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. Stabilisationcan 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 open loop 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 havingthe 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 ofthese 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 likeair-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 performancefigures 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.

This paper presents an in-depth analysis, performance evaluation and comparative study of two 5-kW, 8-pole, 750-rpm laboratory prototypes of a permanent magnet synchronous motor (PMSM) of identical nominal ratings with surface and interior permanent magnet (PM) rotor structures having same stator and armature winding (fractional slot distributed winding). The key electrical (such as rated voltage, current, power, speed, number of poles, etc.) and mechanical variables (such as overall volume, air-gap length, rotor diameter, shaft dimensions and magnetic material) of the fabricated prototypes have also been kept same to pin-point thedirect influence of the two different rotor configurations (surface and interior PMSM) on the parameters, performance and operation of these PMSMs. For the two machines, a detailed comparison of air-gap flux density distribution, THD in induced voltage, torque ripple, losses, efficiency, torque–speed characteristics, field weakening capability, steady-state parameters at different operating conditions, etc. has been conducted. The salient observations from this comparative study have been duly highlighted. This paper also includes an indepthcomparison of volume and cost of PM used in the two types of PMSMs. The short-time performance figures of the said motors have also been presented. The possibility of demagnetisation of PMs, during a sudden fault, has also been investigated for both PMSMs. Challenges of making of both rotors have been discussed. The theoretically determined parameters and analytically evaluated performance figures have been verified through standard FEM packages and then validated experimentally on the prototypes.

This paper presents a novel initial rotor position estimation method for a surface-mounted permanent magnet synchronous motor (SPMSM) using its inherent magnetic features. Here, the initial rotor position has been estimated utilising the variation in phase inductances arising out of the unavoidable but verysmall saliency occurring either out of magnetic saturation of the machine or the magnet shape. Detailed investigations have been carried out to enumerate the actual magnitude of the inductances of the SPMSM with distributed armature winding and the dynamic saturation status with armature current variation. Here, 3-phase balanced voltage of higher frequency (150 Hz) is applied to the motor terminals for a short period of time (for 300 ms) and the corresponding phase currents are indirectly used to determine the rotor position. Innovativesignal processing steps have been used to distinguish small differences in the 3-phase currents caused by the small differences in the phase inductances. The position is determined from the relative values of different phase currents using a novel approach. This still leads to two diametrically opposite (electrical phase) solutions for the instantaneous rotor position. To eliminate this ambiguity, two alternative methods (for pole identification) have been proposed. Extensive co-simulations of finite-element method (FEM)-based electromagnetic simulation andsystem simulation (for logic implementation) have been conducted. The estimation methods have been validated experimentally on a laboratory-developed prototype SPMSM that was designed and fabricated by the authors.The experimental results are found to be in excellent agreement with the FEM-based simulation results. The complete initial position estimation method takes less than 1 s of real time, which is typically less than the prechargingtime of standard commercial inverters.