My homebuilt VFD progress

AC, DC, amps, volts and kilowatt. It's all discussed in here
User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 21:29

Stiive wrote: Haha funny it still uses the Saleae software.

Is Vb meant to turn off halfway through Ut and Wt on time? The current has no path in that 1uS... I would have thought it should switch at the same time as the others?
Not that I think it would cause the problems your seeing, just seems strange to me.

The overall switching seems okay for 3-ph sine wave. Cant see the modulation index getting smaller at the edges though, but that's probably cus its zoomed out a lil too far.


This shows a couple edges a bit better.
Image

The half-way pulse is a part of the centre-aligned waveform generation. All the "top" pulses are centre-aligned, and since the "bottom" pulses compliment the top (low when they're high), they are "shifted" by half a cycle relative to the tops. The current that flows is an average current, so it keeps flowing during switch-off, but through the freewheel diodes. Someone correct me if I'm wrong.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Thu, 08 Nov 2012, 21:40

BigMouse wrote:

This shows a couple edges a bit better.
Image

Looks good to me
BigMouse wrote:
The half-way pulse is a part of the centre-aligned waveform generation. All the "top" pulses are centre-aligned, and since the "bottom" pulses compliment the top (low when they're high), they are "shifted" by half a cycle relative to the tops. The current that flows is an average current, so it keeps flowing during switch-off, but through the freewheel diodes. Someone correct me if I'm wrong.


Yes the inductance in the motor will cause the voltage across the phase (inductor) to increase to try maintain the current. Because U and W side is tied to DC+ potential, Vb will decrease below DC- and therefore the FWD will conduct..

Still, I personally don't like this centre-aligned pulse. Probably because I'm not used to it.
Last edited by Stiive on Thu, 08 Nov 2012, 10:42, edited 1 time in total.
Rgds,
Stiive

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 22:09

A couple more traces to look at.

They are both the filtered (via a voltage divider and capacitor LPF) voltage waveform measured between two phases. The Vrms value shown on the screen is 1/2 the actual value as a result of the voltage divider. For both of these, the controller "thinks" it's putting out 72Vrms L-L.

This one shows what the voltage waveform looks like with no load. Nice pretty sine wave:
Image

This one is with the 11kW motor connected. No other changes:
Image

Here, I've superimposed the two waveforms together. They are the same frequency, and the controller is trying to output the same voltage (72Vrms) for both.
Image

It's pretty clear that about about 60 (and 240) degrees, something happens that causes the voltage to drop. I don't think it's a voltage drop across an IGBT as there is no heating. 20v drop, even at a couple of amps, would cause rapid heating. So I'm pretty sure the IGBTs are fully on. More likely, this sudden drop may be from another IGBT turning off prematurely. I still can't find anything in the code which would cause this to happen, so I'm still suspecting a hardware issue.

Note that I have disconnected the RESET bus from the microcontroller and hard-wired it to the same 5v which supplies the logic-side of the drivers, so there is no way this is pulling low from noise.

The 330pf capacitor and pull-up resistor on the FAULT pin seems only to be there to prevent false FAULT signals from reaching the microcontroller. I don't see how they could effect the noise immunity of the device itself. Regardless, the capacitors are installed.

I'm really running out of ideas here. This is my third solid day of troubleshooting with absolutely no change in observed behavior, no matter what I've tried.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Thu, 08 Nov 2012, 22:15

So all you controller is trying to do is output a 72V 2Hz sine wave? No motor control code or anything?

If not, I would try just outputting the sine wave. That should tell you if its software or hardware.

What is the phase resistance of the 11kw motor?
Rgds,
Stiive

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 22:30

Stiive wrote: So all you controller is trying to do is output a 72V 2Hz sine wave? No motor control code or anything?

If not, I would try just outputting the sine wave. That should tell you if its software or hardware.

What is the phase resistance of the 11kw motor?


