Double-rotor Permanent Magnet Brushless Dc Motor Without Position Sensor Control Study

The availability of high performance magnets, like samarium cobalt and neodymium-boron-iron, has made it possible to improve the performance of BLDC motors significantly. Design engineers now selecting PM BLDC motors over conventional DC or induction motor drives for the following reasons: 1) The absence of brushes results in an essentially maintenance free operation and eliminates the undesirable effects of commutation such as sparks, brush-loss, radio-frequency interference, etc. 2) The low inertia of the rotor enhances the quality of the mechanical response of the motor, shortening the acceleration and deceleration time. 3) Utilizing rare-earth permanent magnet materials with high coercive force results insubstantially higher efficiency than their counterpart with brushes of the same size. 4) Because of the absence of commutation segments, the stator construction is simple.Basically, a BLDC motor consists of a permanent magnet (PM) synchronous motor, an inverter and a position sensor mounted on the motor shaft. The inverter drive signals are synchronized with the position sensor output signals so that synchronism between the stator winding currents and the rotor flux is ensured for any speed.The electromagnetic structure of a double-rotor PM BLDC motor is the same as that of a conventional BLDC motor. The difference is not only the magnet part but also the winding part can turn. The double-rotor PM BLDC motor can be used in opposite-direction-thrust systems. Applying direct-thrust double-rotor motor in opposite-direction thrusters can not only avoid the complexity of mechanical parts but also make it easy to control the speed of the thruster.In this paper computer simulation and experiments will be used to study the double-rotor PM BLDC motor and its drive-control system. Considering the double-rotor PM BLDC motor is a member of PM BLDC motor family, firstly this paper introduces the control strategy of the conventional PM BLDC motor, then the particularity of the double-rotor PM BLDC motor is analyzed.