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Author Topic: Pierre's 170W in 1600W out Looped Very impressive Build continued & moderated  (Read 429856 times)

listener192

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Latest result with 10 coils in series North and 10 coils in series South.An issue in code was giving a bad result for this configuration previously.
If I break the series loop of coils, output falls a little, and waveform distorts.

You can see the input current is 3A, so if this can be increased  9A, there would be 230V RMS across this load.
It will maintain this output to over 70Hz.
I tried Gotoluc's 3 coil scheme however that had a square waveform and lower output.
Perhaps each of the 5 coils have to be on an isolated H bridge.

Note we have a bit of phase shift between voltage and current due to the small clean up cap on the output.
Hardly any recovery current present.
L192

pmgr

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Hi pmgr
Can you please say some more on this? Do you mean just using the body diodes without driving those two mosfets? And if yes, is there any particular reason for choosing this method instead of two simple diodes?

Thanks
Jeg, you can check this TI note on back to back FETs:

http://www.ti.com/lit/an/slva948/slva948.pdf

Compared to using simple diodes, this method won't have the voltage drop of the diode when turned on as the current will flow through the FET. When turned off, the body diodes back-to-back will block any current in any direction.

PmgR

Jeg

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Jeg, you can check this TI note on back to back FETs:

http://www.ti.com/lit/an/slva948/slva948.pdf

Compared to using simple diodes, this method won't have the voltage drop of the diode when turned on as the current will flow through the FET. When turned off, the body diodes back-to-back will block any current in any direction.

PmgR

Nice gift pmgr! Thank you ;)

listener192

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This is a  scope shot that accompanies the last set.
It shows an average of 0.5A recovery current into every bridge board rail cap.
This for a forward pulse current of approx 4A.
This can only be seen by extending the cap off board with wires, so a current clamp be be applied.
This shows that most of the recovery current  is absorbed locally and not on the main cap, bank even though external diodes are provided.
L192

listener192

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To obtain lower input voltage high current operation, each H Bridge could control 1 or 2 coils. In the second coil arrangement the second coil would be 180 deg opposite and would be connected in reverse parallel to form the opposite pole.

As then we would not need to reverse operate the H bridge, in this configuration we could use one Half bridge as a boost converter, which I could never see working with Pierre's series coil connection.
In the figure attached,  Q1 and Q3 are switched on to charge the coil, Q2 is not used and remains open.When the coil turns off, Q3 is opened and Q4 is closed and the inductor charge is pushed by the rail (input) voltage into C. Q1 remains closed.

You may see from the above that Q1 & Q2 are not required, so just a half bridge is used. C = the big cap bank .
The input voltage push ensures all of the coil charge is transferred to C.
In Pierre's series coil arrangement, for the boost to work, the HHS are all connected to the + rail so they cannot have body diodes if they are MOSFETS. Relays would not have that problem. As Pierre has shown, the recovery diode goes from the coil to the super cap.   
The LSS's also don't need a body diode, although the presence of one is not detrimental to operation.So when discharging the coil the HSS charging the coil needs to stay closed. The LSS that was on for charging, then switches off. The recovery diode connected to the LSS and the coil conducts the coil charge pushed by the rail in the cap bank.

So the first thing we are doing wrong is having HSS body diodes in circuit (in the series configuration). These body diodes  left in place, stop the current flow as they are connected to the same DC rail as the input, so no push. There would be some recovery via the current flow through the other LSS body diode but not a boost function. One way of eliminating the action of the body diodes would be series diode in the supply side of the HSS's. This would stop the body diodes conducting during coil discharge and external diodes connected to the coil can need perform a boost recovery

The second problem is the overlap.. not the second HSS switch being turned on, but the second LSS being turned on before the first LSS is turned off. This will stop the boost function by not allowing the end of the coil chain to float, keeping the coil chain in charge. I cannot see anyway of have an overlap and a boost function together in the series configuration.

 So using the half bridge on a parallel coil connection, the HHS body diode (Q4 in this example) is fine, because the it is not connected to the input rail, only the cap bank, so the boost push will function.
Overlap is not a problem, as the adjacent coil has its own Half bridge.
If using the BTS7960B bridge board, the rail connection would have to be split into two i.e. separate + inputs for each half bridge.

You can use the figure attached to visualize this.
Taking the concept further, as Q4 in our half bridge is not connected to rail , we could replace the HSS with a diode, as current only needs to flow in one direction.This leaves us with one LSS Q3, which could have isolated drive, but otherwise simplifies control and reduces cost.


