Hybrid Electric Vehicle System Modeling and Control

Wei Liu

• Publisher: Wiley
• Year: 2017
• ISBN:
  9781119278948
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Automotive Transportation & Engineering
• Index: Technology & Engineering

This new edition includes approximately 30% new materials covering the following information that has been added to this important work:

• extends the contents on Li-ion batteries detailing the positive and negative electrodes and characteristics and other components including binder, electrolyte, separator and foils, and the structure of Li-ion battery cell. Nickel-cadmium batteries are deleted.
• adds a new section presenting the modelling of multi-mode electrically variable transmission, which gradually became the main structure of the hybrid power-train during the last 5 years.
• newly added chapter on noise and vibration of hybrid vehicles introduces the basics of vibration and noise issues associated with power-train, driveline and vehicle vibrations, and addresses control solutions to reduce the noise and vibration levels.

Chapter 10 (chapter 9 of the first edition) is extended by presenting EPA and UN newly required test drive schedules and test procedures for hybrid electric mileage calculation for window sticker considerations.

In addition to the above major changes in this second edition, adaptive charging sustaining point determination method is presented to have a plug-in hybrid electric vehicle with optimum performance.

1
Introduction

In recent decades, hybrid electric technology has advanced significantly in the automotive industry. It has now been recognized that the hybrid is the ideal transitional phase between the traditional all‐petroleum‐fueled vehicle and the all‐electric vehicles of the future. In popular concepts, a hybrid electric vehicle (HEV) has been thought of as a combination of an internal combustion engine (ICE) and an electric motor.

The most important feature of hybrid vehicle system technology is that fuel economy can be increased noticeably while meeting increasingly stringent emission standards and drivability requirements. Thus, hybrid vehicles could play a crucial role in resolving the world’s environmental problems and the issue of growing energy insecurity. In addition, hybrid technology has been a catalyst in promoting the technology of electric motors, power electronics, and batteries to maturity (Powers and Nicastri, 1999; Chan, 2002).

An HEV is a complex system of electrical and mechanical components. Its powertrain control problems are complicated and often have conflicting requirements. Moreover, they are generally nonlinear, exhibit fast parameter variation, and operate under uncertain and changing conditions; for example, the vehicle has to run well on a cold January day in northern Ontario as well as on a sweltering day in Death Valley. Many control design objectives are very difficult to formalize, and many variables that are of the greatest concern are not measurable. The HEV system control is also fundamentally a multivariable problem with many actuators, performance variables, and sensors. It is often important to take advantage of these interactions with multivariable designs; however, multivariable designs may make control strategies less robust to parameter variation and uncertainties, and thus may be more difficult to calibrate. In this book, we will systematically introduce HEVs’ control problems from powertrain architecture and modeling to design and performance analysis.

1.1 Classification of Hybrid Electric Vehicles

In order to cover automotive needs, various hybrid electric vehicle concepts have been proposed and developed. According to the degree of hybridization, nowadays hybrid electric vehicles can be classified as micro hybrid, mild hybrid, full hybrid, or plug‐in hybrid electric vehicles as well as fully electric vehicles. These hybrid electric vehicles are described briefly in the following sections and a classification summary is given in Table 1.1.

Table 1.1 The main features and capabilities of various hybrid electric vehicles

Type of vehicle	Features and capabilities
	Start–stop	Regenerative braking	Boost	Electric‐only mode	Electric range (miles)
Micro hybrid	Yes	Possible	No	No	No
Mild hybrid	Yes	Yes	Yes	No	No
Full hybrid	Yes	Yes	Yes	Possible	Possible (<2)
Plug‐in hybrid	Yes	Yes	Yes	Yes	Yes (20–60)
Pure electric	Yes	Yes	Yes	Yes	Yes (80–150)

1.1.1 Micro Hybrid Electric Vehicles

Micro hybrid electric vehicles are normally operated at low voltages between 12 V and 48 V. Due to the low operational voltage, the electric power capability is often under 5 kW, and thus micro hybrid electric vehicles primarily have auto start–stop functionality. Under braking and idling circumstances, the internal combustion engine is automatically shut down, so fuel economy can be improved by 5–10% during city driving conditions. With the power capability increase of a 12 V battery, some micro hybrid vehicles even have a certain degree of regenerative braking capability and are able to store the recovered energy in the battery. Most micro hybrid electric systems are implemented through improving the alternator–starter system, where the conventional belt layout is modified and the alternator is enhanced to enable the engine to be started and the battery to be recharged. Valve‐regulated lead–acid batteries (VRLAs) such as absorbent glass mat (AGM) batteries and gel batteries are widely used in micro hybrid electric vehicles. The biggest advantage of the micro hybrid vehicle is the lower cost, while the main drawback is the inability to recover all regenerative braking energy.

1.1.2 Mild Hybrid Electric Vehicles

Compared with micro hybrid electric vehicles, mild hybrid electric vehicles normally have an independent electric drivetrain providing 5–20 kW of electric propulsion power, and the electric drive system typically operates at voltages between 48 V and 200 V. Mild hybrid electric vehicles can make use of an electric motor to assist the internal combustion engine during aggressive acceleration phases and enable the recovery of most regenerative energy during deceleration phases. Therefore, mild hybrid electric vehicles have great freedom to optimize vehicle fuel economy and vehicle performance, and improve driving comfort. Mild hybrid electric architecture is often implemented in several ways depending on the degree of hybridization. The belt starter–generator, mechanically coupled via the alternator belt in a similar manner to micro hybrids, and the starter–generator, mechanically coupled via the engine crankshaft, are typical implementations. Nickel–metal hydride and lithium‐ion batteries are often employed in mild hybrid electric vehicles. One distinguishing characteristic of mild hybrid electric vehicles is that the vehicle does not have an exclusive electric‐only propulsion mode. The fuel economy improvement is mainly achieved through shutting down the engine when the vehicle stops, using electrical power to initially start the vehicle, optimizing engine operational points, and minimizing engine transients. Typical fuel savings in vehicles using mild hybrid drive systems are in the range of 15 to 20%.

1.1.3 Full Hybrid Electric Vehicles

Full hybrid electric vehicles (HEVs) are also called strong hybrid electric vehicles. Here, the electric drive system normally has in excess of 40 kW of power and operates on a voltage level above 150 V for the sake of the operational efficiency of the electrical system and the component/wire size. The electric powertrain of a full hybrid electric vehicle is capable of powering the vehicle exclusively for short periods of time when the combustion engine runs with lower efficiency, and the energy storage system is designed to be able to store the free regenerative braking energy during various deceleration scenarios. These vehicles can also provide a purely electric driving range of up to two miles to meet some special requirements such as silent cruising in certain areas and zero emissions for driving in tunnels and indoors. The ideal application scenario for full hybrid electric vehicles is continuous stop‐and‐go operation; therefore, they are widely used as city buses and delivery trucks. Compared with traditional internal combustion engine vehicles, the overall fuel economy of a full hybrid electric vehicle in city driving could improve by up to 40%.

1.1.4 Electric Vehicles

Electric vehicles (EVs) are operated with electrical power only. Presently, most electric vehicles employ lithium‐ion batteries as the energy storage system, with a plug to connect to the electric grid to charge the battery. The capacity of the energy storage system plays a crucial role in determining the electric driving range of the vehicle. However, enlarging the energy storage capacity would result in an increase in vehicle mass and volume, and would also require quite a long time to charge the battery without a fast‐charging facility. Most electric vehicles on the market have an 80–150 mile electric range, while in the near future, 3...