Comparative Analysis of Parallel Hybrid Magnet Memory Machines with Different PM Arrangements
Round 1
Reviewer 1 Report
Fix Fig1 LCF and NdFeB indications are wrong.
Authors should discourse about stator and winding scheme.
Authors should explain better the current angle and the relationship of d-axis.
Authors should explain how experimental results where conducted (how pulse current was injected, experimental basic apparatus and other relevant information that can help other researchers how to perform similar results.
Author Response
Reviewer 1
Comment 1: Fix Fig1 LCF and NdFeB indications are wrong.
Revision 1: Thanks a lot for your comment. As you suggested, the indications of LCF and NdFeB PMs have been corrected.
Comment 2: Authors should discourse about stator and winding scheme.
Revision 2: Thanks a lot for your comment. As you suggested, some descriptions about stator and winding scheme has been added in the revision.
Both two machines employ identical stator structure featuring a 21-stator-slot/4-rotor-pole factional-slot distributed winding. For PM machine design, when the number of pole pairs p is small, the space of each pole in the proposed machine is larger, which is beneficial to expand the design space of the hybrid permanent magnet, as well as increase the flux regulation capability. On the other hand, the iron core saturation is smaller in the case of lower rotor pole number, which is also advantageous to the reduction of the iron loss. However, in the meantime, the pole arc coefficient of the machine is relatively large, resulting in large magnetic flux leakage. Therefore, the number of poles of 2p=4 is selected. In order to reduce high-order back-EMF harmonics and cogging torque, a fractional slot winding is used. Besides, in order to facilitate the comparison with the other similar prototypes in the research group, a 21-slot structure is adopted.
Comment 3: Authors should explain better the current angle and the relationship of d-axis.
Revision 3: Thanks a lot for your comment. As you suggested, the description of the relationship between the current angle and the d-axis has been added in the revision. It should be noted that the current angle is defined as based on the q axis, which is used to express the phase relationship between the EMF E0 and the armature current Ia, that is to say, q axis refers to the current angle of 0 current degrees, and d axis corresponds to the current angle of -90 current degrees.
Comment 4: Authors should explain how experimental results where conducted (how pulse current was injected, experimental basic apparatus and other relevant information that can help other researchers how to perform similar results.
Revision 4: Thanks a lot for your comment. As you suggested, some descriptions on experimental verification has been added in the revision.
Reviewer 2 Report
In the introduction, you should emphasize the requirements set by the EV- applications, what are the most important parameters when designing a motor to be used in EV?
E.g., the rated speed of the is really low, typical EV motors are 10+ krpms.
The efficiency of the machine is not reported or verified, why?
The torque ripple seem to be really high, what is the reason for this?
The experimental testing is defective. It only shows that motor is running, nothing more.
Author Response
Comment 1: In the introduction, you should emphasize the requirements set by the EV- applications, what are the most important parameters when designing a motor to be used in EV?
E.g., the rated speed of the is really low, typical EV motors are 10+ krpms.
Revision 1: Thanks a lot for your comment. The basic characteristics which are required for atraction machine mainly include the following:
1)High torque density and power density; High torque for starting, at low speeds and hill climbing, and high power for high-speed cruising;
2)Wide speed range, with a constant power operating range of around 3~4 times the base speed being a good compromise between the peak torque requirement of the machine and the volt-ampere rating of the inverter;
3)High efficiency over wide speed and torque ranges, including low torque operation;
4)Intermittent overload capability, typically twice the rated torque for short durations;
5)High reliability and robustness appropriate to the vehicle environment;
6)Acceptable cost;
7)low acoustic noise and low torque ripple.
The most important design requirements of traction machines for electric vehicles are to achieve rated operating conditions (torque) and maximum operating range (maximum speed).
It should be further noted that the machine designed in this paper is a prototype for proof-of-principle, which is used to investigate the influence of different permanent magnet arrangements on the electromagnetic performance. Thus, the designed rated speed and power are relatively lower than those EV specifications.
Comment 2: The efficiency of the machine is not reported or verified, why?
Revision 2: Thanks a lot for your comment. As you suggested, the efficiency analysis of the machine has been added in the revision.
Comment 3: The torque ripple seem to be really high, what is the reason for this?
Revision 3: Thanks a lot for your comment.
1) The machine designed in this paper is a proof-of-principle prototype, and hence the number of poles is low, which leads to a large torque ripple
2) The 5th and 7th harmonics of the air-gap magnetic density are high, which are responsible for the torque ripple. In the future improved versions of the prototype, the rotor surface shaping and other similar methods will be used for optimization.
3) Due to the influence of cross-coupling effect, the q-axis armature magnetic motive force (MMF) will distort the main magnetic field waveform of the air gap. The main air-gap magnetic field is no longer a square wave at no-load, and hence the EMF is also distorted. This leads to a mismatch between the induced EMF and the armature current, which in turn causes torque pulsation.
4) In the weak magnetic state of Kmr =-0.5, since the PM magnetic field is mostly saturated in the rotor, resulting in pronounced magnetic saturation and hence higher torque ripple.
Comment 4: The experimental testing is defective. It only shows that motor is running, nothing more.
Revision 4: Thanks a lot for your comment. We mainly conducted no-load experiments on the prototype based on the test platform to study the flux regulation performance of the motor. Fig. 21 shows the measured and FE predicted fundamental phase EMF of the manufactured PHMMM subject to the applied d-axis demagnetizing and remagnetizing current pulses. As expected, the 2D-FEM results are well consistent with the experimental results, which confirms the foregoing FEM analyses. As you suggested, we added some relevant experiments. Fig. 22 shows the torque-speed curves of the prototype, verifying the operating characteristics of the prototype.
Round 2
Reviewer 1 Report
Fig 1 is still in conflict with fig 2.
Green = HCF. However, for fig 1a, green = LCF.
