Abstract

Embodiments of the present invention provide an apparatus for controlling a voltage provided to a load, comprising a transformer having primary and secondary windings in circuit between an AC electrical supply and a load, wherein the primary and secondary windings have a predetermined winding ratio,and a switching device arranged to selectively connect the primary winding of the transformer in first and second configurations to the AC electrical supply, such that, in the first configuration, a voltage output from the secondary winding is subtracted from a voltage of the electrical supply and, in the second configuration, the voltage output from the secondary winding is added to the voltage of the electrical supply.

IPC Classes  ?

• H02M 5/12 - Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC by static converters using transformers for conversion of voltage or current amplitude only
• G05F 1/30 - Regulating voltage or current wherein the variable is actually regulated by the final control device is AC using bucking or boosting transformers as final control devices combined with discharge tubes or semiconductor devices semiconductor devices only