Zhengang Shi

Unbalance Compensation of a Full Scale Test Rig Designed for HTR-10GT: A Frequency-Domain Approach Based on Iterative Learning Control

Unbalance vibrations are crucial problems in heavy rotational machinery, especially for the systems with high operation speed, like turbine machinery. For the program of 10 MW High Temperature gas-cooled Reactor with direct Gas-Turbine cycle (HTR-10GT), the rated operation speed of the turbine system is 15000 RPM which is beyond the second bending frequency. In that case, even a small residual mass will lead to large unbalance vibrations. Thus, it is of great significance to study balancing methods for the system. As the turbine rotor is designed to be suspended by active magnetic bearings (AMBs), unbalance compensation could be achieved by adequate control strategies. In the paper, unbalance compensation for the Multi-Input and Multi-Output (MIMO) active magnetic bearing (AMB) system using frequency-domain iterative learning control (ILC) is analyzed. Based on the analysis, an ILC controller for unbalance compensation of the full scale test rig, which is designed for the rotor and AMBs in HTR-10GT, is designed. Simulation results are reported which show the efficiency of the ILC controller for attenuating the unbalance vibration of the full scale test rig. This research can offer valuable design criterion for unbalance compensation of the turbine machinery in HTR-10GT.

Dynamic Behavior Analysis of Touchdown Process in Active Magnetic Bearing System Based on a Machine Learning Method

Magnetic bearings are widely applied in High Temperature Gas-cooled Reactor (HTGR) and auxiliary bearings are important backup and safety components in AMB systems. The performance of auxiliary bearings significantly affects the reliability, safety, and serviceability of the AMB system, the rotating equipment, and the whole reactor. Research on the dynamic behavior during the touchdown process is crucial for analyzing the severity of the touchdown. In this paper, a data-based dynamic analysis method of the touchdown process is proposed. The dynamic model of the touchdown process is firstly established. In this model, some specific mechanical parameters are regarded as functions of deformation of auxiliary bearing and velocity of rotor firstly; furthermore, a machine learning method is utilized to model these function relationships. Based on the dynamic model and the Kalman filtering technique, the proposed method can offer estimation of the rotor motion state from noisy observations. In addition, the estimation precision is significantly improved compared with the method without learning. The proposed method is validated by the experimental data from touchdown experiments.

The Study of the Multi-Sensors’ Reliability on the AMB System of HTR-10GT

This article uses the Markov process to analyze the displacement redundant unit on the active magnetic bearings (AMB) system in HTR-10GT, especially on the aspects of the reliability, redundancy and maintenance issues. The reliability mathematical model is established, and the state transition diagram and the state transition matrix are deduced under the different conditions, furthermore the expression on reliability of the displacement redundant sensors is given. According to the different failure rate of single degree speed sensor, the curve about the measurement unit reliability versus time is calculated. The method mentioned above provides a new and practical approach to improve the reliability of the system and to optimize the displacement measurement redundant unit, which also can to be as a guiding role for the fault diagnosis of system.Copyright

Research About Eddy Effect and Dynamic Force of the Magnetic Thrust Bearing

The eddy effect of the magnetic thrust bearing (MTB) is researched by the finite element analysis (FEA). The active magnetic bearing (AMB) is an advanced bearing, used in HTR-PM. The alternating current in the bearing windings will decrease the electromagnetic force and cause phase lag, especially in the MTB which has no lamination structure. According to the calculation in this paper, simple sinusoidal current has large eddy effect. The force decreases obviously and the phase lag is large. However, the current containing direct part and sinusoidal part, which is closer to actual current, has less eddy effect. That is to say, because of the direct part in the current, the eddy effect of the sinusoidal part decreases.Copyright

The FEM Calculation of Iron Loss in the Active Magnetic Bearing

The active magnetic bearing (AMB) is a new kind of high-performance bearing which suspends the rotor with controlled electromagnetic force. It was chosen to support the rotor of the helium blower in HTR-PM instead of conventional bearings. The power losses in the active magnetic bearings compose of three components: copper loss, iron loss and windage loss. In this paper, the iron loss, which composes of the eddy current loss and the hysteresis loss, is researched. The power loss of silicon steel lamination (35H300) was measured. Experimental data was taken over a range of 50Hz to 25,000Hz (sinusoidal current) for several magnetic field intensities. According to the experimental data, the eddy current loss and hysteresis loss increase with the frequency. And the hysteresis loss in the silicon steel lamination occupies the major part when the frequency of current is low, however the growth rate of eddy current is much faster than that of the hysteresis loss. And the FEM calculation of power loss in the magnetic bearing, which rotor and stator are made from silicon steel lamination (35H300), is also presented. The result shows the core loss of magnetic bearing also follow the separation theory. We can separate the core loss of magnetic bearing into two parts: hysteresis loss and eddy current loss. It will be very useful to calculate the power loss in the magnetic bearing.Copyright

