High performance current regulator for a field-oriented controlled induction motor drive

A novel strategy of current regulation of a field-oriented controlled induction motor using a gate turn-off thyristor (GTO) inverter is proposed which is based on multivariable state feedback control with an integrator. The controller is designed by the pole placement technique of multivariable system regulation theory. Feedforward control is included in the control laws to improve transient responses. For the full state feedback control, the rotor flux is estimated with a reduced-order state observer. A good steady-state performance is obtained by means of an integral compensation, and fast transient response is also feasible since the required voltage is directly calculated from the feedforward control. Space voltage vector pulse width modulation is adopted as a switching strategy. A variable modulation scheme is presented which is changed from three-phase to two-phase modulation in the high modulation range, which gives lower current ripple over the whole operating range