Abstract
Wave energy converters (WECs) generally use a mechanical solution such as hydraulics or gearing to optimise the extraction of energy from the incoming waves prior to converting it into electrical energy via a high-speed rotating generator. This simplifies the electrical power conversion system (EPCS) design and facilitates the use of mechanical energy storage such as springs, compressed air, or hydraulic accumulators. The naturally peaky nature of the WEC power can thus be reduced and there is potential to tune the resonant frequency of the WEC. The potential design of a current source converter (CSC) for an integrated low-speed direct-drive power take-off (PTO) for a WEC is described here. Silicon carbide (SiC) devices which enable high switching frequencies with a beneficial reduction in passive component dimensions are considered. Issues such as fault tolerance, protection, and parasitic inductance are investigated leading to an improved layout proposal.
Highlights
Defining the functional requirements for a Wave Energy converters (WECs) Power Take-Off (PTO) is not straightforward
A reduction in passive component energy storage requirement applies for both the Voltage Source Converter (VSC) and the Current Source Converter (CSC) with increased switching frequency and in both cases, issues such as switching losses, parasitic inductances and gate drive requirements become more challenging at these higher switching frequencies
The Finite Element Analysis (FEA) approach is well suited to making incremental improvements or validating an existing design, but the shear range of variables involved in the prototype stage, such as optimal choice of capacitors, heat sinks, power devices makes it very difficult to apply in any general way
Summary
Defining the functional requirements for a WEC PTO is not straightforward. The range of variables include: wave resource, location, device type, structure, mooring, PTO components and control methodology. The WEC has a 10 module linear generator, each module having an associated EPCS rated to supply the combination of mechanical reactive power needed to tune the WEC and any electrical reactive power for the generator whilst extracting the maximum available energy from the incoming waves [3] In this case, the converter kVA rating is 10x the generator maximum average power rating of the module. Interest in applying wide bandgap devices to enable low-loss, high switching frequency variants of the CSC have been reported [8, 9]. These new variants offer potential advantages in terms of increased robustness, reduced inductor size as well as improved operating efficiency.
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