Provision of frequency support by offshore wind farms connected via HVDC links

The high penetration levels of wind power will obligate wind farms to contribute to the mitigation of frequency drops. Comprehensive case studies are presented to investigate the different methods of frequency support provision by wind power. The implemented test system is composed of an offshore wind farm connected to an external grid through a point-to-point HVDC link. Three different frequency support methods are compared; droop de-loading, battery storage banks and a mix between the two methods. Moreover, two different methods of sensing the frequency drop, at the point of common coupling, by the wind farm are examined. The impact of the HVDC is highlighted, especially its role to transmit the power surge provided by the wind farm. A modified de-loading controller is developed and integrated to all the wind turbines, according to the executed case studies. Results show that the proposed frequency support solutions have almost similar impact on the natural frequency response at the point of common coupling. The HVDC link does not worsen the frequency response, and the fluctuations in voltage levels at onshore and offshore buses are very minor. DIGsILENT PowerFactory is integrated as a simulation environment

Frequency stability analysis in low frequency AC systems for renewables power transmission

The foreseen high penetration levels of wind energy will have serious implications on frequency stability, hence developed control methods of wind turbine and alternative technologies including energy storage should enable the provision of frequency support by wind power. Active research is ongoing to investigate the possibility of collecting and transmitting offshore wind power through low frequency alternating current systems (LFAC). This paper develops a novel method to enhance frequency support capability of generators connected to a LFAC system. The leveraged frequency regulation ability of the generators at LFAC system is emphasized. The voltage is proportional to the frequency of the LFAC system, so that the transformers can be protected when frequency drops. Then the generators at LFAC system acquire sufficient time for frequency regulation. In this paper, a hydro generator at LFAC system is regarded as an energy storage plant, which is connected to the LFAC system rather than normal frequency grid

Fulfilment of grid code obligations by large offshore wind farms clusters connected via HVDC corridors

The foreseen high penetration levels of wind power will force the systems operators to apply restrictive constraints on wind power plants. The ability of offshore wind clusters, which are connected via HVDC, to fulfill the grid codes, especially those related to voltage stability is investigated. This came in the frame of a project to develop an integrated and practical tool to design offshore wind clusters (EERA-DTOC). The applied case studies examine the system stability during and after severe disturbances, and the compliance with the grid codes. Additionally, this paper explains the applied procedure to utilize the outcomes of Net-OP tool, which proposes an optimized topology to connect the wind power clusters to the interconnected power systems. The integrated simulation environment, namely, PSS/E, is used to implement a highly detailed and dynamic model based on the recommendations of Net-OP tool. The results confirm that wind farm clusters respond to faults and disturbances as desired by the grid codes

Novel concept of renewables association with synchronous generation for enhancing the provision of ancillary services

Renewable energy sources are foreseen as a provider of full range of ancillary services. An innovative concept of alignment between renewable power generation elements and synchronous generators is proposed: Renewables Association with Synchronous generators (RAS). It mitigates the dependence on direct frequency measurements, which are prone to noise and lack of accuracy, and enables perfect coordination between the responses of renewable and conventional power plants. RAS relies on a leader synchronous generator, connected at the point of common coupling of the renewable power plant or close to it. This synchronous generator is able to provide ancillary services (e.g. frequency support and reactive compensation). The renewable power plant is controlled to provide such services similar to the leader synchronous generator, but scaled down/up to match the rating of the renewable power plant by integrating supplementary controllers that are associated with the synchronous generator response. Two approaches are proposed to provide voltage support, besides a supplementary frequency support controller. These RAS-based voltage and frequency support methods are compared to other methods proposed in the literature. Results show the positive impact of RAS concept on the provision of active power and reactive compensation to tackle frequency and voltage events respectively, following the response of the leader synchronous generator. DIgSILENT PowerFactory is the applied simulation environment

A review on frequency support provision by wind power plants : current and future challenges

The continuing increase of wind energy penetration into power systems, in combination with the retirement of conventional generation, raises new challenges for the maintenance of power system stability. This paper presents a comprehensive review of wind power plant capabilities to provide frequency support and the corresponding methods available in the published literature are thoroughly analysed and compared. The topic is covered from different perspectives giving a comprehensive overview on the work carried out in this field. In addition, the integration of energy storage technologies and dispatching of wind farms during frequency deviations are thoroughly discussed. Finally, technical challenges, future research lines and general recommendations are provided

Wind farms dispatching to manage the activation of frequency support algorithms embedded in connected wind turbines

Wind energy development in power systems and their replacement for conventional generation plants are considered to be a two sided coin. Wind energy penetration process depends on two aspects, namely, the technical and economical impacts on power grid and electricity market. This paper focuses on the technical section and aims to solve a major problem related to the high wind energy penetration levels. This dilemma arises due to the intermittent nature of wind speed which mitigates its capabilities compared to conventional generation, especially in dealing with frequency drops. This research work focuses on a basic sector from this problem, particularly, dispatching the wind turbines, inside wind farms, during frequency drops mitigation. The proposed algorithm integrates several factors to determine the number of wind turbines which should contribute in system frequency recovery. Wind speed nature in the wind farm location, installed wind turbines types and their numbers are examples for these factors. However, this dispatching process is instantaneous and counts on other dynamic factors (e.g. average wind speed at wind turbine and frequency deviation severity). In addition, conventional generation is controlled based on wind farms reactions during frequency drops, likewise at normal operation. Certain zone from the Egyptian grid is integrated in this research work as a benchmark to apply the offered algorithm whereas real data for wind speeds and grid specifications are applied. MATLAB and Simulink are the implemented simulation environments

Evaluation of system reliability using seasonal and random operation techniques

The target of any power system is to deliver stable, clean and cheap electrical power to the customer. This paper offers two independent approaches to simulate the operation of the generating units in a power network. The first methodology depends on the load variation in each season while the other one is random through a certain sequence. Using the proposed approaches a comparison between the different suggested PDF that describes the failure and repair for any component is made. The simulation is done based on Monte Carlo method through a small radial system and the IEEE 13 node test system