GRID IMPACT OF A WAVE FARM ON ITS LOCAL NETWORK: ANALYSIS OF VOLTAGE AND FLICKER LEVELS

International audienceMost oscillating wave energy converters without significant amounts of energy storage capacity generate significant electrical power fluctuations in the range of seconds. Because of these fluctuations, a wave farm may have a negative impact on the power quality of the local grid to which it is connected. Hence, the impact of these devices on both distribution and transmission networks needs to be well understood, before large scale wave farms can be allowed to connect to the grid. This paper details a case study on the impact of a wave farm on the distribution grid around the national wave test site of Ireland. The electrical power output of the oscillating water column (OWC) wave energy converters was derived from experimental time series produced in the context of the FP7 project " CORES ". The results presented in this paper consider voltage fluctuation levels and flicker levels for a typical time series. Simulations were performed using DIgSILENT simulation tool " PowerFactory "

Small-signal modeling of the incremental optical encoder for motor control

The small-signal model of the incremental optical encoder introduced in this paper provides an insight on the impact of this sensor in the dynamics of the motion control loop of a motor drive. The model is derived and validated for the most commonly employed speed estimation methods: the pulse count and elapsed time methods. Using the model, the reduction of the phase margin due to the encoder phase lag can be quantified at an early design stage. This model facilitates the design of control techniques to compensate for the phase margin reduction due to the associated feedback delays

DYNAMIC CHARACTERISTICS OF WAVE AND TIDAL ENERGY CONVERTERS & A RECOMMENDED STRUCTURE FOR DEVELOPMENT OF A GENERIC MODEL FOR GRID CONNECTION: A report prepared by HMRC-UCC for OES-IA under ANNEX III - Integration of Ocean Energy Plants into Distribution and Transmission Electrical Grids, OES-IA Document No: T0321

In order to connect an electricity generating plant to the electrical grid there are a series of rules and guidelines that must be adhered to. One of these is that the generator owner must provide a dynamic electrical model of their system that is compatible with the network planners and operators software. This model should take into account time series variation of the resources such as wave elevation and tidal flow velocity. The model should be usable in simulations of both normal operation and operation in the presence of grid faults

Dimensioning the Equipment of a Wave Farm: Energy Storage and Cables

International audienceStill largely untapped, wave energy may represent an important share in the energy mix of many countries in the future. However, the power fluctuations generated by most wave energy devices with little to no storage means, or without suitable control strategies, may cause power quality issues that must be solved before large wave energy farms are allowed to connect to the network. For instance, large power fluctuations may induce an excessive level of flicker in the distribution networks to which they are currently envisaged to be connected. Although storage appears to be a technically feasible solution, the minimum amount of storage required for a wave farm to become grid compliant with respect to typical flicker requirements is still unknown and is therefore investigated. This study constitutes the first part of the paper. Another issue, on which the second part of this paper focuses, concerns the optimal dimensioning of wave farm electrical components which is traditionally performed assuming steady-state conditions (i.e. constant current level), and it thus irrelevant in the case of wave farms outputting power fluctuations of significant amplitude. Hence, a second study, whose results are presented in this paper, focuses on the minimum current rating for which a submarine cable may be safely operated without thermal overloading. Addressing both these issues is essential to the economic viability of a wave farm as the cost of both storage means and electrical components is highly dependent on their rating and may represent a significant percentage of the capital expenditure

Impact of a Medium-Size Wave Farm on Grids of Different Strength Levels

International audiencePower fluctuations generated by most oscillating wave energy converters may have a negative impact on the power quality of the local grid to which the wave farms will be connected. Hence, assessing their impact is an important step in the selection process of a suitable deployment location. However, site-specific grid impact assessment studies are relatively time-consuming and require a high level of detail on the local network. Both of these constraints mean that grid impact studies are usually not performed in the preliminary stages of the site selection process, despite the extremely negative consequences resulting from poor power quality. This paper details a comprehensive study based on a relatively typical wave farm design connected to networks of different strength levels. The study was performed using experimental electrical power time series of an oscillating water column (OWC) device generated under the framework of the European FP7 project " CORES ". Simulations were performed using DIgSILENT power system simulator " PowerFactory "

Simplified estimation of the flicker level induced by wave energy farms

International audienceWave energy farms may cause voltage flicker on the local grid to which they will be connected due to the strong fluctuations that their output power may present. IEC standard 61400-21 describes methods for estimating the flicker level for different short-circuit ratios as well as for different numbers of devices composing the farm. This method was initially developed for wind farms but is applicable to wave energy farms as well. However, besides the short-circuit ratio and the number of devices composing the farm, the grid impedance angle has also a strong influence on flicker. Despite this, no method exists in the literature for estimating flicker as a function of this variable. This paper presents the results of a study intended to fill this gap by focusing on developing a simplified method for estimating the flicker level induced by a wave energy farm as a function of the grid impedance angle. The results obtained through this method are compared with those obtained from numerical load flow simulations performed with PowerFactory. These simulations were based on experimental power output time series of a wave energy prototype deployed at sea as part of the European CORES project. The voltage profiles thus generated were then processed by means of a flickermeter compliant with IEC standard 61000-4-15