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Parallel Hybrid Vehicles Using Fuzzy Logic Control

A fuzzy logic controller for hybrid vehicles with parallel configuration was proposed. Using the state-of-charge (SOC) of the energy storage, the driver command, and the motor/generator speed, a set of rules was developed. The fuzzy logic controller can determine the split between the electric motor and the internal combustion engine to achieve better fuel economy and low emission performance without losing vehicle performance.

Hybrid systems use a combination of an internal combustion engine (ICE) and an electric motor (EM). This combination has the potential of improving fuel economy by making use of regenerative braking on deceleration. There are three different types of hybrid systems:

  • Series — The internal combustion engine (ICE) is used as a generator, providing electrical power to the electric motor (EM) and the battery.
  • Parallel — The electric motor (EM) supplements torque to the internal combustion engine (ICE), both of which are connected to the drive train.
  • Series-Parallel — A combination of the two configurations.

In parallel configuration, the ICE is connected to the drive train, and the electric motor by the mechanical torque/speed coupler. The battery is also connected to the electric motor. There are five different ways to operate the system:

  1. Provide power to the wheels using the EM only.
  2. Using the ICE only.
  3. Using both the ICE and the EM simultaneously.
  4. Charge the battery using the ICE power to drive the EM as a generator.
  5. Slow down the vehicle by letting the wheels drive the EM as a generator that provides power to the battery (regenerative braking).

In order to manage the flow of energy among all components, a power controller is required to take into account the energy available in the battery.

It is important to optimize the architecture and components of the hybrid vehicle. The energy management strategy used is just as important as the architecture and components. A power controller is used to control the energy flow among all components, and optimizes power generation and conversion in the individual components. The energy in the system should be managed as follows:

  1. The driver input (from brake and accelerating pedals) is satisfied consistently.
  2. Battery has full charge at all times.
  3. All four components — ICE, EM, battery, and transmission — should have an optimized overall system efficiency.

During the operation of the parallel hybrid vehicle, the power controller should determine how much power is needed to drive the wheels based on the driver input and how much is needed to charge the battery. Then, the power controller should split the power between the ICE and the EM. If the battery is low on charge, the controller will assign negative power to the EM. Meanwhile, the ICE will provide the power for both driving the

wheels and charging the battery.

The difference between using the ICE or the EM to drive the wheels is as follows. When the ICE is used, the energy flows directly from the ICE through the transmission to the wheels, meaning that the mechanical power produced will promptly be used to drive the wheels. When the EM is used, energy first flows from the ICE through the transmission to the EM, operated as a generator, to charge the battery. Then, the energy will flow from the battery to the EM, operated as a motor, to the wheels, meaning that the same mechanical power has been converted to electric power, and then back to mechanical.

The power controller optimizes the energy flow among the components of the parallel hybrid vehicle, the energy generation, and conversion in the components (ICE, EM, battery, and transmission). The accelerator and the brake pedal inputs of the driver power command are converted by the power controller. The fuzzy logic controller computes the optimal generated power by using the driver power command, state-of-charge battery, and the EM speed, which are also used to compute the optimal ICE and EM power. The driver inputs (from braking and accelerating) are satisfied consistently by the power controller to ensure the battery is charged all the time.

This work was done by Ali Almufti for the U.S. Army RDECOM-TARDEC. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Mechanics/Machinery category. ARL-0098

Topics:
Analysis methodologies Batteries Brake components Brake pedals Braking systems Combustion and combustion processes Electric motors Electric power Electrical systems Electronic braking systems Energy storage systems Engines Fuel economy Fuzzy logic Hybrid electric vehicles Machinery Mechanical Components Off-board energy sources On-board energy sources Powertrains Regenerative braking Vehicles
This Brief includes a Technical Support Package (TSP).
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Parallel Hybrid Vehicles Using Fuzzy Logic Control

(reference ARL-0098) is currently available for download from the TSP library.

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    Magazine cover
    Defense Tech Briefs Magazine

    This article first appeared in the December, 2010 issue of Defense Tech Briefs Magazine (Vol. 4 No. 6).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document presents a project by Ali Almufti from TARDEC, focusing on the development of a fuzzy logic controller for parallel hybrid vehicles. The primary objective of this project is to optimize the energy management of hybrid systems, which combine an internal combustion engine (ICE) and an electric motor (EM) to improve fuel economy and reduce emissions while maintaining vehicle performance.

    Hybrid vehicles can operate in various configurations, including series, parallel, and series-parallel. In a parallel configuration, both the ICE and EM are connected to the drivetrain, allowing them to work together to provide power to the wheels. The document outlines five operational modes for the hybrid system, including using the EM only, the ICE only, both simultaneously, charging the battery using the ICE, and employing regenerative braking to recharge the battery.

    A key component of the hybrid vehicle's operation is the power controller, which manages the flow of energy between the ICE, EM, battery, and transmission. The energy management strategy aims to ensure that the vehicle operates efficiently by satisfying driver inputs, maintaining a full battery charge, and optimizing the overall system efficiency of all components. The power controller determines the necessary power to drive the wheels based on driver commands and adjusts the power split between the ICE and EM accordingly.

    The document also introduces a fuzzy logic control (FLC) system that utilizes a set of rules based on the state of charge (SOC) of the battery, driver power commands, and EM speed. These rules dictate how much power should be generated by the EM to ensure optimal performance. For instance, if the SOC is too high, the controller will not generate power, while if the SOC is low, it will generate power based on the driver’s commands and EM conditions.

    In conclusion, the fuzzy logic controller aims to enhance the efficiency and performance of parallel hybrid vehicles by intelligently managing energy flow and optimizing the interaction between the ICE, EM, and battery. This innovative approach promises to improve fuel economy and reduce emissions, contributing to more sustainable transportation solutions. The project highlights the importance of advanced control strategies in the evolution of hybrid vehicle technology.

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