A simple and accurate method for the experimental performance evaluation of high speed sensorless brushless dc motors

One of the common problems of testing high speed sensorless brushless dc (BLDC) motors is the lack of the torque transducers that are capable of operating at speed higher than 25000 rpm as well as the difficulty of separating the iron loss from friction and windage losses. This paper describes a method of determining these types of losses by using a special ldquodummyrdquo motor, in which rotor magnets are not magnetized. The paper also presents a simple test method, which can be used for testing high speed sensorless BLDC motors and drives without the direct torque measurement. The absence of torque transducers eliminates the speed limits introduced by them. In this case, the speed limit is determined by the motor construction only. That is achieved by performing a load test by mechanical coupling of two BLDC motors together when one is operating as a motor, and the second as a generator. The paper describes the method of performing 3-phase symmetrical load for the generator using the single phase rheostat connected through a 3-phase rectifier. The method is used for the high speed sensorless BLDC motors employed in medical industry devices like sleep apnea treatment and the ventilation systems.