Build Log: Servo Drive and VFD with vector control

[Jonathan]

I seem to have made some progress:



So need to buy VFDs from China now. I was intending to split the design into a logic board and power board, but realised that realistically it's going to be a some time until I have time to complete that design, so instead I made a few improvements to the previous PCB and got a heap of them made.

I've worked a bit on the code too - it can now drive motors with hall sensors. I'm using the sensors to generate a position reference field oriented (vector) control, so it's smoother than the generic method of just switching on hall signal transitions. I'll take a video soon, but for now here's a picture:



With the previous design and more-so with this one, I've made is so spare I/O and signals are available on headers, so I can make 'expansion boards'. Here's one to add a 4th output to enable controlling stepper motors:



Now I've actually thought about it, I'm pretty confident you can control a stepper motor properly with a 3-phase inverter, so I might instead use this board to do power factor correction or just an isolated buck converter to eliminate the need for a transformer when using low voltages. If you connect the two phases of a stepper motor together, then connect the center point and two ends to the 3-phase inverter, you can still apply bipolar voltages to each.

I also mounted a 12-bit encoder on a 3Nm stepper motor yesterday, so I'm planning to use that to implement sensored vector control, rather like the Leadshine closed loop version ... but open source and cheap. There's plenty of information on how to do it, such as this, so I'll try it and see. That paper makes it look straightforward ... watch this space.