Adaptive Control of the WaveSub WEC

Overview

The University of Bath had two projects in Stage 1 of the Control Systems programme. This project investigates the feasibility of applying an adaptive control methodology specifically to the WaveSub Wave Energy Converter (WEC) in conjunction with the Romax electro-mechanical Power Take Off (PTO) system. The two systems are, in principle, compatible and well suited to provide an efficient and cost-effective overall solution.

Detailed modelling and simulation activities are undertaken for the WEC and PTO subsystems, and then these are combined in a unified model and the adaptive control system is applied in order to assess the performance of the complete system against WES target performance metrics.

The proposed control methodology is computationally simple and is designed to keep the WEC velocity in phase with the wave excitation (a necessary condition for efficient power conversion) while also accommodating physical constraints such as position limits in a simple and robust manner. The control strategy employs the Minimal Controller Synthesis (MCS) algorithm. This is a form of Model Reference Adaptive Controller (MRAC) which has been widely applied, for example in shaking table control and active vehicle engine mounts. MCS may be beneficial for application to WEC control as it requires no a priori knowledge of plant dynamics.

This is a great advantage over other strategies as:

1. Implementation becomes very straightforward.
2. An accurate estimate of the plant (sensors, PTO and WEC) is not always easy or even possible to achieve.
3. It is robust to parameter variation and nonlinearity (e.g. plant ageing or damage), and fault tolerant.
4. It is applicable to any WEC/PTO system combination without the need for extensive re-tuning.

Advanced control strategies such as this have not been tested in realistic situations, so the project pathway through stages 1-3 under the WES controls program will represent a step change in technology advancement within the wave energy field. The general applicability of the proposed methodology also makes it an enabling technology across a broad range of WEC and PTO types.

The University of Bath also presented a poster on this Stage 1 Control Systems project at the 2017 WES Annual Conference.