The controller is set up for "slip" control, but the encoder isn't hooked up to it won't go beyond 2Hz. I'll make a few quick tweaks to the code to have it simply output a 2Hz sine wave at 72V and see what happens. I expect the result will be same, but I won't be disappointed if it's smooth!

The motor is wired in Delta at the moment and the resistance measured between any two terminals is 2.4ohm.

User avatar
weber
Site Admin
Posts: 2626
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

My homebuilt VFD progress

Post by weber » Thu, 08 Nov 2012, 22:48

BigMouse wrote:It's pretty clear that about about 60 (and 240) degrees, something happens that causes the voltage to drop. I don't think it's a voltage drop across an IGBT as there is no heating. 20v drop, even at a couple of amps, would cause rapid heating. So I'm pretty sure the IGBTs are fully on. More likely, this sudden drop may be from another IGBT turning off prematurely. I still can't find anything in the code which would cause this to happen, so I'm still suspecting a hardware issue.
I agree with all of your reasoning here.
Note that I have disconnected the RESET bus from the microcontroller and hard-wired it to the same 5v which supplies the logic-side of the drivers, so there is no way this is pulling low from noise.
OK. So it's not desat. So what else can cause an IGBT to be turned off prematurely? Undervoltage lockout (UVLO).

So now I'm thinking your high-side driver's IGBT-side supply is the usual bootstrap arrangment with a diode and a cap, and it's drooping for some reason. Possible reasons: bootstrap diode too slow, bootstrap cap too small or too much ESR or ESL, going too close to 100% duty cycle.

The trouble with this theory is that I can't figure out why it would be dependent on the load on the drain/source side of the IGBTs.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 23:09

weber wrote:
BigMouse wrote:It's pretty clear that about about 60 (and 240) degrees, something happens that causes the voltage to drop. I don't think it's a voltage drop across an IGBT as there is no heating. 20v drop, even at a couple of amps, would cause rapid heating. So I'm pretty sure the IGBTs are fully on. More likely, this sudden drop may be from another IGBT turning off prematurely. I still can't find anything in the code which would cause this to happen, so I'm still suspecting a hardware issue.
I agree with all of your reasoning here.
Note that I have disconnected the RESET bus from the microcontroller and hard-wired it to the same 5v which supplies the logic-side of the drivers, so there is no way this is pulling low from noise.
OK. So it's not desat. So what else can cause an IGBT to be turned off prematurely? Undervoltage lockout (UVLO).

So now I'm thinking your high-side driver's IGBT-side supply is the usual bootstrap arrangment with a diode and a cap, and it's drooping for some reason. Possible reasons: bootstrap diode too slow, bootstrap cap too small or too much ESR or ESL, going too close to 100% duty cycle.

The trouble with this theory is that I can't figure out why it would be dependent on the load on the drain/source side of the IGBTs.


I'm not using bootstrap as I need negative gate drive for turn-off. I have 6 isolated SMPS supplies which are more than capable enough. I have more than 100uf of low ESR capacitors on the output for each gate, and the voltage never drops below about 15v while running (see gate drive trace from earlier today).

I just tested it with nothing going on in the controller except a 2Hz 72v sine wave output, no change. I've also verified that the inputs to all 6 IGBT gates appears as I expect on my scope. I really should get ahold of an analog scope to verify this.

One thing I DID notice is that while running the motor at 2Hz, the vibration it's having starts out rather harsh, then slowly quiets down (but doesn't go away), then suddenly starts again and fades away. It does this over about a 4-5 second period. That screams code to me, so I'm going to do some more digging and see if I can find a possible cause for that.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Thu, 08 Nov 2012, 23:13

BigMouse wrote: I have more than 100uf of low ESR capacitors on the output for each gate


So the gate driver is driving the gate capacitance of the IGBT + 100uF of low ESR?
Rgds,
Stiive

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 23:18

Stiive wrote:
BigMouse wrote: I have more than 100uf of low ESR capacitors on the output for each gate


So the gate driver is driving the gate capacitance of the IGBT + 100uF of low ESR?


