Fig. 5. The average power profile against the electric load for different rotation frequencies.

Curves are plotted for two different lubricating liquids, a PC and b IL mixture. Each case is presented for three different rotation frequencies (typical and different for each case, due to the difference in drag torques). Parameters: a $N={10}^2$, $V_{\mathrm{ref}}=50\mathrm{V}$; b $N={10}^3,V_{\mathrm{ref}}=4\mathrm{V}$. Note that the optimal power regimes and structures for these two systems (a and b) are achieved for different number of stages, frequencies and voltages; and the graphs of the power, in a and b, have been plotted for different parameter domains.