And synchronous motor adjustable quantity only one,grid tie inverter namely field current amplitude

So to adjust the excitation of synchronous motor normally only for reactive grid tie inverter compensation.

Unlike the doubly-fed motor excitation besides can adjust current amplitude, also can adjust the phase, when the rotor current phase change, the rotor magnetic field in air gap generated by the rotor current position is to create a displacement of the space,grid tie inverter change the dual feed mechanical and electrical potential with the grid tie inverter voltage vector position, will change the power Angle of the motor.

So the doubly-fed motor adjustable reactive power inverter not only, also can adjust the active power.

In general, when motor absorption power inverter reactive power, power Angle greaten, often decreased the stability of the motor.

And doubly-fed motor can be adjusted through the phase of excitation current, reduce the unit power inverter Angle, increase the stability of unit operation, which can absorb reactive power, overcome the late due to load falling, difficult to solar grid tie inverter voltage is too high.

Induction generator, by contrast, actually because of the need to absorb reactive power from the solar grid tie inverter field current, and run in parallel with the solar grid tie inverter, the power factor of power inverter caused by bad.

So the doubly-fed motor is a synchronous motor and induction motor has more superior performance.

(2) the control of the doubly-fed motor in the wind