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    heres a couple questions and comments i got from a family friend

    i answered a few of the simple ones but thought i'd share 

    7kW at 120 volts requires 58 amps, before any losses are added in.
    This translates to switching (as per project, 72 volts) a LOT of amps [namely 97.2 amps! @ 72 v dc].
    Big power = big amps = big wire = big cost = big weight (for the step-up transformer).
    Usually, as the power requirement increases, so does the input voltage.
    Changing 120 volt DC to 120 volt AC would eliminate the need for a transformer.

    According to link provided, there are questions to be firmed up.

    A few that come to my mind are:
    Is the electrical load predominately resistive?  If not (then it's inductive) then a power factor of the design load should be specified.  For example, 5kW@0.85 power factor [this is a vector, 5kw in length, at an angle, such that the COS(angle)=0.85 or 85%, which has both real or resistive, and reactive components.

    In the AC world, a power factor must be specified.

    Also, harmonic content is not specified.  Some types of equipment must have low harmonic sine wave [computers, for example] while a simple light bulb does not care.

    Also, not specified is the output waveform -- is it square wave AC, modified sine or pure sine wave?
    Sine wave output is very difficult to achieve....but it is the most desired.

    There are many world wide research teams working on this type of goal, and usually staffed with PhD's with budgets of $150,000.

    Try looking at this link:

    Development of a New Class of Low Cost, High Frequency Link Direct DC to AC
    Converters for Solid Oxide Fuel Cells (SOFC)

    Also, INTEL, Texas Instruments,  and others have design contests and application notes which may offer designs that are acceptable to the goals of this project.  I would search under "PLC based DC-AC inverter designs" [PLC = programmable logic controller, essentially a CPU computer on a special chip allowing easy interfacing].  One page with more on PLC's is  .


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