Real-time energy management of the electric turbocharger based on explicit model predictive control

The electric turbocharger is a promising solution for engine downsizing. It provides great potential for vehicle fuel efficiency improvement. The electric turbocharger makes engines run as hybrid systems so critical challenges are raised in energy management and control. This paper proposes a real-time energy management strategy based on updating and tracking of the optimal exhaust pressure setpoint. Starting from the engine characterisation, the impacts of the electric turbocharger on engine response and exhaust emissions are analysed. A multivariable explicit model predictive controller is designed to regulate the key variables in the engine air system, while the optimal setpoints of those variables are generated by a high level controller. The two-level controller works in a highly efficient way to fulfill the optimal energy management. This strategy has been validated in physical simulations and experimental testing. Excellent tracking performance and sustainable energy management demonstrate the effectiveness of the proposed method

Optimising the energy efficiency and transient response of diesel engines through an electric turbocharger

The electric turbocharger provides great potential for vehicle fuel efficiency improvement, exhaust emissions reduction and transient response acceleration. It makes the engine runs as a hybrid system so critical challenges are raised in energy management and control. This paper proposes a realtime energy management strategy for the electric turbocharger. A multi-variable explicit model predictive controller is designed to regulate the key variables in the engine air system, while the optimal setpoints of those variables are generated by a high level controller. The controllers work in a highly efficient way to achieve the optimal energy management. This strategy has been validated in simulations and experiments. Excellent tracking performance and high robustness demonstrate the effectiveness of the proposed method

Prediction of the fuel economy potential for a skutterudite thermoelectric generator in light-duty vehicle applications

© 2018 The Authors Thermoelectric generators (TEGs) have the characteristics of low maintenance, silent operation, stability, and compactness, which make them outstanding devices for waste heat recovery in light-duty vehicles. Significant strides have been made in the high temperature (300–800 °C) thermoelectric materials and recent work is beginning to translate those material improvements into TEG performance. Recently developed modules that incorporate new, competitive formulations of skutterudite form the basis for this study. Vehicular TEGs have not had real commercial applications yet and faced commercialization challenges. Simply estimating the fuel saving potential from the TEG output is not sufficient and due consideration must also be given to the system integration effects. Thus, a new approach for predicting the fuel saving potential of a vehicular TEG while also considering integration effects is developed in this paper. The prediction is based on a recently developed high temperature skutterudite thermoelectric modules [1]. Based on this method, the benefit of a skutterudite TEG is investigated by balancing the benefits with the added complexity of a TEG and improvement measures are explored. Based on two scenarios of the TEG integrated in different positions of a conventional light-duty vehicle, a semi-empirical model is developed, which includes a quasi-static vehicle model, a dynamic exhaust model, a dynamic coolant model, and a dynamic TEG model. Four integration effects: the additional mass, the power consumption of an electric circulation pump, the effect of exhaust back-pressure and the energy loss in the DC-DC converter, are studied in the semi-empirical model. The evaluation results show the TEG installation position has a significant influence on the fuel saving potential due to the higher quality of the exhaust gas. Placing the TEG closer to the exhaust manifold can increase fuel saving potential by 50%. The four integration effects taken together cause a 25% reduction of fuel saving potential. The energy loss in DC-DC convector and added weight are the main contributors to this reduction. An optimised design for the TEG installation operating under an optimised control strategy delivers a fuel consumption reduction of 4% over the constant-speed 120 km/h driving cycle

Three-input-three-output air path control system of a heavy-duty diesel engine

In this paper, the control requirement of the air path system of a Heavy Duty (HD) diesel engine which was equipped with a High Pressure (HP) Exhaust Gas Recirculation (EGR), a Variable-Geometry Turbocharger (VGT), and an Electric Turbocharge Assist (ETA) is discussed. A Three-Input-Three-Output (3130) multivariable control structure is proposed. The engine dynamic model required for controller design was obtained using system identification and the controller was tuned by solving an Hoo optimization problem. The engine experimental test results show that this 3130 closed-loop control system has excellent tracking performance, disturbance rejection performance, and gain scheduling capability. The control system has been demonstrated to work with a practical ETA device to make a substantial improvement to engine transient performance

A dynamic model for thermoelectric generator applied to vehicle waste heat recovery

Waste heat recovery using a thermoelectric generator (TEG) is a promising approach for vehicle original equipment manufacturers to reduce fuel consumption and lower CO2 emissions. A TEG can convert otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems. This paper focuses on the development of a dynamic model of TEG system designed for vehicle waste heat recovery, which is made up of counter-flow heat exchangers (HXRs) and commercial thermoelectric modules (TEMs). The model is built from thermoelectric materials into a TEM and then into a TEG system. Compared to other TEG models, the tuning and validation process of the proposed model is more complete. Experiments are done on both a TEM test rig and a heavy-duty diesel engine, which is equipped with a prototype TEG on the exhaust gas recirculation (EGR) path. Simulations of steady-state operating points as well as the response to typical engine cycle test show good agreement with experimental data. A TEG installed upstream of the after-treatment system in a heavy-duty truck has been modelled to predict the temperatures and power output in a dynamic driving cycle. The simulation results of temperatures show the model can be used as a basis to develop a control system for dynamic operation to ensure safety operation of TEG and efficient operation of the after-treatment system. A comparison of power output of the systems under different scenarios underlines the importance of integration of TEM with HXRs. Based on the simulation results, around 20% average power output increase can be expected by optimizing the thermal contact conductance and the heat transfer coefficient of hot side HXR

