Irregular internal excitation (engine excitation and motor excitation) and external excitation (road excitation) can cause torsional vibration which even leads to the break of shaft of parallel hybrid electric vehicle (HEV) powertrain. Moreover, the current energy management control strategy ignores the significance of torsional stability of HEV powertrain when formulates the operating domain. The objective of this paper is to optimize the control strategy of parallel hybrid electric vehicle with multiple excitation sources to improve the torsional stability. To achieve the goal, the simplified two-mass nonlinear dynamic model of HEV powertrain is established. Then we apply the nonlinear dynamics to predict the torsional instability range of HEV powertrain. The theoretical analytical results are used to instruct to optimize the control strategy. Finally we set up the experimental platform and perform the experiment to verify the optimization of control strategy. The experimental results show that the HEV powertrain experience torsional instability under current control strategy. The critical speed when the operation mode of HEV switches from electric driving mode to hybrid driving mode was optimized to vc = 16km/h. The operating domain of engine was optimized to 1670 < n1 < 1850rpm under hybrid driving mode and driving and charging mode. The results reveals that optimization of control strategy can improve torsional stability of HEV powertrain effectively.

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Oscillation of torque and speed occurs in the electric powertrain based on permanent magnet synchronous motor under field-oriented control when we set an unreasonable proportional control parameter of proportional-integral regulator. Thus, it influences the stability and reliability of electric powertrain. The objectives of this article are to study nonlinear dynamics of electric powertrain under various complex operating conditions and settle a minimum stable range of proportional control parameter of proportional-integral regulator. To achieve these goals, nonlinear dynamic model of electric powertrain was established. Then, we solved equilibrium points and analyzed the stability of equilibrium points. Finally, we set different control parameters of proportional-integral regulator and various complex working conditions of electric powertrain to simulate nonlinear dynamics of electric powertrain. The simulation results show the electric powertrain operates stably when the control parameter is set in the area where there is only one stable equilibrium point. Chaos do exist in the electric powertrain with field-oriented control under different working conditions. Our analysis reveals the dynamics of electric powertrain are dependent on proportional control parameters of proportionalintegral regulator and electric powertrain performs unstably most likely under the operating condition with no-load and zero reference rotational speed.

Abstract. In this paper, the optimal design and control method of electromagnetic brake for a typical city driving cycle are studied to improve its energy consumption characteristics. The prediction models of the braking performance and power consumption for electromagnetic brake were established, and their accuracies were verified on the hardware of the loop simulation platform. Moreover, the energy consumption based on the ECE-EUDC driving condition was taken as the objective function, and a mathematical model for the optimal design of the electromagnetic brake was established. Genetic Algorithm was used to seek global optimal solution of these design variables on the premise of the given electrical and space constraints. Finally, the effect of thermodynamic properties of electromagnetic brake on the energy consumption characteristics was analyzed, and the energy saving control method of electromagnetic brake was also proposed. Experimental results show that the energy saving optimal design and control that this paper investigates can significantly improve the energy efficiency of electromagnetic brake.

Aiming at the dynamic behavior of hybrid powertrain under multi-frequency excitations with two time scales, this paper has carried out related research work. A nonlinear dynamic model of hybrid powertrain is established by taking engine excitation, load excitation and electromagnetic excitation into consideration. Considering the order gap between the excitation frequency and the natural frequency, slow variables are introduced to transform this model into a fast-slow model. Through introducing the De Moivre equation, slow variables are unified into a single one. The dynamic equations under different excitation frequencies and amplitudes are obtained. Bifurcation theory is applied to study the bifurcation behavior when the equilibrium point is unstable, and the conditions for the generation of fold bifurcation are derived. By means of numerical analysis, the influence of excitation frequency and amplitude on dynamics behavior is investigated by curve of equilibrium point, transformed phase portrait and time history. The simulation results show that fold bifurcation may lead to jumping phenomenon of the system trajectory and bursting oscillation is generated correspondingly. Additionally, the bifurcation characteristics of the hybrid powertrain may change with the excitation frequency and amplitude, making the pattern of bursting oscillation more complicated. The conclusion provides a reference for further analysis of dynamic behavior of hybrid powertrain.