Virtual DC Motor Stability Control Method Considering New Energy Generation Fluctuation

With the rapid development of new energy generation, the intermittence and randomicity of its power output will have a significant impact on the transmission capacity of DC motor. Therefore, a virtual DC motor stability control method considering the fluctuation of new energy generation is proposed. The natural frequencies and modes of the virtual DC motor shafting rotor are analyzed by means of a steady sinusoidal excitation at zero speed. Considering the transient dynamic response of the shafting rotor of virtual DC motor under the fluctuation of new energy generation, Taylor series and transfer acceleration matrix method are used to calculate the transient dynamic response of shafting rotor under the fluctuation of new energy generation, and the parameters of virtual DC motor are identified and estimated. Based on this, a proportional resonance controller is designed to realize the stability control of virtual DC motor. Experimental results show that the interactive power curve between virtual DC motor and regional distribution network is smoother after optimal control, and this method can effectively improve the power balance ability of virtual DC motor.

Dynamic Modeling and Vibration Characteristics for a High-Speed Aero-Engine Rotor with Blade Off

Blade off that occurs during operation will generate a sudden imbalance excitation and make the rotor become inertially asymmetric, which leads to large instantaneous impact load and induces more complex rotor dynamic phenomena. In order to study the transient dynamic characteristics for complex rotors suffering from blade off, a mathematical model for solving the response of the gas generator rotor in the aero-turboshaft engine is established based on the FE method and DOF condensation, in which the complex structural characteristics, transient impact load, and inertia asymmetry of the rotor are considered. The complex impeller structure is modeled by piecewise linear fitting with cylindrical beam elements and tapered beam elements. Without loss of generality, the modeling method suitable for complex rotors is verified through a general complex test rotor with modal experiments. Based on this, the responses are solved for carrying out parametric studies and an understanding of the transient dynamic characteristics of the rotor under the extreme working conditions of blade off. The results show that the blade off has a great impact effect on the time-domain waveform, frequency components, and rotor orbits. At the instantaneous stage after blade off, the complex motion is composed of synchronous motion and some lower-order natural modes excited by blade off. Although the transient responses with blade off at different rotational speeds have similar time-varying characteristics, the impact factor is sensitive to the rotating speed. Most important is that the parameter of the blade off location will not only have a significant effect on the impact factor, but also on the frequency spectrum. These dynamic characteristics as well as impact effect provide certain guidance for the fault recognition and dynamic analysis to these complex rotors suffering blade off.

Investigation of Valvetrain Dynamics Using Transient Dynamic Simulation in ANSYS

Engine valvetrain is one of the complex mechanisms in internal combustion engine as it involves many components namely, cam, pushrod, rocker lever, crosshead, intake and exhaust valves etc. Due to many components, their interactions with each other and presence of valve lash makes the system complicated to simulate. Typically, engine system level valvetrain dynamic simulation is performed in 1D software. Aim of this study is to understand the physics governing interactions and motion of the components in the valvetrain. This is done by simulating an inline 6-cylinder engine valvetrain mechanism through transient dynamic analysis in Ansys. This paper describes an approach used to simulate the valvetrain mechanism in Ansys and associated learnings. Finite Element Analysis model considers actual stiffnesses of all components. Appropriate joints/contacts are used to model the interactions. The comparative assessment of the valvetrain forces between Ansys results and 1D simulation results shows a good match. Further, 3D simulation in Ansys captures the key characteristics of valvetrain like crosshead tilting, uneven valve actuations and closing. It is also able to predict uneven contact and polishing observed on valve tip face. Overall, this study helped to ascertain the validity of 3D FEA method. This method also enhances the understanding of the valvetrain dynamics which can be helpful in further design improvements. This paper also includes a discussion on further steps to improve analysis model to make it more realistic e.g. including hot valve lash, valve seat wear etc. These improvements will help to understand effects of valve lash on valve velocities, sudden impact loads on valves, valve stresses/fatigue, pushrod buckling etc.