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Design of a 100 KW SRM For Traction Applications

Motors & Generators with MotorSolve

Switched reluctance machines have been gaining increasing attention lately on account of their simplicity and their "non-use" of permanent magnets, especially, rare earth types that are commonly used for traction applications.

Using MotorSolve SRM, a 100 KW SRM is designed for traction application. It is 3-phase and 12/8 type. The design specifications:

  • DC link voltage: 600 V
  • Maximum outer diameter: 32 inches
  • Rated speed: 1000 RPM
  • Rated Current: 300 Amps peak
  • Output Power: 100 KW
  • Efficiency > 92%

Typical results that are needed for the design of such machines are presented: magnetization characteristics, static torque, torque speed characteristics, optimization of firing angles.

100 KW 3-phase 12/8 SRM traction machine

METHODS and RESULTS

MAGNETIZATION CURVES

The plots of flux Linkage vs. current, with varying rotor positions from the unaligned to the aligned position are shown in the figures. These are the magnetization characteristics of the machine being designed. Such results, based on FEA based calculation and using analytic approximations can be obtained readily using MotorSolve SRM.

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INDUCTANCE PROFILES

The plots of flux Linkage vs. current, with varying rotor positions from the unaligned to the aligned position are shown in the figures. These are the magnetization characteristics of the machine being designed. Such results, based on FEA based calculation and using analytic approximations can be obtained readily using MotorSolve SRM.

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STATIC TORQUE

Another important design characteristic for SRMs is the static torque values as a function of rotor position at various peak phase current. Here, an example of such results is shown for current ranging from zero to 300 Amps.

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FLUX DISTRIBUTION

The instantaneous flux distribution in the machine at a specific position and speed taking into account possible continuous conduction in other phases is important for optimizing the geometry as well as the firing angles. In this figure the instantaneous field distribution from such an analysis has been presented.

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OPTIMAL FIRING ANGLES

A significant challenge for SRM design is to optimize the firing angles at a particular speed. Setting speed dependent firing angles can be a challenging and time consuming set of calculations. In MotorSolve SRM, this can be done readily by simply supplying a speed dependent firing angles table as shown here.

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TORQUE-SPEED CHARACTERISTICS

Using the table of speed dependent firing angles, complete dynamical simulation at each speed taking continuous conduction mode into consideration allows the user to accurately obtain the torque versus speed characteristics of the machine.

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PHASE CURRENTS

The dynamical simulation in MotorSolve SRM automatically restricts the phase currents as per a half-bridge circuit that typically drives such machines. The current limiting factors include the DC link voltage as well as the phase inductance and the firing angles. The results of dynamical simulation at various speed and firing angles are shown here.

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DESIGN SUMMARY

The performance of the traction motor at rated speed is summarized here. Note that the results include a breakdown of ohmic and iron losses at the component level.

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