| Organic Rankine cycle technology is widely used in low-temperature waste heat power generation systems with the residual heat generating units usually adopting a direct drive structure of a turbine-permanent magnet generator to achieve a good seal and effectively preventing the leakage of organic working substances.With the advantages of small size,simple structure and reliable operation,the permanent magnet rotor can realize high-efficiency energy conversion by direct drive connected with a high-speed turbine.However,the method of balancing the axial force of the turbine using the thrust bearing connection structure of the conventional unit has the disadvantages of difficult maintenance,low life and reliability.In this paper,a method for balancing the axial force of a turbine using the axial force of a conical rotor motor is proposed,while maintaining the direct connection of the turbine and the motor for high-performance power generation,the bearing structure at the joint is simplified,and the stability and reliability of the unit operation are enhanced.This paper first introduces the structure and working principle of the turbine and the generator in low-temperature residual heat generating units,and analyzes the characteristics of their operating modes and the causes of their axial forces.The structure type of the conical rotor is proposed according to the operating characteristics and basic requirements of the turbine unit and conical generator,the characteristics of the generator magnetic circuit along the axial direction brought by the conical structure are analyzed,and the equivalent magnetic circuit model of the generator is established.The expression of the magnetic circuit parameters of the tapered generator is derived.The phasor diagram of the generator is plotted,and the equations for the no-load back-EMF,output voltage,and electromagnetic torque of the conductive machine are derived.Then,according to the parameters of motor design,the two-dimensional and the three-dimensional finite element simulation models were established.The magnetic flux leakage at the end of the motor is analyzed by comparing the distribution of radial and axial air gap magnetic densities and magnetic cloud maps when the taper angle is zero.The changes in the rotor density and the radial and axial magnetic fields of the air gap during the change of cone angle were further studied.The influence of taper angle on the magnetic field inside the generator and the magnetic leakage at the end and the characteristics of no-load back electromotive force when the stator and rotor are staggered are analyzed.The mechanism of the axial force of the tapered permanent magnet generator is studied.The formulas for calculating the axial force by the virtual displacement method and the nonlinear integral method are deduced.The analytical expressions of the magnetic field in the d and q coordinate systems when the magnetic circuit of the conducting machine is not saturated are derived and as basis of further qualitatively analyze of the magnetic field distribution on the rotor surface and its influence on the axial force of the conical rotor.,then analyzed the effects of direct and quadrature axis currents and rotor axial displacement on electromagnetic torque.Simulation results verified the above analysis and conclusion.The characteristics of the axial force of the turbine during the operation of the turbine unit are analyzed,and the feasibility of using the axial force of the cone motor to achieve axial balance is explained combined with axial force characteristics of tapered motor.The method of adjusting the axial balance of the unit by adjusting the straight and quadrature axis currents during rated condition and variable condition is proposed,and the working point and running characteristics of the motor with fixed load and 85%rated load are verified. |
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