Hydrostatic Dynamometer Research Articles

Design, Modeling and Control of a Hardware-in-the-Loop Testbed for Off-Road Vehicles

Abstract This paper presents the design, modeling, and control of a hardware-in-the-loop (HIL) testbed for off-road vehicles. The proposed HIL testbed employs a transient hydrostatic dynamometer to load a diesel engine to emulate any loading cycles of a wheel loader, which is a representative off-road vehicle. A fully validated wheel loader model is used to calculate the engine load, including both the drive and work functions. Besides, Iterative Learning Control (ILC) has been designed for the loading torque tracking of the hydrostatic dynamometer to ensure accurate emulation of real-world operation scenarios. The developed HIL testbed is used to demonstrate more than 26% energy benefits of automated wheel loaders through systematic optimization compared with human-operated wheel loaders. This HIL testbed serves as a robust platform for advancing research and development across various off-road vehicles, including excavators, tractors, and harvesters.

Dynamics and Control of an Energy-Efficient, Power-Regenerative, Hydrostatic Wind Turbine Dynamometer

Dynamometers are used to evaluate the real-world performances of drivetrains in various loading conditions. Due to its superior power density, high bandwidth, and design flexibility, a hydrostatic power-regenerative dynamometer is an ideal candidate for hydrostatic wind turbine transmission testing. A dynamometer can emulate the wind turbine rotor dynamics and allow the investigation of the performance of a unique hydrostatic drivetrain without actually building the physical system. The proposed dynamometer is an energy-efficient system with counter-intuitive control challenges. This paper presents the dynamics, control synthesis, and experimental validation of a power-regenerative hydrostatic dynamometer. A fourth-order non-linear model with three inputs was formulated for the dynamometer. The strength of input–output couplings was identified, and two different decoupling controllers were designed and implemented. During wind turbine testing, the synchronous generator turns at a constant speed and the system model is linear. A steady-state decoupling controller was developed for independent control of the drive and transmission. The implemented decoupling controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure, but a 20 bar pressure spike for a 4 rpm step change in rotor speed. However, during starting and stopping, the synchronous generator speed is not constant, and the system model is nonlinear. Therefore, a steady-state decoupling controller will not work. Thus, a decentralized controller with feed-forward control and gain scheduling was designed and implemented. A reference command was designed to avoid cavitation, pressure spikes, and power flow reversal during start-up. The experimental results show precise tracking in steady-state and transient operations. The decentralized controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure but a 100 bar pressure spike for a 4 rpm step increase in rotor speed. The pressure spike was reduced by 80 bar with the implementation of feed-forward gain. The proposed electro-hydro-mechanical system requires less power and has the potential to reduce energy expenditure by 50%.

Experimental Validation of a Hydrostatic Transmission for Community Wind Turbines

Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, for the first time, a validated dynamical model and controlled experiment have been used to analyze the performance of a hydrostatic transmission with a fixed-displacement pump and a variable-displacement motor for community wind turbines. From the dynamics of the HST, a pressure control strategy is designed to maximize the power capture. A hardware-in-the-loop simulation is developed to experimentally validate the performance and efficiency of the HST drive train control in a 60 kW virtual wind turbine environment. The HST turbine is extensively evaluated under steady and time-varying wind on a state-of-the-art power regenerative hydrostatic dynamometer. The proposed controller tracks the optimal tip-speed ratio to maximize power capture.

Evaluating connected and autonomous vehicles using a hardware-in-the-loop testbed and a living lab

