name of device to provide MPPT and supply VFD DC rail

[winnie]

I was wondering if there exists an off the shelf component which provides MPPT tracking for a PV string, but with DC output which is intended for connection to the DC rail of a VFD.

I've been pondering an 'air gapped' PV system (part of this discussion: https://forums.mikeholt.com/threads/zero-export-system-without-interconnection-agreement.2565790/ ) where the PV output is behind a rectifier and can _never_ feed to the grid.

I was wondering if off the shelf modules are available to do this, but my google foo is weak searching them out. I can describe the circuit topology of what I want, but not the name of something to buy

Thanks
Jon

 

[synchro]

I was wondering if there exists an off the shelf component which provides MPPT tracking for a PV string, but with DC output which is intended for connection to the DC rail of a VFD.

I assume that the load on the VFD would have to be consuming at least as much power as the PV system is producing at the MPP. Otherwise the PV power would have to be going somewhere else to maintain operation at the MPP.

I think the outputs of DC/DC converters for grid-tied inverters are designed to act as a DC current source supplying the output switching devices of the inverter. And therefore the inverter output acts as an AC current source to the grid (which can be considered a voltage source for this discussion). The DC bus voltage on the inverter output devices (which is fed by the DC/DC converter output) will then be established by the synchronous rectification of the grid voltage by the PWM on these output devices.

In the situation you mention where the DC/DC converter feeds the rail of a VFD (and which is also fed by a rectifier off the grid), a current source output on the DC/DC converter should be OK as long as there's a sufficient load current to consume all of that converters DC output current, plus at least a small current from the grid. In that siituation the rectifiers off the grid will still be forward biased and will establish the VFD bus voltage. Otherwise, the converter's DC output voltage will not be constrained because the rectifiers off of the grid will be reverse biased.

 

[winnie]

I believe you are correct about the issue of needing the load to exceed PV output for the system to remain in MPP mode. My assumption is that for this system to work without having some sort of 'dump load' is that the unit would need to have a maximum output voltage and drop out of MPP mode when this voltage is hit.

But I am not looking to re-invent the wheel; I'm trying to find out if this sort of device is available as an off the shelf module.

Is there a name (or a product link) for a DC/DC converter designed for PV input and VFD rail output, which provides MPP on the input and appropriately controls voltage on the output to match the VFD rail voltage without exceeding the maximum VFD rail voltage.

Thanks
Jon

 

[pv_n00b]

You can check out Alencon Systems and Ampt. Both make PV MPPT devices that can feed a fixed-voltage DC bus.

 

[winnie]

Thanks. The Ampt DC/DC string optimizers look very close. The 'V-match' that they claim would probably do the trick; though the power levels are likely too high for a small AC unit.

-Jon