UPS Design - Page 1
Forum section: electronics / projects

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: October 20, 2014, 09:56:13 am
content: Hi everyone,Well am designing a UPS ( 200W , powered from 12V battery , under normal load (100W) it should run for 100h ) and am facing two choices , first design that include DC/DC boost than H-Bridge to get sin signal. A second design, H-Bridge to get sin signal and a 50Hz transformer that will step up 12VAC to 230VAC. And am not sure which road i take.Second point , the H-Bridge driver , i saw this chip SM72295 from Texas instrument, i think it's perfect for the task, any experience with this device or any suggestion.Thanks

author: Phoenix
author_rank: Frequent Contributor
timestamp: October 20, 2014, 10:31:48 am
content: Quote from: hamdi.tn on October 20, 2014, 09:56:13 amYou're a few steps away from selecting this yet IMO.In a high level sense, the order I'd tackle this is:First would be to get the topology down pat, and understand what voltage and current levels will be present. Then you'll also want to consider what control algorithms (modulation, voltage/current feedback) you will use. This can all be done in simulation (provided you have appropriate software, PSpice sucks for power electronics in my experience) and requires no parts. This will also give you an idea of size requirements of passives and switching frequencies, controller response times etc.Second would come critical component selection. Probably the most critical would be the switching devices, as these (together with topology) will then dictate the gate drive requirement. Also the controller ICs and/or microcontroller would be quite important. This is where I'd start considering safety and EMI aspects too.Third would come a detailed design/schematic and detailed component selection.

author: Richard Head
author_rank: Frequent Contributor
timestamp: October 20, 2014, 11:21:53 am
content: All power processing should be done at high frequency (50-200Khz) to minimise the magnetics volume. That means synthesizing the sinewave using PWM at say 100kHz. Then filter out the high frequency 100kHz signal leaving the 50Hz component. This approach yields the smallest magnetics and generally lowest cost also.

author: Circlotron
author_rank: Super Contributor
timestamp: October 20, 2014, 11:45:20 am
content: Is this UPS for a known load or just general purpose? If it is for a known switchmode load you don't necessarily need a H-bridge; just feed high voltage DC straight into the SMPS.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: October 20, 2014, 12:39:39 pm
content: Quote from: Phoenix on October 20, 2014, 10:31:48 amYou absolutely right, i never did a serious power design ,so no practical knowledge , i only kind of have an idea how it suppose to work ,so am a bit lost in the details.Quote from: Richard Head on October 20, 2014, 11:21:53 amSureQuote from: Circlotron on October 20, 2014, 11:45:20 ama known load, a switchmode load and an AC motor.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 20, 2014, 03:19:35 pm
content: A 400W or so inverter is very cheap and there's little reason to build your own. Then use a modified ATX PSU to maintain a float voltage on the battery bank. For a little more efficiency, you can add a bypass relay.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: October 20, 2014, 03:47:16 pm
content: Quote from: NiHaoMike on October 20, 2014, 03:19:35 pmTotal agree, am not doing it for funclient request to be integrated in a custom system