Experimental characterization of a supercapacitor-based electrical torque-boost system for downsized ICE vehicles

The need to improve fuel economy and reduce the emission of CO2 and other harmful pollution from internal-combustion-engine vehicles has led to engine downsizing. However, downsized turbocharged engines exhibit a relatively low torque capability at low engine speeds. To overcome this problem, an electrical torque boost may be employed while accelerating and changing gear and to facilitate energy recovery during regenerative braking. This paper describes the operational requirements of a supercapacitor-based torque-boost system, outlines the design and sizing of the electrical drive-train components, and presents experimental characterization of a demonstrator system

Powertrain sizing of electrically supercharged internal combustion engine vehicles

We assess the concept of electrically supercharged internal combustion engines, where the supercharger, consisting of a compressor and an electric motor, draws electric power from a buffer (a battery or a supercapacitor). In particular, we investigate the scenario of downsizing the engine, while delivering high power demands by supercharging. Simultaneously, we seek the optimum buffer size that provides sufficient electric power and energy to run the supercharger, such that the vehicle is able to deliver the performance required by a driving cycle representing the typical daily usage of the vehicle. We provide convex modeling steps that formulate the problem as a second order cone program that not only delivers the optimal engine and buffer size, but also provides the optimal control and state trajectories for a given gear selection strategy. Finally, we provide a case study of sizing the engine and the electric buffer for different compressor power ratings

Control and Optimization of Fuel Cell Based Powertrain for Automotive Applications

Fuel cell powered electric vehicles, with fast-refueling time, high energy density, and zero CO2 emissions, are becoming a promising solution for future fossil-free transportation. However, the relatively slow dynamic response and the inability of recovering the regenerative energy make vehicles solely powered by fuel cells not an immediately attractive solution. Instead, hybrid vehicles powered by fuel cells combined with energy buffers such as batteries and supercapacitors could be of more interest. Due to the unique characteristics of each energy buffer, the vehicle performance may vary with the hybrid energy storage system configuration. This thesis performs a comprehensive study on various energy storage configurations for applications in fuel cell hybrid electric vehicles. This thesis first examines the fuel cell/supercapacitor passive hybrid configuration where the fuel cell and supercapacitor share the same DC-link voltage. The power distribution between them is inherently determined by their internal resistances. Therefore, the DC-link voltage varies and depends on the vehicle power demand. In this work, a fuel cell/supercapacitor passive hybrid powertrain is first modeled and evaluated. Simulation results show that the energy efficiency is 53%–71% during propulsion and 84%–94% during braking, respectively. Moreover, a 3 kW lab-scale fuel cell/supercapacitor passive hybrid system is designed and investigated. Experimental results show that the fuel cell takes time to respond to a load change, while the supercapacitor provides the transient power, which makes it possible to downsize the fuel cell.Since the passive configuration loses the active controllability, this thesis further considers a fully-active fuel cell/supercapacitor system to improve the controllability of the power distribution. This configuration requires a boost converter for the fuel cell and a buck-boost converter for the supercapacitor. In this work, an adaptive power split method is used to smooth the fuel cell current and prevent the supercapacitor from exceeding its lower and upper charge limits. The cut-off frequency of the low-pass filter is adaptively controlled by the spectrum area ratio. Experimental results show that the supercapacitor state-of-charge is effectively controlled within the desired range. Moreover, a load disturbance compensator is proposed and demonstrated to improve the control performance such that the DC-link voltage fluctuation caused by the load current variation is significantly reduced.This thesis also investigates the cost-effectiveness of different energy buffers hybridized with fuel cells in various trucking applications. First, a chance-constraint co-design optimization problem is formulated. Convex modeling steps are presented to show that the problem can be decomposed and solved using convex programming. Results show that the power rating of the electric machine can be dramatically reduced when the delivered power is satisfied in a probabilistic sense. Moreover, the hybridization of fuel cells with lithium-ion batteries results in the lowest cost while the vehicle using lithium-ion capacitors as the energy buffer can carry the heaviest payload. This work also develops a robust co-design optimization framework considering the uncertainties in parameters (e.g., vehicle movement) and design decision variables (e.g., scaling factors of fuel cells and batteries). Results show that these uncertainties might propagate to uncertainties in state variables (e.g., battery energy) and optimization variables (e.g., battery power), leading to a larger battery capacity and therefore a higher total cost in robust optimal solutions. In summary, this thesis performs a comprehensive study on control and optimization of fuel cell based powertrains for automotive applications. This will provide a guidance on component selection and sizing, as well as powertrain system configuration and optimization for design of fuel cell powered electric vehicles

