Wayne,
It's for product development. We have a 60Hz product and want to manufacture a product for parts of the world that use 50Hz.
That's one of the things that's most interesting about PV -- all the different systems in use out there. For example, Mexico is mostly 127/240 Wye, as I understand it. Any country that's small (and doesn't get along with its neighbors ...) or is an island has unstable voltage and frequency.
Your suggestion that the power be converted on a DC bus is what I'd suggested -- some vendors inverters can be AC coupled (one inverter backfeeding the output of another) and that can be used for frequency or voltage conversion. Stick batteries in the middle and DC output of one AC coupled inverter can be DC coupled to another with a completely different frequency system.
Actually it's 127/220 volt wye 240 volt line to line on a wye would produce a 138.6 volt neutral voltage as found on some generator configurations.
I'm a little confused? are you saying that you can feed from one inverter into another inverter then DC coupled to another to get a different frequency? how does a inverter that is outputing AC output DC?
The way I was thinking is that the PV cells produce DC, this then charges batteries that become the DC buss, from this DC buss we take DC power to feed inverters at which frequency we need such as 50hz.
At work we have trains and cranes that run on 250 volt DC, we have inverters that take this 250 volts DC and change it to 120/240 volts AC 60hz for different electronics that are used on them.
I wonder if any inverter manufacture could design an inverter that could be switched between 50hz and 60hz and the output voltage readjusted for different voltages, kind of a one size fits all inverter? I could not see it being hard to do as the voltage output is adjustable on most inverters and the frequency is fairly easy to change depending upon the design of the oscillator circuit?
As far as the unstable voltages and frequency on these remote parts of the world, you already have one of the things that will stabilize them and thats DC, convert the incomming power to DC to charge the batteries, then create a DC buss then design a PV system to recharge this DC buss then re create the AC through the inverters, Dual conversion UPS systems already do this as does VFD drives, the problem is going to be able to design a inverter that can stay in sync with the incomming supply to always be putting kws back into the grid if the frequancy is not stable, it would require a frequency regulation system that can respond fast enough to keep the inverters output always leading the grids frequency with regulation that also monitors the amount of current it is trying to upload.
The problem with the above is going to be that when the grid frequency varies so will your inverters output so the only way around this would be to use two inverter systems and let a main inverter take care of the main loads then use a special inverter to take care of the back feeding into the grid this way the two are isolated like any dual conversion UPS, no matter which way you look at it, the inverter tied to the grid will always have to follow the frequancy of the grid.
We are not used to dealing with this type of problem as we are so very acustom to having a stable grid but I can envision the problems when we don't have it, and some examples are UPS systems running off generators that have speed regulation problems that can cause the UPS to trip out on out of sync issues.
With our stable grid when we load our service down it only cause a voltage drop problem but if we are running on a generator it causes the engine to slow down causing the frequency to change at least till it speeds back up to catch up to the load so a test using a generator can be good to test whether a inverter can follow the changes in frequency when it is loaded if you can get a inverter designed to follow the frequancy and keep it leading the supply frequancy.