L192
« Last Edit: July 04, 2018, 11:19:25 AM by listener192 »

listener192

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Attached is a snapshot of Falstad running a boost circuit for a single coil. Simulation is attached.The shot shows the boost charge in progress and it has got to the point where the cap bank starts to charge the 220uF cap to a voltage higher than rail.
Across the bottom  left to right we have..

Voltage across 27F cap bank:
Voltage across 220uF cap:
Current through 5ohm resistor acting as a load: - normally the load would be coupled by the coil to the rotor winding.
Current through the 4ohm resistor: - the 4 ohm resistor is needed for the circuit to work. It isn't just a cap bank charge limiter.

If you leave out the diode connected between the cap bank and the 4 ohm resistor, then  the cap bank charges first through the 4 ohm resistor.
DC supply is 25V and has a diode isolated pre-charge of 25V for the cap bank. Note this is just to speed up the simulation, in practice a resistor needs to be in series to limit the current.

If you imagine that you have 20 single coils active, you can see there would be continuous boost and that 4 ohm resistor would get very hot.Also attached are circuit examples for uni polar and bi polar boost circuits.
L192
« Last Edit: July 04, 2018, 11:06:15 PM by listener192 »

e2matrix

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I think this statement from pmgr in the Figuera message thread may be relevant here also:
"EMF = d(flux)/dt = d(L*I)/dt which only simplifies to L*dI/dt in case L is constant (and this last simplification is the only thing we are taught in school).Adding or subtracting windings to an inductor changes L itself and thus L*dI/dt no longer applies. Instead d(L*I)/dt should be used. And with that it is very simple to obtain an overunity system as long as the amount of energy that it costs to change L is less than the amount of excess energy you obtain with the system.The more difficult part of this is to design a system that will do exactly this and which can be built in practice. The Figuera device is such a device.PmgR"

listener192

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Attached are few scope shots of a discrete switch running in boost mode.
The switch is driving 2 stator coils connected in inverse parallel, rotor in registration no load on rotor.
10.5V DC input

Not shown, the coil current is actually over 8A due to the boost configuration.
The recovery current/power is shown. Note: use average power reading.
In a working system, 10 pairs of coils would be powered at any one time, which in this example would be over 600W.
You can see this configuration has no problem achieving high power levels.

I did try to use the BTS7960B H bridge boards, with modifications however the voltage rating of the MOSFET's in the devices was not high enough and this type of converter is prone to switching node transients.

Tests conducted at 20V DC input, the  last photo shows voltage at the node, after a snubber was added immediately after the recovery diode.
Originally, the transient was 100V in this example, now reduced to 60V. This really needs to be reduced further perhaps by slowing the switching speed down, trading a little heat in the MOSFET.


The due to track inductance and working space difficulties, I was unable to reduce the switching transient on the BTS-7960B lower than 40V  @10V DC input, which is too close to the maximum rating of the device. The over voltage protection also proved to be problematic.

A discrete H bridge design is the only reliable way forward.




L192

listener192

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The first photo shows the improved rising edge transient suppression after snubber addition.

Now only a 10v overshoot at 25V input, so a 60V device with a low RDS (4 mohm) can now be used.
This will show a current drive improvement over the 28 mohm 200V MOSFET used in this example.
An H bridge built with 4 of these MOSFET's will have a combined RDS of 8 mohm plus, the isolation diode volt drop.

The second photo shows another problem that you can get with boost converters, falling edge ringing. Some MOSFET driver devices do not like the negative excursion.

Pmgr suggested  another diode is added in the source to ground path to stop this, although this will add to effective path resistance  and limit current.

The driver currently used does not exhibit any problem with this -4 volt excursion, however I do have 18V zener protection between gate and source for extra protection.

Attached is an experimental circuit to determine if a discrete H bridge boost converter can be constructed from these cheap Chinese boards.
The intention is not to use P channel MOSFET's for the HHS, as these have higher RDS than N channel devices. By maintaining very low device RDS, it will not be necessary to employ large heat sinks.
The boards need some modification, with removal of some parts and addition of others.. with some external diodes etc.
The two HSS would have complementary switching, 15 arduino outputs go to one HSS and same lines are inverted via TTL and these go to the other HHS. These only switch once every half cycle. The LSS's are controlled by individual arduino outputs (30), 45 outputs in total.
The floating supplies I have used are rectified & regulated 15V rails obtained from individual winding's on a central pot core inverter stack. This allows for a compact low cost design.

