Design and Voltage Supply of High-Speed Induction - Aaltodoc

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14 1.2 Aim and contents of this work The motivation and aim of this work is to find good designs for high-speed induction machines. Special attention is paid to rotors suitable for these machines. Another goal is to find supply voltage waveforms appropriate for a high-speed induction machine with a solid rotor. In order to design good high-speed machines, modeling is modified and verified. In this thesis, comparisons of different rotor constructions are made. A trade-off situation between mechanical and electromagnetic properties is studied. In two measurement cases, different rotors for high-speed induction machines are tested. Different rotor constructions are also studied in two cases of numerical optimization. The optimization algorithm is modified in order to decrease the calculation time and provide data for the post processing of results. Different voltage supply waveforms for a high-speed induction machine are tested. Circulatory currents in a stator winding of a high-speed machine are shown to produce extra power loss and discrepancy between electromagnetic loss measured and calculated. Separate 2D FEM modeling of end ring inductance and effective length of a machine are implemented in the model of the machine. In Chapter 2 some basic aspects in the design of a high-speed induction motor drive are discussed with references to the field of science. Effects of a high supply frequency on the selection of magnetic materials, slotting and winding are commented on. The importance of dimensioning the air gap is emphasized as perhaps the most important single design parameter. The cooling of a motor is acknowledged as an important subject since loss distribution and loss densities are different from the conventional motors. The frequency converters used and the voltage modulation are presented in the last section. Chapter 3 concentrates on the rotors of the high-speed induction machines. Section 3.1 describes the mechanical constraints limiting the rotor design. As a starting point for a development, a commercially used copper coated solid steel rotor is presented in Section 3.2. Two alternative approaches are suggested. In Section 3.4, a laminated rotor suitable for high speeds is presented. In Section 3.5, two solid steel rotors with a squirrel cage are presented for a comparison against a copper coated solid steel rotor. Chapter 4 presents the comparison of the laminated rotor and a copper coated solid steel rotor for a 65 kW 30600 1 /min compressor motor. Section 4.1 describes the measurement setup and Section 4.2 is for the results of the comparison. The compressor itself is used to load the high-speed induction motor. The results are concluded in Section 4.3.
Chapter 5 reports the comparison of the squirrel cage solid steel rotors and a copper coated solid steel rotor for a 60 kW 60000 1 /min motor in a similar fashion. In this case, a back-to-back measurement setup is used. Two identical machines are coupled together, one working as a motor and the other as a generator. This setup provides more information and makes it easier to divide the power loss into components. The actual measurements were made at 50100 1 /min. The effect of different supply voltage waveforms on the performance of the high-speed drive is studied in Chapter 6. Comparison between pulse amplitude modulation and pulse width modulation is presented in Section 6.1. The comparison is done both theoretically and by using measurements. The same back-to-back measurement setup and the same high-speed drives are used as in Chapter 5. The results of the comparison are concluded in Section 6.2. The modeling and optimization methods used in this study are presented in Chapter 7. Handling of 3D phenomena in a 2D modeling are discussed. End ring inductance is modeled with a separate 2D FEM model in Section 7.1. The effective length of a machine is also modeled with a separate 2D FEM model in Section 7.2. Section 7.3 presents the calculation results for the motor with the copper coated rotor tested in Chapter 5. The results of the calculations are compared against the results from the measurements. Circulatory currents in parallel paths of a stator winding are studied in Chapter 8. They are shown to generate a considerable amount of extra loss, which is not modeled in the calculation software. Section 8.1 provides the results of individual strand current measurements for the 60 kW 60000 1 /min motor presented in Chapter 5. The circulatory current loss factors are calculated from the results. Impedance of a circulatory current loop is measured in Section 8.2. Using information gained in the sections above, an estimation model for the loss factor is defined in Section 8.3. The model is used to estimate the values of the loss coefficient in the operation points measured in Chapter 5. Taking into account the circulatory current effect, it is shown in Section 8.4 that the model discussed in Chapter 7 gives relatively accurate results. Circulatory currents and voltage modulation are discussed in Section 8.5. Chapter 9 presents two optimization cases and proposes an improvement to optimization algorithms used with time consuming numerical models. The improvement based on discretization and use of a solution history is presented in Section 9.1. Section 9.2 presents the first optimization case, where a squirrel cage solid steel rotor is optimized. The optimized rotor design is compared against the designs measured in Chapter 5. In the second case, a general topology of a rotor suitable for a highspeed induction machine is studied. This optimization case with results and discussion is presented in Section 9.3. The Summary of the work is given in Chapter 10. 15
