Decoupled direct control for PWM inverter-fed induction motor drives

A new direct torque and stator flux control method is presented for PWM inverter-fed induction motors. This new strategy, called decoupled direct control (DDC), is based on the concept of a decoupling matrix that allows separate control of the stator flux and the torque. This method is compared to the well known direct field oriented control (FOC) and stator flux vector control (SFVC) methods. Two DDC-based methods are presented. The first determines the stator voltage vector such that the torque and the flux track their respective reference trajectories in one sampling time. The second sets separately the dynamic behavior of the torque and stator flux errors by the use of PI-type controllers. These methods take into account the full motor dynamics without the need of a coordinate transformation and reduce significantly computation requirements compared to FOC and SFVC. The two proposed strategies have been implemented experimentally and comparisons with FOC and SFVC were carried out. The obtained results show the superiority of the proposed PI-DDC strategy.

NOMENCLATURE

stator fixed reference frame

(d,q)

rotor flux vector fixed reference frame

stator voltage vector

stator current vector

stator flux vector

rotor flux vector

modified rotor flux vector

stator and rotor phase resistances

stator and rotor self inductances

M

stator to rotor mutual inductance

magnetizing inductance

total leakage factor

P

number of pole pairs

electrical rotor speed

motor electromagnetic torque and load torque

shaft inertia and mechanical friction coefficient