrid electric vehicles; power electronics
Other keywords: hybrid vehicle testing; hybrid power plant specification; drive system control; AC drive; electric drive system sizing; hybrid vehicle propulsion system; drive system efficiency; power electronics; energy storage
Subjects: Power convertors and power supplies to apparatus; Drives; Transportation; Control of electric power systems; Power systems
This chapter presents the hybrid electric vehicles which the global distribution of automobiles will be assumed to be split as 18M in each of the three major geographical regions: The Americas, Europe, and Asia-Pacific. At the time of writing, the automotive industry is awakening to the fact that indeed, hybrid electric vehicles are one answer to the world's need for lower polluting and more fuel efficient personal transportation. Studies have been done that show if gasoline electric hybrids were introduced into the market starting today and reaching full penetration in ten years, and estimating that 40% of the oil consumption is used for transportation, then it would be equivalent to doubling the annual rate of new oil fields brought on line. In North America transportation is 97% dependent on petroleum, primarily gasoline and diesel fuels and even more to the point, transportation con sumer 67% of total petroleum usage. There are now only 130 000 gasoline-electric hybrids on the streets that are being used for personal transportation. All the major automotive manufacturers have announced plans to introduce hybrid propulsion systems into their products. Some manufacturers see hybrid vehicles as supplementary actions or 'bridging actions' leading to an eventual fuel cell and hydrogen driven economy. More visionary companies see hybrid vehicles as viable long term environ mental solutions during the period when internal-combustion engines (ICEs) evolve to cleaner and more efficient power plants. Today, Toyota Motor Company is a member of the visionary camp and clearly the leader in hybrid technology. Toyota Motor Co. has announced that by CY2005 they will have an annual production rate of 300 000 hybrids per year. Of the approximately 55M vehicles sold each year globally, this is a small, but significant, fraction of sales.
This chapter looks at the hybrid powertrain configurations now in production plus other hybrid propulsion system architectures. There may indeed be other, more novel, hybrid propulsion architectures not covered here, but these are likely to be developed for very specific mission profiles or niche markets.
The vehicle power plant is designed to deliver sufficient propulsion power to the driven wheels to meet performance targets that are consistent with vehicle brand image. The previous two chapters described how conventional engines and electric drive systems are matched to meet performance and economy targets. In this chapter we continue to evaluate the matching criteria between combustion engines and ac drives for targeted road load conditions.
The vehicle power plant must be sized for the target vehicle mass, load requirements and performance goals. Vehicle propulsion system traction is set by the vehicle design mass and acceleration performance according to Newton's law, F = ma. Acceptable acceleration levels are 0.15 to 0.3 g, which for a 1500 kg vehicle requires an accel erating force F of 2205 to 4410 N. Aggressive acceleration levels are ~0.6g, which amounts to a tractive wheel force of 8820 N or higher. The limit to tractive force is set by the vehicle mass in terms of normal force at the tyre patches in contact with the road surface. The typical rubber tyre to asphalt road surface coefficient of friction is μ=0.85; surface coefficient of friction is generally lower than these values due to air conditions, presence of dirt and oil films, etc. Tractive force limits at a tyre patch are given as μFNqc, where the normal force is that due to quarter car mass. Tractive force at the tyre patch in excess of the traction limit results in wheel slip and a dramatic drop in tyre to road adhesion.
This chapter explores the four classes of electric machines having the most bearing on hybrid propulsion systems: the brushless permanent magnet machine in its surface permanent magnet (SPM) configuration; the interior permanent magnet (IPM) synchronous machine in either inset or buried magnet configuration; the asynchronous or cage rotor induction machine (IM); and the variable reluctance or doubly salient machine (VRM).
As the highest cost component of the hybrid propulsion system, with the possible exception of the vehicle battery, the power electronics represents one of the most complex power processing elements in the vehicle. In this chapter the various types of semiconductor devices are summarised along with their applicability for use as in-vehicle power control. The assessment of power electronics for ac drive systems then continues with discussion of various modulation techniques, thermal design and reliability considerations. Modulation techniques are important for many reasons. Most of the present modulation methods are capable of synthesising a clean sinusoidal ac waveform from the vehicle's on-board energy storage system but not all do so with equal efficiency, noise emissions or dc voltage utilisation.
