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Half-Bridge 0-30V, 0-20A Feedback loop problem

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xavier60:

--- Quote from: paladyn on July 03, 2019, 08:57:54 am ---I will try to do some pictures today how it looks. See how the common mode choke and the rest. You write to connect the loop amplifier to pin 9 SG3525, but what to do with the SG3525 amplifier inputs? I could simply desoldute the coupler adding diodes and solder the loop amplifier to pin 9 to leave the internal SG3525 amplifier as it is today, i.e. a voltage follower (pin 9 connected to pin 1).

As for compensation according to your description, I only tried without a C1 capacitor. Do you suggest using compensation as you did in the first post? Should there be voltage feedback? Possibly, could you suggest some element values to start with for testing?

My loop is adapted to 3V voltage.

--- End quote ---
I didn't fully understand what you said about the SG3525 amplifier, My suggestion about driving pin 9 directly is likely a waste of time and voltage clamping is required to prevent it going above 5V. The internal error amp can source/sink only 100µA.
Do bridge out D8 though.
Yes, use the compensation as I describe earlier. Voltage feedback is still required.
Did you ever try someone else's suggestion of running the power supply in open loop by applying a fixed voltage to pin 9?
The idea is to find stable state to work from.
Actually I would prefer that the internal amplifier only to be used with the simple compensation.

paladyn:
When writing about the internal amplifier, I thought of pin 1 and pin 2 of the SG3525 chip.
I've done a little bit already, so I'll try to make a summary.

1. Unsolder diode D8 and diode D9. The output of the TL3474CDR amplifier of the voltage loop (pin 7 in the diagram) should be connected to the pin 9 of the SG3525 system. After this procedure pin 2 SG3525 have a pull-up to Vref, pin 1 hangs in the air.

2. Unsolder C1 and R1

Can I run a test on such a configuration as above or change something?

xavier60:

--- Quote from: paladyn on July 03, 2019, 10:23:48 am ---When writing about the internal amplifier, I thought of pin 1 and pin 2 of the SG3525 chip.
I've done a little bit already, so I'll try to make a summary.

1. Unsolder diode D8 and diode D9. The output of the TL3474CDR amplifier of the voltage loop (pin 7 in the diagram) should be connected to the pin 9 of the SG3525 system. After this procedure pin 2 SG3525 have a pull-up to Vref, pin 1 hangs in the air.

2. Unsolder C1 and R1

Can I run a test on such a configuration as above or change something?

--- End quote ---
Pin 1,2 of the SG3525 can be left floating or connected to something. The main thing is to put a zener diode between pin 9 and ground so that it can't go above 5V.
You can then test, If the result is still poor, try changing R9, C8 to 5.6K,1uF.

paladyn:
Yesterday I did not have much time to test, but I changed the control loops as we agreed. The omission of the diode D8, D9 and the internal amplifier SG3525 (pins 1 and 2) did not give much. Loop configuration with 5.6k and 1uF I have not tested enough time.
I did a test where C8 is 27nF and R9 is an adjustable 500k resistor and I noticed a certain dependence. Noise occurs anyhow in the entire adjustment range, but the inverter in most cases works quietly above the load of 10A up to 20A. When the load is eg 5A and I tried to adjust the loops with the potentiometer, the converter works relatively quietly when the noise shape is sinusoidal, when the sinusoid disappears and the noise has a shape similar to the straight line the transformer begins to squeak.

I tried to see what the case with an additional 4000uF capacitor set and the CMC filter on the output is a little better than without it, but if I tried to wind the Umes measurement cable on the same CMC choke as the inverter output I can not stabilize the loop anymore. Similarly, if I use some other choke, e.g. on a yellow core, and make a few loops.

I will try to take pictures of the inverter today and carry out further tests.

paladyn:
After a long break, I put pictures of the inverter.

I tested feedback where the output of the TL3474CDR operational amplifier is connected to pin 9 of the SG3525, and the pins of its amplifier are not connected. No positive results.
However, I was able to determine that when the operational amplifier SG3525 works as a voltage follower, the noise generated at the output is noticeably higher. When I am connected directly to pin 9, COMP is much better even when using two couplings as at the very beginning of our discussion.

After combining with the 250uH reactor I returned to the 47uH choke and again I used a type 3 compensator. However, this time I tried the brutal-force method and instead of the R1 and R9 resistors soldered the 10k and 500k potentiometers.

I observed that it is not possible to set the coupling correctly. When the loop is too fast you can see distortions of the waveform at high currents, a waveform similar to a one-wave rectifier, maybe the 47uH choke, but with a slower loop, a sawtooth shape is also obtained with a large amplitude. At low currents the squeaking occurs on the fast loop and on the slow loop.

Somewhere, I read that it is impossible to design loops for every load. I wonder if I should replace the analog loop and just do a simple PID on the STM32 without any coefficients etc.

Due to the fact that the photos are large, I will post them in several posts.

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