L192 

listener192

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Attached are current waveforms for two sets of anti parallel coils (180 degs spaced on stator)25V DC input voltage.
The coil sets are momentarily overlapped, no load on rotor.

Shown..Input currentcombined coil currentcombined recovery current.

Note the recovery duration for the last coil  is greater however, this coil turns completely off, something that wont happen in the complete circuit.The first coil recovery represents what would be achieved by each coil pair turning off.
Note current is a respectable 15A peak.

L192
 

listener192

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Attached are scope shots showing rotor output for he 2 overlapped coils @25V DC input.

This output is only 20% of the full set of energised coils however, it is lighting the 25W bulb.
Addition of the second coil set with the output loaded, the output voltage  increases from 86V to 122V.
 
L192

pmgr

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I think this statement from pmgr in the Figuera message thread may be relevant here also:
"EMF = d(flux)/dt = d(L*I)/dt which only simplifies to L*dI/dt in case L is constant (and this last simplification is the only thing we are taught in school).Adding or subtracting windings to an inductor changes L itself and thus L*dI/dt no longer applies. Instead d(L*I)/dt should be used. And with that it is very simple to obtain an overunity system as long as the amount of energy that it costs to change L is less than the amount of excess energy you obtain with the system.The more difficult part of this is to design a system that will do exactly this and which can be built in practice. The Figuera device is such a device.PmgR"
Let me explain this a bit further. You need to a way to vary the inductance as a function of time such that

1. the energy required to vary the inductance is less than the energy you will get from the overunity system. Or in other words, how much energy does it cost you to vary the inductance?

2. you vary the inductance on a continuous time-basis. That means there can be no discontinuities in the current in/voltage over the inductor

There are a few ways to change inductance as a function of time that everyone can think of, but unfortunately, they don't comply with the above two conditions, either the energy expended is the same or more than the energy the overunity system produces, or the current/voltage doesn't change on a continuous time-basis.

Feel free to post your ideas!


PmgR

cheors

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Vary the power supply ?

konehead

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Hi Pmrg
To radically change inductance as well as creating hyper ringing situation to the inductor, (which fills caps X20 or X 50 higher in voltage) short circuit the inductor's  in and out leads together just for short blip during peak voltage period.
Run through fwbr and dc into cap.
Unload cap by itself to load.
Use slow mechanical relays that are slowly burning up and sticking closed!  (haha Pierre's method)
Seriously must be very low ohm AC capable switching
Brush-commutator switching probably ideal or else if solid state, clusters of parralled mosfets connected bidirectionally also fast diode from soure to drain on each cluster to sustain ringing during switch closure period.

listener192

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I decide to model my rotor/stator in FEMM to determine why the rotor coil output collapses under load.
The first thing was to trim the rotor down to 5 poles. The coil pitch is still 5 slots, required to fit the 30 slot stator.
You may see that the 6 slot pitch of a 36 slot stator would have better linkage with a 5 pole wide rotor, with 5 coils overlapping.


I tried reducing the rotor width to 4 poles, but this resulted in a lower output, so 5 pole rotor width was the best compromise, this only has 4 coils overlapping so output will always be lower than the 36 slot  scheme.I had been running a two stator pole scheme, with 10 coils either side on at any time.With the simulation I could see that switching more than 8 coils either side would be a waste of energy.Coil  input was 5A (each).


A load was simulated with -1A of counter flux applied to the 1370T rotor coil, the first picture shows the result of that.

The stator flux from the outer most coils wants to close through their teeth.
The next picture shows the situation if I increased the coil current to 10A. Rotor flux increase to 1.1T close to the 1.15T value with coils @5A (no rotor load).
The next picture shows 5A through the coils but with the addition of a 5A bias coil on the rotor. This coil can be split and wrapped slot to outside of stator (in line with flux) however, it is convenient to have the coil on the rotor.
The polarity of this coil needs to change when the poles reverse. Flux level is about 0.9 T.So this coil makes a large difference for a much smaller energy input.  The issue is coupling the flux into the rotor, so just doubling A/T via the coil set does not increase the rotor flux above 1.2T, as the linkage is still the same and a large portion of input is wasted as heat.
The bias coil ensures the stator flux closes around the stator and through the rotor, where it can do useful work. 
So the bias coil makes a 0.7T step with the step switched coils adding the a sine component on top up to 1.15. As there is an un-energized gap between the two poles, the end result will average to a sine.
Until I try this out I am not sure what output into a load will be seen.

The bias coil only switches every half sine.




L192 
« Last Edit: July 18, 2018, 06:29:04 PM by listener192 »