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 scaled
appropriately 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): schematic
Generator 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.