No, that's the smoothing/storage capacitance for the gate drive power supply, just down stream of the rectifier.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Thu, 08 Nov 2012, 23:20

BigMouse wrote:
Stiive wrote:
BigMouse wrote: I have more than 100uf of low ESR capacitors on the output for each gate


So the gate driver is driving the gate capacitance of the IGBT + 100uF of low ESR?


No, that's the smoothing/storage capacitance for the gate drive power supply, just down stream of the rectifier.


*Phew* Image
Rgds,
Stiive

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Thu, 08 Nov 2012, 23:35

Stiive wrote:*Phew* Image


Hah, I'm not THAT clueless.

User avatar
weber
Site Admin
Posts: 2626
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

My homebuilt VFD progress

Post by weber » Thu, 08 Nov 2012, 23:53

BigMouse wrote:I'm not using bootstrap as I need negative gate drive for turn-off. I have 6 isolated SMPS supplies which are more than capable enough. I have more than 100uf of low ESR capacitors on the output for each gate, and the voltage never drops below about 15v while running (see gate drive trace from earlier today).

Then I'm all out of theories. Sorry.

BTW, negative gate drive doesn't preclude bootstrap. The high-side negative supply could be generated off the bootstrapped positive one by a non-isolated inverting DC-DC converter. But what you've done should be much better.

I assume you can use dual channels of DSO to compare driver input and output waveforms (for pulse width) for the low-side device, during the period that the output droops, but there's really no way to do that on the high-side device.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Fri, 09 Nov 2012, 01:56

Stiive wrote:Still, I personally don't like this centre-aligned pulse. Probably because I'm not used to it.
What do you use? Edge aligned? Are all the pulses aligned on the rising edge on your controller, with variable width?

User avatar
coulomb
Site Admin
Posts: 3780
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

My homebuilt VFD progress

Post by coulomb » Fri, 09 Nov 2012, 04:56

This image:

Image

looks a lot like one I've studied on my DSO at work. The difference is scale. You seem to be dropping 20 V where I would expect more like 2 V.

So here's a whacko suggestion for you: Image

Is your DSO probe set to x1 when you've told the DSO it's x10? Image

If so then the voltage is actually 10x lower than what you think.

Then the discontinuity at 60 degrees, only under load, is actually expected. This would be where the current crosses zero. Remember, you have a highly inductive circuit here, since you are not loading the motor much, so this is mostly magnetising current.

(I don't drive a motor; I have a resistive load, so my L is explicit and known, though split into pieces with my LCL filter. Your discontinuity is at about the same point to where I see it [ edit: was different ], but I see it about 40 degrees. That's just because my load has about the same reactance as resistance; yours has about 7:4 (tan^-1 60 degrees). The shape and the "it only happens under load" aspect matches exactly what I see.

Remember that the current is actually not a pure sine wave, but a sine wave with a triangle wave superimposed. So as the current increases from negative to positive, at first only the tiniest peak of the triangle crosses zero, then more of the peak, and so on, then after a millisecond or so, most of the current is positive with only the negative peaks of the triangle dipping negative, then only the very negative most peaks cross zero, and finally the current stays positive even at the negative peaks of the triangle.

When the current is positive (depending on convention of course), it is coming out of the IGBT, so the output is about 1.5-2 V less than the DC+ rail (considering the top IGBT now). When the current is negative, it is flowing through a free-wheel diode into the pack. The free-wheel diode has a voltage drop, say 0.8 V, so the output will be around 0.8 V more than the DC+ rail. So you see 2-3 V difference in amplitude (depending on the magnitude of the current, and the size of the IGBTs) as the current crosses zero. When there is no or very light load, you don't see the 2 V drop across the IGBTs, and somehow you don't see the diode drop either (maybe at light loads, the diode drop is say 0.3 V and gets lost in the noise).

