Motor controller circuit analysis 3

[Tunalover]

Folks-
I'm a mechanical engineer and I'm starting a job soon involving a 270VDC, 600amp electric motor for driving a high torque hydraulic motor. To do the electronic packaging and circuit design of the controller and power supply circuits, we have to be careful about causing arcing or excessive temperatures and about the circuit inductance (want to keep it low). Can anyone recommend a PC-based, inexpensive tool that will allow us to model the air, cables, spacing between conductors, conductor sizes, trace widths, trace thicknesses, components, grounds, etc.? This is to help us optimize cable routings and PCB trace routings while minimizing inductance and the probability of arcing.

I'm no EE but I am comfortable with simple analog circuit analysis. Your help is MUCH APPRECIATED!

Regards,
Tunalover

 

[buzzp]

You should review UL508(UL508A for complete panel). This would be the standard used to certify your board/enclosure design. In this standard, they identify spacing based on potential between two areas of the board. This guideline should be followed for spacing issues.
As far as reducing inductance, capacitance there are many web pages that talk about this. I will try to round some up. More important parameters to reduce arcing are spacing, humidity, and elevation of equipment. Also, keep your high current devices (relays etc) away from your controls on your PCB as much as possible. There absolutely is no substitue for good board layout when dealing with something like your making. It will save you lots of headaches. Do some more web research. I will try to post some links for you later.

 

[jOmega]

Buzzp

Doesn't UL 508C replace 508A ?

jO

 

[buzzp]

I don't know. Never heard of UL508C. Been out of that area for a couple years. Its possible. In any case regular 508 will have the data the poster needs. UL508A (or UL 508C) is just for panel makers and does not address PCB trace spacing, etc. The other info he needs is basic PCB layout techniques and pitfalls.

 

[jOmega]

I may be wrong but, I beleve that 508C is the current standard.

I know that drive manufacturers have to conform to 508C and I beleive that PCB designs as well as spacings are governed by it.

 

[buzzp]

508C is for power conversion equipment. 508A is still for panels. Quoted below from UL.com

Standard Name Edition Doc Type Date Of Publication Description
UL 508 17 Standard Jan 28 1999 Standard for Industrial Control Equipment
UL 508A 1 Standard Apr 25 2001 Standard for Industrial Control Panels
UL 508C 3 Standard May 03 2002 Standard for Power Conversion Equipment
I think, ultimately, the standards reference just 508 for spacing. Maybe not. But I know for sure 508 has spacing requirements within that is applied to all sorts of control equipment. Perhaps spacing is more strict with power conversion due to high dv/dt.

The poster may have to use 508C depending on his equipment. Below is the link for standards searches to see where which standards apply.

http://www.comm-2000.com/

 

[jOmega]

buzzp:

Clarification much appreciated.

Thanks.

jO

 

[Skogsgurra]

Dear tunaloer,

A general thought about motor controllers: You say DC 270 A at 600 V and then you mention PCB and lay-out for minimum inductance and how to reduce arcing.

I get the feeling that you are going to put high amp and rather high voltage circuits on a PCB. Please do not. Keep your control circuitry on the PCB and do the power wiring with cables or copper bars. Your SCRs (or IGBTs or MOSFETS) will be quite big and will need heat sinks that will weigh ten kilograms or more.

Most people buy off-the-shelf equipment from AB, Siemens, ABB and such companies. The new breed of DC drives are very flexible and contain programmable analog and logic blocks that you can use to customise your drive.

Finally: Economics, safety, customer acceptance, service issues all point to the fact that "rolling your own" DC drive is a very bad deciscion.

 

[Tunalover]

buzzp and jOmega-
Thanks for any help you can provide. Also I do appreciate your pointing the way to the right industry specs. I will cerainly make sure that we use them and will insure that we heed your advice.

skogsgurra-
Thanks to you too! We are using busbars to move the power around and, yes, the PCB is for logic and control rather than for current carrying. Also, I will certainly indicate the high risk with a custom design vs. a COTS one as soon as I get there.

Notes to all: While the info provided is good and will be used, what I was really fishing for was some kind of modeling tool, ala PSPICE, that would help us do detailed modeling (see orginal post).

H. Bruce Jackson
aka Tunalover

 

[ScottyUK]

Tunalover,

One of the big problems you will encounter when modelling a system like this is the number of parasitic inductances and capacitances which will appear, normally where you least want them. It's difficult to incorporate these in to your model, because you don't know their values without a layout. The PCB is a good way to provide immunity for the small-signal stuff - use a ground plane, or better still, a multi-layer board. Similar techniques apply to the power stages - use power planes (copper sheets separated by insulator) rather than busbar to reduce inductance in the system, and local decoupling close to switches.

The switching devices will need a fairly advanced model which can provide the non-ideal characteristics such as charge storage within switching devices, gate capacitance of IGBTs and MOSFETs, etc, etc.

As far as practicality of the project, at this power level buy a ready made unit if possible. If not, you should try to involve someone with experience in this type of product.

 

[Tunalover]

SCottyUK-
Thanks a bunch for the advice. I'll bring all this stuff to the table when I get there.

You guys were a big help!

If you ever need help with thermal, shock, or vib stuff, look me up!

Regards,
H. Bruce Jackson
aka Tunalover

 

[jbartos]

Suggestion: The Electromagnetic Interference (EMI) should not be overlooked. It can cause some additional modifications/additions and expenses.

 

[Tunalover]

Thanks jbartos! Maybe they will take it into consideration. Another candidate for the contract job was hired over me because his rate was lower. Oh well, it's a buyer's market as they say. Any got a contract job for an ME with heaps of experience in the electronics business? If in driving distance from Frederick, MD will certainly look at direct opportunities! The most expensive candidates are those that are underqualified.
Regards,
Tunalover
aka H. Bruce Jackson
Principal MDE