shows the line electromotive force per unit rotor speed. It can be seen that the waveform is almost an ideal sinusoid of which the amplitude is approximately equal to 0.2 V/r/min and the flux linkage induced by permanent magnets is 0.276 V·s. The total harmonic distortion of the waveform is 0.019 by using series expansion. As there is little ripple in the acquired data of no-load pressure difference, the cogging torque of the machine can be considered as very small and negligible.Then experiments under loaded conditions with various rotor speeds and electrical loads are implemented.