Maxime Boisvert

Designing a set of efficient regenerative braking strategies with a performance index tool

The goal of this study is to design efficient regenerative braking strategies for a recreational three-wheel rear-wheel-drive hybrid electric vehicle. Current studies provide several optimal regenerative braking strategies, but no tool to obtain a set of acceptable strategies. A performance index tool is thus proposed and used to evaluate the efficiency of a given strategy. With this tool it is then possible to define a set of efficient regenerative strategies. The performance index is based on knowledge of a global efficiency map defined as the ratio of the incoming battery power to the extracted kinetic power. Two simulators of the vehicle are implemented in MATLAB/Simulink: one with a rear-wheel slip model and the other without slip considerations. They also include the longitudinal dynamics of the vehicle and the efficiency of the electrical drive from the electric motor to the battery. They were validated with experimental measurements of several accelerations and decelerations on a dry asphalt road from 0 km/h to 60 km/h. The simulated global efficiency map was also experimentally validated by regenerative braking measurements on a dry asphalt road from 50 km/h to 0 km/h. The simulated global efficiency map is used to design the optimal strategy (with and without wheel slip considerations). The performance map deduced from the global efficiency map was used to define the boundaries for the optimal strategy deviations and hence to limit the regenerated energy drop. Simulations show that there is a wide range of acceptable strategies from 0 km/h to 50 km/h on a dry asphalt road and hence give the driver the possibility of modulating the regenerative braking within a good energy recapture level. Finally, the design methodology presented with a simulated global efficiency map is also applicable with an experimental efficiency map which can be updated online.

Comparison of two strategies for optimal regenerative braking, with their sensitivity to variations in mass, slope and road condition

Abstract A three wheels recreational vehicle is studied for the purpose of regenerative braking control. Most of the existing literature propose optimal methods which consist in defining the braking torque as a function of the vehicle speed. The originality of this study is to propose a new strategy based on the control of the rear wheel slip. A simulator based on Matlab/Simulink and validated with experimental measurements compares the two strategies and their sensitivities to variation in mass, slope and road condition. Numerical simulations show that the regenerative braking based on a slip controller is less affected by parametric changes. It thus becomes possible to ensure optimal recovery of energy and vehicle stability even in case of parametric fluctuations.

Implementation of a Cooperative Strategy between a Vehicle's Mechanical and Regenerative Brake System

A hybrid vehicle equipped with a hydraulic and a regenerative brake system needs collaboration between both actuators. It is clearly the case, if the pedal input integrates the drivers brake demands. The challenge is to deal with vehicle safety and recovery efficiency. Thus, this work focuses on the implementation of a cooperative braking strategy, involving brake pressure control and regenerative brake control. The objectives are to trade, until limits, the rear wheel friction brake by regenerative brake and to improve the brake performance. To achieve this, this paper proposes a cooperative brake force distribution strategy. For design purpose, a simulator based on empirical results has been developed and the feasibility of the strategy is evaluated through experimentation.

Model-Based Predictive Control Applied to a Dual Regenerative and Hydraulic Brake System

A cooperative control strategy can improve the efficiency of the dual regenerative and hydraulic brake system of an electric vehicle. Considering delays and constraints for both actuators, model- based predictive control (MPC) is an attractive approach. Its prediction capability is used to adjust the optimal input sequence according to the future system variations predicted. Therefore, this asset can improve the control performances compared to common closed loop control methods (e.g., LQR optimal control, PID). Thus, this paper proposes a simulation framework to evaluate the implementations feasibility of a blended MPC strategy applied to a vehicle dual brake system.

Wheel slip controller for the regenerative braking of electric vehicle: Experimental results with a three wheels recreational hybrid vehicle

In any hybrid or electrical vehicle, the electric motor can be used as an electric generator to impose a negative torque to the wheel providing the braking effect by recovering part of the kinetic energy used for charging the batteries. The main hypothesis of this study is to propose that a slip control is preferable to a braking torque control during the regenerative braking. The experimental results obtained with a three wheel recreational electric vehicle validate that the wheel slip control is an efficient regenerative braking strategy to ensure both the optimal energy recovery and the wheel adherence in spite of road uncertainties.

Nonlinear LQG Slip Controller Based on an Empirical Model for a Three Wheel Hybrid Vehicle

A three wheels recreational vehicle propelled by its unique rear wheel is studied for the purpose of regenerative braking control. To ensure the stability of the vehicle and the safety of the pilot, the slip ratio of the powered wheel must be limited during regenerative braking. In this study, a design of a LQG slip tracking algorithm is proposed. The non-linear model is based on experimental tests and the controller has been validated by simulations and road tests.

Collaborative control of a dual electro-hydraulic regenerative brake system for a rear-wheel-drive electric vehicle:

Within the field of electric vehicles, the cooperative control of a dual electro-hydraulic regenerative brake system using the foot brake pedal as the sole input of driver brake requests is a challenging control problem, especially when the electro-hydraulic brake system features on/off solenoid valves which are widely used in the automotive industry. This type of hydraulic actuator is hard to use to perform a fine brake pressure regulation. Thus, this paper focuses on the implementation of a novel controller design for a dual electro-hydraulic regenerative brake system featuring on/off solenoid valves which track an “ideal” brake force distribution. As an improvement to a standard brake force distribution, it can provide the reach of the maximum braking adherence and can improve the energy recovery of a rear-wheel-drive electric vehicle. This improvement in energy recovery is possible with the complete substitution of the rear hydraulic brake force with a regenerative brake force until the reach of the electric powertrain constraints. It is done by performing a proper brake pressure fine regulation through the proposed variable structure control of the on/off solenoid valves provided by the hydraulic platform of the vehicle stability system. Through road tests, the tracking feasibility of the proposed brake force distribution with the mechatronic system developed is validated.

Ideal regenerative braking torque in collaboration with hydraulic brake system

In the presented hybrid vehicle, the electric motor is used in collaboration with the hydraulic brake system to impose an ideal braking torque to the rear wheel. This, in order to recharge the battery. The first objective aims to recover the maximum kinetic energy available. To achieve this task, the electric motor is used until the reach of its torque limits while an additional hydraulic brake force is exerted at the rear wheel only when it is needed. The second objective aims to improve the brake efficiency by performing the tracking of the ideal brake force distribution. An original aspect of this paper is the proposal of a brake force distribution strategy between the front and rear axles which is based on the tracking of the ideal brake torque (I-curve). The experimental results obtained with a recreational three-wheel electric vehicle validates the implementation of the proposed ideal collaborative braking control strategy.

Real Time Evaluation of the Driver Ability to Recover Energy during Braking, by Observing the Slip Ratio of the Powered Wheels, on an Electric Vehicle

This article is about a new method to evaluate the ability of the pilot to recover energy during the regenerative braking period. In order to optimize the amount of energy recovered from electrical braking, most of the existing literatures present optimal methods which consist in defining the optimal braking torque as a function of vehicle speed. The originality of the present study is to propose a new strategy based on the observation of the powered wheel slip. It has been proved that regenerative braking based on a slip controller was less affected by the majority of the parametric changes [1], including the type of road. This method proposes to evaluate the pilot by observing the slip ratio instead of the applied torque. Thus, the optimal engine torque is reduced when the pilot is on a slippery road. Thereby the pilot evaluation is possible in all road conditions.