Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1254
| Posted: 03:51am 21 May 2021 |
Hi Nicks, my start up scheme currently just uses a small toggle switch. My method might not suit you at all, but perhaps it might so here goes.
I use a 24V KiloVac relay (solenoid?) rated at 900V 500ADC for applying full current to the inverter power section, I paid $AUD ~ $111 most other Kilovac types are $200+ but the 24V one is a good price, They come from Digikey - I see the price is now AUD$139 and they are waiting on overdue stock . My inverter also has an 80A breaker from the batteries which is typically left on.
When I turn the Inverter small toggle switch on, it applies 48V to the DC/DC converters for 12 & 5V for uC power etc. It also applies the 48V to a resistor in series with the Main inverter power board capacitors, the inverter soft start is inhibited for now.
The circuitry now waits until the Vcaps on the power board are >95% of the input voltage (48V/50V whatever). When this threshold is reached the solenoid is commanded to pull in and the Inverter (soft start) is commanded to run
The Kilovac is now driven by 2 sequential duty cycle trains which causes an average of 24V for pull in and then after a short delay (<500mSecs) reduces to ~7V for hold in.
There are a few minor tricks to make it shut down nicely, but the short version is; turn off the small toggle switch, this triggers input VLow to be sensed which commands stop the inverter (soft stop), at the end of soft stop the solenoid is commanded to open and the inverter is now totally galvanically isolated from the battery supply.
You can even leave the small toggle switch in the start/Run position and then close the 80A breaker. No splat or bang just a repeat of the above sequence, I haven't tried turning it off the same way, I prefer to just turn the small toggle to off and take advantage of the soft stop.
I am reliant on Poidas help for a couple of software tweaks to make this all work nicely, but the same software should be able to be used without the Kilovac and using the old precharge approach.
My Nano Pico version will have 3 sets of full bridge power drives and I intend it to have 3,6 & 9KW flavours but requiring a separate choke for each 3kW stage. I am designing my Power stage to be a 100mm x 100mm 1oz copper 1/2 bridge board with 3 high and 3 low side FETs of which I believe only 4 FETs total should be needed for 3kW.
The Power drive scheme is the inverse connected opto LED drive that ensures no cross conduction can occur, followed by a buffered output . Note I currently use this method and on my power board easily achieve 5+kW with just 4 Fets per leg. Scalability for HF inverters has always been difficult/too hard, I hope to make it a relatively straight forward task with this topology.
I am also opting for a small 2mA to 2mA output voltage sense transformer on my version of a nano pico and an over current, adjustable setting, latched stop.
The reason for posting this is not as a boast but because some of these are current point of interest. If anyone has a wish list not covered here I am happy to receive input but can't guarantee it will sway my direction. I am also happy to share any files PDFs Gerbers etc I create with whoever wants to have a play too.
Incidentally I forgot to add that it will be an all through hole design.
Edited 2021-05-21 15:16 by wiseguy