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N° 43 - October 2003 - CEDRAT - CEDRAT TECHNOLOGIES - MAGSOFT Corp.

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Electrical distributed generation produced with renewable energy (wind,

solar, biomass, fuel-cells,etc.) takes more and more importance in the global electrical production.The power which can be produced with a windmill (2.5 MVA), as well as the committed sums (1000€ for 1 KW installed) imply to carry out simulations in order to make the good technological choices and analyze the network connection consequences as well as study economic profi tability.PSCAD integrates all tools necessary to simulate a windmill and its connection to the network. Such a study has been performed in CEDRAT and is presented in the technical paper «Wind Turbine and Grid Connection Modelling with PSCAD».

The tools

These 3 components (fi g.1), designed according to IEEE models, are available in the PSCAD Master library and make it possible to simulate all the parameters involved in a wind mill study : ● Wind sources: possibility to simulate different wind distributions (gusts, random,etc.),● Pitch regulation : the «passive pitch control» and the «dynamic pitch control» which play on incidence angle of the blades (Beta),● The choice of the number of blades from which depends the power coeffi cient characteristics of the turbine (Cp),● The blade length (R) and the air density (ρ) which make it possible to calculate the output power of the turbine (P = ½ Cp ρ π R2 Vvent3) and the corresponding torque,● The step-up ratio and the ef-fi ciency of the gear box located

between the turbine hub and the genera-tor hub.

The model

Many recent wind mills use synchro-nous brushless ma-chines like annular or discoidal multipo-lar generators with permanent magnets. They are weaker than traditional ge-nerators at identical torque and speed (the mass reduction according to techno-logy can reach from 20 to 40%). Another advantage is that these machines can have a great num-ber of poles (200) and thus rotate at low speed without mechanical multi-plier. A conversion stage AC/DC/AC is necessary in order to be connected to the network at the con-venient frequency. The PSCAD models make it possible to simulate this type of generator with all the required power elec-tronic devices. The complete simu-lation scheme is pro-posed on fi g. 2.

Simulations

The simulations performed with PSCAD allowed us to study the dimensionning of the wind turbine and the generator, the DC bus voltage regulation and the connection to the distribution network.In fi gure 3, you can observe the difference in the power produced by a wind generator in static pitch control (blue curve) or dynamic pitch control (green curve) with a variable wind speed.

Faults analysis have been made with PSCAD allowing to know the infl uence of the wind mill on the network in such confi gurations and to defi ne the protections to choose.

Finally, an entire wind farm (300 MVA) has been modelled in PSCAD. Voltage and frequency stability investigations at the connection point have been performed, de to the high power level of the windfarm compared with the connected grid.

Conclusion

PSCAD tools and capabilities allowed to see a large part of the technical aspects of a wind-mill dimensionning and its connection to the network. You will fi nd all the details of this study in the technical paper: «Wind Turbine and Grid Connection Modelling with PSCAD», available on software@cedrat.com.

Wind Turbine and Grid Connection Modelling with

PSCAD. Eric Flammier - EDF; Augstin M'Panda - ESIEE; Fabrice Foucher - CEDRAT.

Figure1: PSCAD model deicated at wind turbine.

Figure 2: PSCAD model.

Figure 3: Power received on the network in static and pitch control.