Lets say you have 10 thyristor controlled heaters in a 3-phase system. The control of these thyristors is sync'd, so the current draw is spiky (all of the heaters draw current from the same phase when its voltage is high). The heaters are connected to a triangle/star configuration.

50Hz system, the cycle is 20ms, if you were to delay all(but one) 10 heater controls by 2ms apart from each other, would the current draw smooth out from a spiky system to more sine-wave type?

Since the power needs to be delivered from somewhere, the phases would be at a differend angle and would distribute the loads on differend phases more equally. since I=U/R

Currently the current draw looks like a camel back in half wave

-Wacky-enter image description here

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    \$\begingroup\$ Schematic(s) and a screen-shot of the oscilloscope would help readability. \$\endgroup\$
    – Syed
    Jan 28, 2022 at 14:38

1 Answer 1


You may consider to turn on thyristors at zero voltage, for an integer number of periods each heater and control power by adjusting number of skipped periods (looks like Bresenham control), then syncronize periods of different heaters in such a way that total system current remains as constant as possible. This second part seems to be a fascinating mathematical challenge :)


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