Hybrid Electric Propulsion System Research Articles

Real-time coordinated control strategy for the hybrid electric propulsion system of a flying car with model adaptation and game theory

Coordination among the multiple power components is essential for the hybrid electric propulsion systems since the decision made by one impacts the state and decisions of others due to the coupling mechanical and electrical dynamics. Traditional model-based approaches with weight-sum objectives may result in misleading optimization or even unstable situations because of the inherent poor scalability and synergy. To overcome this issue, this paper proposes a novel game theory-based control strategy with model adaptation mechanism for the hybrid electric flying car to enhance the control performance, system stability, and robustness. Firstly, a control-oriented model of the system is derived with the utilization of the recursive least square parameter estimation method. The non-cooperative game framework is then established with the turboshaft engine subsystem and electric supply subsystem treated as two independent players. The performance of Nash equilibrium solutions with closed-loop and open-loop information structures are investigated where the problem is iteratively solved by exploiting Pontryagin’s Minimum Principle and dynamic programming, respectively. The simulation results demonstrate that the game theory-based controllers can outperform MPC with the weight-sum objectives in terms of control efficiency and robustness improvement and the game theory-based controller with open-loop information structure shows excellent computation efficiency. Moreover, the result of the hardware-in-the-loop experiment demonstrates the real-time performance of the proposed controller.

Modelling the nonlinear system performance of hybrid-electric propulsion systems with aerothermodynamic interdependencies

The development of commercial aircraft with hybrid-electric propulsion systems is currently a subject of extensive research in order to improve local air quality and reduce combustion emissions. Among the various types of engines being studied, the two-spool parallel hybrid-electric turbofan engine is particularly challenging due to the low-pressure compressor (LPC). The hybridisation process tends to throttle the LPC, accentuating its significance in the propulsion system. For reliable operation of such systems, accurate predictions of the LPC performance during time-sensitive manoeuvres such as a go-around are important. These manoeuvres are heavily influenced by time-dependent effects that govern the propulsion system’s performance. Often, the aerothermodynamic interplay between these effects is overlooked in propulsion models. In this study, the influence of these aerothermodynamic interdependencies on the modelling results is investigated. To investigate these aerothermodynamic interactions, a dynamic model is developed to simulate the performance of the hybrid-electric turbofan engine. In comparison, a constant mass flow model is used, which is not able to simulate these interdependencies. The results show that the aerothermodynamic interdependencies significantly affect the modelled time-resolved performance, especially for surge margin of the LPC, with this effect becoming more pronounced at higher levels of hybridisation. Therefore, the study recommends the adoption of dynamic simulation methodologies for hybrid-electric engines to guarantee high simulation precision, enhance reliability, and satisfy safety standards.

Integrated Hybrid Engine Cycle Design and Power Management Optimization

Abstract A novel integrated gas turbine cycle design and power management optimization methodology for parallel hybrid electric propulsion architectures is presented in this paper. The gas turbine multipoint cycle design method is extended to turboprop and turbofan architectures, and several trade studies are performed initially at the cycle level. It is shown that the maximum degree of electrification is limited by the surge margin levels of the booster in the turbofan configuration. An aircraft mission-level assessment is then performed using the integrated optimization method initially for an A320 Neo style aircraft case. The results indicate that the optimal cycle redesigned hybrid electric propulsion system (HEPS) favors takeoff and climb power on-takes while optimal retrofit HEPS favor cruise power on-takes. It is shown that for current battery energy density (250 Wh/Kg), there is no fuel burn benefit. Furthermore, even for optimistic energy density values (750 Wh/kg) the maximum fuel burn benefit for a 500 nm mission is 5.5% and 4% for redesigned and retrofit HEPS, respectively. The power management strategies for HEPS configurations also differ based on gas turbine technology with improvement in gas turbine technology showing greater scope for electrification. The method is then extended to ATR 72 style aircraft case, showing greater fuel burn benefits across the flight mission envelope. The power management strategies also change depending on the objective function, and optimum strategies are reported for direct operating cost or fuel burn. The retrofit case studies show a benefit in direct operating cost compared to redesigned case studies for ATR 72. Finally, a novel multimission approach is shown to highlight the overall fuel burn and direct operating cost benefit across the aircraft mission cluster.

