VFD and HPWM

[shawn]

Hello,
Ok here we go. I have come across a bunch of Baldor VFD Inverters. On most of them, the switch mode power supply is burnt up. I would like to build my own drive baseing it around the mosfet power chip on them. The Drive input will be 230v Single Phase and the output will be 0 to 230 vAC Single or Three Phase. I've got my head around most the circiut side but I need to come up with a solution to the PWM part. I would realy like to use a PIC. My questions are.

1) I read somewhere that PBP 2.50 will allow you to use 4 HPWM lines at the same time. Is that correct? I think I need 3 HPWM lines for my project.
2) The drive I am going to make will be a 3 phase VFD. So some how I need to get the 3 HPWM signles 120 degrees out of phase. Is that possible.
3) I have PBP 2.46 is there away to legaly and moraly make that run 3 HPWM lines at the same time without buying PBP 2.5? Is there a free update to for that issue?
4) I've seached the forum for hours now it seems and I have not been able to find anyone who has built a Variable Frequency Drive (VFD). Can anyone point me to a thread if I have missed it.

The 2 main chips that I am going to use to generate the 3 Phase is the IRPT3054 and the IR2233.

Thanks
Shawn

[HenrikOlsson]

Hi,
You can get any PIC with enough PWM-channels to output the required PWM, you may just have to set the registers "manually" instead of using the HPWM command.

Have a look at the 18F2431 for example, it's designed for motor control applications, has 3 complementary pairs of PWM output (one pair per half bridge) with 14bit resolution, quadrature encoder counter module, high speed ADC with 2 channel simultaneous sampling and more.

If you just want to spin the motor it may very well be doable but the more advanced stuff like flux/vector control, slip compensation etc is probably too much for this PIC, a dsPIC would probably be a better choise in that case but then you can't use PBP.


You can upgrade your 2.46 to 2.50 by contacting your dealer or Melabs directly, the cost is $25, I believe (including new manual).

[shawn]

Chip I am using is the 18LF6722, the data sheet says it has 3 ECCP pins. Using pbp 2.46 is it possible to run 3 seperate HPWM pins. I assume that the frequency has to be the same for all three, but that is ok.

I read in a post that pbp 2.50 allows up to 4 HPWM channels but I can not found how many channels pbp 2.46 allows. I only need three so if pbp 2.46 allows three I do not want to buy pbp 2.5. I can't find a sales reciept although I think I bought pbp 2.46 directly from the melab site. If PBP 2.46 allows 3 HPWM channels I have yet to figure out how to access the third. Can someone help please.

[Charles Linquis]

The PBP HPWM command is very limiting, so I have never used it, although I use th HPWM features extensively.

You can use all the channels your chip has by directly writing to the CCPx registers. *ANY* version of PBP will work.

The part where most people get messed up is that you have to write bit 0 of the PWM value to CCPxCON.4 and bit 1 to CCPxCON5. The
rest of the value (shift the value right two places) goes to CCPRxL.