Three phase inverter

Thread Starter

idrees.engineer

Joined Jan 7, 2012
6
I am using three half bridge IGBT modules specified as above in Three phase inverter.

My design is as under

Driver IC = IR2235
Vg(ON) =15V for high side and also for low side
Vg(OFF) =0V for high side and also for low side
Rg(ON) = 25 Ohm
Rg(OFF) = 5.6 Ohm
Bootstrap capacitor value is = 1uF/25V
Switching frequency is = 4KHz
Dead Time = 6uSec.
DC BUS Voltage = 600V
Microcontroller= PIC18F4431.
Optoisolater = HCPL2631.
snubber capacitor across IGBTs C1 and E2 of value 0.22uF 1200VDC/600VAC.


i have tested the inverter at 150VDC. with 500Watt motor.

it is working good but there is a problem.

From each half bridge when upper or lower IGBT is off and after dead time when other is going to ON a spike of 1.2uSec appears at rising edge of IGBT which is going ON and also this pulse appears in off time of other IGBT whis is OFF.
The load current which is being drawn by load is = 1.2Amp.

Although it did not give any problem but as i increase DC bus voltage the amplitude of this spike also increasing so i limited the DC bus to 150V.

I have to apply 600VDC but i am afraid to spike which appears on both pulses

Please suggest me the solution to remove this spike.

Thanks in advance
 

kubeek

Joined Sep 20, 2005
5,732
Post a schematic and pictures/drawings of the spikes.
Also, unless you forgot to mention a transformer on the output, then this is not an inverter but something along the lines of VFD or variable frequency driver.
 

praondevou

Joined Jul 9, 2011
2,942
Rg(ON) = 25 Ohm
Rg(OFF) = 5.6 Ohm
snubber capacitor across IGBTs C1 and E2 of value 0.22uF 1200VDC/600VAC.
If you have headroom in terms of temperature rise for the IGBTs you can try to increase the gate resistor values.

I used for a 2kW inverter up to 56 Ohms.
What type is that capacitor you mentioned? It has to be a low ESR type for this kind of application. I used up to 1uF for DC bus voltages of 460V.

Post what Kubeek suggested and also a picture of the IGBT/capacitor layout.
 

Thread Starter

idrees.engineer

Joined Jan 7, 2012
6
Post a schematic and pictures/drawings of the spikes.
Also, unless you forgot to mention a transformer on the output, then this is not an inverter but something along the lines of VFD or variable frequency driver.
I have attached the schematic of my inverter control PCB also spike picture is attached as well

Kind regards
View attachment THREEPHASEINVERTER.pdf

View attachment SCHEMATIC1 _ IGBT Drive.pdf

View attachment Waveform.pdfView attachment THREEPHASEINVERTER.pdf

View attachment SCHEMATIC1 _ IGBT Drive.pdf
 

praondevou

Joined Jul 9, 2011
2,942
I take as an example R7 and R23 in your second schematic. You are using the diode to discharge the gate faster than it was charged I suppose? Then these two resistors shouldn't have the same values. R7 would need to be higher to get different charge discharge times.

Since you measured the voltage peak I suppose you have an oscilloscope. Please post the waveform captured on the scope.

A voltage peak is normal when switching off IGBTs. How much is it at 150V?

What IGBT are you using?
 

Thread Starter

idrees.engineer

Joined Jan 7, 2012
6
I take as an example R7 and R23 in your second schematic. You are using the diode to discharge the gate faster than it was charged I suppose? Then these two resistors shouldn't have the same values. R7 would need to be higher to get different charge discharge times.

Since you measured the voltage peak I suppose you have an oscilloscope. Please post the waveform captured on the scope.

A voltage peak is normal when switching off IGBTs. How much is it at 150V?

What IGBT are you using?
The spike magnitude is 4V at 150V DC Bus voltage.
I am using semikron IGBT "SKM400GB123D"
The captured waveform is attached herewith

regardsView attachment Waveforms.pdf
 

praondevou

Joined Jul 9, 2011
2,942
The spike magnitude is 4V at 150V DC Bus voltage.
I am using semikron IGBT "SKM400GB123D"
The captured waveform is attached herewith

regardsView attachment 38711
Now I get it. You are talking about the gate voltage and you are worried about it being turned on when the other IGBT starts conducting.

Try to increase the gate resistor values a bit, e.g. 10 Ohm for the ones that charge the gate ( not the ones with the diodes in series)
 

shortbus

Joined Sep 30, 2009
7,926
Is your gate driver mounted close(less than 1 inch/25mm) to the IGBT? If you have a length of wire between the drivers and gates you maybe getting an inductive kick on the wires.
 

praondevou

Joined Jul 9, 2011
2,942
Is your gate driver mounted close(less than 1 inch/25mm) to the IGBT? If you have a length of wire between the drivers and gates you maybe getting an inductive kick on the wires.
Good point, I always forget to ask this question. Where exactly did you measure the pulse, at the gate or at the driver output? It may not seem to but this makes a huge difference.
 

Thread Starter

idrees.engineer

Joined Jan 7, 2012
6
I did also increase the charge resistor step by step up to 56 ohm
but the problem is still there.

Secondly i have mounter IGBT drive directly on the IGBT so there is not wire distance between IGBT and driver
 

Hansh

Joined Jun 16, 2009
1
I see some designs that each MOSFET / IGBT a Capacity of + / - 4n7 .. 12n over the drain / source is connected. (= 6x is a 3 phase motor).
Could this be necessary?
 
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