??? 11/27/05 18:32 Modified: 11/27/05 18:37 Read: times |
#104231 - Integral Cycle Voltage Control Responding to: ???'s previous message |
Hi,
In the applications where thermal/mechanical constats are of order of seconds, the system power can be controlled by switching the load for whole cycles instead of phase agle control(noisy). the idea is to switch the load on or off for integral number of cycles . First one has to calculate a number N called periodicity so that the system can not notice the absence of the power for those number of mains cycles and N = (m + n)i.e. we turn the load on for n cycles and turn it off for rest of the m cycles. Naturally this depends upon the thermal time constant of your heater. the PWM like duty cyle is defined as k = n/N = n/(m + n) n = number of on cycles m = number of off cycles load voltage is given as Vo = Vrms * sqrt(k) and load current = Io = Vo/R. you will require a Zero Cross Detector to turn the thyristor on synchronously with the mains and a counter to count cycles. The direct gain is, this kind of control puts less noise back on the mains. Abee |
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