Microsoft Word - ETASR_V13_N1_pp9807-9811 Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9807-9811 9807 www.etasr.com Manh et al.: Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start … Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start Permanent Magnet Assistance Synchronous Reluctance Motors Tien Ho Manh University of Transport and Communications, Vietnam hotien.ktd@utc.edu.vn Dinh Bui Minh School of Electrical and Electronic Engineering, Hanoi University of Science and Technology, Vietnam dinh.buiminh@hust.edu.vn Tu Pham Minh School of Electrical and Electronic Engineering, Hanoi University of Science and Technology, Vietnam tu.phamminh@hust.edu.vne-mail address Vuong Dang Quoc School of Electrical and Electronic Engineering, Hanoi University of Science and Technology, Vietnam vuong.dangquoc@hust.edu.vn (corresponding author) Received: 2 September 2022 | Revised: 27 October 2022 | Accepted: 27 October 2022 ABSTRACT A permanent magnet assistance synchronous reluctance motor can start directly with a net voltage or a power converter via a torque control method. However, this motor has usually a higher irreversible demagnetization level in comparison with interior permanent magnet motors, due to the fewer permanent magnets in rotor slots. In order to cope with this disadvantage, different arrangements of permanent magnets in the rotor of the line-start permanent magnet assistance synchronous reluctance motor are proposed in this paper. The V magnet shape taking skewed slots and demagnetization effect into account with the short circuit current are investigated by the finite element approach. The efficiency, torque, and output power of the proposed model have been also improved. Finally, the rotor with 3V layered magnets is prototyped to verify the efficiency of the proposed motor. Keywords-line start permanent magnet assistance-synchronous reluctance; magnet shape; skewed slots; demagnetization effect; finite element method I. INTRODUCTION The Line Start Permanent Magnet Assistance Synchronous Reluctance Motors (LS-PMA-SynRMs) have recently been presented [1]. Authors in [2] proposed the design and optimization of low torque ripple and high torque by using ferrite magnets. However, the influences of skewed slots and the demagnetization effects on the LS-PMA-SynRMs have not been mentioned so far. In this paper, different arrangements of permanent magnets in the rotor taking skewed slots and the demagnetization effects taken into account are developed to improve the efficiency of the LS-PMA-SynRMs. Normally, when the LS-PMA-SynRMs are operated at synchronous speed, the secondary copper loss is eliminated, leading to efficiency improvement. Less use of rare-earth materials, low cost, comparable constant-power speed range, maximum torque, and the efficiency of the LS-PMa-SynRMs will be considered. In particular, this is an interesting choice for the application of electric traction because it has a special flux barrier and suitable magnet arrangement to improve the constant torque in a wide speed range. In addition, it has a lesser risk of irreversible demagnetization in the short circuit and overheat temperature [3]. Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9807-9811 9808 www.etasr.com Manh et al.: Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start … II. MODEL OF LS-PMA-SYNRMS A 7.5kW LS-PMA-SynRM model for 6 poles is shown in Figure 1. The stator has 36 slots and the 3-layer rotor has 36 round bars. The magnetic material and silicon steels are made in N38UH and 35A350. The response of magnets to the demagnetizing influence is considered in this research. Depending on the type of magnets, the motor can either need to withstand irreversible demagnetization during a transient short circuit fault condition or only require that the demagnetization is avoided during the steady-state operating conditions. For the sintered NdFeB and SmCo magnets, an irreversible demagnetization will occur at the very high temperature of 120°C. On the other hand, the irreversible demagnetization will occur at low temperatures (i.e. below 0°C) for the sintered ferrite magnets. Initially, a temperature value can be fixed to investigate the possible demagnetization. For example, it will be assumed that the magnet temperature is 160°C. Hence, for a selected N38UH magnet, the knee point of the demagnetization curve at the specified temperature is indicated in Figure 2 [4]. It can be seen that the flux density of the B-H curve