Patent ID: 7982426

Claim:
An electric power system, comprising: an AC motor including a coil; a first DC voltage unit having a positive pole and a negative pole; a power converter connected between the AC motor and first DC voltage unit, the power converter for exchanging power between the AC motor and the first DC voltage unit; and a controlled DC power supply having a first terminal and an output terminal, the output terminal directly connected to an arbitrary spot of the coil of the AC motor, and the first terminal directly connected to either the positive pole or to the negative pole of the first DC voltage unit, wherein the controlled DC power supply comprising at least one semiconductor switching element connected in series with a second DC voltage unit, the at least one semiconductor switching element including a first electrode and a second electrode, the second DC voltage unit including a third electrode and a fourth electrode, and wherein the first electrode of the at least one semiconductor switching element is directly connected to the output terminal and to the arbitrary spot of the coil of the AC motor, the second electrode of the at least one semiconductor switching element is directly connected to the third electrode of the second DC voltage unit, and the fourth electrode of the second DC voltage unit is directly connected to the first terminal of the controlled DC power supply.