Patent ID: 7042204

Claim:
A voltage source comprising a serial capacitor connected in series between an AC power source and a load, and a first voltage limiting circuit and a second voltage limiting circuit connected in parallel to the load, the first voltage limiting circuit comprising a first switching element and a first capacitor connected in series, the second voltage limiting circuit comprising a second switching element and a second capacitor connected in series, wherein the first switching element is constantly conductive to an electric current flowing in one direction for charging the first capacitor in a positive half cycle of the AC power source, and is controllably turned on and off for an electric current flowing in the other direction, wherein, when a voltage of the first capacitor exceeds a predefined positive voltage level (E 1 ), the first switching element is turned on to keep the first capacitor at the predefined positive voltage level (E 1 ) and, when the voltage of the first capacitor is reduced below the predefined positive voltage level (E 1 ), the first switching element is turned off, wherein the second switching element is constantly conductive to an electric current flowing in one direction for charging the second capacitor in a negative half cycle of the AC power source, and is controllably turned on and off for an electric current flowing in the other direction, wherein, when a voltage of the second capacitor is reduced below a predefined negative voltage level (−E 2 ), the second switching element is turned on to keep the second capacitor at the predefined negative voltage level (−E 2 ) and, when the voltage of the second capacitor exceeds the predefined negative voltage level (−E 2 ), the second switching element is turned off.