Type 5 wind turbine technologies: three main candidates compared

Type 5 wind turbines drive synchronous generators which are directly grid-connected, just like conventional power plants. The generator is the self-exciting electromagnetic type controlled by an automatic voltage regulator (AVR), capable of the same amount of system strength (being fault current at more than 3 times rated (3 pu) for fault and post-fault conditions) as thermal and hydro turbine-generators. Historically, system strength from conventional power plants has ensured system stability. However, the mainstream of the wind industry is dominated by Type 3 and Type 4 wind turbines, with inverters capable of typically only 0.4 pu and 1 pu current respectively. The degradation of system strength because of wind and solar inverter- based resources (IBRs) is a major concern facing the zero-carbon transition. As renewables’ penetration increases, synchronous condensers are increasingly being required to avoid curtailing IBRs. The directly-connected synchronous generator of Type 5 wind turbines avoids the need for separate synchronous condensers. There are three main Type 5 designs, which use different mechanical variable-speed (VS) systems so the generator can run at synchronous speed. This paper describes recent research into these three systems and compares their levelized cost of energy (LCOE) against Type 3 and 4 systems, and against each other.