Robust control of electrified turbocharged diesel engines

Electrified turbocharger is a critical technology for engine downsizing and is a cost-effective solution for exhaust gas energy recovery. In conventional turbocharged diesel engines, the air path holds strong nonlinearity since the actuators are all driven by the exhaust gas. In an electrified turbocharged diesel engine (ETDE), the coupling is more complex, due to the electric machine mounted on the turbine shaft impacts the exhaust manifold dynamics as well. In distributed single-input single-output control methods, the gains tuning is time consuming and the couplings are ignored. To control the performance variables independently, developing a promising multi-input multi-output control method for the ETDE is essential. In this paper, a model-based multi variable robust controller is designed to control the performance variables in a systematic way. Both simulation and experimental results verified the effectiveness of the proposed controller

Modelling the exhaust gas recirculation mass flow rate in modern diesel engines

The intrinsic model accuracy limit of a commonly used Exhaust Gas Recirculation (EGR) mass flow rate model in diesel engine air path control is discussed in this paper. This EGR mass flow rate model is based on the flow of a compressible ideal gas with unchanged specific heat ratio through a restriction cross-area within a duct. A practical identification procedure of the model parameters is proposed based on the analysis of the engine data and model structure. This procedure has several advantages which include simplicity, low computation burden and low engine test cost. It is shown that model tuning requires only an EGR valve sweep test at a few engine steady state operating points. It is also shown that good model accuracy can be achieved when the control variables of other air path devices, e.g. The vane position of a Variable Geometry Turbocharger (VGT) and the torque demand of an Electric Turbo Assist (ETA), are kept constant during the EGR valve sweep test used to tune the model. Two different diesel engines are used in this work to demonstrate the model tuning procedure and the model validation results. Both engines are equipped with a high pressure external EGR system and a VGT. One of the engines has a relatively new air system device - an ETA. The model validation results of both engines show good model accuracy not only at steady state engine operating points but also during engine transients

Characterisation, control, and energy management of electrified turbocharged diesel engines

The electrification of engine components offers significant opportunities for fuel efficiency improvements. The electrified turbocharger is one of the most attractive options since it recovers part of the engine exhaust gas mechanical energy to assist boosting. Therefore, the engine can be downsized through improved transient responsiveness. In the electrified turbocharger, an electric machine is mounted on the turbine shaft and changes the air system dynamics, so characterisation of the new layout is essential. A systematic control solution is required to manage energy flows in the hybrid system. In this paper, a framework for characterisation, control, and energy management for an electrified turbocharged diesel engine is proposed. The impacts of the electric machine on fuel economy and air system variables are analysed. Based on the characterisation, a two-level control structure is proposed. A real-time energy management strategy is employed as the supervisory level controller to generate the optimal values of critical variables, while a model-based multi-variable controller is designed as the low level controller to track the values. The two controllers work together in a cascade to address both fuel economy optimisation and battery state-of-charge maintenance. The proposed control strategy is validated on a high fidelity physical engine model. The tracking performance shows the proposed framework is a promising solution in regulating the behavior of electrified engines

Decoupling control of electrified turbocharged diesel engines

Engine electrification is a critical technology in the promotion of engine fuel efficiency, among which the electrified turbocharger is regarded as a promising solution for its advantages in engine downsizing and exhaust gas energy recovery. By installing electrical devices on the turbocharger, the excess energy can be captured, stored, and re-used. The control of the energy flows in an electrified turbocharged diesel engine (ETDE) is still in its infancy. Developing a promising multi-input multi-output (MIMO) control strategy is essential in exploring the maximum benefits of electrified turbocharger. In this paper, the dynamics in an ETDE, especially the couplings among multiple loops in the air path are analyzed. Based on the analysis, a model-based MIMO decoupling control framework is designed to regulate the air path dynamics. The proposed control strategy can achieve fast and accurate tracking on selected control variables and is successfully validated on a physical model in simulations

Control-oriented dynamics analysis for electrified turbocharged diesel engines

Engine electrification is a critical technology in the promotion of engine fuel efficiency, among which the electrified turbocharger is regarded as the promising solution in engine downsizing. By installing electrical devices on the turbocharger, the excess energy can be captured, stored, and re-used. The electrified turbocharger consists of a variable geometry turbocharger (VGT) and an electric motor (EM) within the turbocharger bearing housing, where the EM is capable in bi-directional power transfer. The VGT, EM, and exhaust gas recirculation (EGR) valve all impact the dynamics of air path. In this paper, the dynamics in an electrified turbocharged diesel engine (ETDE), especially the couplings between different loops in the air path is analyzed. Furthermore, an explicit principle in selecting control variables is proposed. Based on the analysis, a model-based multi-input multi-output (MIMO) decoupling controller is designed to regulate the air path dynamics. The dynamics analysis and controller are successfully validated through experiments and simulations