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Why Switched Reluctance Motors?
Let’s Focus on 3 Motor Types
• AC Induction• Brushless DC• Switched Reluctance
AC Induction
Source: “AC, Brushless, Switched Reluctance Motor Comparisons” James R. Hendershot, Magna Physics Corporation
Brushless DC
Source: “AC, Brushless, Switched Reluctance Motor Comparisons” James R. Hendershot, Magna Physics Corporation
Switched Reluctance
Source: “AC, Brushless, Switched Reluctance Motor Comparisons” James R. Hendershot, Magna Physics Corporation
Dimensions, Volumes & Weight Comparisons of the 3 Motor Types (NEMA 184 T Frame)
Source: “AC, Brushless, Switched Reluctance Motor Comparisons” James R. Hendershot, Magna Physics Corporation
Motor Comparison for BEVs & HEVs
Design # Accel 0-60 SRM kW SRM KVA AC Induc kW AC Induc KVA BLDC kW BLDC KVA1 13.00 42.1 69.80 57.88 72.35 75.50 83.902 13.25 42.56 69.86 56.90 71.13 74.43 82.703 13.48 42.61 69.90 56.00 70.00 73.27 81.414 13.58 45.88 69.85 55.68 69.60 72.78 80.865 13.85 39.1 64.76 54.70 68.38 71.46 79.406 14.78 34.6 59.35 51.68 64.60 67.39 74.887 14.10 38.98 64.68 53.85 67.30 70.34 78.158 15.01 35.38 59.32 50.10 62.60 66.40 73.779 10.10 68.12 101.40 72.70 90.88 95.67 106.30
10 8.74 69.95 109.30 83.04 103.80 109.60 121.80Source: “Advantages of Switched Reluctance Motor Applications to EV and HEV: Design and Control Issues” M. Ehsani, et al, IEEE Transactions on Industry Applications, Vol. 36, No 1, January/February 2000
What About Noise?
In Summary• Due to the absence of rotor windings, SRM is very simple to construct, has a low inertia and allows
an extremely high-speed operation. SRM operates in constant torque from zero speed up to the rated speed. Above rated speed up to a certain speed, the operation is in constant power. The range of this constant power operation depends on the motor design and its control. Designing a motor with high constant power range to base speed (e.g. at least 4:1), is not hard to achieve with SRM, and has a great effect in designing a lower power motor that can produce significant torque.
• The absence of rotor copper loss eliminates the problem that the induction motor has associated with rotor cooling due to its poor thermal effects. The absence of permanent magnets on the rotor eliminates the problem that the Brushless DC motor has with high temperature environments whereby the magnets can lose their magnetization.
• The SRM has many advantages, mostly resulting from its simple structure. SRM is normally low cost because of its extremely simple construction. Moreover, The SRM operation is extremely safe and the motor is particularly suitable for hazardous environments. The SRM drive produces zero or small open circuit voltage and short circuit current.
• Furthermore most SRM converters are simple because the current is unipolar. The SRM drive is immune from shoot through faults, unlike the inverters of induction and brushless dc motors. Due to the inductive nature of the motor, the power factor of the SRM is lower and requires a higher rated converter when compared to induction or BLDC motors.
