FPGA-Based Cascade Control of a Piston-Type Wave Maker with Height Feedback

The traditional control approach for piston-type wave makers is reduced to a piston position tracking problem based on open-loop wave-maker theory; however, due to hydrodynamic loading, nonlinear effects, and propagation delays, the target wave condition at the measurement section cannot be guaranteed. This experimental study involves controllers tuned offline through numerical simulations and validated in real time on a 24 m wave channel. The novelty of this work is a two-layer field-programmable gate array (FPGA) cascade that regulates the measured wave height in closed loop, not just the piston position. In the inner layer, the hydraulic servo cylinder position is controlled within a 1 ms cycle using a proportional–integral (PI) or a Takagi–Sugeno (T–S) fuzzy controller; the outer layer, in a 20 ms cycle, updates the position reference via real-time wave height feedback. Controller parameters were tuned using three meta-heuristic algorithms under the integral of time-weighted absolute error criterion, and a similarity-based rule reduction reduced the T–S consequent parameters from 27 to 9, yielding 66.7% and 62.5% reductions in FPGA execution time and digital signal processing slice usage with tracking-error changes of only 2.2–2.3%. Experiments confirm high-accuracy position tracking and steady-state wave height regulation, verified by fast Fourier transform analysis.