Modeling and control of three-phase regenerative AC-DC converters

A mathematical model of the power circuit of a three phase voltage source converter (VSC) was developed in the synchronous reference frame. The mathematical model was then used to design an algorithm to estimate position of line voltage essential for operation of regenerative three-phase PWM controlled VSC. The PI current regulator in the D axis of VSC current control was modified to obtain the angle error signal. The angle error signal drives the observer (similar in structure to PLL) which provides position or angle of line voltages. To achieve fast and reliable lock with the utility system with minimal duration of transients, initial line voltage position was estimated first. The initial line voltage position estimation was done by measuring amount of current change when zero state voltage vectors were applied at the output of the inverter for defined time intervals.