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DC-DC Converter Toplogy for 1kW Grid Tied Inverter

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pradhan.rachit

pradhan.rachit

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Dear Experts,

I am in the process of designing a Single Phase Grid Tied Inverter with the following specifications.

Input Voltage Range: 90V - 180V
Vmpp Range: 120 - 150V
Output AC Power: 1 kWatt

The targetted Efficiency of this Inverter will be close to 90% while designing. As I am aiming for a 230V/50 Hz AC Distribution System, the required voltage of the DC-DC Converter will be close to 400V DC. I am having trouble while chosing the right DC-DC converter toplogy.

Could you highlight some suitable toplogies for the specified power levels and voltage gains required with an explanation of how to get started to shortlist the toplogy?

- Rachit
 

You will have to use a boost topology, that is for sure.

Use an interleaved (two phase) boost topology, to decrease the power losses.
 

Do you mean that a non-isolated interleaved boost converter would be sufficient to fulfill the above requirements? The maximum voltage gain requirement is 4.44 whereas the minimum voltage gain requirement is 2.22 ...

Before posting, I was interested in using a Phase Shifted Full Bridge(PSFB) topology to fulfill the requirement, as it will provide isolation between the panels and the grid.

How does interleaving reduce the power loss? Is there any other specific topology that can be useful for the same?

- Rachit
 

There are many ways to skin a cat. I'm suggesting one of them.

But you are correct, if you do require isolation (and I believe in a GTI circuit you do require it) then a PSFB may be a better solution.
 

Couldn't find much literature about implementing MPPT on a PSFB, which an essential requirement in the GTI.

Some papers of comparing converter topologies suggest that PSFB offers better efficiency compared to a standard Transformer driven full-bridge, but I'm concerned about the implementation of MPPT on it.

Any suggestions on how to go around it?

- Rachit
 

Not sure if you understand MPPT, otherwise what's the problem?

There are two requisites for MPPT implementation:
- an inverter with variable DC input voltage, e.g. 120 - 150 V as specified in post #1
- a MPPT control algorithm varying the inverter voltage ratio continuously to achieve maximum output power for the respective solar irradiation level.

The inverter voltage ratio is the ratio between a DC input and a sine output voltage. In so far the MPPT controller output isn't directly setting the PSB duty cycle, it's setting the magnitude of a sine modulator. In a grid-tied inverter implementation, it's more suitable to set a sinusoidal output current than a voltage.
 
FvM said:
Not sure if you understand MPPT, otherwise what's the problem?

There are two requisites for MPPT implementation:
- an inverter with variable DC input voltage, e.g. 120 - 150 V as specified in post #1
- a MPPT control algorithm varying the inverter voltage ratio continuously to achieve maximum output power for the respective solar irradiation level.

The inverter voltage ratio is the ratio between a DC input and a sine output voltage. In so far the MPPT controller output isn't directly setting the PSB duty cycle, it's setting the magnitude of a sine modulator. In a grid-tied inverter implementation, it's more suitable to set a sinusoidal output current than a voltage.
Click to expand...

Thanks for the better clarity. As per my previous understanding, the PSFB's duty ratio was directly linked with the MPPT algorithm, while the inverter was only used to match the phase angle and frequency of the grid. I remember seeing such control schemes in literature, but I agree with your comment on the modulator gain control of the inverter.

What are your views upon using PSFB for a GTI application?
 

I was considering a topology where the FSB is directly generating the AC output. If you have a separate DC/DC boost converter and sine inverter, the MPPT controller manipulated value may be the FSB duty cycle.
 

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