Hybrid Electric Propulsion System Research Articles

Optimization Design and Analysis of Power Management for Serial Hybrid-Electric Propulsion System Under Aircraft/Engine Integrated Framework

Optimization Design and Analysis of Power Management for Serial Hybrid-Electric Propulsion System Under Aircraft/Engine Integrated Framework

Energy analysis and control scheme optimizations for a recuperated gas turbine with variable power offtakes/inputs

An innovative hybrid electric propulsion system (HEPS) is used for recuperated gas turbine (RGT) to avoid partial-load efficiency deterioration. Power offtakes/inputs of high and low-pressure shafts can be regulated by electric machines to achieve decoupling control in the innovative HEPS. The HEPS brings higher heating temperature in the combustor and significantly higher thermal efficiency at partial-load by optimizing the control scheme. A component-level model is used to conduct energy and performance analyses for RGT. The control scheme is optimized to enhance partial-load efficiency and protect RGT from temperature overrun, rotational speed overrun, and compressor surge.The optimal control scheme keeps the combustor exit temperature constant at the maximum restricted value to attain minimum combustor exergy loss under partial-load. The optimal control scheme brings smaller surge margins, but it successfully reverses the deterioration trend of efficiency with decreased load. The thermal efficiency of the original RGT decreases by 8.2 % as the load decreases from 100 to 40 %. The HEPS makes the efficiency curve of the RGT almost keep horizontal as the load ranges from 100 to 40 %. The specific fuel consumption decreases by 29.1 %, and the thermal efficiency increases by 11.5 % at 40 % load, compared to the original RGT.

Deep Reinforcement Learning-Based Energy Management for Liquid Hydrogen-Fueled Hybrid Electric Ship Propulsion System

This study proposed a deep reinforcement learning-based energy management strategy (DRL-EMS) that can be applied to a hybrid electric ship propulsion system (HSPS) integrating liquid hydrogen (LH2) fuel gas supply system (FGSS), proton-exchange membrane fuel cell (PEMFC) and lithium-ion battery systems. This study analyzed the optimized performance of the DRL-EMS and the operational strategy of the LH2-HSPS. To train the proposed DRL-EMS, a reward function was defined based on fuel consumption and degradation of power sources during operation. Fuel consumption for ship propulsion was estimated with the power for balance of plant (BOP) of the LH2 FGSS and PEMFC system. DRL-EMS demonstrated superior global and real-time optimality compared to benchmark algorithms, namely dynamic programming (DP) and sequential quadratic programming (SQP)-based EMS. For various operation cases not used in training, DRL-EMS resulted in 0.7% to 9.2% higher operating expenditure compared to DP-EMS. Additionally, DRL-EMS was trained to operate 60% of the total operation time in the maximum efficiency range of the PEMFC system. Different hydrogen fuel costs did not affect the optimized operational strategy although the operating expenditure (OPEX) was dependent on the hydrogen fuel cost. Different capacities of the battery system did not considerably change the OPEX.

Model Predictive Control Strategies for Turbine Electrified Energy Management

Abstract The increasing electrification of aircraft propulsion systems is leading to new control architectures being developed to address integration between electric machines and gas-based turbine engines. For hybrid-electric propulsion systems, current conceptual architectures often couple electric machines with the shafts of gas turbine engines and introduce energy storage. Leveraging the electrical power system of hybridized engines, Turbine Electrified Energy Management (TEEM) is a recent control approach that improves transient operability in an effort to enable more efficient and lighter weight turbomachinery. This study seeks to expand TEEM's application beyond traditional proportional-integral (PI) control by presenting linear model predictive control (MPC) schemes to execute the TEEM concept. Through constraint selection and cost function design, transient operability goals for TEEM are considered with no external logic or saturation. Unique to the designs are the use of a washout filter, which simplifies transient detection and motor activation logic. The proposed architectures are implemented with both centralized MPC and distributed MPC approaches, and comparisons are drawn to a benchmark PI controller simulated on a nonlinear turbofan engine model at one ground condition and one cruise condition. Performance is evaluated using compressor maps, stall margin performance, and two novel metrics: transient stack usage and transient excursion integral. Results reveal the linear MPC scheme performs comparably to the baseline controller and can be implemented in at least two distinct configurations with potential for further modifications, thus establishing the groundwork for future investigations.

