The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

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Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

In this paper, a solution is described that makes it possible for wind turbines using doubly-fed induction generators to stay connected to the grid during grid faults. The key of the solution is to limit the high current in the rotor in order to protect the converter and to provide a bypass for this current via a set of resistors that are connected to the rotor windings. With these resistors, it is possible to ride through grid faults without disconnecting the turbine from the grid. Because the generator and converter stay connected, the synchronism of operation remains established during and after the fault and normal operation can be continued immediately after the fault has been cleared. An additional feature is that reactive power can be supplied to the grid during long dips in order to facilitate voltage restoration. A control strategy has been developed that takes care of the transition back to normal operation. Without special control action, large transients would occur.

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Ridethrough of wind turbines with doubly-fed induction generator during a voltage dip

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

The steady growth of installed wind power together with the upscaling of the single wind turbine power capability has pushed the research and development of power converters toward full-scale power conversion, lowered cost pr kW, increased power density, and also the need for higher reliability. In this paper, power converter technologies are reviewed with focus on existing ones and on those that have potential for higher power but which have not been yet adopted due to the important risk associated with the high-power industry. The power converters are classified into single- and multicell topologies, in the latter case with attention to series connection and parallel connection either electrical or magnetic ones (multiphase/windings machines/transformers). It is concluded that as the power level increases in wind turbines, medium-voltage power converters will be a dominant power converter configuration, but continuously cost and reliability are important issues to be addressed.

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Power Electronics Converters for Wind Turbine Systems

Microgrids and Active Distribution Networks offer a potential solution for sustainable, energy-efficient power supply to cater for increasing load growth, supplying power to remote areas, generation of clean power and reduction in emission of greenhouse gases & particulates as per Kyoto protocol.

Microgrids and Active Distribution Networks

This article shows that adjustable speed generators for wind turbines are necessary when output power becomes higher than 1 MW. The doubly fed induction generator (DFIG) system presented in this article offers many advantages to reduce cost and has the potential to be built economically at power levels above 1.5 MW, e.g., for off-shore applications. A dynamic model of the DFIG was derived to develop a vector controller to decouple dynamically active and reactive power control. Simulations show excellent response of the DFIG independent of speed. Measurements obtained from 1.5 MW units currently in operation confirm the theoretical results.

Doubly fed induction generator systems for wind turbines

Wind turbines are being built at power levels above 1.5 MW. Higher power levels are being anticipated for offshore applications. To limit mechanical stresses and power surges in these high power systems, speed control is necessary. The doubly-fed induction generator (DFIG) system is investigated as a viable alternative to adjust speed over a wide range while keeping the cost of the power converters minimal. A four-quadrant IGBT AC-to-AC converter is used to feed power bi-directionally to the rotor circuit. Decoupled control of active and reactive power can be realized using the dynamic model of the DFIG. Simulations and measurements confirm the validity of the model and the viability of the DFIG wind turbine.

M. Deicke

Papers

Doubly fed induction generator systems for wind turbines

Adjustable speed generators for wind turbines based on doubly-fed induction machines and 4-quadrant IGBT converters linked to the rotor