Multimegawatt wind-turbine systems, often organized in a wind park, are the backbone of the power generation based on renewable-energy systems. This paper reviews the most-adopted wind-turbine systems, the adopted generators, the topologies of the converters, the generator control and grid connection issues, as well as their arrangement in wind parks.

Overview of Multi-MW Wind Turbines and Wind Parks

In electrical islands, frequency excursions are sizeable and automatic load shedding is often required in response to disturbances. Moreover, the displacement of conventional generation with wind and solar plants, which usually do not provide inertial response, further weakens these power systems. Fast-acting storage, by injecting power within instants after the loss of a generating unit, can back up conventional generation assets during the activation of their primary reserve. This paper relies on dynamic simulations to study the provision of such a dynamic frequency control support by energy storage systems in the French island of Guadeloupe with large shares of wind or solar generation. The results show that fast-acting storage, by acting as a synthetic inertia, can mitigate the impact of these sources on the dynamic performance of the studied island grid in the case of a major generation outage. The other concerns raised by renewables (e.g., variability, forecast accuracy, low voltage ride-through, etc.) have not been addressed within this project.

Dynamic Frequency Control Support by Energy Storage to Reduce the Impact of Wind and Solar Generation on Isolated Power System's Inertia

Doubly fed induction generators (DFIGs), often organized in wind parks, are the most important generators used for variable-speed wind energy generation. This paper reviews the control systems for the operation of DFIGs and brushless DFIGs in wind energy applications. Control systems for stand-alone operation, connection to balanced or unbalanced grids, sensorless control, and frequency support from DFIGs and low-voltage ride-through issues are discussed.

Overview of Control Systems for the Operation of DFIGs in Wind Energy Applications

The inertia of today׳s power system decreases as more and more converter connected generation units and load are integrated in the power system. This results in a power system which behaves differently from before which causes concerns for many grid operators. Therefore, a detailed study is needed to investigate the relevance of this inertia in the operation, control and stability of the system. Moreover, a new definition of the term system inertia is necessary since is it expected that in the future also the renewable electricity generation units will deliver the so-called virtual (synthetic) inertia. In this paper a review of the research related to inertia in a power system is given. Both the challenges as the solutions from an operator point of view to control a system with low inertia are discussed. Also a new definition of inertia is proposed to incorporate the different forms of inertia which are each described in more detail. From recent studies, it can be concluded that the influence of reduced inertia on frequency stability is generally considered as the main challenge for system operators, but with the additional measures listed in this paper, this impact can be mitigated.

/pdf/the-relevance-of-inertia-in-power-systems-3frw82b3ct.pdf

The relevance of inertia in power systems

In this paper an extensive literature review on load–frequency control (LFC) problem in power system has been highlighted. The various configuration of power system models and control techniques/strategies that concerns to LFC issues have been addressed in conventional as well as distribution generation-based power systems. Further, investigations on LFC challenges incorporating storage devices BESS/SMES, FACTS devices, wind–diesel and PV systems etc have been discussed too.

A literature survey on load–frequency control for conventional and distribution generation power systems

The paper investigates contribution of doubly fed induction generator (DFIG) to system frequency responses. Impact of different governor settings and system inertia are investigated. Three distinct cases are simulated in order to illustrate the influence of DFIG penetration on frequency regulation. Provision of inertial response by DFIG through artificial speed coupling is also presented. The effects of the inertial response on the machine behavior and its significance for frequency regulation are discussed. The influence of converter current limits and auxiliary loop parameters on the inertial response are illustrated and a novel control algorithm is developed for extracting maximum energy from the turbine in a stable manner. The results of the study are illustrated on the example of an isolated power system consisting of a diesel generator and a DFIG.

Dynamic Contribution of DFIG-Based Wind Plants to System Frequency Disturbances

This paper explores and compares the performance of alternative voltage control strategies applied to doubly fed induction generator (DFIG) Different combinations of reactive power control of rotor- and grid-side converters are investigated for voltage-control purposes Simulations are performed using detailed models built in DIgSILENT PowerFactory in order to illustrate the influence of controllers on transient stability and steady-state operation of the DFIG-based wind plant This paper also proposes appropriate control strategies for different sets of network operating conditions and topologies Operational limits, such as current margins and pulse-width modulation limits, are also taken into account

Reactive Power Control Strategies for DFIG-Based Plants

There has been a fast growing demand for the application of doubly fed induction generators (DFIG) in wind power plants in recent years. They have in particular dominated the market in last two years. DFIG is an ideal candidate to satisfy the requirements of the recently proposed challenging grid codes. However, many uncertainties still exist or at least there are no published reports regarding validated comprehensive DFIG models. This paper attempts to clarify the existing ambiguities in modelling of DFIG under various operating conditions using the power system analysis package DIgSILENT PowerFactory. This paper uses available DFIG models and investigates/demonstrates the influence of various model parameters and simplifications (for both mechanical and electrical subsystems) on DFIG-based wind plant transient responses. It further explores and compares the performance of different crowbar protection and rotor side converter restart schemes. Realistic operational limits, such as current margins and PWM modulation limits, are taken into account in all simulations.

Assessing Transient Response of DFIG-Based Wind Plants—The Influence of Model Simplifications and Parameters

The impact of distributed synchronous generators on quality of electricity supply and transient stability of real distribution network

This paper assesses the transient operation and possible improvements of the voltage quality/stability of an 11kV distribution network-cell (DNC) with renewable energy sources (RES). The generators considered include synchronous generators (SG), doubly-fed induction generator (DFIG) and fixed-speed induction generator (FSIG) based wind plants and converter-connected generators (CCG) (e.g. photovoltaics, fuel cells, etc.). The generators are modelled in detail (considering voltage/current limits, aerodynamics, multi-mass models, etc.) in order to reflect appropriately their participation regarding system stability. Various DNC operating conditions, load type and compositions and a diverse range of generation scenarios are considered. Extensive results are presented and conclusions are drawn from a set of more than 500 case studies together with potential corrective actions to improve DNC stability. DNC MODELLING

/pdf/improvement-of-transient-responses-of-distribution-network-2xhtq4admx.pdf

M. Kayikci

Papers

Dynamic Contribution of DFIG-Based Wind Plants to System Frequency Disturbances

Reactive Power Control Strategies for DFIG-Based Plants

Assessing Transient Response of DFIG-Based Wind Plants—The Influence of Model Simplifications and Parameters

The impact of distributed synchronous generators on quality of electricity supply and transient stability of real distribution network

Improvement of transient responses of distribution network cell with renewable generation