Instantaneous switching pattern change method for onboard three phase inverters

The ease of use and low cost of sequential microcontrollers makes them a very interesting option for controlling power converters in the scope of 3-phase inverters for railway applications. This kind of converter is characterized for its slow dynamics and a quasi-static regulation due to the input LC filter intended for protection purposes. Moreover, assuming a Look Up Table (LUT) modulation, the apparition of multiple transients during the regulation of the system is an important problem. An effective method to reduce the transients is making the modulation index changes instantaneous, this is, changing the three phases at the same time as is described in this paper. On the other hand, the utilization of look up tables for the modulation allows the utilization of different modulation techniques even the combination of them to optimize a selected parameter such as the THD, coil weight, capacitor size, etc. The bottleneck of this method is the slowness of the pattern change algorithm. In this paper, a fast pattern change algorithm for sequential microcontrollers is presented. Simulation and experimental results are shown to validate the proposed methodology.