[ Edit: I forgot to say what the point of the above is: this explains why the discontinuity isn't abrupt, but takes about 10 ms on your slow wave (less than a millisecond with my 50 Hz waves). ]

[ Edit2: remember the current lags the voltage, here by about 60 degrees, so when the voltage is at 60 degrees, the current is only just crossing zero from negative to positive. ]

Notice that after the discontinuity, the shape of the curve is basically right, just reduced in amplitude, until the voltage crosses zero (and at that point, some other current is crossing zero, since it is 120 degrees later).

[ Edit3: my circuit has the load basically as one delta leg. So I only see two discontinuities, one at about 40 degrees, and another at 180+40 = 220 degrees. You may care to disconnect one leg of your motor to see if this makes any more sense that way. ]

But what you seem to be seeing is a 20 V drop, and that can't be right. If it's actually around 2 V drop, then this is to be expected. Apparently, this is moderately well known, and good inverters actually detect the zero crossings and compensate by increasing the PWM amplitude at just the right point. I've actually done this recently, and it works to a point. It's hard to get the timing just right, so what happens is that there is a spike at the crossover point, and the output rings badly after that point, almost to the next half cycle. (I'm doing only one phase, remember.) I actually don't mind this too much, as the 2.4 kHz ringing (from my LCL filter's resonance) is something that we want to try to compensate for in software, if possible, as a future research project.

Of course, if the amplitude of the signal is always quite large, then none of this matters, as 2-3 V is small potatoes compared to your ~300 V bus voltage (mine will be over 700 V).

So perhaps you could verify the line to line amplitude with a multimeter?

My apologies if this has already been checked; I've only had time to skim this whirlwind flurry of posts.
Last edited by coulomb on Thu, 08 Nov 2012, 19:05, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Fri, 09 Nov 2012, 06:02

Hi Coulomb,

Thanks for the suggestion. Unforunataly, both the probe and the scope are set to x10, so that actually is a 20v drop. If the probe were set to x1, then the scope would show a Vrms of 356v, which through the voltage divider would mean over 700v.

It doesn't only "happen" under load, it's heavily dependent on load. To the point where if I put my big 48vac 132 frame motor on it, I get 0v (L-L) and a measured 50% duty cycle at the IGBT phase output, despite a varying pulse width gate drive. (this still makes zero sense to me)

On my 11kW motor, the motor shaft turns at 1rpm with a 2Hz input (as expected for a 4-pole motor), but the motor vibrates and "pulses". If I had to guess, I'd say the frequency of the vibration is about 12Hz, which would make sense for having such massive discontinuties twice per cycle per phase at 2Hz. Something is definately wrong. I put my cheap $130 chinese VFD on the same motor and the same battery pack and it's smooth as silk even at very low speed.

Another thing I've noticed is that 20v is the magic number when it comes to my voltage drops.

-The peak voltage with a load is 20v less than without the load.
-When I connect the scope to the a phase with the mid-point of the DC bus as the GND reference, I get Vdc-20 as the amplitude (that drop can ONLY be across the IGBTs since it's not measured against another phase).
-While experimenting with my big motor, I had to set the inverter's output voltage to around 20v before ANY output voltage was measured, and the motor started turning (again, with lots of vibration).

So either: the filter is attenuating my readings somehow, I am actually dropping 20v across my IGBTs, or there's a problem with my method of commutation.

The only way I could be dropping 20v across my IGBTs is if they're not turned on fully. 20v is well past desaturation, and the desat detecting optocouplers should trip if that's the case. I imagine they'd destroy themselves very quickly if this were actually the case.

What sort of filter do you use for measuring PWM signals? Do you have any specs or a schematic? I just have two large value resistors in a voltage divider with a capacitor in parallel with one of them to make a very crude LPF with 1/2 the input amplitude.

I should try to sleep on this. I'll be spending the rest of the day tomorrow trying to get it going... again.

Thanks everyone for your suggestions so far.

