The nonlinear model of rotor-labyrinth seal system is established using Muszynska's nonlinear seal forces. We deal with dynamic behaviors of the unbalanced rotor-seal system with sliding bearing based on the adopted model and Newmark integration method. The influence of the labyrinth seal on the nonlinear characteristics of the rotor system is analyzed by the bifurcation diagrams and Poincare' maps. Various phenomena in the rotor-seal system, such as periodic motion, double-periodic motion, quasi-periodic motion and Hopf bifurcation are investigated and the stability is judged by Floquet theory and bifurcation theorem. The influence of parameters on the critical instability speed of the rotor-seal system is also included.Nomenclature c d radial clearance of seal l length of seal
The sliding mode observer (SMO)-based approach known for its robustness towards parameter variation (external disturbance) has been used for the sensorless motor drive system. Delay compensation is commonly added to overcome the phased delay resulted from the introduction of the low-pass filter for chattering suppression. In this paper, a new extended sliding mode disturbance observer (ESMDO)-based sensorless control of interior permanent magnet synchronous motor for the medium and high-speed range is presented. The effect of parameter variation and coordinate transformation is considered as a lumped disturbance, and ESMDO is designed to compensate for the imminent impact of such scenarios. A Lyapunov stability theory is adopted to guarantee the stability of the proposed ESMDO-based sensorless control method. The ESMDO has an inbuilt low-pass filter and does not introduce a phased delay. A very large load change/reference speed variation may result in system instability or require higher controller gains that lead to system chattering. Hence, a PI-based compensation is incorporated to achieve a smooth and robust sensorless control algorithm considering the d-axis disturbance. Finally, extensive simulation and hardwarein-the-loop (HIL) test using the TMS320F28335 control unit in a real-time environment are conducted to verify the effectiveness of the proposed sensorless control method.INDEX TERMS Extended sliding mode disturbance observer (ESMDO), IPMSM, sensorless control, traction drive.
In the railway traction drive system, the reliability of DC-link capacitor banks faces enormous challenges due to the multi-operation conditions, the complex physical structures, and the safe operation requirements. Considering these issues, this paper proposes a reliability evaluation method of the DC-link capacitors banks to provide a guideline for preventive maintenance in the traction drive system. In the electro-thermal stress analysis, different from the conventional methods, the dynamic power loss profile is obtained by the sliding-window discrete Fourier transform (DFT) and the equivalent series resistance is fitted by the neural network. Afterward, a bidirectional thermal model is established to estimate the thermal stress under the dynamic power losses, considering the impact of thermal capacity, thermal coupling, and air-cooling heat dissipation. In addition, according to stability analysis and the rated temperature limitation, an end-of-lifetime standard that meets the safe operation requirement of the train is firstly proposed, thereby evaluating the lifetime bottleneck of the DClink capacitor banks. The evaluation results can provide a reference to use the lower-cost on-condition maintenance instead of scheduled maintenance in the railway traction drive system. Furthermore, a prototype experiment is performed to verify the effectiveness of the electro-thermal stress model.
Speed estimation schemes based on the closed-loop synchronization (CLS) methods for speed-sensorless control of motor drives attract much popularity due to several advantages, e.g., easy implementation, high flexibility, and acceptable performance. However, most of the existing CLS-based estimation schemes may suffer from performance degradation during frequency ramps. Considering this, an attempt of the type-3 phase-locked loop (PLL)-based scheme is made. This solution, however, may adversely affect the system dynamics and stability margin. To address these issues, an open-loop synchronization (OLS) method is proposed for speed-sensorless control of induction motor drives in this paper. In the proposed scheme, the estimated speed is obtained according to the sinusoidal signals and their time-delay signals, rather than increasing the system order. With this, system dynamics and stability margin are maintained. In practice, the disturbance of DC offsets is of concern in induction motor drives. Thus, a closed-loop flux observer is adopted to guarantee the estimation performance under DC offsets. The performance of the proposed OLS scheme is investigated and compared with that of the CLS schemes and the type-3 PLL scheme through experimental tests.Index Terms-Open-loop synchronization (OLS), speed estimation scheme, closed-loop flux observer, induction motor drives I. INTRODUCTIONWith strong demands of reliability enhancement and cost reduction, speed-sensorless control becomes increasingly popular in induction motor drives. The procedure involves estimating the speed information properly, and accordingly, removing speed sensors. This task is mostly carried out by using various speed estimation schemes, which can be roughly categorized into non-ideal-phenomena-based and model-based schemes [1], [2]. Poor flexibility and high complexity are two main barriers of the widespread application of the non-idealphenomena-based estimation schemes [3], [4].
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