Permanent-magnet-excited electrical devices are becoming more and more important as demands for improved mechanical and energy efficieny grow. Nevertheless, the required properties can no longer be determined or simulated exclusively by classical analytical methods. The use of software tools based on the finite element method (FEM) is therefore particularly in the case of complex laminations and saturation – and enables their optimisation to achieve the device parameters required.
The simulation of the magnetic field at the beginning of a development process is essential to ensure the optimum design of the magnetic circuit. In addition to the ideal utilisation of the materials employed, this step is also used to determinde other important properties, such as the rotor-position-dependent induced voltage.
In the example shown here, it is noticeable that the stator teeth at certain rotor positions are too strongly saturated. The logical consequence is that the stator teeth must be made wider to avoid this problem. It can also be seen there is no risk of demagnetisation fort he magnets.
In the case of grooved laminates used in combination with permanent magnets, cogging torque effects occur that may or may not be desirable, depending on the intended application. The cogging-torque curve and ist maximum are determined by material properties and the geometry. As a result of the pole/groove combination, the following example shows a cogging-torque period of 30°.
Modifications to various parts of the geometry are an appropriate solution fort he reduction of cogging torque. However, this also causes changes in the induced voltage and ist harmonics, which must also be appropriately analysed.
Induced voltage harmonics
Induced voltage curve
Further computations and evaluations in the time domain, e.g. with PWM-controlled motor voltage, complement and finalise the simulation model. The following illustrations show the dynamic motor behaviour in the strating phase with the depiction of rotational speed, torque and phase current simulated fort he rotor position and in the time domain.
Internal rotors are employed when applications demand extreme speed ranges and dynamic properties and when motors are tob e designed for a high protection class.
Some typical applications for this type are servo-motors, actuators in automated systems and in packaging technologies.
with 15 grooves and 14 surface magnetsn
with 6 grooves and 4 embedded magnets
with 15 grooves and 14 embedded magnets, ´spoke design´
An external rotor ist he appropriate choice for slow-moving drives with the highest torque requirements.
They possess good speed constancy as a result of their higher moment of inertia. They are suitable for all applications in which the rotor can be directly employed as the power take-off, for example, as it is usually the case in ventilators or pumps.
with 9 grooves and 12-pole ring magnet
with 6 grooves and8 rectangular magnets
A linear motor is employed when a transverse motion without transmission components is required to achieve extreme positioning accurarcy and high positioning speeds.
By the combination oft wo axial directions, it is easy to realise arbitary motion and positioning in a single plane. Linear motors are therefore predominantly employed in automation technologies.
Single-phase motors with bipolar ring magnets are generally employed as reluctance motors.
They are therefore suitable for applications requiring a rotational direction that only needs to overcome a low starting torque. They are typically employed as cooling-fan motors in electronic systems an das aquarium pumps.
with 6 grooves and n magnets
with bipolar ring magnet