This chapter gives an assessment of the most popular and relevant control techniques for hybrid propulsion systems. Generally confined to the traction system 'outer loop', the techniques to be described determine how torque is regulated and speed controlled. Because of the presence of multiple torque sources in the hybrid drivetrain it is necessary to employ torque control of all the sources, including engine, hybrid M/G(s), and any other source of motive power (flywheels). Sensorless control is gaining more acceptance, especially for brushless dc and induction machines. This chapter looks at some promising sensorless control techniques and gives an assessment of where this technology is going. Fault management, diagnostics and prognostics are important aspects of hybrid powertrain development. How are faults sensed, what the consequences of a faulted driveline component, particularly the electric M/G are, and how fault recovery is managed are topics that face the hybrid propulsion control system designer. Hybrid propulsion system M/G control is nearly universally implemented with field orientation techniques, regardless of the electric machine type. It is the main focus of this chapter to present field oriented control principles in an uncomplicated manner with the essential principle of field oriented control as the enabler for any electric machine to deliver the same performance and response as if it were a dc armature controlled machine.
It should not be surprising that the most important attribute of today's hybrid propulsion system is that total driveline efficiency exceed 80%. When vehicle fuel economy is in excess of 40mpg, a 100 W power loss due to core heating in the traction motor or its attendant power inverter represents a significant impact. Weight is another very important attribute, but its impact is not as noticeable until performance on grades is required. This chapter provides an assessment of the complete hybrid drive system and where the prominent loss mechanisms reside. Particular attention is paid to the traction M/G core and copper losses and the inverter conduction and switching losses. Mechanical friction contributions are noted, particularly with regard to non-conventional designs due to adding the hybrid components.
This chapter describes how passenger vehicles are characterised first as to drag and rolling resistance coefficients and second according to fuel economy over standard drive cycles. Vehicle data necessary to compute rolling resistance and aerodynamic drag coefficients are taken from coast down tests. This procedure is further described in Chapter 11 along with some actual test data about how this applies to characterising the hybrid propulsion system. In this chapter the various standard drive cycles employed in various geographical and demographic areas are compared and rationale given for their selection.
Energy storage systems are tailored to the type of fuel being used or to the mechanical, chemical, thermal or electrical form of energy directly stored. Liquid fossil fuels that will be used as feedstock for the engine include gasoline, liquefied petroleum gas (LPG), natural gas (NG) or hydrogen. Mechanical storage systems include flywheels, plus pneumatic (hydraulic) and elastic mediums to store energy in its kinetic and potential energy forms, respectively. Hydraulic storage systems generally use pneumatic means such as a nitrogen bladder as the actual storage medium with the hydraulics as the actuation system. A taxomomy of energy storage systems has been done that shows the relative energy density of the various media. Table 10.1 is a summary of these fundamental energy storage systems. Fundamental energy storage systems in the ideal case can be differentiated by the medium of storing energy whether it is nuclear bond, covalent bond or molecular bond. Storage in nuclear bonds (fusion and fission) has energy storage densities some six to seven orders of magnitude higher than storage in covalent bonds (gasoline), which in turn has energy storage density some three orders of magnitude greater than electro-chemical, mechanical or electro-magnetic systems (molecular bonds). The remainder of this chapter will be devoted to understanding energy storage systems of a practical nature that are suited to hybrid propulsion.
Development of hybrid propulsion systems requires knowledge of the vehicle attributes in terms of mass, frontal area, tyre rolling radius and rolling resistance, plus its aerodynamic drag coefficient. The accepted procedure for obtaining these data comes from vehicle coast down testing. This chapter illustrates the coast down process on two very different vehicles seen often on highways in North America and Europe: the sport utility vehicle and tractor-trailors (semis).