Current detector for three-phase brushless direct current motor, has buffers which detect neutral point voltage of motor and voltage with respect to motor rotation speed, based on which motor current is determined

摘要

Three resistors (R0) are connected to nodes of two phase windings of motor (2). Buffer (BUF1) detects neutral point voltage (V1) of motor based on common node voltage of resistors. Buffer (BUF2) detects voltage (V2) based on rotational speed of motor. Operational amplifier determines voltage (Vo) that represents motor current, based on voltages (V1,V2,VB) where VB is source voltage applied to invertor (6). The voltage (V2) of the armature winding is determined by the buffer (BUF2) based on the rotational speed (N) of the motor detected by the sensor (8), using the formula V2= A*N, where A is the proportionality constant and A=k* phi /2, where k is emf constant of winding, phi is the flux. The voltage (Vo) is determined by the operational amplifier based on the voltages (V1,V2,VB) using the relation Vo=VB-V1-V2, where V1 is the neutral point voltage of the motor and VB is the source voltage applied to the invertor.