The utility model discloses a there is not broad width of isolation alternating voltage modulating device based on frequency transformer coupling, including converter and power frequency isolation transformer, the input of converter is inserted respectively at input voltage's both ends, and the output of converter and power frequency isolation transformer's high -pressure side winding are connected, and power frequency isolation transformer's low tension side winding and voltage output end are connected, and input voltage US and the offset voltage UC that the converter produced carry out the vector stack, produce output voltage U0. The utility model discloses contactless, stepless, the sinusoidal wave power electronic voltage regulator of broad width, the stabiliser that have that frequency transformer keeps apart, be applicable to single, the three -phase system of different capacity grades, high performance -price ratio, etc.