Grid Integration and Dynamic Impact of Wind Energy

Growth of wind power in the United States and around the world continues to surpass even optimistic projections of the past years with a string of record breaking years. In 2009 alone, 10 GW of new wind power capacity was added in the United States, which is 20 % higher than the record set in 2008, and represents 39 % of all new capacity added in 2009 [1]. Figure. 1.1 [1], which superimposes the actual installed wind generation with the deployment path laid out by [2] to realize the vision of 20 % wind by 2030, shows dramatically that the actual growth in the last 4 years and the projected growth in 2010–2012 far exceeded the deployment plan.

The distinguishing feature of wind and photovoltaic generators compared with conventional generators is that they are controlled and interfaced to the grid through power electronic converters. The characteristics and performance of these generators, both static and dynamic, are to a large extent determined by the design of the power electronic converters. Hence, it is important to have a good understanding of the operating principles, characteristics, and basic design of these converters in the study of integration of wind and PV systems and their impact on power systems. The power converters for wind energy systems are based on voltage source converter (VSC) topologies employing pulse width modulation (PWM) methods at a relatively high frequency, usually in the order of a few kHz for the utility-scale applications considered here. Therefore, the focus of this chapter is on understanding the basic principles of operation of typical voltage source converters used in grid interface applications.

This chapter focuses on the power electronic converter topologies used in grid integration of wind generators. The need for variable speed operation in order to capture the maximum possible energy at different wind velocities is discussed first. Based on this requirement, as well as to support emerging requirements on grid support features, a majority of the new wind generator designs employ the doubly fed induction generators with partial rated power converters or permanent magnet synchronous generators with fully rated power converters. Hence, the focus of this chapter is specifically on the power converter topologies for these two types of wind generators. The circuit configurations, basic operation and overview of control structure, and some relevant design details are presented. The capabilities of each of these two types of wind generators to support existing and emerging standards on grid interconnection are discussed

In the previous chapters some details regarding the types of wind generators, converter configurations used in wind turbine generators, and the nature of controllers used in the wind generators were provided. In this chapter, a description of the mathematical models used for the time domain simulation of the electro-mechanical phenomena associated with wind turbine generators will be provided. A discussion regarding the suitability of these models for time domain simulation will also be presented.