Hello. I have built a phase shifted converter based in the UCC28951 from TI, but I have problems with stability. The load has built-in capacitors and the converter oscillates wildly. I have changed the Type-II compensator to a Type-III one, but oscillations do not stop. Calculation of the Type-III compensator is based in application note SLVA662 from TI. The input voltage is 48 V, output is 311 V, nominal output power is 600 W and the output capacitance is about 2000 uF. Fsw = 100 kHz. Is this kind of converter valid at all for this output capacitance? -- Regards Miguel Gimenez
Stability of phase shifted converters
Started by ●November 28, 2023
Reply by ●November 28, 20232023-11-28
On Tue, 28 Nov 2023 14:13:25 +0100, Miguel Gimenez <me@privacy.net> wrote:>Hello. > >I have built a phase shifted converter based in the UCC28951 from TI, >but I have problems with stability. The load has built-in capacitors and >the converter oscillates wildly. I have changed the Type-II compensator >to a Type-III one, but oscillations do not stop. Calculation of the >Type-III compensator is based in application note SLVA662 from TI. > >The input voltage is 48 V, output is 311 V, nominal output power is 600 >W and the output capacitance is about 2000 uF. Fsw = 100 kHz. > >Is this kind of converter valid at all for this output capacitance?Usual method of tackling this is to overcompensate massively first, in order to troubleshoot the power train over load and line conditions. You can even run it without feedback by manually controlling the transferred phase width by overiding pin4. When all your ducks are in a row, for basic DC transfer and crude control, you can address finer points of transient reponse and compensation. RL
Reply by ●November 28, 20232023-11-28
On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez <me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>:>Hello. > >I have built a phase shifted converter based in the UCC28951 from TI, >but I have problems with stability. The load has built-in capacitors and >the converter oscillates wildly. I have changed the Type-II compensator >to a Type-III one, but oscillations do not stop. Calculation of the >Type-III compensator is based in application note SLVA662 from TI. > >The input voltage is 48 V, output is 311 V, nominal output power is 600 >W and the output capacitance is about 2000 uF. Fsw = 100 kHz. > >Is this kind of converter valid at all for this output capacitance?I maye be totally wrong here, but the guy who wrote that paper is maybe not aware you may need a differentiator in the feedback with high capacitance load All he does is basically low pass, ? This is more clear perhaps: https://www.ni.com/en/shop/labview/pid-theory-explained.html scroll down to 'Iuning' I would experiment to get it right...
Reply by ●November 28, 20232023-11-28
On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez ><me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>: > >>Hello. >> >>I have built a phase shifted converter based in the UCC28951 from TI, >>but I have problems with stability. The load has built-in capacitors and >>the converter oscillates wildly. I have changed the Type-II compensator >>to a Type-III one, but oscillations do not stop. Calculation of the >>Type-III compensator is based in application note SLVA662 from TI. >> >>The input voltage is 48 V, output is 311 V, nominal output power is 600 >>W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >> >>Is this kind of converter valid at all for this output capacitance? > >I maye be totally wrong here, but the guy who wrote that paper is maybe not >aware you may need a differentiator in the feedback with high capacitance load >All he does is basically low pass, >? > >This is more clear perhaps: > https://www.ni.com/en/shop/labview/pid-theory-explained.html > scroll down to 'Iuning' > >I would experiment to get it right...Or Spice it. Usually just a pole-zero is all you need in the control loop. Output cap ESR can help there. My latest trick is to take the AC feedback from the raw switch node and DC from the final, filtered output. This is for a power supply that might drive weird, unknown customer loads where we have no control of the loop dynamics if we take our feedback from the output.
Reply by ●November 28, 20232023-11-28
On Tuesday, November 28, 2023 at 12:10:37 PM UTC-5, John Larkin wrote:> On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <al...@comet.invalid> > wrote: > >On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez > ><m...@privacy.net> wrote in <uk4p1p$9fur$1...@dont-email.me>: > > > >>Hello. > >> > >>I have built a phase shifted converter based in the UCC28951 from TI, > >>but I have problems with stability. The load has built-in capacitors and > >>the converter oscillates wildly. I have changed the Type-II compensator > >>to a Type-III one, but oscillations do not stop. Calculation of the > >>Type-III compensator is based in application note SLVA662 from TI. > >> > >>The input voltage is 48 V, output is 311 V, nominal output power is 600 > >>W and the output capacitance is about 2000 uF. Fsw = 100 kHz. > >> > >>Is this kind of converter valid at all for this output capacitance? > > > >I maye be totally wrong here, but the guy who wrote that paper is maybe not > >aware you may need a differentiator in the feedback with high capacitance load > >All he does is basically low pass, > >? > > > >This is more clear perhaps: > > https://www.ni.com/en/shop/labview/pid-theory-explained.html > > scroll down to 'Iuning' > > > >I would experiment to get it right... > Or Spice it. > > Usually just a pole-zero is all you need in the control loop. Output > cap ESR can help there. > > My latest trick is to take the AC feedback from the raw switch node > and DC from the final, filtered output. This is for a power supply > that might drive weird, unknown customer loads where we have no > control of the loop dynamics if we take our feedback from the output.You take DC from the final filtered output AND then find you have no control of loop dynamics if you take your feedback from the output. How exactly does that work?
