Shared Control Research Articles

On model-based time trend adjustments in platform trials with non-concurrent controls

BackgroundPlatform trials can evaluate the efficacy of several experimental treatments compared to a control. The number of experimental treatments is not fixed, as arms may be added or removed as the trial progresses. Platform trials are more efficient than independent parallel group trials because of using shared control groups. However, for a treatment entering the trial at a later time point, the control group is divided into concurrent controls, consisting of patients randomised to control when that treatment arm is in the platform, and non-concurrent controls, patients randomised before. Using non-concurrent controls in addition to concurrent controls can improve the trial’s efficiency by increasing power and reducing the required sample size, but can introduce bias due to time trends.MethodsWe focus on a platform trial with two treatment arms and a common control arm. Assuming that the second treatment arm is added at a later time, we assess the robustness of recently proposed model-based approaches to adjust for time trends when utilizing non-concurrent controls. In particular, we consider approaches where time trends are modeled either as linear in time or as a step function, with steps at time points where treatments enter or leave the platform trial. For trials with continuous or binary outcomes, we investigate the type 1 error rate and power of testing the efficacy of the newly added arm, as well as the bias and root mean squared error of treatment effect estimates under a range of scenarios. In addition to scenarios where time trends are equal across arms, we investigate settings with different time trends or time trends that are not additive in the scale of the model.ResultsA step function model, fitted on data from all treatment arms, gives increased power while controlling the type 1 error, as long as the time trends are equal for the different arms and additive on the model scale. This holds even if the shape of the time trend deviates from a step function when patients are allocated to arms by block randomisation. However, if time trends differ between arms or are not additive to treatment effects in the scale of the model, the type 1 error rate may be inflated.ConclusionsThe efficiency gained by using step function models to incorporate non-concurrent controls can outweigh potential risks of biases, especially in settings with small sample sizes. Such biases may arise if the model assumptions of equality and additivity of time trends are not satisfied. However, the specifics of the trial, scientific plausibility of different time trends, and robustness of results should be carefully considered.

Obstacle Avoidance in Highly Automated Cars: Can Progressive Haptic Shared Control Make it Safer and Smoother?

Haptic shared control has proven to be an effective method to assist a driver in controlling a vehicle. This method is now being considered for use in developing strategies for smooth transitions between manual and autonomous driving modes. This article has two objectives. First, it proposes to adapt an existing haptic shared control strategy to achieve transitions between manual and autonomous modes and to evaluate this approach with real drivers on a driving simulator. Second, it proposes to evaluate four different transition profiles in an obstacle-avoidance context. The first profile is a gradual transition from the autonomous mode to shared control mode, followed by another transition from the shared control mode to autonomous mode once the obstacle is passed. The second is a gradual transition from autonomous mode to manual mode. The third is a binary transition from autonomous mode to manual mode. Finally, in the fourth condition, the driver overrides the autonomous mode. These transition profiles were evaluated in curves and straight lines on a driving simulator. The results first validated the use of the haptic shared control strategy to execute transitions between manual and autonomous modes. The distribution of the torques delivered by the automation system and the driver corresponded to the progression of the expected sharing level. Second, the gradual transitions showed advantages over binary transitions and the override of the autonomous mode, both in terms of steering performance and subjective evaluation.

Human-Machine Shared Steering Control for Vehicle Lane Keeping Systems via a Fuzzy Observer-Based Event-Triggered Method

This paper is concerned with the human-machine shared control issue for vehicle lane keeping systems via a new fuzzy observer-based event-triggered method. In order to capture system nonlinear and uncertain characteristics such as nonlinear tire dynamics, varying velocity and driver behavioral uncertainties, Takagi-Sugeno fuzzy approach is employed to model the global driver-vehicle-road system. After system modeling, the fuzzy observer-based control structure is considered because a full states information is not available in practical driving environment. Then, most existing human-machine shared control methods are based on the periodic sampling communication mechanism. However, since the network bandwidth is limited, the above mechanism may cause oversampling and communication congestion. Thus, an adaptive event-triggered mechanism is introduced between the observer and the controller to mitigate the communication burden and improve the bandwidth utilization. Based on Lyapunov functional theory, a set of sufficient conditions are given to calculate desired human-machine shared controllers. Finally, simulation tests are implemented on Matlab/Simulink-CarSim platform and simulation results illustrate that the proposed method can achieve a favorable improvement in the lane keeping capability, the driver handling comfort and the network bandwidth utilization.

