Controlling a VFD for a large A/C motor

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello all,

I will (hopefully!) be controlling a large A/C motor with an Arduino. I plan on using this VFD:

http://www.factorymation.com/s.nl/it.A/id.193/.f

There's a quick spec sheet for it here:

Look at page 2, lower left corner, for specs regarding the control signal(s).

Basically, I want the motor running all the time, but I want to be able to use a signal from the Arduino to set the frequency. It looks like the VFD wants a 0-10v analog signal on the MVI connection. The schematic shows a 10k pot on that pin to control speed - basically, I want the Arduino to be able to provide that signal.

So, I'm having trouble deciding the best way to implement this. Do I design some sort of circuit to step a PWM pin up to 10v, then filter it to get an analog 0-10v signal? I'd rather not use up a PWM pin, but I suppose that would work. It looks like there's a +10v and GND pin

Or, do I implement some sort of DAC chip? If so, any suggestions? I'm using I2C for several other purposes, so an I2C DAC chip would be nice.

It looks like I could also program some presets and use digital signals to switch between them, but I'd rather have full control from the Arduino.

Has anyone interfaced to a VFD like this before? General thoughts or suggestions?

2

The easiest would be to get a PWM signal to switch a transistor with the collector load connected to 10V and then smooth it.

using an D/A would involve first of all interfacing it and then amplifying the signal to 10V. This would probably involve a power supply of about +/- 12v so it's a lot of extra parts.

3

I will admit I don't have a concrete grasp on designing a filter to smooth the signal. Any links to a basic walkthrough? Rather than just "oh use X resistor and Y capacitor" I'd like to actually understand how the values are chosen. :slight_smile:

Same for choosing the most appropriate transistor. . .

4

For a discussion about what values do and why for PWM filters see:-
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

5

I am currently controlling 200 Kw pumps using an arduino and a LM358 Op-Amp to provide the 0-10 v input required by the VFD. I use a 12 volt, 500 ma plug pack to power the arduino and provide the power for the LM358. (I started using the LM324 but only used one of the four op-amps on the chip.

It works well and allows fine control of the motor and does not require smoothing.