FPGA based Synchronized Sinusoidal Pulse Width Modulation with smooth transition into overmodulation and six step modes of operation for three phase AC motor drives

This paper presents a triangular carrier comparison based Synchronized Sinusoidal Pulse Width Modulation (SPWM) for medium voltage inverters with low switching frequency (less than 500Hz). The basic requirements of synchronous PWM like 3-phase symmetry, quarter wave symmetry and half wave symmetry are maintained. To have very good dynamic behavior of the synchronization scheme, the triangular carrier is generated from the instantaneous voltage references in a phase locked manner. The triangular carrier comparison based method is extended in the overmodulation zone too. An inverse gain based linearization method is used to match the reference and inverter output voltage fundamental. This overmodulation strategy fails at the zone of high values of modulation index and a reference modification approach is used in that zone. These synchronization and overmodulation strategies are implemented in an FPGA platform and the results are presented.