This blog will discuss how to design synchronous reluctance machines in Opera. Here is some sample geometry of a typical Synchronous Reluctance, or SyncRel, machine, showing a cross-section of the laminations.
Obviously, this happens because you are affecting the Ld:Lq ratio. As you increase the thickness of the bridges to improve mechanical stiffness, we reduce the reluctance on the quadrature axis. So we have a trade-off between electromagnetic and mechanical design, which means that if we design for one set of physics exclusively, we will end up with, overall, a poor design. And we cannot analyse the different physics in isolation because of the inter-dependence of loadings. For example, we need to add electromagnetic forces to the mechanical forces when performing the structural analysis, or we will possibly exceed allowable stresses. And we need to feedback the deformed shape into the electromagnetic analysis because this will tend to close the airgap and affect the torque curve in an unpredictable fashion.
Opera has, for some time, contained a module called the Machines Environment, which uses a wizard-style data-entry for ease-of-use. The Environments are written in the Opera programming language that is fully documented and available to users, so they are not merely a closed executable. Common types of machines are offered, but in the Developer version the command files are, mainly, open-source so the user is free to make adjustments to the standard command file. This could be a small tweak to a slot shape right through to a completely new topology of rotor or winding. Relevant data, in terms of standard machine parameters, is gathered for the machine being analysed then the environment builds a full-fidelity finite element model. Analyses are submitted automatically to the Batch processor, then standard post-processing commands automatically generate plots and reports such as torque-speed curves. This Environment has been extended under this program for SynchRels.
Following this, the geometric model and the mesh are created automatically. The mesh size is calculated automatically, but the user has the chance to override the default setting to either perform a quick, coarse analysis, or to define a fine, high-resolution mesh for final detailed checking.
Further dialogs prompt for the required material properties, and also the properties of the drive. For example, the user can specify the windings, operating voltage and current, and the frequency and speed. Users have the chance to override default drive circuits with circuits or their own. If loss calculations are required the user enters properties required for copper and iron losses.
There are a list of analyses to choose from in the Machines Environment for a SynchRel, or any other type of machine for that matter. The simplest is an electromagnetic analysis looking at static torque vs angle at multiple current levels. This is performed automatically in the static electromagnetic solver for a given number of rotor positions. The next is one of two possible dynamic analyses. The user can choose to run a fixed speed of rotation in an electromechanical analysis, and generate iron loss calculations. Or you can run a transient analysis against a given mechanical load. The user is also given a choice of two pure mechanical analyses – an eigenvalue analysis of the unloaded structure, or a static stress analysis of the rotor under centrifugal loading.
Next on the menu is the option to run investigations of mechanical effects on electromagnetic performance. This consists of, again two choices. Firstly, an iterative coupling of electromagnetics and stress to look at the effect of the rotor deformation on the electromagnetic behaviour. Or, secondly, a perturbation analysis, looking at the effects of manufacturing tolerances on the electromagnetic performance, including unbalanced magnetic pull. The final choice on the menu is an option to calculate D, Q and crosscoupling inductances using a series of static analyses at different rotor positions. This will produce a look-up table against current for use in a system-level analysis.