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Research Papers

Virtual Vehicle Control Concept for Hydrostatic Dynamometer Control1

[+] Author and Article Information
Zhekang Du

Center of Compact and Efficient Fluid Power,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: duxxx139@umn.edu

Tan Cheng

Center of Compact and Efficient Fluid Power,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: cheng164@umn.edu

Perry Y. Li

Center of Compact and Efficient Fluid Power,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: lixxx099@umn.edu

Kai Loon Cheong

Center of Compact and Efficient Fluid Power,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: cheo0013@umn.edu

Thomas R. Chase

Center of Compact and Efficient Fluid Power,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: trchase@umn.edu

2Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received August 14, 2015; final manuscript received September 16, 2016; published online November 11, 2016. Assoc. Editor: Ardalan Vahidi.

J. Dyn. Sys., Meas., Control 139(2), 021009 (Nov 11, 2016) (9 pages) Paper No: DS-15-1379; doi: 10.1115/1.4034803 History: Received August 14, 2015; Revised September 16, 2016

An approach for controlling a hydrostatic dynamometer for the hardware-in-the-loop (HIL) testing of hybrid vehicles is proposed and experimentally evaluated. The hydrostatic dynamometer, which is capable of absorbing and regenerating power, was specifically designed and built in-house to evaluate the fuel economy and control strategy of a hydraulic hybrid vehicle being developed. Unlike a chassis dynamometer whose inertia is similar to the inertia of the vehicle being tested, the inertia of this hydrostatic dynamometer is only 3% of the actual vehicle. While this makes the system low cost, compact, and flexible for testing vehicles with different weights and drag characteristics, control challenges result. In particular, the dynamometer must apply, in addition to the torques to mimic the wind and road drag, also the torques to mimic the acceleration and deceleration of the missing inertia. To avoid estimating the acceleration and deceleration, which would be a noncausal operation, a virtual vehicle concept is introduced. The virtual vehicle model generates, in response to the applied vehicle torque, a reference speed profile which represents the behavior of the actual vehicle if driven on the road. This reformulates the dynamometer control problem into one of enabling the actual vehicle dynamometer shaft to track the speed of the virtual vehicle, instead of directly applying a desired torque. To track the virtual vehicle speed, a controller with feedforward and feedback components is designed using an experimentally validated dynamic model of the dynamometer. The approach has been successfully tested on a power-split hydraulic hybrid vehicle with acceptable virtual vehicle speed and dynamometer torque tracking performance.

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References

Figures

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Fig. 1

Virtual vehicle dynamometer control concept

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Fig. 2

Schematic of the hydrostatic dynamometer

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Fig. 3

Free-body diagram of vehicle dyno shaft

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Fig. 4

Speeds (top) and torques (bottom) if the acceleration estimation approach is used for the example

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Fig. 5

Speeds (top) and torques (bottom) if the virtual vehicle approach is used

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Fig. 6

Controller scheme of the hydrostatic dynamometer

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Fig. 7

Frequency response of the closed-loop transfer function Gp(s) using a proportional control gain of Kp=0.01 compared with a second-order model (dashed) and a third-order model (solid)

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Fig. 8

Target and experimental complementary sensitivity function To

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Fig. 9

Top: hydrostatic dynamometer (rear) connected to an experimental hydraulic hybrid vehicle (front). Bottom: components of the hydrostatic dynamometer.

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Fig. 10

Dynamometer testing of hydraulic hybrid vehicle involves three independent controllers: dynamometer controller, hydraulic hybrid powertrain controller, and virtual driver controller

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Fig. 11

Actual speed and virtual vehicle speed of the vehicle dyno shaft while driving the modified UDDS

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Fig. 12

Actual speed and virtual vehicle speed of the vehicle dyno shaft while driving the modified HWFET

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Fig. 13

Error between actual speed and the desired virtual vehicle dyno shaft speed while driving the UDDS (top) and HWFET (bottom) cycles

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Fig. 14

Vehicle torque obtained using real-time observer (Eq. (20)) and using offline calculation in portion of the modified UDDS test

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Fig. 15

Applied dyno torque and desired dyno torques computed from output speed and from virtual vehicle speed while driving the modified UDDS: full cycle (top) and zoomed-in view (bottom)

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Fig. 16

Applied dyno torque and desired dyno torques computed from output speed and from virtual vehicle speed while driving the modified HWFET

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Fig. 17

Error between actual dyno torque and postprocessed desired dyno torque from output speed and from virtual vehicle speed while driving the UDDS (top) and HWFET (bottom)

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Fig. 18

Feedforward versus feedback control efforts (top) and the variation of dynamometer system pressure (bottom) during the UDDS drive cycle test

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