Adaptive Steering Torque Coupling Framework Considering Conflict Resolution for Human-Machine Shared Driving

Human-machine shared control has become an effective cutting-edge approach to enhance driving safety and assist in the transition from manual to autonomous driving. However, driving authority allocation when conflict occurs between a human driver and a machine still represents an intractable problem. In order to solve this problem, this paper proposes an adaptive steering torque coupling framework to achieve the human-machine shared control with conflict resolution. Additionally, a driver trajectory prediction method considering human-machine interaction is established based on the extended state observer and long short-term memory network. In addition, the human-machine shared steering system is modeled based on a non-cooperative dynamic game by the prediction model method for path-tracking, and the obtained solution is given according to the Nash equilibrium. Particularly, a dynamic load allocation approach is designed to resolve human-machine conflict and relax the driver. In order to verify the strategy formed based on the proposed framework, a driver-in-the-loop experiment is conducted. The experimental results reveal that the proposed strategy can effectively reduce the human-machine conflict torque and ensure a driver has absolute control authority. Furthermore, the proposed strategy can also transfer the driving workload between the driver and machine, provide driving experience, or improve driving comfort when there is no conflict.

Distribution Voltage and Output Power Sharing Control for DC Microgrids using Fuzzy Control and Gain-Scheduling

Abstract: A dc microgrid has gained popularity in recent years due to dc sources such as solar panels, fuel cells, and batteries. Interconnections can be made without AC to DC conversion, which improves system efficiency. Furthermore, when a utility grid is experiencing voltage sags or blackouts, A continuous supply of high-quality power is possible. Parallel operations have been proposed with several types of droop controls and microgrids, including DC and AC, were also used in some cases. Sharing the storage unit outputs via a gain scheduling scheme would result in unbalanced storage energy. Therefore, this research integrates fuzzy control with gain-scheduling techniques to create a new voltage control system that can both share energy and optimize power consumption. A microgrid consists of a variety of distributed energy sources used for the energy storage system. Fuzzy control is used to maintain power quality. Controlling fuzzy is based on different rules with the goal of maintaining constant droop.

Shared Control of Elbow Movements with Functional Electrical Stimulation and Exoskeleton Assistance.

Individuals who suffer from paralysis as a result of a spinal cord injury list restoration of arm and hand function as a top priority. FES helps restore movement using the user's own muscles, but does not produce accurate and repeatable movements necessary for many functional tasks. Robots can assist users in achieving accurate and repeatable movements, but often require bulky hardware to generate the necessary torques. We propose sharing torque requirements between a robot and FES to reduce robot torque output compared to a robot acting alone, yet maintain high accuracy. Cooperative PD and model predictive control algorithms were designed to share the control between these two torque sources. Corresponding PD and MPC algorithms that do not use FES were also designed. The control algorithms were tested with 10 able-bodied subjects. Torque and position tracking accuracy were compared when the system was commanded to follow a functional elbow flexion/extension trajectory. The robot torque required to achieve these movements was reduced for the shared control cases compared to the algorithms acting without FES. We observed a reduction in position accuracy with the MPC shared controller compared to the PD shared controller, while the MPC shared controller resulted in greater reductions in torque requirements. Both of these shared algorithms showed improvements over existing options, and can be used on any given trajectory, allowing for better transferability to functional tasks.

Enabling 4-DoF hand guidance using a portable haptic device exerting tangential force on the user's finger pads

Body-grounded kinesthetic haptic devices can provide cues for movement in multiple degrees of freedom by exerting forces directly on users, as in dexterous robot teleoperation tasks. However, these haptic devices have limited workspaces, can destabilize a teleoperation control loop, and can be expensive. Portable haptic devices can approximate the sensations of a kinesthetic device by exploiting diverse human sense of touch principles without these shortcomings. Our goal is to analyze the feasibility of hand guidance (HG) using tangential force stimuli. Here we reveal and quantify users’ interpretation of simultaneous tactile stimulation (STS) applied to multiple finger pads of the same hand. We completed an extensive experiment on different users to reveal a maximum number of understandable cues which can be used as movement commands for HG. As expected, many tactile stimuli tested were meaningless for users, but a few could be clearly interpreted — we call these “intuitive movement cues”. For the experiment, we designed a device that can be held in the palm and exerts tactile stimuli to the user's finger pads on the thumb and index fingers, or the thumb and middle fingers. We performed two studies in which we identified the extent of salience of different movement cues. In particular, commands to redirect the hand position and orientation in four axes: moving forward/backward, wrist twisting right/left (rotate clockwise/counter-clockwise), moving right/left, and wrist tilting up/down (rotate upwards/downwards). The results revealed that this approach provided 7 intuitive directional movement cues for relative HG in 3D space. The proposed HG principle is promising for applications such as robotic surgery training, laparoscopic training, and needle insertion training, during which surgical trainees must learn dexterous hand movements involving motion paths. There are many applications for 3D movement guidance outside the medical domain that could benefit from this haptics technology, including training for precise manipulation and assembly tasks, augmented teleoperation, and communication during shared control in collaborative human-machine systems.

