Electronic Speed Control of a Generator

[Soul21]

I am trying to better understand methods that can electronically control the speed of a generator (specifically). The generator will be spinning using mechanical energy generated by air through a pipe. The electricity will be sent to a load or battery bank.

I thought a VFD might be the solution, but have begun second guessing if it is feasible. Another solution that may be adjusting the resistive load using a phase angle fired. A third option might be to use a controller such as ODrive (link). I am open to any input or suggestions.

For clarity sake - I know there are mechanical ways to control speed used on most large geneators (e.g., brakes, blade pitch, control valves), that are the preferred method due to efficiency. I am looking for electronic solutions due to surplus of energy and no control over the mechanical input.

Thanks in advance!

 

[Pommie]

Assuming your generator is wind powered or otherwise unpredictable input powered, then I thought that a torque measuring device would help in producing a Max Power Point. The torque produced would indicate Amperage produced and the RPM the voltage. However, the torque is the Amperage so no increase in knowledge.

I know wind turbines "Feather" in high winds but wonder if slowing could be achieved by greater take of.

As you probably guessed, too many beers so rantings of an intoxicated man. But, who knows, might start an idea.

Mike.

 

[Soul21]

I appreciate the replay.

The prime mover would be air through a pipe that can not be regulated.

 

[Pommie]

So, do you just need to extract as much energy as possible?

Mike.

 

[Soul21]

I do not. If the generator's rotational speed needs to be slowed it is acceptable to waste energy in order to do so.

 

[alec_t]

Is the piped air driving a rotary impeller/turbine or a positive-displacement piston? Either way, slowing the generator will create back pressure affecting the air flow, which you presumably don't want?

 

[shortbus=]

Asking here because you didn't get the answer you want at AAC isn't going to get you very far. The only solution for your problem is still managing the prime mover of your generator/alternator. It's just the physics of the thing.

 

[Soul21]

I am getting second and third opinions, its important to do so. I haven't found AAC to be much help as it is dominated by overly assertive individuals. I must give Strantor kudos though - the most helpful contributor I have found on there.

I also (obviously) disagree with you and believe there are other solutions. I challenge you to be open minded and help me find them. Maybe try thinking along the lines of eddy brakes.

 

[Soul21]

Is the piped air driving a rotary impeller/turbine or a positive-displacement piston? Either way, slowing the generator will create back pressure affecting the air flow, which you presumably don't want?

The piped air is coming from a pressure reservoir. The back pressure on the air flow is acceptable.

 

[alec_t]

The prime mover would be air through a pipe that can not be regulated.

The back pressure on the air flow is acceptable.

These two statements seem to contradict each other, unless you are giving 'regulated' a very specific meaning?

 

[Soul21]

That's fair. The primary purpose of air flow is for other uses that supersede energy generation. If the end use of the air flow is in high demand the generator must spin as free as possible. The air flow speed/pressure fluctuates quite a bit both from supply and demand sides. I understand a smart valve system with bypass could also be put in place, but I wanted to explore the option of controlling generator speed.

 

[alec_t]

If you change the generator speed then won't that introduce the possibility that the demand can't be satisfied?

 

[Soul21]

Ideally the generator speed would increase when demand decreased and supply remained the same.

 

[shortbus=]

I am getting second and third opinions, its important to do so. I haven't found AAC to be much help as it is dominated by overly assertive individuals. I must give Strantor kudos though - the most helpful contributor I have found on there.

I also (obviously) disagree with you and believe there are other solutions. I challenge you to be open minded and help me find them. Maybe try thinking along the lines of eddy brakes.

I don't think you understood what Strantor was saying, not at all. Being open minded doesn't change things that only work in one way.

Think of it like this. Your driving a car going 50MPH, you slow it down by letting up on the throttle, because if you just apply the brakes and not slow down the motor all that will happen is the brakes wear out.

 

[BobW]

I can think of only two reasons why you would need to control generator speed:
1. Prevent it from running too fast and flying apart.
2. Vary the output power.
If it's the first reason, then the only solution will be mechanical or electro-mechanical.
If it's the second reason, then there are other means to control the output power easier to implement than speed control. The only practical way to control speed is to control air flow. The impractical way to control speed is to use a brake or put a varying load on the generator to slow it down, but if it takes a very big load to slow it down enough, then this could cause the generator to overheat and fail.

It would help immensely to know what your ultimate goal is.

 

[Soul21]

My goal is to keep it from running too fast or impeding the flow of air when demand is high.

could you elaborate on the electro-mechanical method you mentioned?

 

[Soul21]

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[BobW]

The problem is that you can't avoid physics. What the turbine/generator takes in, in mechanical energy, must be delivered to the final load as electrical energy. Anything that's left over is converted to heat. Unless you get rid of the heat, you have problems. You have two options:
1. Don't allow the turbine/generator to receive any more mechanical energy than it needs to deliver to its electrical load, so that there's no waste heat.
2. Provide a means to dissipate the waste heat.

With the first option, you would either have to divert air flow away from the turbine/generator, or feather the turbine blades, neither of which appear to be practical in your case.

In the second case, you need to dissipate the generated waste heat. Since you seem to have lots of air flow, you could divert the electrical power not required by your electrical load to a bank of power resistors, cooled by the same air stream that supplies power to the generator. In this case, the problem reduces to a load controller circuit.

 

[rjenkinsgb]

If the generator is DC, a simple shunt regulator to prevent overvoltage would probably fit the requirements?

As long as that is set to near the maximum permitted load voltage, it should limit the speed without causing too much unwanted load otherwise.

 

[shortbus=]

Finally over at ACC he's giving some more of his "secret information" out.

The "generator", I don't think he understands much about electricity, because he's talked about using both an induction motor or a BLDC motor to make the electrical out put. Both of them would have a n AC output, but the final result is to charge some batteries. Which are DC.

The air source is a piping system that he wants to bleed off some air to run the "generator". He want's the genertor to freewheel when the air supply is low? If the turbine running the generator is sized right it won't allow a low air supply to overcome the permanent magnetic force to spin the generator if he would just use a PM DC motor as the generator.