Dynamic Behavior Analysis of Touchdown Process in Active Magnetic Bearing System Based on Kalman Filtering

Magnetic bearings are widely applied in High Temperature Gas-cooled Reactor (HTGR) and auxiliary bearings are important backup and safety components in AMB systems. The dynamic analysis of the AMB rotors touchdown process is an important foundation for designing auxiliary bearings. In this paper, a data-based dynamic analysis of the touchdown process is proposed. The dynamic model of the touchdown process is firstly established and then the nonlinear extended Kalman filtering technique is applied. Based on the dynamic model and Kalman filtering technique, the proposed method can offer estimations of rotor’s displacements, velocities and accelerations from noisy observations. The proposed method is validated by the experiment data from touchdown experiments. The touchdown experiments are performed on an experimental system with a 440kg heavy rotor, the rotational speed in the experiments is 5000RPM and no brake is applied.Copyright

Behavior of a Magnetically Suspended Rotor Dropped Into Auxiliary Bearings

Auxiliary bearings (ABs), as the back-up support when the Active Magnetic Bearing (AMB) system doesn’t work, play an important role on the assurance of AMB system’s safety. According to the structure design of ABs-rotor system on back-up helium circulator of 10MW high temperature gas-cooled reactor (HTR-10) equipped with AMB, this paper presents a simplified finite element model (FEM) in Ansys, applied in the transient response of the dropped rotor. The ABs load characteristics were determined based on Hertz contact theory. Furthermore, a special spring element named Combin40, which is coupled to a gap, was introduced to communicate information of displacement and force between auxiliary bearings which were simplified into nonlinear spring elements and rotor which was simplified into beam elements. Based on the developed FEM, the behavior of vertical and horizontal magnetically suspended rotor dropped into the ABs was analyzed respectively and the safety of the rotor and ABs was evaluated. The results provide an important reference to the ABs design and application in HTR-10 and High Temperature Reactor-Pebblebed Modules (HTR-PM).© 2013 ASME

Interference Fit Design for Rotor Components of the Active Magnetic Bearing

The method to design the interference fit for the rotor components of the active magnetic bearing (AMB) was proposed. The rotor components include the thrust collar, the radial bearing rotor components and the sensor rotor components. Four main influencing factors and the machining accuracy are considered during the designing, such as the centrifugal force, the loadings, the thermal expansion coefficient, the electromagnetic force, and the coupling surface roughness. Some calculation examples were presented. These examples are base on the AMB of a helium blower, which is going to be applied in the High Temperature Reactor-Pebblebed Modules (HTR-PM) in Rongcheng City, Shandong province. Both the analytical calculation and the finite element analysis were carried out, and then were compared. The method of design based on the simple analytic formula was proved to be available.© 2013 ASME

Identification of Flexible Rotor Suspended by Magnetic Bearings

Magnetic bearings are widely applied in High Temperature Gas-cooled Reactor (HTGR), where the rotating machineries are running under high purely helium environment. In designing and adjusting a magnetic bearing system, the mathematical model of the rotor plays an important role. Identification is a useful method to obtain the model of a rotor. However, there are some practical difficulties of identifying a magnetic bearing-rotor system without force sensors. This paper proposes an identification method for flexible rotor suspended by magnetic bearings. In this method, two experiments under different bearing stiffness are performed, the models obtained by these two experiments are then transformed to the desired rotor model and the influence of bearing stiffness is eliminated in this transformation. The proposed method is validated on an experimental system with a five degree-of-freedom suspended flexible rotor.Copyright

Magnetic Field Analysis of Active Magnetic Bearings for Helium Blower of HTR-PM

High-temperature gas-cooled reactor-pebble bed module (HTR-PM) of China, based on the technology and experience of the 10MW high-temperature gas-cooled reactor (HTR-10), is currently in the design and experiment phase. The helium blower is the key equipment in the first loop of the HTR-PM.Active magnetic bearings (AMBs) are replacing ordinary bearings as the perfect sustaining assembly for the helium blower because they have several advantages: they are free of contact, do not require lubrication, are not subject to the contamination of wear, have endurance, and control performance very well. So the AMB is the appropriate supporting assembly.The rotor’s length of the helium blower is about 3.3 m, its weight is about 4000 kg and the rotating speed is 4000 r/min. The maximal radial load of the upper AMB or the lower AMB is about 1950kg, and the maximal axial load is about 4500kg. So the axial and radial AMBs must have enough carrying capacity to support the rotor. It is difficult to design the AMB in limited space. Many factors may restrict the AMB design, for example, clearance between AMB and rotor, electric current, and environment temperature, etc.In this paper, design of magnetic field will be analyzed. Heat loss of AMB will be discussed. The designing scheme of magnetic field will offer the important theoretical base for AMB design of the helium blower of HTR-PM.Copyright