Hi. I've been given a very vague remit for a summer project, basically "here's a Solar Explorer board, go do stuff." I must apologise, I have no training in electronics and will need to be spoken to very simply. So, my questions:
1. How might I go about changing the values in the I-V lookup tables? As pointed out in this thread e2e.ti.com/.../455407, the values programmed on to the device are physically incorrect. (I was very relieved to learn that TI had cocked up, and it wasn't just me failing to understand this. And don't give me **** about the board being simplified - if you wanted to simplify it, you could've fixed the open-circuit voltage and made the current scale with light level, rather than fixing the short-circuit current and scaling voltage with light level - they're the same to implement but the former would've been closer to physical reality!) Anyway, this quite fortunately gives me something to work on. Unfortunately, I can't find where the lookup tables are stored or how they're accessed?
2. Where can I find a datasheet for the MOSFETs on the board?
3. I've been trying to measure the inverter efficiency as a function of switching frequency (while MPPT is running, as per Build 2 - I had to change sgen.frequency correspondingly in order to keep the sine reference at 50 Hz while I change the unipolar switching period - I change nothing else). At frequencies below 20 kHz I hear a rapid clicking, like a buzzing - I assumed something was happening at the switching frequency and that was all I was hearing. But above 20 kHz, I still hear it (in fact, I don't hear it at all when close to 20 kHz) - but 20 kHz is the limit of human hearing, no? And both the pitch and the volume of the buzzing seems to increase when I increase Gui_LightCommand. What is going on?
4. Can I check what the inverter (M2) efficiency is expected to be? I got around 40% - and don't get all defensive about the board not being optimised, I just want to know if my measurement technique is way off. (I use an oscilloscope to probe Vac-fb, Vin-fb, and a current clamp for the output ac (through some wires to a 12-ohm power resistor connected to the terminal block) and the incoming dc (in the banana connector),
convert to Vac = 100*Vac-fb/9,
Vin = 109*Vin-fb/9, according to the circuit diagram;
calculate output power = mean(Vac.*Iac)
input power = mean(Vin.*Iin);
efficiency = output power / input power.)
5. I think I've broken something. I turned the switching frequency up to 40 kHz (stupid idea, I know) and the inverter failed (I think due to output resistor overheating rather than inverter over-switching) so I stopped the run. Fortunately the board still works and my power resistor was not permanently damaged. But now when I measure efficiency, it's closer to 20%, or less. The ac voltage output is extremely low, like 2 V peak, and the very high frequencies seem to not be rejected as well as before. Do you think I've broken the transistors? The LCL filter? Both? What can I do to find out?
Thank you!
