Analysis of electrical drive speed control limitations of a power take-off system for wave energy converters

Abstract

The active control of wave energy converters with oil-hydraulic power takeoff systems presents important demands on the electrical drives attached to their pumps, in particular on the required drive accelerations and rotational speeds. This work analyzes these demands on the drives and designs reliable control approaches for such drives by simulating a wave-to-wire model in a hardware in-theloop simulation test rig. The model is based on a point absorber wave energy converter, being the wave, hydrodynamic and oil-hydraulic part simulated in a computer that sends and receives signals from the real embedded components, such as the drive generator, controller and back-to-back converter. Three different control strategies are developed and tested in this test rig and the results revealed that despite the drive limitations to acceleration levels, well above 1x10 4 rpm/s, these do not significantly affect the power takeoff efficiency, because the required acceleration peaks rarely achieve these values. Moreover this drive is much more economical than an oil-hydraulic and equivalent one that is able to operate at those peaks of acceleration.

Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review

“…In addition, the flushing valve, overflow line and the charge module are also considered in this concept. Besides that, further studies, according to the CP-Type XIV concept, has been carried out in [62,95]. In these studies, the CP-Type XIV concept has been modified by connecting the overflow line to the secondary hydraulic PTO system in parallel, as presented in Figure 7d.…”

“…Single action of constant-pressure hydraulic PTO based on hydraulic transformer concepts. (a) CP-Type XII[46]; (b) CP-Type XIII[93,94]; (c) CP-Type XIV[45] and (d) CP-Type XV[62,95].…”

On Real-Time Hybrid Testing of Ocean Wave Energy Conversion Systems: An Experimental Study

“…These techniques are also gaining popularity in the WEC development sector [24], and hardware-in-the-loop (HIL) experiments can be a very powerful tool; for example, controller hardware-in-the-loop (CHIL) and power hardware-in-the-loop (PHIL) experimental testing for a renewable energy system integration [25]. The majority of the literature related to HIL focuses on experimental setups consisting of small scale rotatory motor-generator testbeds to simulate ocean hydrodynamics and wave energy converter dynamics [26]- [30], or hardware test rigs tailored for some particular type of WEC device, such as hydraulic PTO [31] and raft-type WEC [32], inertial mechanism-based WEC [33] and dielectric elastomer generators [34]. A limited amount of work is directed towards HIL testing of Linear PTO mechanisms, such as in [35], [36]; however, the scope of the work is limited to specific WEC in their facilities.…”