Load sharing

From the initial operating point introduced above, the output power of converter 2 increase by 10% of rated power at t=0.5 s and the output power of converter 4 increase by 10% of rated power at t =1.0 s, see Figure 4.5.

750 745 740 735 730 725 100 50

-100

Figure 4.5: Converter DC side voltage (top) and power (bottom) for an output power increase of 0.1 p.u. of rated load converter power at 0.5 s for converter 2 and 1.0 s for converter 4 starting from 0.5 p.u. in both cases.

In Figure 4.5 it is shown that load sharing works properly both in stationary and transient conditions. Note the rapid steps in the DC bus voltage when the output power is changed, illustrated in Figure 4.5. These are due to voltage droop control action, reducing the voltage because of the increased loading. The slow variation in DC bus voltage is a consequence of internal droop offset-adjustment caused by the speed error resulting from the reduced actual speed. The droop offset also strives to reduce the voltage in order to distribute the total load among the wind power units.

Actual mechanical speed of the wind turbines is shown in Figure 4.6. The mechanical speed is reduced due to the increased loading. Consequently, the speed error increases resulting in a downward shift of the droop characteristic of each source converter. At the same time, the power removed by pitch angle control reduces due to the decreasing speed error. Therefore, a new operating point is established.

Figure 4.6: Wind power turbine speed.

Figure 4.6: Wind power turbine speed.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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