A simple pulsewidth modulator for an inverted fed AC motor

Simple near-optimal modulators of inverters for feeding AC motors based on the control of the inverter´s output current in field coordinates are described. The choice of the inverter´s switching state depends on the nonlinear controller´s state and the value of the magnetic field angle in the air gap. The switching pattern is determined by offline analysis of possible trajectories of the stator current space vector forced by the inverter output voltage and is saved in a look-up table. The connection of the inverter and AC motor is assumed to be a variable structure system. In such system it is possible to achieve sliding mode control. Adapting the proposed modulator for this case is also described.