The path-following problem for four-wheel independently actuated autonomous ground vehicles is investigated in this paper. A novel output constraint controller is proposed to deal with the lateral ...offset control in path following and maintain the vehicle lateral stability in the presence of tire sliding effects. The innovations of this work lie in the following two aspects: 1) A novel output constraint control strategy, namely, the hyperbolic projection method, is proposed to strictly bound the lateral offset to prevent the vehicle from transgressing the safety bound in path following; 2) an adaptive and robust linear quadratic regulator controller is adopted to obtain the optimal active front-wheel steering and direct yaw-moment control inputs with vehicle lateral stability consideration and to eliminate the effect of parameter uncertainties. CarSim-Simulink joint simulation results indicate that the proposed controller can compactly bound the lateral offset to avoid transgressing the safe boundary during path following, particularly in extreme driving conditions, in the presence of tire sliding effects and system uncertainties.
This paper investigates the path-following control problem for four-wheel independently actuated autonomous ground vehicles through integrated control of active front-wheel steering and direct ...yaw-moment control. A modified composite nonlinear feedback strategy is proposed to improve the transient performance and eliminate the steady-state errors in path-following control considering the tire force saturations, in the presence of the time-varying road curvature for the desired path. Path following is achieved through vehicle lateral and yaw control, i.e., the lateral velocity and yaw rate are simultaneously controlled to track their respective desired values, where the desired yaw rate is generated according to the path-following demand. CarSim-Simulink joint simulation results indicate that the proposed controller can effectively improve the transient response performance, inhibit the overshoots, and eliminate the steady-state errors in path following within the tire force saturation limits.
This paper presents a model predictive control (MPC) torque-split strategy that incorporates diesel engine transient characteristics for parallel hybrid electric vehicle (HEV) powertrains. To improve ...HEV fuel efficiency, torque split between the diesel engine and the electric motor and the decision as to whether the engine should be on or off are important. For HEV applications where the engines experience frequent transient operations, including start-stop, the effect of the engine transient characteristics on the overall HEV powertrain fuel economy becomes more pronounced. In this paper, by incorporating an experimentally validated real-time-capable transient diesel-engine model into the MPC torque-split method, the engine transient characteristics can be well reflected on the HEV powertrain supervisory control decisions. Simulation studies based on an HEV model with actual system parameters and an experimentally validated diesel-engine model indicate that the proposed MPC supervisory strategy considering diesel engine transient characteristics possesses superior equivalent fuel efficiency while maintaining HEV driving performance.
This paper addresses the transient performance improvement for path-following control of underactuated surface vessels (USVs) in the presence of oceanic disturbances. The traditional practice that ...chooses the tangent direction of the desired path as the desired heading may deteriorate the tracking performance in the curve following due to the nonzero sideslip angle therein. Also, the disturbances in wave filed greatly affect the transient path-following control. To this end, three contributions are made in this paper: (1) an amendment to the definition of the desired heading using the sideslip-angle compensation is presented to achieve a more accurate path-following maneuver; (2) a novel disturbances observer-based composite nonlinear feedback (DO-CNF) controller is proposed to restrain system overshoots and eliminate steady-state errors while dealing with multiple oceanic disturbances with unknown bounds; and (3) the variation of the yaw-rate reference for path-following objective is handled in the controller design, which can enhance the vessel's robustness to the changing of the path curvature. Comparative simulations verify the reasonability of the desired-heading amendment and the effectiveness of the DO-CNF approach in improving the transient path-following performance of USVs while satisfying actuator saturation considering the unknown disturbances and changing reference.
This paper presents a robust H ∞ path following control strategy for autonomous ground vehicles with delays and data dropouts. The state measurements and signal transmissions usually suffer from ...inevitable delays and data packet dropouts, which may degrade the control performance or even deteriorate the system stability. A robust H ∞ state-feedback controller is proposed to achieve the path following and vehicle lateral control simultaneously. A generalized delay representation is formulated to include the delays and data dropouts in the measurement and transmission. The uncertainties of the tire cornering stiffnesses and the external disturbances are also considered to enhance the robustness of the proposed controller. Two simulation cases are presented with a high-fidelity and full-car model based on the CarSim-Simulink joint platform, and the results verify the effectiveness and robustness of the proposed control approach.
The quantity and quality of tillers determine the yield of rice. In order to explore how optimized nitrogen fertilizer application (OFA) increases rice yield by affecting tiller growth, a pot ...experiment with three nitrogen treatments was performed on the basis of previous researches to investigate the growth and development of tillers. Results showed that under OFA, the emerging rate of secondary tillers and high leaf position tillers decreased, which increased with the number of primary tillers. The decrease of ineffective tillers increased the accumulation of biomass and nitrogen per tiller, which promoted the development of panicles. Compared with traditional nitrogen fertilizer application (TFA), the differentiated number of spikelets increased by 10.85%–21.70%, which led to the total number of filled spikelets increasing by 9.67%–18.95%, resulting in 9.6% increase in rice yield. Primary tillers, especially at the first, second, fifth, and sixth leaf positions, were the superior tillers in good quality, which made great contribution to rice yield and were significantly affected by nitrogen application. Making full use of the regulation effect of nitrogen on the quality of tillers will help to stabilize rice yield with less nitrogen input or increase rice yield without adding nitrogen input.
