An analytical approach for determining harmonic cusps and torque dips in line start synchronous reluctance motors

Abstract

Excellence of line start synchronous reluctance motors (LS-SynRM) such as their high efficiency amongst other types of line start motors necessitates the existence of analytical methods in their design. The start-up period of these motors is of high importance and regarding this, the cage design needs to be discussed thoroughly since the squirrel cage is responsible for speeding up the motor to reach at synchronism. One of the issues in this sense is the rich harmonic content of the air-gap MMF arising from irregular bars configuration which afterwards could lead to creation of the torque dips in the torque-speed characteristic of the machine and making it incapable of synchronization under load. An analytical approach to calculate these harmonic effects while also considering the reluctance rotor contribution on them is proposed in this paper. This scheme starts from the stator winding configuration as a known parameter, obtaining the air gap MMF due to only the stator magnetic field, calculating the current and voltages induced through the rotor bars considering the effect of saliency using the model proposed in [1, 2]. Next, harmonic contribution of the rotor cage in the air gap MMF is derived. Finally, probable harmonic cusps and consequently torque dips is found in the torquespeed characteristic of the motor which is helpful in anticipating the synchronization capability under various loads. The results have been verified with a sample 4-pole, two flux barriers per pole LS-SynRM which suffers crawling due to the existence of the torque dips in its torque-speed characteristic. All simulations have been done by finite element analysis (FEA) software and a comprehensive program was written in Matlab to implement the proposed algorithm.

Verification of effect of secondary conductor bar on starting characteristics in line‐start type self‐excited wound‐field synchronous motor

“…The other type is a line-start type synchronous reluctance motor (LS-SynRM) [13][14][15][16][17][18][19][20][21]. This motor is based on the structure of a reluctance motor having a multi-layer flux barrier and has a structure in which a secondary conductor bar is embedded at an appropriate position in the flux barrier.…”

Position sensorless and adaptive speed design for controlling brushless DC motor drives

“…Synchronous motors are gaining much attention compared with induction motors [1][2][3][4][5][6]. Brushless DC (BLDC) motors are classified as synchronous AC electric motors, which play a significant role in contemporary applications, such as: industry, transportation, visual and sound equipment in medical applications, with a large variety of power ranges.…”