Research On The Instability Of Casting Crane In Low Speed Energy Feedback State

In the application of industrial cranes,the motor often runs in the low speed(below 10Hz)area.The load carried by the crane when it is lowered is a potential energy load.At this time,the motor drive system works in the state of feedback power generation.Under severe working conditions,the speed sensor may fail.To ensure the safety and reliability of the crane drive system,it is usually required to design a sensorless control scheme for backup.Literature reports and engineering practice have consistently shown that the full-order observer speed adaptive system working in low-speed energy feedback mode will produce instability problems.The study of the causes of instability and effective stability measures has broad engineering application value.Based on the background and support of the project “Frequency Converter Speed Controller for Casting Cranes” commissioned by the enterprise,the main research contents for the above issues are as follows:Theoretical analysis is carried out from four aspects: mathematical models and error equations,stability measures,energy feedback states,and simulation and experimental design.Based on the mathematical model of the motor,the full-order observer and the speed adaptive identification system,the error equations between the asynchronous motor full-order observer and the speed adaptive identification system and the mathematical model of the motor are established separately.By analyzing the transfer function of the error equation,the theoretical reason for the instability of lowspeed power generation in the speed sensorless vector control system is derived,and two stability measures are proposed to increase the rotor flux and the closed-loop observer method.In addition,from the perspective of the steady-state mathematical model and mechanical characteristics of the asynchronous motor,the energy feedback state of the asynchronous motor at different speeds(low / high)is analyzed.Aiming at the problem of low-speed power generation instability,a system simulation model based on a full-order observer sensorless vector control strategy was established in MATLAB / Simulink environment.The simulation verified the effectiveness of the low-speed power generation instability of the motor drive system and the effectiveness of the two stability measures.4.Energy feedback status under different speed working conditions.After conducting the above experiments on a 2.2k W asynchronous motor in the laboratory,the prototype of the inverter was designed to be tested on a 15 k W experimental platform,and finally tested at the factory.Consistent with the simulation,the experiment was also carried out in three aspects: verification of instability,application of stability measures,and low-speed and highspeed energy feedback.The results of simulation,experiment and factory test are consistent,verifying the phenomenon of low-speed power generation instability,the effectiveness of two stability measures,and the difference between low / high-speed energy feedback states.