becomes non-linear. The irreversible demagnetization in the magnet will appear if the flux density is depressed below that point. It should be noted the curve becomes non-linear at about 0.2T – at 160°C (the magnet temperature of our model). When the knee point is higher, then the magnet is more easily irreversibly demagnetized at high temperatures. Fig. 1. LS-PMA-SynRM with 3V layer. Fig. 2. Magnetization curve of B-H. The magnetization curve with a higher temperature is pointed out in Figure 3 [4]. The curve of irreversible demagnetization is described by [5-7]: � = �� + ���� �� − ∙ � ��������� (1) where B is the flux density, Br is the remanent flux density, Hc is the coercivity, E is the electrical field, and �� and �� are respectively the factors of the magnets, where the factor �� can be defined as [8, 9]: �� = �� [������� ��� .����"] �� − �� (2) The working point of the magnet is defined by the intersaction between the flux density (Bm) and magnetic field strength (Hm). A point on the demagnetization characteristic of the magnet and load line is also defined. The slope of the load line is called the permeance coefficient. It is determined principally by the ratio of the magnet length to the air gap (g). When the machine is under load, the whole load line shifts, usually to the left, so the working point is shifted further down the curve. Once it overcomes the knee of the curve, an irreversible loss of magnetization will appear. Via the computation of demagnetization, it is certain that the operating point of the magnet stays above the knee. It also needs to be ensured that the magnet is working with the worst-case parameters. In particular, temperature is critical. For high- energy magnets, when the temperature increases, both Br and Hc decrease. However, the knee moves to a lower value of Hm, which means that less current is required to demagnetize the magnet. The maximum current that can flow and its phase angle must also be considered. Normally, the current is regulated by the inverter unit, thus the maximum current is tightly controlled. But there may be fault conditions where the current reaches a value much higher than normal. Fig. 3. B-H magnetization curve with higher temperature. In the worst conditions, for a three-phase short-circuit, the temperature of the magnet is 25 0 C. For that, the current can be presented as [4]: Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9807-9811 9809 www.etasr.com Manh et al.: Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start … $%[&�] = '(�)* (3) where Eq1 is the Root Mean Square (RMS) of the Electromotive Force (EMF) per phase and Xd is the d-axis synchronous reactance. Normally, this current is 2 to 5 times the maximum working current. The design parameters of LS- PMA-SynRM are given in Table I. The schematic diagram of the proposed PMA-SynRM machine is presented in Figure 4. In the proposed motor, the magnet shape is arranged with the U-shape. This arrangement is regarded as requisite for the efficient operation in the type of I-W-U shape. The total weight of the magnet segment and copper winding is presented in Table II. TABLE I. GEOMETRY PARAMETERS OF LS- PMA-SYNRM Parameter Values Unit Slot number 36 slot Outer stator 210 mm Inner stator 132 mm Tooth width 5 mm Slot depth 19 mm Motor length 180 mm Stator Lam length 180 mm Magnet length 150 mm Magnet size 5×2 mm Air gap 0.4 mm Turn per coil 20 turn Fig. 4. Schematice driagram. TABLE II. WEIGHT OF LS- PMA-SYNRM Parameter Kg Stator lam (back iron) 8.26 Stator Lam (yooth) 5.245 Stator lamination (total) 13.5 Armature winding (active) 4.138 Armature EWdg (front) 1.027 Armature EWdg (rear) 1.027 Armature winding (total) 6.193 Rotor lam (back iron) 5.37 IPM magnet pole 4.833 Rotor lamination (total) 10.74 Magnet 0.5 Total 33.98 III. LS-PMA-SYNRM PERFORMANCE IN DIRECT START AND TRACTION The proposed PMA-SynRM machine was designed and analyzed in traction. The electromagnetic torque is formed from two components of magnetic reluctance torques. The Permanent Magnet (PM) component is produced via the interaction between the air-gap magnetic field and the armature reaction magnetic field. The reluctance component is instead based on the asymmetry between the magnetic circuit of d-axis and q-axis. The electromagnetic torque can then be defined as [5-9]: +', = -..� /0.1 . 2% + 34% − 45 6. 2%. 