Newbie
Joined: 04/06/2025
Location: AustraliaPosts: 2
| Posted: 08:41am 06 Jun 2025 |
Hi,
I think I understand the circuit operation but I'm lost on a couple of things.
Firstly, the IGBT used appears to be a IKW30N60T. It's a bit hard to see as the backshed id obscures some of the markings in the schematic. If it is this device, the safe operating area graph on the datasheet gives the maximum current at 200V to be about 0.9A. The 3 IGBTs in parallel gives a safe current of 2.7A.
In a post earlier, the average power was given as 1.47KW with an average voltage of 187V, giving a current of 1470\187 or 7.8A.
I'm assuming here that a pulse length of 98ms is close to DC.
Where am I going wrong? Why don't the IGBT's cook?
Another question I have is with the capacitor in parallel with the solar panels. The original author, warpspeed, indicates that the size of this capacitor is flexible. So why not have a much smaller, and cheaper, capacitor? Like the units that are used for motor start applications? It seems frequencies of up to 2MHz are OK with the LM555 timer. However the FOD3182 has a maximum switching speed of 250KHz. Even at 200KHz the discharge pulse becomes 5us, raising the safe current maximum of the IKW30N60T to 80A per device.
I assume the role of the capacitor across the solar panels is to provide a load that pulls the output voltage down to maximum power point.So you don't want the capacitor to fully discharge either as you would have effectively a short across the solar panel. So how much should the capacitor be discharged?
My heater has a resistance of 15R (ohms). If the capacitor is discharged by one third in each 5us pulse, the capacitor size to do this is 0.33uF.
Could someone enlighten me as to where I'm going wrong? Thanks in advance,
Brendan