Abstract
When controlling the voltage and speed of the asynchronous motor, to expand the speed control range and reduce the speed fluctuation, the speed control system adopts two feedback control loops, i.e. the speed feedback control loop and the current feedback control loop. The principle and components of the double-closed loop three-phase asynchronous variable voltage control system are studied, and the simulation model and the test result based on MATLAB/Simulink are provided in this article through the system modeling and the parameter setup of the main circuit and the control circuit.
Highlights
When controlling the voltage and speed of the asynchronous motor, to expand the speed control range and reduce the speed fluctuation, the speed control system adopts two feedback control loops, i.e. the speed feedback control loop and the current feedback control loop
In variable voltage control of asynchronous motor, because the synchronous speed is invariant and the mechanical character is rigid, the speed adjustable range is limited for common asynchronous motor, without practical value, but for moment motor or coiling asynchronous motor, the mechanical character will become soft if the proper resistance is bunched into the motors, and the speed adjustable range will be expanded, and even the speed fluctuation becomes very obvious when the loads or the voltages of the grid fluctuate, so the double-closed loop variable voltage control system is often adopted
System simulation The principal circuit of the variable voltage control structure of double-closed loop 3-phase asynchronous motor is composed by the 3-phase SCR AC voltage regulator and the 3-phase coiling asynchronous motor
Summary
In variable voltage control of asynchronous motor, because the synchronous speed is invariant and the mechanical character is rigid, the speed adjustable range is limited for common asynchronous motor, without practical value, but for moment motor or coiling asynchronous motor, the mechanical character will become soft if the proper resistance is bunched into the motors, and the speed adjustable range will be expanded, and even the speed fluctuation becomes very obvious when the loads or the voltages of the grid fluctuate, so the double-closed loop variable voltage control system is often adopted. To reduce the start, braking, and rollback time of the motor, the revolving speed negative feedback of the proportional integral controller is adopted in the system. The current loop has good anti-jamming function for the fluctuation of the grid, but in the starting process, the current loop could only limit the maximum current, and the constant-current characteristics of the best starting will not occur, and the constant torque starting will not occur too. The variable voltage control structure of asynchronous motor is simple, and the static voltage error is small when the double-closed loop system is adopted, and the rollback, the inversed joint, and the dynamic braking, are easy to be realized. Bu in the load of constant torque, the system could not run in lower speed, because in lower speed, the slip power PS SPM will completely be consumed in the rotor resistance, and the rotor will become too hot
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