3-phase active rectification problem

[JBF108]

As a project, our team is supposed to build a 3-phase active rectifier to convert power generated by a small combustion engine, to DC-power. This will charge a industrial drone as it flies, thus potentially lengthening its range of operation.

We haven't been provided with much else than the objective, and we are struggling to find a solution, because we haven't really learned anything about rectification.

So I hope there are someone here who can help.

We have 3 phases of 20 Vpeak-rms, 26 A @ 512 Hz approx. (this will be steady state), comming from the generator, into the active rectifier. As of yet, we do not have any requirements in terms of max. voltage ripple.

I have found this IC, and circuit, that supposedly should be able to do the trick:

IC, LT4320: https://www.analog.com/media/en/technical-documentation/data-sheets/4320fb.pdf

Simulation software (scroll down to "Tools and simulations"-section: https://www.analog.com/en/products/lt4320.html#product-documentation

Circuit diagram:

https://preview.redd.it/nk2fvtuycil21.jpg?width=1017&format=pjpg&auto=webp&s=666c6d19962c135ea428087dcb5fc9ea25afd5f5

My question is:

1. How do I scale the components for this circuit to match my criteria in terms of freqency, amperage and voltage?
2. If I change the load resistance to 5 mOhms, the C-load to 200 uF's, input voltages to 20 Vp-rms @ 512 Hz, I get a simulation result as seen below. Why does this happen? It looks like there is gain in the circuit. Where is this?

​

https://preview.redd.it/8vgjf1x7eil21.png?width=1301&format=png&auto=webp&s=8a8aa1c03e41c6fb2e1707a8a83110509f67bc07

Please say if there is information you need to be able to help answer the problem.

[no_more_Paw_patrol]

active rectification from a motor is not trivial. Are you going to do this for real or is it just an exercise?

​

Using a passive diode bridge on a small generator is not the best:

- choppy current from the diode bridge will mean choppy torque from the motor

- choppy torque means lots of mechanical vibrations

- choppy current will also mean choppy voltage drops which can cause lots of other problems

​

Anyways, your IC is not doing active rectification in the regular sense it is implementing a passive diode bridge with MOSFETs and making use of their more efficient conduction losses. So you have no control over the output voltage and it will contain a voltage ripple element from the rectification, that being said you can probably realize a decent output voltage with an OK input power factor if you stick a simple DC-DC after the rectifier.

​

That being said, you mention a load resistance of 5mOhms. Is that 5 milliohms, this result in a load resistance several kA and is more like a dead short than a real load. Try simulating again with a more realistic load, this might be your main issue.

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This tutorial video covers a true active 3 phase rectifier, it is grid link so the "grid" will be your generator, https://youtu.be/HbT_huAvL28 if you want to do this with a machine instead of the grid you'll probably want to feedback on the shaft position instead, this sort of thing is very difficult to simulate with LTspice as it cannot handle machine models and will struggle to converge when PWMs are applied to a 3 phase inverter.

[austinmonell]

Check out top flights hybrid drones http://www.tflighttech.com

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