Fancy VFD speed control (non-RS485)

[guru_florida]

I have an AskPower VFD in -sheeps clothing- that doesnt support RS485. Hunyang model# on the unit enclosure does but it is definitely an AskPower A131 inside. I made a 10v analog-out using PWM output and opto-isolator to dual op-amps in voltage follower config with the RC filter in between and this works but has terrible non-linearity. I am looking at my options. I could (1) just best-fit the quadratic and use a formula to compute output. I am using LinuxCNC+Mesa7i42 so not sure how to do that in hal yet but I am sure I could somehow. (2) Use an arduino and feedback the voltage back into the ADC and close the loop. (3) Use a digital pot.

I am leaning towards #2 because I like that it would generate perfect voltage reference (with the arduino & precision reference of course). #2 also means I can read the VFD analog-out that is the actual speed and I can use that to close a second loop. I can also use it to generate a FAULT signal that will stop the machine if speed stalls, and an "at speed" signal as well. Although I have no shortage of inputs with the Mesa card I would probably use the usb-serial connection on the arduino in this case and pass all the FAULT, AT-SPEED, and RPM in/out through that to LinuxCNC using a python hal module.
Here are the caveats:
(option 2) to feed the voltage back into ADC means the opto isolation is broken.
(option 3) digital pots I see only support 5v, not 10v. I would have to feed this into an opamp anyway, so I might as well stick with opamps...unless anyone found a better way.

I've also used PDM instead of PWM, both work fine but I think the PDM works a bit better. I've made many Arduino-like boards so #2 is easy for me both code and wiring.

Anyone have experience I can learn from here? Success and failures welcome!

Colin

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[Al_The_Man]

Does it have the Huanyang RS485 input?
If so it may take the odd ball Modbus input such as the one supplied here that works on the Huanyang Mach3 plugin for Huanyang VFD | Le royaume d'éole
Most VFD's have configurable outputs that can be set for to up-to-speed etc.
Al.

[ger21]

Can't use the Mach3 plugin with LinuxCNC.

[Al_The_Man]

I missed the Linux bit!
It does appear to have a RS232 port and data length that resembles the odd Modbus format of the Huanyang.
I made a DC drive using a Picmicro that used the Royaume Mach data format, I tested running a Huanyang VFD with a RS232 COM program on the PC first.
Al.

[guru_florida]

Hi guys,

It's not the Huanyang VFD...otherwise I would use the modbus. LinuxCNC does support RS485 modbus now and specifically the Huanyang. My VFD says Huanyang on the enclosure so I was excited but after scratching my head over the terminal pinouts (very different than Huanyang pics) I discovered my internals are actually an AskPower A131 which doesnt support modbus. It's awesome, the Chinese sell AskPowers inside of Huanyang enclosures. lol. (Thus the VFD in sheep's clothing comment.) Oh well, I guess I do pay 1/10th the price of US models.

So unfortunately no modbus. I do have the electronics done for closed loop control of PWM or PDM output using an arduino. I just captured a screenshot of the non-linearity. This is the output of a perfect digital step wave (i.e. counting 0-255 then back to 0) generated using arduino PDM. This matches what I was seeing at the VFD as far as non-linearity. Now to close the loop by reading the waveform back into the arduino via the ADC and we should be able to *bend* this waveform back to a sawtooth like one. Since this feedback path get's rid of the galvanic isolation I had through the opto, any suggestions on how to isolate the feedback path?

[mactec54]

guru_florida

The AskPower A131 supports RS232

[guru_florida]

....and...holy cow, that was easy! lol. My code worked the first build. Attached is the output linearly controlled via a simple proportional error control system. I didnt even need the integral/derivative part of the controller. Now to figure out how to regain isolation.

[guru_florida]

Hi mactec,

I dont have a RJ connection like you have in the picture. I saw that page in the downloaded manual I have but I think I dont have the model that supports that. The last page of the manual states in Chapter 13 there are 4 different models. I dont know what my exact model is but I dont have a RJ connection so I assume I have one of the ones without communication. Do you have any idea where this jack is supposed to be? I even looked inside on the main board and I dont see a PCB footprint for it. I'd love to have an RS232 connection.

C

[Al_The_Man]

I know some of the early Huanyang had the space on the board for the RS485 IC but those that needed it just had to solder the IC in.
The fact the manual does not appear to show the communication codes, probably means it does not have?
Al.

[mactec54]

Hi mactec,

I dont have a RJ connection like you have in the picture. I saw that page in the downloaded manual I have but I think I dont have the model that supports that. The last page of the manual states in Chapter 13 there are 4 different models. I dont know what my exact model is but I dont have a RJ connection so I assume I have one of the ones without communication. Do you have any idea where this jack is supposed to be? I even looked inside on the main board and I dont see a PCB footprint for it. I'd love to have an RS232 connection.

C

Yes you do it's what the Key pad is plugged into, or some have an extra input behind the keypad, then again it may not have anything like you saying

[guru_florida]

The keypad is a 10pin 0.1" header...which is often used for RS232 motherboard connections soooo maybe. However, I am not sure this is in fact RS232. It is not the RJ style that is in the manual. Looking at the main board there is a Silabs C8051 processor which has 1 UART module. This chip has a crossbar for IO so the UART is not fixed like an Atmel but can be on any of the the port 1 pins which is shown in yellow in the pic or the UART module may not even be in use/connected at all. These all lead to the Altera CPLD so from there they could go anywhere. I would have to spy the pins to see if it is in fact in use.

[Al_The_Man]

Generally you would see a RS232 IC such as a MAX232 etc for the level translation.
Al.