Voltage-Sourced Converters in Power Systems

13

Variable-Speed Wind-Power System

13.1 INTRODUCTION

This chapter deals with the principles of operation and control of a class of grid-connected variable-speed¹ wind-power systems, that is, the doubly-fed asynchronous generator-based wind-power system.²

Chapters 7 and 8 introduced the controlled DC-voltage power port, and Chapter 10, introduced the variable-frequency VSC system. This chapter demonstrates that a grid-connected variable-speed wind-power system, more specifically a doubly-fed asynchronous machine-based wind-power system, in principle, consists of a variable-frequency VSC system and a controlled DC-voltage power port. The variable-frequency VSC system controls the turbine-generator set of the wind-power system, whereas the controlled DC-voltage power port provides the grid interface.

13.2 CONSTANT-SPEED AND VARIABLE-SPEED WIND-POWER SYSTEMS

Wind-power systems are broadly classified as either the constant-speed or the variable-speed systems. The following subsections provide a brief review of the two classes.

13.2.1 Constant-Speed Wind-Power Systems

Figure 13.1 illustrates a simplified schematic diagram of a constant-speed wind-power system. The wind-power system is composed of a wind turbine that is mechanically coupled, via a gearbox, to an asynchronous generator. Wind turbines naturally rotate at relatively low speeds. Thus, the gearbox is employed to elevate the machine rotor speed, close to the machine synchronous speed. Figure 13.1 also shows that in a constant-speed ...