Virtual Multi-Criterial Calibration of Operating Strategies for Hybrid-Electric Powertrains

In hybrid vehicle development, the operating strategy has a decisive role in meeting the development goals, such as compliance with emission standards and high energy efficiency. A considerable number of interactions and cross-influences on other topics, such as emissions, on-board diagnostics, or drivability, must be considered during the calibration process. In this context, the given time constraints pose further challenges. To overcome these, approaches for virtualization of the calibration process are an effective measure. For this purpose, in the current study, a real engine control unit is embedded into a virtual simulation environment on so-called hardware-in-the-loop (HiL) testbenches, which allow virtual calibration and validation of the complete target vehicle. In this context, the paper presents a novel method for virtual calibration of operating strategies for hybrid-electric propulsion systems. This includes an innovative multi-criterial approach that considers the requirements of several development tasks, such as emission and OBD calibration. Measurement data for this optimization is generated on a HiL testbench setup tailored for the described methodology, including both the electrical setup and the simulation environment. To validate the selection of modeling approaches and the parametrization, the simulation environment is operated in open loop. The results of the open loop validation show promising behavior regarding the proposed use case. Finally, the presented methodology is evaluated regarding time and cost savings compared to a conventional approach.

Fuel cell hybrid electric propulsion system for a lightweight helicopter: Design and performance analysis in urban air mobility scenario

The main purpose of this work is to investigate the performance of a hybrid fuel cell/battery powertrain concept for a lightweight helicopter in an urban air mobility scenario. Three different hybrid configurations are compared with a battery-electric design and a performance study is carried out over three specific missions, to identify the most appropriate design in each considered operative condition.Results show that a hybrid configuration may outperform the battery-electric one if a suitable balance between power sources is found. The hybrid design with a 70 kW fuel cell triplicates the number of regional transports completed by the battery-electric configuration, but it is less performing on urban routes. On the other hand, a 90 kW fuel cell, turned out to provide enhanced performance for high-power duty cycles, as for an urban mission.In general, the optimal hybrid configuration, in terms of achievable range, strictly depends on the specific duty cycle.

Investigation of hybrid-electric propulsion system applied on Cessna 172S aircraft

In this study, hybrid-electric propulsion systems, which have become a focal point in aviation in recent years, were addressed. In order to see the effects of hybrid-electric propulsion systems on fuel consumption, greenhouse gas emissions and flight costs, five different flight times (60, 90, 120, 150, 180 min) and five different cruise altitudes (1200, 1800, 2400, 3000, 3600 m) were compared with conventional flights. The widely used Cessna 172S aircraft was taken as a reference for the conceptual applications in the study. As a result of the study, the hybrid-electric propulsion system achieved the highest fuel and cost savings of 15.1% and 14.2%, respectively, for 120 minutes flight time and 2400 m altitude, while the lowest fuel and cost savings of 9.7% and 9.1% were achieved for 60 minutes flight time and 1200 m cruise altitude. The highest CO2 reduction was 6.86 kg per hour for 120 minutes and 1200 m altitude flight, while the lowest CO2 reduction was 4.47 kg for 180 minutes and 3600 m altitude flight. It has been determined that flights with hybrid-electric configuration have advantages over conventional flights.

The perspective of hybrid electric hydrogen propulsion systems

Electric cars are becoming increasingly popular, with the European Union and the United States administrations committed to making their share overwhelming by the end of this decade. In analogy, electric powerboats and aircraft are also being proposed. Here we show as hybrid electric vehicles (HEVs) have advantages vs. battery-only electric vehicles (BEVs) for all these applications. Adopting a hybrid propulsion system based on storing most of the energy in hydrogen, and producing electricity on board through a fuel cell (FC) stack, or an internal combustion engine (ICE) plus a generator, gives a much better techno-economic perspective, and reduced life cycle analysis CO2 emissions, than the use of huge lithium-ion batteries. An HEV having plug-in capability and a relatively small battery permits pure electric operation on short travel, without the burden of huge batteries to deliver range. The battery of the HEV buffers the upstream hybrid generation system, which may recharge the battery and/or power directly the electric motor, and store the braking energy in ground vehicles. HEVs fuel energy storage and onboard electricity generation on demand permit reduced total mass of the propulsion system for the same design range as huge batteries. HEVs with ICE working on hydrogen offers the minimum total mass of the propulsion system, then HEVs with FC. This assessment is correct for the current liquid electrolyte batteries and the near-future solid-state electrolyte batteries, based on their energy density per unit mass, and the indirect emissions of batteries.

