Lately, I've been working on a project to control a model of a wind turbine. My goal is to control the mechanical torque that a DC generator applies to the rotor in order to change the rotation speed.
My current setup involves an Arduino that connects and disconnects various resistors via relays to vary the load on the DC generator, thereby changing the rotation speed. However, my problem is that I would like to have direct control over the load as an input, rather than indirectly through resistors.
As far as I know, the torque applied to the generator is linearly independent of the current load in a DC generator. I've been considering changing the configuration to have direct control over the current.
The idea is to use an NPN transistor and short-circuit the DC generator between the collector and emitter. Then, I would control how much current passes between the collector and emitter by controlling the base current of the transistor. This would essentially keep the potential of the base constant and change the resistance to alter the base current and therefore the current passing through the other circuit.
This way, I could have direct control over the torque of the system, which is my goal. Do you think this could be a good solution? What could be the potential issues?
To be clear, the torque is proportional to the current flow, in either a DC motor or generator. In the case of a generator with fixed resistance load, the current flow depends on both the generated voltage (the shaft rotational speed) and load resistance.
For informed advice, please post the details of your system.
The idea is to use an NPN transistor and short-circuit the DC generator between the collector and emitter.
A variable resistance load is possible, but not simple to implement for high currents because of the heat dissipated.
It sounds like it should work, with the power dissipation caveat that @jremington mentioned. It would be a fun reason to explore oil cooled heatsinks
I'd use a MOSFET though: easier to control since there's a linear relationship between Ids and Vgs in the region below saturation. If you use a bipolar NPN transistor, you'd want to have a small emitter resistor (which will also dissipate power!) to provide feedback and linearize the behavior.
So if I understand this correctly, you're basically turning a wind turbine into a fan, by using the generator as DC motor (or even having a DC motor in its place).
The most common way of controlling the speed of a motor is by PWM and a MOSFET. Simple and very effective.
Is this a dynamometer. setup? How much power are we talking about? You can also control the load the generator applies by varying the field and dump the current into a heavl load resistor etc. It would be very similar to your car alternator system and by adjusting the field you switch a considerable lower amount of energy. Posting a schematic would help us help you.
Hi,
sorry for the late response. Yes, this is for a university project. I'm dealing with a wind turbine powered by the wind, and I need to use a DC motor as a generator. Currently, the setup involves some resistances directly connected to the generator, controlled by an Arduino through MOSFETs to change the resistance and adjust the load on the turbine.
Now, the issue arises because I've measured the voltage of the generator and the rotational speed, and I've found that the induced voltage is linearly proportional to the rotational speed (V = k_v * omega). However, I've noticed that when varying the current, both the rotational speed and voltage depend on the current passing through (so I have something like: V = k_v(I) * omega).
At this point, I'm considering bypassing this setup by directly imposing the current. How can I achieve this? One idea I have is to short-circuit the generator and use a transistor instead. This way, I can control the base current and consequently the collector current. I'll include some schematics. I have some experience in coding, having worked with Arduino and Raspberry Pi for about a year. It's not a coding issue but rather an electronics one.
I am shocked that the OP does not know that there is NO rotational component to torque. As soon as you add rotation, you now are dealing with "POWER". Your motor/generator converts the power from the rotating wind turbine to electrical power.
You build a (constant) current source as can be found in many places. Take care that the transistors and resistors can consume enough energy. Use heat sinks and fans for cooling. Possibly the driving wind can be routed through the heat sinks.
Sorry? Have you read what I want to do? I apologize for the misunderstanding. In my current setup, I adjust the rotational speed of the generator connected to the wind turbine by switching resistances connected to the motor. Now, I'm considering changing this setup to the one I posted earlier, where I would directly control the current using a transistor circuit. I want to know if this new setup could work for my purpose.
Thank you so much. The problem that I have is, can I impose a current that has to pass through the collector (in the generator circuit) by simply changing the base current of the transistor? I want to use the linear relationship I_c = beta * I_b. Are there any problems caused by the fact that the voltage generator changes over time?
I think the temperature will remain the same, since I have very low power (it is a small model). Now the problem comes with voltage. Is there something that doesn't depend on voltage? So that I can use my linear relation directly? Otherwise, I have to measure the voltage for each time step (which changes) and perform complex calculations to impose the correct Ib to achieve the desired Ic.
Ok. And by reducing the rotation of the generator, are you trying to reduce the power being generated? If so, the method used for over 100 years is to vary the magnetism of the field coils of the generator. Are you trying to do the equivalent with a generator with fixed magnets?
