Nonlinear model predictive torque control of a load commutated inverter and synchronous machine

The paper at hand considers the design of a controller for torque regulation of a variable speed synchronous machine fed by a line commutated rectifier and a load commutated inverter. The control approach is model predictive control where a constrained optimal control problem is solved to minimize the deviation of the torque from its reference. The dynamic model of the converters and drive is nonlinear and considers both the rectifier and inverter firing angles as control input. Controlling both firing angles simultaneously, as opposed to in a cascaded manner, implies improved potential for dynamic performance and disturbance rejection. In particular, the controller handles voltage dips on the line better than a conventional PI controller. The nonlinear MPC solution is implemented through on-line optimization. The optimization algorithm has been implemented on an embedded system and has been shown to execute sufficiently fast for the targeted control frequency.