Design of a cylindrical, permanent magnet synchronous generator

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Kohári Zalán
Department of Electric Power Engineering

In the present master thesis work I write about designing a three-phase, 19 kW permanent magnet synchronous generator (PMSG) for U=460 V nominal (line) voltage, with 500 rpm rotor speed and square–wave air-gap flux distribution.

The design process was based on analytical calculations, which I describe in details. I present the used equations and the theoretical background. However, finite element software (FEMM4.2) was also used for verification of the analytical results, in case of examining the effect of the rotor length to the effective length of the machine, and, when determining the flux distribution in the air-gap.

I determined the main dimensions of the machine from analytical equations. An iterative process was needed for finding the correct rotor dimensions (diameter and length) and open-circuit e.m.f. to get the nominal terminal voltage at nominal load conditions.

I verified the rotor dimensions of a mechanical point of view. I determined the maximum rotor length for the nominal angular speed on the machine which is the highest possible length to avoid resonance. I also determined the maximal centripetal stress of the rotor. Then, I calculated the parameters of the slots, teeth and yokes. The winding was designed for eliminating the harmful harmonics in the generator voltage waveform, to get as sinusoidal waveform as possible.

Based on different methods, the required magnet height was also determined and compared with the finite-element software given results. I pay special attention to choosing the optimal relative magnet width. I examine the optimal relative magnet width for

1) minimizing the air-gap flux density harmonics

2) minimizing the generator no-load voltage total harmonic distortion (THD)

3) minimizing the iron losses

The magnetizing inductance, slot leakage inductance, tooth tip inductance and end winding inductance were determined. I present the equivalent electrical circuit of the machine. Iron losses, copper losses, additional mechanical losses (i.e. bearing losses, windage and ventilator losses) as well as eddy-current losses in the permanent magnets were calculated. Based on these, I determined the efficiency of the machine.

I made most of the analytical calculations on a MathCad worksheet, which can be found in the appendix. I also used Microsoft Excel and AutoCad software.


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