An efficient energy management strategy based on heuristic dynamic programming specialized for hybrid electric unmanned delivery aerial vehicles

Large-sized unmanned delivery aerial vehicles (UDAVs) stand out as prominent vertical take-off and landing aircraft, benefiting from integrating a hybrid electric propulsion system (HEPS) to enhance the power-to-weight ratio. Despite this advancement, UDAVs encounter challenges regarding range limitations and the need for swift computational solutions. Addressing these issues necessitates a computationally efficient energy management strategy (EMS) that optimizes power distribution to properly plan engine working points, ultimately aimed at enhancing fuel economy to increase flight range. This study proposes a heuristic dynamic programming (HDP)-based EMS tailored for the HEPS of a large-sized UDAV. In this strategy, the HDP framework is adopted to improve computational efficiency by iteratively updating control variables. To account for the specific flight characteristics, a flight state identifier incorporating selected flight command flags applicable to UDAVs is designed. This identifier aids in predicting velocity changes for different flight states by amalgamating corresponding prediction networks into an integrated velocity prediction network (IVPN). Substituting the model network with IVPN in the HDP framework significantly enhances prediction accuracy and guides power distribution towards optimal results, signifying an efficient EMS specialized for UDAVs. The proposed strategy is evaluated against baseline strategies in designed flight scenarios, highlighting a remarkable 51.37% improvement in prediction accuracy, a noteworthy 6.04% reduction in equivalent fuel consumption, and an impressive 95.81% reduction in global computation time. Finally, the actual applicability of the proposed strategy is validated in a hardware-in-loop test. Consequently, the proposed strategy can provide theoretical support for the efficient energy management of diverse large-sized UDAVs.

Tri-objective optimal design of a hybrid electric propulsion system for a polar mini-cruise ship

The environmental impact, economic considerations, and passenger comfort of hybrid electric propulsion systems (HEPSs) are significantly influenced by the design phase. However, a design method solely focused on minimizing annual fuel consumption may inadvertently lead to increased life-cycle cost and decreased annual pure-electric sailing time. To address this issue, this paper presents a tri-objective optimization design method to achieve an optimal trade-off among the objectives for a polar mini-cruise ship. First, a scalable mathematical model is established for a hybrid diesel engines/batteries/shore power propulsion system. Then, a refined, rule-based energy management strategy is developed to control the power flow among energy sources. Next, a tri-objective optimization model with detailed descriptions of objectives, variables, constraints, and method is formulated. Finally, the performances of three optimal designs, obtained through tri-objective optimization, single-objective optimization, and conventional heuristics, are compared through simulations based on a typical real-world navigation case. The results highlight the clear advantages of the proposed method over the other two methods. Furthermore, sensitivity analysis underscores that the parameters of the diesel engine, battery, and gear ratio exert a greater impact on HEPS performances than other factors.

Powertrain Design For Small Scale Parallel Hybrid-Electric Test Bench

Parallel hybrid-electric propulsion systems for small scale unmanned aerial systems (UAS) when tested with an internal combustion engine are susceptible to damage due to increased torque compared to all-electric configurations. The University of Victoria Centre for Aerospace Research has conducted testing and identified several locations in the system for potential upgrades. One of the largest issues identified was the electromagnetic clutch’s inability to handle the torque of the Corvid-50 engine. Thus, a new clutch and powertrain system was specified which is better rated for combustion operation. Similar findings are reported based on testing performed at Ł-Institute of Aviation, where a hybrid-electric powertrain stand experienced torque spikes. The spike amplitude was several times higher than the nominal momentum of the ICE, given in the specification sheets. In result, at some working modes, a strong slippage of the clutch has been observed. It is also of highest importance to propose and test potential methods to minimize momentum influence to the powertrain. The goal is to increase robustness of such hybrid systems, and decrease the overall mass of the system.

