Torque Ripple Suppression of Doubly Salient Brushless DC Machine With Even-order Current Harmonic Injection

Abstract

Doubly salient brushless DC (DSBLDC) machine has been attracting much attention for aviation and vehicular applications, owing to its simple structure, adjustable flux, and reliability. Despite those merits, the torque ripple of DSBLDC machine limits its applications at medium-and-low speeds. The current harmonic injection (CHI) method has been proposed to reduce torque ripple, dealing with the subsequent issue, such as vibrations, acoustic noise, even starting failure.The traditional CHI choice of odd order harmonics to limit torque ripple is almost useless for the 3-phase 12/8-pole DSBLDC machine, due to the excitation and armature winding configurations, which generate its unique magnetic circuit and inductance characteristics. Firstly, A new instantaneous torque model from the perspective of harmonics has been derived. The main components of the excitation inductance are the 1st, 2nd and 4th harmonics. Only the armature current harmonics interact with the same-order inductance harmonics can contribute to the average torque, otherwise it will lead to torque harmonics. Thus, a harmonic injection algorithm based on the 2nd and 4th current harmonics is proposed to reduce the torque ripple.Fig.1(a) shows the topology of the DSBLDC machine, which is marked by the concentrated stator-field-winding and the absence of rotor excitation. Experiment platform is shown in Fig. 1(b). The instantaneous torque as shown in Fig. 1(c) can be divided into two parts: average torque and torque ripple, which is used to solve the current amplitude and phase parameters of injected current as shown in Fig.2(a). Fig.2 shows the solution based on the harmonic injection algorithm. Case I contains only the fundamental wave. The 2nd harmonic is added into Case II. Case III contains the 1st, 2nd and 4th harmonics, reducing the torque ripple from 54.84% to 44.28%. The torque waveform and its FFT results are shown in Fig. 2(b) and Fig. 2(c). Using the system diagram in Fig. 2(d) can experimentally validate the foregoing simulation, the partial result about Case I is given in Fig. 2(e).  Fig.1 topology and torque model of the 12/8-pole DSBLDC machine.  Fig.2 simulation and experimental results based on the harmonic injection algorithm.