| The RM type control rod drive mechanism is the main model currently used in reactor nuclear islands,and the wear margin of the mechanical bearings determines the service life of the control rod drive mechanism.In this paper,the mechanical bearings are replaced by electromagnetic bearings from the principle innovation to solve the wear problem fundamentally.To this end,this paper proposes an Isolated Type Active Magnetic Bearing(IAMB)for the different operating environments of the stator and rotor in the mechanism.The isolated type active magnetic bearing is affected by the eddy current in the shield shell,and,the electromagnetic force model and control method are different from the general active magnetic bearing(AMB);In addition,the eddy current displacement sensor commonly used in engineering cannot penetrate the shield shell to detect the position of rotor,so the rotor position detection method must be studied for the IAMB.To this end,the main work of the thesis is as follows:Firstly,the electromagnetic force characteristics of IAMB were studied.The static equivalent magnetic circuit of the IAMB is established,and the static equivalent circuit is simplified after the linear working area of the IAMB is analyzed,and the difference between the static electromagnetic force characteristics of the IAMB and the general active magnetic bearing is analyzed;The dynamic reluctance due to eddy current effect is analyzed,and the dynamic reluctance is introduced on the basis of the static simplified magnetic circuit,so as to explain the problem of the lag of the electromagnetic force response of the IAMB and the winding current;On this basis,the electromagnetic force and winding current transfer function is given,which provides a theoretical basis for the control of IAMB.Secondly,the special problems in the IAMB control process are analyzed.The influence of the electrical time constant brought by the static inductor on the current loop response speed is studied,and the static inductor nonlinearity problem is solved by using the static operating point;The problem of large ripple in the output current of IAMB switching power amplifier is studied,and the current ripple of AMB and IAMB under the two-level driving method of switching power amplifier is compared and calculated,and a simplified equivalent inductance model is proposed for the ripple problem,based on which the current ripple is reduced by using three-level driving method;on the basis of the PID control algorithm,the control strategy of open-loop current compensation is proposed to solve the IAMB electromagnetic force response hysteresis problem to achieve stable rotor suspension.Then,the Isolated Type Linear Variable Differential Transformers(ILVDT)for the displacement sensor for IAMB is studied.The operating principle of the ILVDT is analyzed,its operating point is determined,and the relationship between the sensor output signal and with the excitation voltage,rotor position,and excitation frequency is derived based on the dynamic magnetoresistance when eddy currents are considered.For the characteristics of the ILVDT that must have DC static bias flux and the need to filter out high frequency interference from switching power amplifiers,a bandpass filter is added to the multiplier phase-sensitive detector circuit to achieve effective detection of rotor position.Finally,the control experiment platform of the DSP microcontroller-based digital control system was built,and the stable suspension of the rotor was realized.An ILVDT multiplier phase-sensitive detector circuit was built to initially verify that the detector method proposed in the paper can effectively detect the rotor position.This thesis provides experience as well as basic analysis methods for the control of active magnetic bearings with isolation function and its rotor displacement detection method,which has important academic and engineering significance. |