This paper investigates utilizing the front-wheel differential drive-assisted steering (DDAS) to achieve the path-following control for independently actuated (IA) electric autonomous ground vehicles ...(AGVs), in the case of the complete failure of the active front-wheel steering system. DDAS, which is generated by the differential torque between the left and right wheels of IA electric vehicles, can be utilized to actuate the front wheels as the sole steering power when the regular steering system fails, and thus avoids dangerous consequences for AGVs. As an inherent emergency measure and an active safety control method for the steering system of electric vehicles, DDAS strategy is a valuable fault-tolerant control approach against active steering system failure. To improve the transient performance of the fault-tolerant control with the DDAS, a novel multiple-disturbance observer-based composite nonlinear feedback (CNF) approach is proposed to realize the path-following control for IA AGVs considering the tire force saturations. The disturbance observer is designed to estimate the external multiple disturbances with unknown bounds. CarSim-Simulink joint simulation results indicate that the proposed controller can effectively achieve the fault-tolerant control and improve the transient performance for path following in the faulted-steering situation.
This paper presents three discrete observer designs for cycle-by-cycle estimation of the in-cylinder oxygen mass fraction at the intake valve closing (IVC) on diesel engines equipped with exhaust gas ...recirculation systems. These observers can provide critical in-cylinder condition oxygen fraction information that is useful for control of combustion, in particular advanced combustion modes on a cycle-by-cycle basis. The observers were designed based on Lyapunov analysis and linear matrix inequality techniques. By input-to-state stability analysis, robust properties of the three observers were revealed. Simulations using a high fidelity, computational, GT-Power engine model exhibited that the observers can effectively estimate the in-cylinder oxygen mass fraction at IVC on a cycle-by-cycle basis at both steady-state and transient operations. In addition, comparisons were made to evaluate the observers' robustness against measurement and parametric uncertainties/inaccuracies, such as volumetric efficiency uncertainty, exhaust pressure sensor uncertainty, and temperature sensor dynamics. Experimental results from a medium-duty diesel engine were provided to show the effectiveness of the observers and to validate the in-cylinder oxygen fraction estimation in an indirect and innovative way by utilizing the measured cylinder pressure signals.
This paper presents a fast and accurate robust path-following control approach for a fully actuated marine surface vessel in the presence of external disturbances. The path following is realized by ...simultaneously converging the yaw rate and sway velocity to their respective desired values, which are generated according to the path-following demand. An improved combined control strategy using an integral terminal sliding mode (ITSM) based composite nonlinear feedback (CNF) technique considering the external disturbances, time-varying tracking reference, input saturations and transient performance improvement is proposed in this study. The proposed ITSM-CNF combines the advantages of the CNF control in improving the transient performance and of the ITSM control in guaranteeing good robustness and finite-time convergence. A continuous and smooth sliding mode controller, based on an integral nonsingular terminal sliding surface, is added to the CNF controller to eliminate chattering. The overall stability of the closed-loop system is strictly proved based on the Lyapunov method. Simulations verify the effectiveness of the ITSM-CNF controller in improving the transient path-following performance, inhibiting overshoots, eliminating steady-state errors, rejecting external disturbances and removing chattering effects, considering input saturations, varying path curvature and finite-time convergence.
Rice alternated with upland crops has become increasingly popular in recent years. To investigate the residual effects of nitrogen from the previous upland crop on rice growth, two cropping systems, ...garlic-rice and wheat-rice, were studied from 2014 to 2017 under field conditions and from 2016 to 2017 under pot conditions. The results showed that the total nitrogen content in the 0–0.2 m soil was higher for the garlic-rice cropping system than for the wheat-rice cropping system and the
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N isotope abundance of the soil after harvesting garlic was 63% higher than that after harvesting wheat. Residual nitrogen from the preceding crops was one of the main nitrogen sources for rice growth. The contribution of residual nitrogen accounted for 17% to 60% of the total nitrogen accumulation by rice plants during the vegetative stage, which gradually decreased after the rice jointing stage. Most of the residual nitrogen absorbed by rice plants was transported to the reproductive organs for grain growth. Therefore, the growth of vegetative organs, viz., tillers and leaves, was more vigorous under the garlic-rice cropping system than under the wheat-rice cropping system. This led to a significant increase in total nitrogen accumulation in rice plants and an increase in rice yield by 8% to 16%, even under identical management of rice under upland crop–paddy rice systems. Thus, under upland crop–paddy rice systems, high-yield and high-efficiency rice production can be achieved by utilizing residual nitrogen from the preceding crops and decreasing the application of base and tiller nitrogen.
