**6. Conclusions**

**Parameter**

198 Advances in Wind Power

**Generator active material cost**

**(kEuro)**

Performance indicator

**Power supply**

**Voltage**

**Converter scale**

**y**

**Activereactive power control**

**Controllabilit**

**Grid-support capability**

DC generators

directly to the grid

no depende nt

directly to the grid

**1-stage geared**

**Gearbox cost (kEuro)** 120 220 120

**FSIG DFIG Electromagne**

**Table 1.** Quantitative comparison of three major wind turbine generators [38; 30].

partially statorconverter **3-stage geared**

**Air-gap diameter (m)** 3.6 0.84 5 3.6 5 **Stack length (m)** 0.6 0.75 1.2 0.4 1.2 **Iron weight (ton)** 8.65 4.03 32.5 4.37 18.1 **Copper weight (ton)** 2.72 1.21 12.6 1.33 4.3 **PM weight (ton)** 0.41 1.7

**Converter cost (kEuro)** 40 40 120 120 120 **Generator construction cost (kEuro)** 60 30 160 50 150 **Total generator system cost (kEuro)** 287 320 567 333 432 **Annual electricity yield (MWh)** 7760 7690 7740 7700 7890 **Yield/total cost (kWh/Euro)** 4.22 4.11 3.67 4.09 3.98

**Induction generators Synchronous generators**

totally via converters

separate separate separate separate separate

**t**

100% 0% app. 30% 100% 100% 100% 100%

low low high medium very high medium high

**Efficiency** low low high high very high medium extremely high

**Reliability** poor medium high high high very high high

poor poor good good good good very good

**Speed** variable fixed variable variable variable variable variable

**fluctuation** high high low low low medium very low

totally via converters

**DFIG Synchronous generators**

67 30 287 43 162

**PM 1-stage geared**

**PM Reluctance HTS**

totally via converters

totally via converters **PM direct drive**

**Electro-excited direct drive**

> Wind energy has attracted much attention from research and industrial communities. One of growth areas is thought to be in the offshore wind turbine market. The ongoing effort to develop advanced wind turbine generator technologies has already led to increased produc‐ tion, reliability, maintainability and cost-effectiveness. At this stage, the doubly-fed induc‐ tion generator technology (equipped with fault-ride-through capacity) will continue to be prevalent in medium and large wind turbines while permanent magnet generators may be competitive in small wind turbines. Other types of wind turbine generators have started to penetrate into the wind markets to a differing degree. The analysis suggests a trend moving from fixed-speed, geared and brushed generators towards variable-speed, gearless and brushless generator technologies while still reducing system weight, cost and failure rates.

> This paper has provided an overview of different wind turbine generators including DC, synchronous and asynchronous wind turbine generators with a comparison of their relative merits and disadvantages. More in-depth analysis should be carried out in the design, con‐ trol and operation of the wind turbines primarily using numerical, analytical and experi‐ mental methods if wind turbine generators are to be further improved. Despite continued research and development effort, however, there are still numerous technological, environ‐ mental and economic challenges in the wind power systems.

> In summary, there may not exist the best wind turbine generator technology to tick all the boxes. The choice of complex wind turbine systems is largely dictated by the capital and op‐ erational costs because the wind market is fundamentally cost-sensitive. In essence, the deci‐ sion is always down to a comparison of the material costs between rare-earth permanent magnets, superconductors, copper, steel or other active materials, which may vary remarka‐ bly from time to time.
