Study On Shaft Voltage And Bearing Current Of Permanent Magnet Synchronous Machine

With high efficiency, simple structure, high power factor, wide speed range and soon. Permanent magnet synchronous machine is widely used in frequency controlsystem and has good prospects for development at present. But with the increase of itsunit capacity, the bearing damage accident caused by the shaft voltage and bearingcurrent becomes more serious. For the cause of shaft voltage and bearing current are thefollowing: common mode voltage generated by the SPWM inverter power; magneticflux leakage in the end; asymmetric flux; electrostatic effects. Because of the greatnegative impact on the reliability of the motor’s running bring by shaft voltage andbearing current, its research has important practical significance. This thesis mainlystudies the shaft voltage and current in the permanent magnet synchronous motor powerby SPWM inverter.This thesis introduces the basic principles, the advantages and disadvantages ofdifferent rotor structures of permanent magnet synchronous motor, and gives a briefoverview to the frequency control technology. Secondly, the common-mode voltagespectrum and its influencing factors under SPWM inverter power supply have beendeduced and analyzed through the simulation. This thesis explained the generatingmechanism of the shaft voltage and bearing current and launched a qualitative analysisof the interior coupling capacitors in the permanent magnet synchronous machine. Thenthe thesis introduced the electromagnetic field theory and the analysis theory of electricfield. The permanent magnet synchronous motor model was established byJMAG-designer software. The thesis calculated the bearing capacitor and couplingcapacitor inside the motor, focusing on research of the coupling capacitance’s influenceproduced by the motor geometry and end winding. Finally the model was simulated inMatlab/Simulink combining the corresponding common-mode model and theparameters. So we can observe the current size of the shaft before and after thebreakdown of oil film, analyses the influence of DC bus voltage, the dead zone effectand common-mode voltage parameters on the shaft and observe the degree of risk tobearing oil film’s breakdown.The results showed that the harmonic content of common mode voltage decreasedslightly but the magnitude increased with dead-time increasing, and leading to the riskof axle bearing oil film breakdown voltage rises; In addition, the internal dimensions of the motor also has a greater impact on the coupling capacitor: The air gap width andnotch width have a great influence on the coupling capacitors Crfbetween stator androtor; Air gap width, addendum, winding insulation thickness and width of the slothave a certain impact on both the coupling capacitance Csrbetween the rotor and thestator winding; Slot width and thickness of the winding insulation have a certain effecton the coupling capacitors Csfstator windings and stator. The bearing oil filmbreakdown risk of permanent magnet synchronous motor are related to common-modevoltage, common mode parameters and the loop.