A variable frequency controller for three phase DC/AC inverters

In this paper a multiprocessing system for variable amplitude/frequency control of three phase DC/AC power inverters is presented. The controller consists of four microcontrollers connected in a master-slave configuration. A single microcontroller is used for generating the PWM pulses of each phase and a master microcontroller for determining the system operational parameters. Each phase microcontroller operates as a state machine with analog feedback capabilities and uses an internal look-up table for specifying the duration of the open-loop PWM pulses. Variable frequency is achieved by controlling the clock of the phase microcontrollers, while the modulation depth is determined by the master controller, using a unidirectional high speed synchronous link. The modulator can be used for generating sinewaves in a large frequency range (from 6.25 Hz up to 100 Hz), has very good resolution (0.2% up to 0.4%) and is transient free in amplitude/frequency changes