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Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
Hello. I am looking for a circuit that would allow me to take 170VDC (rectified 120VAC or DC from solar panels) and convert it to 120VAC Sine Wave.
I may need frequencies that are slightly greater or lower than 60Hz. I may also need frequencies around 10KHz. Power of about 1000Watts
What circuit would you recommend? A combination of 555 timer and a full bridge rectifier comes to my mind. However I am not educated enough to design one myself.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
The simplest approach would be to buy a VFD, e.g. for uk 50 Hz; although 400 Hz is maximum sinewave frequency Different models are available for 50/60 Hz, 1/3 phase, 115/230/380.... Vac input and different output powers.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
I'm not sure you can get single phase VFDs. Single phase motors don't tend to work well when used outside their intended operating frequencies.
You might be able to get by on a three phase one, although it will probably be very unhappy at the current imbalance. I have the drive in Sulaiman's link, and it's cheap and cheerful. The only problem is that under sudden heavy currents it tends to shut down with a short circuit protection trip. My solution was the remove the little blue potentiometer responsible (buried deep in the drive) and move it to the outside so the current trip could be adjusted.
By modifying the connections to the current transformers you might be able to get to run happily with a single phase load.
Edit: When it says single phase it means single phase input, not output.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
hen918 in your drive, how many current sensors are there, and where are they ?
If, as I suspect, these cheap models only monitor dc-link current, then single phase output should be no problem at all. Many drives that do monitor output current only operate as current-limiters, so also can be used un-modified of course many drives do much more with the current sense signals.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
The CTs are on the outputs to the motor, but there are only two of them, so it might be all right going between the outer two phases with the CTs, although the current monitoring will be all wrong.
You can see the CTs on this video: But this version doesn't have an over current trip adjust pot next to the CTs. (the SOIC-14 packaged device next to them is a quad comparator chip that triggers an short circuit signal to the uC) There must also be a current sense input to the uC, as the comparator is only for fast reacting overcurrent protection, an ADC gives the uC a current reading to display on screen.
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170VDC multivibrator ~10KHz
