Minimum copper loss drive method of three-phase dual-rotor BLDC machines

Three-phase dual-rotor brushless DC machine (DR-BLDCM) is constructed with two concentric machines which have inner and outer surface-mounted permanent-magnet rotors. Dual-stator is located between the dual-rotor. The machines have advantages such as high power density and high torque due to the structural characteristic in the restricted circle space. However, the system with DR-BLDCM requires double 3-phase PWM inverters. In this system, the current division control of the torque command into the inner and the outer machine should be determined to satisfy the maximum torque and the system efficiency because the entire torque is the sum of the inner and the outer torque. If current is divided without considering the features of the inside and the outside machine, the efficiency can be lower because of the copper loss increase. Therefore, this paper proposes the current distribution method to increase the produce of the torque, and minimize the copper loss in the DR-BLDCM control system.