PWM signal generation by varying duty cycle on USB NI-6366

[seanabmoore]

Good day

I am trying to perform Impedance Spectroscopy (IS) on a Lithium Ion battery while it is supplying power to a load.

I am using a usb NI-6366. 

To perform IS I need to inject small sinusoidal signals onto a DC current bias. What I am currently doing is creating a PWM waveform by comparing a triangle waveform (Switching Frequency of 20kHz) to a DC bias with a sine wave. The duty cycle is given by the following equation:

duty cycle = 0.5 + 0.05*sin(2pi*f), where f varies from 0.01Hz - 1kHz. 

The PWM signal outputs on an Analog out port of my NI 6366

The issue is, I am unable to produce a decent looking waveform for the low frequencies (0.01Hz) because the number of samples I need to send to the NI-6366 (for the PWM signal) is too large and I am getting buffer overflow issues. 

Is there a better way that I can create the PWM waveform, so that I do not have to send so many data points to my NI-6366? Is there a way I can dynamically vary my duty cycle

I also have access to a myRio which has FPGA functionality, if that will be an easier solution.

Any help will be great.

Regards

Sean Moore

[GerdW · Accepted solution]

Hi Sean,

the example VI "Cont Gen Voltage Wfm-Int Clk-Non Regeneration" explains how to output large amounts of waveform data.

You might split your waveform into smaller parts suitable for your hardware…

[seanabmoore]

Thank you so much. That did the trick.

Regards

Sean Moore