# Analysis of Permanent Magnet Motors in High Frequency--A Review
## 5 Influence of Design Parameters on EMC
### Additional Actions  
After the basic machine design, some additional actions may be taken to decrease EMI in electrical machines once they are manufactured. For instance, in [53] insertion of additional grounded electrodes into the slot wedge leads to reduce the winding-to-rotor capacitance, minimizing the non-circulating bearing currents.  
Moreover, [100] proposes reducing the absolute value of the magnetic flux leakage by a two-layer shielding of the machine, intending to reduce the induced voltage in the surrounding electrical loop. However, as shielding the whole machine may be too expensive and bulky, in [10] shielding of the end windings is proposed to reduce the winding-to-rotor capacitance and the bearing currents, as the end winding represents less than the 1% of winding-to-stator capacitance but up to 40% of the total winding-to-rotor capacitance and it influences the phase-to-phase capacitance [10; 54]. Different shielding methods are proposed, showing different \(C_{wr}\) reductions, and a good achievement is made for bearing health and life expectancy. Even if the mayor reduction would be achieved with the solid shielding, as it increases the iron losses, the [PERSON]'s cage shielding could be a better option.  
Additionally, there are some external factors beyond the machine that can affect EMI behavior, such as inverter modulation pattern and frequency, DC bus voltage, but there are out of the scope of this work [1; 12].  
Although the machine operating point or its torque angle may also affect DM EMI level, this cannot be used as an EMI improvement way, because it would reduce the working range of the machine [26]. Something similar happens with the influence of airgap size on the stator-to-rotor capacitance, as it affects to the EMI behavior but also to the machine performance [12].  
Finally, as an introduction to the future work, in [101] a new systematic method is proposed to quantify the influence of tolerances on PMSM performance to identify possible non-compliant-dimensional variables and material characteristics, based on the results of the open-circuit and short-circuit procedures of IEEE Std 1812. Design of Experiments (DOE) is used to analyze the influence of each analyzed parameter. In this case, short-circuit current, torque ripple, open-circuit voltage, and core losses are analyzed as output variables, but it may be useful when analyzing the influence of tolerances and design parameters on high-frequency behavior.  
Summarizing, an overview of the different studied design parameters influencing the high-frequency behavior of the machine is shown in Table 6.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameter** & **Impact** & **Optimum** \\ \hline Parallel Circuits & First resonance frequency & \(f_{sSeries}=\frac{1}{2}f_{Parallel}\) \\ \hline Y-\(\Delta\) Connection & First resonance frequency in CM Impedance & (\(\Delta\) higher than Y) \\  & DM Impedance Amplitude & (Y higher than \(\Delta\)) \\ \hline \multirow{4}{*}{Conductor placement} & _Cur_ \& insulation stress \\  & Bearing \& CM Currents & Furthest from rotor \\  & Shaft Voltage & Middle of the slot \\  & Copper Losses & Strands aligned with flux lines \\ \hline Winding Topology & Winding-to-ground capacitance & Circumferential winding \\ \hline Impregnation level of conductors & Stray Capacitance & Low (affects thermal) \\ \hline Slot Shape & \(C_{wr}\), Shaft voltage & - \\ \hline \multirow{2}{*}{Electrodes in slot wedge} & _Cur_ \& insulation stress & High diameter \\  & Bearing \& CM Currents & Nearest from rotor \\  & Shaft Voltage & \textgreater{}1 electrodes together \\ \hline Airgap size & \(C_{rs}\) & Minimum \\ \hline Shielding & Induced voltage & Depends on frequency \\ \hline End-winding shielding & \(C_{wr}\) & Faraday’s cage * \\ \hline \hline \end{tabular}  
* An equilibrium must be made between the shielding structural complexity and the \(C_{wr}\) desired reduction.  
\end{table}
Table 6: Design parameter influence review.