An ASTA-Based Variable-Damping Control with Five-Vector MPCC for a Dual Three-Phase PMLG in Wave Energy Conversion System

An adaptive super-twisting algorithm (ASTA)-based variable-damping strategy coordinated with five-vector model predictive current control (FV-MPCC) is proposed for a dual three-phase permanent magnet linear generator (DTP-PMLG) wave energy conversion system. In the upper-level controller, the power take-off (PTO) damping coefficient is adjusted online based on the captured power gradient, and finite-time convergence of the power-gradient variable is established via Lyapunov analysis. In the lower-level controller, four active voltage vectors and one zero voltage vector are applied in each sampling period, so that the d–q–x–y current components are directly included in the action-time calculation. Therefore, q-axis current tracking and x–y harmonic-current suppression are achieved simultaneously. Simulation results under two irregular-wave conditions show that the proposed variable-damping law approaches the optimal fixed-damping performance without requiring prior sea-state-specific damping selection, increasing the mean captured power by 2.38% and 3.44% relative to the optimal fixed-damping cases. Experimental results further confirm that the proposed FV-MPCC reduces the d-axis and q-axis current ripples by 35.92% and 40.66%, respectively, compared with conventional MPCC.