Design and experimental validation of a virtual vehicle control concept for testing hybrid vehicles using a hydrostatic dynamometer

An approach to control a hydrostatic dynamometer for the Hardware-In-the-Loop (HIL) testing of hybrid vehicles has been developed and experimentally tested. The hydrostatic dynamometer used, which is capable of regeneration, was specifically designed and built in-house to evaluate the fuel economy and control strategy of a hydraulic hybrid vehicle. The control challenge comes from the inertia of the dynamometer being only 3% of that of the actual vehicle so that the dynamometer must apply, in addition to any drag torques, acceleration/deceleration torques related to the difference in inertias. To avoid estimating the acceleration which would be a non-causal operation, a virtual vehicle concept is introduced. The virtual vehicle model generates a reference speed profile which represents the behavior of the actual vehicle if driven on the road. The dynamometer control problem becomes one of enabling the actual vehicle-dyno shaft to track the speed of the virtual vehicle, instead of directly applying a desired torque. A feedback/feedforward controller was designed based upon an experimentally validated dynamic model of the dynamometer. The approach was successfully tested on a power-split hydraulic hybrid vehicle with acceptable speed and torque tracking performance.