Re: [pvusers] RE:Question on inverting DC to AC

["Scott Willing" <willing@mb.sympatico.ca>]

On 7 Sep 2002 at 16:39, Robert Warren wrote:

> Chris,
> 
>  If you were building an inverter (and I know you aren't from the
>  question you asked), then it is no big deal to step up the DC voltage
>  with a bridge rectifier/capacitor circuit:

[Nitpick warning]

You'll need more than a bridge and a cap to boost a DC voltage.

Where

Vi = DC input voltage
Vo = DC output voltage
Vd = diode forward voltage drop

|Vo| = |Vi| - 2Vd

In other words, the magnitude of the output voltage will be the 
magnitude of the input voltage minus the drop across two diodes.

> a lot of inverter
>  manufacturers have entirely gotten away from using big transformers.

True, and FWIW there are two common circuit topologies: 

1. non-isolated DC/DC step-up converter feeds inverter, or
2. isolated (i.e. transformer-coupled) DC/DC step-up converter feeds 
inverter. 

In the second case, high switching frequency permits relatively small 
transformer, compared to one of equivalent power handling that must 
operate at line frequency.

The former topology is common for inverters that are primarily 
designed for temporary / occasional use; these are usually equipped 
with a cigarette lighter plug. With this non-isolated topology, it is 
not possible for both the negative DC input terminal and the 
"neutral" AC output terminal to be grounded. This rules out the first 
topology for permanent installations -- assuming you want to play by 
the rules.

** This unsolicitied lecture brought to you by fair trade coffee. **

[balance of useful comments snipped for bandwidth]

-=s

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