Optimierung von Brennstoffzellen-Hybridfahrzeugen

The limited fossil fuel resources and the environmental concerns associated with burning those fossil fuels lie behind the increasing interest in hydrogen as a clean and sustainable alternative to fossil fuels, and in fuel cells as a clean converter of hydrogen into electrical energy especially in the transportation sector. Fuel cell hybrid vehicles (FCHVs) are characterized by the use of a fuel cell system (FCS) as the main power source and a battery, a supercapacitor or both as an energy storage system (ESS). Hybridizing the FCS with an ESS significantly improves the hydrogen economy, helps downsize the FCS, and resolves the issues related the long start-up time and slow dynamics of the FCS. The existence of multiple power sources in the powertrain gives rise to two important questions: How to coordinate the power contribution of the sources (i.e., power management strategy (PMS)), and how to size these sources in order to exploit the advantages of hybridization. The goal of this thesis is to develop a comprehensive framework for the optimization of PMS and size of FCHV powertrains. Depending on the type of ESS, three topologies are considered: fuel cell/ battery, fuel cell/ supercapacitor, and fuel cell/ battery/ supercapacitor. The PMS optimization is investigated on two levels; i.e., the vehicle level by simulation and the developed optimization algorithms are then validated on a small-scale test bench. When the driving cycle is known a priori, the off-line optimal PMS that globally minimizes the hydrogen consumption is calculated by two algorithms, namely, Dynamic Programming (DP) and Pontryagin’s Minimum Principle (PMP), and the two algorithms are compared. It has been found that PMP can be a superior approach for off-line optimization since it requires negligible computation resources without sacrificing the global optimality. The off-line optimal strategy is not real-time capable; hence, real-time strategies are designed and optimized while using the off-line optimal PMS as a benchmark. Special emphasize is put on the inclusion of multiple driving cycles, of different nature, in the optimization of the real-time PMS to increase its robustness. The sizing of the power sources of fuel cell/ battery and fuel cell/ supercapacitor hybrids considers hydrogen consumption and powertrain cost as two objectives and takes into account the drivability constraints such as top speed, gradeablity and acceleration time. The interesting designs (i.e., FCS size and ESS size), which represent the most efficient trade-off between the objectives, are then extracted and analyzed. The effect of battery aging on the optimal powertrain size is investigated by an Ampere-hour throughput model. It has been found that the battery aging leads to less efficient powertrain designs and the supercapacitor can become a more efficient option in comparison to batteries of poor lifetime.Die begrenzten fossilen Ressourcen und die Umweltsorgen, die mit der Verbrennung dieser fossilen Brennstoffe verbunden sind, stecken hinter dem steigenden Interesse am Wasserstoff als sauberer und nachhaltiger Alternative, und an Brennstoffzellen als sauberen Wandlern des Wasserstoffs in elektrische Energie, vor allem im Verkehrssektor. Ein Brennstoffzellen-Hybridfahrzeug (FCHV) verwendet ein Brennstoffzellensystem (FCS) als eine Hauptenergiequelle und eine Batterie, einen Superkondensator oder beide als Energiespeichersystem (ESS). Hybridisierung des FCS mit einem ESS verringert erheblich den Wasserstoffverbrauch, hilft das FCS zu verkleinern, und behebt das Problem der langen Anlaufzeit und der langsamen Dynamik des FCS. Die Existenz von mehreren Stromquellen im Antriebsstrang wirft zwei wichtige Fragen auf: Wie ist die Leistungsanforderung des Fahrzeugs zwischen den Quellen zu verteilen (d.h. Power-Management-Strategie (PMS)) und wie sind diese Quellen zu dimensionieren, um die Hybridisierung auszunutzen. Das Ziel dieser Arbeit ist es, einen umfassenden Rahmen für die Optimierung der PMS und Dimensionierung der Brennstoffzellen-basierten hybriden Antriebsstränge zu entwickeln. Abhängig von der Art des ESS werden drei Topologien berücksichtigt: Brennstoffzelle/ Batterie, Brennstoffzelle/ Superkondensator und Brennstoffzelle/ Batterie/ Superkondensator. Die PMS-Optimierung wird auf zwei Ebenen untersucht, und zwar die Fahrzeugebene durch Simulation und die Prüfstandsebene, worauf die entwickelten Optimierungsalgorithmen experimentell validiert werden. Wenn der Lastzyklus im Voraus bekannt ist, kann die offline optimale PMS, die den Wasserstoffverbrauch global minimiert, berechnet werden. Dazu werden die zwei Algorithmen, Dynamische Programmierung (DP) und Pontryagins Minimumprinzip (PMP), verglichen. Es wurde herausgefunden, dass das PMP ein überlegener Ansatz für die offline-Optimierung sein kann, da es viel weniger Rechenressourcen braucht, ohne die globale Optimalität zu opfern. Die offline optimale Strategie ist nicht echtzeitfähig, und deshalb werden Echtzeit-Strategien entworfen und optimiert, indem die offline optimale PMS als Maßstab verwendet wird. Beim Designen der echtzeitfähigen Strategien werden mehrere Fahrzyklen unterschiedlicher Natur beachtet, um die Robustheit der Strategien zu erhöhen. Die Dimensionierung der Stromquellen der Brennstoffzelle/ Batterie und Brennstoffzelle/ Superkondensator Hybriden betrachtet den Wasserstoffverbrauch und die Kosten des Antriebsstrangs als zwei Ziele. Es wird dabei die Fahrbarkeit, d.h. Höchstgeschwindigkeit, Steigfähigkeit und Beschleunigungszeit, berücksichtigt. Die interessanten Konfigurationen (FCS-Größe und ESS-Größe), die den effizientesten Kompromiss zwischen den Zielen darstellen, werden dann herausgefunden und analysiert. Die Wirkung der Batteriealterung auf die optimale Antriebsstrang-Größe wird durch ein Ampere-Stunden-Durchsatzmodell untersucht. Es wurde herausgefunden, dass die Batterie-Alterung weniger effiziente Antriebsstrang-Konfigurationen ergibt, und dass der Superkondensator eine effizientere Alternative zur Batterie sein kann, wenn er mit Batterien von schlechter Lebensdauer verglichen wird

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries