Design and control methods for a conjoined automotive regenerative braking dynamic system
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2010-12
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University of Hawaii at Manoa
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Abstract
Along with the diminishing supplies of fossil fuels, the continually increasing price of oil, and the deterioration of the environment as an effect of fossil fueled vehicles, the world now focuses its attention on green energy and vehicle hybridization. This has given rise to many alternatives in internal combustion engine vehicle hybridization such as the parallel and series hybrids, as well as plug-in hybrid electric vehicles. This paper proposes a new method of hybridization which allows ICE vehicles to be retrofitted to take advantage of regenerative braking and acceleration assistance. The conjoined automotive regenerative braking system is a small trailer like device that can be attached via trailer hitch to the ICE vehicle in order to create a pseudo parallel hybrid. The CARB will be connected to the trailer hitch of the ICE vehicle through a series elastic element in order to filter impulse shock loads as well as provide stability and robustness in force control. This thesis explains the dynamic modeling of the system as well as the response of the system to varying control schemes. Firstly, the system was analyzed analytically as a Series Elastic Actuator. The system model is very simple and a PD force controller is implemented to regulate the force in the spring connecting the CARB and the Vehicle. The closed loop transfer function is determined and the step response of the system was analyzed to determine that the closed loop natural frequency of the system needed to be above 100Hz in order for the transients in the response to die out within half of a second. Secondly, a simulink model of the system was created. A linear damper is added in parallel with the series elastic element between the vehicle and the CARB. The system input is a feed forward desired force for the vehicle determined from the Federal Urban Driving Schedule and the mass of the vehicle. A proportion of this feed forward desired force of the car is used as the desired force from the CARB. A PID controller regulates the torque of the CARB to minimize the force error between the desired force and the load force. The control parameters for this load force control scheme are determined using the signal constraint block in simulink and are determined for a variety of linear spring constants and linear damping constants. The velocity error of the system velocity response versus FUDS is less than 0.3 m/s for any simulation, and the load force error was limited to less than 150 N. The power used by the vehicle was shown to be significantly lessened by the addition of the CARB. Thirdly a more detailed Simulink model was created using the Simscape toolbox which allowed for highly detailed simulated physical entities, such as drivelines, inertias, electronics, etc. This system uses a battery model and DC/DC converter which is connected to a 50kW PMSM to simulate the electronics of the CARB, The longitudinal and tire dynamics of the car and of the system are accounted for. A model of an ICE was used to act as a torque source for the driveline of the vehicle based on an input throttle signal. This model also used a feed forward desired force as the input into the system. The CARB was limited in this model to provide torque assistance below 40km/h. This strict guideline of CARB "on" below 40km/h and CARB "off" above caused high frequency oscillations in the system velocity response when the system is near 40km/h. The power consumed by the ICE was compared with the power consumed by the ICE for a vehicle model without the CARB attachment. The addition of the CARB resulted in large power savings for low speeds when the CARB was activated, but caused an increase in engine power for speeds above the CARB activation speed since the CARB acted like a passive mass attached to the car. Fourthly the detailed Simulink model was adjusted to utilize a PI speed control to control the throttle of the ICE and brake, and the load force control from the first simulink model was implemented to control the CARB based on a desired force determined from the throttle and brake of the ICE vehicle. Unfortunately, the PID load force control interaction with a vector control contained within the motor model caused high frequency fluctuations in torque output which caused high frequency oscillations in the load force and ICE torque as well. Therefore to do any significant power study of this model, the torque control of the CARB must be resolved first.
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Dynamic System Modeling, Simulink, PID Control
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Mechanical Engineering.
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