User avatar
coulomb
Site Admin
Posts: 3780
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

My homebuilt VFD progress

Post by coulomb » Fri, 09 Nov 2012, 06:18

BigMouse wrote: If the probe were set to x1, then the scope would show a Vrms of 356v, which through the voltage divider would mean over 700v.
Oops, yes, wrong way around. But it could still be the mismatch. So your multimeter definitely agrees with the DSO?
It doesn't only "happen" under load, it's heavily dependent on load.
Yes, still sounds like current crossing zero.
To the point where if I put my big 48vac 132 frame motor on it, I get 0v (L-L) and a measured 50% duty cycle at the IGBT phase output, despite a varying pulse width gate drive. (this still makes zero sense to me)
I have to admit I can't fathom that one.

[ Edit: experience tells me that those really odd things that you notice and can't explain right now often turn out to be the keys. So I think that there is a big clue right there, and you should start with that tomorrow, perhaps. ]
(that drop can ONLY be across the IGBTs since it's not measured against another phase).
Can you perhaps measure the C and E of one IGBT, and use the subtract mode of the DSO to read the difference? Then you would see if there is a 20 V drop across the IGBTs when on.

-While experimenting with my big motor, I had to set the inverter's output voltage to around 20v before ANY output voltage was measured, and the motor started turning (again, with lots of vibration).
Ok, that pretty much puts paid to the x10 theory, assuming you're not fooling yourself about the DC bus voltage by a factor of 10 as well. I assume that this is not possible.
What sort of filter do you use for measuring PWM signals? Do you have any specs or a schematic? I just have two large value resistors in a voltage divider with a capacitor in parallel with one of them to make a very crude LPF with 1/2 the input amplitude.
That sounds fine. I use a single RC filter, with a time constant of the order of 1-10 milliseconds (from memory).
I should try to sleep on this.

Great idea.
Last edited by coulomb on Thu, 08 Nov 2012, 19:20, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

My homebuilt VFD progress

Post by Johny » Fri, 09 Nov 2012, 14:24

BigMouse wrote:On my 11kW motor, the motor shaft turns at 1rpm with a 2Hz input (as expected for a 4-pole motor),....
Just a trivial point here. A 4 pole motor should be rotating around 60 RPM for 2Hz. Maybe you meant rotates once per second.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Fri, 09 Nov 2012, 14:26

Not sure if it'll help by maybe connect up a purely resistive 3-phase load of around 2.4 ohm (start higher if you can and slowly make your way down), and see if you get the same results.
Rgds,
Stiive

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

My homebuilt VFD progress

Post by Johny » Fri, 09 Nov 2012, 14:51

Stiive wrote: Not sure if it'll help by maybe connect up a purely resistive 3-phase load of around 2.4 ohm (start higher if you can and slowly make your way down), and see if you get the same results.
I've been thinking something similar Stiive. Even a highish power light globe across 2 phases would provide information (or a bar radiator).
BigMouse, in an earlier post yopu mentioned that you would install bus bars and bigger DC Bus caps before you connected the big motor. Did you do this?
Can you show us some real pictures of the setup - showing DC Bus, caps, IGBTs and the connections/wiring to the motor(s).

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Fri, 09 Nov 2012, 15:38

coulomb wrote:
BigMouse wrote: If the probe were set to x1, then the scope would show a Vrms of 356v, which through the voltage divider would mean over 700v.
Oops, yes, wrong way around. But it could still be the mismatch. So your multimeter definitely agrees with the DSO?
I checked the switches on the probes and the settings in the DSO, I'll verify with a multimeter today. I'm not sure how well it'll work with such a low frequency.
coulomb wrote:
BigMouse wrote: It doesn't only "happen" under load, it's heavily dependent on load.
Yes, still sounds like current crossing zero.
So the shape is normal, but the magnitude of the drop is not. Fair enough. I'd be happy with a 2v drop ;-)
coulomb wrote:
BigMouse wrote: To the point where if I put my big 48vac 132 frame motor on it, I get 0v (L-L) and a measured 50% duty cycle at the IGBT phase output, despite a varying pulse width gate drive. (this still makes zero sense to me)
I have to admit I can't fathom that one.

