The effect of supercapacitors in a tidal current conversion system using a torque pulsation mitigation strategy

Abstract

The research presented in this paper investigates the effect of connecting supercapacitors at the DC link of a hypothetical 1.5MW three-bladed variable-pitch horizontal-axis tidal current turbine that uses a torque pulsation mitigation strategy. Torque pulsations are classified into fatigue torque and ultimate or peak torque. Both can lead to premature components failure or system overdesign and costly maintenance. Research has suggested that torque pulsations can be mitigated by using a novel control strategy with which pulsations created by the unsteady tidal current flow are reduced by changing the generator speed. Increasing the variation of the generator speed increases the variation of the electrical power output of the generator. The electrical power output of the generator is injected to the grid through back-to-back AC to DC, DC to AC converters. The increased variation of the electrical power output of the generator causes DC link voltage spikes, increases the stress of electrical components and affects the compliance of the tidal current conversion system for grid connection. In order to tackle these problems a supercapacitor module is proposed to be connected at the DC link. The supercapacitor is able to absorb the fast short-term variations of the electrical power and keep the DC link voltage within limits. The potential benefits of using supercapacitors for connection in weaker grids and in tidal current arrays are also studied. Results show that DC link voltage and grid side harmonics are positively affected from the installation of a supercapacitor at the DC link.

Modelling and Performance Analysis of a Tidal Current Turbine Connected to the Grid Using an Inductance (LCL) Filter

“…It is noted that tidal power is a predictable energy resource, whose accuracy has been within 98% for decades. This predictability allows tidal power generation to be successfully integrated into electrical grids [4][5][6][7][8]. The typical behaviour of the power system has changed because of the increasing use of renewable energy sources.…”

“…However, tidal energy generation comes with many challenges, and its integration into the grid presents numerous operational and control difficulties that limit the grids' ability to run steadily and dependably. Therefore, it is important to maintain the stability of voltage and frequency in the power network by ensuring that harmonic distortions are kept as low as possible [7,10]. In power converters with a rectifier input stage, LCL filters are specially designed to cut down on harmonic current absorption (frequency converters for UPS, motors, etc.).…”

Double Adaptive PI-Structure for Regulating a Microgrid DC Bus Using a Flyback-Based Battery Charger/Discharger Converter

“…In the literature it is possible to find charging/discharging systems implemented with different bidirectional converters like Boost [6,7], Buck-Boost [8,9], Cuk [10,11], Zeta/Sepic [12], Sepic/Zeta [13,14], or flyback [15]. The Boost converter has some advantages like its simplicity, reduced number of components, and simple control system, regarding Buck-Boost, Cuk, Zeta/Sepic, and Sepic/Zeta.…”

An Inter-Comparison of Dynamic, Fully Coupled, Electro-Mechanical, Models of Tidal Turbines

“…The study demonstrated that cascaded ADRC approach slightly improved a tidal turbine system production during swell wave disturbance periods in contrast with the conventional PI controllers. An investigation about the mitigation of undesired torque pulsations by changing the generator speed was presented by Sousounis et al [4]. The authors propose that the DC link voltage spikes, the electrical components stress increment, and the hazard to grid connection produced by increasing the variation of the generator rotational speed can be overcome by installing a supercapacitor module at the DC link.…”