# Static Frequency Converter(SFC)



## nick (Feb 14, 2008)

well a basic static inverter , starts as a ac source say 3 phase what ever voltage you need , this is now changed to dc thur a full bridge 3 phase rectifier with filter and chokes to give pure dc output to 6 thyristors each pair of two thyristors are connected to a transformer primary of three primarys abc this primary is a center tapped primary connection on each of the three with the thyristors on each opposite winding end of that center tap of that primary transformer winding ,two for transformer one[ a phase] .two for transformer two[ b phase] and two for transformer three [ c phase] this is the primary the secondary is wye connection on this transformer just by example . the thyristors are controlled by a pwm oscillator to ther gates which can be switched on or off in a sync like a phase pri trans one side negative or the other side negative on that primary winding , the center tap is positive so thyristors are now switching or making current flow back and forth one way thur primary than the next direction thur that primary winding using the positive center tap as a commom point .like a fly back transformer .or a flip flop circuit like ac but actually we use a dc pulse to make a magnetic flux induced in the windings one way then the next way .the secondary a phase now can produce ac power to the load thur the secondary winding . only thing left is each set of thyristors are switched in rotation in a abc cw direction and you have 3 phase power freq controlled man made . but its done in a order of controlled switching of the thyristors on these primary transformers,and you have 3 phase power the freq is controlled by the oscillator to the gates, meaning the distance between the pulses. the voltage will be at or follow the amount of the time the pwm wave is to be adjusted for .meaning the square wave dc length of duration of that pulse high point of the pulses or peak of the dc pulse and can be adjusted by the oscillator , wide cycle pulse meaning one single pulse higher voltage it can be adjusted also if needed. but follows the load. it does change with frequency up or down . hope this makes sense its a lot to explain but thers lots of books on this stuff . there are some that do not use a transformer . this is a example of just one type of static converter its a old type most have or had a transformer . if your looking for the digital type ask ill be happy to do it on a post ?take care best to ya


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