[ Edit: experience tells me that those really odd things that you notice and can't explain right now often turn out to be the keys. So I think that there is a big clue right there, and you should start with that tomorrow, perhaps. ]
It was one of the first things I discovered while troubleshooting, and is still the most confusing thing. I have used both channels of my scope, one on the output, and the other on a gate and have verified that they have different varying pulse width. It's really doing my head in.
coulomb wrote:
BigMouse wrote: (that drop can ONLY be across the IGBTs since it's not measured against another phase).
Can you perhaps measure the C and E of one IGBT, and use the subtract mode of the DSO to read the difference? Then you would see if there is a 20 V drop across the IGBTs when on.
I will do this today as well.

Johny wrote:
Stiive wrote: Not sure if it'll help by maybe connect up a purely resistive 3-phase load of around 2.4 ohm (start higher if you can and slowly make your way down), and see if you get the same results.
I've been thinking something similar Stiive. Even a highish power light globe across 2 phases would provide information (or a bar radiator).
BigMouse, in an earlier post yopu mentioned that you would install bus bars and bigger DC Bus caps before you connected the big motor. Did you do this?
Can you show us some real pictures of the setup - showing DC Bus, caps, IGBTs and the connections/wiring to the motor(s).
I'll see if I can track down a suitable load. A guy who comes in to my work has offered to let me use some large light globes for testing before. I may stop in and see if I can take him up on that.

I haven't taken a photo of it all hooked up, but here is a photo of the inverter with the bus bars and caps installed:
Image

The connections are pretty straight forward.
>Battery input (from contactor) on the two bars on the right.
>Motor phases on the bars along the left edge.
>Battery+ (not switched) on the spade terminal at the far left corner of the board near the fuse, for precharge.

The DC bus bars are connected across the IGBTs mounted under the board. The phase bus bars are connected to the phase outputs (C2E1) of the IGBTs.

I have 600uF of film caps installed. Tritium uses 800uF for their wavesculpter 200, so 600uF should be fine for testing with no motor load. I did, at one point connect a 2400uF electrolytic across the bus to see if there was any change, which there wasn't.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Fri, 09 Nov 2012, 15:44

And your SURE your battery pack is healthy? lol
Rgds,
Stiive

User avatar
BigMouse
Senior Member
Posts: 600
Joined: Thu, 28 Oct 2010, 02:39
Real Name: Vincent Tannahill
Location: Silicon Valley
Contact:

My homebuilt VFD progress

Post by BigMouse » Fri, 09 Nov 2012, 15:51

Stiive wrote: And your SURE your battery pack is healthy? lol
I'm sure there is no more than a 3v drop across it during this testing, yeah. There are some weak cells (bought some counterfeit A123 cells by accident. They have nowhere near the discharge capability of the rest of the cells, but there aren't many of them in the pack. I haven't managed to pull more than 5-10 amps from the pack during any of this testing anyway, since I haven't exceeded 50Hz even when I was doing the "boosted by 20v" testing on my big motor.

User avatar
weber
Site Admin
Posts: 2626
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

My homebuilt VFD progress

Post by weber » Fri, 09 Nov 2012, 18:11

BigMouse wrote:It was one of the first things I discovered while troubleshooting, and is still the most confusing thing. I have used both channels of my scope, one on the output, and the other on a gate and have verified that they have different varying pulse width. It's really doing my head in.

Your anti-parallel diodes are all blown and the IGBT's are going into reverse breakdown at about 20 volts?
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

My homebuilt VFD progress

Post by Johny » Fri, 09 Nov 2012, 18:32

Nah - the gate wires are connected the wrong way around. The IGBTs are conducting when your software is saying DON'T.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

My homebuilt VFD progress

Post by Stiive » Fri, 09 Nov 2012, 18:33

there is no spoon
Rgds,
Stiive

Post Reply