Analyses of the Vector Control of an Induction Motor Controlled by a Voltage Model Operation with and without Current Control Loop

In the vector control of an induction motor with controlled voltage source, the control operation based on the motor voltage model is used and the motor voltages are controlled without detecting them in general. In the vector control with controlled current source, the control operation based on the motor current model is used and the motor currents are controlled with detecting them. The variation of rotor flux interlinkage caused by the change of rotor resistance with temperature in the former vector control is smaller than that in the latter. But the deviation of the actual torque from the ordered torque caused by it is larger in the former, so the former is not applicable to the use of torque control. And, sicne the mortor voltages are controlled without detecting them in the former, the deviation of the actual voltages of the PWM inverter from the ordered voltages increases in low voltage operation, so the controllability in low speed operation deterirorates. In this proposed system, a current control loop is added to the already reported vector control with controlled voltage source, based on the polar coordinate voltage equations without voltage detection. The PI-regulator of this current control loop has low proportional gain, its transfer function doesn't change the voltage model control opration for keeping the rotor flux interlinkage constant, and both its input and output have the dimension of current. The systems characteristics are analyzed by computer simulation. As a result, the bad effects of the change of stator and rotor resistance with temperature are almost completely removed, so the above mentioned defects of the vector control with controlled voltage source are greatly improved.