This paper presents a novel, reliable and efficient V/f control implementation on a 8-pole, 750 rpm, 5 kW surface-mounted permanent magnet synchronous motor (PMSM) without damper winding. In the absence of a damper winding, open loop V/f control of SM is inherently unstable, particularly at high speeds. Stabilisation can be done with proper stator frequency modulation in accordance with the change in rotor speed to provide for effect of damping. This has been implemented here without use of any shaft-mounted encoder. The change in rotor speed is observed from power perturbation, thereby eliminating the need for using a speed sensor in the drive. The efficiency of the drive is further increased with appropriate control of the power factor, irrespective of load and frequency variations. Simulated and experimental results are presented for both openloop and the proposed V/f control. These results establish the accuracy of the design of the proposed V/f control strategy and the precision of hardware implementation. A comparative study between the proposed V/f control method and standard vector control method, as implemented on this PMSM, has also been presented here to establish the advantages of the proposed scheme. The PMSM itself was designed and fabricated in the laboratory.
This paper presents a novel and exhaustive investigation involving in-depth analysis, performance evaluation and comparative study of two 0.75 hp, 4-pole, 1500 rpm laboratory prototypes of Brushless DC (BLDC) motors of identical nominal ratings with surface and interior permanent magnet rotor structures having the same stator and winding (integral slot distributed winding). Both the motors were designed and developed in the lab. The major electrical variables (such as rated power, speed, voltage, current, number of poles, etc.) and the stator (such as core material, stator lamination, stack length, winding pattern and wire gauge) of the fabricated prototypes have also been kept identical to pin-point the direct influence of the two different rotor configurations (viz., surface vs interior permanent magnet) on the parameters, performance and operation of these BLDC motors. Additionally, to ensure unbiased basis for appropriate comparison, the overall volumes of magnets/pole in both the motors have also been kept similar. A detailed comparison of different quantities like air-gap flux density distribution, THD in induced voltage, torque ripple, losses and efficiency, torque-speed characteristics with field-weakening capability, steady state parameters at different operating conditions, etc. has been conducted for the said motors and the salient points duly highlighted. The vulnerability of the permanent magnets to demagnetisation based on armature reaction, particularly during a sudden fault, has also been investigated in both the cases. The theoretically determined parameters and analytically evaluated performance figures have been verified through standard FEM packages, and later validated experimentally on the fabricated prototypes. Very good mutual agreement has been observed between predicted and experimental values.
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