An FPGA-based real-time simulator for HIL testing of modular multilevel converter controller

Recently, two Modular Multilevel Converter (MMC) projects are under construction in China. Since these are the first two multi-terminal MMC projects in the world and the controllers are sophisticated, a real time simulation platform becomes critical to enable hardware-in-the-loop (HIL) test and validation of the MMC controllers in various scenarios, before applying them in the field. This paper presents an FPGA-based real time simulator to simulate electromagnetic transients of MMC systems and connect to external controllers through fiber optics for HIL tests. The MMC valve model is implemented in the FPGA with a time step of 500 ns while the power system is simulated in the CPU. Protocol drivers are implemented in the same FPGA to secure fast communication and low latency on MMC signals through optical fibers. Each FPGA board can simulate one MMC station with 6 valves and total of up to 1530 sub-modules (SM). This simulator supports multiple FPGA boards, and is thus able to HIL test very large multi-terminal MMC systems. This study case demonstrates that the simulator is able to connect to an external controller and simulate the MMC behaviors in steady states, transients, and various fault conditions in real time. The parameters for the MMC model and communication protocol can be adjusted during simulation. The HIL test gives results closer to reality than tests using an internal controller. Accordingly, the presented real-time simulator is qualified as an HIL test bench for MMC controllers.