A data-driven model-based shared control strategy considering drivers’ adaptive behavior in driver-automation interaction

Shared control scheme improves the driving performance while having an impact on driver behavior, drivers would constantly adapt their steering behavior mechanism in interaction with a shared controller. This paper proposes a novel data-driven model-based shared control strategy which is capable of considering drivers’ adaptive behaviors in driver-automation interaction to improve safety. The Koopman operator theory, which is a pure data-driven modeling technology, is adopted to yield an explicit control-oriented driver-vehicle model for shared controller design. Besides, a weighted online extended dynamic mode decomposition (WOEDMD) algorithm is proposed to update the Koopman driver model online for better capturing the driver’s adaptive behavior in driver-automation interaction, which settles the problem of driver’s potential behavior mechanism variations in practice. Based on the Koopman driver-vehicle model, a model-based shared controller is proposed in the model predictive control (MPC) framework, and the potential fields are incorporated in the optimization objectives to ensure safety. A group of human-in-the-loop experiments are conducted on a driving simulator to demonstrate the effectiveness of the modeling and shared control methods. The results show that the Koopman operator theory can be exploited for modeling the dynamics of the driver-vehicle integrated system, and the drivers’ adaptive behavior can be captured by the WOEDMD algorithm. Moreover, the shared controller considering the driver’s adaptive behavior improves the driving safety in the collision avoidance task.

CPI: Conservativeness, Permissiveness and Intervention Metrics for Shared Control Evaluation

This paper presents an approach to measure the ability of a shared control system to track user input while simultaneously ensuring safety. These CPI metrics, based on reachability theory, are used to measure the Conservativeness (C), Permissiveness (P) and the amount of Intervention (I) applied to a user nominal control. The metrics apply to arbitrary dynamic systems, state and control constraints, and unlike other existing metrics, they apply to non-differentiable shared controllers including controllers implemented in procedural code. Moreover, we propose a parallel algorithm based on Rapidly-exploring Random Trees (RRTs) for conducting the reachability analysis necessary for computing conservativeness and permissiveness metrics efficiently. We demonstrate how CPI metrics may be used to evaluate a Linear-Quadratic Regulator (LQR) and two different Model Predictive Controller (MPC) based safe shared controllers applied to the cartpole system, for different control parameters.

A Multi-Filter Based Dynamic Power Sharing Control for a Hybrid Energy Storage System Integrated to a Wave Energy Converter for Output Power Smoothing

The output power fluctuations from the wave energy converters (WECs) with a high peak-to-average ratio need to be smoothed out before supplying power to electric loads or power grids. Usually, short-term energy storage is used to smooth out the output power fluctuations of WECs. In this article, a novel multi-filter-based dynamic power-sharing control is devised for a hybrid energy storage system (HESS) integrated with a grid-connected WEC. An advanced model of HESS-integrated WEC consisting of a direct-drive permanent magnet linear generator, a supercapacitor, and a battery system is developed to test the proposed multi-filter-based dynamic control strategy under realistic conditions. The distinguishing features of this study are as follows; 1) the power-sharing strategy is based on a dynamic filter that is designed to change its corner frequency depending upon the incoming ocean wave, 2) the low and the high-frequency power components are allocated based on ocean wave conditions, 3) the proposed strategy is suitable for the real-time control of the proposed HESS integrated with the WEC, and 4) a detailed model of the WEC is used instead of using a pre-saved power profile. The results suggest that with the implementation of the proposed multi-filter-based dynamic power-sharing scheme in the HESS integrated WECs, the output power can be effectively smoothed out before supplying the power to the grid.

