M. B. C. Salles

Justified Fault-Ride-Through Requirements for Wind Turbines in Power Systems

In this paper, a novel adaptive strategy to obtain technically justified fault-ride-through requirements for wind turbines (WTs) is proposed. The main objective is to promote an effective integration of wind turbines into power systems with still low penetration levels of wind power based on technical and economical considerations. The level of requirement imposed by the strategy is increased stepwise over time, depending on system characteristics and on wind power penetration level. The idea behind is to introduce stringent requirements only when they are technically needed for a reliable and secure power system operation. Voltage stability support and fault-ride-through requirements are considered in the strategy. Simulations are based on the Chilean transmission network, a midsize isolated power system with still low penetration levels of wind power. Simulations include fixed speed induction generators and doubly fed induction generators. The effects on power system stability of the wind power injections, integrated into the network by adopting the adaptive strategy, are compared with the effects that have the same installed capacity of wind power but only considering WTs able to fulfill stringent requirements (fault-ride-through capability and support voltage stability). Based on simulations and international experience, technically justified requirements for the Chilean case are proposed.

Control strategies of doubly fed induction generators to support grid voltage

The use of wind power has been increasing very fast in the last 10 years. Many new projects for the next 10 years including offshore and onshore wind farms are been developed and planned. The fast growing of the use of wind power has brought new challenges to the Transmission System Operators (TSO) in regions where wind power has reached significant penetration levels like Denmark, United Kingdom, Spain and Germany. According to new grid code requirements wind turbines must remain connected to the grid during grid disturbances and, moreover, they must also contribute to voltage support during and after grid faults. Dynamic models of doubly fed induction generator (DFIG) were developed to investigate the behavior off different converter control and protection strategies of the back-to-back IGBT-based converters during grid fault. The results have showed that reactive power injection by DFIG-based wind farms is limited when the rotor side converter is blocked.

Comparative analysis between SVC and DSTATCOM devices for improvement of induction generator stability

This work presents a comparative analysis between a SVC (static VAr compensator) and a DSTATCOM (distribution static synchronous compensator) for improvement of induction generator stability. Although both approaches of dynamic reactive power compensation can improve the stability performance of induction generators, simulations results show that the utilization of a DSTATCOM with the same power capability of a SVC leads to a greater gain of the dynamic performance of induction generators.

Dynamic analysis of wind turbines considering new grid code requirements

E.ON Netz new grid code requires the ability from the wind turbines to remain connected to the network when terminal voltage level drops to zero for at least 150 ms. Moreover, wind turbines must also contribute with voltage regulation during and after grid faults. A comparative study analyzing the dynamic behavior of conventional versions of wind turbines based on doubly-fed induction generator and on permanent magnet synchronous generator is presented in this paper. Computational simulations have showed that wind turbine based on PMSG can contribute with more injection of reactive power to the network. The converters nominal power and the strategy of its current controllers can impact the dynamic behavior of wind turbines.

Wind Electrical energy generating systems EMC. A dedicated experimental simulator for tests

In wind electrical energy generating systems, due to fast voltage and current fluctuations, the power converter represents a source of electromagnetic disturbances. EMI problems of stand alone wind generators are here analysed in order to take into account many different power quality problems which result in voltage fluctuations and harmonics in the net. This paper, moreover, presents a wind turbine experimental simulator (WTES) that moves a wind electrical energy generating system (WEEGS) to carry out EMI measurements and the relative experimental results. The WEEGS here taken into account comprises a wound rotor induction generator (WRIG) in which the frequency transformation from the rotor to the stator windings generate interharmonics and the direct connection between stator and grid increase the sensitivity to voltage sag. These two aspects are here discussed and the existing solutions are pointed out.

Impacts of dynamic reactive power compensation devices on the performance of wind power generators

This paper investigates the main impacts of dynamic reactive power compensation devices on the performance of induction machine-based wind power generators. The dynamic reactive power compensation devices analysed are the SVC (Static Var Compensator) and the DSTATCOM (Distributed Static Synchronous Compensator). The usage of these devices as a power factor regulator or a voltage regulator is investigated. The technical factors analysed are small-signal voltage stability, transient stability and interactions with the anti-islanding protection system. The analyses are carried out by using a wind farm composed of 30 units of 1 MW induction generators. Such wind farm is connected to a 60 Hz, 33 kV distribution system. The results are a useful guideline to evaluate which control strategy and device are suitable for a determined application as well as to understand the dynamic interactions that can occur.

The influence of the applied rotor voltage on ride-through capability of doubly fed induction generator

This paper presents a discussion about the large disturbance instability phenomenon of grid-connected doubly fed induction generators. The behavior of squirrel cage induction generator (SCIG) on large disturbance stability depends basically on the ability of the blade pitch angle control and the injection of reactive power during contingency on the network. However, the behavior of the doubly fed induction generator (DFIG) is also affected by the applied rotor voltage. The instability behavior of the SCIG is well documented in the literature, on the other hand this behavior is not well described for the case of DFIG. The analyses performed in this paper evaluate the effect of different rotor voltage applied during grid fault on the DFIG stability. A sensitive study using dynamics simulations was performed to determine the critical fault tolerance time. The results have shown that when enlarging the direct axis voltage the DFIG has better stability performance.

Dynamic modeling of transverse flux permanent magnet generator for wind turbines

The transverse flux permanent magnet machines have become an interesting possibility for offshore wind turbines. These machines have the highest relation between electrical torque and weight of active materials. The pole pair modular construction could eliminate or lower the gear ratio used in conventional wind turbines. This paper presents a dynamic model of a wind turbine equipped with a transverse flux permanent magnet generator connected to a direct-current power system using a combination of 3D finite element generator model and an aerodynamic model. The results indicate that the model can give accurate response for steady-state operation and for wind speed variations.

Electromagnetic Analysis of Submarine Umbilical Cables With Complex Configurations

These studies present the electromagnetic analyses of different configurations of the so called “Integrated Production Umbilical,” or simply Umbilical Cables. Modern Umbilical Cables can have more than 4 independent 3-phase power circuits as well as steel tubes. There is no 2-D symmetry for these cable configurations and the 3-D simulations are very undesirable due to cable length. The adopted methodology to evaluate cable performance is a combination of 2-D-finite element analyses (coupled with electric circuit) and the transposition technique. The results have shown that the configuration B in which all power circuits rotates along its own center has better performance considering the load terminal voltages due to the compensation of the induction effect along the cable.

A study on the rotor side control of DFIG-based wind turbine during voltage sags without crowbar system

The connection of wind farms to the electrical power system has increased very fast in the last years requiring the ability of the wind turbines to assist network during voltage sags. Most of the modern wind turbines are based on doubly fed induction generator with a back-to-back power converter connecting the rotor windings to the grid. One limitation of doubly fed induction generator is the operation during grid faults. The rotor side converter can be damage by high currents induced by the stator windings. This article investigates the behavior of the wind farm during voltage sags using 2 different control strategies. The results have indicated that the strategy which the reference currents are calculated to compensate the stator flux variation during voltage sags can avoid overcurrents in the rotor windings, in some cases, without the use of a crowbar system.