Hybrid Implementation of Cascade Control for GaN-Based Modular Multilevel Converter for Low-Voltage Grid

A hybrid control system implementation for a Modular Multilevel Converter (MMC) prototype is presented in this paper. The cascade control using an ARM processor for the energy controller and a field programmable gate array (FPGA) for the current controllers, allows the GaN semiconductors to generate an output current with an effective ripple frequency of 200 kHz. The MMC system model and the partitioning of the cascade control are shown. With its dynamic current limit, implemented in the FPGA, the MMC is able to provide AC currents above the nominal current. Finally, prototype measurements of an emulated grid fault are shown.