Reply by ●November 28, 20232023-11-28
On 2023-11-28 12:09, John Larkin wrote:> On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <alien@comet.invalid> > wrote: > >> On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez >> <me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>: >> >>> Hello. >>> >>> I have built a phase shifted converter based in the UCC28951 from TI, >>> but I have problems with stability. The load has built-in capacitors and >>> the converter oscillates wildly. I have changed the Type-II compensator >>> to a Type-III one, but oscillations do not stop. Calculation of the >>> Type-III compensator is based in application note SLVA662 from TI. >>> >>> The input voltage is 48 V, output is 311 V, nominal output power is 600 >>> W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >>> >>> Is this kind of converter valid at all for this output capacitance? >> >> I maye be totally wrong here, but the guy who wrote that paper is maybe not >> aware you may need a differentiator in the feedback with high capacitance load >> All he does is basically low pass, >> ? >> >> This is more clear perhaps: >> https://www.ni.com/en/shop/labview/pid-theory-explained.html >> scroll down to 'Iuning' >> >> I would experiment to get it right... > > Or Spice it. > > Usually just a pole-zero is all you need in the control loop. Output > cap ESR can help there. > > My latest trick is to take the AC feedback from the raw switch node > and DC from the final, filtered output. This is for a power supply > that might drive weird, unknown customer loads where we have no > control of the loop dynamics if we take our feedback from the output. >If you put a buffer on the DC to prevent kickout, you can sneak a cap multiplier inside that loop too. Good Medicine for many things. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●November 28, 20232023-11-28
On Tue, 28 Nov 2023 15:09:07 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2023-11-28 12:09, John Larkin wrote: >> On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <alien@comet.invalid> >> wrote: >> >>> On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez >>> <me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>: >>> >>>> Hello. >>>> >>>> I have built a phase shifted converter based in the UCC28951 from TI, >>>> but I have problems with stability. The load has built-in capacitors and >>>> the converter oscillates wildly. I have changed the Type-II compensator >>>> to a Type-III one, but oscillations do not stop. Calculation of the >>>> Type-III compensator is based in application note SLVA662 from TI. >>>> >>>> The input voltage is 48 V, output is 311 V, nominal output power is 600 >>>> W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >>>> >>>> Is this kind of converter valid at all for this output capacitance? >>> >>> I maye be totally wrong here, but the guy who wrote that paper is maybe not >>> aware you may need a differentiator in the feedback with high capacitance load >>> All he does is basically low pass, >>> ? >>> >>> This is more clear perhaps: >>> https://www.ni.com/en/shop/labview/pid-theory-explained.html >>> scroll down to 'Iuning' >>> >>> I would experiment to get it right... >> >> Or Spice it. >> >> Usually just a pole-zero is all you need in the control loop. Output >> cap ESR can help there. >> >> My latest trick is to take the AC feedback from the raw switch node >> and DC from the final, filtered output. This is for a power supply >> that might drive weird, unknown customer loads where we have no >> control of the loop dynamics if we take our feedback from the output. >> > >If you put a buffer on the DC to prevent kickout, you can sneak a cap >multiplier inside that loop too. Good Medicine for many things. > >Cheers > >Phil HobbsWe're lately doing power supplies and dummy loads for aircraft systems testing, which is high power but rude and crude stuff. Our world is plenty noisy. One of my units is a 3-phase AC source that the customer regulates by PWM shorting it. Envision some really ugly waveforms.
Reply by ●November 28, 20232023-11-28
On Tue, 28 Nov 2023 10:47:04 -0800 (PST), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Tuesday, November 28, 2023 at 12:10:37?PM UTC-5, John Larkin wrote: >> On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <al...@comet.invalid> >> wrote: >> >On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez >> ><m...@privacy.net> wrote in <uk4p1p$9fur$1...@dont-email.me>: >> > >> >>Hello. >> >> >> >>I have built a phase shifted converter based in the UCC28951 from TI, >> >>but I have problems with stability. The load has built-in capacitors and >> >>the converter oscillates wildly. I have changed the Type-II compensator >> >>to a Type-III one, but oscillations do not stop. Calculation of the >> >>Type-III compensator is based in application note SLVA662 from TI. >> >> >> >>The input voltage is 48 V, output is 311 V, nominal output power is 600 >> >>W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >> >> >> >>Is this kind of converter valid at all for this output capacitance? >> > >> >I maye be totally wrong here, but the guy who wrote that paper is maybe not >> >aware you may need a differentiator in the feedback with high capacitance load >> >All he does is basically low pass, >> >? >> > >> >This is more clear perhaps: >> > https://www.ni.com/en/shop/labview/pid-theory-explained.html >> > scroll down to 'Iuning' >> > >> >I would experiment to get it right... >> Or Spice it. >> >> Usually just a pole-zero is all you need in the control loop. Output >> cap ESR can help there. >> >> My latest trick is to take the AC feedback from the raw switch node >> and DC from the final, filtered output. This is for a power supply >> that might drive weird, unknown customer loads where we have no >> control of the loop dynamics if we take our feedback from the output. > >You take DC from the final filtered output AND then find you have no control of loop dynamics if you take your feedback from the output. How exactly does that work?I don't understand your question. My problem is that the customer could load my supply with a giant solenoid, or a motor, or a huge capacitor, or a battery, or a negative-impedance switcher, all of which change loop dynamics if I sense (or worse, remote sense) from my output.
