Low Speed VAWT - Turbine Startup

[Mohame AbouElNaga]

Hi,

We are building a low vertical axis wind turbine and we are actually facing a problem which is the high cogging torque in the ac generator which prevent the generator from being a self starter. we are a thinking for a solution for that issue so we thought why wouldn't we drive the generator with an ac voltage coming from an inverter which is driven by the batteries, but actually we are not sure about that solution. Briefly, we have a controller that have some feedback such as RPM, wind speed, voltage, current measurements so I think we can use those variables in order to control whether or not to feed the generator from the inverter through some sort of controllable switching so would anyone please advise us if that is possible or not and if its possible how could we calculate the amount of power needed to overcome that cogging torque and start the generator as a motor.


Thanks

[Rob Beckers]

Mohame, what type of generator are you using? You mention AC, so is this an induction motor that's being used as a generator? Those can be motored up to speed. A PMG could be motored as well, but that requires electronics to generate the right phasing to drive the windings.

On the turbine side, what type of VAWT is this? A Darrieus type turbine is not considered self-starting (generally). They need to get going first, before generating the torque needed to continue. I've heard some are combined with a small Savonius rotor to get them started.

-RoB-

[Mohame AbouElNaga]

Rob Thanks for your reply, we are using a 3 phase AC PMG. you said that they can be motored but they need electronics. Does an inverter with the right power and phasing would do that function???

[Rob Beckers]

Inverters, in this context, generally turn DC from a permanent magnet alternator like the one you have (after rectifying) into AC for the grid. They don't run a PMG as a motor.

I don't know what would do that, I've never looked into this. A PMG is in essence the same as a servo-drive, and drivers for those would be more like it. But, again, I don't have details and since these things need to be tailored to the specific drive I doubt you'll find something off-the-shelf that can be just hooked up and work.

How about adding a regular motor with some type of mechanism that engages when it's motoring up, disengages when the turbine RPM exceeds that of the motor? Much like the free-wheeling mechanism in a bicycle axle.

-RoB-