Dissipating Energy Flow Analysis of a Constant Power-controlled MMC for Sub-synchronous Oscillation

When a modular multilevel converter (MMC) is connected to a weak grid or wind turbine, there’s a risk of sub-synchronous oscillation. Due to the complexity of MMC topology, conventional time/frequency-domain methods may have drawbacks in studying MMC sub-synchronous oscillation. This paper proposed a dissipating energy-based method for sub-synchronous oscillation analysis of MMC. First, considering the role of PLL and constant power control loop, the AC terminal dynamic of MMC is studied. Then, the expression of the average slope of MMC dissipating energy flow is derived, which reflects the source/sink characteristic associated with the damping level of MMC. Finally, simulations are made on a MMC-integrated system. Simulation results demonstrate the relationship between system parameters and sub-synchronous oscillations from the perspective of dissipating energy flow.