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A position strategy for the WTGs in Grid-off condition Disclosure Number: IPCOM000240352D
Publication Date: 2015-Jan-26
Document File: 7 page(s) / 131K

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This solution is valid for permanent magnet generators (PMGs). The 1st start-up turbine should be based on PMG because DFIG or Induction Generator still need external energy source to initiate their rotor magnetizing current. It can be considered to use both PMG turbines and IG turbines in a same wind farm to deal with this. Alternatively, a small external source of energy can be used to support one WTG then rest of the process remains same. This solution can also be used to power up and yaw WTGs when WTG is shut down but storm is predicted and there is a need to power up and yaw out of the wind.

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A position strategy for the WTGs in Grid-off condition

It can be beneficial to eliminate the dependence on external power/energy source for the WTG start when the wind picks up after a long duration.

In current WTG control strategy, the WTG in operation will keep facing the wind for largest energy capture with the assistance of yaw system. The yaw system controls the yaw motors to adjust the facing direction of turbine blade plane (see Fig. 1) in the whole operation process aka keeping upwind the turbine.

When the WTG is stopped, the facing direction of turbine blade plane will be maintained as the final wind direction at the moment of turbine stop.

When the WTG needs to be restarted, the wind direction may change. In this case, external energy from grid is needed to power yaw motors (also for the auxiliary system of the turbine) for adjusting the turbine blade plane to new wind direction for capture the wind energy (refer to Fig. 2).

However, in grid-off conditions (grid loses or WTG loses connection to grid), an external energy source (e.g. diesel generator or energy storage system) is a must.

However, it is also possible to make WTG power up the yaw system (also the auxiliary power systems) by itself and without depending on external power source such as diesel generator in case of grid off conditions.

The solution is to adjust the blade planes of individual WTGs face to different directions when the wind speed turn lower than cut-in speed. Thus, when the wind speed recovers, one WTG at least in wind farm level can have correct blade plane position to capture wind energy. Fig. 3 shows the basic position strategy to make sure WTG can cover all potential wind direction.

Thus, even in grid-off conditions, it can be ensured that at least one turbine could be powered up and produce energy to the yaw systems (also the auxiliary power systems) of other WTGs in the same wind farm.

When the WTGs need to be restarted after a long duration, the proposed WTG position strategy can ensure that at least one turbine can meet the minimum requirement of yaw degree for effective energy capture. As long as the WTG begins to produce energy, it provide power to its own yaw motors first to adjust its yaw position accurately then provide the power to the yaw systems (also the auxiliary power systems) of adjacent WTGs. Once the adjacent turbines are yawed to face the wind direction, they start to produce energy for the non- operated WTG beside them.

Besides using just one WTG to provide power to yaw system (also the auxiliary power systems) of all other WTGs, the position strategy can also be extended to

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• Use a few WTGs with yaw errors within acceptable range to power up other WTGs

• Use one WTG to provide power to the next WTG with smallest yaw error, and both WTGs can provide power to next few WTGs and so on.

Fig. 3 just shows the basic concept of turbine blade plane position. According to the actual need for minimum yaw degree, mo...