Precise Cable-Suspended Pick-and-Place with an Aerial Multi-robot System

This work introduces the G-Fly-Crane, a proof-of-concept aerial multi-robot system designed to demonstrate the advantage of using multiple aerial robots as a valuable tool for novel construction techniques, not requiring the use of heavy engines and costly infrastructures. We experimentally demonstrate its capability to perform pick-and-place and manipulation tasks in a construction scenario, with an increased payload capacity and dexterity compared to the single robot case. The system is composed of three aerial robots connected to a platform by three pairs of cables. The platform is equipped with a gripper, enabling the grasping of objects. The paper describes in detail the hardware and software architecture of our prototype and explains the implemented control methods. A shared control strategy incorporates the human operator in the control loop, thus increasing the overall system reliability when performing complex tasks. The paper also discusses the next steps required to bring this technology from indoor laboratory conditions to real-world applications.

The Role of Women on Dairy Goat Farms in Southern Spain.

Simple SummaryThe involvement of women in livestock production is a tradition around the world, where women have been associated with small animal farming, mainly based on family production systems. They used to be responsible for animal care (feeding and milking) and family care (children and the elderly), with the working hours exceeding the daily working time defined in developed countries. Men are responsible for the farm’s management and finances. In Europe, small ruminants are mainly raised in adverse environments. Nevertheless, they contribute to maintaining an open environment and the prevention of fire damage in times of drought. On the farms studied, a lower incidence of mastitis in goats was found when a woman worked on the farm (they milk with more care and patience). In this study, there is a predominance of farms with women and men (a family unit), where the genders both equally participate when making decisions that involve household expenses; however, this shared control usually ends up being transferred to the man. In addition, very few women are the owners of farms or make binding decisions. Finally, the inclusion of women should be recommended throughout the small ruminant productive process: this would help improve farming results and provide an incentive to keep women in rural areas.One of the factors involved in goat milk production is the role of women as farmers. The aim of this study was to evaluate the role of women on dairy goat farms, considering: (1) the profile of women occupationally involved, (2) the organization of the women’s work, (3) the degree of involvement by women in the decision-making on these farms, and (4) the influence of women’s work on productive results. This study was conducted on 52 dairy goat farms in southern Spain. A descriptive analysis and means comparisons were performed to describe the farms where any women were involved or not. In 61.5% of the farms, at least one woman was involved, with an age of 42.2 ± 8.8 years. Very few women were farm owners, although women took binding decisions in 81.25% of these farms. Their work is dedicated to milking and caring for the kids. Women had a positive influence on the productive variables analysed, and for mastitis in herds, the incidence was lower in herds where women participated (p < 0.01). In conclusion, it is recommended to include women’s work as a factor when characterizing dairy goats farms’ systems to evaluate their positive effect on a farm’s performance.

Shared Control of Bimanual Robotic Limbs With a Brain-Machine Interface for Self-Feeding.

Advances in intelligent robotic systems and brain-machine interfaces (BMI) have helped restore functionality and independence to individuals living with sensorimotor deficits; however, tasks requiring bimanual coordination and fine manipulation continue to remain unsolved given the technical complexity of controlling multiple degrees of freedom (DOF) across multiple limbs in a coordinated way through a user input. To address this challenge, we implemented a collaborative shared control strategy to manipulate and coordinate two Modular Prosthetic Limbs (MPL) for performing a bimanual self-feeding task. A human participant with microelectrode arrays in sensorimotor brain regions provided commands to both MPLs to perform the self-feeding task, which included bimanual cutting. Motor commands were decoded from bilateral neural signals to control up to two DOFs on each MPL at a time. The shared control strategy enabled the participant to map his four-DOF control inputs, two per hand, to as many as 12 DOFs for specifying robot end effector position and orientation. Using neurally-driven shared control, the participant successfully and simultaneously controlled movements of both robotic limbs to cut and eat food in a complex bimanual self-feeding task. This demonstration of bimanual robotic system control via a BMI in collaboration with intelligent robot behavior has major implications for restoring complex movement behaviors for those living with sensorimotor deficits.

The cross-cultural validation of the technology-enhanced social constructivist learning environment questionnaire in the Iraqi Kurdistan Region