Page 1 and 2: El 108 ACTA POLYTECHNICA SCANDINAVI
Page 3 and 4: PREFACE This thesis is the result o
Page 5 and 6: 5 Comparison of rotors for 60 kW 60
Page 7 and 8: LIST OF SYMBOLS a Number of paralle
Page 9 and 10: Rn Resistance of a parallel conduct
Page 11 and 12: 1 INTRODUCTION The need for high ro
Page 13: Conventional (high-speed) drive Hig
Page 17 and 18: Some penetration depth values are c
Page 19 and 20: 2.2 Stator windings for high-speeds
Page 21 and 22: ⎛ π ⎞ sin⎜ν ⎟ ⎛ π ⎞
Page 23 and 24: Table 2.3 Air gap characteristics o
Page 25 and 26: Cooling of the stator could need ax
Page 27 and 28: f sw N p = (2.9) fs The switching f
Page 29 and 30: 3 ROTOR CONSTRUCTIONS Starting from
Page 31 and 32: and eddy-currents traveling on the
Page 33 and 34: support the squirrel cage winding,
Page 35 and 36: 3.1.3 Rotor loss and friction loss
Page 37 and 38: Table 3.1 High-speed induction moto
Page 39 and 40: critical speeds are passed relative
Page 41 and 42: Table 3.2 The free-free natural fre
Page 43 and 44: Table 3.3 The free-free natural fre
Page 45 and 46: 4 COMPARISON OF ROTORS FOR 65 KW 30
Page 47 and 48: Temperature [ºC] 110 109 108 107 1
Page 49 and 50: Temperature rise [K] 120 100 80 60
Page 51 and 52: improve the laminated design, more
Page 53 and 54: The copper coated solid steel rotor
Page 55 and 56: As reported in Lähteenmäki et al.
Page 57 and 58: Temperature rise [K] 100 80 60 40 2
Page 59 and 60: Temperature rise [K] 140 120 100 80
Page 61 and 62: 6. The rest of the loss is defined
Page 63 and 64: Temperature rise [K] 100 80 60 40 2
Page 65 and 66:
5.2.7 About the mechanical robustne
Page 67 and 68:
6.1 Comparison of PAM and PWM for 6
Page 69 and 70:
h d = , (6.2) I I h, PAM where Ih,P
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Fig. 6.4 Phase-to-phase voltage and
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Temperature rise [K] 120 100 80 60
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Machines loss [W] 12000 10000 8000
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considerably higher than expected.
Page 79 and 80:
In order to improve the performance
Page 81 and 82:
l = + , (7.2) sλs 2leλ e l wλ w
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gap of 1 mm would yield an effectiv
Page 85 and 86:
Table 7.1 Calculated effective leng
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Input current [A] 170 160 150 140 1
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8 CIRCULATORY CURRENTS IN A STATOR
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Table 8.1 Circulatory current loss
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Fig. 8.4 Strand currents in the two
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8.2 Impedance of the circulatory cu
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Because Φ l is approximately at th
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Table 8.2 Circulatory current loss
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Power loss [W] 3500 3000 2500 2000
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k cc 600 500 400 300 200 100 0 0 50
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9 OPTIMIZATION OF SOLID STEEL ROTOR
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whole solution space determined by
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the average time saving is 39 %. Th
Page 111 and 112:
Fig. 9.3 Cross sections of the 16,
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Height of bar slot [mm] 8 6 4 2 0 R
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The different rotor topologies were
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possible. The coating practically v
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Table 9.3. Optimization results for
Page 121 and 122:
Fig. 9.11 Initial (left) and opt. (
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high-speed induction machine. Accor
Page 125 and 126:
Foelsch K. 1936. Magnetfeld und Ind
Page 127 and 128:
Pyrhönen J. and Kurronen P. 1994.
Page 129 and 130:
APPENDIX 129
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currents in the solid iron flow mor
Page 133 and 134:
where the C sw E is the loss coeffi
Page 135 and 136:
B. CALCULATION OF THERMAL CHARACTER
Page 137 and 138:
Axial cooling duct Frame R fr3 Stat
Page 139 and 140:
Linear equalities Ax = b, (C3) wher
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Design and Voltage Supply of High-Speed Induction - Aaltodoc

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