Design and operating characteristics of electrical machines with focus on permanent magnet synchronous machines

This seminar will not focus on learning the usage of simulation tools. Instead the primary objective of the seminar is to study the design of permanent magnet synchronous machines (PMSM) with various construction solutions and for an array of applications within the power range spanning several kW for industrial drives and up to several MW for PM generators.

In order to approach the seminar content to the usual machine design workflow, the design of PMSM will be explained in logical sequence of steps starting with the customer requirements (e.g. rated speed, power, desired efficiency) and going through the selection of fundamental design parameters (e.g. number of slots and pole pairs), the optimisation of machine geometry (e.g. optimisation of PM shape), the choice of the materials (lamination, PM type) to the calculation of key operating characteristics of the designed machine (e.g. efficiency, power factor)

For each of these steps various design solutions will be proposed and their influence on the relevant operating characteristics will be explained (key points listed below), allowing seminar participants to observe how a minor but “smart” change in the machine construction can, for instance, enhance the efficiency of the entire drive.  In order to comprehend the theoretical basics for this, various physical effects in electric machines and their calculation will be discussed: higher spatial harmonics and winding factors, skin effect, saturated inductances, eddy currents, losses in lamination (calculation analytically and as approximation of measured loss curves), BH-curves of permanent magnet etc. …

• Winding design comprising the choice of winding types (distributed / tooth coil, round wire / profile) and winding techniques considering influence on the following factors:
  ▪ additional losses, torque pulsations and noise due to higher spatial harmonics in the airgap field
  ▪ equivalent circuit elements like main and leakage inductances due to winding factors
  ▪ additional losses due to the skin effect
• Selection of materials, incl. lamination, PM-material and solid steel having an impact on the following factors:
  ▪ losses due to the eddy currents and hysteresis effect in lamination
  ▪ additional losses in permanent magnets and solid iron parts due to eddy currents
  ▪ risk of poor performance or even damage of the machine due to demagnetization of PM and its
  sensibility to the temperature
• Optimization of stator and rotor geometry including the design of tooth/slot form, the choice of PM shape (such as ring magnets or V-shape magnets), the incorporation of flux barriers for flux concentration within the rotor and skewing impacting the overall performance such as:
  ▪ torque due to flux concentration and due to rotor saliency
  ▪ cogging torques due to the stator slotting and rotor shape
  ▪ additional eddy current losses in PM due to stator slotting
  ▪ All inductances and consequently total machine behaviour due to the saturation in different areas of the machine
  ▪ Leakage inductances and transient behaviour of the machine, what is particularly important for
  the induction and salient pole synchronous machines

Due to the similarities between various AC machine types, some design solutions are applicable to and will be discussed for induction machine, reluctance machine and salient pole synchronous machine (for example skin effect and iron losses in stator)

A special part of the seminar is devoted to the methods of parameter identification and will help to answer the question “how can I get the required data sheet values from FEM-simulation?” including the following topics:

• Calculation of the full inductance matrix using the method of “frozen permeabilities”, problems of interaction between d- and q-axis over saturation, problem of exact calculation of torque using a full inductance matrix vs. conventional methods (useful for calculation of L_d, L_q and ψ_PM)
• Considering skin effect in the stator winding using FEM and simplified numerical methods, choice of optimal mesh density for a good balance of accuracy and calculation effort, calculation of the resistance increases factor k_r (important for resistance and efficiency calculation)
• Characteristic reactances and time constants (e.g. subtransient reactance for salient pole synchronous machine), their influence on critical transient processes (e.g. short circuit), simplified methods of calculation in FEM (without full transient simulation) considering eddy currents in rotor
• Identification of operation point in case if some non-directly definable values (e.g. power factor) are required, concept of time efficient operation point search without long transient simulation
• Basics of calculation of Mn-curves and efficiency maps

The theoretical part of the seminar will be based on the slides and materials created by Prof. Miller. The practical examples will be drawn from calculations and machine design work carried out by ProFluxx GmbH for industrial clients.

Your background — The seminar should be meaningful to a wide range of engineers of different levels of experience, no matter what software they use from day to day.  A basic first degree in electric power engineering would be a suitable academic background, because the theme of the seminar is quite electrical; even so, many experienced mechanical engineers and some postgraduate students may find themselves comfortable with the material.  In previous seminars, the class members have typically had quite varied backgrounds, and the seminars have evolved in such a way as to benefit from this.

Dr. Andreas Biebighäuser brings over 30 years of experience in electromagnetic design and calculation of synchronous and induction machines in both industrial and academic sector. He previously worked at the Leibniz University Hannover, Siemens AG, and Cummins Generator Technologies, where he held different positions as Research Scientist, EM Design Lead and Global Chief Engineer, respectively. In 2015, he co-founded ProFluxx GmbH and currently is working as Managing Director and Chief Engineer. His primary areas of expertise are optimisation of synchronous generators in the power range of up to 40 MW and induction motors to improve their basic operating characteristics.

Olga Korolova has over 10 years of experience in electromagnetic design and calculation of synchronous and induction machines. She was a Research Scientist at Leibniz University Hannover where she also taught courses on small machines. Currently she is working as Senior Electromagnetic Design Engineer at ProFluxx GmbH, specializing in FEM analysis, transient simulations of synchronous machines, and developing analytical-numerical tools for high-efficiency performance calculations. She is also holding seminars on topics ranging from basics to special effects, calculation, and control of electrical machines.