Sine wave generator - problem - Page 1
Forum section: electronics / beginners

author: Matthew266
author_rank: Newbie
timestamp: July 05, 2022, 06:41:48 pm
content: Hello,I'm trying to make sine wave generator for an older VFD which requires 2 sine waves with a 120' phase shift to work properly. I tested the VFD with a commercial function generator and it's in working condition. I then designed my of PCB and tried using that, but unfortunetly it doesn't seem to work. I use a STMF103 to generate a PWM output whitch is then smoothed by a RC low pass filter, and scaledappropriately by a amplifier in the range of V_MOTOR+, V_MOTOR-.The commercial unit is a NIU fy3200s.Here is the schematic of my circuit (in attachment): schematicGenerator output shows the output of my circuit, and comparison the commercial one and mine.I tried to compare the 2 PCB's but the only difference that i could easly find was that the bought one had 50 Ohm output resistors (2x 100 Ohm in parallel). I tried adding them too but it didnt't change anything. i tried also swapping the phase shift , and changing them to 240' but that didnt work either.The schematic of the vfd is in the attachements. I attach my sine waves to pins 8,10 and the GND to 7,9 on page 3.If anybody has any suggestions what could be the problem I would highly appreciate it.

author: Benta
author_rank: Super Contributor
timestamp: July 05, 2022, 07:12:27 pm
content: Why does your "comparison" file show three sine waves?

author: Matthew266
author_rank: Newbie
timestamp: July 05, 2022, 07:44:40 pm
content: If You look closely there are 4 but the osciloscope uses 2 similar colors for channel 2 and 4 so it's a bit hard to see.In the attachment You can see where the signals from the 2 channels meet.(edit) The signals from the two different generators have also different Vpp because in My version I implemented a U/f (voltage/ frequency) characteristic for the motor. While testing with the commercial function generator I used a potentiometer to adjust the voltage.

author: Benta
author_rank: Super Contributor
timestamp: July 05, 2022, 08:20:22 pm
content: OK, so why are you generating/showingfoursinewaves when your drive only needs two?You've lost me completely.

author: Matthew266
author_rank: Newbie
timestamp: July 05, 2022, 08:28:52 pm
content: I added this so maybe someone spots some differences in the outputs of these two which I haven't noticed, and to show that the output of my version really is a sine wave.

author: Benta
author_rank: Super Contributor
timestamp: July 05, 2022, 08:31:42 pm
content: Well, your trace #1 and #2 seem to be 120 degrees apart. Everything fine, no? No idea what you want with #3 and #4.

author: Matthew266
author_rank: Newbie
timestamp: July 05, 2022, 08:43:42 pm
content: Yes they are, as well as trace #3, #4, so why is it that when i use My version ( traces #1, #2 ) the VFD isn't working, and when I use the commercial generator (traces #3, #4) it works.

author: WatchfulEye
author_rank: Regular Contributor
timestamp: July 05, 2022, 11:27:39 pm
content: Why is the amplitude of waveform 2 is much smaller than waveform 3 and 4? The scale for waveform 2 is labelled as 200 mV/div, but 3 & 4 are labelled 2 V/div

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 06, 2022, 02:24:42 am
content: Also first picture has 3 and 4 at a different voltage also.Jeff

author: Matthew266
author_rank: Newbie
timestamp: July 06, 2022, 02:19:55 pm
content: Quote from: WatchfulEye on July 05, 2022, 11:27:39 pmAs qouted, I implemented a U/f characteristic here and thats why they have different scales.Quote from: Matthew266 on July 05, 2022, 07:44:40 pm

author: Matthew266
author_rank: Newbie
timestamp: July 06, 2022, 02:24:49 pm
content: Quote from: Jeff eelcr on July 06, 2022, 02:24:42 amIf You referring to the picture with only the 2 traces, they weren't used as You can see in the picture.

author: jwet
author_rank: Frequent Contributor
timestamp: July 06, 2022, 02:32:05 pm
content: Can you remove your V/F correction, its in software, correct? This has to be the problem. Your signals look great but the fact that the amplitudes are out of whack is the only difference that I can see.

author: Matthew266
author_rank: Newbie
timestamp: July 06, 2022, 03:16:11 pm
content: Yes it's in software so I could but it doesn't work even without, and also I has to be implemented so the motor doesnt stall, and if I would set a voltage to high it would fry the motor. And as I said before:Quote from: Matthew266 on July 05, 2022, 07:44:40 pmso I dont think it because of the characteristic. Also the characteristic changes the voltage only when I change the frequency, but it doesnt even work with the default frequency that I set.