INSTANTANEOUS TORQUE ANALYSIS OF HYBRID STEPPING MOTOR

Originally, stepping motors are electromagnetic incremental-motion act uators, which, when energized by a voltage and current input, index in given angular increments. On the other hand, the hybrid stepping moto r is promising as a high-torque and low-speed servomotor, since the mo tor can be considered as a multipole synchronous motor. For this appli cation, it is necessary to have a clear equivalent circuit under the s inusoidal current drive just like the conventional brushless dc motor. For the given stator/rotor teeth and winding arrangements of the hybr id stepping motor, the permeance distribution with respect to the roto r position is obtained by a well-known permeance-based method. Based o n the calculated permeance distribution, an equivalent magnetic circui t of the given motor can be obtained, from which the basic voltage equ ation can be deduced. Following this procedure, electric parameters in the voltage equation are related to the machine construction constant s such as stator-rotor pole dimensions, air-gap length, number of turn s of the stator windings, and magnetomotive force (MMF) of the permane nt magnet. The analysis shows that a fundamental component of the perm eance distribution produces the average torque and that harmonic compo nents produce the ripple torque under the sinusoidal current drives. T he cogging torque is also produced by the 4th harmonic component of th e permeance distribution. For the laboratory testing, the two-phase hy brid stepping motor connected to the current-controlled voltage source inverter was used. The experimental results showed quite reasonable a greement with the predicted instantaneous torque.