Compound control for power quality in grid-connected wave energy system

Combined with the rapid volatility and spatial distribution characteristics of wave energy, the output power of wave energy devices is relatively unstable. When the wave energy device group is connected to the grid, the power grid after the power generation device is converged may still experience a voltage dip, which will affect the power quality and system stability of the load grid. This paper is based on the modular multilevel converter (MMC) to develop the wave energy device group flexible direct current transmission (MMC-HVDC) system. Combining the internal topological structure of the system and the MMC mathematical model, the system compound control strategy under the island operation mode is proposed. The control system operates in a synchronous reference frame (SRF). In addition to the basic controller, it also includes a circulating current suppression controller (CCSC) and a zero sequence current suppression controller. A MATLAB/Simulink simulation model is established based on the actual project. The simulation results show that the system can effectively compensate for transient voltage sags. In addition, the system also has power quality adjustment capabilities such as low harmonic distortion, reactive power compensation and circulating current suppression.