Working principle of doubly-fed wind turbine

In the doubly-fed wind power generation system, the stator of the generator is directly connected to the power grid, and the rotor is AC excited under the control of the converter.

In order to keep the stator constant frequency and constant voltage output, the basic operation steps are as follows:

1. When the self-inspection of the generator set is normal, the impeller is in a state of free movement; When the wind speed meets the operating conditions and the impeller is facing the wind direction,

The pitch control system will constantly adjust the optimal pitch angle to keep the no-load speed of the generator at the grid-connected speed. If the master control system decides everything,

When it is ready, issue a grid-connected command.

2. After receiving the grid-connected command, the converter will pre-charge the bus first. When the bus voltage reaches a certain level, the network side will convert.

The modulator starts modulation; However, when the grid-side converter runs normally, the machine-side converter starts self-checking, and the excitation starts after the self-checking passes.

The amplitude, phase and frequency of the current are controlled so that the no-load voltage of the generator stator and the grid voltage have the same frequency, phase and amplitude.

Value, and then close the grid-connected contactor to realize grid connection.

3. When the wind speed changes, the frequency converter changes the rotation of the rotor magnetic field by controlling the excitation current frequency of the rotor.

Frequency, amplitude, phase and other parameters make the output voltage and frequency of the generator consistent with the power grid, thus realizing wind power generation.

Variable speed constant frequency power generation system