Problem with PMSG turbine modelling

I am currently trying to create a Permanent Magnet Synchronous Generator Model coupled with a wind turbine model. Instead of using the conventional blocks ie the wind turbine and pmsg block set that are already created in Simulink i have created my own subsystems. I believe all the theory is correct however i am receiving and error between the turbine model and the drive train due to the state of the mechanical torque feeding to the drive train being not finite. I understand the error but i dont know how to fix it because the turbine needs the generator speed to calculate the torque but to calculate the electrical torque the mechanical torque is needed.

[Rishabh Shah]

In PMSG no need of Gear box. turbine can be directly coupled to the generator as it is going to rotate at fixed speed provided constant wind speed.

Answer 1

[KL]

The PMSM has two inputs, One is three phase voltage and the other is load torque. I understand in your case, you must get the load torque from the wind turbine and the voltages should also be somehow related to the wind speed based on your control system. This working principle is basically the same no matter if it's a generator or a motor, just the flow direction changes. From the three phase voltages you do the transformations, find the currents and then find the electromagnetic torque. Solving these two torques you must be able to get the rotor speed.

[Thomas Rhodes]

I understand this however to calculate the mechanical torque you need the rotor speed. As the equation i am using to calculate the mechanical torque is Tm=Pm/ωr and the electromagnetic torque (3/2(Vds.ids+Vqs.ids))/ωe.

[KL]

In wind turbine generator simulations, this rotor speed in your mechanical torque equation is calculated based on wind speed and tip speed ratio. So you must be aware of the blade specifications to do this.

Electromagnectic torque doesn't depend on speed, it just depends on the flux linkages and the currents.

[Thomas Rhodes]

sorry yes i understand this but i still have a issue with a on finite result at my drive train a similar paper that describes my model is http://inpressco.com/wp-content/uploads/2014/02/Paper78421-426.pdf

[Thomas Rhodes]

I am also unsure why the mechanical torque is the input to the PMSG simulink and not the speed as its the speed of the rotor that is needed in calculating the d and q axis currents.

[KL]

Okay, I didn't read the whole paper, though Fig.13 explains the problem. It's also the answer to your next question (why not speed is the input?!). The missing part is the control system. Speed to the machine is generally controlled by a suitable control system which controls the voltages from/to the machine. The sign of your load torque decides if it's a generator or motor.

So wind speed > turbine specifications > speed set point > controller > voltage to machine > currents > elec. torque > mechanical equation > speed

Goodluck

[Thomas Rhodes]

Okay thankyou so much for your help i think i understand

[Raed Ibrahim]

Hi Guys,I am currently using a permanent-magnet synchronous machine as a generator in my wind turbine model in simulink. The model works very good when the simulation time between 2-4sec, but when I increase the simulation time to 8sec or more. The output values of the generator like stator currents, the speed and torque will change. I don't know why??? I really appreciate the help :)