25 7 (4) 4% = 8* 89:;* < 2% = 0 (5) 45 = 8(;( > 25 = 0 (6) where λpm is the flux linkage generated by the PM field, 2% and 25 are respectively the direct and quadrature axis currents, and 4% and 45 are the direct and quadrature axis inductances. The term λpm depends on magnet sizes. The terms (4% and 45 ) are computed following to the rotor magnet barrier and magnet pole U shape. Fig. 5. Comparison of dynamic starting torque and speed with different types of I-W-U. Database Program Interface Material Library Analytical Calculations Export Drawings FEM Simulator Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9807-9811 9810 www.etasr.com Manh et al.: Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start … Fig. 6. Comparison of dynamic starting torque and time with different types of I-W-U. The dynamic starting torque and speed with different types of I-W-U are shown in Figures 5 and 6. For the U-shape, the peak torque has been verified at 1500rpm. When increasing the phase current density up to 10A/mm 2 , the peak torque is 340Nm. It should be noted that the LS-PMA-SynRM can be pre-determined by 11kW under the direct start. If this motor is operated with the power inverter, the maximum power is doubled, and the peak torque is about 800Nm (Figure 5). The parameter comparison of the LS-PMA-SynRM with different types of I-W-U is given in Table III. TABLE III. PARAMETER COMPARISON OF LS-PMA-SYNRM Parameters I shape W shape U shape Unit Shaft torque 53.67 54.267 55.667 Nm Input power 9123.3 9213.4 9273.3 W Output power 8644.1 8474.3 8744.1 W Total losses 519.5 522.1 529.15 W System efficiency 93.24 94.3 94.68 % Armature DC copper loss 340 340 340 W Magnet loss 178.8 168.3 168 W Stator iron loss 10.33 10.33 10.33 W Phase terminal voltage 289.1 289.1 289.1 V Harmonic distortion line-line terminal voltage 4.89 4.289 3.089 V Harmonic distortion phase terminal voltage 13.7 12.2 11.27 % Back EMF line-line voltage 111 112 114 % TABLE IV. TEMPERATURE OF LS-PMA-SYNRM No Component T ( 0 C) 1 T (ambient) 40 2 T (housing - active) 78.717 3 T [stator lam (back iron)] 84.833 4 T (stator surface) 88.403 5 T (rotor surface) 88.65 6 T (airgap banding) 88.651 7 T (magnet) 88.197 8 T (airgap banding) 88.651 9 T (rotor lamination) 88.674 10 T (shaft - center) 87.375 13 T (active winding minimum) 87.352 It can be seen that the maximum efficiency is 94%. The total loss errors between the three cases are smaller than 5%. For the errors on the harmonic distortion line, they are lower than 14%. The temperatures of the LS-PMa-SynRM are presented in Table IV. The maximum temperature of the winding is 90.7 o C, which is much lower than isolation class H (180 0 ). The temperature of the magnet is 88.17 o C. The dynamic starting torque and speed of the U shape is shown in Figure 7. The output power of the U shape is indicated in Figure 8. The map distribution of the rotor temperature with the U shape is shown in Figure 9. The maximum temperature is 88.7 o C. Fig. 7. Dynamic starting torque and speed of U shape design. Fig. 8. Output power and speed map of the U shape. Fig. 9. Rotor temperature with the U shape. IV. CONCLUSION In this paper, the influence of skewed slots and demagnetization effects on the LS PMA-SynRM has been successfully investigated and analyzed. The values of dynamic starting torque and speed with different types of I-W-U have been also compared. The obtained results have shown that for the U shape, the torque and power density are noticeable improved, and the volume of magnets is the lowest. For a short starting time, the speed is considered as a constant in Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9807-9811 9811 www.etasr.com Manh et al.: Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start … comparison with the I and W shapes. The validation of the selected machine in the traction application and the full map of dynamic starting torque and power have been presented. In particular, the comparison of efficiency performances have been investigated with three different shapes, i.e. I, W, and U. Thermal simulation is also implemented to validate overheat capacity. ACKNOWLEDGEMENT This study was funded by the University of Transport and Communications, Hanoi, Vietnam under grant number T2022- DT-005. REFERENCES [1] H. Kim et al., "Study on Analysis Method of Asymmetric Permanent Magnet Assistance Synchronous Reluctance Motor Considering Magnetic Neutral Plane Shift," IEEE Transactions on Applied Superconductivity, vol. 30, no. 4, pp. 1–4, Jun. 2020, https://doi.org/ 10.1109/TASC.2020.2968012. [2] C. Gong and F. 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