[Feature] Adding two level inverter description to the MAS model.

[jalinei]

A proposal for supporting inverters in OM.
The goal here is to have a generic representation of a two level inverter and its load.
From that generic model we can then derive constraints on the filtering elements of the inverter, that will in turn permit to design magnetics.

Having a proper description of:

• the modulation
• the load
• the filter topology
• and the inverter ratings

is necessary to fully derive the voltage and current harmonics applied to the magnetic elements.

The proposed description permits to derive design constraints for L, LC, and LCL filters.

[jalinei]

I propose to add :

• A dc bus capacitor object containing capacitance and ESR.
• The number of leg (one leg being two switches). This way the same .json representation would cover both single and 3 phase inverters.

I propose to remove :

• dcVoltageRipple as it is in fact an output parameter that depends on quite a lot of things (operating point and modulation)

[jalinei]

In case of single phase inverter there are two major modulation technics :

• Unipolar
• Bipolar

This could be conditionally added if numberOfLeg = 2