PV input module for DC bus systems

W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Does anyone here know if a 'solar input module' exists as a stand alone purchasable component? I'm specifically looking for a DC-DC converter intended to connect a PV input with MPPT to the DC bus of a VFD.

This would seem to be a standard piece of a complete inverter, but I don't know if this can be purchased 'stand-alone'.

Thanks
Jonathan
 
No battery? Just a PV module to a VFD? Or a PV string?

I think a PV charge controller *might* work for your application, depending on specs and how much precision you need. MPPT charge controllers are a thing. But what kind of voltage are you going for?

My guess is the setup will work better with a battery, to provide a buffer and stabilize voltage, even if you're not interested in overnight storage.
 
Right now this is just curiosity. I want to know if the PV interface component found in a 'PV hybrid minisplit' is available commercially for other uses.

Voltage would be in the 350V range. Often no battery is used but rectified grid power creates a voltage floor that keeps the equipment operating.

For an example of a hybrid minisplit, see:


It seems that some common 3 phase VFDs are available with custom firmware that simply connect the PV string to the normal DC bus, and then do MPPT tracking by just adjusting the output. Generally this is for water pumping:


Thanks
Jonathan
 
If a DC/DC converter is used without a battery, the converter would need to provide a constant output voltage over the range of load currents drawn by the VFD, which then corresponds to a range of delivered power up to a maximum value. And so the voltage at the input to the DC/DC converter will have to move to a point on the panels I/V curve such that the power from the PV panel is supplying the instantaneous power demand from the VFD (plus the losses in the converter). And so it will be operating away from the MPPT, unless the VFD is drawing the maximum power available from the panels. The I/V curve to the right of the MPPT has the challenge that it is very nonlinear, but at least the required voltage range to vary the power output is relatively limited. On a PV constant current curve to the left of the MPPT, the power is linear.vs. voltage. But the duty cycle of a buck or boost switching supply would have to move over a wide range to accommodate the variations in instantaneous power demand from the VFD.

I think having a battery is a much better option for a number of reasons, and beyond what I'm mentioning here. You could use an available charge controller for the battery. And the requirements for a DC/DC converter to provide a constant output voltage from a battery's ~constant voltage should be a lot easier to satisfy, and standard designs can be used.
 
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