Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection

Abstract

In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.

An experimentally determined field winding model with frequency‐dependent parameters

“…where L p,in and L p,out stand for the field winding inductance measured with the rotor set in the machine bore and outside it, respectively. Results ( 14) and (15) proves that the inductance of the rotor winding drops when the frequency increases, regardless of the relative position between rotor and stator. Moreover, equation (15) shows that the field winding inductance is weakened by the presence of the stator around the rotor.…”

“…Results ( 14) and (15) proves that the inductance of the rotor winding drops when the frequency increases, regardless of the relative position between rotor and stator. Moreover, equation (15) shows that the field winding inductance is weakened by the presence of the stator around the rotor. When the armature surrounds the rotor the enhanced demagnetising effect of the eddy currents in the rotor core [27,33] produces a steeper inductance decrease with the frequency.…”

“…Finally, some very recent studies on flexible ES have focussed on the AC current injection in the field winding, in order to target-specific effects such as the unbalanced magnetic pull compensation [13], the synchronous motor start by polarity inversion [14] and the airgap harmonics control by field current injection [15]. These innovative techniques are all based on the topologies ofs H bridge built with IGBTs.…”

Research and calculation of the levels of higher harmonics of rotary electric machines in active-adaptive networks

“…Determining the levels of higher harmonics by experimental removal of curves taking into account electromagnetic asymmetry on real electric machines is associated with a large amount of labor, due to the need to manufacture special calibration stands [25,26].…”