Pierre's 170W in 1600W out Looped Very impressive Build continued & moderated

[listener192]

So the stator cross sectional area must be greater than or equal to that of the rotor? Why aren't the pole ribs a flux limiting bottleneck if they have the smallest area?

If I have digested your posts correctly, then the coils at either end of the rotor are used for EMF collection. So can the same results be achieved with 120 degrees of stator (9 coils) and a half length rotor, or even 90 degrees (3 stator coils) with extra coils also at both ends of the rotor? I ask because this could cut the cost of the electronics by 60 or 70 percent. It could also allow for simple fabrication of the array of stator segments. I'm thinking bars machined over the length with a bull nosed cutter then welded together in a radial arrangement so the coil field focal point is the end of the half length rotor.

Hi FixedSys,


Yes, the FEMM plots confirm that the stator CSA has to equal or exceed the rotor CSA, if you want most of the stator flux to cross the rotor.
5HP upwards motors, have greater stator thickness in proportion to the teeth depth and offer that larger CSA.


In the thin stator FEMM plot, the stator thickness (both sides combined) is equivalent to about 4 teeth thickness of the 5 teeth shown, so the flux impediment is the stator. The stator enters saturation before the rotor even gets close.

In the thick stator FEMM plot, the stator thickness (both sides combined) is equivalent to about 8 teeth thickness, so the flux impediment is the teeth feeding the rotor, however we can still easily get the flux level through the rotor up to saturation, which for M15 steel is about 1.5T 

On the face of it, other geometries could offer improvements however, not something I am considering at this time, as this would be introducing another variable into a mix that we still don't understand.


Regards
L192

[listener192]

Attached.

1. Output power @15V DC input
2. Unfiltered output voltage showing recovery voltage transitions
3. Unfiltered output voltage driven to maximum. Note: stator in full saturation, as predicated by FEMM simulations.
4. Picture of finished Boost H bridges x 15 driving opposite stator coils in parallel. Note: control/driver hardware behind the bridge boards.
5. Super cap recovery current (yellow) and voltage(about 25V DC for approx 15V DC input) [/size]

7 coils either side are energised (2 pole), 5 slot pitch. Rotor covers 6 poles.

Some further experimentation with software planned however, main push now will be to find new stator from 5HP to 10HP motor.


Highly inefficient at this time, as saturation of stator causes coil inductance to fall rapidly above 10A total input draw. If the stator was thicker and did not saturate, the coil inductance would be higher and recovery voltage/current would increase.


The maximum input on this test was 47A @ 15.5V DC.


The H bridge and recovery circuits remain cool. 4 Ohm resistor (large heatsink), gets warm.


The other two 58A diodes on heatsinks are...


A. Isolation for DC Switch Mode power supply input.
B. In series with 4 Ohm resistor to block initial charging of 27F super cap bank.


The bank charges initially through the H bridge isolation diodes when the HSS switches are turned on.
As the circuit runs straight away the bank charges fast through the recovery diodes, as well.


At the moment the parallel connected coils are 180 degs apart.
There maybe some improvement in rotor coupling by offsetting the coils, so they couple through through the rotor by the shortest path.


L192

[gotoluc]

WOW L192, you are the most dedicated true builder I have ever seen so far.

Thanks for sharing
Kind regards
Luc

[listener192]

Just an update on the analysis of my scheme as it stands...


The move to 30 x  H bridges driving  parallel coils was largely influenced by the need to increase coil current drive, as the inductance of 6 coils in series was limiting current, demanding a higher supply voltage and this device needed to function on 25V DC. As I wanted to use a 2 pole scheme, H bridges seemed the best way to proceed.



Setting aside the my stator saturation issues, identified in FEMM, the main problem is input current not contributing to output.
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The 50/60Hz output is a composite of discrete MMF steps with individual pole reversals only occurring after pole 15 is switched.


The large static current draw is present with or without the rotor, and is due to the low inductance seen for each pair of parallel coils, switched by the individual H bridges. 


The very low inductance is largely a product of  each coil pair being switched on for 6 steps. This maintains the continuity of MMF however, once inductance is overcome (within the first ON step), very little current is required to maintain a static magnetic field, so in this case, the applied power is largely wasted as heat for at least 5 step periods.


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The scheme Pierre showed for series parallel operation, was really suited to 4 pole operation, (if you work through it), with 6 coils per pole and three coils in each pole in parallel.


As 2 x 3 coils are energized in series, every time the pole advances, there is a new coil switched into each chain. This make a change to the series inductance, as the new coil(s) charge, while maintaining the pole MMF.

It should be noted that this circuit is effectively a current multiplier* and the voltage increase on the cap bank, over input voltage is constrained by the feed back to the input via the 4 ohm resistor.
Coil energy aided by the boost function of the DC supply rail when the coils are released, the current developed charges the next coil to be activated. The continued current from the supply ensures series coil current is maintained, which in turn maintains MMF.

*I have found an example of a current multiplier that uses multiple pulse transformers that has similarities however, no examples of this this exact configuration.

This direct reuse of coil energy is an important feature of how the device achieves its performance and also explains why the coils have to be kept in a series configuration within an active pole group.
Step charging an inductor is largely a lossless process when the supply is a voltage source. 
The trailing coil(s) in a pole group are being sequentially switched out of the pole group, with the energy being recovered into the cap bank via the LSS body diodes and the recovery diodes. 
This arrangement limits the power wasted as heat.

So, the challenge is to modify my scheme, so the individual coil pairs, see inductance change at every step but without a dropout in the composite MMF i.e. an unbroken sine distribution.


L192


   

[TinselKoala]

WOW L192, you are the most dedicated true builder I have ever seen so far.

Thanks for sharing
Kind regards
Luc

It's really too bad that all that dedication, talent, knowledge, effort and money is being spent on chasing a hoax.