Losses in MMC

Question

Hello to everyone,

I’m working on my masters’thesis and the main topic is about the losses on a MMC converter. I have seen the DEMO model on HVDC Transmission system with MMCs. Do you know how to calculate the switching and conduction losses on MMC using this model or otherwise by means of an another model that probably I should create?

Thank you.

Answer 1

Hello,

Currently this model uses both Power Module blocks with a Sub-Cycle Average implementation for AC side I, and Averaged models for AC side II. In order to do loss modeling, you will need to replace the power semiconductors in that model with our standard IGBT/Diodes components from our library. Have you looked at any of our demo models that use the thermal modeling features of PLECS? There are none currently for multilevel converters, but you can certainly build this. How many power levels are you looking for?

Thanks,

Kris

Comments

Hello Kris,

Thanks for your answer. My purpose is to build a model with 400 cells, I hope it is feasible. Do you think that I should remove the averaged model for the AC side II and its control and replace the IGBT in the side I?

What about the parameters of the heat sink and the thermal chain?

Thank you,

Marzio

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Hello Marzio,

Yes, that is feasible, but it is true that modeling an MMC of this size would be much easier to do the existing way using the Power Module blocks and their inbuilt vectorization capability. Do you think it's accurate to get the loss and junction temperature information for just a single cell and extrapolate the losses for all cells/legs from there? If so, you could place a pair of standard IGBTs and Diodes in the series stack and then use n-1 for the remaining cells in the Power Module.

Regarding the thermal parameters, I think you should contact the manufacturer for recommendations.

Kris

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I tried to calculate the losses taking into account your suggestions. I have some questions:

 

- What happen if I remove the MMC on the side II, is the system stable?

- Which are the roles of the two MMCs? One of that works as an inverter and the other as a rectifier? Which one?

Thank you,

Marzio

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Hello Marzio,

You may remove the MMC on side II, however it's better then to use a resistor for the load.

The MMC on side I controls the DC voltage, while the other one defines the amount of power transmitted between two systems.

I hope this helps.

Regards,

Kris

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Hello Kris,

What do you think instead about this configuration?

Thank you for your support,

Regards,

Marzio

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Hello,

I don't understand your question here.

Kris