Fuzzy-based optimal energy management strategy of series hybrid-electric propulsion system for UAVs

Hybrid-electric propulsion system (HEPS) has gained significant attention in unmanned aerial vehicles (UAVs) due to its potential to significantly reduce fuel consumption and pollutant emissions. Effective energy management strategies are crucial in ensuring the efficient operation of HEPS in UAVs, as they involve multiple power and energy sources. While conventional equivalent consumption minimum strategy (ECMS) is effective in distributing engine and battery output power, it struggles to maintain the battery’s state of charge (SOC) within desired levels in case of engine failure. The present study introduced the fuzzy logic control-equivalent consumption minimum strategy (FLC-ECMS), a fuzzy-based composite energy management strategy that incorporates the robustness and adaptability of fuzzy logic control. Through simulation tests under general aviation cruise flight and cargo transport flight scenarios, the results indicated that hybrid UAV equipped with the HEPS can decrease fuel consumption and CO2 emissions by at least 18.6% and NOx emissions by 10.1% in the first profile and by 23.6% and 11.2% in the second profile, compared to conventional oil-powered UAV. The FLC-ECMS method not only reduces fuel consumption and emissions, but also maintains the battery SOC within permitted range and minimizes the difference between front and back SOC. This study provides new insights into the optimal energy management of HEPS for complex profiles in UAVs, highlighting the significance of UAVs in reducing environmental impacts, and has the potential for broader application in other electric propulsion systems.

Study on Power-Split Hybrid Electric Propulsion Systems for Lightweight Helicopters

Study on Power-Split Hybrid Electric Propulsion Systems for Lightweight Helicopters

Multivariable optimization of pyramidal compound substrates for cooling of power-electronics in modern hybrid and electric propulsion systems

We present a method for the optimization of the thermal cooling of heat sources mounted on top of layered composites and pyramidal substrates, that are widely used in the power electronics of hybrid-electric propulsion systems. The analytical solution of the Laplace’s heat equation is approximated via Fourier expansion series and it is coupled to the Influence Coefficient Method (ICM) to provide a functional of the overall thermal stress to minimize. A multivariable optimization method is derived by coupling the equations for the heat transfer with the Sequential Least-Square Quadratic Programming (SLSQP), or the Bounded Limited-Memory BFGS (L-BFGS-B) algorithm. Code validation is performed against three-dimensional simulations and experimental data available from the literature. It is shown that an optimal component relocation and apportionment of the overall thickness of the multilayer substrate promotes a sensible reduction of the thermal stress.

Integrated optimization of speed schedule and energy management for a hybrid electric cruise ship considering environmental factors

Severe global energy crisis and greenhouse effect have promoted the rapid growth of hybrid electric propulsion systems (HEPSs) applied to cruise ships. However, the conventional methodologies, which optimize sailing speed and energy management separately, restrict the improvement of the ship energy efficiency. This study proposes an integrated optimization of speed schedule and energy management considering changes in wind, waves, and drifting ice during the voyage. First, a refined energy flow model of the HEPS against the resistance from wind, waves, and drifting ice in addition to the hydrostatic pressure is established. Second, the integrated optimization problem of speed schedule and energy management is formulated to pursue minimal fuel consumption. Third, the complex optimization problem is solved by a low computation load algorithm, in which the K-means algorithm and physical turning points divide the target route into several segments considering environmental characteristics, the particle swarm optimization algorithm optimizes the speed in each segment, and the equivalent fuel consumption minimization strategy optimizes the energy management during sailing. Finally, two case studies of a cruise ship sailing in the Drake Passage validate the effectiveness of the proposed method. The results show that the integrated optimization significantly reduces fuel consumption compared with the conventional separation optimization in terms of either speed schedule or energy management, as well as the conventional heuristic strategy. Furthermore, the integrated optimization demonstrates advantages in reducing greenhouse emissions caused by fuel and electricity consumption of the HEPS.

