The Operating Point in Motor Wiz represents the combination of motor speed, torque, current, voltage, and thermal conditions under which the motor functions. From a user perspective, this module allows designers and engineers to analyze the performance boundaries of their motor design and understand how it behaves in real-world conditions, including torque-speed behavior, thermal constraints, and efficiency.
The Operating Point section integrates data from Motor Attributes, Material & Thermal properties, Geometry, Stator and Rotor parameters to simulate realistic performance for EVs, industrial drives, and specialized applications. Users can visualize motor behavior dynamically and make informed design decisions before prototyping.
i. RPM – Rotor Speed (rpm)
Definition: The rotational speed of the motor’s rotor, measured in revolutions per minute.
Purpose in Simulation:
Determines induced voltage, back-EMF, and torque generation.
Influences core losses, eddy currents, and efficiency at higher speeds.
Sets the synchronous operating condition of the motor model.
Machine-Type Specifics:
IPMSM: Wide speed range, strong flux weakening; high-speed capable (~20,000 rpm in EVs)
SPMSM: Moderate speed operation, simpler rotor
SynRM: Efficient at medium-to-high speeds with lower torque ripple
SCIM: Broad speed range, rugged, efficiency drops at very high rpm
User Perspective: Motor Wiz allows users to:
Enter rotor speed range for simulations
Observe torque-speed and power-speed curves
Compare predicted speed with vehicle dynamics requirements
Typical Range for EVs: 1,000 – 20,000 rpm depending on motor type, design, and vehicle class.
ii. Id – Direct Axis Current
In a motor constraint curve context, "Id" refers to the d-axis current component in the rotating d-q reference frame representing the motor currents. It is the current along the direct axis aligned with the rotor magnetic field in synchronous motors like Permanent Magnet Synchronous Motors (PMSM).
The Id component, together with the quadrature axis current (Iq), defines the operating point of the motor with respect to torque and flux control within the motor constraint curves, such as the current limit circle and constant torque curve. Id is essential in determining torque production and motor control limits.
iii. Iq – Quadrature Axis Current
In motor control, particularly in synchronous motors, Iq (quadrature-axis current) refers to the component of the motor current that is responsible for producing torque. It is the current component aligned 90 degrees (in quadrature) to the rotor magnetic field and directly controls the motor's torque output.
In vector control or field-oriented control (FOC) of motors, the current is decomposed into two components:
Id (direct-axis current): Controls the magnetic flux
Iq (quadrature-axis current): Controls the torque
The Motor Constraint Curve often plots constraints such as current limits (Id, Iq), voltage limits, and torque limits to describe the safe and efficient operational boundaries of the motor under different conditions. The Iq component is a key parameter in this curve as it relates directly to achievable torque.
In brief: Iq in Motor Constraint Curve represents the torque-producing current component under motor control, which, along with Id (flux-controlling current), defines the motor's operational limits and performance constraints.
iv. Magnet Temperature
Definition:
The temperature of the permanent magnets influences their remanent flux density (Br).
Purpose in Simulation:
Higher temperatures reduce magnet strength due to thermal demagnetization.
FEMM adjusts the remanent flux density (Br) based on the temperature.
Important for evaluating temperature-dependent performance in high-power motors.
Typical Values:
Standard operating range: 25°C to 150°C.
NdFeB magnets lose 0.1% to 0.12% of their flux per °C increase.
At 150°C, some NdFeB magnets can lose up to 30% of their strength.
v. I0 – Stator External Radius (Arms)
Definition:
The stator external radius (I0) refers to the outer radius of the stator core or stator frame in an SCIM, which defines the outer cylindrical dimension enclosing the stator windings and core lamination.
Design Importance:
This radius is critical for motor design because it impacts the magnetic flux path, heat dissipation surface area, and the mechanical strength of the stator structure.
Typically, the stator core is constructed from thin, laminated electrical steel sheets stacked cylindrical to reduce eddy current losses; the outer radius includes the stacking length plus any insulation and housing thickness.
The stator outer radius influences the air gap length (the gap between stator and rotor), which affects motor performance parameters like magnetizing current, torque ripple, and losses.
Design Integration:
The stator external radius is usually defined in conjunction with other motor dimensions like stator bore diameter (internal radius), core length, slot dimensions, and winding layout in the design specification.
Empirical formulas and motor design standards help optimize the stator external radius to balance electromagnetic performance, thermal management, and material costs.
Typical Range:
For example, in typical industrial SCIMs, stator outer diameter ranges from a few centimeters for small motors to several tens of centimeters for higher power motors, corresponding to external radius values proportionally half of that.
Applications:
Accurate measurement or calculation of this radius is essential for simulations, electromagnetic field modelling, assembly fitting, and ensuring compatibility with mounting and cooling systems.
vi. Φ₀ – Stator External Radius
Definition:
Φ₀ typically denotes the external radius of the stator in a Squirrel Cage Induction Motor (SCIM). It represents the outer boundary of the stator core, which holds the stator windings.
Role in Motor Construction:
The stator external radius determines the overall size of the stator frame, including the core and slots where the windings are placed. It impacts the magnetic circuit, mechanical strength, and cooling surface area of the motor.
Magnetic Flux Path:
The external radius (Φ₀) confines the magnetic flux within the stator core lamination. A larger Φ₀ usually allows more room for winding and magnetic material, affecting the motor's magnetic flux density and performance.
Thermal Considerations:
The stator outer radius influences heat dissipation. Larger Φ₀ provides a bigger surface area for heat to escape, aiding motor cooling which is critical for maintaining performance and longevity.
Design Balance:
Choosing Φ₀ involves trade-offs between motor size, efficiency, power output, and mechanical robustness. It must fit within physical constraints while optimizing electromagnetic and thermal performance.
Typical Values:
The exact Φ₀ depends on motor power rating and frame size standards, often specified in design documentation or motor datasheet.
vii. Angular Points
Definition:
Number of angular discretization points used to break the rotor and stator geometry into small angular segments.
Purpose in Simulation:
More points lead to higher resolution but increased computation time.
Fewer points reduce accuracy but speed up the simulation.
Typical Values:
Default: 360 points (1-degree resolution).
Higher accuracy: 720–1440 points (0.5-degree to 0.25-degree resolution).
viii. Time Steps
Definition:
Number of discrete time intervals used for transient or dynamic simulations.
Purpose in Simulation:
More time steps improve accuracy in dynamic simulations like torque ripple analysis.
Too many time steps increase computational load.
Typical Values:
Steady-State Simulation: 1–10 steps.
Transient Simulation: 100–1000 steps.
ix. Mesh Fineness Factor
Definition:
A global coefficient used to adjust mesh fineness in FEMM, where:
Purpose in Simulation:
Fine mesh improves accuracy but increases simulation time.
Coarse mesh speeds up simulation but reduces accuracy.
Typical Values:
Default:1
Fine Mesh: 1.2 – 2.0 (for detailed loss analysis)
Coarse Mesh:0.8 – 0.9 (for fast initial analysis)
x. Parallelization
Definition:
Number of parallel processing threads used by FEMM to run simulations.
Purpose in Simulation:
More workers reduce computation time by parallelizing the workload.
Requires a multi-core processor for full benefits.
Typical Values:
Single-threaded:1 (default)