VFD is blowing my RCD

[cropwell]

No. The MEGA328/2560 based arduinos do not have a DAC, or any other form of analogue output. They provide a number of PWM-enabled discrete outputs (those prefixed with a tilde on the board silk-screening) with the signal value switched between GND and VCC - which if used for e.g. LED drives allows a direct control over the LED luminance, similarly for a DC motor drive; but the output remains a digital PWM signal (they do, however, support multiple ADC inputs)

You are right Doddy, I have had a closer look at the AnalogueWrite function. The DAC converters in the arduino put out a variable duty cycle PWM 0-5v. I have a feeling that that is where the OP's problem lies. I fell into the trap of assuming that, when Arduino described the board as having DAC function they meant in in the true sense. Maybe a simple RC integrator would prove the root of the problem, but in the long term an OpAmp circuit would be better (to give a better 0-5v). I am surprised that the inverter does not have an integrator on the input VI.