Investigation On Rotordynamic Stability Evaluation And Control Theory And Method Of High-speed Turbo Machinery

The increasing capacity in process industrial equipment, such as the ethylene, refinery, LNG and fertilizer plants, will lead to a high parameterization of rotating machinery with high-speed, high-flow and high-pressure-ratio. This needs an increasing of the bearing span, resulting in the rotor system more flexible; thus, the rotordynamic stability will face serious problems. Aiming at the rotordynamic stability problem in high-speed rotating machinery, the prediction, evaluation and control of the rotordynamic stability were investigated, the parameter identification methods of the mode damping ratio and bearing coefficients of flexible bearing-rotor system were presented, and a new active electromagnetic damper with seal function was invented for rotordynamic stability control. Specific studies were listed as below:(1) A new damping ratio estimation method (which combined the Short-Time Fourier-Transform filter, directional frequency response function and prediction error method) was presented, solving the identification problems of rotordynamic stability such as the noise interface, multiple order modes mixture, and gyroscopic effect. The identification method has a good abilities of anti-noise, high accuracy and stable results, and these abilities were was validated by both numerical and experimental methods. This method can combine all the frequency response functions (FRFs) to entirely estimate the mode parameters, improving the accuracy of the identified results. In addition, two typical centrifugal compressors were adopted to simulate the sine-swept process, and the identification method was investigated with the consideration of the seal structure parameters and bearing preloads; the results show that the identification method can solve the problem of mode-overlap and can be widely applied to the identification of rotordynamic stability parameters of high speed rotating machinery. Meanwhile, two signal preprocessing methods were presented for the sine-swept method, having advantage in improving the signal-noise-ratio of FRF and the relibility of the identified stability parameters.(2) The effects of the bias and perturbance currents of the coil, as well as the rotor eccentricity, on the identification results of the stability parameters were analyzed. The bias current introduces negative stiffnesses into rotor system, leading to a change of rotordynamic stability parameters, and the effect law is corresponding to the installation position of actuator. The perturbance current almost has no effects on the identification results at the same bias current. A small bias current was recommended in the practical excitation process, and the perturbance current was chosen according to the unbalance vibration magnitude. Moreover, when the bias current is small, the displacement feedback force at magnetic bearing can be ignored, and the perturbance currents are taken as inputs to directly identify parameters.Aiming at how to implement the sine-swept excitation, the hard and software of sine-swept excitation were developed for practical industrial machines.Besides, based on the sine-swept technique, the effects of bearing preload,rotating speed, lubricating oil supply parameters, and specific load of bearing on the rotordynamic stability of bearing-rotor system were studied, resulting in that the increase of bearing preload, rotating speed and specific load leads to a decrease in the rotordynamic stability, and the increase of lubricating oil temperature(43-48?) and pressure (0.1 MPa-0.175 MPa) makes the rotor system more stable.(3) The online bearing identification method based on the magnetic excitation and finite element (FE) mode was presented. (?) The double-section interpolation- iteration method is used for the case that the sensor installation space is enough. This method interpolates and iterates the measured data based on the FE model, solving the problem that bearing node is not consistent with the location of the vibration sensor. The method converges fast and has a small fluctuation in the estimated principle stiffness and damping,and the measured and predicted vibration shapes are highly consistent. (?) A closed-loop system parameters identification method is adopted for the case that the sensor installation space is limited. This method transfers the bearing-rotor system to a closed-loop system with controller and controlled object, and the bearing force coefficients are taken as controller parameters to identify; moreover, the method can avoid the inconsistent problem of bearing node and measurement sensor. For the two methods, the mode parameters predicted by the estimated bearing coefficients at a single frequency excitation are consistent with the mode parameters measured by sine-swept, and this consistence demonstrates that the estimated results based on the two methods are accurate and believable, providing the basis of simplifying the rotordynamic stability test process by using sine-swept. Moreover, after obtaining the accurate bearing force coefficients, the costly full-load shop test can be avoided.(4) An electromagnetic damping seal and a structure of centrifugal compressor with this seal structure were invented, solving the engineering installation problem of controller in the centrifugal compressors, and the calibration test result indicates that the active electromagnetic damper seal structure has good force performance and meets the requirement of vibration control. The control theoritical equation was derivated by combining the linearized control force equation of magnetic bearing. Based on the control theory, two control algorithms, active reverse cross stiffness and active damping augmentations, were presented for instability faults. Both the numerical and experimental study validated the two algorithms can on-line solve the rotordynamic instability and improve the rotordynamic stability of the rotor-bearing system.In summary, the research findings have the theoretical and practical engineering significance in guiding the design, conformity inspection and instability control of high-speed turbo machinery. The rotordynamic stability evaluation and stability test technique can be applied to engineering tests and provide technique support for the experiment studies related to the rotordynamic stability and bearing coefficients test. The invented actuator enables the active electromagnetic control go a step further in industrial applications and solves the instability problems.