An exciterless- and brushless-type commutatorless motor fed from a transformer in parallel with a voltage source inverter

A novel exciterless- and brushless-type commutatorless motor driven by a voltage source inverter is presented, and the analysis of the characteristics and the test results are reported. In the commutatorless motor, the stator armature winding is connected electrically with the secondary winding of a transformer. An AC exciting current flows in the armature winding simultaneously with the load current. The ratio between the number of poles made by the load current and the number of poles by the AC exciting current is 2 or 1/2. Thus, the motor can be made exciterless and brushless. Since the rotating direction of the rotating field made by the AC exciting current is opposite to that of the rotor in this commutatorless motor, speed control in a low-speed range is possible, because a large current can flow in the field winding even if the rotor rotates in a low-speed range. As a result, the motor can be controlled in a wide range, from high speed to low speed. It has been found from the analysis and the test results that a shunt wound characteristic between the speed and the torque and other characteristics can be obtained