Electric circuit for generating electric power

1. A method for operating an electric circuit for generating electric power, in which an asynchronous generator includes a stator and a rotor, the method comprising:

measuring, a rotor current flowing to the rotor and a stator current flowing to the stator, during a fault-free operation of the power grid;

calculating, during the fault-free operation, a stator current based on specified ratios of the rotor current measured, the stator current measured and a magnetizing current;

determining differences between the stator current measured and the stator current calculated, and adjusting the specified ratios based on the difference; and

calculating, during a power grid fault, a stator current to flow to the stator based on the adjusted specified ratios.

2. A method according to claim 1 , wherein the stator current calculated is a function of the specified ratio which include an Rs/Xs ratio, where Rs=stator active resistance and Xs=stator reactance.

3. The method according to claim 2 , wherein the Rs/Xs ratio is obtained from a datasheet of the asynchronous machine or is set to zero.

4. A method according to claim 1 , wherein the stator current calculated is a function of the specified ratio which include a Xh/Xs ratio, where Xh=main line inductivity reactance and Xs=stator reactance.

5. The method according to claim 4 , wherein the X h /X s ratio is obtained from a datasheet of the asynchronous machine or is set to be equal to “1”.

6. The method according to claim 1 , wherein the magnetizing current is determined from a characteristic curve that is dependent on a main voltage of the power grid.

7. A method according to claim 1 , wherein the stator current flowing to the stator of the asynchronous generator is calculated according to the following equation:

[

i

S_a

i

S_r

]

=

X

h

*

X

S

R

S

2

+

X

S

2

⁡

[

-

1

R

S

X

S

-

R

S

X

S

-

1

]

*

[

i

R_a

i

R_r

+

i

μ

⁢

⁢

0

]

|

having the following parameter;

i S — a stator active current

i S — r stator reactive current

i R — a rotor active current

i R — r rotor reactive current

i μ0 magnetizing current

R S stator active resistance

X S stator reactance

X h main line inductivity reactance.

8. A control device of an electric circuit, the electric circuit being for generating electric power, using an asynchronous generator that includes a stator and a rotor, the control device comprising:

a controller configured to:

obtain a measured rotor current flowing to the rotor and a stator current flowing to the stator, during fault-free operation of the power grid,

calculate during the fault-free operation, a stator current based on specified ratios of the rotor current measured, the stator current measured and a magnetizing current,

determine differences between the stator current measured and the stator current calculated and adjust the specified ratios based on the difference, and

calculate, during a power grid fault, a stator current to flow to the stator based on the adjusted specified ratios.

9. An electric circuit for generating electric power, in which an asynchronous generator includes a stator and a rotor, the electric circuit comprising:

a first measuring device configured to measure a rotor current, flowing to the rotor during a fault-free operation of the power grid;

a second measuring device configured to measure a stator current, flowing to the stator during a fault-free operation of the power grid; and

a control device configured to:

calculate during the fault-free operation, a stator current based on specified ratios of the rotor current measured, the stator current measured and a magnetizing current,

determine differences between the stator current measured and the stator current calculated and adjust the specified ratios based on the difference, and

calculate, during a power grid fault, a stator current to flow to the stator based on the adjusted specified ratios.