Abstract
Wave Energy Converters (WECs) generally use a Mechanical Power-Take-Off (MPTO) involving hydraulics or gearing to optimise the extraction of energy from the incoming waves before converting it into electrical energy via a high speed rotating generator. This simplifies the design of the Electrical Power Conversion System (EPCS). Further, it facilitates the use of mechanical energy storage such as hydraulic accumulators to reduce the peaky nature of the power flow and allows the WEC resonant frequency to be tuned for maximum energy capture. This work compares two power electronic converter topologies for an Electrical PTO (EPTO). This EPTO is intended to replace the aforementioned MPTO and generator with a Permanent Magnet Linear Machine (PMLM) directly coupled to the WEC. The compared topologies comprise either a Current Source Converter (CSC) or a Voltage Source Converter (VSC) as the generator interface working in combination with a DC-DC converter and an Energy Storage System (ESS). The principle differences between the two topologies are explored and losses are evaluated in a modular EPCS working with a WEC. Wide-bandgap power electronic switches are assumed for both topologies over a range of switching frequencies. The evaluation concludes that the CSC topology is advantageous at higher switching frequencies.
Highlights
Replacing the mechanical power-take-off (MPTO) in a wave energy converter (WEC) is the underlying objective of E-Drive
From the perspective of the power electronic converter, the most important factors are the magnitudes of generator terminal voltages and currents as well as their time varying nature when operating with the WEC
The analysis presented here, provides some insight into the potential benefit of adopting a Current Source Converter (CSC) based topology compared to the more conventional Voltage Source Converter (VSC) based topology for this WEC application, but only if it can be operated with a high switching frequency
Summary
Replacing the mechanical power-take-off (MPTO) in a wave energy converter (WEC) is the underlying objective of E-Drive. The idea is to replace the MPTO with a direct-drive electrical solution, an electrical direct-drive PTO (EPTO), which is capable of reducing the naturally peaky nature of the WEC power flow and to tune the natural resonant frequency of the WEC, maximising energy capture by the use of reactive power control [1]. From the perspective of the power electronic converter, the most important factors are the magnitudes of generator terminal voltages and currents as well as their time varying nature when operating with the WEC. The force applied by the generator on the WEC is a combination of the time-varying real and reactive mechanical vectors which typically have an operating frequency of
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