Ask about protection method in 3 phase inverter

[kirkpong]

Dear Sir
Now, I have 3 phase inverter for induction motor (space vector control method). Anyway, I am new for this field, I do not know about protection circuit for power devices in my inverter.
Please advise me, too.
Regards,

 

[ctolbert]

Kirkpong:

Always go by the mfg. specs. for protection of the inverter itself.

I would also suggest reviewing the following:

NEC 430
NEMA ICS 7 and 7.1

You must always have the correct feeder/branch protection, but things like line reactors and emi filters are optional based on application. Speak with the tech support group from the mfg. if you are unsure.

Carl

 

[kirkpong]

For ctolbert
In this case, I mean it is my inverter, I make it by myself.
I assembly circuit by myself and write the program by myself.
Anyway, I do not how to protect my power device in this inverter
Waitng for your help

 

[visitor]

1. You must be sure the deadtime is longer than the turned off time of the IGBT or MOSFET, otherwise the power device on the same leg will be destroyed by the short current. The turned off time can be found on the spec. of the device. Normally the turn-off time of IGBT is in microsecond(us) order, and much longer than the MOSFET. I know the some people lost many IGBTs by this mistake.

2. If you use MOSFET, the internal body diode can protect itself from the high back emf voltage. but if you use the IGBT, perhaps you need add the free wheeling diode by youself because there are another forward placed diode on the anode.

3.Make sure the rating breakdown voltage is high enough in your application.

Min

 

[electricuwe]

At first I would like to add some comments to the Visitors post:

1. That's true, but that's a basic requirement and not a form of protection

2.Its true that the IGBT-chip itself doesn't contain an internal antiparallel diode, but for inverter applications a broad range of IGBT-power module are available where at least one IGBT and an approbiate antiparallel diode are integrated in one package. There are also small discrete devices availabel where an IGBT and an diode are integrated in one package e.g. TO220.

3. Breakdown volatge is an issue, but the most important thing is a low inductance design of the DC-link. Otherwise you will blow 3300 V devices with 100 V DC-link voltage.
The intrinsic diode in a Power Mosfet is usually not suitable for inverter applications (For rated breakdown voltages above 200 V) because of its poor reverse recovery characteristic. Only special devices containing an improved diode are suitable (e.g. FREDFETs from the SIPMOS-family)

Usually MOSFETs and especially IGBTSs can be protected against short circuit by a driver sensing drain resp. collector-voltage and turning a of the device within 10us.
In some modules IGBTs, diodes, driver, short cicruit protection, current sensor and tempeature sensor are already integrated.
(Visit

http://www.semikron.com

and look for Skiip-Modules).
If you want to work on space vector control you should avoid to reinvet the wheel and try to buy a suitable subsystems for the inverter. About ten years ago I even used an industrial manufactured inverter where I removed the controller-board for doing research an control methods.

 

[cbarn24050]

Hi,protecting igbt against short circuits is a very complex subject, its best to avoid it by using the newer modules that have all the drivers and protection allready built in.Ok so you've rejected that idea here's what you need to do.an igbt will be destroyed in a micro second if it switches into a short, the anti parallel diode in the other half of the bridge is a short at the time af swich on, you can reduce the short current by reducing the drive to the igtb gate to about half value, this will give you around 5 micro sec for the short current to fall. At the end of that time you must either apply full gate drive,if the current is now ok, or cut off the drive for around 10 micro, then try again.Good luck!