Fundamental Research On Homo-polar Radial Hybrid Magnetic Bearing

Supercritical carbon dioxide power generation system is a new type of turbine power generation equipment,and the power generation efficiency and system power consumption of it are directly related to the rotational speed of the turbine rotor.However,due to contact friction and mechanical wear in mechanical bearings,it is difficult for the turbine rotor to smoothly cross over critical speed under the support of conventional mechanical bearing,the maximum speed of rotor cannot be break through,the power generation efficiency cannot be improved,and the system power cannot be reduced too.According to relevant researches,mechanical friction and wear can be eliminated by introducing hybrid magnetic bearing into the support system,as well as the power consumption of active magnetic bearing can be reduced effectively,at the same time the bearing stiffness and damping can be adjusted online and in a real-time manner,which can change the rotor support characteristics,so the problem of mechanical bearing support system can be solved.Therefore,a levitation support method which replaces the traditional mechanical bearing with hybrid magnetic bearing was proposed,and then the following contents were studied in this paper:(1)The basic structural characteristics and advantages and disadvantages of the homo-polar and hetero-polar hybrid magnetic bearing were summarized.And then,a type of homo-polar Radial Hybrid Magnetic Bearing(RHMB)was researched.The magnetic circuit model was established by using the equivalent magnetic circuit method,the method is based on magnetic flux leakage and magnetic resistance correction factor,the levitation force model was obtained,the mechanism of permanent magnet negative stiffness was qualitatively analyzed too.Finally,the structure parameter design formula of RHMB was provided.(2)Orthogonal experiment method was used to optimize some important structure parameters through simulation.And then the three-dimensional magnetic field simulation and analysis were carried out to get the magnetic field distribution,which has verified the correctness of the theoretical design.Deviation of stiffness curve was corrected using the ratio of air gap flux density calculated by theory and simulation.The analysis results of radial coupling characteristics has indicated that the air gap flux density or levitation force in the X and Y direction do not affect each other,before the coil current or rotor offset has reached its maximum.Finally,the radial low-current power levitation strategy was presented under the premise of hypothesis,the relationship between eccentric distance and power consumption reduction ratio was given too.(3)The homo-polar RHMB experimental apparatus was designed and fabricated,and the experimental platform was also built for experiments.The measurement of magnetic field distribution was completed to verify the correctness of theoretical design and simulation analysis,due to the actual magnetic flux leakage is larger than simulation,there are some deviations between the theoretical design and simulation analysis.The results of static levitation experiment have showed the RHMB can complete the initial levitation.The current stiffness was obtained by measurement,and the displacement stiffness was obtained by i-y stiffness matching method,even if there are certain errors with the simulation,the measurement results still meet the design requirements.The homo-polar RHMB which was studied in this paper is short in axial length compared with traditional homo-polar structure,and it has the function of self-protected bearing,the volume of support system can be reduced too.Because of the simple magnetic circuit and week magnetic field coupling and force coupling,the difficulty of control was reduced at the same time.Permanent magnet was used to generate bias magnetic field,which can reduce power consumption.The research contents of this paper can provide a certain reference for the design of hybrid magnetic levitation support system.