## 2 System Description
### Array  
To increase the output power, and to improve the output power quality, several WECs may be linked together into an array. Figure 7(a) shows the proposed layout that was put forward in our previous study described in [12, 13]. The fundamentals behind this design is the need to space the WECs along the incoming wave direction to gain power quality from intermediate wave smoothing, while simultaneously achieving a good capture ratio, which requires spacing perpendicular to the incoming wave direction. Thus, a 45\({}^{\circ}\) angle to the incoming wave direction was found to be optimal. Also, the array design should endeavor to cover a full wave length along the predominant wave direction to maximize the effect of power smoothing. With Lifesaver as the basis, this amounts to around seven absorbers per array.  
It is FO's point of view that the devices within the array should be positioned close together and interconnected so that the array can be viewed and operated as a single system. Furthermore, this allows for sharing a common mooring system and simplifies the electrical connections between the devices as the cable can run along the floater topside. The exact configuration of the mechanical interfaces is not yet decided, but preliminary studies indicate that a combination of strong moorings pulling the devices apart and flexible bumper connections between the devices can maintain the mechanical integrity of the array within reasonable cost. In this work, a spacing of 2 m is chosen between the devices to account for the interface structure. Figure 8 illustrates an array based on Lifesaver with this configuration.  
The array is electrically connected to DC by coupling the DC-Link on the inverters. The configuration is illustrated in Figure 7(b), and shows how the power can flow freely between the WECs without additional conversion or transmission equipment. This allows a producing WEC to directly transfer power to a consuming WEC that is running in pull-back, and allows the sum of WEC powers to be directly transferred. However, the low DC-link voltage poses a practical limit to the size of the array due to the sea cables that have to run between the WECs. As a rule of thumb, 1000 A is used as a current limit for low voltage sea cables. This limits the number of WECs in the array to around ten, and supports the earlier stated figure of seven absorbers in the array. Thus, this array size is adopted for the following simulation work.  
As the allowed current transfer capacity is fully utilized within the array, the array output must be transformed to a higher voltage before export from the array. The middle WEC should act as a _mother WEC_ and house the electrical conversion equipment and connect to the export cable. Since the aggregated array power is low voltage DC, an active front-end inverter and a transformer is required to convert the output to medium voltage AC. The cost of this equipment is directly influenced by the peak power requirement and power quality at this point. In our earlier publication [13], we showed that the peak to average ratio would be directly reduced by a factor of 3-5 due to natural power smoothing between the devices. The peak-to-average ratio could be further improved towards 1.5 by implementing a small energy storage, as shown in our work [14]. As will be demonstrated in the following, the peak power rating for the current configuration is close to three, which will require a rated installed converter capacity of about twice the average exported power. This is illustrated in Figure 3 on page 422.