Reply by ●November 29, 20232023-11-29
On a sunny day (Tue, 28 Nov 2023 09:09:44 -0800) it happened John Larkin <jl@997PotHill.com> wrote in <bd7cmi1iaui01tmdti32c7bi71u41rtjmk@4ax.com>:>On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <alien@comet.invalid> >wrote: > >>On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez >><me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>: >> >>>Hello. >>> >>>I have built a phase shifted converter based in the UCC28951 from TI, >>>but I have problems with stability. The load has built-in capacitors and >>>the converter oscillates wildly. I have changed the Type-II compensator >>>to a Type-III one, but oscillations do not stop. Calculation of the >>>Type-III compensator is based in application note SLVA662 from TI. >>> >>>The input voltage is 48 V, output is 311 V, nominal output power is 600 >>>W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >>> >>>Is this kind of converter valid at all for this output capacitance? >> >>I maye be totally wrong here, but the guy who wrote that paper is maybe not >>aware you may need a differentiator in the feedback with high capacitance load >>All he does is basically low pass, >>? >> >>This is more clear perhaps: >> https://www.ni.com/en/shop/labview/pid-theory-explained.html >> scroll down to 'Iuning' >> >>I would experiment to get it right... > >Or Spice it. > >Usually just a pole-zero is all you need in the control loop. Output >cap ESR can help there. > >My latest trick is to take the AC feedback from the raw switch node >and DC from the final, filtered output. This is for a power supply >that might drive weird, unknown customer loads where we have no >control of the loop dynamics if we take our feedback from the output.Nice idea!
Reply by ●November 29, 20232023-11-29
On Wed, 29 Nov 2023 05:49:47 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Tue, 28 Nov 2023 09:09:44 -0800) it happened John Larkin ><jl@997PotHill.com> wrote in <bd7cmi1iaui01tmdti32c7bi71u41rtjmk@4ax.com>: > >>On Tue, 28 Nov 2023 16:08:32 GMT, Jan Panteltje <alien@comet.invalid> >>wrote: >> >>>On a sunny day (Tue, 28 Nov 2023 14:13:25 +0100) it happened Miguel Gimenez >>><me@privacy.net> wrote in <uk4p1p$9fur$1@dont-email.me>: >>> >>>>Hello. >>>> >>>>I have built a phase shifted converter based in the UCC28951 from TI, >>>>but I have problems with stability. The load has built-in capacitors and >>>>the converter oscillates wildly. I have changed the Type-II compensator >>>>to a Type-III one, but oscillations do not stop. Calculation of the >>>>Type-III compensator is based in application note SLVA662 from TI. >>>> >>>>The input voltage is 48 V, output is 311 V, nominal output power is 600 >>>>W and the output capacitance is about 2000 uF. Fsw = 100 kHz. >>>> >>>>Is this kind of converter valid at all for this output capacitance? >>> >>>I maye be totally wrong here, but the guy who wrote that paper is maybe not >>>aware you may need a differentiator in the feedback with high capacitance load >>>All he does is basically low pass, >>>? >>> >>>This is more clear perhaps: >>> https://www.ni.com/en/shop/labview/pid-theory-explained.html >>> scroll down to 'Iuning' >>> >>>I would experiment to get it right... >> >>Or Spice it. >> >>Usually just a pole-zero is all you need in the control loop. Output >>cap ESR can help there. >> >>My latest trick is to take the AC feedback from the raw switch node >>and DC from the final, filtered output. This is for a power supply >>that might drive weird, unknown customer loads where we have no >>control of the loop dynamics if we take our feedback from the output. > >Nice idea!Here's the idea. FB is a combination of a sorta fast (lowpass filtered a bit) path from the switch node, blended with slow feedback from the final output. Seems to work. https://www.dropbox.com/scl/fi/pgw70e2ls16i66pj0hl5b/P943_Loop_1.jpg?rlkey=hc1ske5u41ylhfnazuj4t27k5&raw=1 The transfer function of the switcher path into the FB network is basically 48, which is easy to close a loop aound. In real life, the control loop will be in an FPGA. I'd keep the R4 etc parts but FB will drive an ADC that makes the PWM signals into the fet driver. I like to Spice a system mostly analog, and hand it over to the FPGA kids to implement.
