Inverter

[Electronics4you]

Could you check my pre-schematic for fatal errors?
It's an IGBT inverter for a 3-phase induction motor (5.3A, 0.750kW) from a 230V mains supply.
Can the IGBTs by driven like a MOSFET?
In what sequence should the IGBTs be switched on to turn the motor in both directions?

Thanks

 

[Zed]

The 1st constructive criticisms that I see are that if the supply is direct from the mains i.e. 230VAC then because the negative side of the bridge rectifier is grounded the metal casing of the motor will not be isolated from the mains.
The other thing is that with a mains supply of 230VAC then the DC supply will be 230 x 1.414 = 325VDC approx and not 230VDC.

 

[Electronics4you]

I don't quiet understand the 1st criticism. The negative side of the bridge has to be grounded to get 230VDC out of it.

The other thing is a term we normally use in Denmark. It's actually the effective voltage therefore so 325Vrms.

 

[Zed]

The 230VAC would go through the diode in the bridge rectifier and directly to the metal casing of the 3 phase motor.
If you were to touch the motor and an earthed appliance then you would get a nasty electric shock and if the motor casing was connected to the mains earth then either the earth leakage divice in your house will trip (if one is fitted) or the fuse will blow.

 

[Electronics4you]

What to do, I need earth to the motor and ground to the bridge to get the right voltages, but they'll have to be in the same loop to get connection, right?

 

[Zed]

The bridge rectifier should not be earthed as shown in your diagram just the metal casing of the motor.
Mains earth is at 0 volts as is neutral ( the star point of the transformer at the sub-station i.e. the neutral is spiked to earth ). Live is at 230 volts with respect to both earth and neutral.

 

[Electronics4you]

So I should do like this?
All grounds from PIC and drivers should be connected to earth then?

 

[Zed]

Pin 2 on U2 U4 and U6 need to be connected togeather and connected to the negative of the bridge rectifier without an earth connection. The only earth connection you should make is to the metal casing of the motor.

 

[Zed]

I'm not sure about the drive arrangements yet as I haven't looked into it just the main power connections.
You need to get this design right on paper 1st before going ahead as it has the potential to be lethal as it is.

 

[Electronics4you]

Maybe I used the GND-symbol wrong, but I just ment that minus and GND of the driver IC's should be connected together - my bad.

Should the U2, U4 and U6 IGBT be flipped vertical like with p-channel MOSFETs on the high side (positive power on the source)?

 

[Zed]

I need more thinking time on this one as I'm a bit rusty to be honest but I think U2 U4 and U6 should be N channel and U1 U3 and U5 P channel but I'd have to go look it up.
I've not done this sort of thing for a few years now.
The main power arrangement is on the right track but the power arrangement to the drivers need's to be worked out as a wrong connection could put a high DC voltage on the device that would destroy them and possibly anything connected to them.

 

[Electronics4you]

Normally IGBT's are N-channel, but you can use them in both upper and lower side as in MOSFET motor drives. The only diadvance is the saturation voltage drop over the transistor (a bit higher for the n-channel in high side).

By the way I don't think they schould be flipped anyway cause they are like FET's. The only simillarity to the MOSFET is the gate.

Why not just put the GND from the driver circuit to earth. It's only 15.6V, so it won't give any chock?

http://www.irf.com/technical-info/guide/mount.html

 

[Zed]

Yeah I can see what you mean. That arrangement looks right to me and I have worked on a very similar drive but it was over 15 years ago. This thread is great revision for me to be honest
I haven't had chance to go dig some books out and remind myself yet but I will this weekend. Input from other members would be nice too.

 

[Electronics4you]

Thanks for the interest
Looking forward to hear from you

 

[cool100ism]

hey someone help me in multilevel inverter project...i m gonna use irfz44n mosfet..so how do i make gate drive ckt ... plz help me with appropriate ckt diagram.....