On the Potentials of the Integration of Pressure Gain Combustion with a Hybrid Electric Propulsion System

As the issue of pollutant emissions from aviation propulsion escalates, research into alternative powertrains is gaining momentum. Two promising technologies are the Hybrid Electric Propulsion System (HEPS) and Pressure Gain Combustion (PGC). HEPS is expected to reduce pollutant emissions by decreasing fuel consumption, whereas PGC uses detonation in the combustor to increase the thermal efficiency of engines by elevating the total pressure during combustion. This study extensively explores the integration of these two emerging technologies, thoroughly assessing the advantages that arise from their combination. First, the renowned turboprop engine PW127 is benchmarked and modeled using Gasturb software. The model is integrated into Simulink using the T-MATS tool, with HEPS and pressure gain components added to analyze the thermodynamics of various configurations under different pressure gain values and HEPS parameters. The analysis, conducted up to the cruise phase of the baseline aircraft, reveals that applying pressure gain combustion through Rotating Detonation Combustion (RDC) results in a more significant increase in efficiency and decrease in fuel consumption compared to HEPS with conventional gas turbines. However, HEPS helps maintain a more uniform combustor inlet condition and reduces the Turbine Inlet Temperature (TIT) at the takeoff phase, where the highest TIT otherwise occurs. The results suggest that integrating HEPS with PGC can be beneficial in maintaining optimal combustor conditions and mitigating turbine efficiency degradation.

Hydrogen fuel cell integration and testing in a hybrid-electric propulsion rig

On the road towards greener aviation, hybrid-electric propulsion systems have emerged as a viable solution. In this paper, a system based on hydrogen fuel cells is proposed and evaluated in a laboratory setting with its future integration in a propulsive system in mind and main focus on the ability to lessen the power demand on the opposing side of the bench. The setup consists in a parallel architecture with two power sources: a hydrogen fuel cell and a battery. First, the performance of the fuel cell and its capability to provide power to one of the motors are analyzed. Then, the entire parallel hybrid system is evaluated. Although the experimental setup was shown to be sub-optimal, the results demonstrated the ability of this greener alternative to reduce power demand on the opposing side of the parallel configuration, with a reduction of up to 40.3% in the highest load scenario, and maximum power output on the fuel cell of 257.8 W. The stack performance was also concluded to be very dependent on the operating temperature.

An efficient intelligent energy management strategy based on deep reinforcement learning for hybrid electric flying car

Hybrid electric flying cars hold clear potential to support high mobility and environmentally friendly transportation. For hybrid electric flying cars, overall performance and efficiency highly depend on the coordination of the electrical and fuel systems under ground and air dual-mode. However, the huge differences in the scale and fluctuation characteristics of energy demand between ground driving and air flight modes make the efficient control of energy flow more complex. Thus, designing a power coordinated control strategy for hybrid electric flying cars is a challenging technical problem. This paper proposed a deep reinforcement learning-based energy management strategy (EMS) for a series hybrid electric flying car. A mathematical model of the series hybrid electric flying car driven by the distributed hybrid electric propulsion system (HEPS) which mainly consists of battery packs, twin turboshaft engine and generator sets (TGSs), 16 rotor-motors, and 4 wheel-motors is established. Subsequently, a Double Deep Q Network (DDQN)-based EMS considering ground and air dual driving mode is proposed. A simplified method for the number of control variables is designed to improve exploration efficiency and accelerate the convergence speed. In addition, the frequent engine on/off problem is also taken into account. Finally, DDQN-based and dynamic programming (DP)-based EMSs are applied to investigate the power flow distribution for two completely different hypothetical driving scenarios, namely search and rescue (SAR) scenarios and urban air mobility (UAM) scenarios. The results demonstrate the effectiveness of the DDQN-based EMS and its capacity of reducing the computation time.

Systems Integration Framework for Hybrid-Electric Commuter and Regional Aircraft

System integration is one of the key challenges to bringing future hybrid-electric and all-electric aircraft into the market. In addition, retrofitting and redesigning existing aircraft are potential paths toward achieving hybrid and all-electric flight, which are even more challenging goals from a system integration perspective. Therefore, integration tools that bridge the gap between the aircraft and the subsystem level need to be developed for use in the conceptual design stage to address current system integration challenges, such as the use of space, the share between propulsive and secondary power, required level of electrification, safety, and thermal management. This paper presents a multidisciplinary design analysis (MDA) framework that integrates aircraft and subsystem sizing tools. In addition, this paper includes improved physics-based subsystem sizing methods that are also applicable to smaller, commuter, or regional aircraft. The capabilities of the developed framework and tools are presented for a case study covering the redesign of the DO-228 with a hybrid-electric propulsion system in combination with the electrification of its systems architecture and different subsystem technologies.

