Input-output linearizing control with load estimator for three-phase AC/DC voltage-source converters

Nonlinear differential-geometric techniques are proposed for the design of feedback controller and load estimator for three-phase voltage-source PWM AC/DC boost converters. The input-output linearizability of the system modeled in d-q synchronous reference frames is first examined. Two possible solutions (called voltage control and current control) to input-output linearize and decouple the PWM AC/DC converter are presented. The voltage control approach tries to linearize the PWM converter with output variables including DC-bus voltage and a linearized system possessing unstable internal dynamics is exploited, which indicates that this approach is untractable. The current control approach provides a viable solution, in which the output variables are redefined as d and q components of the input line currents and the internal dynamics of the linearized system become stable. The output voltage on DC-side will be regulated to the desired level indirectly once line current tracking is achieved. Finally, a load estimator based on a nonlinear observer with linearized error dynamics is developed to counteract large perturbation in load and eliminate the use of load current sensor. The validity of the proposed control schemes is demonstrated via computer simulation.