Method and device for continuous adjustment and regulation of transformer turns ratio, and transformer provided with such device

A switching device for adjusting, within a predetermined adjustment range, the turns ratio between a primary and a secondary winding of an AC power transformer having at least first and second taps on at least a portion of the primary winding of said transformer, the switching device comprising:

• at least first and second electronic switches that can be made to conduct unidirectionally or bidirectionally;
• a first terminal on each of said switches adapted to be coupled to one of said first and second taps;
• a second terminal on each of said switches adapted to be connected to one of the first and second terminals of at least one other of said electronic switches;
• a control device coupled to said at least first and second electronic switches for supplying control signals to said switches to obtain a transformer turns ratio that is essentially continuously adjustable within said predetermined adjustment range;
• a reference signal coupled to said control device;
• a first control signal generated by said control device for causing said first electronic switch to couple an AC voltage to said first tap during a first time period of a cycle of the AC voltage;
• a second control signal generated by said control device for causing said second electronic switch to couple said AC voltage to said second tap during another time period of the cycle of the AC voltage;
• and
• the ratio of the time periods in which the first and second taps are switched being dependent upon said reference signal coupled to said control device.

An AC power transformer comprising:

• at least one regulating winding having a plurality of taps thereon;
• a primary and a secondary winding;
• a switching device for adjusting, within a predetermined adjustment range, the turns ratio of the primary and secondary windings of the power transformer;
• said switching device comprising a plurality of electronic switches, each having the capability of conducting unidirectionally or bidirectionally;
• a first and a second terminal on each of said electronic switches;
• said first terminal of each of said electronic switches being connected to a corresponding one of said plurality of taps on said regulating winding;
• said second terminal of each of said electronic switches being connected to one of said first and second terminals of at least one other of said electronic switches;
• a control device for supplying control signals to said electronic switches so as to obtain a transformer turns ratio that is essentially continuously adjustable within said adjustment range;
• a reference signal coupled to said control device;
• a first control signal generated by said control device for coupling an AC voltage to one of said taps during a first time period of a cycle of the AC voltage;
• and
• a second control signal generated by said control device for coupling said AC voltage to a different tap during a second time period of said cycle of the AC voltage;
• the ratio of said first and second time periods being dependent upon said reference signal fed to said control device.