Design of the LCL+Trap Filter for the Two-Level VSC Installed in a Large-Scale Wave Power Plant A. M. Cantarellas1, E. Rakhshani1, D. Remon1, P. Rodriguez1,2 1
2
Abengoa Research Seville, Spain
[email protected]
Technical University of Catalonia Electrical Engineering Department Barcelona, Spain
electronics emerge as the preferred solution for interfacing grid connected wave energy converters, as they can successfully provide variable speed control of the generator, acceptable grid voltage regulation and fault-ride through capabilities [2]. Despite of the previously identified benefits, the implementation of grid connected power electronic converters produces large current harmonic distortions, which need to be accurately mitigated by suitable passive filter solutions, with the purpose of ensuring acceptable grid connection standards compliance.
Abstract— This paper presents a methodology for designing the link passive filter of the power converters installed in a multi-megawatt wave power plant. Such filter is based on the superposition of both LCL and trap filter configurations with the purpose of achieving enhanced grid interaction of a twolevel voltage source converter. The LCL+Trap filter design is highly dependent on the electrical network characteristics; hence the distribution system of the plant is introduced in the paper to take into account its effects on the tuning parameters. The proposed LCL+trap filter topology arises as a successful alternative solution for the conventional LCL filter topology, thanks to its improved filtering capability while ensuring a reduced filter size. The validation of the proposed filter performance is evaluated in simulation by performing a comparative analysis between the LCL+trap and the LCL filters when operate in a wave farm application.
I.
For this type of applications, such as large scale wave power plants, in which passive filters appear interfacing the grid connection of high power converters, special attention need to be paid to the filter design procedure. The reduced switching frequencies required, may introduce a significant challenge in achieving acceptable filtering capabilities while ensuring reduced filter sizes. In the case of the conventional LCL filters, the resonant frequency needs to be selectively placed with the purpose of providing sufficient harmonic mitigation for the switching frequency harmonics, while avoiding any interaction with the controller bandwidth [3-4]. The implementation of grid connected multi-level converters through LCL filters appeared as a suitable approach for achieving acceptable grid connection standards compliance, since this converter topology provides low dv/dt and reduced harmonic distortion levels. Despite of its successful grid interconnection, this power processing approach results in a more expensive and less reliable solution when compared with the implementation of conventional two-level converters. Unlike many approaches based on the grid connection of advanced power converter technologies interfaced by LCL filters [4-6], this paper proposes the use of a LCL+trap filter as the link between the grid connection of a conventional two-level high-power converter. Such LCL+Trap filter configuration becomes an interesting alternative to the widely used LCL filter, since high harmonic attenuation is achieved while ensuring reduced filter size [7]. The grid connection of two-level converters through the proposed advanced filter configuration arise as a suitable power processing solution for achieving a successful
INTRODUCTION
Nowadays, a growing effort is being experienced in supporting more clean, affordable and sustainable forms of energy. As a result, in the field of renewable energy, wind, hydro and solar appear as the leading technologies, which have already achieved a considerable maturity level when compared with other renewable energy sources. However, with the purpose of overcoming the main challenges related with the climate change and finding reliable and alternative energy sources, ocean waves arise as one of the most extensive inventories of unexplored renewable power. The growth and interest in expanding towards the development of the wave energy sector comes mainly motivated due to its tremendous potential, since ocean waves are considered to be the largest potential renewable energy resource which remains commercially unexploited [1]. Up to date, the greatest research effort experienced in the wave energy sector was focused on hydrodynamics and survivability studies of different WEC concepts, as well as in the primary power take-off mechanisms. Nevertheless, it has not been until now, when several WEC prototypes are close to reach a commercial stage, that the electrical concerns in finding suitable grid interconnection solutions has become under serious consideration [2]. In this regard, the use of power
978-1-4799-0336-8/13/$31.00 ©2013 IEEE
707