Flight-Path Optimization for a Hybrid-Electric Aircraft

Abstract This study aims to illustrate a sequence that optimizes the flight-path trajectory for a hybrid-electric aircraft at mission level, in addition to identifying the respective optimum power management strategy. An in-house framework for hybrid-electric propulsion system modeling is utilized. A hybrid-electric commuter aircraft serves as a virtual test-bench. Vectorized calculations, decision variable count, and optimization algorithms are considered for reducing the computational time of the framework. Performance improvements are evaluated for the aircraft's design mission profile. Total energy consumption is set as the objective function. Emphasis lies on minimizing the average value and standard deviation of the energy consumption and timeframe metrics. The best performing application decreases computational time by two orders of magnitude, while retaining equal accuracy and consistency as the original model. It is employed for creating a dataset for training an artificial neural network (ANN) against random mission patterns. The trained network is integrated into a surrogate model. The latter part of the analysis evaluates optimized mission profile characteristics with respect to energy consumption, against a benchmark flight-path. The combined optimization process decreases the multihour-scale timeframe by two orders of magnitude to a 3-min sequence. Using the novel framework, a 12% average energy consumption benefit is calculated for short, medium, and long regional missions, against equivalent benchmark profiles.

Hierarchical Control Strategy for the Hybrid Electric Propulsion System of a Flying Car with Engine Start-Stop System and Dynamic Coordination

Hierarchical Control Strategy for the Hybrid Electric Propulsion System of a Flying Car with Engine Start-Stop System and Dynamic Coordination

Data-Driven Cooperative Differential Game Based Energy Management Strategy for Hybrid Electric Propulsion System of a Flying Car

Data-Driven Cooperative Differential Game Based Energy Management Strategy for Hybrid Electric Propulsion System of a Flying Car

A New Method for Solving Objective Function of Hybrid Electric Propulsion System for Intelligent Design

A New Method for Solving Objective Function of Hybrid Electric Propulsion System for Intelligent Design

A Back–Forward Approach-Based Efficiency Performance Analysis Model for Hybrid Electric Propulsion Ships Using the Holtrop–Mennen Method

Due to tightening regulations on exhaust emissions from ships, there is a growing need to develop electric or hybrid electric propulsion systems to replace conventional diesel-based ship power systems. The hybrid electric propulsion system is suitable for small and medium-sized vessels and its energy efficiency significantly depends on the arrangement of different power sources, power control strategies for energy sources, and energy storage system (ESS). Therefore, an analytical simulation to evaluate the energy efficiency of ships with their structure and control strategies is needed. In this study, a back–forward approach-based efficiency performance analysis model was developed using the Holtrop–Mennen resistance model to calculate ship resistance and power demand based on a given ship’s speed profiles. This model has the advantages of using easily obtainable ship speed profiles as the input and can be modularized for each power source and ESS, incorporating mechanical performance limitations, and allows for rapid analysis. The developed analytical model was applied to a hybrid electric propulsion system in a marine support vessel and its energy efficiency was evaluated by establishing rule-based power control strategies. As a result, the engine efficiency of the hybrid electric propulsion system increased from about 27% to 30% compared to the existing system, and the final effect of reducing fuel consumption by about 10% compared to the existing system was confirmed through the developed simulator. In the future, this analytical model could be utilized to derive the optimal layout of hybrid electric propulsion systems, and to formulate power control strategies.

A method for an efficiency and weight-optimised preliminary design of a hydrogen-powered fuel cell-based hybrid-electric propulsion system for aviation purposes

There is a worldwide effort to advance the usage of zero-emission propulsion systems for aircraft. Due to their high thermodynamic efficiency and the fact that they produce no CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{CO}_{2}$$\\end{document} and NOx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{NO}_{x}$$\\end{document} emissions, hydrogen-powered fuel cells are becoming increasingly popular for aviation purposes. However, fuel cell systems suffer from lower power density and higher cooling requirements when compared to conventional propulsion systems. Harnessing the high potential requires an optimised design of the whole propulsion system and its heat management system. This paper aims to present a method for the preliminary design and dimensioning of a fuel cell-based hybrid-electric propulsion system, which respects the limits of the heat management system and is weight and efficiency optimised. Thermodynamic models of the whole propulsion system are a crucial element to enable further investigations. Such a model has been developed, which is suitable for unsteady simulations of the propulsion and the heat management system performance of a short-range four-seater aircraft. A parameter study of the design parameters has been performed to display their impact on the system mass, the overall efficiency and the total hydrogen consumption. These results enable the identification of an overall optimised configuration. The study indicates that fuel cell-only configurations with an oversized fuel cell stack are beneficial for the analysed aircraft and flight mission.

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.