Experimental PWM method validation of a 9-level 4.16 kV series connected H-bridge grid simulator

Controllable ac sources, sometimes referred to as grid simulators, are becoming more common for grid integration testing of inverters as new grid interactive inverter functions develop. Due to the relatively niche application, high power grid simulators are often made by repurposing commercial drives with additional systems integration by the manufacturer or end user including filters, transformers, and control features. Simulation models, invaluable for pre-test simulations and future retrofits to the drive, are not usually provided with the drive and must therefore be developed by end users. Pulse-width modulation details are often overlooked in this process, using defaults within the simulation environment. Validating the digital implementation of PWM, including sampling method, is beneficial as it can have significant effects on control bandwidth especially on multi-level and interleaved converters. The grid simulator considered here utilizes 9-level series-connected H-bridge topology. Experimental setup and results are shown for two carrier frequencies, 600 Hz and 2 kHz, verifying an effective phase shifted carrier each with double-edge sampling.