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Voltages for 650 Vdc DC link with differential probe x500 (Ch1) across
Phase leg midpoint and DC+; Fig. 1: Full pulse, Fig 2. Turn-on, Fig. 3: Turn-off
Phase leg midpoint and DC-; Fig. 1: Full pulse, Fig 2. Turn-on, Fig. 3: Turn-off
It took some time and work, but I finally got to 650 Vdc link voltage. As a last acttion, I was looking at how to reduce inductance in the DC link and did some major rearrangements.
Here is a summary of work and modifications:
Increased Rgon from an initial 6.66 Ohm to 80 Ohm.
Added RC...
Active PRC at 500 Vdc output voltage, turn on and turn off waveforms across boost IGBT... though, not sure if managed to I capture it at the peak current.
Differential probe x500
Switching period (several and one)
Turn on (different time base)
Turn off
I'll order 82R and 100R and see how it goes first. step by step
I was looking at the turn off period and measuring oscillations on the yellow signal.
Smaller one directly on MOSFETs DC+/-: https://uk.rs-online.com/web/p/products/8752144/
Bigger 2.2 uF replacement for existing 450 V...
If I measure the ringing frequency, especially visible during the turn-off period on the yellow signal (Ch1), I get fringing0 = 10 MHz. So to reduce the ringing frequency, I should be increasing capacitance.
I can assume that the current capacitance in the circuit is equal to or higher than the...
Recordings with Rgon = 47 Ohm, at 500 Vdc
One switching event
Turn on (zoomed)
Turn off (zoomed)
Should I be increasing the Rgon even more, or should I increase snubber capacitance?
Btw. this reference says to add RC snubber across low-side MOSFET.
There are two electronic capacitors (400...
When there is no power and no input voltage I can see input voltage on the scope. This could explain why I see this signal superimposed on my PWM signal... though, not sure why I see the AC signal in the first place :confused:
Already have that.
Ch2: differential probe x200, DC+ to DC-
Ch3...
There is already 2.2 uF across upper MOSFET drain and lower MOSFET source.
PFC is switching at 20 kHz and the noise is at 8 kHz. Also when I tested only the PFC circuit at 700 Vdc out and full power, the communication was not breaking down and the noise was not visible on the signals on the...
After some trial and error and finding the optimal resistors, I put them the closest I could; all under MOSFET drivers. Values are still 2200 pF and 120 ohm.
I was able to go to 650 Vdc and I recorded voltage between the leg midpoint and the ground.
I am still seeing switching noise similar to...
Should I then keep 2.2 nF or change to 10 nF or even increase to 20 nF :unsure:
In that case, is 120 Ohm okay, or should I change that as well? 10 nF showed slightly better noise reduction when comparing oscillograms, but power will increase proportionally :(
I can solder RC snubber on PCB...
Another update:
I added Schottky diode to MOSFET driver board so that Rgon is 23.5 Ohm and Rgoff is 10 Ohm
I added an RC snubber circuit to every MOSFET, R = 120 Ohm, 4 W, C = 2200 pF, 2 kV
I can notice that the noise at switching frequency slightly increased compared to the previous case...
I can add resistors in series with the capacitors. There is space for the lower IGBTs.
Not sure how to add it to the upper. I am not seeing any accessible place.
This is my next step. To add Schottky diode to separate Rgon and Rgoff.
Pout = 3 kW at 3x400 Vac, line current = 4.3 Aacrms
Yes...
Quick update.
I can go now up to 650 Vdc and full power without serial communication breaking down :)
First, I increased gare resistance from 6.66 Ohm to 10 Ohm (max. DC voltage before comms breaking was 600 Vdc). Now I have it at 23.5 Ohm (Rgon and Rgoff) and I can go up to 650 Vdc.
In the...
Bottom: Inverter card (PCB layout shown in one of the previous posts). X100, X101, ... X400, X401 are places for MOSFET drivers. Eight connectors on the side are for PWM pulses. On the bottom side are mounted MOSFETS on a heatsink (not grounded). A lower leg RC snubber components are not...
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