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Three Phase inverter Drawing current with no load

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Amr Wael

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Hello ,
I am testing a PCB for a three phase inverter it's mainly based on the circuit in the following photo
I am using Isolated DC to DC converter to isolate the VDD from the VCC.
My DC-Link voltage is 24V in a dual configuration +/- 12V
I am using an STM32 MCU to generate the PWM signal using famous SPWM algorithm.
The inverter output isn't actually bad however , there is a fluctuation in the DC Power supply voltage and the inverter is drawing current in milliamps without connecting any load.
The fluctation reaches 13V and sometimes even 14V then returns to 12V and sometimes it fluctuates below 12V. These supply fluctuations do not happen normally they occur only while the DC Link is connected to the inverter.
Ofcourse this leads to an output ripple voltage. Also, the value of the current drawn increased when tried increasing the dc link voltage because my inverter is supposed to work up to 400V , i Was just starting at low voltage. The dc supply indicated suddenly a short cirucit and one of the phases is actually not working as an IC is damaged.
Another point is that I hear low volume sound while the switching control signals are connected to the board. I tried monitoring the switching signals on the oscilloscope and they look fine. There is no overlapping between the signals with around 1 to 2 micro seconds between the switching of the complementary control signals for each bridge.
I tried adding a DC Link capacitors of values between 470 uF and 2000 uF between the DC Link +/- and the COM Respectively and the presence of these capacitor improved the supply fluctation. It now fluctuates between like 11.5 and 12.5V but it didn't affect the value of the drawn current at no load.
Any ideas on how to solve this problem and the reasons behind it ?
Thank you very much in advance !
1654597744604.png
 

DC link voltage fluctuations - what's your power supply source, how can it fluctuate? How do you measure it?

"inverter is drawing current in milliamps without connecting any load" - just expectable, depending on transistor output capacitance and switching frequency.

"one of the phases is actually not working as an IC is damaged" - which "IC"? Gate driver or what? Damage happened at which DC link voltage and current consumption?

"I tried adding a DC Link capacitors of values between 470 uF and 2000 uF between the DC Link +/- and the COM Respectively and the presence of these capacitor improved the supply fluctation." - your schematic shows single supply, where is DC- and COM?

You have an actual schematic with component values?
 
Do you have current limiting in the inverter?
How is your layout...those bootstrap hi side drives can go wrong if the switching node goes below ground too much eg because layout is not optimal.
You woudl expect the various control chips to draw millamps even in no load on inverter.
 
you have described nothing about the power source and the load - therefore no intelligent comment can be made regarding your " predicament "
--- Updated ---

as you increase the supply volts the level of RFI generated by your circuit will increase - at some point this will interfere with your control and/or gate drive - this is when you will see failures.

what dead time are you using ? IGBT's or other ?
 

@cupoftea - that particular TI driver chip may be more or less immune to neg volts on sw node due to its fully isolated construction ....
--- Updated ---

... however overly neg volts on the switching node can add volts to Cboot - if one is not careful.
--- Updated ---

also - the OP has given no info regarding Ron for the design.
 

Do you have current limiting in the inverter?
How is your layout...those bootstrap hi side drives can go wrong if the switching node goes below ground too much eg because layout is not optimal.
You woudl expect the various control chips to draw millamps even in no load on inverter.
I solved the problem by improving the dead time control of the algorithm that produces the PWM signals.
 
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