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Torque at low speeds in v/hz technique?

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seyyah

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I implemented V/Hz technique to the ind. motor. According to the theory i apply an offset voltage to overcome the stator resistance. But it doesn't suffice to revolve the motor at low frequencies. I further increased the offset voltage and motor began to turn at low frequencies. But according to the theory, musn't i get a good torque? The torque is very little at low frequencies. If i further increase the offset voltage then motor draws large currents and doesn't move smoothly. How is the situation in practical V/Hz drives? My system is open loop, by the way. Can i achieve full torque at low frequencies with this technique and/or with closed loop control?
 

How low frequency is low for you ?
With vector drives 0.5Hz is fine.
 

According to practice in this range it's hard to get more then 30% of nominal torque (for 50 Hz motor). You can still do what you want with open loop but you will need implement vector control algorithm.
 

So you say, this is normal in open loop control. How is the situation, in closed loop scalar control? I know vector control can develop full torque at zero speed. I'm progressing step by step but my concern is now scalar control for a while.
 

I think that closing loop could help only to control speed but not to develop more torque with scalar control.
 

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    seyyah

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I'm trying to simulate v/f control in Simulink.Does anybody have model of scalar control in Simulink.I've ben trying to do this for 2 weeks but still i don't have any result
 

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