Connected and autonomous vehicle (CAV) applications focusing on energy optimization have attracted a lot of attention recently. However, it is challenging to evaluate various optimizations and controls in real-world traffic scenarios due to safety and technical concerns. In light of this, our previous work has developed a hardware-in-the-loop (HIL) testbed with a laboratory powertrain research platform to evaluate CAV applications. An actual engine is loaded by a hydrostatic dynamometer whose loading torque is controlled in real-time by the simulated vehicle dynamics. The HIL testbed mimics the performance of a target vehicle and the dynamometer generates the same load as the target vehicle. In this work, the HIL testbed is further enhanced to match the performance of actual testing vehicles at the Federal Highway Administration (FHWA) and a living lab is developed to incorporate real traffic information. The same engine as the actual testing vehicles at the FHWA was installed and the vehicle models were calibrated using testing data from actual vehicles. The same roadway conditions (speed limit, the degree of road slope, etc.) were input into the testbed and the dynamometer generates the same load as an actual vehicle’s engine is getting. The HIL testbed emulates the performance of an actual vehicle and both fuel consumption and emissions are measured by precise instruments in the lab. In eight testing scenarios, the results have shown that the performance of the HIL testbed matches very well with the actual testing vehicles with about 1% error. In addition, the living lab has enabled the HIL testbed to interact with real traffic and extended the testing capabilities of the HIL testbed. Two new testing capabilities have been demonstrated through two CAV applications. This is an exciting result since the HIL testbed could provide an effective and economical way for the testing of fuel consumption and emissions on various roadway conditions for CAVs and other types of vehicles.

Hardware-in-the-loop testbed for evaluating connected vehicle applications

Connected vehicle environment provides the groundwork of future road transportation. Researches in this area are gaining a lot of attention to improve not only traffic mobility and safety, but also vehicles’ fuel consumption and emissions. Energy optimization methods that combine traffic information are proposed, but actual testing in the field proves to be rather challenging largely due to safety and technical issues. In light of this, a Hardware-in-the-Loop-System (HiLS) testbed to evaluate the performance of connected vehicle applications is proposed. A laboratory powertrain research platform, which consists of a real engine, an engine-loading device (hydrostatic dynamometer) and a virtual powertrain model to represent a vehicle, is connected remotely to a microscopic traffic simulator (VISSIM). Vehicle dynamics and road conditions of a target vehicle in the VISSIM simulation are transmitted to the powertrain research platform through the internet, where the power demand can then be calculated. The engine then operates through an engine optimization procedure to minimize fuel consumption, while the dynamometer tracks the desired engine load based on the target vehicle information. Test results show fast data transfer at every 200 ms and good tracking of the optimized engine operating points and the desired vehicle speed. Actual fuel and emissions measurements, which otherwise could not be calculated precisely by fuel and emission maps in simulations, are achieved by the testbed. In addition, VISSIM simulation can be implemented remotely while connected to the powertrain research platform through the internet, allowing easy access to the laboratory setup.

Virtual Vehicle Control Concept for Hydrostatic Dynamometer Control1

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.

Modeling, Control, and Experimental Validation of a Transient Hydrostatic Dynamometer

Due to its superior power-to-weight ratio, a hydrostatic dynamometer is an ideal candidate for transient engine or powertrain testing. It can load or motor the engine to follow any desired speed and acceleration profiles for real-world applications. Given its high bandwidth, the hydrostatic dynamometer can be further used to emulate the dynamics of hybrid powertrains and, therefore, investigate the interactions between the engine and the hybrid power source in real time. This will greatly expedite the research of various hybrid powertrain architectures and control methodologies, without actually building the complete physical system. This paper presents the design, modeling, tracking control, and experimental investigation of a transient hydrostatic dynamometer. A ninth-order physics-based dynamic model for the dynamometer is formulated and then identified and validated with experimental data. To control the dynamometer to emulate the real-world engine speed/torque profiles, two different nonlinear control strategies are investigated and implemented. First, a nonlinear model-based inversion plus PID control is designed to achieve precise tracking. Then, a state feedback control via feedback linearization is designed and implemented. Experimental results demonstrate precise tracking performance with less than 5% tracking error for both transient and steady-state operations.

Stabilization of the Mechanical Dynamics of a Road Load Simulator Using Classical Control Techniques

The open-loop transfer function of a complex hydrostatic pump-motor dynamometer system was derived from an analysis of the dynamics of the individual components. Many system components exhibit non-linearities; however, internal feedback mechanisms contribute to linearization of sub-systems. The resulting model, which was in good agreement with the system's open-loop performance, was used to predict the behaviour of the closed-loop system, this indicated that the system would be unstable. Classical control theory was used to analyse the performance of a number of stabilizing control strategies, with root locus plots, Bode diagrams and Nichols charts being used to assess the resultant performance. A lead compensation, designed as a differential controller, combined with a bi-linear gain was predicted to provide acceptable speed control. The performance of the system with this controller installed was found to satisfy the design requirements of speed of response, limited overshoot and zero steady-state error.