风力异步电动机_中英文翻译_毕业论文(10)

purpose of this paper is to present simulation results which illustrate the dynamic performance of the controller for both doubly-fed induction generator connection methods for a 2 MW wind turbine. A simple analysis of the rotor voltage for the doubly-fed connection method is included as this demonstrates the dominant components that need to be considered when designing such advanced control strategies.

Keywords: Doubly-fed, Induction generator, Wind turbine

1. INTRODUCTION

There is continuing interest in wind turbines, especially those with a rated power of many megawatts.This

popularity is largely driven by both environmental concerns and also the availability of fossil fuels. Legislation to encourage the reduction of the so called carbon footprint is currently in place and so interest in renewables is

currently high. Wind turbines are still viewed as a well established technology that has developed from fixed speed wind turbines to the now popular variable speed technology based on doubly-fed induction generators (DFIGs). A DFIG wind turbine is variable speed with the rotor converter being controlled so that the rotor voltage phase and magnitude is adjusted to maintain the optimum torque and the necessary stator power factor [1, 2, 3]. DFIG technology is currently well developed and is commonly used in wind turbines. The stator of a DFIG is directly connected to the grid with a power electronic rotor converter utilised between the rotor winding and the grid. The variable speed range is proportional to the rating of the rotor converter and so by limiting the speed range to ±30%

[4, 5, 6, 7] the rotor converter need only be rated for 30% of the total DFIG power whilst enabling full control over the full generator output power. This can result in significant cost savings for the rotor converter [4]. The slip ring connection to the rotor winding however must be maintained for reliable performance.

The power – generator speed characteristic shown in figure 1 is fora commercial 2 MWwind turbine. The generator speed varies with wind speed however this relation is set for a specific location. As wind speed, and therefore machine speed, falls the power output of the generator reduces until the wind turbine is switched off when the power extracted from the wind is less than the losses of the generator and converter. An operating mode has been proposed by a wind turbine manufacturer that is claimed to extend the speed range so that at lower speed the power extracted from the wind is greater than the losses in the system and so the system can remain connected. This proposed that the standard doubly-fed (DF) connection is used over the normal DF speed range and the

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