This study’s primary aim is to validate a research instrument in Iraqi Kurdistan middle and secondary schools to explore learners’ perspectives concerning social constructivist learning environments and e-learning outcomes. The research instrument was updated and devised based on Aldridge, Fraser, Taylor, and Chen's (Aldridge et al., International Journal of Science Education 22:37–55, 2000) Constructivist Learning Environment (CLES) Survey. Additionally, it also contains two newly developed rating scales that have been taken from Luckay and Laugksch (Luckay and Laugksch, Research in Science Education 45:1–22, 2015), and a perceived e-learning outcomes scale adopted from Sultan, Woods, and Koo (Sultan et al., Educational Technology and Society 14:149–163, 2011). The instrument included seven prominent social constructivist learning dimensions and plus perceived e-learning outcomes, namely: Respect for Difference, Learner Investigation, Critical Voice, Learner Negotiation, Individual Relevance, Shared Control, Uncertainty and Perceived e-Learning Outcomes. For this study, empirical data were gathered from 1289 upper primary and secondary school students in the Iraqi Kurdistan Region. The research instrument possessed factor structure, discriminant validity, and internal consistency reliability based on the results of data analysis. Consequently, the validity and reliability of Arabic language and Kurdish language versions of the survey were verified. Hence, the principal data are sufficient for additional empirical research involving path model evaluation in order to discern any correlations between the variables included in the research model.

Design of a "Cobot Tactile Display" for Accessing Virtual Diagrams by Blind and Visually Impaired Users.

Access to graphical information plays a very significant role in today’s world. Access to this information can be particularly limiting for individuals who are blind or visually impaired (BVIs). In this work, we present the design of a low-cost, mobile tactile display that also provides robotic assistance/guidance using haptic virtual fixtures in a shared control paradigm to aid in tactile diagram exploration. This work is part of a larger project intended to improve the ability of BVI users to explore tactile graphics on refreshable displays (particularly exploration time and cognitive load) through the use of robotic assistance/guidance. The particular focus of this paper is to share information related to the design and development of an affordable and compact device that may serve as a solution towards this overall goal. The proposed system uses a small omni-wheeled robot base to allow for smooth and unlimited movements in the 2D plane. Sufficient position and orientation accuracy is obtained by using a low-cost dead reckoning approach that combines data from an optical mouse sensor and inertial measurement unit. A low-cost force-sensing system and an admittance control model are used to allow shared control between the Cobot and the user, with the addition of guidance/virtual fixtures to aid in diagram exploration. Preliminary semi-structured interviews, with four blind or visually impaired participants who were allowed to use the Cobot, found that the system was easy to use and potentially useful for exploring virtual diagrams tactually.

Interdependence Analysis in collaborative robot applications from a joint cognitive functional perspective

This paper sets up a framework to assess co-agency in human-robot interactions, and applies it specifically to the socio-technical safety analysis of collaborative robots. We also examine to what extent the concept of Situation Awareness can be applied to assess collaborative robots as efficient team members in socio-technical systems. We explain some theoretical concerns with traditional concepts of Situation Awareness and defend why the concept of Joint Cognitive Systems, which maps the conceptualization of the cognitive system onto the work system as a whole, is best suited for issues of distributed cognition and controllability in human-robot interaction. Thereafter we present a five-step methodology specifically conceived for cobot applications serving the aim of goal coordination between multiple agents by functional interactions. The proposed framework merges two existing safety and resilience analysis methods, being the Functional Resonance Analysis Method and Interdependence Analysis. These methods are used in combination to assess shared control in safe and efficient human-robot interaction from a systems-thinking perspective. This allows to describe the systemic conditions for Distributed Situation Awareness in terms of observable system interactions and as an emergent object of distributed cognition. Instead of looking at undesirable safety outcomes, we have imposed the focus of co-agency as the unit of analysis in line with the Joint Cognitive Systems perspective. The theoretical insights from this paper are additionally applied to a hypothetical but credible demonstration case study with collaborative warehouse robots.

Genetic control of the operculum and capsule morphology of Eucalyptus globulus.

Background and aimsThe petaline operculum that covers the inner whorls until anthesis and the woody capsule that develops after fertilization are reproductive structures of eucalypts that protect the flower and seeds. Although they are distinct organs, they both develop from flower buds and this common ontogeny suggests shared genetic control. In Eucalyptus globulus their morphology is variable and we aimed to identify the quantitative trait loci (QTL) underlying this variation and determine whether there is common genetic control of these ecologically and taxonomically important reproductive structures.MethodsSamples of opercula and capsules were collected from 206 trees that belong to a large outcrossed F2E. globulus mapping population. The morphological variation in these structures was characterized by measuring six operculum and five capsule traits. QTL analysis was performed using these data and a linkage map consisting of 480 markers.Key resultsA total of 27 QTL were detected for operculum traits and 28 for capsule traits, with the logarithm of odds ranging from 2.8 to 11.8. There were many co-located QTL associated with operculum or capsule traits, generally reflecting allometric relationships. A key finding was five genomic regions where co-located QTL affected both operculum and capsule morphology, and the overall trend for these QTL was to affect elongation of both organs. Some of these QTL appear to have a significant effect on the phenotype, with the strongest QTL explaining 26.4 % of the variation in operculum shape and 16.4 % in capsule shape. Flower bud measurements suggest the expression of these QTL starts during bud development. Several candidate genes were found associated with the QTL and their putative function is discussed.ConclusionsVariation in both operculum and capsule traits in E. globulus is under strong genetic control. Our results suggest that these reproductive structures share a common genetic pathway during flower bud development.

