DC Bus Capacitance of Large PV Inverters

[MWh_Pro]

Hi Guys/Gals,

Can anybody give me a range of DC bus capacitances (between DC+ and DC- of inverter input) on large, 250-500 kW PV inverters? I am interested in the following configurations:

- Grounded, isolated inverters
- Ungrounded, isolated inverters
- Ungrounded, non-isolated inverters

Bonus points if you can send me a link to a product that is used in such an inverter. I was looking at Vishay low ESR capacitors, but they only go up to 470 uF, which feels low...

Motive: I am trying to understand charge/discharge phenomena of PV inverters and, as I am not an employee of an inverter company, I am finding it a little difficult to obtain realistic capacitance values.

Any help you can offer is really appreciated. :thumbsup:

Thanks,
Dave

 

[beanland]

None

None

The inverter diagrams I have seen have no intentional capacitor on the DC bus. The PV modules are current sources and the switching array just connects the PV modules to the grid using a PWM algorithm.

This is unlike a VFD where a voltage source (AC line) is used to develop a DC source to drive a voltage-source inverter to drive the motor.

 

[GoldDigger]

The inverter diagrams I have seen have no intentional capacitor on the DC bus. The PV modules are current sources and the switching array just connects the PV modules to the grid using a PWM algorithm.

This is unlike a VFD where a voltage source (AC line) is used to develop a DC source to drive a voltage-source inverter to drive the motor.

In fact, IMHO, a single phase grid interactive inverter would have to have some internal DC energy storage, otherwise the current limit of the panel array would limit the output of the GTI to far less than the continuous DC output of the inverter.
How this is normally done, I do not know, but if there is an MPPT circuit involved, there has to be a DC to DC conversion in the system and that DC to DC converter will necessarily have an energy storage component. Not just pure PWM, which would leave more than half of the panel output unusable.