Simultaneous and Global Optimizations of LNG-Fueled Hybrid Electric Ship for Substantial Fuel Cost, CO2, and Methane Emission Reduction

Natural gas (NG) is a promising low-carbon fuel to replace diesel for heavy-duty marine propulsion with prominent fuel cost and carbon dioxide equivalent (CDE) emissions reduction potential. However, using NG in compression ignition (CI) engines presents several inherent drawbacks. This research addresses the central issue of an NG-diesel CI engine with increased methane emissions, resulting in minor CDE emission reduction. The hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emissions are minimized in addition to fuel consumption and carbon dioxide emission reduction as in the current practice. The simultaneous optimizations of powertrain component sizes and the NG-engine hybrid electric propulsion control are introduced to minimize NG fuel consumption and CDE emissions globally. The top-level powertrain component sizing and bottom-level optimal power control and energy management are conducted simultaneously to achieve global optimization with balanced fuel cost and CDE emissions reductions. The new method reduced the fuel cost by about 75 percent and well-to-wake CDE emissions by about 40 percent over the traditional diesel-mechanical propulsion for the test ferry running under an actual operation profile. The research opened a new path to the global design and control optimization of the NG-diesel CI engine-powered hybrid electric marine propulsion system.

Investigation of the operational flexibility of a regional hybrid-electric aircraft

The complexity of hybrid-electric aircraft propulsion systems is also characterized by the greater number of degrees of freedom of the energy management system, whose objective is to split the required power to fly the aircraft to the different available powertrains (i.e., gas turbines, electric motors, fuel cells, etc.). Typically, a single design mission is considered for assessing the performance of a hybrid-electric propulsion system, often with a simple constant split power between the batteries and gas turbine. A probabilistic set-based design space exploration methodology is used and allows us to study the effects of lifecycle analysis of the battery pack of a hybrid-electric 50-seater turboprop, while different mission scenarios are considered. Using this approach, it is possible to flexibly find multiple families of energy management strategies that can satisfy battery capacity requirements and the reduction of emissions simultaneously. Furthermore, the generated data can help the designers to understand the hierarchy of the requirements that drive the design of the propulsion system for a range of operating scenarios, with emphasis on the energy storage system. Hence, the airliners are offered enhanced operational flexibility of the aircraft for different and desirable mission profiles.

Electric and hybrid-electric aircraft propulsion systems: development, difficulties and opportunities

As the world has grown rapidly over the past century, so has the aviation industry as a whole. This has led to a huge volume of aviation market and at the same time the aviation market excessive reliance on fuel, with a consequent huge environmental impact. As a global community, we are moving towards an electrified transport architecture. And some studies of aircraft propulsion systems have shown that electric and hybrid electric propulsion systems offer significant benefits over conventional fuel propulsion systems. However, there are also some researches have shown that while some electrified propulsion strategies can result in significant reductions in CO2 emissions, the overall cost of the aircraft can also increase significantly. The economic efforts made in terms of purely electric and hybrid propulsion have not been significant, so this technology is not yet in significant use in the aviation market. This paper considers some of these systems and analyses their structural advantages, technical requirements, etc. This is followed by a discussion of the current difficulties and future trends in the application of purely electric and hybrid propulsion systems. It is also significant to convey that the current immaturity of this technology and the areas for improvement.

Coordinated clutch actuation for drivability improvement and energy management of a novel multi-mode hybrid electric vehicle and HIL validation

This article presents a novel architecture of a particular class, i.e., multi-mode hybrid electric propulsion systems that utilize two planetary gear sets, multiple clutches, two electric motors, and an internal combustion engine. Although this class of propulsion systems offers architectural compactness, improved fuel economy, and operational versatility, it faces a drivability issue arising from simultaneous clutch engagement and disengagement during mode shift events. Such drivability issues cannot be addressed by baseline motor-torque compensation-based coordinated control that is typically employed to address the drivability issues in power-split and parallel hybrid propulsion systems. Therefore, this article proposes an enhanced version of the coordinated control that includes the clutch’s torque capacity control. The enhanced coordinated control module augments with the energy management system, making the mode shift schedule drivable and near-optimal. A real-time hardware-in-the-loop test bench is developed to accurately evaluate the enhanced coordinated control’s impact on the energy management system’s performance. Test bench results demonstrate that the enhanced coordinated control is more effective than the baseline coordinated control in attenuating the propulsion system’s perturbations during mode shift events and making the overall mode shift schedule drivable. The enhanced energy management system consumes 7%–8% more fuel while transforming the mathematically optimal mode shift schedule into a drivable one.