Shared Control in Robot Teleoperation With Improved Potential Fields

In shared control teleoperation, the robot assists the user in accomplishing the desired task. Rather than simply executing the user’s command, the robot attempts to integrate it with information from the environment, such as obstacle and/or goal locations, and it modifies its behavior accordingly. In this article, we propose a real-time shared control teleoperation framework based on an artificial potential field approach improved by the dynamic generation of escape points around the obstacles. These escape points are virtual attractive points in the potential field that the robot can follow to overcome the obstacles more easily. The selection of which escape point to follow is done in real time by solving a soft-constrained problem optimizing the reaching of the most probable goal, estimated from the user’s action. Our proposal has been extensively compared with two state-of-the-art approaches in a static cluttered environment and a dynamic setup with randomly moving objects. Experimental results showed the efficacy of our method in terms of quantitative and qualitative metrics. For example, it significantly decreases the time to complete the tasks and the user’s intervention, and it helps reduce the failure rate. Moreover, we received positive feedback from the users that tested our proposal. Finally, the proposed framework is compatible with both mobile and manipulator robots.

316-OR: Genetic Deletion of Beta-Cell Pkm1, Pkm2, and Pck2 Identifies PEP as an Essential Signal for Compartmentalized KATP Closure and Cycling of the Insulin Secretory Pathway

β-cells use pyruvate kinase to sense nutrients and respond with appropriate insulin secretion. Here, we used β-cell deletion to identify the functions of constitutively active PKm1 and allosterically recruitable PKm2, and assess their regulation by mitochondrial PEP from PCK2. We demonstrate that both PKm isoforms are present in the KATP channel microcompartment. Compartmentation nullifies the disparities in PK isoform expression and activity, allowing the minor but recruitable PKm2 isoform to fully participate in KATP regulation. However, this shared control does not extend to β-cell response to amino acids, which requires PKm1 for the initiation of Ca2+ influx and insulin secretion and PKm2 for their termination. Mitochondrial PEP is required for this cycling between “on” and “off” states, as demonstrated by β-cell-specific deletion of PCK2. PCK2 was revealed to be an essential mechanism of β-cell cataplerosis, possessing metabolic control over cytosolic ATP/ADP generation in response to anaplerotic fuels. Further, PCK2 is required for amino acid-stimulated Ca2+ influx (via PKm1) and efflux (via PKm2) . These data provide strong genetic evidence for a revised oscillatory model of β-cell metabolism in which PKM1- and PKM2-driven PEP cycles play unique roles in the initiation and termination of nutrient-stimulated insulin secretion. Disclosure H.R.Foster: None. T.Ho: None. E.Potapenko: None. R.L.Cardone: n/a. R.Kibbey: Consultant; Agios, Inc. M.J.Merrins: None. Funding NIH/NIDDK (R01DK113103) HRSA (T32HP10010) NIH/NIA (T32AG000213)

Power Sharing Control Algorithm for Direct Integration of Fuel Cells in a Dual-Inverter Electric Vehicle Drivetrain

Fuel cell (FC)-battery hybrid electric vehicles (EVs) are an alternative to emergent battery EVs. Normally, a dc–dc converter is used to connect the low-voltage dc output of the FC to the high-voltage EV battery and ensure that a slow-changing unidirectional power flow is maintained from the FC. This article proposes to directly integrate the FC as one of the two energy sources in a dual-inverter-based EV drive. A conventional EV battery is used as the second energy source. A power sharing algorithm is introduced, which allows the dual-inverter drive to be modulated such that unidirectional power flow is maintained from the FC. In addition, power flow is controlled such that the minimum FC power to avoid its unnecessary shutdown is maintained under all operating points of an EV drive cycle, including regenerative braking. A key aspect of this algorithm is the injection of motor reactive current as a means to achieve desired FC power transfer during fast mechanical power reduction transients or when low mechanical power is required from the drive. This method allows for the motor to achieve fast mechanical power transients while respecting the slowly changing power reference of the FC.