Electric motor design has become increasingly critical in many applications including automotive electrification, aerospace and defense technology, industrial equipment, and renewable energy systems. Ansys Maxwell is a leading electromagnetic simulation software package used to optimize motor designs for efficiency, performance, and reliability. As motor geometries become more complex and performance requirements more stringent, Maxwell continues to introduce breakthrough simulation technologies that address the industry's most pressing challenges. This article highlights several advanced capabilities available in Maxwell for electric motor simulation: slice-only solutions and the continuum air formulation.
Slice-Only Solutions
Engineers have traditionally faced obstacles when simulating electric motors due to the computational resources and time required to solve full 360-degree models. Using partial models defined by two radial cuts is a typical method which takes advantage of circumferential symmetry, but introduces new complications for complex geometries such as skewed rotor and stator configurations. For these cases, the conventional method of creating planar radial cuts can result in finite element mesh mismatches, geometric artifacts, and accuracy issues at the matching boundary conditions. This method also requires manual setup of the partial model from the full geometry with appropriate boundary conditions and solution settings.
To eliminate these issues, Ansys Maxwell offers built-in slice-only solutions which significantly advance how engineers approach electric motor simulation. Rather than requiring planar cuts to be implemented by the user, Maxwell intelligently analyzes the full structure and automatically determines the optimal simulation slice based on the motor's inherent symmetry. The software handles all the complexity behind the scenes to virtually divide the geometry and take advantage of cyclic repeatability, allowing engineers to focus on the design rather than the simulation setup.
Figure 1: Example full motor model (left) with automatically created non-planar symmetry boundary (center) and fields and mesh displayed on full model (right)
What sets this novel approach apart is its use of non-planar matching boundary conditions. Unlike traditional planar cuts, these sophisticated boundaries better accommodate complex geometries such as skewed components. The technology maintains high mesh quality at boundaries while ensuring perfect symmetry in the solution. It generates a partial mesh in one periodic region, complete with an arbitrary non-planar matching boundary mesh. By automating the process of determining appropriate boundaries and mesh configurations, the potential for user error is greatly reduced and simulation reliability is guaranteed.
Figure 2: Slice-only modeling of skewed stator with automatically created identical mesh on rotationally periodic geometry
With slice-only solutions automatically replicating the results of the partial solution onto the full model, engineers are free to directly work with the complete 3D model from initial setup to final visualization. Results can be interpreted in the context of the complete design, which is especially valuable during design reviews and when communicating with stakeholders.
Figure 3: Menu settings easily enable the slice-only solution
The use of slice-only solutions enables faster simulation times without sacrificing accuracy, often reducing computation time by orders of magnitude. The automatic mesh cloning capability ensures consistent mesh quality across the model, reducing non-linear meshing errors and accelerating convergence. It reduces the expertise required for successful setup, making advanced simulation capabilities accessible to a broader range of engineers. For example, engineers can import complete motor designs directly from template-based solutions such as Ansys Motor-CAD or mechanical CAD software without the need for geometry modifications.
Continuum Air Formulation
Electric motor transient simulations face a fundamental challenge when modeling rotational motion. As the rotor turns, the finite element mesh nodes at the interface between the moving and stationary parts slide past each other and can become misaligned. This misalignment can create numerical artifacts in the magnetic field calculations at the interface boundaries since an interpolation technique is necessary to map the fields from one side to the other. The air gap region is an important part of electric motor simulation models, and proper meshing is a critical factor in achieving accurate results.
Numerical inaccuracies in this region can impact motor design parameters such as cogging torque, forces which cause noise and vibration, and core losses in the stator. Engineers often needed to implement careful mesh alignment strategies and maintain constant time steps and rotational speeds. These requirements not only increase simulation setup time, but can limit the ability to model operating conditions where speeds and time steps vary.
Figure 4: Example mesh complexity at interface between moving and stationary components
Ansys Maxwell has introduced a sophisticated new approach named continuum air which accurately handles the sliding mesh interface between rotating and stationary components during transient solutions. This advancement fundamentally changes how the solution is calculated in the airgap region during motion, significantly improving the smoothness of the magnetic fields. The innovation lies in its high-fidelity solution which couples the stationary and moving components of the model without requiring mesh-time step alignment.
This improved solution technique eliminates mesh and time step alignment requirements, simplifying the simulation setup process. It supports variable rotor speeds and non-constant time steps, improving the ability to simulate different operating conditions. The enhanced solution produces smoother magnetic fields at the interface which reduces numerical artifacts and improves accuracy in sensitive calculations such as cogging torque. 
Figure 5: Example mesh at sliding interface and improved cogging torque calculation for axial flux motor
Continuum air supports all standard excitation winding types and the use of full and partial models. It also supports the powerful time decomposition method which solves multiple time steps simultaneously to dramatically reduce total computation time for a transient solution. The formulation is available for both 2D and 3D motor simulation models, making it a versatile tool for various design scenarios. The solver automatically handles the calculations required for accurate field representation at interfaces, saving time and reducing the potential for setup errors.
Figure 6: Example improved force calculation for motor stator using the continuum air formulation
Summary
Ansys Maxwell continues to bring the power of advanced simulation technology to engineers in a user-friendly interface, solidifying its position as the premier solution for electric motor design. Slice-only solutions allow engineers to easily and confidently model complex skewed geometries while the continuum air formulation for sliding mesh interfaces provides unprecedented and robust accuracy for rotating machine simulation. As electric motor technology continues to evolve, engineers can rely on Maxwell's comprehensive capabilities to efficiently simulate leading-edge designs which can meet demanding challenges.