Theoretical Solution of the Output Voltage Harmonic Spectra of Dual-Inverter Fed Open-End Winding Loads with Dead Time Effect

Open-end winding electrical machines with one solid-state converter connected to each end of the stator windings are being considered in recent researches for numerous applications including high-power multilevel converters. Due to the absence of the neutral point, this topology creates a path for zero-sequence current, which affects the operation of the machine, increases the losses in the stator windings and raises the voltage of the shaft, leading to potential problems in the bearings. Although many strategies have been proposed to avoid the application of space vectors that generate common-mode voltage across the windings, zero-sequence current still flows due to nonidealities like voltage drops in the solid-state switches and the dead time applied to avoid DC link shoot-through. This paper presents the use of the double Fourier series adapted to extract symbolically the coefficients of the harmonic spectra of open-end winding loads with dualinverter subjected to dead-time effect. This approach is verified using examples and the predictions are confirmed with the results obtained from Simulink simulations. The influence of dead time in the quality of the synthesized voltage is demonstrated by spectral analysis.