Unified time-domain formulation of switching frequency for hysteresis current controlled AC/DC and DC/AC grid connected converters

This study presents a unified time-domain formulation of switching frequency for hysteresis current controlled AC/DC and DC/AC grid connected converters. It is shown that the generalised expression of switching frequency obtained can be used for any mode of operation of the converter based on phase relation between the reference AC current and grid voltage. The presented analysis provides information of maximum, minimum and average switching frequencies for all modes of the converter operation. The analytical results derived under different configurations are verified through the experimental results obtained using FPGAbased implementation of the controller for the converter. The applications of the results are shown on the three different singlephase systems operating in current control mode: (i) static synchronous compensator, (ii) boost rectifier and (iii) grid interface of wind-turbine system. The results of switching operations in these applications are verified using simulation studies performed in power systems CAD/electromagnetic transients including DC (PSCAD/EMTDC) software.