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Forum Index : Solar : PV Charge Controller for 100v Battery Bank Designs

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Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 655
Posted: 02:05am 17 Jul 2020
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Here is the final schematic for the 100 Khz (or higher) buck converter driver.

TL598 switch mode PSU chip manages the switching at whatever frequency has been set by its RC timing components. Its dead-time control input voltage is set by the cpu control low frequency pwm signal; the dead-time input overrides the internal comparators and allows external control of the output pwm to the mosfet driver.

The controlling cpu generates a 1 Khz pwm signal that is averaged by a low pass Bessel filter, 0v out = 100% dead-time (no pwm), 3.4v out = full output from the PSU chip.

The various voltage and current sense inputs connect to the existing outputs from the main power board; how well this scheme will work is unknown, I may require some frequency compensation in the voltage sense inputs, will find out once its built up.





cheers
Mike
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3324
Posted: 04:50am 17 Jul 2020
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I have tried something similar in the past, but I used a D/A converter to adjust the high frequency pwm duty cycle. It worked very well.
Cheers, Tony.
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 655
Posted: 08:28am 17 Jul 2020
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Yes a D/A chip  would be a good idea also, one that used a I2C interface to set the output analog voltage perhaps. This circuit used as I already have all components on hand; will look online an see what modern D/A chips are available, possibly a digital pot chip would also work if they have enough resolution bits.

Perhaps I need to expand my programming knowledge a bit and go to a faster 32bit cpu, to achieve fast high resolution pwm and avoid these hacks.


Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 655
Posted: 11:34am 17 Jul 2020
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Looked online, there are numerous D/A devices...

The MC4921, 12 bit with SPI serial interface seems quite easy to use, its data sheet is readily understandable with 2 minutes reading.
Another variant with an I2C, 12 bit is the MC4726, I guess after 2 hours careful reading and lots of stuffing around one could get it to work, seems overly complicated.

Have ordered a couple of the SPI versions to have a play with, these would have a much faster update speed over the I2C and seem better suited to my application. Will do a pcb that plugs onto the CPU control ribbon cable for the existing schematic, and then modify it for the SPI device on the same layout, so can experiment with both.

Edit:
PCB for above design, 57 x 63mm: Most components bottom mounted, as board flips over, top of controller.







Mike
Edited 2020-07-18 10:47 by Solar Mike
 
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