FR-A701 INSTRUCTION MANUAL (Applied) - Automation Systems ...

Control mode4.3.1 What is vector control?Vector control is one of the control techniques for driving an induction motor. To help explain vector control, thefundamental equivalent circuit of an induction motor is shown below:imr11 2idMiqr2Sr1 : Primary resistancer2 : Secondary resistance1 : Primary leakage inductance2 : Secondary leakage inductanceM : Mutual inductanceS : Slipid : Excitation currentiq : Torque currentim : Motor currentIn the above diagram, currents flowing in the induction motor can be classified into a current id (excitation current) formaking a magnetic flux in the motor and a current iq (torque current) for causing the motor to develop a torque.iqmotor current imIn vector control, the voltage and output frequency arecalculated to control the motor so that the excitation currentand torque current (as shown in the left figure) flow to theoptimum as described below:torque currentexcitation currentid(1) The excitation current is controlled to place the internalmagnetic flux of the motor in the optimum status.(2) Derive the torque command value so that thedifference between the motor speed command and theactual speed (speed estimated value for realsensorless vector control) obtained from the encoderconnected to the motor shaft is zero. Torque current iscontrolled so that torque as set in the torque commandis developed.Motor-generated torque (TM), slip angular velocity (ωs) and the motor's secondary magnetic flux (φ2) can be found bythe following calculation:T M ∝ φ 2 ⋅ iqφ 2 = M ⋅ idωs = r2L2iqidwhere, L2 = secondary inductanceL2 = 2 + MVector control provides the following advantages:(1) Excellent control characteristics when compared to V/F control and other control techniques, achieving thecontrol characteristics equal to those of DC machines.(2) Applicable to fast response applications with whichinduction motors were previously regarded as difficultto use. Applications requiring a wide variable-speedrange from extremely low speed to high speed,frequent acceleration/deceleration operations,continuous four-quadrant operations etc.(3) Allows torque control.(4) Allows servo-lock torque control which generates atorque at zero speed (i.e. status of motor shaft =stopped). (Cannot be performed under real sensorlessvector control.)72