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In this study, a multi-objective optimization method based on the Radau pseudospectral method is proposed for the energy management strategy in the hybrid energy storage system (HESS). In the proposed method, by approximating state and control variables in the system with global interpolating polynomials, the optimal control problem (OCP) is transformed into a nonlinear programming problem (NLP) and solved by a sparse nonlinear optimizer. Further, the Pareto solution set is obtained by taking the energy consumption of the HESS and the equivalent life of the battery as objective functions. Three solutions representing different tradeoffs were selected for comparative analysis: minimum system energy consumption (5819.60 kJ), with battery life 68368 cycles; maximum battery life (76227 cycles), with energy consumption 5865.68 kJ; and the balanced tradeoff optimal solution with battery life 72488 cycles and energy consumption 5841.96 kJ. The results showed that for every additional 5 kJ in system energy consumption, the battery Ah-throughput was reduced by 0.053 Ah and its equivalent life extended by 876 cycles. Further, compared with the single-cell energy source, the balanced tradeoff optimal solution increased the battery life by 29.92% and decreased the system energy consumption by 1.79%. Thus, this work provides a fast and stable multi-objective optimization method for the energy management strategy of HESS and lays the foundation for obtaining optimal system parameters. INDEX TERMS Energy management strategy, hybrid energy storage system, multi-objective optimization, Radau pseudospectral method.

For a seamless two-speed transmission specially equipped in electric vehicles, the global trajectory optimization problem of the overlapping shift process with multiple stages and complex path/point constraints is investigated in this article. The overlapping shift principle and the dynamic models in each phase are also demonstrated in detail. The parameters to evaluate the shift quality are analyzed and then introduced into the objective function and constraints, respectively. The jerks in process and at the key moments have been distinguished and selected as the path and point constraints, respectively. Moreover, considering the joint characteristics of the torque phase and the inertia phase, the trajectory optimization problems in the above two phases are summarized as a multi-stage global trajectory optimization problem. Then, Legendre pseudo-spectral method is used to transfer the multi-stage global trajectory optimization problem into a nonlinear programming problem for numerical solutions. Finally, the effectiveness and feasibility of the multi-stage global trajectory optimization method have been verified through the comparison of the optimal shift trajectories under different conditions with that obtained by the piecewise trajectory optimization method.

Abstract:In recent years, increasing concerns regarding environmental pollution and requirements for lower fossil fuel consumption have increased interest in alternative hybrid powertrains. As a result, this paper presents a novel hydraulic/electric synergy powertrain with multiple working modes. The three energy sources (i.e., engine, battery, and hydraulic accumulator) in this configuration are regulated by a dual planetary gear set to achieve optimal performances. This paper selects the component sizes of a hybrid electric vehicle (HEV), a hydraulic hybrid vehicle (HHV), and a hydraulic/electric synergy vehicle (HESV), based on the dynamic performance of a target vehicle (TV). In addition, this paper develops the forward simulation models of the four aforementioned vehicles in the MATLAB/Simulink/Driveline platform, in which the fuel economy simulations are carried out in relation to the Chinese urban bus cycle. The simulation results show that the fuel consumption of the three hybrid vehicles is similar, but much better than, that of the TV. Finally, based on the operating cost calculations over a five-year working period, the lowest cost ranges of the three hybrid vehicles are determined, which provides a method for choosing the optimal hybrid scheme.

Based on a nonlinear two-degree-of-freedom model of active suspension systems, an approach of the sliding mode control with disturbance observer combining skyhook model sliding mode control with disturbance observer combining is proposed for improving the performance of active suspension systems, and the effectiveness of the proposed approach is validated by the active suspension system plant. Two problems of active suspension systems are solved by using the proposed approach when the tire is excited by the step displacement. One problem is that the suspension deflection of active suspension systems, i.e. the difference between the sprung mass displacement and the unsprung mass displacement, using conventional sliding mode control with disturbance observer not converges to zero in finite time, and the phenomenon of the impact of suspension against the limit block is produced. This problem is solved by providing a reference value of the sprung mass displacement in an active suspension system, which is obtained from the skyhook model. The other problem is that disturbances exist in active suspension systems, which are caused by the inaccurate parameters of stiffness and damping. This problem is solved by designing a disturbance observer to estimate the summation of the disturbances. Finally, the performance indexes of the active suspension system with the sliding mode control with disturbance observer combining skyhook model are calculated and compared with those of using the conventional sliding mode control with disturbance observer and the linear quadratic regulator approach.

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The cross-section of an injection-molded plate of foamed long glass fiber reinforced polypropylene was analyzed using scanning electron microscopy. The distribution of the glass fiber orientations and the microcellular structure in the thickness direction were also studied. A multilayer representative volume element was constructed based on the fiber orientation tensors and the cell distribution. Nested and two-step homogenization methods based on the Mori–Tanaka and Voigt models were used to homogenize each layer of the representative volume element. Finally, classic laminate theory was used to obtain the effective elastic modulus of the material. The computed elastic moduli of the single-layer and multilayer representative volume element models with different loading directions predicted by the homogenization and finite element methods were compared with the experimental results. We found that the constructed multilayer representative volume element model can predict the elastic moduli of the foamed glass fiber reinforced polypropylene effectively and that the predicted results were accurate and stable.