## 1 Introduction  
_Wave Energy Converters_ (WECs) are different from most other energy producers in that the prime mover operates with a sinusoidal velocity. When such a producer is directly connected to its generator, the output power is continuously fluctuating with zero crossings in every wave, resulting in a high peak-to-average power ratio. _[PERSON]'s_ (FO) power plant _Lifesaver_, pictured in Figure 1, illustrates this typical behavior, as plotted in Figure 2. This level of power distortion is unlikely to be suitable for export to the grid as the utilization of installed power capacity is very low. In this article, the method of aggregate power smoothing from multiple WECs in order to improve the power quality will be investigated. As the incoming wave energy is close to constant when averaged over longer periods of time, the power production can be equally averaged by covering a large distance of the incoming wave. Substantial work has previously been performed within this topic, and the articles ([PERSON] _et al._, 2008) [1], ([PERSON] _et al._, 2011) [2] and ([PERSON] _et al._, 2012) [3] demonstrate successful integration of WECs into a farm system. The focus of this work is the specific integration of Lifesaver into a WEC farm system, and the potential for economical optimization of the power transfer chain from wave to wire.  
The power quality is very poor when the wave energy enters the WEC, mainly due to two factors. Firstly, the sinusoidal shape of the incoming wave causes a sinusoidal movement of the _power take-off_ (PTO) system, and does not allow the PTO to run constantly at rated speed. Secondly, waves tend to group into _wave trains_ that consist of series of waves with similar amplitude ([PERSON], 1988) [4]. This adds subharmonic fluctuations with respect to the incoming wave period and further reduces the utilization factor of installed PTO power. Moreover, WEC systems that utilize the mooring line as a production force can only extract power during the upwards motion. This unidirectional production pattern adds another doubling to the peak-to-average ratio. This can subsequently add up to a total peak-to-average ratio in the high tens, depending on the system configuration.  
Figure 1: _Lifesaver_ on site outside Falmouth, England.  
Lifesaver has a peak-to-average ratio of approximately 60 on the entry point of mechanical wave power. Thus, in the design wave state, the PTO is designed for power peaks up to 60 _per unit_ (pu), while only 1 pu is transferred on average. If the PTO was constantly operated at rated speed and rated force, on average 60 pu of power could be transferred. This exceptionally low utilization factor is a major challenge for the profitability of WECs and must be managed carefully. Moreover, it is important to  
Figure 3: Illustration of the improved power quality through the power transfer chain. The power quality is given as the peak-to-average ratio and illustrated with orange bars. The nominal oversize factor is denoted with parentheses (_i.e._, the name plate rating on the generator divided by the average produced power).  
Figure 2: Actual production and system operation measured with Lifesaver.  
quickly reduce the peak-to-average ratio in the downstream power system towards the grid. The poor mechanical utilization factor is not necessarily an issue in and of itself, as the mechanical transmission cost can be low compared to the cost of the total system. However, it is important that this poor utilization factor not be carried forward to the rest of the system. Figure 3 illustrates the gradual increase in power quality that is required from an economical point of view, and is the focus of this work. The underlying details of the figure will be explained and analyzed in detail in the following sections.