Modeling and Control of Hybrid Electric Vehicles

 Prof. Ardalan Vahidi (Clemson University)
Dr. Anthony Phillips and Dr. Ming Kuang (Ford Motor Company)
 Prof. Huei Peng (University of Michigan)
Prof. Lino Guzzella (ETH, Zurich)
Prof. Giorgio Rizzoni (Ohio State University)

Summary

This tutorial session on hybrid electric powertrains brings together some of the leading university and industry experts to provide an overview of the history, current state of the technology, modeling, control and system integration challenges of hybrid powertrains and the prospects for future.

While the first hybrid vehicle was introduced more than a century ago, more recent government regulations on vehicle emission levels, increased environmental awareness among people and increasing cost of gasoline fuel, have resulted in a growing interest in hybrid vehicle technologies in the past 15 years. Control engineers have played a key role in architecture selection, design of energy management strategy and system integration of hybrid powertrains; all challenging tasks because of the complex and dynamic multi-subsystem nature of hybrid energy systems. Over the past few years many different configurations, technologies and energy management strategies have been proposed, developed and some have been implemented on today’s hybrid vehicles.

The session begins by a tutorial overview of the topic by Prof. Ardalan Vahidi covering the history of hybrids, and providing a pedagogical description of the existing hybrid configurations, propulsion and energy storage technologies and modeling and control techniques.

The second talk by Dr. Tony Phillips and Dr. Ming Kuang from Ford Motor Company, besides bringing interesting industry perspectives to the session, presents a new fundamental look at how hybrids improve fuel economy and the role of different powertrain configurations in this regard.

The third talk by Prof. Huei Peng focuses further on the more complex power-split hybrid configuration and presents a design process that enables systematic search through the three: configuration, design, and control dimensions for enhancing the fuel economy of a hybrid.

In the fourth talk Professor Lino Guzzella takes a system-theoretic look at energy optimization of hybrids and exemplifies some of the theoretic concepts on the ETH PAC Car II vehicle, which holds the world record in fuel consumption according to the Shell Eco-marathon rules.

The last presentation by Professor Giorgio Rizzoni concludes the talks by taking a preview look at the future and how hybrid vehicles (also known as plug-in vehicles)s may play a role in a futuristic but realistic interconnected ``smart’’ energy grid.

1. Title: Tutorial Overview of Modeling, Control and System Integration of Hybrid Electric Powertrains - 40 minutes
   Presenter: Ardalan Vahidi (Clemson University)
   Abstract: After providing a short historical overview of hybrid vehicle technology, different hybrid technologies, configurations and energy management strategies will be presented from a system engineering perspective and in the following topical order:
   • Main Propulsion Source: gasoline and diesel engines, HCCI engines, fuel cells, electric motors (plug-in hybrids)
   • Electrical System: motors, power electronics
   • Energy Storage: batteries, ultracapacitors, flywheels, hydraulics
   • Configurations: series, parallel, power split, other.
   • Modeling: Vehicle dynamics, propulsion and energy storage system models, driver models, drive cycles, stochastic modeling
   • Energy Management Control Strategies: rule-based methods, optimization-based methods, dynamic programming, analytical optimal control, role of telematics, real-time implementation issues
   • System integration and issues at a lower level: interconnections, power electronics, vehicle microcontroller limitations, etc.
     
2. Title: Understanding Opportunities for Energy Management Control in HEVs through Degree-of-Freedom Analysis-20 minutes
   Presenters/Authors: Anthony M. Phillips (Ford Motor Company), Ming Kuang (Ford Motor Company)
   Abstract: Hybridization of automobiles through the addition of electric motors, power electronics, and batteries is a high leverage way of increasing the fuel economy of the vehicles. The fuel economy improvement comes as a result of four basic opportunities that are possible as a result of the hybridization: 1) Engine start/stop during periods of inefficient engine operation, 2) Capture of vehicle kinetic energy through regenerative braking, 3) Ability to downsize the engine as a result of the electric motor boost potential, and 4) Energy management control to take advantage of the relative efficiency differences between the engine and the high-voltage electrical system.

   The energy management control problem is often thought of "simply" as battery state of charge management. In this case, the problem reduces to one of determining how to charge and discharge the battery most efficiently, while maintaining the battery state of charge within a desired range. More generally, however, the energy management problem is one of choosing themost efficient operating set points for all of the actuation systems in the vehicle while still satisfying the driver demand. The hybridization provides more flexibility (degree of freedoms) in selecting these operating set points. Depending on the vehicle configuration, the number of degrees of freedom available in this selection can vary from one to three or more.

   This presentation will describe the formalism for understanding the number of degrees of freedom available for energy management in a vehicle, starting from a conventional vehicle. From there, a number of hybrid vehicle configurations will be considered, demonstrating the range of opportunity available. Then it will describe the selection of practical control variables based on the available degrees of freedom, and the methodology of determining these control variables through optimization. Various constraints that inhibit flexibility in the set point selection will also be discussed.

3. Title: Configuration, Sizing and Control of Power-Split Hybrid Vehicles – 20 Minutes
   Presenter: Huei Peng (University of Michigan)
   Abstract: Power-split hybrid vehicles use planetary gears as power transmission and ratio devices, which are compact, efficient, and provide continuously variable gear ratio using a simple, low-cost and reliable structure. Many prominent hybrid vehicles currently on the market or under development are power-split hybrids. To take advantage of this type of hybrid powertrain, it is beneficial to fully explore various configurations, select proper power-train design parameters, and obtain optimal control algorithms. This talk presents a design process that enables systematic search through all three dimensions (configuration, design and control) under imposed performance and component constraints. A case study for the design of a split hybrid vehicle with optimal fuel economy while satisfying specified driving performance is demonstrated.

4. Title: The Role of System Theory in Reducing Energy Losses in Hybrids – 20 minutes
   Presenter: Lino Guzzella (ETHZ)
   Abstract: This contribution focuses on fuel efficiency of road-vehicles using a "tank-to-wheel" perspective. The most important influencing factors are discussed and the role that system theory play in reducing the energy losses is discussed. All ideas are exemplified on the ETH PAC Car II vehicle, which holds the world record in fuel consumption according to the Shell Eco-marathon rules.

   The following points are particularly interesting from a system-theoretic point of view:
   - For power sources with affine input/output characteristics it is shown that the optimal control solution always requires a two-motors power train, with one motor optimized to work on heconstant-speed singular arc portion and the other to work during acceleration phases.
   - In the case of fuel-economy contests (and many other cases) the driving profile is known in advance. In this situation non-causal controller obtained using dynamic programming can be employed. The benefits of this approach are discussed as well.

5. Title: Design And Control Of A Renewable Energy-Based Eco-System With Plug-In/V2G Hybrid Electric Vehicles – 20 minutes
   Presenter/ Authors: Giorgio Rizzoni, Vincenzo Marano, T. Gabriel Choi, Yann Guezennec
   Abstract: This presentation is aimed to show the potential benefits of a "big energy network" approach, consisting of interconnected renewable energy-based systems for transportation and residential/commercial buildings. The ability to integrate multiple energy systems including plug-in-hybrids is the key to a successful implementation. Optimization techniques and automatic control will play a crucial role in designing these systems and managing much more complex energy flows.