Modeling And Simulation Research Of Motor Frequency Conversion Control For Drilling Platform

Drilling process can be divided into manual drilling and automatic drilling.Compared to the larger intensity of labor and security responsibility of manual drilling,automatic drilling can realize the digital control, dynamic control and closed-loopcontrol better. According to different using environment and operation process, theautomatic drilling can realize the given speed automatically drilling and constant bitweight automatically drilling. These two kinds of automatic drilling ways askingdrilling machine can realize constant speed and constant torque control, generallyusing the frequency conversion control to realize.In this paper, drilling motors is control object. Firstly, bases on steady statemodel of motor, sets up the constant voltage frequency ratio control simulation modelin SIMULINK environment, respectively, the constant speed control, constant torquecontrol and low frequency load performance are simulated. Simulation results showthat the constant voltage frequency ratio control can realize the request of general ACspeed regulation system, but the system performance is not good, the speed dynamiccharacteristics is poor, overshoot and volatile exist, motor torque utilization rate is low,the control curve may change as the load changes. When in low frequency working,torque will reduce, torque ripple and harmonic increase; therefore not suitable forrunning in low frequency.For high performance speed control system, need to be based on the dynamicmodel of induction motor, the mathematical model of induction motor in thethree-phase static coordinate system is a complex set of nonlinear equations.Simulation models of Clarke and Park transformation are presented in this paper.Coordinate system transformation between three-phase static and two-phase staticcoordinate system, two-phase static and two-phase rotating coordinate system aredone. The results show this coordinate transformation method can convert the sinesignal of three-phase static coordinate system into DC signal under the two-phaserotating coordinate system, provides the condition for the establishment of inductionmotor dynamic model.Then, this paper sets up asynchronous motor indirect vector control simulationmodel based on dynamic model, the same parameters as the constant voltagefrequency ratio control, simulations of the constant speed control, constant torquecontrol and low frequency load performance are done. The simulation results show that the indirect vector control system is stable, speed adjustable and tracking abilityare strong, also without overshoot, the speed and torque change quickly and smoothly,low frequency load performance is good. Compared to the constant voltage frequencyratio control, vector control is more suitable for application on drilling machine. Thesmooth and continuous speed and torque output of this control method can protectdrilling equipment well, also high accuracy drilling control can be achieved, thedrilling process can be smooth, and the quality of borehole can be improved.Of course, constant voltage frequency ratio control has the advantages of themethod is simple and easy to implement, for the devices on drilling platform whichthe requirements of dynamic performance and stability performance are not too highsuch as fans, water pumps, etc. constant voltage frequency ratio control is suitable.