| Variable frequency motors have the advantages of fast response speed,precise control accuracy and high efficiency.They are widely used in fields such as intelligent manufacturing,industrial robots,and advanced medical treatment.Unexpected motor failures will cause a lot of downtime and economic losses.Stator insulation failure is the most common failure in AC motors.According to the survey results,30%-40% of AC motor faults are related to the stator,and it has the characteristics of difficult repair and long repair period.For variable frequency motors powered by inverters,the insulation degradation and failure problems are more prominent than conventional power frequency motors.The reasons are as follows: First,the high dv/dt repeated voltage shock generated by the inverter will increase the electrical stress of the insulating material and accelerate the degradation and degradation of the insulation;the second is that the high-frequency voltage harmonics will increase the insulation medium when the inverter is working.Electric loss,current harmonics will increase the loss of winding coils and iron cores,which greatly increases the thermal stress on the insulation.The motor turn-to-turn,phase-to-phase and ground faults caused by insulation failure can cause economic losses due to unplanned shutdown of the equipment,and endanger personal safety and have catastrophic consequences.Therefore,timely and effective monitoring of the insulation operation status of the frequency conversion motor is essential to the safe and reliable operation of the frequency conversion speed control system! The main research contents are as follows:First,it mainly discusses the research background and significance,analyzes the current research status at home and abroad,and looks forward to the development trend of on-line monitoring of inverter motor insulation.Due to the combined effects of electrical,thermal,mechanical,and environmental stresses during operation,the insulation state of the motor is prone to deterioration.Analyze common motor insulation degradation faults,and understand the necessity and importance of motor insulation status monitoring and diagnosis.Second,the inverter’s high-speed switching excitation acts on the distributed parameters of the variable frequency speed regulation system to produce widefrequency domain current oscillations.By establishing a wide frequency domain model of the variable frequency speed regulation system of the power device switching transient process,the influence of the insulation state degradation on the transient broadband oscillation characteristics of the variable frequency motor switching is studied,and the actual operating state is simulated.Thirdly,through the establishment of the simulation and experimental model of the variable frequency speed regulation system,the influence of the deterioration of the insulation state on the transient broadband oscillation characteristics of the variable frequency motor switch is explored.The dominant mode and conduction path of the broadband switching oscillation response current are analyzed,and the effect of the change of insulation capacitance on the response characteristics of the switching oscillation current is explored.The switching time,cable length,and the distributed capacitance of the inverter to the ground are discussed.The influence of response characteristics.Fourth,after understanding the influence of insulation degradation on the response characteristics of switching oscillation current,continue to analyze the sensitive characteristics of switching oscillation of variable frequency motors.Using transient response characteristics and multi-frequency characteristics,online monitoring of motor insulation degradation is carried out. |
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