The difference between double-fed and direct drive and their respective advantages

Advantages:

Double-fed: The doubly-fed motor has low cost and mature technology; the capacity required by the power electronic converter device is small; it can be used in cases of small capacity

Fully air-cooled;

Direct drive: can generate electricity in a very wide wind speed range; eliminating the need for a 1:80 three-stage planetary gearbox, high reliability and good maintenance

; The power electronic conversion device does not require an Active Crowbar; the power factor is almost unlimited and can be regarded as a reactive power generator hanging on the power grid

Disadvantages:

Double-fed: The wind speed range required for power generation is too high, generally within +20%--20% of the synchronous speed. The power generation capacity

is limited and easy to go off the grid. The economical power generation And the stability is very poor; there is a three-stage planetary gearbox, which needs to be replaced once every 5 years

The maintenance cost is very high (this thing is on a tower, think about maintenance at more than 70 meters in the sky

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A ton-level thing); there is Active Crowbar, which is technically extremely difficult, and now only ABB in the world can do it; the adaptability of the power grid is poor, and the power factor is limited, generally It can only reach 0.9

Direct drive: The cost of direct drive motors and power electronic devices is high; the direct drive motor technology is immature; in order to allow the direct drive motor to generate electricity when the wind speed is very low, As a result, the number of stage pairs of the motor is extremely large, generally more than 100 pairs, making the motor very large. It can only be water-cooled, which is too troublesome

Outlook:

Double-feedback: The poor economics and stability of power generation and the poor adaptability of the power grid determine that wind power has no future development prospects

Maybe the AC excitation of hydraulic turbines is its development direction

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Direct drive: It has no fatal shortcomings and is the mainstream technology in the future. In fact, Europe has already shown this trend

Conclusion:

Direct drive is better than double feed.

Personally, I think the best technology is hybrid direct drive, which uses a small-proportion gearbox to increase speed, which can balance

the life of the gearbox and the size of the motor.

I think Goldwind has a good vision in the wind power field. It is a good idea to skip double-feedback and do direct drive. In addition, Goldwind

started applying for patents on permanent magnet motors in 2004, and the layout is still good.

Grid-connection method:

Double-fed: There are two main methods: island grid-connection and no-load grid-connection. The key is to adjust the rotor excitation to allow the voltage emitted by the stator

Direct drive: Just make the output voltage of the inverter and the grid voltage meet the grid connection conditions

Doubly-fed wind turbines currently on the market It is mainstream and the technology is relatively mature, but it has many shortcomings, especially the gearbox which increases the complexity of the system.and maintenance costs, etc.

Direct-drive wind turbine is an emerging type of generator that eliminates the need for a gearbox and can achieve better power generation efficiency at low wind speeds.

Currently, multinational giants are developing direct-drive wind turbines. And a 1.5MW direct-drive wind turbine has been put into mass production.