On Key Technologies Of Electromagnetic Active-passive Composite Isolator

Along with the advances in modern science and technology, high requirement on vibration environment has been put forward in more and more fields. Vibration control technology is drawing increasing attention in modern production and life, and there has been plentiful and substantial achievements in this filed. It can be applied in seismic design of building structures, vibration and noise reduction of of the ship machinery structure, structural vibration control in aerospace, stabilization control of precision machinery, instruments and platform or ride comfort improvement of vehicle traffic tools etc. Traditional passive vibration isolation technology has a good high frequency vibration isolation effect, but the low frequency effect is not ideal. So it is unable to meet the requirements of high damping performance.In view of this situation, research in this dissertation is focused on how to design and control an electromagnetic active-passive composite isolator, combined with the advantages of active and passive vibration isolation, for which the vibration and noise reduction of underwater quiet type vehicle is a pratical example. The following contents are included:design and implement of electromagnetic active-passive composite isolator, design of adaptive feedforward controller based on FIR filter, design of adaptive feedforward controller when acoustic feedback exists, study on active-passive composite vibration isolation effect evaluation methods and active vibration control experiments on the experimental platform.Vibration isolation device is the key component of active-passive composite vibration isolation system. The basic design principles of an electromagnetic active-passive composite vibration isolator that combined with the existing vibration isolation theory are proposed. On the basis of these principles, the design process of an isolator is carried out. Characteristics on passive vibration isolation system and the influence of introducing active vibration isolation into vibration isolation system are analyzed in this dissertation. It is pointed out that when the ratio of excitation frequency and natural frequency is greater than the critical frequency ratio, the introduction of active vibration isolation will not exacerbate vibration of isolation object, even that the vibration amplitude will be inhibited near natural frequency. Then, a design method of active-passive composite isolation system based on the quality of power equipment, the lower frequency value of vibration frequency and the critical frequency ratio is derived. Finally, the active and passive links of an active-passive composite isolatior are designed.The analytic model of electromagnetic suspension element is presented under the assumption of uniform magnetic field, and its application filed is concluded based on the Ansoft simulation results and the design experience. Then, the design requirements and steps of an active-passive composite isolator electromagnetic actuating element are derived. According to the design steps, the electromagnetic actuating element is designed under the restriction of minimizing quality. Considering the influence of coil time constant on the actuator performance, relationship in the thickness of coil, the weight of electromagnet element and the time constant of coil is derived, and the current loop correction technology is introduced. Finally, the electromagnetic force model of the novel isolator is established, which shows that electromagnetic actuator can reach the design object.At present, the filtered-x LMS algorithm is the most common algorithm applied in harmonic vibration active control due to its ease of implementation. Most available active noise control algorithms, including the filtered-x LMS algorithm, require identification of the secondary path. It can cause several problems to the control system:1) it increases the complexity of the control system implementation;2) errors in identifying the secondary path may cause the adaptive algorithm to diverge. Combine with the geometric analysis of filtered x-LMS algorithm and LMS algorithm, a modified LMS algorithm that requires no secondary path identification is put forward. Finally, the shortage that the algorithm used for multi frequency vibration control is analysised, and the algorithm is expanded by utilizing multiple parallel adaptive filters.The reference signal for the adaptive filter can become unstable when acoustic feedback exists. The adaptive FIR filter can’t be used in this case, because it is difficult to guarantee the stability of the algorithm. The filtered-U LMS algorithm which has both zeros and poles is introduced to address the problem of acoustic feedback, then a modified algorithm namely the IIR-LMS algorithm that requires no secondary path identification is proposed. The ODE method is used to study the asymptotic behavior of the IIR-LMS algorithm, considering general stationary disturbances and with/without acoustic feedback. Finally, the IIR-LMS algorithm shows good performance in simulation experiment.A "full-feedback" structure with both zeros and poles is introduced into adaptive IIR filter. The full-feedback IIR-LMS algorithm are proposed and compared with the general IIR-LMS algorithm, and then the full-feedback filter-U LMS algorithm is derived. A commutation error (CE) that results from a difference associated with the altered sequence in real active noise control (ANC) applications as compared with that at the derivation stage is considered. A new adaptive algorithm is developed as full-feedback filtered-U LMS/CE in an aim to eliminate the CE-associated disturbance and to liberate the restriction of slow adaptation imposed on the existing adaptive algorithms in the ANC applications. Computer simulations show that the performance of convergence is improved for the new adaptive algorithm as compared with that of the conventional algorithm.Several traditional isolation performance indices, such as force transmissibility, insertion loss, vibration level difference, power flow, are summarized on a typical isolation system. The relationship between traditional performance indices and theory design targets of the isolator is study through theoretical analysis and numerical simulation. Then, a new performance index for active-passive composite isolator, which is based on the correction of vibration level difference, is proposed. It can reflect contributions of the passive vibration isolation and active vibration isolation in different frequency bands as well as the interation between the two indices. Finally, the new performance index is simplified according to the vibration isolation simulation experiment system, so that it is simple for engineering realization.At the end of this dissertation, a vibration isolation simulation experiment system, for which the electromagnetic active-passive composite isolator is the actuator, is established. Then, active vibration control experiments, for which the modified LMS algorithm that requires no secondary path identification, the multi channel decoupling control algorithm and the IIR-LMS algorithm that requires no secondary path identification are used, are carried out. Experiment results demonstrate that that the damping effect of vibration isolation simulation experiment system in experimental frequency band is significantly improved by active vibration control methods proposed in this paper.