An Observer of the Rotor Speed in a DC Electric Drive with a Magnetic Field Reversal
The article deals with the method of indirect speed calculation in DC electric drives where the reverse and braking is performed by changing the magnetic flux. In these electric drives, determination of speed through electrical parameters of the system (armature current, armature voltage, EMF) is not accurate enough since reversal and braking processes reduce the magnetic flux to zero. This leads to a significant calculation error. To correct this disadvantage, it is proposed to use an observer with a switching structure, which contains two models of speed calculation. One model calculates the speed by the electric signals of the motor. Another one, which is a model of the mechanical part of the electric drive, calculates the speed based on the equation of motion of the electric drive. The structure of the observer is proposed and the principle of its operation is described. Linearized structural circuits of the closed control system of the electric drive "Adjustable current source - motor" are considered in various modes of operation of the observer. The speed controller is synthesized and recommendations are given on the calculation of its parameters when the observer is controlled by the electric and magnetic variables of the motor. The stability of the electric drive system in other modes has been verified. A simulation model of the system "Adjustable current source - motor" was developed in the system MatLab Simulink. Experimental oscillograms confirming the theoretical positions and the adequacy of the simulation are presented. The efficiency of the electric drive control system with feedback from the observer is checked when the moment of inertia of the mechanism changes, the static load moment. Thus, the conclusion is made about the possibility of using the proposed sensorless system in electric drives for turning and lifting of mining excavators.